VOCATIONAL TRAINING REPORT

Submitted in partial fulfillment of the requirements for the award of degree of

BACHELOR OF TECHNOLOGY

IN

MECHANICAL ENGINEERING

Submitted by:

Keyur D.Dalal

Roll No:13me023

MECHANICAL ENGINEERING DEPARTMENT

Chandubhai s. patel institute of technology

From 22/5/2015 to 23/6/2015

ACKNOWLEDGMENT

We all marvel at the beautiful rose. The rose, with all its beauty and grandeur. But seldom we pause and thank the kind grandeur who patiently manure and watered it.

The report produced here is the kind and sincere efforts produced by our practice and practical work in the plant. It is also like a rose which is nurtured by the guidance of many skilled minds in the plant.

It is also said that “Theory helps understanding things well, while practical experience helps to do the things beautifully.”

I am very grateful to the KRIBHCO Ltd. that has given us an opportunity to do vocational training in the plant.

It was a great experience to sharpen a theoretical sculpture with practical knowledge. This little experience of training in industry was adding a lot of sugar in the milk i.e. our theoretical studies.

For guiding me during this training for going through the practical aspects of the engineering field I sincerely thank all the members of Mechanical Maintenance Department here at KRIBHCO Ammonia, Urea and Power Plant.

I would also like to thank all members of NDT department to provide me valuable knowledge about the latest inventions and technologies.

In the end I would like to specially thank HRD department for giving us an opportunity to get the best of practical from here.

This experience over here is like a foundation for our engineering carrier.

CONTENTS

(i) Acknowledgement

(ii) Contents

1. Ammonia Plant

2. Urea Plant

3. Power Plant

4. Efficiency Calculation(Excel File Attached)

5. Mechanical Maintenance

6. NDT Department

7. Discussions with on-duty engineers

(a) Valves

(b) Pumps

8. Activities Witnessed

Block Diagram Of Ammonia Plant

Block Diagram Of

Purge Gas Recovery Plant

Ammonia Process Description

Two types of gas pressure lines come from ONGC:

1. High pressure about 42 kg/cm2 (which is used for Process)

2. Low pressure about 2-3 kg/cm2 (which is used for Burning purpose in Primary Reformer)

Process Equipment Description:

1. Knock Out Drum(120-F):

High pressure gas of 42kg/cm2 pressure and 30 temperature pass through HPNG knock out Drum where Moisture contains and liquid are removed from the gas. The pressure is maintained constant through PRC-15 control valves at 42 kg/cm2.

2. L.T. Convection Zone:

The natural gas leaving the top of drum is heated in a feed preheat coil, located in L.T. convection zone of the primary reformer (101-B) below steam Super Heater coil.

3. Desulphuriser Drum (102-D1):

Temperature of the preheated gas at inlet of CoMoX bed is controlled at 4000 C by TRC-01 control valve. The gas at 4000 C passes through the CoMoX bed and Desulphuriser 102-D & DA which is packed with ZnO catalyst. 102-D top bed is packed with 12 m2CoMoX catalyst. The un-reactive sulphur if any in the gas reacts with hydrogen in presence of CoMoX catalyst to form H2S. The HS and other reactive sulphure in the gas is absorbed by ZnO. The natural gas is expected to contain less than 0.25 ppm of Sulphur based on 50 ppm sulphure in inlet gas.

ZnO + H2S = ZnS + H2O

4. Primary Reformer (101-B):

The mixture of the steam and gas is heated from 371 C to 510 C in the mixed feed preheating coils. The mixed gas is than feed to the twelve sub headers. Each of the sub headers distributes the flow down ward through 42 parallel catalyst packed tubes in the radient section of the Primary Reformer furnace (101-B). The bottom of each of 42 tubes terminates in collection headers located near the floor of the Reformer furnace. There are twelve centrally located risers on each of these collection headers that return the flow to a cooling water jacketed transfer line 107-D located the top of the furnace 101-B which directs the flow toward the Secondary Reformer (103-D).

In the catalyst tubes hydrocarbon is react with steam to form H2, CO and CO2. To supply the heat of reaction the primary Reformer is equipped with 234 burners in 13 rows on either side of the Reformer tubes. The combustion flue gases supplying endothermic reaction heat travel downwards parallel to reformer tubes and are collected in chequered brick flue gas ducts at the floor of the furnace. The flue gases pass through these ducts to convection section for maximum heat recovery.

CH4 + H2O = CO + 3H2

CO + H2O = CO2 + H2

CH4 + 2H2O = CO2 + 4H2

The waste heat from the furnace flue gases is used to preheat the following in sequence.

1. Steam and natural gas feed to reformer

2. Process air to secondary reformer

3. Superheat the high pressure steam from boiler drum

4. NG feed preheat coil

5. Fuel gas

6. Combustion air to the burners

5. Secondary Reformer:

The process air required for secondary reformer is sucked from atmosphere through 102-L air filter by 101-J process air compressor and is compressed up to 37 kg/cm2 abs and 131.60 C in four stages. The air from 101-J is preheated to 4820 C in the both convection zone of primary reformer and is fed to secondary reformer.

The process gas at 8240 C from primary reformer enters the secondary reformer via water jacketed transfer line 107-D and a chamber near the top of secondary reformer 103-D and directed down ward through a diffuser ring to enter the combustion zone. Preheated air is introduced through a nozzle located just below the diffuser ring. The O2 gas burns with the hydrogen of the process gas and raise the gas temperature. At higher temperature balance methane reacts with steam and its content is reduced from 10% to 0.34% approx. The gases leave the secondary reformer at 10000 C and split to pass through the shell sides of two “bayonet type” primary waste heat boiler 101-CA and 101-CB.

Air(N2 + O2) + H2 = H2O + N2

6. Shift Converters:

There are two types of shift converters:

I. High Temperature shift

II. Low Temperature shift

The gas from waste heat boiler pass through 102-D1 HT shift converter where the CO is converted into CO2 by reaction with steam in presence of Cu promoted Iron-catalyst. The reaction is exothermic because of that the gas temperature goes up by 500-600 C. Waste heat from gasses is recovered by passing it through primary shift effluent waste heat boiler 103-C. the process gas from 103-C at 3320 C passes through 104-C giving up heat to the stream entering the methanator. The gas from 104-C at 2520 C passes through 112-C where it preheats the boiler feed water and gets cooled to 2000 C. the gas than pass through low temperature shift convertors 108-D and 104-D2 where balance amount of CO is converted into CO2 by the reaction with the steam in presence of Cu catalyst. The CO content is reduce to 0.3% at out let of 104-D2.

CO + H2O = CO2 + H2

The purpose of LT guard vessel 108-D is to protect the 104-D2 catalyst from poisoning Sulphur and Chloride that may be present in the process gas.

7. Absorber and Stripper:

The CO2 removal from the raw synthesis gas is accomplished by absorption using Benfield system. The Benfield solution consists of a solution containing 30% K2CO3, 3% Di-ethanol Amine (DEA) and 0.8% V2O5. K2CO3 absorbs the CO2 from the gas through the chemical reaction where as DEA acts as promoter for the reaction and V2O5 as corrosion inhibitor.

Removal of CO2 from raw synthesis gas is carried out in two stages of absorption by counter current contacting of the gas with Benfield solution in packed bed tower. The gas passes through a distributor in the bottom of CO2 absorber 101-E. the up flowing gas pass through four beds of packing and comes out from the top of absorber. The top two beds contain 38 mm S.S. slotted rings. The bottom two layers consist of 50 mm S.S. slotted rings. As the gas flow up the packing it contacts down flowing semi lean and lean Benfield solution, which absorbs CO2. The process gas leaving the absorber contains 0.1% CO2 and flow through knock out drum 103-F for removal of entrained Benfield solution.

Benfield solution enters the CO2 absorber at two levels. In the lower section semi lean Benfield solution effects the bulk removal of CO2 from the up flowing gas. This semi lean solution is taken from an intermediate point of the CO2 stripper into the semi lean solution flash tank 132-F where in the solution is cooled to a temperature of 1110 C from 1210 C in four stages of flashing under reduced pressure. The cooled semi lean solution is pumped by semi lean solution pump 107-JA/B/C to the top of lower section of the absorber. Level in 132-F is controlled by LIC-196. The flash vapours from all the stages of flashing are sucked by the respective ejectors and sent to the bottom of top section of stripper along with motive steam from 111-C for effective utilization of the heat in regeneration of Benfield solution.

CO2 + K2CO3 + H2O = 2KHCO3

The rich Benfield solution from the bottom of absorber is at high pressure and is used as a driving medium for the hydraulic turbine integrated with the pumps 107-JA/B. the solution is sent from the absorber to the hydraulic turbines 107-JHT A/B and power is recovered for semi lean solution pumps before it is flashed into the CO2 stripper feed flash drum 122-F. here the dissolved inerts in the rich solution are flashed off thus the yielding a high purity of CO2 product at the stripper top. The flashed rich solution is then delivered to the flashed zone of CO2 stripper 102-E directly above the top bed. The upper section is provided with two beds of 50 mm SS slotted hypack rings where the solution flowing down wards is partially stripped of CO2 by the up flowing vapours. A portion of semi lean solution is taken out and balance continues flowing down through the bed 38 mm SS slotted Hypack rings to bottom section of the stripper where it accumulates on a trap out pan from which it flows into the CO2 stripper reboiller 105-C. the stripper is operated at a temperature of 1300 C and 2 kg/cm2 abs. pressure at the bottom. Regeneration heat is obtained from three sources:

1. Low temperature shift effluent gas in 105-C.

2. Reboiling reflux condensate from water wash trays with LT shift effluent gas in

160-C.

3. Returning flash steam from semi lean solution along with steam from 111-C generated with wash tray condensate.

2KHCO3 + heat = K2CO3 + CO2 + H2O

8. Methanator:

The process after CO2 gas removal in absorber through 103-F enters the top of the methanator 106-D after being heated up to 3200 C in exchangers. Methanator contains a bed of Nickel catalyst where the traces of the CO and CO2 in process gas react with hydrogen to form methane and water. This gas is reuse in the reformer as fuel.

CO + 3H2 = CH4 + H2O + heat

CO2 + 4H2 = CH4 + 2H2O + heat

9. Synthesis gas Compressor:

The purified gas is compressed to about 57 kg/cm2 in the 1st stage of compression in the 1st case of the synthesis gas compressor 103-J. the gas is then cooled about 400 C. the gas and the water flow in the knock out drum 142-F, from which the water flows to the condensate stripper 103-E. the gas re enters the 1st case of the compressor and is further compressed to about 103 kg/cm2 and leaves the 1st case of 103-J and is cooled again. The chiller condenses out most of the remaining water, which is separated from the gas in the second stage separator 105-F and flows to the condensate stripper 103-E. The low moisture synthesis gas enters in the second case of 103-J and pressure is increased to about 175 kg/cm2.

A portion of the gas from third stage discharge is sent to HAEP plant from 140-C outlet and return gas from HAEP again joins at the same outlet line downstream of outgoing tapping.

This stream is heated against the converter effluent stream in exchanger 121-C and enters the synthesis converter at approximately 1400 C.

10. Synthesis gas Convertor:

Iron Oxide catalyst containing potassium, calcium, aluminum oxide as a stabilizer and promoter is used as a catalyst in the Synthesis gas convertor vessel. Compressed Synthesis gas containing hydrogen and nitrogen gas brought into this vessel from syn. Gas compressor. In the presence of catalyst this gases reacts with each other and converts into the Ammonia according to ‘Heber Method’. Then this produced ammonia along with other mixture gases is sent to the purge gas recovery plant to separate it from the mixture.

N2 + 3H2 = 2NH3

PURGE Gas Recovery Plant

The purge gas plants allows in the 1st step to recover ammonia contained in the purge gas coming from two ammonia plants. Secondly the purge gas is washed off the traces of ammonia and water in the purification section before going to the cryogenic separation. The recovery of hydrogen product stream returns to the suction of the second stage of the synthesis gas compressor, while the residual gas stream goes to the fuel gas network.

1) Ammonia Recovery System:

In this section ammonia is recovered from the incoming gas as it contains considerable amount of ammonia. In this section purge gas is washed off the ammonia with dematerialized water in the washing column by absorption. The rich aqueous ammonia from the bottom of the washing column is fed to the distillation column where the ammonia is recovered in the anhydrous form and fed to the main ammonia receiver of the both ammonia plants. The regenerated solution again recycles back to absorption column for the further absorption in fresh gas.

2) Purification Section:

Traces of the ammonia and water are removed so as to avoid freezing in the cryogenic section. This is performed in the two stages:

i. In 1st stage the purge gas is cooled to 350 C which is coming from the washing column top in an exchanger.

ii. In 2nd stage the purge gas is then purified in one of the two absorbers. Each of the absorber contains one bed of activated Alumina and one bed of molecular sieves.

Regeneration of absorbers is done by part of the fuel gas stream.

3) Cryogenic Separation Section:

In this section temperature is progressively cooled down, the liquid of condensation contains a mixture of all gas constituents, but in the different proportion from that of the initial gas mixture, it mostly contains easily condensable products and only a small portion of the bodies difficult to condense, as these bodies are dissolved in the liquid.

This process is used in the cold box to separate hydrogen from methane and argon. Nitrogen is partially recovered with hydrogen and partially carried over into the liquefied mixture.

The purified gas is cooled down in aluminum exchanger to a temperature low enough to obtain desired purity of hydrogen. At the outlet of the exchanger the gas and liquid fractions are separated. Gaseous fraction is warmed up as it passes up through exchanger, giving it’s cold to warm purge gas.

Block Diagram Of

Steam Path

UREA PLANT

INTRODUCTION :-

Urea plant is laid four streams each of 1100 MTD capacity . the plant is based on the proven “ SNAM PROGETTI “ Ammonia strapping process . the Ammonia & CO2 obtained from the Ammonia plant is pressurized & allow to react in an autoclave at a pressure of 155 ate & temperature of 180°c maintaining a NH3 / CO2 bulk ratio of 3:5 . they react in the autoclave to from a mixer of Ammonia carbonate , Urea & water , this mixture flows to a stripper where in the excess NH3 helps to strip of the unconverted carbonate . with the aid of heat . the urea solution is further concentrated in the vacuumed evaporates & made as pills . the unconverted NH3 & CO2 are recombined to from carbonate & recycled back in to the autoclave to achieve further conversion.

There are four streams of urea each having capacities of 1100 MT/ day two streams are present in each phase. Phase -1 has stream 11 & 21 & Phase -2 has stream 31 & 41 . Each Substation in phase 2& 1 are divided in two parts . To look over each stream along with some common MCC, which is supplied to both stream .

As start up Urea plant is easier then Ammonia plant hence power to Urea plant comes from low risk bus A1C & A1D .

Cooling tower for both phases are common hence a separate substation is meant for cooling tower . Which provides power to cooling water to cooling water pumps & to cooling fans .

BLOCK DIAGRAM :-

BRIEF PROCESS DESCRIPTION :

The urea production takes place through the following main operations:

a) Urea synthesis and high pressure recovery

b) Urea purification and low pressure recovery

c) Urea concentration

d) Urea prilling

e) Waste water treatment

UREA SYNTHESIS:

Liquid NH3and gaseous CO2are the two raw materials for manufacture of Urea, both obtained from NH3plant. The reaction between NH3and CO2has to be carried out under high pressure and temperature to first form ammonium carbamate, a portion of which gets dehydrated to form urea and water as per the following reactions:

2 NH3 (l) + CO2 (g)=NH2COONH4(aq)................(1)

H= -38000 KCal/Kg mole

NH2COONH4(aq) = NH2CONH2(aq) +H2O (l).............(2)

H= 7700 KCal/Kg mole

The first reaction is highly exothermic and rapid while the second one is endothermic and slow. The first reaction rapidly goes to completion under synthesis conditions while the second reaction remains always incomplete.

The conversion of ammonium carbamate to urea increases with the increase of temperature, NH3/CO2ratio & residence time.

POWER PLANT

STEAM DISTRIBUTION SYSTEM :

The three boilers are designed to generate 275MT/Hr at a pressure of 105 kg/cm2 and temperature of 510`c at the outlet of the boilers. All the three boilers are connected to a single common-header to supply high pressure steam to different use point. proper drains/vent and isolation valves are provided to put one or two boilers in service while the remaining boilers may be supplied to ammonia plants phase 1 & 2 both, urea plants phase 1 & 2 both, turbo generators 1 & 2 both , boiler feed pump turbines and no.2 & 4, PRDS of power plant and to offsite plants.

Ammonia plants are supposed to be self sufficient for steam requirement during normal running conditions. however , during startup, shutdown or during emergency periods whenever they get insufficient steam from their internal generation , ammonia plants may draw steam from power plant header , to the extent of 100MT/hr/Phase.

Urea plant is totally dependent on power plant for steam requirements. high pressure steam will be used by urea plant for the turbines of CO2 compressors. These turbines being bleed type condensing turbines, give medium pressure extraction steam for various process requirement. The requirement of steam caries according to plant load. Once the plant has stabilized and production has commenced , the urea plants being very long and zigzag , has been provided with a number of drain off condensate etc. this steam line should be isolated only when the urea plants wants to do some maintenance on it, otherwise , it must always remain charged and hot. The steam supply to urea plant will come down as soon as the CO2 compressors trip but it will continue at minimum rate for process use till prilling is completed. The urea plant being prime user of steam and being wholly dependent on power plant gets priority over TG and other steam users and will draw steam to the extent of 275-280 MT/Hr.

Figure No 1.1

Two number of BHEL make turbo generators are provided to generate power, which meets the entire requirement of the complex. Each set is capable to generate 15MW, runs at 10 to 12 MW during normal load conditions. These turbines are partial condensing type. High pressure steam from the common header is introduced and medium pressure and low pressure steam in extracted. This medium/low pressure steam is used for re- generative heating of feed water. Medium pressure steam from the TG extraction at 13Ata is used for high pressure heaters, air ejectors and turbine gland sealing. The low pressure steam at 1.8Ata is used for deaeration cum direct contact heating of condensate. The askania governor in combination with SR-IV governor controls the input of HP steam and output of medium pressure steam. The low pressure steam extraction is uncontrolled and its output depends on the consumption of steam in deaerator. Pressure reducing station 1 & 2 are located in power plant to let down high pressure steam to get medium pressure steam. Medium pressure steam header will be controlled by one PRDS station while the second will stand spare. The controller of this PRDS station will reduce steam pressure from 105 ata to 13 ata and the temperature will be reduced to 270`c to match extraction steam condition and will be controlled from the common panel of steam generation plant.

There are four number of boiler-feed pump out of which two are motor driven and the rest are driven by steam turbines. These steam turbines are non-condensing back pressure type. The HP steam after working on the turbine blades exhaust at 1.8Ata to the low pressure header. This exhaust steam may be used for dearation of feed water or may be dumped into the condenser of running TG set, if remains surplus. To maintain LP header pressure PRDS 3 & 4 are installed to let down high pressure steam and feed to LP steam header. Medium pressure steam, from power plant MP steam header, is used for chemical heating in DM plant of offsite section. This steam requirement is intermittent, however, the steam line is kept charged and traps will operate to drain off any condensate etc. operators have to be extra careful in charging steam distribution system to avoid steam hammering and consequent failure. When ever a cold line is to be charged, one must not make haste to charge the line at once.

LIST OF WATER CIRCUIT EQUIPMENT

Make-up water storage:

No off: Two

Capacity: 140MT

Dimension: Internal dia 6.566 m and straight height 7.355 m

Make-up water pump:

Manufacture: Mather & Platt limited

No off: 3 (2 running+1 standby)

Quantity: 286 MT/Hr.

Delivery head: 6.77 kg/cm2

Speed: 2970 rpm.

Drive: 82 KW, 415 V, 3 Ph., 50Hz

Boiler Feed pumps:

Boiler feed pump Motor.

No off: Two

Speed: 2983 rpm

BHP: 1800KW at 11KV

Starting current: 650% of full load current

Boiler feed pump Turbine.

No off: Two

Speed: 2983rpm

BHP: 1723 KW max.

INLET steam: 100kg/cm2, 505`c, 10.8 MT/Hr.

Exhaust pressure: 2.0kg/cm2

Turbine speed: 12090rpm

IST critical speed: 14400rpm

Over speed trip: 12940 rpm

Deaerator:

A steam generating boiler requires that the circulating steam, condensate, and feed water should be devoid of dissolved gases, particularly corrosive ones, and dissolved or suspended solids. The gases will give rise to corrosion of the metal. The solids will deposit on the heating surfaces giving rise to localized heating and tube ruptures due to overheating. Under some conditions it may give rise to stress corrosion cracking.

Feed water Heaters:

The two horizontal single-pass, U tubes , shell and tube high pressure feed water heaters received the feed water from the feed pumps; heating steam being derived from the associated pass out condensing power turbine or from the PRDS. The overall length is 13.26 m.

A Feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system.This reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the feedwater is introduced back into the steam cycle

Economizers:

In boilers, economizers are heat exchange devices that heat fluids, usually water, up to but not normally beyond the boiling point of that fluid. Economizers are so named because they can make use of the enthalpy in fluid streams that are hot, but not hot enough to be used in a boiler, thereby recovering more useful enthalpy and improving the boiler's efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water used the fill it (the feed water).

Boiler drum

Steam drums are a regular feature of water tube boilers. It is a reservoir of water/steam at the top end of the water tubes in the water-tube boiler. They store the steam generated in the water tubes and act as a phase separator for the steam/water mixture. The difference in densities between hot and cold water helps in the accumulation of the "hotter"-water/and saturated-steam into the steam-drum.

Dimension: 1.5m internal diagram with wall thickness of 56 mm and 8944mm long with dished ends.Bothtorispherical ends are fittrd with an inward opening ,internally hinged,308mm x 409mm oval mandoor.

Super Heater

A superheater is a device in a steam engine that heats the steam generated by the boiler again, increasing its thermal energy and decreasing the likelihood that it will condense inside the engine. Superheaters increase the efficiency of the steam engine, and were widely adopted. Steam which has been superheated is logically known as superheated steam; non-superheated steam is called saturated steam or wet steam.

There are 3 types of super heaters are installed as followed.

Primary Super Heater

Steam flow from the inlet header is upward through the primary super heater elements to the final elements,then downwards to the outlet header.when firing fuel gas the incoming steam temperature is 330`c and the output steam temperature is 378`c.

Platen Super Heater

The platen superheater consists of 15 multi-tube pendant non drainable elements uniformly arranged across the boiler and suspended into the furnace from the inlet and outlet headers located in the pent house above the furnace roof.

The incoming steam tempareture is 351`c , while the output steam temperature is 440`c. The steam pressure at inlet is 112.2kg/cm2 respectively.

Secondary Super Heater

The secondary super heater is the final super heater providing the output steam. It consists of thirty multi-tubes. Temperature rise across the final super heater is from 423`c to 515`c. The steam inlet pressure of 106kg/cm2 reduces to 104.2kg/cm2 at the outlet.

Secondary super heater outlet header is provided with main steam safety valves, main steam-up vent valve.

Description of Boiler Chemical Conditioning.

The desired analysis of boiler water and feed water is:

(i)Boiler make-up water

pH - 8.5 to 9.5

Conductivity - less than 1 micro siemens per Cm.

Silica – less than 0.02 ppm

(ii)Boiler feed water

pH - 8.5 to 9.5

Conductivity - less than 1 micro siemens per Cm.

N2H4 – 20 to 30 ppb

(iii)Boiler water

pH – 9.0 to 10.5

Conductivity - less than 50 micro siemens per Cm.

Silica – less than 1 ppm

Phosphate – 5 to 10 ppm

In order to maintain the above mentioned chemical condition of water, we have to treat DM water with certain chemicals and we have to give blow down to boilers to remove certain impurities from it. The blow down maintains silica and TDS or conductivity so CBD valve operation should be regulated to meet this demand pH, N2H4, PO4 are maintained by LP and HP chemical dosing.

Blow down System

The boiler should be blow down at regular intervals to limit the total dissolved solids in the boiler water and to remove any sludge resulting from water treatment. Continuous blow down is used to control the concentration of boiler solids by means of CBD control valve.

The water wall header should never be blown down when the boiler is steaming. Similarly the pairs of steam blow down valves are opened only during boiler start-up.

Low pressure chemical dozing

Low pressure chemical injection is for injection hydrazine into feed water in the suction line to the feed water pups and into the boiler filling line. Interlinked valve pipe work is arranged to enable any pump to deliver to either or both deaerator.

High pressure chemical dozing

High pressure chemical injection is for injecting Tri-sodium phosphate and alkali into the steam drums to maintain boiler water pH and to maintain a certain residual phosphate level in boiler water

Draught System

The draught plant for each boiler comprises two forced draught fans supplying combustion air and two induced draft fans for extracting flue gases. Through put of the FD & ID fans are controlled by radial and differential vane control mechanisms respectively.

Two main air heaters from part of the system to exchange heat from flue gas by combustion air and thus save heat loss.

The heat supplied to the incoming forced draught is extracted by the air heaters from outgoing boiler gases. The air heater ensures a minimum gas temperature to avoid condensation of flue gas in its way to chimney.

Two induced draft fans extract the flue gases from the boiler, through the main air heaters and precipitators to discharge into the chimney.

Forced draft fans

Manufacture: Davidson & Co. Limited

No off per boiler: Two

Capacity: 50.4 M3/sec. At 35 m bar, 40`c

Output: 270 KW

Speed: 980rpm

Supply: 3300V, 50Hz, 61 AMP

Induced draft fans

Manufacture: Davidson & Co. Limited

No off per boiler: Two

Capacity: 75 M3/sec. At 38.2 m bar, 150`c

Output: 430 KW

Speed: 740rpm

Supply: 3300V, 50Hz, 100 AMP

Rotary air pre-heaters

Tri-sector types are the most common in modern power generation facilities. In the tri-sector design, the largest sector (usually spanning about half the cross-section of the casing) is connected to the boiler hot gas outlet.

The hot exhaust gas flows over the central element, transferring some of its heat to the element, and is then ducted away for further treatment in dust collectors and other equipment before being expelled from the flue gas stack. The second, smaller sector, is fed with ambient air by a fan, which passes over the heated element as it rotates into the sector, and is heated before being carried to the boiler furnace for combustion.

The third sector is the smallest one and it heats air which is routed into the pulverisers and used to carry the coal-air mixture to the boiler burners

Chimney

A flue gas stack is a type of chimney, a vertical pipe, channel or similar structure through which combustion product gases called flue gases are exhausted to the outside air. Flue gases are produced when oil, natural gas or any other fuel is combusted in an industrial furnace, a power plant's steam-generating boiler, or other large combustion device. Flue gas is usually composed of carbon dioxide (CO2) and water vapor as well as nitrogen and excess oxygen remaining from the intake combustion air. It also contains a small percentage of pollutants such as particulate matter, carbon monoxide, nitrogen oxides and sulfur oxides.

Dimention: The chimney is 150Mtr. High having bottom and top dia 18.0m and 5.43m respectively

·

DESCRIPTION

TG # I

TG # II

Machine No.:

T-204

T-205

Make & Supplier:

BHEL-Hyderabad

BHEL-Hyderabad

Model:

EHNK 32/45/30-3

EHNK 32/45/30-3

Rated Power:

15 MW

15 MW

Turbine Speed:

7500 rpm

7500rpm

Direction of Rotation

Counter Clockwise

Counter Clockwise

Application:

To Drive Generator

To Drive Generator

Inlet Steam Pressure:

105 ata

105 ata

Inlet Steam Temp:

505 C

505 C

Number of Extraction:

TWO

TWO

STEAM BOILERS IN POWER PLANT

· Total Three No. Boilers

· Single Drum, Dual Fuel Front Fired, Natural Water Circulation, High Pressure Vertical Water Tube Boiler.

· Steam Capacity of Each Boiler: 275 MT/HrAt 102 Kg/Cm2 Pressure& 505 Deg Celsius Temp.Two Number Boilers are Producing Steam at a time and One Boiler kept as Stand By. These Boilers are meeting the Steam Requirement of Kribhco Premises at Hazira.

BASIC DETAILS OF STEAM TURBINE

Figure No: 2.0

BASIC DETAILS OF ELECTRIC GENERATORS

DESCRIPTION

DETAILS

Make & Supplier

BHEL – Hyderabad

Type

TGP 224240 / 27

Rated Capacity

15 MW

Frequency

50 Hz

Rated Speed

3000 rpm

Nos. Phase

Three

Cooling System

Closed Circuit Air Cooled

Stator Volts

11 Kilo Volts

Stator Amps

984 Amps.

Specifications

IS 5422

Permissible Stator Winding Temp.

75 0 C

Permissible Rotor Winding Temp.

85 0 C

DESIGN PARAMETERS & IMPORTANT DETAILS:

· Date of First Synchronization

1. TG # I----17-03-1985

2. TG # II---01-01-1985

· Date of Guarantee Test Run: 2nd Week,Apr’86 1st Week,Dec’87

· Main Steam: 101 Kg/Cm2, 5050C Temp.

· Rated Flow of Steam: 80.75 MT/Hr

· First Extraction: 14 Kg/Cm2, 2800C Temp.

Rated Flow of Steam: 35.83 MT/Hr

· Second Extraction: 1.5 Kg/Cm2, 1500C Temp.

Rated Flow of Steam: 15.62 MT/Hr

· Steam Condenser: 0.1 Kg/Cm2, 45 0C Temp.

Rated Flow: 29.3 MT/Hr

· Heat Rate : 2180 Kcal/KW.

· Specific Steam Consumption: 2.464 MT/MWH

MECHANICAL MAINTENANCE

Introduction

At KRIBHCO, the plant is run by Production Deptt. by Chemical Engineers and Operators, who possess Diploma in Chemical Engineering or B.Sc. degree holders. They operate the plant in three 8 hourly shift and are the custodian of the plant. To assist Production Deptt.in every plant there is a Maintenance Deptt. which consists four streams i.e. Mechanical, Instrumentation, Electrical and Civil. These Deptt.are run by qualified engineers and technicians possessing Diploma or ITI in the concerned branch of engineering. Mechanical Engineers are responsible for Mechanical Maintenance. At KRIBHCO all modern techniques of maintenance are practiced with latest machines, tool & tackles. The main maintenance technique used are as under:

1. Preventive maintenance1. Predictive maintenance1. Proactive maintenance1. Break down maintenance1. Annual shut downPreventive Maintenance

Much as the name implies, preventive maintenance, often abbreviated PM, refers to performing planned maintenance of plant and equipment that is designed to improve equipment life and avoid any unplanned maintenance activity. PM includes painting, lubrication, cleaning, adjusting, and minor component replacement to extend the life of equipment and facilities. Its purpose is to minimize breakdowns and excessive depreciation. Neither equipment nor facilities should be allowed to go to the breaking point. In its simplest form, preventive maintenance can be compared to the service schedule for an automobile. A bona fide preventive maintenance program should include:

1. Non-destructive testing

1. Periodic inspection

1. Preplanned maintenance activities

1. Maintenance to correct deficiencies found through testing or inspections

The amount of preventive maintenance needed at a facility varies greatly. It can range from a walk through inspection of facilities and equipment noting deficiencies for later correction up to computers that actually shut down equipment after a certain number of hours or a certain number of units produced, etc.

Many reasons exist for establishing a PM program. Listed below are a few of these. Whenever any of these reasons are present, a PM program is likely needed. Reasons for Preventive Maintenance are:

1. Increased Automation

1. Business loss due to production delays

1. Reduction of insurance inventories

1. Production of a higher quality product

1. Just-in-time manufacturing

1. Reduction in equipment redundancies

1. Cell dependencies

1. Minimize energy consumption

1. Need for a more organized, planned environment

The most important reason for a PM program is reduced costs as seen in these many ways:

1. Reduced production downtime, resulting in fewer machine breakdowns.

1. Better conservation of assets and increased life expectancy of assets, thereby eliminating premature replacement of machinery and equipment.

1. Reduced overtime costs and more economical use of maintenance workers due to working on a scheduled basis instead of a crash basis to repair breakdowns.

1. Timely, routine repairs circumvent fewer large-scale repairs.

1. Reduced cost of repairs by reducing secondary failures. When parts fail in service, they usually damage other parts.

1. Reduced product rejects, rework, and scrap due to better overall equipment condition.

1. Identification of equipment with excessive maintenance costs, indicating the need for corrective maintenance, operator training, or replacement of obsolete equipment.

1. Improved safety and quality conditions.

As mentioned above preventive maintenance does involve risk. The risk here refers to the potential for creating defects of various types while performing the PM task. In other words, human errors committed during the PM task and infant mortality of newly installed components eventually lead to additional failures of the equipment on which the PM was performed. Frequently, these failures occur very soon after the PM is performed. Typically, the following errors or damage occur during PM’s and other types of maintenance outages.

1. Damage to an adjacent equipment during a PM task.

1. Damage to the equipment receiving the PM task to include such things as:

1. Damage during the performance of an inspection, repair, adjustment, or installation of a replacement part.

1. Installing material that is defective, incorrectly installing a replacement part, or incorrectly reassembling material.

1. Reintroducing infant mortality by installing new parts or materials.

1. Damage due to an error in reinstalling equipment into its original location.

Predictive Maintenance

The next improvement in maintenance technology was the advent of predictive maintenance, which is based on the determination of a machine's condition while in operation. The technique is dependent on the fact that most machine components will give some type of warning before they fail. To sense the symptoms by which the machine is warning us requires several types of non-destructive testing, such as oil analysis, wear particle analysis, vibration analysis, and temperature measurements. Use of these techniques to determine the machine condition results in a much more efficient use of maintenance effort compared to any earlier types of maintenance.

Predictive maintenance allows plant management to control the machinery and maintenance programs rather than vice versa. In a plant using predictive maintenance, the overall machinery condition at any time is known, and much more accurate planning is possible.

Predictive maintenance utilizes many different disciplines, by far the most important of which is periodicvibration analysis. It has been shown many times over that of all the non-destructive testing that can be done on a machine, the vibration signature provides the most information about its inner workings.

Certain machines, which would affect plant operations adversely if they were to fail, can be subjected to continuous vibration monitoring, in which an alarm is sounded if the vibrationlevel exceeds a predetermined value. In this way, rapidly progressing faults are prevented from causing catastrophic failures. Most modern turbine-driven equipment is monitored in this way.

Oil analysis and wear particle analysis are important parts of modern predictive programs, especially in critical or very expensive equipment. Thermography is the measurement of surface temperature by infrared detection, and is very useful in detecting problems in electrical switchgear and other areas where access is difficult.

Motor current signature analysis is another technique that is very useful in detecting cracked or broken rotor bars while the motor is in operation, and electrical surge testing of motor stators is used for detecting incipient electrical insulation failure.

Benefits of Predictive Maintenance

The major benefit of predictive maintenance of industrial mechanical equipment is increased plant readiness due to greater reliability of the equipment. The trending over time of developing faults in machines can be carefully done so as to plan maintenance operations to coincide with scheduled shutdowns. Many industries report from two to ten percent productivity increases due to predictive maintenance practices. Similar percentages of increased mission readiness are expected in shipboard systems.

Another benefit of predictive maintenance is reduced expenditures for spare parts and labor. Machines that fail while in service often cost ten times as much to repair than if the repair were anticipated and scheduled.

A great many new machines fail soon after startup due to built-in defects or improper installation. Predictive techniques can be used to assure proper alignment and overall integrity of the installed machine when first brought into service. Many plants base the acceptance of new machine installations on a clean bill of health as determined by vibration measurements.

Predictive maintenance reduces the likelihood of a machine experiencing a catastrophic failure, and this results in an improvement in worker safety. There have been many cases of bodily injury and even death due to sudden machine failures.

Pro-active Maintenance

The latest innovation in the field of predictive maintenance is so-called pro-active maintenance, which uses a variety of technologies to extend the operating lives of machines and to virtually eliminate reactive maintenance. The major part of a pro-active program is root cause failure analysis, which is the determination of the mechanisms and causes of machine faults. The fundamental causes of machine failures can thus be corrected, and the failure mechanisms can be gradually engineered out of each machinery installation.

It has been known for a long time that imbalance and misalignment are the root causes of the majority of machine faults. Both of these conditions place undue forces on bearings, shortening their service life. Rather than continually replacing worn bearings in an offending machine, a far better policy is to perform precision balance and alignment on the machine, and then to verify the results by careful vibration signature analysis.

Benefits of Pro-active Maintenance

A successful pro-active maintenance program will gradually design the problems out of the machines over a period of time, resulting in greatly extended machine life, reduced down time, and expanded production capacity. One of the best features of a pro-active approach is that the techniques are natural extensions of those used in a predictive program, and they are easily added to existing programs.

It is apparent today that we need a balanced approach to maintenance, including the appropriate use of preventive, predictive, and pro-active methods, and these elements are not independent, but should be integral parts of a unified maintenance program.

Break down Maintenance

Inspite of Maintenance Departments’ best efforts, using all the maintenance techniques, tools & tackles, the machinery break down takes place. This disrupt the plant production and many times leads to emergency shut down of the plant, if standby machinery/ equipment is not provided or standby machinery doesn’t pick-up the process parameters within stipulated time.

In such a break down, where plant shut down takes place, Maintenance Department try to repair the machine in shortest possible time by working round the clock to minimize the production loss.

Annual shut Down

KRIBHCO’s Ammonia-Urea Complex is a continuous processing industry. Only in few of the rotating machinery standby arrangements are provided, so the compressors, turbines, vessels, towers, heat exchangers, furnaces, piping and valves etc. work continuously for months. Therefore, maintenance of these machine couldn’t be performed during running of plant. Secondly, for replacement of some equipment or installation of a new equipment or to complete statutory requirements like IBR Inspection for boiler, plant shut down is required.

Earlier fertilizer plants used to take annual shut down especially for IBR Inspection for boilers, though plant could run continuously for about two years. Now statutory bodies has allowed the fertilizers unit to carry out IBR Inspection for boilers after every two years. So every year KRIBHCO take shut down of one phase only. Round the year jobs are clubbed to be performed during annual shut down.

COMPRESSOR

Centrifugal Compressors

The centrifugal compressor has an impeller with radial or backward leaning vanes usually between two shrouds. The gas is forced through the impeller by the mechanical action of the rapid rotating impeller vanes, there being a component around the shaft forming a vortex and a component through the impeller. The velocity generated is converted into force in the stationary diffusers following the impeller.

Multi stage centrifugal compressor utilizes two or more impellers arranged for series flow each with a radial diffuser and return channel separating impellers. The isothermal cycle is more economical in power consumption compared to adiabatic cycle used in reciprocating units. Cooling the gas after partial compression to a temperature equal to original intake temperature reduces the power required in the second stage.

Hereunder the parts of BHEL make Centrifugal type CO2 Compressor of Urea Plant is briefly described:

Parts of CO2 Centrifugal Compressors

CO2 Compressor comprises of the following principal components :

a) Casing

b) Rotor

c) Impeller

d) Diaphragms and guide vanes

e) Labyrinth seals

f) Journal bearing

g) Thrust bearing

Casing

The wide variety of casing design is depend on many factors such as size, pressure, temperature, gas composition and presence of corrosive elements. In a large multi-stage unit, the intake end of the casing may not be designed for pressure existing at the discharge end. In such case, each end may be tested separately.

In CO2 compressor casing is 2MCL-527 for the first two stages followed by BCL-305A and BCL-205A for third and fourth stages respectively. 2MCL-527 is horizontally split comprising two half casings. The suction and discharge nozzles as well as auxiliary connections are on the lower half and the upper half serves only as a cover which may be lifted by removing the bolts on the parting plane giving free access to the internals of the compressor.

BCL-305 A and BCL-205A are vertically split and made of barrels closed at the ends by two vertical flanges with the help of stud-bolts.

Rotor

Rotor transmits kinetic energy to the gas by the effect of centrifugal force which is transformed into pressure, partly in the impellers and partly in the diffusers. Each rotor consists of a shaft on which the impellers with their positioning sleeves, the balance piston and thrust disc are mounted.

For 2MCL-527, the suctions of the impellers for the two stages are opposed so as to partially balance the axial thrust. For BCL-305 and BCL-205, the axial thrust is balanced by means of balance piston. Almost 90% of the axial thrust due to the gas being compressed is compensated by the opposite axial thrust acting on this piston. Thrust disc mounted on each shaft transmits the residual thrust which has not been absorbed by the balance piston to the thrust bearings constantly adherent to it.

Impeller

Impeller can be classified as open, semi-open and enclosed type. The open and semi-closed impellers may be cast, milled from a forging or built up by welding. The closed impellers can be built by welding, three or two piece riveting, single piece or two piece casting.

Proper selection of vane exit angle determines to a considerable degree the shape of characteristic curve as well as the head rise and efficiency. Vanes are either forward curved, radial or backward covered. Only the last two are normally used. The vane curvature is designated with reference to the direction of rotation.

The backward curved vane impeller will generally be more efficient than an impeller with radial vanes. The former also will have wider stable operating range at the same impeller diameter and speed but will produce less head rise.

Diaphragm and Guide Vanes

Diaphragms are the dividing walls between individual stages in multistage compressor. Diaphragms combine in a single item the diffuser at the impeller outlet which converts the velocity energy of the gas into pressure energy and the return bend which turns the gas from the diffuser to the next stage. There is one diaphragm between each impeller and it holds the differential pressure between adjoining impellers.

Guide vanes are mounted on the exit of the return bend and direct the gas into the eye of each impeller at the required angle. Each guide vane carries two labyrinths, one sealing on the shaft, the other on the impeller eye, thus reducing the interstage leakage. of the gas.

Labyrinth Seals

Labyrinth seals are the simplest and most prevalent on air and gas compressors. The sealing is the result of flow resistance by repeated throttling across the labyrinth teeth. Labyrinth seals are made so one of the two adjacent parts is relatively soft. It will yield on metal contact without damage. Labyrinth seals are the normal knife edge type of seals made of aluminum alloy so as avoid damage to the shaft in case of accidental rubbing.

The gas enters the narrow passage between the shaft & a series of labyrinth strips, while passing thro' each labyrinth strip the gas expands and attains lower pressure. Thus the quantity of gas leaking through the last strip will be reduced considerably due to a small P available across it.

Journal Bearings

The journal bearings support the rotor at two ends of each casing. The main bearings are self-aligned, ball or roller bearing. Bearings on most compressors are of the casing to provide greater accessibility and to prevent lubricating oil leakage into the gas stream or contamination of the oil by gas.

In CO2 Compressor white metal lined journal bearings are of elliptical type for 2MCL-527, tilting pad type for BCL-305 (No. of pads 5+5) and 4-lobe type for BCL-205. These are housed outside the compressor casing and can be inspected without dismantling the machine. The journal bearing housings are fitted with an atmospheric vent in ease of 2 MCL-527, while BCL-305 & BCL205 journal bearing housing vents are connected to the suction of ejector (also sucking the leakage gas from end seals).

Thrust Bearings

The residual thrust which has not been compensated by providing opposite suctions in case of 2MCL-527 or balance piston in case of BCL-305 &205, is transmitted by thrust disc to the thrust bearings constantly adherent to it due to the residual thrust.

Normally the thrust acts towards the low pressure end, however thrust bearings are provided on both sides of the thrust disc, so as absorb thrust in either direction. It is especially important during surging when axial load is alternating.

All thrust bearings are of tilting pad type. No. of pads (6+6) for 2MCL-527 and BCL-305 while (4+4) for BCL-20

Compressor Surge

At lower capacities pumping or surge can be expected. For any speed, this is the capacity at which compressor operation becomes unstable can damage. This point will vary from roughly 50 to 90% of the rated capacity, depending upon impeller design. Number of stages, shape of head-capacity curve and gas being compressed etc.

When feed to the compressor is reduced below the peak, the pressure in the discharge line exceeds that is produced by the machine and the flow tends to reverse momentarily. However, as soon as the flow reverses, the system discharge pressure drops and the compressor resumes normal flow. This pulsation in capacity may magnify depending upon the characteristic of discharge system and usually, but not always, result in noisy operation and evidence of distress. This can cause excessive temperature rise in the gas as well as vibration and stress in the machine and should not be permitted to occur.

Stonewalling

Although it is infrequent, a phenomenon known as stonewalling can occur with dynamic machines. This occur when the velocity of flow within the machine approaches the velocity of sound (Sonic velocity or Mach 1) in the gas at the specific points under consideration within the unit. Velocities within these units are usually well below the sonic, but in certain applications, particularly with heavy gases (such as some refrigerants) the designer must give this consideration.

The term stonewalling has been applied because the characteristic pressure-volume curve becomes almost vertical as the capacity is increased and velocity approaches the sonic value. In other words, there is a ‘Stonewall’ limit to capacity.

STEAM TURBINE

Principle of Operation and Design

An ideal steam turbine is considered to be an isentropic process or constant entropy process, in which the entropy of the steam entering the turbine is equal to the entropy of the steam leaving the turbine. No steam turbine is truly “isentropic”, however, with typical isentropic efficiencies ranging from 20%-90% based on the application of the turbine. The interior of a turbine is comprised of several sets of blades, or “buckets” as they are more commonly referred to. One set of stationary blades is connected to the casing and one set of rotating blades is connected to the shaft. The sets intermesh with certain minimum clearances, with the size and configuration of sets varying to efficiently exploit the expansion of steam at each stage. Basically two type of turbines are in practical use i.e. Impulse Turbine & Reaction Turbine

Impulse Turbines

An impulse turbine has fixed nozzles that orient the steam flow into high-speed jets. These jets contain significant kinetic energy, which the rotor blades, shaped like buckets, convert into shaft rotation as the steam jet changes direction. A pressure drop occurs across only the stationary blades, with a net increase in steam velocity across the stage.

Reaction Turbines

In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor. Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the entire circumference of the rotor. The steam then changes direction and increases its speed relative to the speed of the blades. A pressure drop occurs across both the stator and the rotor, with steam accelerating through the stator and decelerating through the rotor, with no net change in steam velocity across the stage but with a decrease in both pressure and temperature, reflecting the work performed in the driving of the rotor.

Hereunder the parts of BHEL make extraction-cum-condensing type Steam Turbine (Called TK1) to drive CO2 Compressor of Urea Plant is briefly described. First stage blading in TK-1 is impulse type, while all subsequent blading stages are of reaction type i.e. 10 Nos. before extraction and 15 Nos. after extraction. In impulse staging, the steam pr. remains constant while the steam velocity decreases as the steam travels through a row of moving blades. In reaction staging, the steam pr. decreases while the steam velocity increases as the steam passes through a row of moving blades.

Parts of Steam Turbine

Steam Turbine comprises of the following principal components :

a) Casing

b) Rotor and blading

c) Gland packing

d) Blade tip sealing strips

e) Bearings

f) HP/LP control valves

Casing

After Leaving the body of Emergency Stop Valve (ESV), which is main isolation valve between turbine and live steam, the live steam enters the valve chest with control valves forming an integral casting with the upper half of outer casing. The outer casing is horizontally split with upper and lower halves flanged and assembled by bolts.

The inner casing is connected with control valve nozzles. The inner casing serves as a support for the guide-blade carriers.

Rotor and Blading

The turbine rotor can be divided into three principal portions, i. e. front portion (1 to 9) and rear portion (10 to 13). The turbine consists mainly the following:

1. Emergency governor eccentric bolt- a safety device against TK-1 over speed.

1. Lifting cam-track - a mechanical safety device against high axial displacement of the turbine rotor.

1. Thrust collar

1. Contact surface of front journal bearing.

1. Outer front packing gland section.

1. Inner front packing gland section.

1. Impulse wheel blade rim

1. Drum blading section (10 Nos. reaction blades before extraction)

1. L. P. blading section (15 Nos. reaction blades after extraction)

1. Rear packing gland section

1. Contact surface of rear journal bearing

1. Sprocket wheel for rotor turning gear

1. Coupling flange cone

Except for the impulse stage wheel (7), the rotor blades with shrouds are used for part (8) of reaction stages. The twisted low pressure blades (9) have a large tip spacing and are without shrouds.

Gland Packing

The points at which shaft passes through the casing are sealed by labyrinth glands with caulked in seal strips. Rear end packing glands are sealed against vacuum for blocking the ingress of air into the casing by the leakage steam from the front end packing glands.

The central portion of packing gland is also connected to sealing steam through a control valve, one part of which goes into the turbine casing and the other to the atmosphere through gland steam stack. Excess leakage steam from front end packing glands is diverted to surface condenser through a control valve.

Blade Tip Sealing Strips

Sealing strips are used to minimize steam leakage through the gaps between stationary and moving blade components. Radial steps machined on the circumferential surfaces of both the stationary and moving blade rows together with sealing strips in the guide blade carries and on the rotor form efficient seals.

The sealing strips are made of stainless steel and can be replaced in the event of damage.

Bearings

Front and rear journal bearings of TK-1 rotor are of tilting pad type with total ten Nos. of pads (five on each side of the contact surface).

Thrust bearings are also of tilting pad type with eight Nos. of pads on each side of the thrust collar.

HP / LP Control Valves

By regulation the opening of the HP/LP control valves, the steam flow can be adjusted to get a desired turbine output.

The valve cones are freely suspended in a valve beam which is accommodated in the steam chest. When the turbine is at standstill, the valve cones are pressed against their seats. After getting a control impulse from the governor, the actuator lifts or lowers the valve beam (via a lever system) which in turn lifts or lowers the loosely suspended cones of the individual valves in a sequence thus controlling the steam flow.

Turbine Governing System

The governing system for TK-1 ensures that its speed for a given speed signal remains constant irrespective of the change of load on the turbine or the change of extraction quantity. The governing system mainly consists of a wood-ward PG-PL type speed governor, an extraction pressure controller, starting device, speed governor, amplifiers, trip gear, H.P./L.P. servomotors and control valves and protections/testing devices.

Governing Oil System

The governing oil system is divided into 3 sections, i. e. Pressure oil, trip oil, and secondary oil. Main oil supply line from g. o. filters d/s upto a restriction orifice at the inlet of emergency trip gear is known as pressure oil. A part of the pressure oil is taken into another oil circuit through the above said R. O. and this oil at d/s of R. O. and upto the emergency stop valve is known as trip oil. Again, a part of the trip oil is taken to the oil headers, through (Restriction Orifice) R. O. s at the inlet of the amplifiers. This is known as secondary oil.

The R. O. s are arranged such that any variation in pressure of pressure oil affects the pr. of trip oil and secondary oil headers but not vice versa.

Starting Device

The speed governor housing accommodates starting device, wood-ward governor and amplifier. The starting device is used to open the ESV and to start the turbine and speed it upto the minimum governor speed at which wood-ward governor takes over.

Wood-Ward Governor

It is a centrifugal type of governor which functions by a hydraulic system. It has its own oil reservoir and built in gear pump. The actual speed of TK-1 is fed to the governor through a worm gear and so the governor will be rotating at a lower speed in proportion to that of the turbine.

A remote controller HIC-241 through I/P converter sends 0.2 to 1.0 kg/cm2 air pr. indicating the desired speed signal to the governor. The governor maintains the speed of the turbine constant regardless of the load on the turbine by varying steam flow through HP/LP valves for varying loads.

The governor can maintain the speed within a certain range only, i. e. from minimum governor speed of 7600 rpm to a maximum governor speed of 9660 rpm.

Amplifiers

The purpose of the amplifiers is to transform the control impulses from the speed governor and the extraction pressure controller into the corresponding secondary oil pressures serving as input signals for the pilot valves of the valve actuators which determine the positions of the HP/LP steam control valves.

The amplifiers consist of HP and LP follow-up pistons and their corresponding control sleeves both provided with ports for draining the oil.

Actuators (Servomotors)

The actuators serve for transmitting the positioning impulses for the control valves to the valve operating lever system which lifts or lowers the HP/LP control valves so as to provide steam flow required for the present turbine output. The pilot valves of the actuators receive their control impulses from the secondary oil circuit.

Protections / Testing Devices

Emergency Stop Valve (ESV)

It is the principal shut off organ in the live steam line to TK-1. In the event of a disturbance resulting in substantial drop of trip oil pr. (below 2 kg/cm2), the ESV will close and cut off the steam supply to TK-1 in a minimum of time. ESV is mounted horizontally on steam chest of the turbine casing. Its principal parts are a steam section and a hydraulic section joined by a barrel shaped connection part.

Solenoid valve

Solenoid valve is installed in the pressure oil line leading to the trip gear. When operated, it interrupts the oil flow in that line connecting simultaneously the trip oil circuit to drain, thereby releasing the emergency trip gear. It can be operated either from the control room or by a protection device.

Emergency Trip Gear

It serves for opening the trip oil circuit in case of some disturbance. This causes a drop in trip oil pressure (pressure prevailing underneath the piston disc. of the EVS) whereby the ESV is closed abruptly.

Emergency Governor for over speed protection

The function of emergency governor is to stop the turbine by means of automatic quick tripping system in case of over speed.

The emergency governor bolt is fitted on the turbine rotor and placed by a compression spring. When the turbine speed rises to the set trip speed, the centrifugal force of the eccentric bolt overcomes the force of compression spring. As a result, the eccentric bolt moves a few mm. out of the shaft thereby striking the lever of the emergency trip gear to stop the turbine immediately.

Axial Motion Protection

The lever of the trip gear is adjusted in between two cams on the turbine shaft. In the event of excessive axial displacement of the turbine rotor, either of the cams on the shaft pushes the lever of the trip gear thereby stopping the turbine immediately.

Extraction Pr. High Protection

It protects the turbine from any damage in case of high extraction pressure when the instrument protection for the same fails. The extraction steam pr. acts on the device against the spring force. When the force due to extraction pr. exceeds the spring force, it moves the device such that the oil supply to trip gear gets interrupted thereby stopping the turbine.

Over speed governor / ESV testing devices

Pressure oil is used for the testing of emergency governor for over speed protection and the emergency stop valve. Over speed governor testing device enables the emergency governor to be tested for satisfactory operation during turbine running condition. ESV testing device permits checking of the valve spindle and piston rod for free movement at any time without interfering with normal turbine operation.

Monitoring Devices

Speed Measurement

It consists of a magnet, a pick-up and an indication instrument. The magnet is attached to the front end of the governor impeller shaft by means of a threaded bolt inserted centrally in the direction of the shaft axis. The indicating instrument is connected by a cable to the pick-up.

When the turbine shaft rotates, its movement is transmitted to the governor impeller by means of spur wheels. Thus the magnet fixed to the impeller shaft also rotates inducing an a. c. voltage in the pick-up, the frequency of which is proportional to the turbine speed.

Axial Displacement Measurement

An non-contact type pick-up is mounted against thrust collar of the shaft. The system operates on inductive proximity principle and is composed of two basic units (1) Probe and (2) proximeter.

The proximeter uses the d. c. input voltage to generate radio frequency output voltage which then is applied to probe coil, thereby generating an alternating magnetic field around probe tip. When a conductor enters the magnetic field, the eddy currents are generated. As the conductor approaches the coil, the amplitude of the eddy currents increases. These eddy currents cause a power loss which results in a drop in the amplitude of the R. F. output voltage between the probe and proximeter. The output voltage is thus a function of the gap between the conductor and probe tip.

Vibration Measurement

Non-contact type vibration pick-ups arranged in a pair at 900 to each other are mounted at both ends of bearings. The principle of measurement is same as that of axial displacement except that a. c. component rather than avg. d.c. component of the proximeter output voltage becomes a function of vibration.

Casing Expansion Measurement

The absolute axial elongation of the casing provides information on thermal stage of the turbine. It is measured by means of a pointer screwed to one side of front bearing housing and moving along a scale on the mounting pedestal. Casing expansion should be smooth and not with jerky movement during start up and load variation.

Oil Supply System

The oil supply system ensures the operational safety of bearings/couplings and also secures the oil required for the governing system and safety devices of the turbine. The Indian Oil makes lube oil SERVO PRESS T-46 is used for turbine & compressor both. The oil supply system includes the following:

a) Main oil tank

b) Main oil pumps

c) Emergency oil pump

d) Overhead lube oil tanks

e) Lube oil coolers

f) Lube oil filters

g) Governor oil header

h) Lube oil header

i) Oil accumulators

j) Oil centrifuge

Non Destructive Testing

1. WHAT IS NONDESTRUCTIVE TESTING?

A general definition of nondestructive testing (NDT) is an examination, test, or evaluation

performed on any type of test object without changing or altering that object in any

way, in order to determine the absence or presence of conditions or discontinuities that

may have an effect on the usefulness or serviceability of that object. Nondestructive tests

may also be conducted to measure other test object characteristics, such as size; dimension;

configuration; or structure, including alloy content, hardness, grain size, etc. The

simplest of all definitions is basically an examination that is performed on an object of

any type, size, shape or material to determine the presence or absence of discontinuities,

or to evaluate other material characteristics. Nondestructive examination (NDE), nondestructive

inspection (NDI), and nondestructive evaluation (NDE) are also expressions

commonly used to describe this technology. Although this technology has been effectively

in use for decades, it is still generally unknown by the average person, who takes it for

granted that buildings will not collapse, planes will not crash, and products will not fail.

Although NDT cannot guarantee that failures will not occur, it plays a significant role in

minimizing the possibilities of failure. Other variables, such as inadequate design and improper

application of the object, may contribute to failure even when NDT is appropriately

applied.

NDT, as a technology, has seen significant growth and unique innovation over the

past 25 years. It is, in fact, considered today to be one of the fastest growing technologies

from the standpoint of uniqueness and innovation. Recent equipment improvements

and modifications, as well as a more thorough understanding of materials and the use of

various products and systems, have all contributed to a technology that is very significant

and one that has found widespread use and acceptance throughout many industries.

This technology touches our lives daily. It has probably done more to enhance safety

than any other technology, including that of the medical profession. One can only imagine

the significant number of accidents and unplanned outages that would occur if it

were not for the effective use of nondestructive testing. It has become an integral part

of virtually every process in industry, where product failure can result in accidents or

bodily injury. It is depended upon to one extent or another in virtually every major industry

that is in existence today.

In industry, nondestructive testing can do so much more. It can effectively be used for

the:

1. Examination of raw materials prior to processing

2. Evaluation of materials during processing as a means of process control

3. Examination of finished products

4. Evaluation of products and structures once they have been put into service

To summarize, nondestructive testing is a valuable technology that can provide useful

information regarding the condition of the object being examined once all the essential elements

of the test are considered, approved procedures are followed, and the examinations

are conducted by qualified personnel.

2. CONCERNS REGARDING NDT

There are certain misconceptions and misunderstandings that should be addressed regarding

nondestructive testing. One widespread misconception is that the use of nondestructive

testing will ensure, to a degree that a part will not fail or malfunction.

This is not necessarily true. Every nondestructive test method has limitations. A nondestructive test

by itself is not a panacea. In most cases, a thorough examination will require a minimum

of two methods: one for conditions that would exist internally in the part and another

method that would be more sensitive to conditions that may exist at the surface of the

part. It is essential that the limitations of each method be known prior to use. For example,

certain discontinuities may be unfavorably oriented for detection by a specific nondestructive

test method. Also, the threshold of detectability is a major variable that must be

understood and addressed for each method. It is true that there are standards and codes

that describe the type and size of discontinuities that are considered acceptable or rejectable,

but if the examination method is not capable of disclosing these conditions, the

codes and standards are basically meaningless. Another misconception involves the nature

and characteristics of the part or object being examined. It is essential that as much

information as possible be known and understood as a prerequisite to establishing test

techniques. Important attributes such as the processes that the part has undergone and the

intended use of the part, as well as applicable codes and standards, must be thoroughly

understood as a prerequisite to performing a nondestructive test. The nature of the discontinuities

that are anticipated for the particular test object should also be well known and

understood.

Another widespread misunderstanding is related to the personnel performing these examinations.

Since NDT is a “hands-on” technology, the qualifications of the examination

personnel become a very significant factor. The most sophisticated equipment and the

most thoroughly developed techniques and procedures can result in potentially unsatisfactory

results when applied by an unqualified examiner. A major ingredient in the effectiveness

of a nondestructive test is the personnel conducting it and their level of qualifications.

Dye penetrant inspection

· Dye penetrant inspection (DPI), also called liquid penetrant inspection (LPI) or penetrant testing (PT), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials (metals, plastics, or ceramics). The penetrant may be applied to all non-ferrous materials, but for inspection of ferrous components magnetic-particle inspection is preferred for its subsurface detection capability. LPI is used to detect casting and forging defects, cracks, and leaks in new products, and fatigue cracks on in-service components.

Principles

DPI is based upon capillary action, where low surface tension, fluid penetrates into clean and dry surface-breaking discontinuities. Penetrant may be applied to the test component by dipping, spraying, or brushing. After adequate penetration time has been allowed, the excess penetrant is removed, a developer is applied. The developer helps to draw penetrant out of the flaw where a visible indication becomes visible to the inspector. Inspection is performed under ultraviolet or white light, depending upon the type of dye used - fluorescent or non fluorescent (visible).

Materials

Penetrants are classified into sensitivity levels. Visible penetrants are typically red in color, and represent the lowest sensitivity. Fluorescent penetrants contain two or more dyes that fluoresce when excited by ultraviolet (UV-A) radiation (also known as black light). Since Fluorescent penetrant inspection is performed in a darkened environment, and the excited dyes emit brilliant yellow-green light that contrasts strongly against the dark background, this material is more sensitive to small defects.

When selecting a sensitivity level one must consider many factors, including the environment under which the test will be performed, the surface finish of the specimen, and the size of defects sought. One must also assure that the test chemicals are compatible with the sample so that the examination will not cause permanent staining, or degradation. This technique can be quite portable, because in its simplest form the inspection requires only 3 aerosol spray cans, some paper towels, and adequate visible light. Stationary systems with dedicated application, wash, and development stations, are more costly and complicated, but result in better sensitivity and higher sample through-put.

Inspection steps

Below are the main steps of Liquid Penetrant Inspection:

1. Pre-cleaning:

The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or cause irrelevant or false indications. Cleaning methods may include solvents, alkaline cleaning steps, vapor degreasing, or media blasting. The end goal of this step is a clean surface where any defects present are open to the surface, dry, and free of contamination. Note that if media blasting is used, it may "work over" small discontinuities in the part, and an etching bath is recommended as a post-bath treatment.

2. Application of Penetrant:

The penetrant is then applied to the surface of the item being tested. The penetrant is allowed time to soak into any flaws (generally 5 to 30 minutes). The dwell time mainly depends upon the penetrant being used, material being testing and the size of flaws sought. As expected, smaller flaws require a longer penetration time. Due to their incompatible nature one must be careful not to apply solvent-based penetrant to a surface which is to be inspected with a water-washable penetrant.

3. Excess Penetrant Removal:

The excess penetrant is then removed from the surface. The removal method is controlled by the type of penetrant used. Water-washable, solvent-removable, lipophilic post-emulsifiable, or hydrophilic post-emulsifiable are the common choices. Emulsifiers represent the highest sensitivity level, and chemically interact with the oily penetrant to make it removable with a water spray. When using solvent remover and lint-free cloth it is important to not spray the solvent on the test surface directly, because this can remove the penetrant from the flaws. If excess penetrant is not properly removed, once the developer is applied, it may leave a background in the developed area that can mask indications or defects. In addition, this may also produce false indications severely hindering your ability to do a proper inspection.

4. Application of Developer:

After excess penetrant has been removed a white developer is applied to the sample. Several developer types are available, including: non-aqueous wet developer, dry powder, water suspendable, and water soluble. Choice of developer is governed by penetrant compatibility (one can't use water-soluble or suspendable developer with water-washable penetrant), and by inspection conditions. When using non-aqueous wet developer (NAWD) or dry powder, the sample must be dried prior to application, while soluble and suspendable developers are applied with the part still wet from the previous step. NAWD is commercially available in aerosol spray cans, and may employ acetone, isopropyl alcohol, or a propellant that is a combination of the two. Developer should form a semi-transparent, even coating on the surface.

The developer draws penetrant from defects out onto the surface to form a visible indication, commonly known as bleed-out. Any areas that bleed-out can indicate the location, orientation and possible types of defects on the surface. Interpreting the results and characterizing defects from the indications found may require some training and/or experience

5. Inspection:

The inspector will use visible light with adequate intensity (100 foot-candles or 1100 lux is typical) for visible dye penetrant. Ultraviolet (UV-A) radiation of adequate intensity (1,000 micro-watts per centimeter squared is common), along with low ambient light levels (less than 2 foot-candles) for fluorescent penetrant examinations. Inspection of the test surface should take place after a 10 minute development time. This time delay allows the blotting action to occur. The inspector may observe the sample for indication formation when using visible dye. It is also good practice to observe indications as they form because the characteristics of the bleed out are a significant part of interpretation characterization of flaws.

6. Post Cleaning:

The test surface is often cleaned after inspection and recording of defects, especially if post-inspection coating processes are scheduled.

· Advantages and Disadvantages

The main advantages of DPI are the speed of the test and the low cost. The main disadvantages are that it only detects surface flaws and it does not work on very rough surfaces. Also, on certain surfaces a great enough color contrast cannot be achieved or the dye will stain the work piece.

Limited training is required for the operator — although experience is quite valuable. Proper cleaning is necessary to assure that surface contaminants have been removed and any defects present are clean and dry. Some cleaning methods have been shown to be detrimental to test sensitivity, so acid etching to remove metal smearing and re-open the defect may be necessary.

Ultrasonic testing

· In ultrasonic testing (UT), very short ultrasonic pulse-waves with center frequencies ranging from 0.1-15 MHz and occasionally up to 50 MHz are launched into materials to detect internal flaws or to characterize materials. The technique is also commonly used to determine the thickness of the test object, for example, to monitor pipework corrosion.

· Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on concrete, wood and composites, albeit with less resolution. It is a form of non-destructive testing used in many industries including aerospace, automotive and other transportation sectors.

· An example of Ultrasonic Testing (UT) on blade roots of a V2500IAEaircraftengine.Step 1: The UT probe is placed on the root of the blades to be inspected with the help of a special bore scope tool (video probe).Step2: Instrument settings are input.Step 3: The probe is scanned over the blade root. In this case, an indication (peak in the data) through the red line (or gate) indicates a good blade; an indication to the left of that range indicates a crack.

· How its Works

In ultrasonic testing, an ultrasound transducer connected to a diagnostic machine is passed over the object being inspected. The transducer is typically separated from the test object by a couplant (such as oil) or by water, as in immersion testing.

There are two methods of receiving the ultrasound waveform, reflection and attenuation. In reflection (or pulse-echo) mode, the transducer performs both the sending and the receiving of the pulsed waves as the "sound" is reflected back to the device. Reflected ultrasound comes from an interface, such as the back wall of the object or from an imperfection within the object. The diagnostic machine displays these results in the form of a signal with an amplitude representing the intensity of the reflection and the distance, representing the arrival time of the reflection. In attenuation (or through-transmission) mode, a transmitter sends ultrasound through one surface, and a separate receiver detects the amount that has reached it on another surface after traveling through the medium. Imperfections or other conditions in the space between the transmitter and receiver reduce the amount of sound transmitted, thus revealing their presence using the couplant increases the efficiency of the process by reducing the losses in the ultrasonic wave energy due to separation between the surfaces.

· Advantages

1. High penetrating power, which allows the detection of flaws deep in the part.

2. High sensitivity, permitting the detection of extremely small flaws.

3. Only one surface need be accessible.

4. Greater accuracy than other nondestructive methods in determining the depth of internal flaws and the thickness of parts with parallel surfaces.

5. Some capability of estimating the size, orientation, shape and nature of defects.

6. Nonhazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity.

7. Capable of portable or highly automated operation.

· Disadvantages

1. Manual operation requires careful attention by experienced technicians

2. Extensive technical knowledge is required for the development of inspection procedures.

3. Parts that are rough, irregular in shape, very small or thin, or not homogeneous are difficult to inspect.

4. Surface must be prepared by cleaning and removing loose scale, paint, etc, although paint that is properly bonded to a surface usually need not be removed.

5. Couplants are needed to provide effective transfer of ultrasonic wave energy between transducers and parts being inspected unless a non-contact technique is used. Non-contact techniques include Laser and Electro Magnetic Acoustic Transducers (EMAT).

6. Inspected items must be water resistant, when using water based couplants that do not contain rust inhibitors.

Magnetic particle inspection

· Magnetic particle inspection (MPI) is a non-destructive testing (NDT) process for detecting surface and subsurface discontinuities in ferrous materials. The process puts a magnetic field into the part. The piece can be magnetized by direct or indirect magnetization. Direct magnetization occurs when the electrical current is passed through the test object and a magnetic field is formed in the material. Indirect magnetization occurs when no electrical current is passed through the test object, but a magnetic field is applied from an outside source. The magnetic lines of force are perpendicular to the direction of the electrical current which may be either alternating current (AC) or some form of direct current (DC) (rectified AC).

The presence of a surface or subsurface discontinuity in the material allows the magnetic flux to leak. Ferrous iron particles are applied to the part. The particles may be dry or in a wet suspension. If an area of flux leakage is present the particles will be attracted to this area. The particles will build up at the area of leakage and form what is known as an indication. The indication can then be evaluated to determine what it is, what may have caused it, and what action should be taken if any.

· Types of electrical currents used

· There are several types of electrical currents used in MPI. For a proper current to be selected one needs to consider the part geometry, material, the type of discontinuity you're looking for, and how far the magnetic field needs to penetrate into the part.

· Alternating current (AC) commonly used to detect surface discontinuities. Using AC to detect subsurface discontinuities is limited due to what is known as the skin effect, where the current runs along the surface of the part. Because the current alt