super critical boiler technology skd
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Super Critical Boiler Technology Necessity of Supercritical Boilers. Measures to improve plant efficiency. Necessity of higher temperatures. Material constraints and innovations. Advantages of forced circulation. Types of supercritical boiler construction.
Necessity of supercritical boilers Improvement in plant efficiency. Reduced size in comparison to subcritical. Reduction in CO2 emmission.
Measures to improve plant efficiency Increasing steam parameters. Increasing reheat temperatures. Increasing feed water temperature. Reducing absolute pressure in condenser. Reducing flue gas exit temperature. Optimising excess air Ensuring complete combustion.
Understanding Supercritical / Subcritical cycleSupercritical cycle1-2-3-4-1Critical Point 221 bar-a, 371 deg-C 3 5
Supercritical cycle 1-2 - Feedwater pumping/heating 2-3 - Feedwaterheating / superheating 3-4 - Turbine expansion
T
Sub critical cycle1-2-3-4-5-6-1
4-1 - Condenser ( Latent heat rejection)
Subcritical cycle3 2 2 1 1 4 6 4
1-2 - Feedwater pumping/heating 2-3 - Feedwater heating 3-4 - Evaporation ( Latent heat addition) 4-5 - Superheat
S
5-6 - Turbine expansion 6-1 - Condenser ( Latent heat rejection)
Simple Supercritical / Subcritical cycle
PARAMETERS Vs EFFICIENCY GAIN
PRESSURE > TEMP 538/539 538/566 566/566 580/600 600/620
175 _ 0.75 1.47 2.76 3.74
241 1.78 2.64 3.44 4.81 5.79
300 2.42 3.37 4.26 5.74 6.77
SUPERCRITICAL BOILER TECHNOLOGY THERE ARE TWO TYPES OF TECHNOLOGIES. 1)BENSON TECHNOLOGY-- ADOPTED BY SIEMENS GERMANY 2)SULZER TECHNOLOGY-- ADOPTED BY ABB SWITZERLAND, MHI, ALSTOM
Advantages of SC Steam Generators
I ) Higher cycle efficiency means Primarily less fuel consumption less per MW infrastructure investments, also less emission less auxiliary power consumption less water consumption II ) Operational flexibility Better temp. control and load change flexibility Shorter start-up time Suitable for variable pressure operation
BENEFITS PROJECTED BY BHEL BENEFITS 1) 2) 3) 4) 500 MW STEAM GENERATOR SUBCRITICAL BASE BASE BASE BASE SUPERCRITICAL 68800 88270 385 +1.0
COAL SAVING ( T/YR) CO2 REDUCTION (T/YR) SO2 REDUCTION ( T/YR) CYCLE EFFICIENCY (% )
( ASSUMING OPERATING HOURS 8000 PER YEAR )
Presentations by M/s Doosan Design Engineers:2. Gain in Fuel consumption & plant Efficiency:
ItemGenerator Output Steam Pressure Steam Temperature Boiler Efficiency Plant efficiency Coal Consumption Coal Consumption difference Co2 Generation Co2 Generation difference
Unit Sub criticalMW Kg/cm2g C % % Ton/hr Ton/yr Ton/hr Ton/yr 500 169 538/538 87.31 Base Base Base Base Base
Supercritical500 246 538/538 566/566 87.31 + 1.6 -13.7 87.31 + 3.8 -27.8
-90,009 -182,646 -16.9 -34.3
-11,033 -225,351
Sub-Critical Vs Supercritical boilersTechnoeconomic comparison TypicalBasis Capacity Fuel Fuel GCV : 800 MW : Indian coal with 40 % ash : 3500 kCal/kg
DescriptionTurbine Heat rate Boiler efficiency Plant heat rate Coal consumption Ash Generation CO2 SO2
UnitkCal / kWh % kCal / kWh MM T/Annum MM T/Annum MM T/Annum MM T/Annum
Subcritical1936 87 % 2225 4.068 1.627 7.371 0.0492
Supercritical1835 87% 2109 3.856 1.542 6.986 0.0466
Reduction101 (5.22%) 0 101 (5.22%) 0.212 0.085 0.385 0.003
COST PROJECTIONS BY L&TREDUCTION IN COAL COST : Rs. 17.00 Crores (approx)/ ANNUM CARBON BENEFIT : Rs.34.00 Crores (approx)/ANNUM
INITIAL INVESTMENT (Rs Crores) : SUBCRITICAL : 2800 3000 SUPERCRITICAL : 33OO 3500 DIFFERENCE : 500.00 PAYBACK : 10 YEARS
Pressure part componentsSec SH Final Final SH RH Pri. RH
Pri. SH Upper Furnace
Economiser
Lower Furnace
Hopper
Water / Steam path in Supercritical Boiler
Economiser
Lower furnace
Upper furnace
Furnace roof / 2nd pass
Separator
Primary SH Final SH Secondary SH
2nd stg desuperheater
1st stg desuperheater
Boiler Circulating PumpA boiler recirculation (BCP) will be capable of operating satisfactorily in conjuction with the feed water pumps. The BCP is used during start up and at low loads to provide adequate mass flow through the furnace waterwall tubes.
SH WS SH spray WW BCP ECO BR WSD WDC
HP S/T
Condenser Blow
BFP
BCP System Schematic Flow Diagram
START UP CIRCUIT Function: At low loads, once through flow is not sufficient to cool the furnace and water needs to be circulated. At low loads ( < 25% load), water/steam mix from the 2nd pass rear wall header enters into the separator and is recirculated through the drain tank and recirculation pump. Steam from the separator outlet enters the Pri SH inlet header At normal loads, steam from the 2nd pass rear wall header enters the separator and directly passes to the Pri SH inlet header. There is no recirculation.
Start up system description The normal operation mode of a forced circulation boiler is called the once through mode. In this mode, the entire flow from the evaporator is directed to the superheater because the medium is slightly superheated. To assure the adequate cooling of the furnace tubes of the evaporator during start-up or in low load operation, a minimum flow-rate of approximately 25%MCR is required. At low load the waterwall flow is therefore kept constant at a value corresponding to 25%MCR. As a consequence wet condition persist at the water separator and the saturated water is recirculated by means of the boiler circulation system. For example, at load 20%MCR, the evaporator will generate a saturated steam flow of 20%MCR. Since the total evaporator flow is kept at 25%MCR, a saturated water flow of 5%MCR is directed into the separator and has to be discharged by the boiler circulation system The boiler circulation system consists of drain lines from the water separator, the boiler circulation pump and a set of separator level control valves.
CONTROL CONCEPT Normally the drain flow from the separator is re-circulated via the BCP into the economizer, and control valve situated after the BCP is used for level control. The capacity of the BCP and the direct recirculation system is designed to accommodate the separator drain flow in normal low load operation. Especially during start-up larger amounts of water (swell flow) need be drained from the separator. For this purpose additional drain capacity is provided, dumping the excess water into the condenser flash tank. The respective control valves are situated near the condenser and open when the separator level exceeds a certain threshold lying above the normal set value applicable from normal re-circulation via BCP and control valve
Supercritical Sliding Pressure Boiler Water wall design Comparison of vertical wall and spiral wallVertical Water Wall (with Rifled Tube) Spiral Water Wall
Pressure part components
RIBBED TUBES FOR USE ON VERTICAL FURNACE WALLS
Secondary superheaterInlet header
Outlet header
Function: Second stage superheat. A first stage desuperheater is provided between the primary superheater and secondary superheater Configuration: Coils are arranged in pendant construction in parallel flow. The elements are widely spaced (approx 2 m) Material: SA 213 T22 / SA 213 T91/ SA 213 TP 347H
2ry SH Arrangement
2ry SH Arrangement
Primary ReheaterOutlet header
Function: First stage Reheater Configuration: Coils are arranged in multiple loops. Inlet banks are horizontal, while the outlet bank is vertical. Support: The horizontal coils are supported from economiser sling tubes emerging from the economiser intermediate header. Material: SA 210 Gr C / SA 213 T12 / SA 213 T11 / SA 213 T22
Inlet header
Final ReheaterInlet header Outlet header
Function: Final Reheater. A desuperheater is provided between the primary Reheater and final Reheater Configuration: Coils are arranged in pendant construction in the passage behind the Final superheater in parallel flow. Material: SA 213 T91/ SA 213 TP 347H / CC 2328
Economiser and sling tubes
Sling tubes from the economiser intermediate header act as sling tubes which support the primary superheater / primary reheater coils
Supporting arrangement horizontal coils
SH / RH horizontal tubes
Eco hanger tubes
Buckstay Role of Buckstay : Buckstays are structural members attached to furnaces to prevent implosion & explosion and are provided to retain the shape of Furnace / Secondary Pass. The tubes are connected to tie bars by welding & the tie bars are connected to buckstays by some sliding devices so that the tubes are free to expand along the diameter although the buckstay is not. The buckstays form a rigid frame through corner connections which are welded to corner tubes. The joint between corner plate & the buckstay beam is usually by links & pins to take care of the thermal movement of corner with respect to the buckstay. Although a buckstay can readily take explosion as the beam is held at several places by tie bar connections ,its design becomes critical for implosion when the outer flange is under compressive load and no lateral torsional buckling reastarints are provided.
TYPICAL BUCKSTAY SYSTEM
GA OF TYPICAL SC BOILER Vertical wall with two fire vortex furnace
Air and Flue gas flow in the Boiler
MaterialsS. N o Composition ASME 1 Carbon Steel SA192 SA210 Gr A1 SA210 Gr C SA106 Gr B SA106 Gr C Specification DIN St 35.8 St 45.8 BS BS3059 Pt2 - S2-360, BS3059 Pt2-S2-440 BS3602 Pt1-360 BS3602 Pt1-430 Temperatur e Limit 427 C Waterwalls (nat. circ boilers), downcomers, risers, LTSH coils, Waterwall headers, economisers LTSH, RH coils SH/ RH Used in
2 3
C - 1/2 Mo 1 Cr 1/2 Mo
SA209 T1 SA213 T12 SA335 P12 SA213 T22 SA335 P22 CC 2199 / T23 SA213 T91 SA335 P91
15 Mo3 13 Cr Mo44 BS3059 Pt2 - S2 620 BS3604 Pt 2 620 440 BS3059 Pt2- S2 622490 BS3604 Pt1- 622 BS3059 Pt2 91
482 C 535 C
4 5 6
2 1/4 Cr 1 Mo 2 Cr1.6WVCb 9 Cr 1 Mo 1/2 V
10 CrMo910
577 C 577 C 600 C
SH / RH SH / RH Final SH/ Final RH
X10CrMoVNb 91
7 8 9
18 Cr 10 Ni Cb 18 Cr 9 Ni 3Cu Cb N
SA213 TP347H CC2328 CC 2115
BS3059 Pt2 347251 BS3605 347S59E
635 C 635 C 635C
Final SH/ Final RH Final SH/ Final RH Final SH / RH
Supercritical Sliding Pressure Boiler High Temperature Resistant MaterialSTEAM TEMP. ( ) MS PIPE SH HEATING TUBE H.T.RH PIPE RH HEATING TUBESH RH
5382 1/4 CrMo 18 Cr 2 1/4 CrMo 9 Cr
5669 Cr
600
625
65018 Cr
700
20~25 Cr 9 Cr 18 Cr 18 Cr 20~25 Cr
Ferritic Material
Austenitic Material
Coal, Primary & Secondary Air Flow Diagram
Coal
Coal Bunker
Burner
Coal Piping Primary Air Duct Hot Primary Air Fan Mill Cold Primary Air Fan Secondary Air Duct
Secondary Air Fan
Primary Air Fan
Water & steam Flow DiagramRoof Inlet Manifold 2ry SH Inlet Header 2ry SH Outlet Header Side Outlet Header 2ry SH De-SH Outlet ry 3ry SH 3 SH Inlet 2ry RH Inlet HeaderHeader Header Pry RH De-SH 2ry RH Outlet Header Pry SH De-SH Pry SH Outlet Pry RH Outlet Header Header Eco Outlet Header nd Pass Outlet Header 2 Front Outlet Header Roof Inlet Header 2nd Pass Rear Outlet Header Roof Outlet Header
Water Separator
3ry SH Tube 2ry SH Tube
2ry RH Tube
Pry RH Terminal Bank
Pry SH Terminal Bank
Water Separator Drain Tank
Rear Outlet Header Main Steam Pipe Hanger Inlet Passage Inlet Hanger & Header Passage Header Manifold
Pry RH Bank
Pry SH Bank
Pry RH Bank
Pry SH Bank 2nd Pass Inlet Pipe Pry SH Bank Eco Int. Header
Furnace Intermediate
Furnace Intermediate
Pry RH Bank
Pry RH Bank Eco Int. Header Pry RH Inlet Header Eco Bank 2nd Pass Inlet Ring Header Economizer Inlet Header
Pry SH Inlet Header Eco Bank
Eco Bank
2nd Pass Inlet Manifold
Feed Water
To High Pressure Turbine
To Intermediate Pressure Turbine Boiler Circulating Pump
From High Pressure Turbine
Furnace Inlet Manifold Furnace Inlet Header
Furnace Inlet Manifold
Prepared By: Anup Kumar Singh
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