boiler operation

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‘Open University’ Project Steam Distribution AC/02/01 1 Steam- The Energy Fluid. For many reasons, steam is one of the most widely used commodities for conveying heat energy. 1.Steam is efficient and economic to generate. 2.Steam can easily and cost effectively be distributed to the point of use. 3.Steam is easy to control. 4.Energy is easily transferred to the process . 5.The modern steam plant is easy to manage. 5.Steam is flexible.

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Gas Boiler Operation with all aspect.

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Page 1: Boiler Operation

‘Open University’ Project Steam Distribution AC/02/01 1

Steam- The Energy Fluid.For many reasons, steam is one of the most widely used commodities for conveying heat energy.

1.Steam is efficient and economic to generate. 2.Steam can easily and cost effectively be distributed to the point of use. 3.Steam is easy to control. 4.Energy is easily transferred to the process . 5.The modern steam plant is easy to manage. 5.Steam is flexible.

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Steam Table

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Steam T – h Diagram

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Boiler efficiency

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The boiler

Typical heat path through a smoke tube shell boiler

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External float level controls fitted intwo independent chambers

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The quality of water which is supplied into the boiler is important. It must be at the correct temperature, usually around 80°C, to avoid thermal shock to the boiler, and to keep it operating efficiently. It must also be of the correct quality to avoid damage to the boiler.

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Feed water

Fig:Water temperature versus oxygen content

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Why high feed water temperature?

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Basis for calculation:• The standard dosing rate for sodium sulphite is 8 ppm per 1 ppm of dissolved oxygen.

• It is usual to add an additional 4 ppm to maintain a reserve in the boiler.

• Typical liquid catalyzed sodium sulphite contains only 45% sodium sulphite.

Calculation:

To avoid excess cost for oxygen scavenging chemical.Low blow down.To avoid damage to the boiler itself: thermal shockTo maintain the designed output

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Feed Water

• Cavitation of the boiler feed pump

If water close to boiling point enters a pump, it is liable to flash to steam at the low pressure area at the eye of the pump impeller. If this happens, bubbles of steam are formed as the pressure drops below the water vapour. When the pressure rises again, these bubbles will collapse and water flows into the resulting cavity at a very high velocity.This is known as “cavitation” , it is noisy and can seriously damage the pump.

What is the way to avoid cavitation?

To avoid feed pump cavitation , it is essential to provide the best possible Net Positive Suction Head (NPSH) to the pump so that the static pressure is as high as possible.

Caution: very high condensate return rates (typically over 80%) may result in excessive feedwater temperature and make cavitation in the feed pump.

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Feed TankDesign: cylindrical feedtanks, both vertical and horizontal, the rectangular shape.Materials: Plastic, Cast iron, Carbon steel(Coating), Austenitic stainless steel (SS-304L)Capacity: It should have storage capacity minimum one hour for boiler capacity.Parts: Deareator, manhole, drain valve, steam inlet, dial thermometer, water level indicator, insulation materials mica and air vent.Mainteanance: half yearly clean by water and check any leak.

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Modern Feed Tank.

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Feed tank steam on – off control.

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ABMA Standard for Boiler waterWater Control parameters in PPM.

Constituent Stated as Feed Water BD water

Total Hardness CaCO3 0 - 5 0

P-Alkalinity CaCO3 - 450 – 750

M-Alkalinity CaCO3 - 700 – 1200

O-Alkalinity CaCO3 - 350 – 500

Chloride CaCO3 - < 350

Silica SiO2 -- Max.125

Iron Fe 0.05 – 0.1 --

Phosphate PO4 -- 15 – 30

Sulphite SO3 -- 20- 30

PH 7.5 – 9.5 10.5 – 11.5

TDS -- Max. 3500

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Chloride in terms of NaCl = 1.17 x Chloride in terms of CaCO3

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Feed Water Chemistry

Dissolved Gasses: Oxygen and carbon dioxide can be readily dissolved by water. These gases are aggressive instigators of corrosion. RO or Deareator system.

Water Impurities?Four types of impurities like as suspended solids, dissolved solids, and dissolved gasses and scum foaming substances.

Suspended solids: These are substances that exist in water as suspended particles. They are usually mineral, or organic in origin. Simple multimedia filters are a common way to remove suspended solids. A pressure vessel, filter bed of various sizes of gravel, sand, and anthracite coal is usually sufficient to reduce suspended solids to acceptable levels. Dissolved Solid: The principal ones are the carbonates and sulphates of calcium and magnesium, which are scale-forming when heated. There are other dissolved solids, which are non-scale forming. In practice, any salts forming scale within the boiler should be chemically altered so that they produce suspended solids, or sludge rather than scale. Ion exchange softener or demineralization system are used.

Scum forming substances - These are mineral impurities that foam or scum. One example is soda in the form of a carbonate, chloride, or sulphate.

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Hardness: Hardness is caused by the presence of the mineral salts of calcium and magnesium and it is these same minerals that encourage the formation of scale. There are two common

classifications of hardness:Alkaline hardness (also known as temporary hardness) - Calcium and magnesium bicarbonates are responsible for alkaline hardness. The salts dissolve in water to form an alkaline solution.

When heat is applied, they decompose to release carbon dioxide and soft scale or sludge.

The term 'temporary hardness' is sometimes used, because the hardness is removed by boiling. This effect can often be seen as scale on the inside of an electric kettle.

Non-alkaline hardness and carbonates (also known as permanent hardness) - This is also due to the presence of the salts of calcium and magnesium but in the form of sulphates and chlorides. These precipitate out of solution, due to their reduced solubility as the temperature rises, and

form hard scale, which is difficult to remove. In addition, the presence of silica in boiler water can also lead to hard scale, which can react with calcium and magnesium salts to form silicates which can severely inhibit heat transfer across the fire tubes and cause them to overheat.

Total hardness: Total hardness is not to be classified as a type of hardness, but as the sum of concentrations of calcium and magnesium ions present when these are both expressed as CaCO3. If the water is alkaline, a proportion of this hardness, equal in magnitude to the total

alkalinity and also expressed as CaCO3, is considered as alkaline hardness, and the remainder as non-alkaline hardness. Non-scale forming salts

Non-hardness salts, such as sodium salts are also present, and are far more soluble than the salts of calcium or magnesium and will not generally form scale on the surfaces of a boiler

• pH value :Acids and alkalis have the effect of increasing the conductivity of water above that of a neutral sample. For example, a sample of water with a pH value of 12 will have a higher conductivity than a sample that has a pH value of 7.

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Chemical Reaction

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Water impurities effect on Boiler.

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Why we use Chemical

• Some of the impurities (calcium salts, etc.) begin to precipitate as a result of the higher temperature and pressure of a boiler environment. They either form deposits or react with treatment chemicals to form harmless materials that are removed through blow down. Calcium, for instance, reacts with phosphate at the proper pH to form hydroxyapatite, a harmless precipitate sludge (when dispersed) that falls to the bottom of the boiler where it can be removed through bottom blow down. When boiler water pH is not within the proper range, calcium reacts with phosphate to form harmful calcium phosphate scale. Other impurities such as silica and iron can be tied up by dispersants and chelants and remain suspended in the boiler water where they can be removed by continuous surface or bottom blow down. Left improperly treated silica and iron both can form harmful deposits.

• Chloride control by blow down (bottom and surface)

Sodium hydroxide provides a highly alkaline environment in the boiler. Heat magnifies the• normally corrosive effect water has on steel, since it speeds up chemical reactions.

Maintaining the correct alkalinity range minimizes this highly corrosive effect of water. Alkalinity also plays a critical part in various chemical reactions in the boiler. ,Caustic soda for alkalinity sodium sulfite for oxygen scavenging, phosphate for scale prevention, phosphonates and synthetic dispersants for deposit control and/or removal. Various amines for return condensate treatment, which prevent condensate line corrosion and ultimately corrosion product deposition in the boiler.

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Why we use chemical?

• Sulfite(SO3)Sulfite is used to consume dissolved oxygen in steam boiler systems.

Sulfite reacts with dissolved oxygen to form sulfate, thus making the oxygen unavailable to damage system metals.

• Phosphates

Phosphates are used to react with calcium and magnesium hardness to produce controllable materials (hydroxyapatite and serpentine) removable by blow down.

• Dispersants• Phosphate precipitates (sludge) must be dispersed thoroughly to prevent them• from baking on to the heat transfer surfaces of boilers. A variety of dispersants are

used for this purpose and must be fed in a proper ratio to the phosphate treatment.• Amines• Return condensate is naturally corrosive because of its purity. The pH of pure• water is easily decreased in the presence of carbon dioxide. Carbon dioxide

dissolves in the water to form carbonic acid. Oxygen readily dissolves in pure water also. Both low pH and dissolved oxygen lead to corrosion in any water system especially in the presence of heat. Various amines are used to neutralize the resulting carbonic acid in condensate causing the pH to stabilize at higher less corrosive levels. The return condensate system is then protected from carbonic acid corrosion.

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Test

Conductivity:Conductivity testing is used to monitor the amount of material dissolved in water by measuring its ability to conduct electricity. Its ensuring good steam quality . If a boiler water's conductivity gets too high, indicating excessive dissolved material is present, steam will start to have

trouble escaping the water's surface. This phenomenon is due to increased water surface tension from higher dissolved solids concentrations. The boiler at this point will begin to prime, or foam and bounce, resulting in tiny droplets of boiler water carrying over with the steam

Chlodide Test:

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Blow downChemical dosing of the boiler feed water will lead to the presence of suspended solids in the boiler. These will inevitably collect in the bottom of the boiler in the form of sludge, and are removed by a process known as bottom blow down. This can be done manually - the boiler attendant will use a key to open a blow down valve for a set period of time, usually twice a day.

Two Types of Blow down,1.Bottom Blow down and2.Surface Blow down.

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Level control

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Safety Valve

• The ASME / ANSI PTC25.3 standards applicable to the USA define the following generic terms:• Pressure relief valve - A spring-loaded pressure relief valve which is designed to open to relieve excess pressure and to

reclose and prevent the further flow of fluid after normal conditions have been restored. It is characterised by a rapid-opening 'pop' action or by opening in a manner generally proportional to the increase in pressure over the opening pressure. It may be used for either compressible or incompressible fluids, depending on design, adjustment, or application.

This is a general term, which includes safety valves, relief valves and safety relief valves.• Safety valve - A pressure relief valve actuated by inlet static pressure and characterised by rapid opening or pop action.

Safety valves are primarily used with compressible gases and in particular for steam and air services. However, they can also be used for process type applications where they may be needed to protect the plant or to prevent spoilage of the product being processed.

• Relief valve - A pressure relief device actuated by inlet static pressure having a gradual lift generally proportional to the increase in pressure over opening pressure.

Relief valves are commonly used in liquid systems, especially for lower capacities and thermal expansion duty. They can also be used on pumped systems as pressure overspill devices.

• Safety relief valve - A pressure relief valve characterised by rapid opening or pop action, or by opening in proportion to the increase in pressure over the opening pressure, depending on the application, and which may be used either for liquid or compressible fluid.

In general, the safety relief valve will perform as a safety valve when used in a compressible gas system, but it will open in proportion to the overpressure when used in liquid systems, as would a relief valve.

• The European standard EN ISO 4126-1 provides the following definition:• Safety valve - A valve which automatically, without the assistance of any energy other than that of the fluid concerned,

discharges a quantity of the fluid so as to prevent a predetermined safe pressure being exceeded, and which is designed to re-close and prevent further flow of fluid after normal pressure conditions of service have been restored.

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Safety Valve

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Differ of ASME & DIN

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Safety valve Approval authorities

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Codes and Standards

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Table : Standards relating to safety valves

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Types of Safety Valve

• The ASME standard I and ASME standard VIII for boiler and pressure vessel applications and the ASME / ANSI PTC 25.3 standard for safety valves and relief valves provide the following definition. These standards set performance characteristics as well as defining the different types of safety valves that are used:

• ASME I valve - A safety relief valve conforming to the requirements of Section I of the ASME pressure vessel code for boiler applications which will open within 3% overpressure and close within 4%. It will usually feature two blowdown rings, and is identified by a National Board 'V' stamp.

• ASME VIII valve - A safety relief valve conforming to the requirements of Section VIII of the ASME pressure vessel code for pressure vessel applications which will open within 10% overpressure and close within 7%. Identified by a National Board 'UV' stamp.

• Low lift safety valve - The actual position of the disc determines the discharge area of the valve.• Full lift safety valve - The discharge area is not determined by the position of the disc.• Full bore safety valve - A safety valve having no protrusions in the bore, and wherein the valve lifts to an extent

sufficient for the minimum area at any section, at or below the seat, to become the controlling orifice.• Conventional safety relief valve - The spring housing is vented to the discharge side, hence operational

characteristics are directly affected by changes in the backpressure to the valve.• Balanced safety relief valve - A balanced valve incorporates a means of minimising the effect of backpressure on

the operational characteristics of the valve.• Pilot operated pressure relief valve - The major relieving device is combined with, and is controlled by, a self-

actuated auxiliary pressure relief device.• Power-actuated safety relief valve - A pressure relief valve in which the major pressure relieving device is

combined with, and controlled by, a device requiring an external source of energy.

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Type of safety Valve

• The following types of safety valve are defined in the DIN 3320 standard, which relates to safety valves sold in Germany and other parts of Europe:

• Standard safety valve - A valve which, following opening, reaches the degree of lift necessary for the mass flowrate to be discharged within a pressure rise of not more than 10%. (The valve is characterised by a pop type action and is sometimes known as high lift).

• Full lift (Vollhub) safety valve - A safety valve which, after commencement of lift, opens rapidly within a 5% pressure rise up to the full lift as limited by the design. The amount of lift up to the rapid opening (proportional range) shall not be more than 20%.

• Direct loaded safety valve - A safety valve in which the opening force underneath the valve disc is opposed by a closing force such as a spring or a weight.

• Proportional safety valve - A safety valve which opens more or less steadily in relation to the increase in pressure. Sudden opening within a 10% lift range will not occur without pressure increase. Following opening within a pressure of not more than 10%, these safety valves achieve the lift necessary for the mass flow to be discharged.

• Diaphragm safety valve - A direct loaded safety valve wherein linear moving and rotating elements and springs are protected against the effects of the fluid by a diaphragm.

• Bellows safety valve - A direct loaded safety valve wherein sliding and (partially or fully) rotating elements and springs are protected against the effects of the fluids by a bellows. The bellows may be of such a design that it compensates for influences of backpressure.

• Controlled safety valve - Consists of a main valve and a control device. It also includes direct acting safety valves with supplementary loading in which, until the set pressure is reached, an additional force increases the closing force.

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Type of safety Valve

• EN ISO 4126 lists the following definitions of types of safety valve:• Safety valve - A safety valve which automatically, without the assistance of any energy other than that of the fluid

concerned, discharges a quantity of the fluid so as to prevent a predetermined safe pressure being exceeded, and which is designed to re-close and prevent further flow of fluid after normal pressure conditions of service have been restored. Note; the valve can be characterised either by pop action (rapid opening) or by opening in proportion (not necessarily linear) to the increase in pressure over the set pressure.

• Direct loaded safety valve - A safety valve in which the loading due to the fluid pressure underneath the valve disc is opposed only by a direct mechanical loading device such as a weight, lever and weight, or a spring.

• Assisted safety valve - A safety valve which by means of a powered assistance mechanism, may additionally be lifted at a pressure lower than the set pressure and will, even in the event of a failure of the assistance mechanism, comply with all the requirements for safety valves given in the standard.

• Supplementary loaded safety valve - A safety valve that has, until the pressure at the inlet to the safety valve reaches the set pressure, an additional force, which increases the sealing force. Note; this additional force (supplementary load), which may be provided by means of an extraneous power source, is reliably released when the pressure at the inlet of the safety valve reaches the set pressure. The amount of supplementary loading is so arranged that if such supplementary loading is not released, the safety valve will attain its certified discharge capacity at a pressure not greater than 1.1 times the maximum allowable pressure of the equipment to be protected.

• Pilot operated safety valve - A safety valve, the operation of which is initiated and controlled by the fluid discharged from a pilot valve, which is itself, a direct loaded safety valve subject to the requirement of the standard.

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Table : Safety valve performance summary

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Safety Valve

• Conventional safety valves• Pilot operated safety valve• Full lift, high lift and low lift safety valves• Balanced safety valves

1. Piston type balanced safety valve

2. Bellows type balanced safety valve

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Pilot operated safety valve

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A piston type, pilot operated safety valve

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Materials of construction

• The principal pressure-containing components of safety valves are normally constructed from one of the following materials:

• Bronze - Commonly used for small screwed valves for general duty on steam, air and hot water applications (up to 15 bar).

• Cast iron - Used extensively for ASME type valves. Its use is typically limited to 17 bar g.

• SG iron - Commonly used in European valves and to replace cast iron in higher pressure valves (up to 25 bar g).

• Cast steel - Commonly used on higher pressure valves (up to 40 bar g). Process type valves are usually made from a cast steel body with an austenitic full nozzle type construction.

• Austenitic stainless steel - Used in food, pharmaceutical or clean steam applications.

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Safety valve options and accessories

• Seating material

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LeversOpen and closed bonnetsBellows and diaphragm sealing

LeversLevers

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Atmospheric deareator.

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Pressure deareator

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Method of water level controlling in steam boiler

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Manual level controlling.

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A typical conductivity probe(shown with four tips)

and associated controller

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Typical control using a capacitance probe in a feedtank

(not to scale)

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Typical capacitance probe(shown with head)

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Float control

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Magnetic level controller in a chamber

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Level control using a differential pressure cell (not to scale)

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On – off controll

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Modular controll

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Recirculation feed pump

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Variable speed drive of aboiler water feedpump, with spill-

back

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Two element boiler water level control

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Application of level control

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Protection tubes

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Direct mounted float control with hydraulic cup

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Typical high integrityself-monitoring conductivity probe

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Steam Flow meter

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There are many types of flowmeter available, those suitable for steam applications include:Orifice plate flowmetersTurbine flowmeters (including shunt or bypass types)Variable area flowmetersSpring loaded variable area flowmetersDirect in-line variable area (DIVA) flowmeterPitot tubesVortex shedding flowmeters

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Turbine steam flow meter

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Fire Tube Boiler.

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WHY NEED BOILER MOUNTINGS?

• A number of items must be fitted to steam boilers, all with the objective of improving:

• Operation.• Efficiency.• Safety.

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List of boiler mountings.

• Different fittings and devices necessary for the operation and safety of a boiler are called boiler mountings. The various boiler mountings are:

• 1. Water level indicator• 2. Pressure gauge• 3. Steam stop valve• 4. Feed check valve• 5. Blow-down cock• 6. Fusible plug• 7. Safety valve : spring loaded, dead weight, lever

type.

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1. Water Level IndicatorThe function of the water level indicator is to indicate the level of water in the boiler constantly. Every boiler is normally fitted with two water level indicators at itsfront end. Fig. 12.1 shows a water level indicator used in low pressure boilers. It consists of three cocks and a glass tube. The steam cock I keeps the glass tube in connection with the steam space and cock 2 puts the glass tube in convection withthe water space in the boiler. The drain cock 3 is used to drain out the water from the glass tube at intervals to ascertain that the steam and water cocks are clear in operation. The glass tube is generally protected with a shield.

For the observation of water level in the boiler, the steam and water cocks are opened and drain cock is closed. The rectangular passage at the ends of the glass tubecontains two balls. In case, the glass tube is broken, the balls are carried along its passage to the ends of the glass tube and flow of water and steam out of the boiler is prevented.

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2. Pressure GaugeThe pressure gauge is used to indicate the steam pressure of the boiler. The gauge is normally mounted in the front top of the steam drum. The commonly used pressure gauge is the Bourdon type pressure gauge shown m Fig 12 2 It consists of an elastic metallic tube of elliptical cross-section bent in the form of circular arc. One end of the tube is fixed and connected to the steam of the boiler and other end is convected to a sector wheel through a link. The section remains in mesh with a pinion fixed on a spindle. A pointer is attached to the spindle to read the pressure on a dial gauge.When high pressure steam enters the elliptical tube, the tube section tends to become circular which causes the other end of the tube to move outward. The movement of the closed end of the tube is transmitted and magnified by the link and sector. The sector is hinged at a point on the link. The magnitude of the movement is indicated by the pointer on the dial.

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3. Steam Stop ValveThe function of the stop valve is to regulate the flow of steam from the boiler to the prime mover as per requirement and shut off the steam flow when not required.A commonly used steam stop valve is shown in Fig. 12.3. It consists of main body, valve, valve seat, but and spindle, which passes through a gland to prevent leakage of steam. The spindle is rotated by means of a hand wheel to close or open. 

4. Feed Check ValveThe function of the feed check valve is to allow the supply of water to the boiler at high pressure continuously and to prevent the hack flow of water from the boiler when the pump pressure is less than boiler pressure A commonly used feed check valve is shown in Fig. 12.4. It is fitted to the shell slightly below the normal water level of the boiler. The lift of the non-return valve is regulated by the end position of the spindle which is attached with the hand wheel. The spinfle can be moved up or down with the help of hand wheel which is screwed to the spindle by a nut. Under normal conditions, the non-return valve is lifted due to the water pressure from the pump and water is fed to the boiler. In case pump pressure falls below boiler pressure, valve is closed automatically. or when pump tails.

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5 Blow-Down CockThe function of blow-down cock is to remove sludge or sediments collected at the bottom-most point in the water space in a boiler, while the boiler is steaming. It is also used for complete draining of the boiler A commonly used type of blow- down cock is shown in Fig. 12.5. it consists of a conical plug fitted accurately into a similar casing. The plug has a rectangular opening which may he brought with the line of the passage of the casing by rotating the plug. This causes the water to be discharged from the boiler: [he discharging of water may be stopped by rotating the plug again.the blow-down c’k should be opened when the boiler is in operation br quickforcing out or sediments for maintenance

6. Fusible PlugThe main function of the fusible plug is to put off the fire in the furnace of the boiler when the water level in the boiler falls below an unsafe level and thus avoid the explosion which may occur due to overheating of the tubes and shell. The plug is generally fitted over the crown of the furnace or over the combustion chamber.

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7. Safety ValvesThe function of a safety valve is to prevent the steam pressure in the boiler exceeding the 4esired rated pressure by automatically opening and discharging steam to atmosphere all .Le pressure falls back to normal rated value. There are three types of safety valves spring loaded (Rams bottom) type, dead weight type, and lever type. 

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Boiler Accessories

• Boiler AccessoriesBoiler accessories are those components which areinstalled either inside or outside the boiler to increase theefficiency of the plant and to help in the proper workingof the plant.Various boiler accessories are:1) Air Preheater2) Economizer3) Superheater4) Feed Pump5) Injector

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Air Preheater.

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Super heater

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conomizer

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Feed Pump

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Earlier boiler

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Natural gas is an odourless, colourless, flammable gas. It is non-toxic and lighter than air. The gas chiefly consists of methane (CH4), but also contains other hydrocarbons such as ethane, butane,

propane and naphtha.

We differentiate between rich gas, dry gas and wet gas.

• What is natural gas• Natural gas is a mixture of hydrocarbons, a subject

of a religious cult and academic disputes, as well as an essential resource. It is invisible and odorless. The amount of natural gas in Russia is more than wherever in the world.

• What is the composition of natural gas?• The base of natural gas is methane (CH4), the simplest

hydrocarbon (organic compound consisting of carbon and hydrogen atoms). Normally, it also includes heavier hydrocarbons – methane homologs – such as ethane (C2H6), propane (C3H8), butane (C4H10), and some nonhydrocarbon admixtures.

• Natural gas can exist in the form of gas fields in formations of some rocks, as gas caps (above crude oil), and in dissolved or crystalline forms.

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Fuel consumption

• Gas burners consume fuel based on their BTU output. Natural and propane gas have specific levels of energy contained within them. One cubic-foot of natural gas contains 1075 BTUs of energy. However, gas burners are not 100-percent efficient. If you know the burner efficiency, you can calculate the exact fuel consumption per the output of the burner. If you do not, you will have to use an approximation. LP gas and natural gas contain different amounts of energy, so the conversion factor is different.

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Gas Burner

• A gas burner is a device to generate a flame to heat up products using a gaseous fuel such as acetylene, natural gas or propane. Some burners have an air inlet to mix the fuel gas with air to make a complete combustion. Acetylene is commonly used in combination with oxygen.

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Gas / Fuels Flame temperature

Propane in air 1980 °C

Butane in air 1970 °C

Wood in air (normally not reached in a wood stove)

1980 °C

Acetylene in air 2550 °C

Methane (natural gas) in air 1950 °C

Hydrogen in air 2111 °C

Propane with oxygen 2800 °C

Acetylene in oxygen 3100 °C +

Propane-butane mix with air 1970 °C ~

Coal in air 1900 °C (blast furnace)

Cyanogen (C2N2) in oxygen 4525 °C

Dicyanoacetylene (C4N2) in oxygen 4982 °C (highest flame temperature)

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Table 3: Combustion values of common gases

GasCombustion value

(Btu/ft³) (MJ/m³)

Natural gas (methane) 950 to 1,150 35 to 43

Propane-butane mix 2,500 to 3,200 90 to 120

Propane 2,572 95.8

Butane 3,225 120.1

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Explosive limits and ignition temperatures of common gases

Explosive limits (lower & upper, in %)

Ignition temperatures

Natural gas 4.7 & 15 482-632 °C

Propane 2.15 & 9.6 493-604 °C

Butane 1.9 & 8.5 482-538 °C

Acetylene 2.5 & 81 305 °C

Hydrogen 4 & 75 500 °C

Ammonia 16 & 25 651 °C

Carbon monoxide 12.5 & 74 609 °C

Ethylene 3.4 & 10.8 490 °C