Power plant and calculations

Power plant and calculation site basically includes the detailed study of power plant operation and maintenance, its related all calculations and thumb rules. It also involves detailed troubleshooting guides for operation and maintenance of power plant system/equipments like Boiler, fans, compressors, belt conveyors, ash handling system, ESP, steam turbine, cooling tower, heat exchangers, steam ejectors, condensers WTP. etc. Heat rate, efficiency

Basic calculations on fuels & combustion

Fuel:
It is a substance which releases heat energy on combustion. The principal combustible elements of each fuel are carbon and hydrogen.

Fuels classification:

Primary Fuels: These fuels directly available in nature, Ex: Wood, Peat, Lignite coal, Petroleum and Natural gas.
Secondary Fuel: These are prepared fuels, Ex: Coke, Charcoal, Briquettes, Kerosene, fuel oil, petroleum gas, producer gas etc.

Fuels are also classified as Solid fuels, liquid fuel and Gaseous fuel.

Different types of coals: Peat, Lignite, Bituminous coal, Anthracite coal and Coke.

Gaseous fuels:Natural gas, Coal gas, Coke oven gas, Blast furnace gas, producer gas, Water gas and Sewer gas.

Energy producing elements in fuel: Carbon, oxygen, hydrogen and Sulphur.

Formation of Charcoal & Coke:

Charcoal:It is obtained by destructive distillation of wood.

Coke is formed by destructive distillation of certain types of coal.

Calorific value of fuel: Calorific value (GCV) is the amount of heat released on complete combustion of unit quantity of fuel.It is measured in kcal/kg.

GCV is also known as Higher Calorific Value (HCV),it is given by following formula

GCV or HCV = (8084 X C% + 28922 X (H2%–O2%/8) + 2224 X S%)/100…kcal/kg

Where C, H2, O2 and S are percentage of Carbon, hydrogen, oxygen and Sulphur respectively in fuel.

Net Calorific Value (NCV) or Lower Calorific Value (LCV):

The total heat released by fuel during combustion is not completely utilized. Some heat is taken out by water vapour which is produced during combustion of hydrogen. Such heat value taken by considering heat taken away by water vapour is called NCV or LCV.

LCV = HCV – (9 X H2% X 586), Where H2 = Hydrogen% in fuel and 586 is latent heat of steam

in kcal/kg.

Useful heat Value (UHV) of coal:

NCV = GCV - 10.02 X Percentage of total moisture.

Ultimate analysis:Ultimate analysis indicates the various elemental chemical constituents such as Carbon, Hydrogen, Oxygen, Sulphur etc.

Proximate analysis of coal:Proximate analysis determines fixed carbon, Volatile matter, moisture and percentages of ash.

Volatile Matter (VM) & is its significance:

VM is generally a composition of methane, hydrocarbons, hydrogen and carbon monoxide and other incombustible gases like CO2 and Nitrogen. It is the indication of presence of gaseous fuel in the fuel.

Significance:

Helps in easy ignition of coal by increasing the flame length
Sets minimum limit on the furnace height and volume.

Properties of Coal:

· Caking Index: Indicates binding property of coal.

· Swelling Index: Indicates caking capacity of coal.

· Slacking Index: Indicates the stability of coal when exposed to open atmosphere.

· Grinding Index: It gives the idea of ease of grinding of coal.

· Abrasive Index: Indicates the hardness of coal.

Combustion:

Combustion is the rapid oxidation of fuel accompanied by the production of heat

Oxygen is the major element on earth, making up to 21% (by volume) of our air. Carbon, hydrogen and Sulphur in the fuel combine with oxygen in the air to form carbon dioxide, water vapour and Sulphur dioxide releasing tremendous heat.

Basic requirements of combustion:Fuel, Oxygen and 3T’s

C + O2 = CO2+ Heat 8084 kcal/kg of Carbon.

2C + O2 = 2CO + Heat 2430 kcal/kg of Carbon.

2H2 + O2 = 2H2O 1 Heat 28922 kcal/kg of Hydrogen.

S + O2 = SO2 + Heat 2224 kcal/kg of Sulphur.

Products of Combustion: CO2, CO, O2, SO2 and ash.

Spontaneous combustion: is a phenomenon in which coal bursts into flame without any external ignition source but by itself due to gradual increase in temperature as a result of heat released by combination of oxygen with coal.

Major contents of ash:

Silica (SiO2)
Aluminum oxide (AlO3)
Iron Oxide (Fe2O3)
Sodium Oxide (Na2O)
Potassium Oxide (K2O)
Calcium Oxide (CaO)
Magnesium Oxide or Magnesia (MgO)

Fly ash & Bottom ash :

Fly ash 70–80%, Bottom ash 20–30%.

Fly ash at Economiser : 7–8%, APH: 10–12% and ESP: 80–82% of total fly ash.

Oxygen & Nitrogen present in the air :By weight Oxygen 23% and Nitrogen 77% and by volume Oxygen 21% and Nitrogen 79%.

Stoichiometric air fuel ratio: A mixture of air and fuel, which contains sufficient amount of oxygen for complete combustion.

Rich mixture: Mixture with deficiency of air

Lean mixture: Mixture with excess air

Power generation phenomenon in steam Turbo generators

Theoretical air of combustion:

Minimum amount of air that supplies the sufficient amount of oxygen for the complete combustion of all carbon, hydrogen and any other elements in the fuel that may oxidize is called theoretical air.

Theoretical air required for combustion of carbon:

We know that Carbon on oxidation with Oxygen forms Carbon dioxide.

C + O2 = CO2

12 + 32 = 44 (Molecular weights of Carbon and Oxygen are 12 and 16 respectively)

1 + 2.67 = 3.67

So, 1 kg of Carbon requires 2.67 Kg of Oxygen for complete combustion into 3.67 kg of carbon dioxide.

Similarly

Hydrogen on oxidation forms Water

2H2 + O2 = 2H2O

4 + 32 = 36 (Molecular weights of Hydrogen and Oxygen are 1 and 16 respectively)

1 + 8 = 9

So, 1 Kg of Hydrogen requires 8 Kg of Oxygen for its combustion & forms into water.

Excess air: Amount of extra air given to ensure complete combustion is called excess air.

3T’s of combustion:

Temperature: High enough to maintain the ignition of the fuel.

Turbulence: Is the mixing of fuel and air.

Time: Sufficient enough for combustion.

Specific heat Cp and Cv:

Specific heat is the amount of heat in kcal needed to raise the temperature of 1 kg of substance by 1 °C. Cp and Cv are the specific heat at constant pressure and constant volume of gas.

Solved examples:

Example-1:A Biomass (Bagasse) contains 23% of carbon, 22% of oxygen, 3.5% of Hydrogen and 0.05% of Sulphur, then calculate the theoretical air required for its combustion.

We have, Theoretical air requirement = (11.6 X %C + 34.8 3 (%H2 - %O2/8) + 4.35 X %S)/100…

Kg/kg of fuel.

Therefore, Th air requirement will be = (11.6 X 23 + 34.8 X (3.5 – 22/8) + 4.35 X 0.05))/100

= 2.9 kg of air/kg of fuel.

Example-2:What is the quantity of excess air, if O2 measured in the Boiler outlet flue gas is 6%?

We have, Excess air = (O2%/( 21 - O2%)) X 100

= (6/(21 – 6)) X 100 = 40%

Example-3:A complete combustion requires 2.9 kg of theoretical and 20% of excess air, then calculate the total air consumed for complete combustion per kg of fuel burnt.

Actual quantity of air supplied = (1 + Excess air %/100) X theoretical air

= (1 + 20/100) X 2.9 = 3.48 kg of air/kg of fuel.

Example-4: A flue gas has 10% of CO2 and theoretical calculated CO2 is 12%, then calculate percentage of the excess air.

% of Excess air = ((Theoretical CO2%/Actual CO2%) - 1)) X 100

= (12/10) - 1) X 100 = 20%

Example-5: A Coal sample contains 10% of ash, coal required is 300 MT/day, assuming 100% combustion calculate the mass of ash generated in a day.

Mass of ash generated = (300 X10)/100

= 30 MT

Example-5:A Indonesian coal contains 58% of Carbon, 4.2% of Hydrogen, 11.8% of Oxygen and 0.5% of Sulphur, also needs 20% of excess air for its complete combustion. Calculate the Total air required for complete combustion and O2% in flue gas.

We know that,

Theoretical air required for combustion is = (11.6 X 58 + 34.8 3 (4.2 - 11.8/8) + 4.35 X 0.5)/100

= 5 7.7 Kg/Kg of Coal

Total air = (1 + EA/100) X Theoretical air

= (1 + 20/100) X 7.7

= 9.24 Kg/Kg of Coal

Also we know that EA = (O2 %/(21 - O2%)) X 100

20 = (O2/(21 - O2)) X 100

O2= 3.5%

Safety valves and its basic concepts

Pressure Relief Valve:This device is generally fitted on liquid lines like water, oil line. In this, valve the opening is proportional to increase in the line or vessel pressure. Hence the opening of valve is not sudden, but gradual if the pressure is increased gradually. In relief valve valves may not open 100%, as the line pressure reduces valves closes gradually. Pressure relief valves have higher flow capacities

Pressure Safety Valve: It is fitted on compressible fluid or gas lines. For such a valve the opening is sudden. When the set pressure of the valve is reached, the valve opens almost fully.

Pressure safety valve & relief valves are used for system, equipment & man power protection.

Pressure reducing valve: These may be of hydraulic or pneumatic type used for water lines. This valve reduces the pressure of the water that goes through it, and is used to obtaining a regulated and constant value at its outlet.

Pressure control valves: These may be of hydraulic or pneumatic type used for steam lines

Safety valve:

A safety valve must always be sized and able to vent any source of steam so that the pressure within the protected apparatus cannot exceed the maximum allowable accumulated pressure.Here the valves sizing, manufacturing, installation, positioning & setting are more important.

Factors to be considered for selection/design of a pressure safety valve:

Connection size and type

Operating pressure

Operating Temperature

Back pressure

Service

Required capacity

Thermodisc

Thermal compensation

Blow down & Operating gap

Terminology used in safety valves:

Set pressure: It is the pressure at which safety valve lifts or pops up.It is usually 106-107% of operating pressure.

Reseat pressure: It is the pressure at which Safety valve seats.

Blowdown: It is the Blowdown is the difference between set pressure and reseating pressure of a safety valve expressed as a percentage of set pressure.

Blow down of safety valve = (Set pressure – Reseat pressure) X 100 / Set pressure

Blow down of safety valves is in the range of 2 to 5%.

Chattering: Excessive pressure loss at the inlet of the safety valve will cause extremely rapid opening and closing of the valve, this is called as chattering.

Chattering may result into lowered capacity as well as damage to the seating surface of the valve. Continuous chattering may result into damage to the other parts.

Following recommendation wil assists in eliminating the chattering

The area of the inlet nozzle should be equal to the the inlet area of safety valve & that nozzle should be short as possible

Inlet nozzle corners must be rounded to a radius of not less than ¼ of the diameter opening

Sonic Vibrations: Flashing, choked flow sudden flow or cut/off of steam in safet valves & related lines may result into sonic vibration. This velocity is usually reached when the valve pressure drop rises to 50% of the upstream pressure. Vibration of long pipelines can also occur due to mechanical damage.

IBR acts, regulations & forms used

Precautions to avoid sonic vibrations:

Safety valve should be installed at least 8D to 10D of pipe diameter down stream from any bend in steam line.

Safety valves should not be installed closer than 8D to 10D to pipe diameters either upstream or down stream from the diverging or converging “Y” fittings.

The safety valve nozzle should never be installed in a steam line in a position directly opposite a branch line of equivalent size.

Accumulating test pressure: The accumulation test is done on boilers to limit the excessive pressure rising while the safety valve is in open. The test is carried on new boilers or new safety valves with full firing condition with MSSV and feed water valves closed. It is conducted as long as water in drum permits generally 7 minutes for water tube boilers.

25-Questions & answers on Boilers safety valves

Boiler safety valves overhauling steps

Consideration for installation of safety valve:

Exhaust drain & cover plate vent piping must be installed so that they will not impose under pressure on the safety valve.

Note: Do not plug the cover plate hole or do not reduce the hole piping size.

Discharge pipe of the safety valve should not be supported on the valve body

Clearance between the valve exhaust piping and the discharge stack should be sufficient to prevent contact when considering thermal expansion of the boiler valve

Steam flowing vertically out of the discharge elbow produces a downward reaction on the elbow, in proportion on the quantity of steam flowing & its velocity.
In no case should discharge piping smaller than the outlet valve
For optimum performance safety valves should be serviced regularly

Valve assembly should be within 1⁰ vertical alignments.

Gaskets fitted should be of correct size, should not close the valve inlet opening

10-Tips to reduce LOI in Boilers

Adjustment of set pressure:

Safety valves are set +/- 1% of set pressure.Set pressure should not be changed without the permission of manufacturing unit.

Before proceeding to check the popping (lift) pressure, ensure the pressure gauges used are calibrated. To adjust the popping pressure, remove the lifting gear, exposing the adjusting bolt lock nut. Loosen the lock nut if the opening pressure is low tighten (turn clockwise) the adjusting bolt, if it is high loosen (turn counter clockwise) the bolt. After each adjustment the lock nut should be securely tightened to prevent loosening of the bolt.

Adjustment of blowdown:

If the blow down is not as desired when the set pressure has been obtained, it is must to adjust the rings. The guide (adjusting) ring is the principal blow down control ring. To change its position, remove the guide set screw on the back of the valve body. Insert a screw driver or similar tool and engage one of the notches (these can be seen through set screw hole). The ring can then be turned to the right or left as desired. Turning the guide (upper) ring to the right raises it up and reduces the blow down. Turning the guide (upper) ring to the left lowers it and increases the blow down. After each adjustment always replace and tighten the set screw being careful that its point engages a notch and does not rest on the top of the tooth.

Note: Do not attempt to adjust blow down with lower ring

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Factors which cause safety valve to damage or failure:

Quantity & quality of the steam

Discharge piping stress and back pressure

Variation in ambient temperature

Improper gagging

Improper bolting of flanges

Foreign material in the steam

Improper method of assembly & disassembly

Guidelines for Boiler safety valve setting:

Preliminary checks

Ensure calibrated pressure & temperature gauges are fitted.

Gauges for each individual valves should be fitted

Discharge piping has to be inspected for binding on the valves,supports and welds on piping.

A rope appx. 6-7 meters with a hook one end should be attached to the valve lifting lever before starting the pressure rise. It will help in operating the lever to avoid chattering & over pressure

Have the correct tooling available

Establish the good communication system

Guidelines:

If the unit has Electromatic safety valve, this valve should be in operation firts for more safety of the unit.

Drum valves to should be tested first: Possibilities of valve part damage because of GIRL BLASTING are grater on superheated valves in contrast to the drum valves .If super heater valve is gagged after seat damage while testing other valves, the total valve damage will increase.
Boiler temperature increases during the testing cycle of the Drum valves. Consequently higher temperature steam will be available for super heater steam valves and produce accurate results

Keep water level low as possible, if drum level is high the safety valves may slugged with water causing long blow down & also may result damages to seat & disc.

Maintain pressure rising in the range of 2-3 kg/cm2 per minute, slow pressure rising may result into simmering of the valve.

If fuel feeding system fails at nearer set pressure, then reduce the boiler pressure at least 10% & raise again. Holding the boiler pressure nearer to set pressure for long time may result into simmering & valve lift erratically.

If a valve has to be lifted several times, cooling off period is very must. Cooling period is around 20-30 minutes.

If valves have not been tested with hydro test prior to the steam condition, it is recommended to hand lift before steam actuation.

Challenging situations & troubleshooting during boiler light up & start up

Safety valve floating procedure:

Normally the highest set pressure valve is the valve floated first. While setting this valve other safety valves are gagged.

Start the boiler as per cold start up procedure by modulating the firing.
When the drum pressure reaches about 60–70% of operating pressure gently tighten gage on other safety valve.

Raise pressure slowly by throttling start up vent valve. When 80% of popping up pressure is reached manually operate the safety valve under test. This will blow off any debris or dust left over in the valve internals.

Raise the boiler pressure by modulating the firing

When the pressure reaches nearer to the set pressure close the start up vent. While the safety valve pops (lift), open the start up vent valve and note down the lifting/set pressure value.When the valve sits back, note down the reset pressure

Control of drum level is important to avoid possibility of water carry over from drum to the super heater.

The set pressure is adjusted by either tightening or loosening the adjusting nut. Tightening the nut increases the set pressure and vice versa

Blow down is adjusted by upper rings adjustment.
After setting the set pressure and blow down, bring down the boiler pressure to operating level.

Examples-1: A boiler steam drum safety valve lifts at 125 kg/cm2 and reseats at 120 kg/cm2, then calculate its blow down percentage?

BD% = (125 – 120) X 100/125

=4.0%

Example-2: A boiler super heater safety valve has blow down 3% & has been set at 70 kg/cm2, calculate the reseat pressure.

3% = (70-P2) X 100/70

Reseat pressure P2 =67.90 kg/cm2

Precautions shall be taken during Super heater safety valve set at lower operating temperature than actual:

Safety valves blow down should be set more than required, as blow down percentage decreases as the steam temperature increases. An approximate rule is to add 0.5% of set pressure to the blow down for each 56.5 °C rise in SH steam temperature.

Example-3:
If a Super heater safety valve lifts at 189.5 kg/cm2 & reseats at 180 kg/cm2 at the temperature of 400 deg c, then calculate the blowdown calculation at 540 deg c

We have,

Lift pressure = 189.5 kg/cm2

Reseat pressure =180 kg/cm2

Difference =9.5 kg/cm2

Difference in temperature =540-400 = 140 Deg C

Asper above condition for every 55.6 deg c rise in steam temperature blow down percentage increases by 0.5% of set pressure

140/55.6 X 0.5 X 189.5/100

=2.385 kg/cm2

Hence, blow down at 540 deg c =9.5-2.385 =7.115 kg/cm2

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STEAM CONDENSER,VACUUM AND CALCULATIONS

A steam condenser is device or an appliance in which steam condenses and heat released by steam is absorbed by water. Heat is basically shell & tube type heat exchanger, where cooling water passes through tubes & steam condenses in shell.

The functions of the condensers are:

It condenses the steam exhausted from Turbine last stage

Increase the thermal efficiency of the plant reducing the exhaust pressure and thereby reducing the exhaust temperature

It maintains a very low back pressure on the exhaust side of the Turbine

Supplies feed water to Boiler through deaerator

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Condenser related components:

Hot well
Cooling water inlet & outlet system
Cooling tower
Support springs or expansion neck
Air Ejector system
Condensate extraction system
Cooling water tubes & tube sheet
Vacuum breaker valve
Safety valve or rapture disc
Water box
Air & water vent lines

Types of steam condensers:

Surface Condenser

Air Cooled Condenser

Jet Type Condenser

Types of surface condensers

Down flow type

Central flow type

Inverted flow type

Regenerative type

Evaporative type

Design considerations of surface steam condensers

Design code XEI-IX

Quality & Quantity of steam to be condensed
Exhaust steam pressure and temperatures
Steam velocity
Quantity & quality of cooling water
Operating pressure and temperature of cooling water
Fouling factor
Corrosion allowance

Effects of air leakage in condenser:

Lower Thermal Efficiency: The leaked air in the condenser results in increased back pressure on the turbine this means there is loss of heat drop consequently thermal efficiency of plant will decrease.

Increased Requirement of Cooling Water: The leaked air in the condenser lowers the partial pressure of steam due to this, saturation temperature of steam lowers and latent heat increases. So it requires more cooling water to condense more latent heat steam.

Reduced Heat Transfer: Due to poor conductivity of air heat transfer is poor.

Corrosion: The presence of air in the condenser increases the corrosion rate.

Functions of rapture disc & vacuum breaker valves in surface condensers:

Rapture disc is used to release the high pressure from steam condenser during excess pressure in condenser. Excess pressure may be due to cooling water pump failure or vacuum breaker valve failure etc. Rapture disc is thin steel foil designed to with stand condenser operating pressure, it raptures at high condenser pressure.

Vacuum breaker valve is used to bring down the turbine speed quickly to zero in case of emergency trip of turbine. Valve can be manually or auto opened.

Vacuum:

Vacuum is a sub-atmospheric pressure. It is measured pressure depression below the atmospheric. The condensation of steam in closed vessel produces a partial vacuum by reason of the great reduction in the volume of the low pressure steam or vapour. The back pressure on the steam turbine can be lowered from 1.013 to 0.1bar abs.

Reason for vacuum creation in condensers:

Condenser is mainly used to convert the low pressure steam at the end of the turbine to liquid so that the process is continued. As the pressure in the last phase of turbine is very low so the pressure in the condenser must be lower than that so that the low pressure steam can flow to condenser and get liquefied.

Generally vacuum pumps or ejectors are used to create vacuum in the condenser. Specific volume of water is much lower than the steam. Hence when the condensing process happens, volume of steam reduces and basic vacuum is created.

As liquids takes up less volume than gases whenever a steam is liquefied..there is a huge pressure drop as the drastic decrease in volume of liquids. The volume change takes place in the multiples of thousand at a certain pressure from the original volume of the gas.

Effect of under/low vacuum:

Lesser work done by Turbine & hence lesser power output
Higher steam consumption
Higher exhaust steam temperature

Effect of over/higher vacuum:

It causes sub-cooling effect where hot well temperature reduces more than design which required to be added in boiler leads to heat loss.
Erosion of last stage LP blades due to lower exhaust steam temperature

Reasons for increase in Turbine SSC

16-Perfect reasons for increasing the fuel consumption of Boilers

Vacuum & Condenser efficiency:

It is the ratio of actual vacuum to the maximum obtainable vacuum.

Vacuum efficiency in % =Actual vacuum X 100 / (Atmospheric pressure or barometric pressure-Absolute pressure)

Condenser efficiency =Difference in cooling water inlet & outlet temperatures X 100/(Vacuum temperature-condenser Inlet temperature of cooling water)

Condenser efficiency = (T2 - T1) X 100/(T3 - T1)

T2: Condenser outlet cooling water temperature,

T1: Condenser inlet cooling water temperature,

T3: Temperature corresponding to the vacuum or absolute pressure in the condenser.

Let us have glance over following calculations to for more clear understanding of above script

Example:1

A down flow type surface condenser has vacuum -0.92 kg/cm2 condenses 100 TPH steam at cooling water inlet and outlet temperatures 27 °C and 37 °C respectively, calculate the condenser efficiency.

Given that,

T1 = 27 °C, T2= 37 °C

T3 at vacuum -0.87 kg/cm2 is 48 °C

We have,

Condenser efficiency = (T2 - T1)/(T3 – T1)

= (37 - 27) X 100/(48-27) =47.61%

Example-2:

Exhaust steam from condenser enters at 42 °C, if the vacuum gauge of condenser reads -0.89 kg/cm2, find the vacuum efficiency.

Given that,

Condenser pressure =-0.89 kg/cm2

Exhaust steam temperature = 42 °C

From steam tables, partial pressure of steam at exhaust temperature Ps = 0.084 kg/cm2

Maximum obtainable vacuum by considering atmospheric pressure as 1.033 kg/cm2

= 1.033 - 0.084 = 0.95 kg/cm2

Vacuum efficiency = (Actual vacuum in condenser X 100)/Max. Obtainable vacuum.

= 0.89 X 100/0.95

= 93.6%

Example-3:

The volume of condenser which contains 0.162 kg of air with steam is 4.2 m3.Temperature in the condenser is 42 deg C and there is some water in the condenser. Determine the pressure in the condenser. Take R for air=287/joules/kg K

Given that,

Mass of air Ma =0.162 kg

Volume of air =V=4.2 M3

T=42+273=315 K

We have relation, PaVa=MaRT

Pa X 4.2=0.162 X 287 X 315

Pa=(0.162 X 287 X 315) X 10-5/4.2

Pa=0.035 bar

Partial pressure of water vapour at condenser temperature 42 deg c, Ps=0.08 bar

Pressure in the condenser = Pa+Ps=0.035+0.08 =0.115 bar

Gauge pressure =1.03-0.115 = -0.915 Bar

Example-4:

The air leakage into the steam condenser is 0.721 kg/min.The vacuum near the outlet of ejector is 690 mm of Hg when the barometer reads 760 mm of Hg & temp.at this point is 20 deg c..Calculate the mass of steam condensed.

Solution:

Pressure in the condenser =760-690 =70 mm of Hg

Convert into bar =70 X 0.001333 =0.0931 bar

Partial pressure of steam at 20 deg C =0.022 bar

So partial pressure of air Pa=0.0931-0.022=0.0713 bar

Mass of air leakage =Ma =0.721 kg/min

V = Ma X R X T/Pa

V = 0.721 X 287 X (273+20)/(0.0713 X 105)

V=8.5 M3/min

From the Dalton’s law of partial pressure, volume of the steam is same as air = 8.5 M3/min

Ms =Volume of steam/Specific volume of steam at 0.022 bar

Ms=8.5/62.5 =0.136 kg/min

Example-5:

A down flow type surface condenser is designed to handle 110 TPH of steam, the steam enters the condenser at 0.12 kg/cm2 absolute pressure and 0.9 dryness fraction. Condensate leaves at 45 °C, calculate the quantity of cooling water required, condenser inlet and outlet cooling water temperatures are 29 °C and 37 °C respectively.

Given that,

Mass of exhaust steam Ms = 110 TPH

Condenser pressure = 0.12 kg/cm2a

Dryness fraction x = 0.9

Cooling water condenser inlet temperature T1 = 29 °C

Cooling water condenser outlet temperature T2 = 37 °C

Condensate leaves at temperature Tc = 45 °C

We have,

Latent heat and saturation temperature of steam at exhaust pressure are

Hfg = 569.54 kcal/kg and T3 =49 °C

Mw = (Ms X (hfg X dryness fraction(x) + Cpw (T3 - Tc)))/(Cpw X (T2 - T1))

Mw = 110 X ((569.54 X 0.9) + 1 X (49 - 45))/(1 X (37-29))