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THERMALENGINEERING FOR 500 MW BOILER
The laws of thermodynamics describe the transport of heat and work in thermodynamic processes. These laws have become some of the most important in all of physics and other types of science associated with thermodynamics.Laws of thermodynamics The four laws of thermodynamics:The zeroth law of thermodynamics, which underlies the basic definition of temperature. The first law of thermodynamics, which mandates conservation of energy, and states in particular that the flow of heat is a form of energy transfer.
The second law of thermodynamics, which states that the entropy of an isolated macroscopic system never decreases, or (equivalently) that perpetual motion machines are impossible.
The third law of thermodynamics, which concerns the entropy of a perfect crystal at absolute zero temperature, and which implies that it is impossible to cool a system all the way to exactly absolute zero.
Zeroth law of thermodynamicsIf two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.First law of thermodynamicsEnergy can be neither created nor destroyed. It can only change forms.In any process in an isolated system, the total energy remains the same.For a thermodynamic cycle the net heat supplied to the system equals the net work done by the system.The first law can be expressed as the fundamental thermodynamic relation:
Heat supplied to a system = increase in internal energy of the system + work done by the system
Increase in internal energy of a system = heat supplied to the system - work done by the system
This is a statement of conservation of energy: The net change in internal energy (dU) equals the heat energy that flows in (TdS), minus the energy that flows out via the system performing work (pdV).
Second law of thermodynamics
In a few words, the second law states "spontaneous natural processes increase entropy overall." Another brief statement is "heat can spontaneously flow from a higher-temperature region to a lower-temperature region, but not the other way around." Nevertheless, energy can be transferred from cold to hot, for example, when a refrigerator cools its contents while warming the surrounding air, though still all transfers as heat are from hot to cold.Third law of thermodynamics
As temperature approaches absolute zero, the entropy of a system approaches a constant minimum.
Briefly, this postulates that entropy is temperature dependent and results in the formulation of the idea of absolute zero.
The specific definition, which comes from Clausius, is as shown in equation 1 below. S = Q/T Equation 1
In equation 1, S is the entropy, Q is the heat content of the system, and T is the temperature of the system. So, entropy in classical thermodynamics is defined only for systems which are in thermodynamic equilibrium.
As long as the temperature is therefore a constant, it's a simple enough exercise to differentiate equation 1, and arrive at equation 2. S = Q/T Equation 2
Here the symbol " " is a representation of a finite increment, so that S indicates a "change" or "increment" in S, as in S = S1 - S2, where S1 and S2 are the entropies of two different equilibrium states, and likewise Q.
A thermodynamic process is that when there is some sort of energetic change within the system, generally associated with changes in pressure, volume, internal energy, temperature, or any sort of heat transferAdiabatic process - a process with no heat transfer into or out of the system.
Isochoric process - a process with no change in volume, in which case the system does no work.
Isobaric process - a process with no change in pressure.
Isothermal process - a process with no change in temperature.
An adiabatic process is a thermodynamic process in which there is no heat transfer (Q) into or out of the system. In other words Q = 0. An isentropic process occurs at a constant entropy. For a reversible process this is identical to an adiabatic process.An isenthalpic process introduces no change in enthalpy in the system Thermodynamic Process
Thermodynamic cycle
A thermodynamic cycle is a series of thermodynamic processes transferring heat and work, while varying pressure, temperature, and other state variables, eventually returning a system to its initial state. A thermodynamic cycle is a closed loop on a P-V diagram. A P-V diagram's Y axis shows pressure (P) and X axis shows volume (V). The area enclosed by the loop is the work (W) done by the process:
This work is equal to the balance of heat (Q) transferred into the system:
Thermodynamic power cycles are the basis for the operation of heat engines, which supply most of the world's electric power and run almost all motor vehicles. Power cycles can be divided according to the type of heat engine they seek to model. The most common cycles that model internal combustion engines are the Otto cycle, which models gasoline engines and the Diesel cycle, which models diesel engines. Cycles that model external combustion engines include the Brayton cycle, which models gas turbines, and the Rankine cycle, which models steam turbines.
Types of thermodynamic cycles
thermodynamic cycle can (ideally) be made out of 3 or more thermodynamic processes (typical 4). The processes can be any of these: isothermal process (at constant temperature, maintained with heat added or removed from a heat source or sink) isobaric process (at constant pressure) isometric / isochoric process (at constant volume) .adiabatic process (no heat is added or removed from the working fluid) isentropic process, reversible adiabatic process (no heat is added or removed from the working fluid - and the entropy is constant) isenthalpic process (the enthalpy is constant)
Carnot cycle The Carnot cycle is a cycle composed of the totally reversible processes of isentropic compression and expansion and isothermal heat addition and rejection. The thermal efficiency of a Carnot cycle depends only on the temperatures in kelvins of the two reservoirs in which heat transfer takes place, and for a power cycle is:where TL is the lowest cycle temperature and TH the highest. Thermodynamic power cycles
Types of thermodynamic cycles
Carnot cycle Ideal cycle Otto cycle Diesel cycle Scuderi cycle Stirling cycle Joule or brayton cycleRankine cycle
CARNOT ENGINE1-2 - Isothermal Expansion at T1K2-3 - Adiabatic Expansion up to T2K3-4 - Isothermal Compression at T2K4-1 - Adiabatic Expansion up to T1K
For Carnot Cycle = 1 - T2 T1 T1 = Temp. of heat source where T2 = Temp. of heat sink Carnot Cycle gives maximum possible thermal efficiency which can be obtained between any two given temperature limits.
11234STT1T2
Ideal cycle An illustration of an ideal cycle heat engine (arrows clockwise).An ideal cycle is constructed out of:TOP and BOTTOM of the loop: a pair of parallel isobaric processes LEFT and RIGHT of the loop: a pair of parallel isochoric processes
Ideal cycle
Rankine cycle The Rankine cycle is a cycle which converts heat into work. The heat is supplied externally to a closed loop, which usually uses water. This cycle generates about 80% of all electric power used throughout the world,[1] including virtually all solar thermal, biomass, coal and nuclear power plants. It is named after William John Macquorn Rankine, a Scottish polymath.
A Rankine cycle describes a model of steam operated heat engine most commonly found in power generation plants. Common heat sources for power plants using the Rankine cycle are the combustion of coal, natural gas and oil, and nuclear fission.
The Rankine cycle is sometimes referred to as a practical Carnot cycle as, when an efficient turbine is used, the TS diagram begins to resemble the Carnot cycle. The main difference is that heat addition and rejection are isobaric in the Rankine cycle and isothermal in the theoretical Carnot cycle. A pump is used to pressurize liquid instead of gas. This requires a very small fraction of the energy compared to compressing a gas in a compressor (as in the Carnot cycle).
The efficiency of a Rankine cycle is usually limited by the working fluid. Without the pressure reaching super critical levels for the working fluid, the temperature range the cycle can operate over is quite small: turbine entry temperatures are typically 565C (the creep limit of stainless steel) and condenser temperatures are around 30C. This gives a theoretical Carnot efficiency of about 63% compared with an actual efficiency of 42% for a modern coal-fired power station. This low turbine entry temperature (compared with a gas turbine) is why the Rankine cycle is often used as a bottoming cycle in combined cycle gas turbine power stations.
The working fluid in a Rankine cycle follows a closed loop and is re-used constantly. The water vapor with entrained droplets often seen billowing from power stations is generated by the cooling systems (not from the closed loop Rankine power cycle) and represents the waste heat that could not be converted to useful work. Note that cooling towers operate using the latent heat of vaporization of the cooling fluid. The white billowing clouds that form in cooling tower operation are the result of water droplets which are entrained in the cooling tower airflow; they are not, as commonly thought, steam. While many substances could be used in the Rankine cycle, water is usually the fluid of choice due to its favorable properties, such as nontoxic and unreactive chemistry, abundance, and low cost, as well as its thermodynamic properties.
Processes of the Rankine cycle There are four processes in the Rankine cycle, these states are identified by number in the diagram to the right.
Process 1-2: The working fluid is pumped from low to high pressure, as the fluid is a liquid at this stage the pump requires little input energy. Process 2-3: The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated vapor. Process 3-4: The dry saturated vapor expands through a turbine, generating power. This decreases the temperature and pressure of the vapor, and some condensation may occur.
Process 4-1: The wet vapor then enters a condenser where it is condensed at a constant pressure to become a saturated liquid. In an ideal Rankine cycle the pump and turbine would be isentropic, i.e., the pump and turbine would generate no entropy and hence maximize the net work output. Processes 1-2 and 3-4 would be represented by vertical lines on the T-S diagram and more closely resemble that of the Carnot cycle. The Rankine cycle shown here prevents the vapor ending up in the superheat region after the expansion in the turbine which reduces the energy removed by the condensers.
Q1-Q2 W Useful work = ------- = --- = --------------- Q1 Q Heat supplied
Rejected Heat = 1 - -------------------- Useful Heat
T1 - T2 T2 Carnot = -------- = 1 - --- T1 T1To achieve more efficiency T2 should be as low as possible and T1 should be as high as possible
THERMAL EFFICIENCY OF CARNOT CYCLE
Selection of Optimum Boiler PressurePressure, MPahTmax = 450 oC
Chart1
0.3534656959
0.3535791061
0.3630267273
0.3785054357
0.3888337305
0.3956885262
0.4006685769
0.4022179496
0.403546982
0.4046856506
0.4056319259
0.4064299594
0.4070856329
Efficiency
Sheet1
ph1h2h3h4Pump workTurbine WorkNet WorkHeat InputEfficiencyx 4Overall Eff
3.973209.3213.3333122254110611023117.70.3530.84590.2990
4209.3213.3333022244110611023116.70.3540.84530.2989
5209.3214.3331621855113111263101.70.3630.82930.3011
7.5209.3216.9328021137.611671159.43063.10.3790.79880.3024
10209.3219.43241205610.111851174.93021.60.3890.77520.3014
12.5209.3221.93200200912.611911178.42978.10.3960.75530.2989
15209.3224.431561966.315.11189.71174.62931.60.4010.73740.2955
16209.3225.431381950.416.11187.61171.52912.60.4020.73070.2939
17209.3226.431191934.617.11184.41167.32892.60.4040.72410.2922
18209.3227.431001919.418.11180.61162.52872.60.4050.71770.2904
19209.3228.430801904.219.11175.81156.72851.60.4060.71130.2885
20209.3229.530601889.420.21170.61150.42830.50.4060.70510.2866
21209.3230.530391874.521.21164.51143.32808.50.4070.69890.2845
pEfficiency
3.9730.353
40.354
50.363
7.50.379
100.389
12.50.396
150.401
160.402
170.404
180.405
190.406
200.406
210.407
px 4
3.9730.8459
40.8453
50.8293
7.50.7988
100.7752
12.50.7553
150.7374
160.7307
170.7241
180.7177
190.7113
200.7051
210.6989
pOverall Eff
3.9730.2989966321
40.2988804184
50.3010580649
7.50.302350142
100.3014239079
12.50.2988635439
150.2954530086
160.2939006558
170.2922083696
180.2904428915
190.2885259889
200.2865737644
210.2845121488
Sheet1
3.973
4
5
7.5
10
12.5
15
16
17
18
19
20
24.05
Efficiency
Sheet2
0
0
0
0
0
0
0
0
0
0
0
0
0
Sheet3
0
0
0
0
0
0
0
0
0
0
0
0
0
x 4
Chart2
7.465
7.127
6.921
6.769
6.646
6.448
6.212
6.075
5.881
5.753
5.554
5.407
Pressure, MPa
Entropy, kJ/kg K
Pressure Vs Entroy
Sheet1
17.46530.22767640887.4653096.59367.465326423280.306617.270.8975
27.12733.30628144787.1273080.510267.127324822220.151216.420.8535
36.92135.02529786196.9213063.510736.921323121580.115.90.8267
46.76936.23830625316.7693046.511046.769321421100.07315.520.8068
56.64637.1471025266.6463028.511256.646319620710.057815.210.7908
76.44838.42166861736.4482990.511496.448315820090.039914.720.765
106.21239.64486938716.2122928.511616.212309619350.0246114.130.7343
126.07540.19420842736.0752883.511596.075305118920.021113.780.7164
155.88140.71237756015.8812807.511435.881297518320.0156513.30.6912
175.75340.93801127075.7532750.511265.753291817920.0130212.980.6745
205.55441.08658743635.5542650.510895.554281817290.0099412.480.6485
225.40741.04259871625.4072570.510555.407273816830.00825312.110.6294
Sheet1
00
00
00
00
00
00
00
00
00
00
00
Pressure (MPa)
h, Kj/kg
Pressure Vs Enthalpy
Sheet2
00
00
00
00
00
00
00
00
00
00
00
Entropy, kJ/kg K
h, KJ/kg
Entropy Vs Enthalpy
Sheet3
00
00
00
00
00
00
00
00
00
00
00
00
Pressure, MPa
Qin & Wt (kJ/kg)
Pressure Vs Q & W
0
0
0
0
0
0
0
0
0
0
0
0
Pressure, Mpa
Eff, %
Pressure Vs Eefficiency
00
00
00
00
00
00
00
00
00
00
00
00
Entropy
Q or W
Entropy Vs Q & W
0
0
0
0
0
0
0
0
0
0
0
0
Entropy
Entropy Vs Efficiency
00
00
00
00
00
00
00
00
00
00
00
00
Pmax, MPa
h3 & h4
Optimaization of Boiler Pressure
0
0
0
0
0
0
0
0
0
0
0
0
Pressure, MPa
Entropy, kJ/kg K
Pressure Vs Entroy
Chart1
0.3824540803
0.3971486762
0.4060601925
0.4141263458
0.4218885718
0.4296013824
0.4373888602
0.4454158136
Maximum Temperature C
Efficiency
Effect of Maximum Temperature
Sheet1
Tmax = 450 C
ph1h2h3h4Pump workTurbine WorkNet WorkHeat InputEfficiencyx 4Overall Eff
3.973209.3213.3333122254110611023117.70.3530.84590.2990
4209.3213.3333022244110611023116.70.3540.84530.2989
5209.3214.3331621855113111263101.70.3630.82930.3011
7.5209.3216.9328021137.611671159.43063.10.3790.79880.3024
10209.3219.43241205610.111851174.93021.60.3890.77520.3014
12.5209.3221.93200200912.611911178.42978.10.3960.75530.2989
15209.3224.431561966.315.11189.71174.62931.60.4010.73740.2955
16209.3225.431381950.416.11187.61171.52912.60.4020.73070.2939
17209.3226.431191934.617.11184.41167.32892.60.4040.72410.2922
18209.3227.431001919.418.11180.61162.52872.60.4050.71770.2904
19209.3228.430801904.219.11175.81156.72851.60.4060.71130.2885
20209.3229.530601889.420.21170.61150.42830.50.4060.70510.2866
21209.3230.530391874.521.21164.51143.32808.50.4070.69890.2845
pEfficiency
3.9730.353
40.354
50.363
7.50.379
100.389
12.50.396
150.401
160.402
170.404
180.405
190.406
200.406
210.407
px 4
3.9730.8459
40.8453
50.8293
7.50.7988
100.7752
12.50.7553
150.7374
160.7307
170.7241
180.7177
190.7113
200.7051
210.6989
pOverall Eff
3.9730.2989966321
40.2988804184
50.3010580649
7.50.302350142
100.3014239079
12.50.2988635439
150.2954530086
160.2939006558
170.2922083696
180.2904428915
190.2885259889
200.2865737644
210.2845121488
Sheet1
0
0
0
0
0
0
0
0
0
0
0
0
0
Efficiency
Sheet2
0.2989966321
0.2988804184
0.3010580649
0.302350142
0.3014239079
0.2988635439
0.2954530086
0.2939006558
0.2922083696
0.2904428915
0.2885259889
0.2865737644
0.2845121488
Sheet3
0.8459
0.8453
0.8293
0.7988
0.7752
0.7553
0.7374
0.7307
0.7241
0.7177
0.7113
0.7051
0.6989
x 4
TCh1h2h3h4Pump workTurbine WorkTCNet WorkvmaxvminMEPHeat InputTCEfficiencyTCx 4TCOverall Eff
100419434.63156222315.6933100917.41.3370.001037100686.69566447572721.41000.33710590141000.79921000.2694
90376.9392.23156217415.398290966.71.8580.00102990520.57894280522763.8900.349772053900.7871900.2753
80334.9350.23156212415.31032801016.72.640.00102380385.26292574742805.8800.3623565472800.7748800.2808
70293308.23156207315.21083701067.83.8450.00101770277.78478728962847.8700.3749561065700.7625700.2859
60251.1266.33156202015.21136601120.85.7540.00101160194.82046636972889.7600.3878603315600.7501600.2909
50209.3224.43156196615.11190501174.98.8730.00100550132.42793757212931.6500.4007709101500.7374500.2955
40167.5182.63156191115.11245401229.914.150.0010014086.92487715922973.4400.4136342234400.7246400.2997
30125.8140.83156185515130130128623.40.00099783054.95960849133015.2300.4265057044300.7115300.3035
2083.9498.923156179714.981359201344.0240.350.00099512033.30986732713057.08200.4396417496200.6981200.3069
0
0
0
0
0
0
0
0
0
Tc
Eff
Condenser Temperature Vs Efficiency
0
0
0
0
0
0
0
0
0
Tc
x4
Condenser Temperature Vs Quality
0
0
0
0
0
0
0
0
0
Tc
X4.Eff
00
00
00
00
00
00
00
00
00
0
0
0
0
0
0
0
0
0
Tc
p, kPa
Mean Effective Pressure
Tmaxh3h4
342.226101698342.29122384.6342.20.3824540803342.20.6248342.20.23895730947.518342.2121.308858739
4002975188340010922749.64000.39714867624000.70224000.27887780048.45400129.2307692308
4503156196645011902930.64500.40606019254500.73744500.29942878598.872450134.1298467087
5003309203250012773083.65000.41412634585000.7655000.31680665469.205500138.7289516567
5503449208955013603223.65500.42188857185500.78895500.33282789439.492550143.2785503582
6003582214060014423356.66000.42960138246000.81036000.34810600019.75600147.8974358974
6503712218765015253486.66500.43738886026500.82996500.36298901519.985650152.7290936405
7003840223070016103614.67000.44541581367000.84827000.377801693110.21700157.6885406464
209.3
214.3
2802
1945
857
116.6861143524
301948.658109685
583.430571762
202532.088681447
0.3292499131
181695.198
360.56
0.3534586733
47684.06
169.1523944661
1324
75.5287009063
32024.16918429
1191600
235479.881
67977
0.3295361096
4.2639921722
0.8100301126
977.75
102.2756328305
266571.209409358
Maximum Temperature C
Efficiency
Effect of Maximum Temperature
pmax=10MPa
Chart7
121.308858739
129.2307692308
134.1298467087
138.7289516567
143.2785503582
147.8974358974
152.7290936405
157.6885406464
Tmax, C
MEP, kPa
Effect of Maximum Temperature
Sheet1
Tmax = 450 C
ph1h2h3h4Pump workTurbine WorkNet WorkHeat InputEfficiencyx 4Overall Eff
3.973209.3213.3333122254110611023117.70.3530.84590.2990
4209.3213.3333022244110611023116.70.3540.84530.2989
5209.3214.3331621855113111263101.70.3630.82930.3011
7.5209.3216.9328021137.611671159.43063.10.3790.79880.3024
10209.3219.43241205610.111851174.93021.60.3890.77520.3014
12.5209.3221.93200200912.611911178.42978.10.3960.75530.2989
15209.3224.431561966.315.11189.71174.62931.60.4010.73740.2955
16209.3225.431381950.416.11187.61171.52912.60.4020.73070.2939
17209.3226.431191934.617.11184.41167.32892.60.4040.72410.2922
18209.3227.431001919.418.11180.61162.52872.60.4050.71770.2904
19209.3228.430801904.219.11175.81156.72851.60.4060.71130.2885
20209.3229.530601889.420.21170.61150.42830.50.4060.70510.2866
21209.3230.530391874.521.21164.51143.32808.50.4070.69890.2845
pEfficiency
3.9730.353
40.354
50.363
7.50.379
100.389
12.50.396
150.401
160.402
170.404
180.405
190.406
200.406
210.407
px 4
3.9730.8459
40.8453
50.8293
7.50.7988
100.7752
12.50.7553
150.7374
160.7307
170.7241
180.7177
190.7113
200.7051
210.6989
pOverall Eff
3.9730.2989966321
40.2988804184
50.3010580649
7.50.302350142
100.3014239079
12.50.2988635439
150.2954530086
160.2939006558
170.2922083696
180.2904428915
190.2885259889
200.2865737644
210.2845121488
Sheet1
Efficiency
Sheet2
Sheet3
x 4
TCh1h2h3h4Pump workTurbine WorkTCNet WorkvmaxvminMEPHeat InputTCEfficiencyTCx 4TCOverall Eff
100419434.63156222315.6933100917.41.3370.001037100686.69566447572721.41000.33710590141000.79921000.2694
90376.9392.23156217415.398290966.71.8580.00102990520.57894280522763.8900.349772053900.7871900.2753
80334.9350.23156212415.31032801016.72.640.00102380385.26292574742805.8800.3623565472800.7748800.2808
70293308.23156207315.21083701067.83.8450.00101770277.78478728962847.8700.3749561065700.7625700.2859
60251.1266.33156202015.21136601120.85.7540.00101160194.82046636972889.7600.3878603315600.7501600.2909
50209.3224.43156196615.11190501174.98.8730.00100550132.42793757212931.6500.4007709101500.7374500.2955
40167.5182.63156191115.11245401229.914.150.0010014086.92487715922973.4400.4136342234400.7246400.2997
30125.8140.83156185515130130128623.40.00099783054.95960849133015.2300.4265057044300.7115300.3035
2083.9498.923156179714.981359201344.0240.350.00099512033.30986732713057.08200.4396417496200.6981200.3069
Tc
Eff
Condenser Temperature Vs Efficiency
Tc
x4
Condenser Temperature Vs Quality
Tc
X4.Eff
Tc
p, kPa
Mean Effective Pressure
Tmaxh3h4
342.226101698342.29122384.6342.20.3824540803342.20.6248342.20.23895730947.518342.2121.308858739
4002975188340010922749.64000.39714867624000.70224000.27887780048.45400129.2307692308
4503156196645011902930.64500.40606019254500.73744500.29942878598.872450134.1298467087
5003309203250012773083.65000.41412634585000.7655000.31680665469.205500138.7289516567
5503449208955013603223.65500.42188857185500.78895500.33282789439.492550143.2785503582
6003582214060014423356.66000.42960138246000.81036000.34810600019.75600147.8974358974
6503712218765015253486.66500.43738886026500.82996500.36298901519.985650152.7290936405
7003840223070016103614.67000.44541581367000.84827000.377801693110.21700157.6885406464
209.3
214.3
2802
1945
857
116.6861143524
301948.658109685
583.430571762
202532.088681447
0.3292499131
181695.198
360.56
0.3534586733
47684.06
169.1523944661
1324
75.5287009063
32024.16918429
1191600
235479.881
67977
0.3295361096
4.2639921722
0.8100301126
977.75
102.2756328305
266571.209409358
Maximum Temperature C
Efficiency
Effect of Maximum Temperature
Tmax, C
Quality, x
Effect of Maximum Temperature
Tmax, C
x. eff
Effect of Maximum Temperature
Tmax, C
Wnet & Qin
Effect of Maximum Temperature
Tmax, C
MEP, kPa
Effect of Maximum Temperature
DPNLSHTRPlaten SHTRSCREEnLTSHESPAPHID fanChimneyEconomiserBottom AshDowncomerDrum waterwallFireball Gooseneck Reheater
Steam generation principleSteam power plants operate on Rankine Cycle, DM water as working fluid.Sensible heat is added in economiser +furnaceSteam generation takes place in waterwall.Typical furnace efficiency is 45% approx. Heat transfer in furnace and enclosed superheater takes place thru radiation. condenserCEPLPHBFPHPH+Ecow/wSHHPTIPTRHLPT
Superheater & ReheaterHeat associated with the flue gas is used in superheaters & Reheater, LTSH, economiser.Maximum steam temperature is decided by the operating drum pressure and metallurgical constraints of the turbine blade material.Reheating is recommened at pressure above 100 ksc operating pressure. Reheating is done at 20-25% of the operating pressure.Carbon steel, alloy steel & SS used for tubing of SH & RH.
condenserCEPLPHBFPHPH+Ecow/wSHHPTIPTRHLPT
Principle of circulationDensity water and steam changes with pressure as shown.At higher pressure, density difference reduces.Flow establishment in down comer, waterwall and drum is due to density difference and height of water column (i.e. waterwall) at lower pressure.225ksc185 ksc165 kscPressure (KSC) Sp. gravity
Type of CirculationNatural circulation (upto 165 ksc)
Forced/ assisted circulation (185-190 ksc)Once thru boiler1. Sub critical2. Supercritical
Density difference & height of water columnAssisted by external circulating pump (CC/ BCW pump)
Below 221.5 bar240-360 bar
Circulation ratioIt may be defined as ratio of feed water flow thru down comers to the steam generated in water wall.Ratio of the weight of 2-phase mixture to the weight of dry steam in waterwall.Ratio of the total fluid contained to the weight of the dry steam in waterwall.
CR = 30-35 Industrial boilersCR = 6-8 Natrual cir. BoilersCR = 2-3 Forced cri. BoilersCR = 1 Once thru boilers (Sub critical)CR = 1 Supercritical boilers
Representation of steam/ water parameters on T-S diagram321Sub critical parameterCritical parameter, (225.65 ksc/ 374.16oC)Supercritical parameterTemperature Entropy 374.16oC
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