Computational Approach of Green House Gases in Thermal Power Plant (An Energy Audit Approach) – Process Model

Computational Approach of Green House Gases in Thermal Power Plant (An Energy Audit Approach) – Process Model

Anil B. Onkar , Dr. G. A. Dhomane, Dr. R.M.Moharil, Prashant P.Mawle

Addl.Ex.Engr. Prof. Elect.Engg. Prof. Elect.Engg Asstt.Director

MSPGCL – KTC Koradi, Govt.College of Engg. Y.C.C.E, Hingna, N.P.T.I, Gopal Nagar, Nagpur 444111, India Chandrapur 431001, India. Nagpur 440034, India. Nagpur 440022, India

Abstract — In this paper carbon di oxide, Sulphur di oxide & water vapor liberated from coal based plant process is calculated with the help of visual basic programming language. The basic theme behind this calculation is detail engineering based on basic principles of combustion & their thermodynamics, strongest way to reduce emission and to improve efficiency of combustion process optimization and is mostly conducted through fuel and air flow regulation. This paper also shows SEC can be reduced by regulating other parameter of Boiler and turbine.

Keywords — SEC (Specific Coal Consumption in Kg/KWh), GUHR (Gross Unit Heat Rate in Kcal/KWh), NUHR (Net Unit Heat Rate in Kcal/KWh), Gross unit efficiency, THR (Turbine Heat rate in Kcal/KWh), GCV (Gross Calorific Value of coal in Kcal/Kg), PLF (Plant Load Factor), ( Efficiency), NCV (Net Calorific Value of coal in Kcal/Kg.)

1. INTRODUCTION

   In a thermal power plant various processes are carried out. The coal is conveyed then it is crushed to a smaller size. Coal mills are provided to pulverise the coal to 200 mesh size and carried in a very fine powdered form to the boiler which produces steam. Feed water for boiler is preheated to get better cycle efficiency. Steam covering out from the boiler is super heated before admitting to the turbine. After performing work in a high pressure turbine the exhaust steam is again reheated to 540 0C and then admitted in intermediate pressure turbine from intermediate pressure turbine steam goes to low pressure turbine and then exhaust steam is condensed to water and this water is again used as a feed water for the boiler. Whole process of steam generation is explained in fig (1).

2. DYNAMIC STATE SPACE BOILER MODEL

   1. Inputs

      SIG = Signal to fuel and air regulators CV = Governor valve flow area

   2. Parameters

      TW = Water wall time constant. CD = Drum storage capacitance

      CSH = Super heater storage capacitance K = Friction drop coefficient

      f = Fuel system dead time

      Tf = Fuel system time constant

   3. States

      = Furnace Heat release

      = Mass flow rate of steam generated in water walls (riser) entering the drum.

      PT = Super heater steam pressure at governor valve. PD = Saturated steam pressure in the drum.

   4. Internal Variables

      m = Mass flow rate of steam from drum to superheater.

   5. Algebraic Equations

      = K

      = CV * PT

   6. Dfferential Equations

   7. Outputs

      = Superheated Steam mass flow rate to high pressure turbine stage from the above, by setting the state time derivatives to zero it is straight forward to obtain the condition for steady state equilibrium as.

   8. Steady State Boiler Model

      = = = = SIG PT = SIG / CV

      PD = (SIG/K)2 + SIG/CV.

      Main assumption and features of the model along with some components on these follow. [1, 2, 3]

      1. Heat release in the furnace as a function of the fuel and air input signal is determined by the fuel system dynamics lags and dead-times associated with coal feeder and pulverizes.

      2. The mass flow of steam from the drum to the super heater is proportional to the square root of the pressure drop between the drum and the Super heater.

      3. The steam mass flow to the high pressure turbine stage is regulated by the governor valve.

3. AIR ENVIRONMENT

   The air pollutants relevant to the activities of TPS were identified as CO2, SPM, RPM, SO2, NOX & CO. The 98% values of SPM during winter season varied between 151-245 µg/m3. Higher levels of SPM were contributed due to unpaved roads and heavy transportation activities. The repairable particulate matter (98%) varied from 61-123

   µg/m3. A 500MW plant using coal with 2.5% sulphur (S),16% ash and 30,000 kilojoules/kilogram (kj/kg) heat cotent will emit each day 200 metric tons of sulphur dioxide (SO2),70 tons of nitrogen dioxide (N2O)and 500 tons of fly ash if no controls are present. In addition the plant will

   generate about 500 tones of solid waste and about 17 giga watt hour (GWH) of thermal discharge. Other significant air pollutants are respirable and suspended particulates, contributed mainly due to power plants and stone crushers. The wide spread disposal of fly ash and stone rejects, too contribute in making the ash /dust air born and inflicting air with poor visibility analysis of various data collected for power plant is based on certain relationship

4. CALCULATION OF HEAT RATE

   Heat rate monitoring give the idea where the wastage of energy exists. Heat rate calculation gives new ideas for better design, modernization and innovative ideas. The result of this study can be handled for getting a design with better efficiency while other efficiency improvement measures are being taken simultaneously.

   Heat rate calculation is carried out in two stages

   Coal Cons x GCV +Oil Cons x its Calorific Value NUHR= ————————————————————-

   Generation measured by bus bar

   Where, Coal is primary fuel and oil is used as secondary fuel.

   Normal practice of calculation

   Gross unit efficiency = Boiler x Turbine x Generator

   1. Boiler Efficiency (By Indirect Method)

      Boiler ( Efficiency) = 100 ( l1 + l2 + l3 + l4 + l5) Eq. 1

      l1 = Loss due to flue gas

      l2 = Loss due to H2 in Fuel

      l3 = Loss due to Moisture in Fuel l4 = Loss due to Unburnt

      l5 = Loss due to radiation, conserve action & unaccounted losses.

      For calculation the losses in equation 1 theoretical air and excess air requirement calculation is carried out is as follows.

      (1) Theoretical air requirement for combustion in Kg/Kg of

      (8) l5 = 1.6 to 2 %

      coal

      Where,

      (11.6 x C) + 34.8 (H2-O2/8) + 4.35S

      = ——————————————— 100

      All values of l1, l2, l3 ,l4 , l5 is used to calculate boiler efficiency from equation number.

   2. Turbine Efficiency

      860 860

      C, H2 ,O2 and S are the percentage of carbon, hydrogen, oxygen and Sulphur present in fuel.

      O2 %

      (2) % excess air supplied = ————– x 100

      21 O2 %

      Where, O2% = O2 in flue gas

      (3) Actual mass of air supplied (AAS)

      EA

      = 1 + ——– x Theoretical air required 100

      M x CPg x (Tf Ta)

      (4) l1 = ————————– x 100

      GCV

      Where: M = mass of dry flue gas in Kg/Kg of fuel (combustion product from fuel CO2 + SO2 + N2 + O2 in flue gas)

      = AAS + 1 Kg of fuel.

      CPg = 0.24 (Specific Heat of flue gas in Kcal/Kg 0C. Tf = Flue gas temperature in 0C.

      Ta = ambient temperature in 0C.

      9H2 {584 + CPs x (Tf Ta)

      (5) l2 = ———————————— x 100 GCV

      Where, H2 = % of H2 in fuel

      CPs = 0.45 (Specific Heat of superheated steam in Kcal / Kg 0C

      584 = Latent heat corresponding to partial pressure of

      Gross Unit Efficiency = —— = B x ——— x G Eq. 2

      UHR THR

      Where,

      UHR = Unit heat rate in Kcal // KWH THR = Thermal heat rate in Kcal / KWH

   3. Geerator Efficiency Assumed as 98to 99%

   860

   GUHR = ————————–

   Gross Unit Efficiency

   In case of Turbine with HP heater and reheater

   M.S. flow ( M.S. enthalpy F/W/ enthalpy)

   + CRH flow ( HRH enthalpy CRH enthalpy

   THR = ——————————————————– Eq. 3

   KWH Generation

   Where,

   M.S. Flow = Main Steam Flow in Kg/hr

   1. Enthalpy = Main steam enthalpy in Kcal / Kg F/W/ enthalpy = Feed Water enthalpy in Kcal / Kg CRH flow = Cold reheat flow in Kg/hr. (i.e. CRH

      flow = 14 % of M.S. flow for 210 mw) HRH enthalpy = Hot reheat enthalpy in Kcal / Kg

      860

      Turbine Efficiency = ———-

      THR

      water vapour.

      m x {584 + CPs x (Tf Ta)

      (6) l3 = ———————————— x 100

      GCV

      Where, m = mass of moisture in flue gas

      CPs = 0.45 (Specific Heat of superheated steam in

      Kcal

      / Kg 0C

      %CO x C 5744

      (7) l4 = ——————— x ———- x 100

      % CO + % CO2 GCV

      Where %CO = %CO in flue gas leaving economiser C = % Carbon in flue gas

      The value of temperature, pressure and flow rate are known from instrumentation and specific enthalpy can be known from steam tables. The values of generation is known from energy meters. If the reading of energy meter connected to generator terminal is considered in this formula number (3). The heat rate obtained is gross unit heat rate and if that from bus bar energy meter is considered then it is NUHR from following equation.

      GUHR X Gross MW

      NUHR = ————————— Eq. 4

      Net MW

      Where,

      Net MW (Gross MW Auxiliary consumption)

      Auxiliary consumption energy consumed by various auxiliaries like ID (Induced Draft Fan, FD (Forced draft Fan) PA ( Primary air Fan) , BFP ( Boiler Feed Pump) and other LT /HT auxiliary .

      GUHR Kcal/ KWh

      SEC = ——— = ————— = Kg/ KWh Eq. 5

      GCV Kcal / Kg

      From equation (5)

      SEC can be reduced

      1. By improving quality of coal

      2. By improving gross unit efficiency (i.e.by reducing losses in Boiler, Turbine and Generator)

5. ENVIRONMENT MANAGEMENT PLAN Environment is defined as Surroundings in

   which the organization operates including air, water, land, human and their interaction. Five techniques are available for alleviating environmental degeneration in the context of coal fired thermal power plants viz.

   1. Supply of low Sulphur coal.

   2. Removal contaminants before combustion.

   3. Removal of contaminates after combustion.

   4. Dilution of air pollutions by taller stack and permitting greater dispersion.

   5. Reduction of coal consumption by reducing SEC

      Present study paper is related with point number 5 Calculation of environmental Impact

      Considering sample of 1 Kg of coal Chemical reaction are

      1. C + O2 = CO2 Eq. 6

         atmosphere and reduction in CO2, SO2, H2O vapour , CO , NOx etc.

         d) From equation (6) CO2 liberated in atmosphere cab be calculated as

         % C

         CO2 = ——– x SEC x 3.67 x load T/Hr 100

         From equation (7)

         % S

         SO2 = ——– x SEC x 2 x load T/Hr 100

         From equation (8)

         % H2

         H2O = ——– x SEC x 9 x load T/Hr 100

         From above formulae, we can conclude that with reduction in SEC corresponding values for CO2, SO2 and H2O vapour liberated in atmosphere can be reduced.

6. ABOUT SOFTWARE PREPARED Calculation of various losses in Boiler, Turbine and

   Generator, their efficiency, overall unit efficiency, Gross unit heat rate (GUHR), Net unit heat rate (NUHR) is calculated with the help of Visual Basic software for which input for various parameters is given. Environmental impact with respect to SO2, CO2, H2O vapour liberated in atmosphere can be calculated. Flow chart for SEC calculation is shown as follows. (6)

   12 + 32 = 44

   1 Kg of carbon takes 2.67 Kg of O2 to from 3.67 Kg of CO2

   1. S + O2 = SO2 Eq. 7

   32 32 = 64

   1 Kg of Sulphur takes 1 Kg of O2 to form 2 Kg of SO2

   (3) H2 + ½ O2 = H2O Eq. 8

   02 + 16 = 18

   01 + 08 = 9

   1 Kg of Hydrogen takes 8 Kg of O2 to form 9 Kg of H2O vapour

   Coal is pollutant and when burnt it produces CO2 and CO, extensive use of coal as a source of energy is likely to disturb the ecological balance as the vegetations are not capable of absorbing such large proportions of CO2 produced by burning of large quantity of coal. Reduction in SEC helps to maintain ecological balance, by reducing air from

   1. Login Form

      Fig.(4)

   2. Proximate to ultimate analysis [5]

      C	=	0.97f + 0.70 (V – 0.1A) – 0.6M
      H	=	0.036f + 0.091 (V 0.1 A) – 0.05 M
      C	=	Carbon content of coal
      F	=	fixed carbon
      V	=	Volatile Matter
      A	=	Ash
      M	=	Moisture

      Fig.(5)

      Fig.(6)

   3. Boiler Efficiency Calculation

      Fig.(7)

   4. Turbine Efficiency Calculation

      Fig.(8)

   5. Generator Efficiency (From efficiency V/s Load graph)

      SEC

      SEC

      1. SEC V/s. GCV (Graph)

         0 .7

         0 .6 9

         0 .6 8

         0 .6 7

         0 .6 6

         0 .6 5

         0 .6 4

         0 .7

         0 .6 9

         0 .6 8

         0 .6 7

         0 .6 6

         0 .6 5

         0 .6 4

         3401 3450

         3500 3525

         3401 3450

         3500 3525

         3480

         G C V

         3480

         G C V

   6. SEC Calculation.

   Fig.(9)

   Fig.(13)

   2600

   2550

   2500

   2450

   2400

   2350

   2300

   2250

   84 101 105 126 168 176 202 212

   O u tp u t m w

   2600

   2550

   2500

   2450

   2400

   2350

   2300

   2250

   84 101 105 126 168 176 202 212

   O u tp u t m w

   GUHR

   GUHR

   J. GUHR V/s. Generator Output (Graph)

   Fig.(10)

   G. Environmental impact calculation

   Fig.(14)

   K. Load V/s. Coal required (Graph)

   152

   142

   132

   122

   Coal

   Coal

   112

   102

   92

   82

   0 .6 8

   0 .7

   0 .7 2

   Fig.(11)

   72

   62

   90 120 150 180 210

   L o a d

   Fig.(15)

   0 .7 6

   0 .7 5

   0 .7 4

   0 .7 3

   0 .7 2

   0 .7 1

   0 .7

   0 .6 9

   0 .6 8

   0 .6 7

   0 .6 6

   0 .7 6

   0 .7 5

   0 .7 4

   0 .7 3

   0 .7 2

   0 .7 1

   0 .7

   0 .6 9

   0 .6 8

   0 .6 7

   0 .6 6

   H. SEC V/s. GUHR (Graph)

   L. Load V/s. Air required (Graph)

   850

   750

   Air

   Air

   650

   550

   450

   F or S E C 0 .68

   K g/kw h

   F or S E C 0 .70

   K g/kw h

   F or S E C 0 .72

   K g/kw h

   2536

   2376

   2435

   G U H R

   2496

   2557

   2536

   2376

   2435

   G U H R

   2496

   2557

   Fig.(12)

   SEC

   SEC

   350

   90 120 150 180 210

   L o ad

   Fig.(16)

   1. Oxygen V/s. Load in mw (Graph)

      200

      180

      O2

      O2

      160

      140

      120

      100

      80

      F or S E C 0 .68

      K g/kw h

      F or S E C 0 .70

      K g/kw h

      F or S E C 0 .72

      K g/kw h

7. COMMENT OF GRAPH.

   1. Graph H. SEC V/s. GUHR – For higher value of GUHR coal consumption will be more for reducing coal consumption losses in Boiler, Turbine has to be reduced by means of adequate operational and maintenance practices.

   2. Graph I. SEC V/s. GCV – higher value of GCV means more heating value for higher GCV coal requirement will be reduced.

      90 120 150 180 210

      L o ad

      Fig.(17)

      1. Load V/s. Co2 liberated (Graph)

         180

         F or S E C

         0 .68 K g/kw h

         F or S E C

         0 .70 K g/kw h

   3. Graph J. GUHR V/s. Generator Output – Generator offers more efficiency near to full load. Hence less coal is required per unit output.

   4. Graph K. Load V/s. Coal – As load on generator increases, coal requirement increases. But for lower value of SEC comparatively less value of coal will be required.

   5. Graph L & M. Load V/s. Air/ O2 required – lesser amount of air/O2 is required for combustion if SEC is less.

      CO 2

      CO 2

      130 F or S E C

      0 .72 K g/kw h

      80

      90 120 150 180 210

      L o ad

      Fig.(18)

   6. Graph N, O & P. Load V/s. Co2 / So2 / H2o vapor – If the specific coal consumption is reduced by means of proper combustion & efficiency enhancement of Boiler, Turbine and Generator emission of Co2 / So2 / H2o vapor will be definitely reduced from atmosphere.

   One line monitoring of Co2, O2 & CO (in order to control the combustion quality) is essential. My above software will

   1. Load V/s. So2 liberated(Graph)

      1 .8

      1 .6

      SO 2

      SO 2

      1 .4

      1 .2

      1

      0 .8

      0 .6

      F o r S E C

      0 .6 8 K g /kw h

      F o r S E C

      0 .7 0 K g /kw h

      F o r S E C

      0 .7 2 K g /kw h

      be definitely useful for studying the effect of various Boiler and Turbine related parameter on specific coal consumption.

8. REDUCTION IN NUHR & GUHR.

1. By reducing in house Auxiliary consumption.

2. Capacity utilization of induction motor used for various fan.

3. By reducing Air leakages/wastages.

4. Proper monitoring and targeting

   90 120 150 180 210

   L o a d

   Fig.(19)

   1. Load V/s. H2O Vapour (Graph)

   57

   52 F or S E C

5. Energy Audit / Water Audit / Proper housekeeping.

6. Energy efficiency of various subsystem used.

7. By means of fuel substitution.

8. WHR. (Waste heat recovery) performance.

9. By reducing Various Thermal/ Electrical Parameter.

In order to verify the possibility of using VFD for various in house auxiliary as well as above discussed parameter my developed software will be helpful.

47

H 2O

H 2O

42

37

32

27

22

90 120 150 180 210

L o a d

0 .68 K g/kw h

F or S E C

0 .70 K g/kw h

F or S E C

0 .72 K g/kw h

Fig.(20)

1. REDUCTION IN NUHR & GUHR.

   1. By reducing in house Auxiliary consumption.

   2. Capacity utilization of induction motor used for various fan.

   3. By reducing Air leakages/wastages.

   4. Proper monitoring and targeting

   5. Energy Audit / Water Audit / Proper housekeeping.

   6. Energy efficiency of various subsystem used.

   7. By means of fuel substitution.

   8. WHR. (Waste heat recovery) performance.

   9. By reducing Various Thermal/ Electrical Parameter.

      In order to verify the possibility of using VFD for various in house auxiliary as well as above discussed parameter my developed software will be helpful.

2. CONCLUSION

   1. Following some points can be studied wrto environment.

      1. Effect of coal quality

      2. Effect of Auxiliary consumption.

      3. Effect of combustion quality.

      4. Effect of operational excellence.

      5. Effect of good maintenance practices.

      6. Misc. Factor (External and Internal)

      7. Effect of condenser vacuum.

      8. Weather effect (Ambient Condition)

      9. Effect of plant ageing effect.

      10. Effects Overhaul (Capital/Annual).

   2. Liberation of Co2, So2 & H2o vapor in atmosphere is reduced by reducing SEC.

   3. Cost /Kwh of generation is reduced.

   4. Increased energy security by reducing imports.

   5. Help to save globe by reducing green house gases

   6. Exact integration of Energy/engg./economics/environment is possible.

3. FUTURE SCOPE

EC act issued by Government of India came into force in era of globalization energy, economics and environment is a key issue for captive plant. Software developed in my paper will be really helpful to developed a users friendly software for captive plant (Like RES based, DG based, Co-generation etc.) with the view to carry out detailed energy audit and detailed environmental audit.

REFERENCES

1. Kaminski J. Applied energy, 75 (2003), 3-4, PP.165-172

2. IEEE Trans-on Power System, Vol (6) No. 1, PP 66-74 feb 1991, de Mello F. P. Boiler Model for System Dynamic Performance Studies.

3. IEEE Trans-on energy conversion vol. 6, No. 1, 177-185, March 1991.

4. Kure-Jensen J. and R. Hanisch Integration of steam turbine controls into Power Plant System.

5. A. Chandra & H. Chandra Impact of Indian and imported coal on Indian thermal power plant Journal of scientific and industrial research vol. (63) Feb. 2004, PP. 156-162.

6. Siddhartha Bhatt and Narayana B.H. (2005). Towards bench marking of gross unit heat rate in coal fired thermal power station. Rational approach Journal of CPRI Vol. 2(2) PP 9-18.

7. Anil B. Onkar (2009) Energy Environment Implication by reducing SEC in thermal power plant. Indian journal of environmental protection vol. 29 issue 1 PP. 53.