PERFORMANCE EVALUATION OF
BOILERS (80 AND 40 TPH) AND 21MW
STEAM TURBINE OF COGEN PLANT
D.P.TAWARE
Post Graduate Student, Department of Mechanical Engineering, MIT College of Engineering, Pune -38, Maharashatra, India
P.E.CHAUDHARI
Department of Mechanical Engineering, MIT College of Engineering Pune-38, Maharashtra, India
U.M.SHIRSAT
Nav Sahyadri College of Engineering, Pune, Maharashtra, India [email protected]
Abstract :
The proposed study is conducted at The Malegaon Sugar Mills, Baramati, and District Pune. Data is collected for a high pressure 80 TPH & 40TPH bagasse fired boiler. The boilers are natural circulation and bi-drum water tube type. The both boilers are equipped with super heater, air heater and economizer in order to utilize maximum available heat of flue gases. Boiler efficiency is calculated by indirect method. Also plant has 21 MW cogeneration capacity, with two turbines are installed with capacity 14MW (Back Pressure Type) & 7MW (Extraction Cum Condensing Type). From the heat input given to turbines per unit of electricity generated, the turbine heat rate is calculated. Different instruments and devices are used to record the different parameters of both boilers & turbines. Steam produced per ton of bagasse is being found out for both boilers.
Keywords: Bagasse; HP Boiler; Efficiency; Turbine heat rate. 1. Introduction
Main power generating plants in India are either hydro-power or thermal-power plants. At present, about 30 % of total electricity consumed in the country is being generated by hydro-power plants and the rest is generated by thermal power units i.e. steam run turbines, internal combustion engines, gas turbines and nuclear power plants. With the increasing population and industrial development, the required demand of electricity is being compensated by thermal power plants.
Anjum Munir et.al conducted the trial at Pahrianwali Sugar Mills, Lalian District Jhang and data collected for a 60 tons bagasse fired boiler. Boiler efficiency is calculated on the basis of flue-gases temperature leaving the boiler and total heat values of steam. Different instruments and devices are used to record bagasse flow rates and steam flow rates separately. The efficiencies on both methods are found to be 77.86 % and 78.36 %, respectively. The results obtained from both the methods are not significantly different. Steam produced per ton of bagasse is found to be 2.20 tons for 23 kg/cm2 pressure and 350°C temperatures.[1]
A.N. Anozie et.al. carried out energy and exergy analyses of a thermal power plant in order to evaluate the energetic and exergetic efficiencies and irreversibility’s of units, sections and the overall system. The optimum fuel-air ratio and optimum combustion temperature at different throughputs was determined. It was found that throughput did not influence the energy efficiencies of the units but the exergy efficiencies. Throughput did not influence the energy and exergy efficiencies of the sections.[2]
Ansari et.al. Calculated the efficiency of a bagasse fired boiler having steam generating capacity of 90 tons/hr. Working pressure of steam 24 kg/cm2 for working temperature 350°C. The temperature of feed water is 100°C. The experiments were conducted with 50 % moisture in bagasse. The average quantity of bagasse consumed is 53 tons/hr. The efficiency was found to be 61 % under the existing condition of boiler house.[3].
Jagadeesan et.al. Analyzed the Energy Conservation Measures (ECMs) for Co-generation plant (COGEN) in process industries. The COGEN is aimed at increasing the total power generation and meeting the process steam requirements. The energy conservation study is conducted in the cooling towers in the COGEN plant and a control method is proposed with variable speed drive (VSD) to conserve energy and also to increase the net power generation in the plant.[4]
was done for the existing and the proposed evaporator effects and the results are compared. It is concluded that the amount of steam consumption will reduce by 9 T/h and exergy losses are reduced by48% of its original value if the existing quadruple effect is modified to a quintuple effect. A cost analysis is performed to determine the variation of the average cost of generation of power with the generation temperature of the steam.[5] Marc A. Rosen et.al carried out an efficiency analysis, accounting for both energy and exergy considerations, of a design for a cogeneration-based district energy system. A case study is considered for the city of Edmonton, Canada, by the utility Edmonton Power. For the overall processes, as well as individual sub processes and selected combinations of sub processes, the exergy efficiencies are generally found to be more meaningful and indicative of system behavior than the energy efficiencies.[6]
Minhas et.al. calculated the efficiency of a bagasse-fired boiler having a steam generating capacity of 35 tons/hr whose super-heated steam pressure was 23 kg/cm2 and steam temperature 350°C. The efficiency calculations are based on “total heat values of steam”. The bagasse flow rate is determined by fitting a glass strip in the bagasse chute and the average value is found to be 16 tons/hr. The steam flow rates are recorded from steam totalizer installed at boiler control panel and the average value is found to be 35.40 tons/hr. The boiler efficiency is being calculated and it is 78.57 %.[7]
Mustafa Bayrak et.al.carried out thermodynamic analysis of an actual diesel engine based cogeneration plant with a total capacity of 11.52 MW electrical powers, 9 t/h of steam and 140 t/h of hot water is carried out by analyzing the components of the system separately. In presented study author provided important information regarding exergetic performance of the entire plant and its components through exergy destructions and exergy efficiencies.[8]
Sangamesh Y G et.al. carried out the trial for energy balance of an actual 2500 TCD plant. The turbine hardware model is used to predict the optimum amount of power that can be cogenerated from the system for different generation temperatures at a pressure of 45 bar. The optimum superheat temperature is found to be 500°C for a backpressure turbine with single extraction. Selected actual operating data are employed for analysis and performance assessment. The cogeneration plant performance tests are carried out to determine the power output and plant heat rate. Excess electricity generation has been sold to the utility company. The continuous need for steam combined with the savings on electricity purchases made the cogeneration technology well suited for the company energy needs.[9]
S.K. Tyagi el.al. evaluated the energy efficiency of boiler with different losses. Boiler consumes measure chunk of fuel in any processing industry. Efficiency of any Boiler depends upon minimization of various indirect losses of the boiler so that amount of energy input in the boiler by burning the fuel can be maximum utilized for generation of steam and cost of steam can be minimized ultimately. The proposed data mining technique can prove to be a very effective tool for evaluating and maintain cluster wise boiler efficiency and indirect losses. Also it is very helpful to meet the objective of energy conservation and fuel saving by curbing the losses with the help of various check points. Cluster wise evaluation of boiler efficiency is a major highlight of data mining technique.[10]
2. Methodology
The proposed study is conducted at The Malegaon Sugar Mills, Baramati, District Pune. The two boilers are installed by sugar mill having capacity of 80 & 40 TPH respectively. Steam generation tubes has been arranged vertically between two drums which have a common vertical center line for both the boilers. Super heater is arranged in front of the boiler bank and is screened from the furnace by two rows of tubes. Both boiler are designed for natural circulation of water and is of bottom-supported type. Both boilers are equipped with induced draught fan, forced draught fan and secondary air fans. Boiler accessories air heater and economizer are used to enhance the thermal efficiency of the boiler by utilizing high temperature out going flue gases. A multistage centrifugal feed water pump is also used for both the boilers separately.
The maximum continuous rating of steam of the boiler is 80 tons/hr & 40 tons/hr. The designed superheated steam pressure and temperature are 67 kg/cm2 and 540 °C respectively.14 MW back pressure turbine and 7 MW double extraction cum condensing turbines are installed for generating 21MW electricity. Bagasse is the main fuel used for both the boilers for combustion in furnace. Bagasse is a fibrous material which is left by last mill of the tandem, after the extraction of juice. The calorific value of bagasse mainly depends upon the moisture content and pol content in bagasse.
The main objective of this study is to determine the best utilization of available heat of bagasse by calculating the boiler efficiency, turbine heat rate, steam generated per unit weight of bagasse of The Malegaon Sugar Mills, Baramati, District Pune under prevailing condition. The plant is having the capacity of 4000 TCD in Maharashtra operating for about 200 days a year had the following equipments:
Turbines- 1 No. of 14 MW Back Pressure turbine.
1No.of 7 MW Double extraction cum condensing turbine.
2.1. Experimentation
2.1.1. Computation of Bagasse GCV on the basis of Moisture & Pol
Moisture content of bagasse (w) = 50 % Pol in bagasse (s) = 2.0 %
(Pol is the % of sugar present in bagasse.)
The calorific values is calculated by using formula
Gross calorific value (G.C.V) = 4600 (1 - w) - 1200 s = 4600 (1 - 0.50) - 1200 (0.02) = 2276 Kcal/kg.
= 9529.61 KJ/kg.
2.1.2 Computation of various Heat Losses and Boiler Efficiency by Indirect method
Table.1. Computation of Boiler Efficiency of 80TPH &40 TPH
Sr. No Description 80 TPH 40TPH Unit
1 Theoretical Air required 3.211 3.211 Kg/kg of bagasse
2 Excess Air supplied on the basis of %
O2 (EA) 31.25 23.53 %
3 Actual Air supplied (AAS) 4.215 3.967 Kg/kg of bagasse
4 Actual mass of Dry Flue Gas 4.344 4.096 Kg/kg of bagasse
5 Heat loss in dry Flue gas (L1) 5.268 4.967 %
6 Heat Loss due to moisture formed due to Hydrogen in the Fuel (L2)
9.955 9.955 %
7 Heat Loss due to moisture in Fuel ( L3)
13.966 13.966 %
8 Heat Loss due to Radiation (L4) 1 1 %
9 Heat Loss due to Unburnt Carbon in
Ash ( L5) 0.49 0.49 %
10 Total % Heat Loss= L1 +L2 + L3+ L4 + L5
30.679 30.378 %
Boiler Efficiency =100 – Total %
Heat Loss 69.321 69.622 %
2.1.3 Computation of Steam to Fuel Ratio
The steam to fuel ratio is calculated by using formula
(1) For 80 TPH Boiler
Steam to fuel ratio= (GCV of bagasse x Boiler Effi.) / (Enthalpy of steam –Enthalpy of feed water)
= (9529.61 x 0.69321) / (3454.80- 615.40)
= 2.325 Kg of Steam/Kg of Bagasse. (2) For 40 TPH Boiler
Steam to fuel ratio = (GCV of bagasse x Boiler Effi.) / (Enthalpy of steam –Enthalpy of feed water)
= (9529.61 x 0.69622) / (3454.80- 551.54)
2.2. Turbine Heat Rate
Heat Rate is defined as the Heat Input in KJ per unit of Electrical Energy generated. It is denoted as Heat Rate= Heat input in KJ/kWh.
In the calculation, the Heat Input is considered at Turbine Inlet.
Table.2. Computation of Turbine Heat Rate – For 14MW Back pressure Turbine.
Sr. No Description Value Unit
1 Qty of Steam at Turbine Inlet 79440 Kg/Hr
2 Steam Enthalpy of Steam entering Turbine
3416.38 KJ/Kg
3 Heat Input at Turbine Inlet 2713972272 KJ/Hr
4 Electrical Energy generated in 1 Hour 13730 kWh
5 Turbine Heat rate 16262.68 KJ/kWh
Table.3. Computation of Turbine Heat Rate – For 7MW Extraction cum condensing Turbine.
Sr. No Description Value Unit
1 Qty of Steam at Turbine Inlet 41300 Kg/Hr
2 Steam Enthalpy of Steam entering
Turbine 3416.38 KJ/Kg
3 Heat Input at Turbine Inlet 141096613.8 KJ/Hr
4 Electrical Energy generated in 1 Hour 6937.5 kWh
5 Turbine Heat rate 16954.92 KJ/kWh
3. Conclusion
The efficiency of bagasse fired boiler is calculated by indirect method. Also the turbine heat rate is calculated under prevailing conditions of the boiler. Steam produced per kg of bagasse is calculated at a pressure of 67 kg/cm2. Table-4 shows the results which are found out by evaluating the performance of the boilers and turbines.
Table.4.Results
Sr. No Description 80 TPH 40TPH Unit
1 GCV of Bagasse at 50 % Moisture 9529.61 9529.61 KJ/Kg
2 Boiler Efficiency by Indirect Method 69.321 69.622 %
3 Steam to Fuel Ratio 2.325 2.284 Kg/Kg of bagasse
4 Turbine Heat Rate 16262.68 16954.92 KJ/kWh
References:
[1] Anjum Munir, A.R.Tahir, M.Shafi Sabir, Khuram Ejaz (2004): Efficiency Calculations of Bagasse Fired Boiler on the Basis of Flue Gases Temperature and Total Heat Values of Steam, Pak. j. life soc. sci., 2(1): 36-39.
[2] A.N. Anozie, P.O. Ayoola,(2012): The Influence of Throughput on Thermodynamic Efficiencies of a Thermal Power Plant,
International Journal of Energy Engineering 2012, 2(5): 266-272.
[3] Ansari, A.S.(1988): Trimming Boiler Losses, Saving Steam. Proceedings of 24th
Annual Convention of Pakistan Society of Cane Sugar Technologists. 1988. pp: 223-229.
[4] A. Jagadeesan , T. G. Sundara Raman, R. Sivaraj, S. Sharmilaa and M. Santhoshkumar (2011): Energy Conservation in Co-Generation
Plant Relating to Turbine Exhaust Steam Condensing System, International Journal of Research and Reviews in Computing
Engineering Vol. 1, No. 1.
[5] J. Raghu Ram, Rangan Banerjee (2003): Energy and cogeneration targeting for a sugar factory, Applied Thermal Engineering 23 (2003) 1567–1575.
[6] Marc A. Rosen, Minh N. Le, Ibrahim Dincer (2005): Efficiency analysis of a cogeneration and district energy system, Applied Thermal Engineering 25 (2005) 147–159.
[8] Mustafa Bayrak and Afsin Gungor(2011): Efficiency assessment of a cogeneration system, International Journal of the Physical Sciences Vol. 6(28), pp. 6439-6449.
[9] Sangamesh Y G, Suchitra G, Jangamshetti S H (2012): Performance Assessment of 2500 TCD Cogeneration Plant, International Journal of Scientific & Engineering Research Volume 3.
