MODIFICATIONS OF STEAM POWER PLANT INTO COMBINED CYCLE BY INTRODUCING LNG AS FUEL

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1 MODIFICATIONS OF STEAM POWER PLANT INTO COMBINED CYCLE BY INTRODUCING LNG AS FUEL Akhil Mohandas 1, Subin Thomas 2, Akul Vijay N 3, Gokul V H 4,Jithin Martin 5, Shyam Kumar S 6, Tom M Pynadath 7, Vimal Kumar 8, Rafin T A 9 1-7(B-Tech student, Mechanical Department, Nirmala College of Engineering, Thrissur, Kerala, India) 8(Senior Engineer, Petrochemical Division, FACT, Udyogamandal, Ernakulam, Kerala, India) 9(Assistant Professor, Mechanical Department, Nirmala College of Engineering, Thrissur, Kerala, India) ABSTRACT: The aim of the presented paper is to understand the latest trends in the steam power plant which works on the simple Rankine cycle.steam power plants suffer from limited efficiencies and consequential dominance of fuel prices on generation costs. Combined cycles, however, exploit the waste heat from exhaust gases to boost power output, resulting in overall efficiencies around 50%, which are significantly above those of steam power plants. The underlying idea to write this paper is to study the possibilities of installation of gas turbine with heat recovery steam generator for the required power and steam production, hence determine numerically the cost of power production, steam production, and profit of the company. KEYWORDS: Rankine cycle; Brayton cycle; Cogeneration; Reheat ABBREVATIONS: LNG: Liquefied Natural Gas 1. INTRODUCTION In a steam power plant, power and steam production is done with the help of steam turbines, which works on the basis of simple Rankine cycle. We observe that the use of steam power plant is uneconomical, because it has a lot of disadvantages such as variable heat losses, efficiency is only 35 to 40% and high cost to operate. In a combined cycle power plant (CCPP), or combined cycle gas turbine (CCGT) plant, a gas turbine generator generates electricity and heat in the exhaust is used to make steam, which in turn drives a steam turbine to generate additional electricity. This last step enhances the efficiency of electricity generation. In order to overcome these disadvantages and make economical, we proposed our guide to use the possibilities of a single gas turbine with heat recovery steam generator instead of steam turbines. The gas turbine works on the basis of Brayton cycle. The fuel required for running gas turbine is LNG (Liquefied Natural Gas). Gas turbine with heat recovery steam generator is a form of highly efficient energy generation technology that combines a gas fired turbine with a heat recovery steam generator. The power plant is generates heat. The design uses a gas turbine to create power and then recover the resulting waste heat to produce steam

2 2. LITERATURE SURVEY I. Najjar&Akyurt (1994) reviewed various types of combined cycles, including repowering, integrated gasification and other advanced systems. According to this study: 1). Combined cycles boost power output and efficiency to levels that are considerably above those of steam power plants 2). Repowering, when converting an existing steam plant to combined cycle, offers savings in capital cost as compared to new construction 3). Combined cycle, when integrated with coal gasification, holds promise in converting coal into electric power in an efficient, economical and environmentally acceptable manner 4). The airbottoming cycle (ABC), chemically recuperated gas turbine, compressed air energy storage (CAES) and compressed air storage humidification (CASH) are among advanced concepts with promise II. for combined cycle applications. Khaliq & Kaushik (2004) carried an improved second-law analysis of the combined power-cycle with reheat and showed the importance of the parameters examined. The analysis has included the energy destruction in the components of the cycle and an assessment of the effects of pressure ratio; temperature ratio and number of reheat stages on the cycle performance. The energy balance or second-law approach presented facilitates the design and III. IV. optimization of complex cycles by pinpointing and quantifying the losses. By placing reheat in the expansion process, significant increases in specific power output and efficiency were obtained. The gains are substantial for one and two reheats, but progressively smaller for subsequent stages. Manuel Valdés (2003) shows a possible way to achieve a thermo economic optimization of combined cycle gas turbine (CCGT) power plants. The optimization has been done using a genetic algorithm, which has been tuned applying it to a single pressure CCGT power plant. Once tuned, the optimization algorithm has been used to evaluate more complex plants, with two and three pressure levels in the heat recovery steam generator (HRSG).The variables considered for the optimization were the thermodynamic parameters that establish the configuration of the HRSG. Two different objective functions are proposed: one minimizes the cost of production per unit of output and the other maximizes the annual cash flow. The results obtained with both functions are compared in order to find the better optimization strategy. Bartnik&Ryszard (2011) in their book Conversion of Coal-Fired Power Plant to Cogeneration and Combined-Cycle presents the methodology, calculation procedures and tools used to

3 support enterprise planning for adapting power stations to cogeneration and combined-cycle forms. They alsoanalyse the optimum selection of the structure of heat exchangers in a 370 MW power block, the structure of heat recovery steam generators and gas turbines. Conversion of Coal-Fired Power Plant to Cogeneration and Combined-Cycle also addresses the problems of converting existing power plants to dual-fuel gas-steam combined-cycle technologies coupled with parallel systems. 3. THE EXISTING SYSTEM Fig.1.Schematic Diagram Showing the Simple Steam Cycle in a Power Plant. The schematic diagram Fig.1. Shows a simple steam cycle which works on the basis of simple Rankine cycle. It consists of a boiler, steam turbine, generator, deaerator, pumps, condenser, a source and sink Power and steam production is done with the help of steam turbines. In boiler superheated steam is generated. Steam expands in steam turbine which drives a generator. The cooling water circuit is modelled by sink and cooling water pump. The fuel in the furnace may be furnace oil or coal. It produces an electrical power P el of KW. The mass flow rate of steam through the system is 450kg/s and the enthalpy is kJ/kg. The simple steam cycle is less economical because it has a lot of disadvantages such as variables heat losses, less efficiency and higher cost of operation

4 4. THE PROPOSED SYSTEM Fig.2. Schematic Diagram Showing Combine Power Plant with Gas Turbine. Inorder to overcome the disadvantages of steam power plant we propose a combined cycle power plant with gas turbine which is shown in Fig.2. The above schematic diagram shows a combine cycle power plant with a gas turbine producing an electrical power P el of KW. The mass flow rate of steam through the system is kg/s. We can infer that for the same electrical power the steam production rate is more for a combined. Also the mechanical efficiency and exergy efficiency is more. So the heat loss is less as well the losses in the whole system is less when compared to the simple steam cycle. Combined cycles boost power output and efficiency to levels that are considerably above those of steam power plants

5 6. RESULTS AND DISCUSSION Graph.1. Effect of temperature and entropy of a simple steam turbine power plant system. Graph 2. Effect of temperature and entropy of a combined cycle power plant with gas turbine system. The graphs 1 and 2 show the variation of enthalpy at various temperatures in a steam cycle and a combined cycle power plant. When we compare the cycles obtained we

found that the superheated temperature for combined cycle is 450.4 C while the superheated temperature for simple cycle is 448 C.

The entropy at the superheated stage for simple steam cycle is 6.55KJ/KgK and that of combined cycle is 6.925KJ/KgK. Therefore the efficiency of a combined cycle is better compared to a simple cycle.

6 found that the superheated temperature for combined cycle is C while the superheated temperature for simple cycle is 448 C. This shows the superheated temperature is more for combined cycle than simple cycle. So heat loss is less in a combined cycle than simple steam cycle. The entropy at the superheated stage for simple steam cycle is 6.55KJ/KgK and that of combined cycle is 6.925KJ/KgK. Therefore the efficiency of a combined cycle is better compared to a simple cycle.. Table1 showing different percentage exergy efficiency, losses and exergy transmitted from various equipments in a simple steam power plant. Table 2 showing different percentage exergy efficiency, losses and exergy transmitted from various equipments in a combined cycle power plant. From the above tables 1 and 2 we can infer that the losses in steam power plant are more compared to that of the combined cycle power plant. Also we can conclude that the heat converted into work is more in combined cycle power plant compared to the steam power plant. We can also infer from the above tables that the efficiency of a combined cycle power plant is more compared to that of the steam power plant. This is because steam can be produced from waste heat of the exhaust, and injected into the air delivered by the compressor or into the combustor, thus increasing the electrical output of the gas turbine in a combined cycle

Table 3 Shows gross and net efficiencies of a simple steam power plant. From the above tables 3 and 4 we can infer that net energy for simple steam cycle is 31.

Therefore energy and exergy produced in a combined cycle power plant is more compared to the steam power plant.

7 Table 3 Shows gross and net efficiencies of a simple steam power plant. From the above tables 3 and 4 we can infer that net energy for simple steam cycle is % while that for combined cycle is %. The net exergy for simple steam cycle is % while that for combined cycle is %. Therefore energy and exergy produced in a combined cycle power plant is more compared to the steam power plant. Also we can conclude that the gross efficency of a combined cycle power plant is better compared to the steam power plant. This is also same in case of net efficiencies. Thus dramatic improvements in efficiency at all loads i.e. better efficiency. 7. MERITS OF COMBINED CYCLE Simple-cycle gas turbines that are designed for power generation have often been used when natural gas or distillate fuels can be burned economically. Steam can be produced from waste heat of the exhaust, and injected into the air delivered by the Table 4 Shows gross and net efficiencies of a combined steam power plant. compressor or into the combustor, thus increasing the electrical output of the gas turbine. Dramatic improvements in efficiency at all loads i.e. better efficiency. Improved operating reliability. New modifications can be added at low-cost to existing power facilities. Modifying can greatly enhance the efficiency to levels comparable with those of plants originally constructed as fully-fired combined cycle economic analyses reveal that significant fuel savings justify the capital investment. Cooling requirement of the combined cycle is much lower than the normal steam turbine power plant having same capacity output. It has high ratio of power output to the area occupied. Therefore for designing a combined cycle plant space requirement is not a concern

8 Combined cycle power plant is more suitable for rapid start and shutdown than the steam power plants. Therefore these plants accept load variations quickly and help in maintaining the stability in the electric grid. 8. CONCLUSION Combined cycle generation system features high thermal efficiency, low installed cost, fuel flexibility with a wide range of gas and liquid fuels, low operation and maintenance costs, operating flexibility at base, mid-range and daily start, high reliability and availability, short installation times and high efficiency in small capacity increments. In particular: 1. Combined cycles boost power output and efficiency to levels that are considerably above those of steam power plants. 2. Repowering, when converting an existing steam plant to combined cycle, offers savings in capital cost as compared to new construction. 3. Combined cycle, when integrated with coal gasification, holds promise in converting coal into electric power in an efficient, economical and environmentally acceptable manner. ACKNOWLEDGEMENT This paper is the outcome of hard work with the help and cooperation from many sources. We express our gratitude and sincere thanks to college management and all the faculties of the department of mechanical engineering, Nirmala College of Engineering. Authors are thankful to Petrochemical Division, FACT Udyogamandal for their support and guidance. REFERENCE I. Y. S. H. Najjar & M. Akyurt, Combined cycle with gas turbine engine, Heat Recovery Systems & CHP Vol. 14, No. 2, pp , 1994 II. Khaliq & S.C. Kaushik, Thermodynamic performance evaluation of combustion gas turbine cogeneration system with reheat, Applied Thermal Engineering 24 (2004) III. Manuel Valdés, M Dolores Durán and Antonio Rovira, Thermoeconomic optimization of combined cycle gas turbine power plants using genetic algorithms Applied Thermal Engineering Volume 23, Issue 17, December 2003, Pages IV. Bartnik&Ryszard Conversion of Coal-Fired Power Plant to Cogeneration and Combined- Cycle (2011). V. E. Godoy, S.J. Benz and N.J. Scenna, A strategy for the economic optimization of combined cycle gas turbine power plants by taking advantage of useful thermodynamic relationships, Applied Thermal Engineering Volume 31, Issue 5, April 2011, Pages

9 VI. VII. VIII. IX. Blank and Veatch, Power Plant Engineering, CBS Publishers & Distributors Pvt Ltd., 2005 Edition, Pages Khaliq & S.C.Kaushik, Secondlaw based thermodynamic analysis of Brayton/Rankine combined power cycle with reheats, Applied Energy 78 (2004) Pages Sanjay Onkar Singh and B.N. Prasad Comparative performance analysis of cogeneration gas turbine cycle for different blade cooling means International Journal of Thermal Sciences Volume 48, Issue 7, July 2009, Pages Khaliq & S.C. Kaushik, Secondlaw based thermodynamic analysis of Brayton/Rankine combined power cycle with reheats, Applied Energy 78 (2004), Pages

EFFECT OF AMBIENT TEMPERATURE, GAS TURBINE INLET TEMPERATURE AND COMPRESSOR PRESSURE RATIO ON PERFORMANCE OF COMBINED CYCLE POWER PLANT

EFFECT OF AMBIENT TEMPERATURE, GAS TURBINE INLET TEMPERATURE AND COMPRESSOR PRESSURE RATIO ON PERFORMANCE OF COMBINED CYCLE POWER PLANT Harendra Singh 1, Prashant Kumar Tayal 2 NeeruGoyal 3, Pankaj Mohan