Combined Cycle Thermal Efficiency Research Articles

System Performance and Pollutant Emissions of Micro Gas Turbine Combined Cycle in Variable Fuel Type Cases

This study focuses on an investigation of the operating performance and pollutant emission characteristics of a micro gas turbine combined cycle using biomass gas, replacing natural gas. The models of both recuperative cycle micro gas turbines with a waste heat utilization system and a micro gas-steam turbine combined cycle system are established. When the gas turbine works at 100 kW and the same types of fuel are burnt, the recuperative cycle system consumes less fuel than the gas-steam combined cycle system. The electric efficiency of the recuperative cycle system can reach more than 29%, which is higher than 24% of the gas-steam combined system. The combined cycle thermal efficiency of the recuperative system is as high as 66%, with 36% waste heat utilization efficiency. The electrical efficiency of the recuperative cycle system in the biomass gas case decreases, while that of the gas-steam combined cycle system undergoes little change. When the gas turbine power output increases from 50 kW to 100 kW, the electrical efficiency and combined cycle thermal efficiency increases, but the thermal efficiency of waste heat utilization of recuperative cycle decreases, the NOX and SO2 emissions gradually rise. Under the same working conditions, the NOX emissions of the recuperative cycle system are greater than that of the steam-gas combined cycle system.

Advanced waste heat recovery system based on organic rankine cycle

In this research, Organic Rankine Cycle (ORC) is used to recover heat from exhaust gas of a four-stroke diesel engine. After retrofitting ORC to the engine, Brake power increased from 10473.91 kW to combined – cycle Brake power of 10736.00kW, thermal efficiency increased from 36.01% to combined – cycle thermal efficiency of 51.32% and Exhaust gas temperature decrease from 358oC to 120oC at the exit of the turbocharger. ORC with R12, R22, R134a and R290 as working fluids at saturation and superheated temperatures, pressures and condenser pressures at different ranges were used to compare refrigerants performance in converting low grade exhaust gas waste heat into useful work. This research presents theoretical analysis on four different refrigerants. Applying the above-mentioned refrigerants as working fluid superheated vapour temperature for R12 is 131.72oC, R134a is 129.37oC, R22 is 113.40oC and R290 is 116.95oC. ORC Power generated by turbine gives 94.98kW, 95.56kW. 130.32kW. 262.64kW respectively, ORC Thermal efficiency gives 36%, 29%, 37% and 38% for R12, R22, R134a, and R290 respectively. Combined – cycle power for each of the refrigerant gives 10568.89kW, 10604.23kW, 10569.47kW and 10736.00kW respectively, combined – cycle thermal efficiency for each refrigerant gives 51.14%, 51.18%, 51.14% and 51.32% for R12, R134a, R22 and R290 respectively. R290 offers optimal performance compared to other refrigerants used in this research. The retrofitting of the ORC has saved some supposedly waste exhaust heat energy and has increased both combined cycle power output and thermal efficiency of the engine cycle.

Development and Analysis of the Novel Hybridization of a Single-Flash Geothermal Power Plant with Biomass Driven sCO2-Steam Rankine Combined Cycle.

This study investigates the hybridization scenario of a single-flash geothermal power plant with a biomass-driven sCO2-steam Rankine combined cycle, where a solid local biomass source, olive residue, is used as a fuel. The hybrid power plant is modeled using the simulation software EBSILON®Professional. A topping sCO2 cycle is chosen due to its potential for flexible electricity generation. A synergy between the topping sCO2 and bottoming steam Rankine cycles is achieved by a good temperature match between the coupling heat exchanger, where the waste heat from the topping cycle is utilized in the bottoming cycle. The high-temperature heat addition problem, common in sCO2 cycles, is also eliminated by utilizing the heat in the flue gas in the bottoming cycle. Combined cycle thermal efficiency and a biomass-to-electricity conversion efficiency of 24.9% and 22.4% are achieved, respectively. The corresponding fuel consumption of the hybridized plant is found to be 2.2 kg/s.

FIRST AND SECOND LAW EVALUATION OF COMBINED BRAYTON-ORGANIC RANKINE POWER CYCLE

In the present work, we have conducted thermodynamic analysis of an organic Rankine cycle (ORC) using waste heat from intercooler and regenerator in Brayton cycle with intercooling, reheating, and regeneration (BCIRR). First of all, the first law analysis is used in this combined cycle. Several outputs are revealed in this study such as the cycle efficiencies in Brayton cycle which is dependent on turbine inlet temperature, intercooler pressure ratios, and pinch point temperature difference. For all cycles, produced net power is increased because of increasing turbine inlet temperature. Since heat input to the cycles takes place at high temperatures, the produced net power is increased because of increasing turbine inlet temperature for all cycles. The thermal efficiency of combined cycle is higher about 11.7% than thermal efficiency of Brayton cycle alone. Moreover, the net power produced by ORC has contributed nearly 28650 kW. The percentage losses of exergy for pump, turbine, condenser, preheater I, preheater II, and evaporator are 0.33%, 33%, 22%, 23%, 6%, and16% respectively. The differences of pinch point temperature on ORC net power and efficiencies of ORC are investigated. In addition, exergy efficiencies of components with respect to intercooling pressure ratio and evaporator effectiveness is presented. Exergy destructions are calculated for all the components in ORC.

Performance Evaluation of a Combined Heat and Power Plant in the Niger Delta of Nigeria

This research presents the performance assessment of a combined heat and power plant operating in the Niger Delta region of Nigeria. The main focus is to evaluate the performance parameters of the gas turbine unit and the waste heat recovery generator section of the combined-heat-and-power plant. Data were gathered from the manufacturer’s manual, field and panel operator’s log sheets and the human machine interface (HMI) monitoring screen. The standard thermodynamic equations were used to determine the appropriate parameters of the various components of the gas turbine power plant as well as that of the heat exchangers of the heat recovery steam generator (HRSG). The outcome of all analysis indicated that for every 10C rise in ambient temperature of the compressor air intake there is an average of 0.146MW drop in the gas turbine power output, a fall of about 0.176% in the thermal efficiency of the plant, a decrease of about 2.46% in the combined-cycle thermal efficiency and an increase of about 0.0323 Kg/Kwh in specific fuel consumption of the plant. In evaluating the performance of the Waste Heat Boiler (WHB), the principle of heat balance above pinch was applied to a single steam pressure HRSG exhaust gas/steam temperature profile versus exhaust heat flow. Hence, the evaporative capacity (steam flow) of the HRSG was computed from the total heat transfer in the super-heaters and evaporator tubes using heat balance above pinch. The analysis revealed that the equivalent evaporation, evaporative capacity (steam flow) and the HRSG thermal efficiency depends on the heat exchanger’s heat load and its effective maintenance.

Performance Evaluation of a Combined Heat and Power Plant in the Niger Delta of Nigeria

This research presents the performance assessment of a combined heat and power plant operating in the Niger Delta region of Nigeria. The main focus is to evaluate the performance parameters of the gas turbine unit and the waste heat recovery generator section of the combined-heat-and-power plant. Data were gathered from the manufacturer’s manual, field and panel operator’s log sheets and the human machine interface (HMI) monitoring screen. The standard thermodynamic equations were used to determine the appropriate parameters of the various components of the gas turbine power plant as well as that of the heat exchangers of the heat recovery steam generator (HRSG). The outcome of all analysis indicated that for every 10C rise in ambient temperature of the compressor air intake there is an average of 0.146MW drop in the gas turbine power output, a fall of about 0.176% in the thermal efficiency of the plant, a decrease of about 2.46% in the combined-cycle thermal efficiency and an increase of about 0.0323 Kg/Kwh in specific fuel consumption of the plant. In evaluating the performance of the Waste Heat Boiler (WHB), the principle of heat balance above pinch was applied to a single steam pressure HRSG exhaust gas/steam temperature profile versus exhaust heat flow. Hence, the evaporative capacity (steam flow) of the HRSG was computed from the total heat transfer in the super-heaters and evaporator tubes using heat balance above pinch. The analysis revealed that the equivalent evaporation, evaporative capacity (steam flow) and the HRSG thermal efficiency depends on the heat exchanger’s heat load and its effective maintenance.

Predictive control strategy of a gas turbine for improvement of combined cycle power plant dynamic performance and efficiency.

This paper presents a novel strategy for implementing model predictive control (MPC) to a large gas turbine power plant as a part of our research progress in order to improve plant thermal efficiency and load–frequency control performance. A generalized state space model for a large gas turbine covering the whole steady operational range is designed according to subspace identification method with closed loop data as input to the identification algorithm. Then the model is used in developing a MPC and integrated into the plant existing control strategy. The strategy principle is based on feeding the reference signals of the pilot valve, natural gas valve, and the compressor pressure ratio controller with the optimized decisions given by the MPC instead of direct application of the control signals. If the set points for the compressor controller and turbine valves are sent in a timely manner, there will be more kinetic energy in the plant to release faster responses on the output and the overall system efficiency is improved. Simulation results have illustrated the feasibility of the proposed application that has achieved significant improvement in the frequency variations and load following capability which are also translated to be improvements in the overall combined cycle thermal efficiency of around 1.1 % compared to the existing one.

Design and modeling of an advanced marine machinery system including waste heat recovery and removal of sulphur oxides

Stricter legislation on sulphur oxide emissions from ships will apply as of 2015 in emission control areas. Consequently, prices on low sulphur fuels are expected to increase drastically, providing a strong incentive to find alternative ways of complying with the legislation and improving the efficiency of machinery systems. The wet sulphuric acid process is an effective way of removing flue gas sulphur oxides from land-based coal-fired power plants. Moreover, organic Rankine cycles (ORC) are suitable for heat to power conversion for low temperature heat sources. This paper describes the design and modeling of a highly efficient machinery system which includes the removal of exhaust gas sulphur oxides. The system consists of a two-stroke diesel engine, the wet sulphuric process for sulphur removal, a conventional steam Rankine cycle and an ORC. Results of numerical modeling efforts suggest that an ORC placed after the conventional waste heat recovery system is able to extract the sulphuric acid from the exhaust gas, while at the same time increase the combined cycle thermal efficiency by 2.6%. The findings indicate that the technology has potential in marine applications regarding both energy and the environment; however, further research and development efforts are needed.

Combustion Performance in a Semiclosed Cycle Gas Turbine for IGCC Fired With CO-Rich Syngas and Oxy-Recirculated Exhaust Streams

Our study found that burning a CO-rich gasified coal fuel, derived from an oxygen–CO2 blown gasifier, with oxygen under stoichiometric conditions in a closed cycle gas turbine produced a highly-efficient, oxy-fuel integrated coal gasification combined cycle (IGCC) power generation system with CO2 capture. We diluted stoichiometric combustion with recycled gas turbine exhaust and adjusted for given temperatures. Some of the exhaust was used to feed coal into the gasifier. In doing so, we found it necessary to minimize not only CO and H2 of unburned fuel constituents but also residual O2, not consumed in the gas turbine combustion process. In this study, we examined the emission characteristics of gasified-fueled stoichiometric combustion with oxygen through numerical analysis based on reaction kinetics. Furthermore, we investigated the reaction characteristics of reactant gases of CO, H2, and O2 remaining in the recirculating gas turbine exhaust using present numerical procedures. As a result, we were able to clarify that since fuel oxidation reaction is inhibited due to reasons of exhaust recirculation and lower oxygen partial pressure, CO oxidization is very sluggish and combustion reaction does not reach equilibrium at the combustor exit. In the case of a combustor exhaust temperature of 1573 K (1300 °C), we estimated that high CO exhaust emissions of about a few percent, in tens of milliseconds, corresponded to the combustion gas residence time in the gas turbine combustor. Combustion efficiency was estimated to reach only about 76%, which was a lower value compared to H2/O2-fired combustion while residual O2 in exhaust was 2.5 vol%, or five times as much as the equilibrium concentration. On the other hand, unburned constituents in an expansion turbine exhaust were slowed to oxidize in a heat recovery steam generator (HRSG) flue processing, and exhaust gases reached equilibrium conditions. In this regard, however, reaction heat in HRSG could not devote enough energy for combined cycle thermal efficiency, making advanced combustion technology necessary for achieving highly efficient, oxy-fuel IGCC.

Development of Closed-Cycle Gas Turbine for Oxy-Fuel IGCC Power Generation with CO2 Capture - Emission Analysis of Gasified-Fueled Gas Turbines with Circulating Exhaust & Stoichiometric Combustion -

A CO-rich gasified coal fuel, derived from an oxygen-CO2 blown gasifier, is burnt with oxygen under stoichiometric conditions in a closed cycle gas turbine for the highly-efficient, oxy-fuel IGCC (integrated coal gasification combined cycle) power generation system with CO2 capture. Stoichiometric combustion is diluted with the recycled gas turbine exhaust and adjusted for given temperatures. Since some of the exhaust is used to feed coal into the gasifier, it is necessary to minimize not only CO and H2 of unburned fuel constituents but also residual O2, not consumed in the gas turbine combustion process. In this study, reaction characteristics of reactant gases in the combustor and exhaust have been clarified through numerical analysis based on reaction kinetics. As a result, it was clarified that since fuel oxidation is inhibited due to reasons of exhaust-recirculation and stoichiometric combustion, combustion efficiency was estimated to be lower than those in the cases of the developed H2/O2, LNG/O2 fired closed-cycle gas turbines and a conventional LNG fired-gas turbine. Meanwhile, unburned constituents in exhausts were slowed to oxidize in an HRSG, and exhaust gases reached equilibrium. However, reaction heat in HRSG couldn't devote enough energy for combined cycle thermal efficiency, making advanced combustion technology necessary for achieving highly-efficient oxy-fuel IGCC.

Thermodynamic optimization of solid oxide fuel cell-based combined cycle cogeneration plant

The energy demand is growing worldwide, and this has to be met with various energy resources and with advanced energy technologies. Power plant optimization is one of the ways in which the growing energy demand and call for reduction in greenhouse gas emission can be met. The present work investigates the optimal operating condition of a combined cycle cogeneration power plant with solid oxide fuel cell (SOFC) co-fired with coal and natural gas. The study also looks at an efficient way to perform iterative processes used to find exit conditions from the gasifier, fuel cell, gas turbine, and combustion chamber and exit condition from the gas turbine. The maximum fuel cell net work output, combined cycle net work output, combined cycle thermal efficiency, and cogeneration efficiency are determined. The optimal pressure ratio, temperature of operation of the SOFC, and gas turbine inlet temperature is determined using a sequential quadratic program solver based on the Quasi-Newton algorithm. The maximum cogeneration efficiency obtained from the plant configuration investigated in this study is 82.20% at a pressure ratio of 14.31 and SOFC temperature of 1223 K. Copyright © 2011 John Wiley & Sons, Ltd.

Evaluation of Losses in a Diesel Engine Cycle and Improvement of Its Thermal Efficiency (Capabilities of Diesel Engine Combined Cycle)

The Diesel engine and gas turbine combined cycle has an ability of getting much better thermal efficiency than any other type of cycles owing to its high temperature in the heat receiving process. Increase of expansion ratio in the diesel engine cycle minimizes the exergy loss in the process connecting diesel engine cycle and gas turbine one, and leads a thermal efficiency improvement about 4%. Although disuse of charge air cooling and furthermore heating of the charge air with the exhaust gas from turbine cause reduction of specific power output, they diminish the exergy losses in the heat receiving process in the cylinder and the exhaust process from turbine, and bring an improvenment of thermal efficiency by several %. The charge air temperature rise accompanying further improvement of the combined cycle thermal efficiency, requires the development of high efficiency gas turbine, and realization of the new methods for protecting diesel engine cylinder wall to higher temperature of working gas.

Refuse-fired, pressurized, fluidized-bed combustion combined cycle analysis

Use of pressurized, fluidized-bed combustion (PFBC) has given a new opportunity to use municipal refuse as fuel for combined gas and steam power cycles keeping the pollutants of sulphur and nitrogen oxides to a minimum at reduced capital cost. In combined gas and steam power cycles, the heat energy in the exhaust gases of a simple gas turbine cycle is used to generate steam in a waste-heat boiler and the generated steam is used in the steam turbine for power generation. The effects of gas turbine pressure ratio and inlet temperature on the main parameters of refuse-fired, pressurized, fluidized-bed combustion combined cycles are determined. The results indicate a maximum combined cycle thermal efficiency and work output at a possible range of optimum pressure ratios between 10 and 12 for a range of gas turbine inlet temperatures of 750–1000°C.

Outline of Plan for Advanced Reheat Gas Turbine

A new reheat gas turbine system is being developed as a national project by the “Engineering Research Association for Advanced Gas Turbines” of Japan. The machine consists of two axial flow compressors, three turbines, intercooler, combustor and reheater. The pilot plant is expected to go into operation in 1982, and a prototype plant will be set up in 1984. The major objective of this reheat gas turbine is application to a combined cycle power plant, with LNG burning, and the final target of combined cycle thermal efficiency is to be 55 percent (LHV).