Combined Cycle Cogeneration System Research Articles

Thermo-economic analysis of integrated gasification combined cycle co-generation system hybridized with concentrated solar power tower

Integrated gasification combined cycle (IGCC) systems have the ability to utilize low-quality coal with reduced emissions and multiple co-generation capabilities (i.e., power, chemicals and fuels). Integration of solar power tower (SPT) with IGCC co-generation can provide an opportunity to use lignite coal with lowest greenhouse gas emissions. In this work, thermodynamic and economic evaluations of solar-IGCC 100% power (power only) hybrids and co-generation (electricity, methane and ammonia) hybrids have been performed using Aspen Plus® V.11 and system advisor model (SAM). Two designs (i.e., large and medium solar) of the SPT have been simulated and optimized for Pakistani weather conditions. Thermodynamic evaluations include, net electrical efficiency, effective energy efficiency and solar-to-electric efficiency of hybrid plants. Economic estimations include, levelized cost of energy, total plant costs, operating and maintenance costs for hybrid plants. Specific CO2 emissions after hybridization are also evaluated. Total annualized revenue at flexible market scenarios and production scenarios have also been evaluated. The net boosted electrical efficiency of 100% power (Hyb-1A) is 38.77%, and the improved efficiency after flue gas integration with SPT for the pre-heating of boiler feed water is 39.10%. The minimum specific CO2 emission achieved from one hybrid combination (Hyb-4A) is 42.1 kg/MWhnet.

Thermo-Economic Analysis of Integrated Gasification Combined Cycle Co-Generation System Hybridized with Concentrated Solar Power Tower

Thermo-Economic Analysis of Integrated Gasification Combined Cycle Co-Generation System Hybridized with Concentrated Solar Power Tower

An online parameter identification and real-time optimization platform for thermal systems and its application

Real-time performance optimization of thermal systems is crucial for energy conservation but also challenging because of the high system complexity and time sensitivity. Herein, an online parameter identification and real-time optimization platform for thermal systems is developed, and a gas-steam combined cycle cogeneration system is used to demonstrate its capability. The platform integrates data collection, parameter identification, system simulation, and real-time optimization modules. The data preprocessing and parameter identification modules collects real-time operation parameters for optimization. The system simulation module applies the heat current method to model the cogeneration system precisely, and a high-efficiency simulation procedure is proposed using the hierarchical and categorized (H&C) algorithm. The system optimization module introduces the artificial neural network technology to ensure the response time of real-time optimization. Meanwhile, the H&C algorithm and genetic algorithm are combined to update the database to improve the optimization performance gradually. The platform is first validated on three typical conditions. It is further deployed at a power plant, where a field test is conducted for the practical verification. Field test results show that the standard coal consumption of the cogeneration system could be reduced by 0.415 g/kWh by using the platform, which proves its practicability.

Thermo-economic analysis of integrated gasification combined cycle co-generation system with carbon capture and integrated with absorption refrigeration system

Greenhouse gas emissions have become a major issue during power generation from coal due to global warming effects. Integrated gasification combined cycle (IGCC) power system has been acknowledged as a rare existing opportunity to utilize low-quality solid fuels with reduced emissions and co-generation of power, fuels and chemicals. Country like, Pakistan, where huge reserves of low-quality coal are present can benefit from this technology. In this work, the steady-state thermodynamic and economic evaluation of IGCC co-generation system has been performed for methane and ammonia production along with power generation. Gasification of coal has been simulated using entrained flow Shell gasifier under thermochemical equilibrium with the Gibbs free energy approach using local Thar lignite in Aspen Plus® V.11. The designs simulated include, IGCC 100% power with and without carbon capture, and IGCC co-generation system with carbon capture with varied production of methane, ammonia and electricity. Thermal efficiency, cost of electricity and CO2 avoided costs have been evaluated for 100% power design. Total capital in the form of total overnight cost and operating cost (fixed and variable) has been evaluated to account annualized expenditure for co-generation designs. Absorption refrigeration system (ARS) has been integrated with IGCC designs to meet the partial chilling requirement of lean solvent in Selexol process, which caused the reduction in CO2 emission because of reduced auxiliary power consumption. The net electrical efficiency of 100% power (design-2) is 32.33%, and the improved efficiency after ARS integration is 32.61%. The performance of co-generation designs is evaluated by estimating annualized revenue and annualized expenditures. One of the co-generation cases (design-4) with high methane, low ammonia and medium electricity generation, showed better performance with respect to reduced GHG emissions at almost same revenue to expenditure ratio as compared to design-2.

A study on the variation of the performance and the cost of power generation in a combined heat and power plant with the change of the user facility’s return temperature

A combined heat and power (CHP) system generates electricity from thermal energy and generates heat by utilizing the remaining thermal energy. The system efficiency of the cogeneration system is 75–85 %, which is very high compared to existing only power generation facilities, so it is very useful for energy conservation and environmental protection. For this reason, interest in the cogeneration system is increasing worldwide. Generally, a cogeneration plant consists of a steam turbine alone or the combined power generation of a gas turbine and a steam turbine depending on the scale. The steam turbine is divided into a back-pressure type turbine and a condensing type turbine depending on the operational methodology of the steam turbine. In both cases, the shift in the return temperature of the district heating users influences the performance of the cogeneration plant, thus affecting the power generation costs of the power plant. It is possible to accurately estimate the change in the unit cost of the power generation caused by these changes, and to inflict it on the user, thereby changing the usage pattern of the user and reducing the energy consumption accordingly. In this study, the commercial combined cycle cogeneration system using back - pressure type turbine was simulated, and the change of performance of the combined heat and power plant was analyzed while changing the user facility’s total return temperature. Based on the results of this analysis, a possible loss in the plant according to the change of return temperature was predicted. Also the effect of each user’s return temperature on the plant loss was analyzed using an actual user’s return temperature data. The economic-mechanical approach, such as this study, can alleviate dissatisfaction with the user’s charge and to consume energy in a more rational way. It eventually can play a role in reducing carbon emissions.

Waste heat recovery and water-saving modification for a water-cooled gas-steam combined cycle cogeneration system with absorption heat pump

A new air-cooled gas-steam combined cycle cogeneration system with absorption heat pump for recovering waste heat from exhausted steam of the steam turbine to achieve double effects of waste heat recovery and water saving is proposed based on a conventional water-cooled gas-steam combined cycle cogeneration system in the paper. The property criteria variation is analyzed before and after modification. In addition, the exergy analyses of primary equipments are carried out based upon the exergy analysis theory. The results demonstrate that the net generating power is approximately increased by 11,082 kW, equivalent coal consumption is reduced by 2.71 g/kWh, the net overall thermal efficiency is improved by 0.91% with 334,245 kW heating load at 100% load of the gas turbine in the modified system. Besides, the overall exergy loss is decreased by 6448 kW and exergy efficiency is improved by 0.98%. The overall property of the whole system is improved. The results show that the property reduction caused by air-cooling modification can be made up by the property improvement due to waste heat recovery. Moreover, the cooling circulating water can be saved by 1196.34 kg/s. The presented measure can not only improve performance of the system but also simultaneously achieve energy and water saving on the premise of satisfying user needs, which has a wide application potential in the water-shortage regions.

The Thermodynamic Study of Turbocharger Pressure Ratio and Ambient Temperature Variation on Exergy Destruction Estimation of Homogeneous Charge Compression Ignition Engine Cogeneration System

Homogeneous Charge Compression Ignition (HCCI) technology is different from conventional combustion technologies. It has the combination of lean and premixed fuel air mixture and charge is compression ignited so it has multiple ignition points throughout the combustion chamber thus eliminating the high peak temperature inside the combustion chamber. This new engine technology is helpful in production of ultra low NO and particulate emissions. The use of lean and X unthrottled operation yields higher efficiency and better fuel economy also. In this paper, a new HCCI engine combined cycle cogeneration system is proposed and studied. The system is equipped with turbocharger, fuel vaporizer, engine, catalytic converter, different components of Organic Rankine cycle (ORC) and further heat recovery steam generator (HRSG) for waste heat utilization from the exhaust gases to obtain process heat. An exergy analysis is applied to the different components of HCCI engine cogeneration system to examine the thermodynamic losses in terms of exergy destruction and the effect of ambient temperature and turbocharger pressure ratio is obtained. The result shows a ranking among the components of the system on the basis of thermodynamic losses or the exergy destruction. This paper shows how an exergy method can yield effect of ambient conditions and design parameters values to reduce losses in various components of HCCI engine cogeneration system.

Exergetic analysis of an innovative small scale combined cycle cogeneration system

The purpose of this paper has been to carry out an exergetic analysis of an innovative natural gas (NG) combined cycle cogeneration system (150-kWe, 192-kWt). The combined cycle is composed of a reciprocating Internal Combustion Engine (ICE), which is used as the topping cycle, and a water Rankine cycle (RC), which operates on the exhaust gases from the ICE, as the bottoming cycle. A steady-state model has been developed in order to identify and to quantify the exergetic irreversibilities of each component of the system and of the whole plant. Furthermore, a part-load exergy analysis, which shows the exergy performance in the operating field of the plant, has been carried out; finally, a sensitivity analysis pertaining to some performance parameters is presented.

On the Teaching of Performance Evaluation and Assessment of a Combined Cycle Cogeneration System

Performance evaluation and assessment of combined cycle cogeneration systems are not taught well in academia. One reason is these parameters are scattered in the literature with each publication starting and ending at different stages. In many institutions professors do not discuss or even mention these topics, particularly from a second law perspective. When teaching combined cycle cogeneration systems to undergraduates, the professor should introduce pertinent parameters in a systematic fashion and discuss the usefulness and limitations of each parameter. Ultimately for a given situation, the student should be able to determine which parameters form the most appropriate basis for comparison when considering alternative designs. This paper provides two approaches, one based on energy (the first law of thermodynamics) and the other based on exergy (the second law of thermodynamics). These approaches are discussed with emphasis on the “precise” teaching of the subject matter to undergraduates. The intent is to make coverage of the combined cycle cogeneration systems manageable so that professors can appropriately incorporate the topic into the curricula with relative ease.

EFFECT OF OPERATING VARIABLES ON THE PERFORMANCE OF A COMBINED CYCLE COGENERATION SYSTEM WITH MULTIPLE PROCESS HEATERS

Combined cycle power plants with a gas turbine topping cycle and a steam turbine bottoming cycle are widely used due to their high efficiencies. Combined cycle cogeneration has the possibility to produce power and process heat more efficiently, leading to higher performance and reduced green house gas emissions. The objective of the present work is to analyze and simulate a natural gas fired combined cycle cogeneration unit with multiple process heaters and to investigate the effect of operating variables on the performance. The operating conditions investigated include, gas turbine pressure ratio, process heat loads and process steam extraction pressure. The gas turbine pressure ratio significantly influences the performance of the combined cycle cogeneration system. It is also identified that extracting process steam at lower pressures improves the power generation and cogeneration efficiencies. The process heat load influences combined cycle efficiency and combined cycle cogeneration efficiency in opposite ways. It is also observed that using multiple process heaters with different process steam pressures, rather than a single process heater, improves the combined cycle cogeneration plant efficiency.

Design and performance evaluation of an innovative small scale combined cycle cogeneration system

This paper deals with an innovative natural gas (NG) combined cycle cogeneration system (150-kWe, 192 kWt). The system is made up of a combination of two interconnected combined heat and power (CHP) systems: a reciprocating internal combustion engine cogenerator (ICE CHP) as the topping cycle and a Rankine cycle cogenerator (RC CHP) which operates as the bottoming cycle on the exhaust gases from the ICE. The expander technology chosen for the Rankine cycle prime mover is a reciprocating single expansion steam engine with three cylinders in a radial architecture. The ICE is an automotive derived internal combustion engine with a high part-load electrical efficiency, due to a variable speed operation strategy and reduced emissions. The main design parameter of the Rankine bottoming cycle and of the steam engine are defined in this paper, and the electrical and heat efficiency of the new CHP unit are determined and discussed at full and part-load. Some design criteria and energy balance considerations are introduced and some technical solutions are analysed and studied.

Thermodynamic and thermoeconomic comparison of combined cycle cogeneration systems

In this paper, several configurations of combined cycle cogeneration systems are investigated by energy, exergy and thermoeconomic analyses. In each of these configurations, varying steam demand is considered rather than fixed steam demand. Among the different approaches for thermoeconomic analysis in the literature, the specific exergy costing method is applied. Since the systems have more than one product (process steam and electrical power), systems are divided into several sub-systems and cost balances are applied together with the auxiliary equations. Hence, the cost rate of each product is calculated. Comparison of the configurations, in terms of performance assessment parameters and costs per unit of exergy, are also given in this study. In conclusion, it is found that combined cycle cogeneration systems with extraction condensing steam turbines are thermodynamically and thermoeconomically more advantageous when compared to those with back-pressure steam turbines.

Optimal Efficiency as a Design Criterion for Closed Loop Combined Cycle Industrial Cogeneration

In comparison to conventional industrial cogeneration plants, the closed loop combined cycle cogeneration (CLCC) system has the advantage that it needs virtually no enhancement in steam handling capability of the existing plant, both in terms of steam pressure as well as volume flow rates. An optimal design procedure is introduced in this paper for the configuration of a CLCC system between existing steam headers of an industrial setup. While aiming primarily at maximization of generation efficiency for the CLCC configuration, the design approach simultaneously attempts to configure a suboptimal number of units for each item of cogeneration equipment. The suboptimal (integer) number of units is maintained within a specified suboptimal margin of the corresponding optimal (real) number of units that emerges from efficiency maximization. The design procedure relies heavily on a database including all available makes of cogeneration equipment. Consequently, the approach is very much market dependent, as illustrated adequately by a suitable case study.

Criteria for integration of combined cycle cogeneration systems in the process industries

Cogeneration systems often provide a very effective means of integrating power generation with the provision of thermal energy to an industrial process. Various types of power generating machines can be used, but combined cycle cogeneration systems can offer significant advantages over other technologies in many medium and large scale applications. The systems that are used consist of fired prime movers (usually gas turbines), discharging their exhaust heat into heat recovery steam generators. The steam raised in this way is passed through back-pressure steam turbines to extract additional power before finally delivering its residual heat content to process heating duties. This paper presents an overview of the economic trade-offs in the design of single cycle and combined cycle systems. Generalizations are derived from this investigation, leading to the identification of three distinct classes of problem for which different types of cogeneration systems (combined cycle or single cycle) are appropriate. Case study results are presented to illustrate the principles employed.