Biomass integrated gasification combined cycle power generation with supplementary biomass firing: Energy and exergy based performance analysis

A thermodynamic analysis of a Biomass Integrated Gasification Combined Cycle (BIGCC) plant has been performed based on energy and exergy balances in a proposed configuration. Combustion of supplementary biomass fuel is considered using the oxygen available in the gas turbine (GT) exhaust. The effects of pressure and temperature ratios of the GT system and the amount of fuel burned in the supplementary firing chamber on the thermal and exergetic efficiencies of the plant have been investigated. The plant efficiencies increase with the increase in both pressure and temperature ratios; however, the latter has a stronger influence than the former. Supplementary firing of biomass increases the plant efficiencies of a BIGCC plant till an optimum level of degree of firing. The other technical issues related to supplementary firing, like ash fusion in the furnace and exhaust heat loss maintaining a minimum pinch point temperature difference are accounted and finally a set of optimum plant operating parameters have been identified. The performance of a 50 MWe plant has been analyzed with the optimum operating parameters to find out equipment rating and biomass feed rates. Exergetic efficiencies of different plant equipments are evaluated to localize the major thermodynamic irreversibilities in the plant.     

Comparative analysis of Fischer-Tropsch and integrated gasification combined cycle biomass utilization

Use of agricultural biomass (switchgrass, prairie grasses) through Fischer-Tropsch (FT) conversion to liquid fuels is compared with biomass utilization via (IGCC) integrated gasification combined cycle electrical production. In the IGCC scenario, biomass is co-fired with coal, with biomass comprising 10% of the fuel input by energy content. In this case, the displaced coal is processed via FT methods so that liquid fuels are produced in both scenarios. Overall performance of the two options is compared on the basis of total energy yield (electricity, liquid fuels), carbon dioxide emissions, and total cost. Total energy yield is almost identical whether biomass is used for electrical power generation or liquid fuels synthesis. Carbon dioxide emissions are also approximately equal for the two pathways. Capital costs are more difficult to compare since scaling factors cause considerable uncertainty. With IGCC costs roughly equivalent for either scenario, cost differences between the pathways appear based on FT plant construction cost. Coal FT facility capital cost estimates for the plant scale in this study (721 MW_t LHV input) are estimated to be 410 (MUSD) million US Dollars while the similar scale biomass-only FT plant costs range from 430 MUSD to 590 MUSD.     

火力发电厂效率计算及联合循环发电的优势

论述了火力发电厂的效率计算。数据表明,采用燃气－蒸汽联合循环发电技术的温州燃机电厂效率高,并对此作了经济指标对比。     

Co-utilization of biomass and natural gas in combined cycles through primary steam reforming of the natural gas

Power production from biomass can occur through external combustion (e.g. steam cycles, organic Rankine cycles, Stirling engines), or internal combustion after gasification or pyrolysis (e.g. gas engines, IGCC). External combustion has the disadvantage of delivering limited conversion efficiencies (max 30–35%). Internal combustion has the potential of high efficiencies, but it always needs a severe and mostly problematic gas cleaning.     

The future of biomass energy: A Fermi-calculation perspective

It is argued: (i) that the harvesting of terrestrial solar radiation to perform useful work is at least an order of magnitude more efficient when carried out by solar-thermal or solar-photovoltaic processes than when carried out by way of biomass conversion and (ii) that, therefore, biomass energy is unlikely to compete successfully with inanimately harvested solar energy—except of course in restricted niche applications.     

Gas turbine steam injection and combined power cycles using fog inlet cooling and biomass fuel: A thermodynamic assessment

The results of energy and exergy analyses of two biomass integrated steam injection cycles and combined power cycles are reported. Fog cooling, steam injection and adding steam turbine cycles to gas turbine cycles can enhance the performance of power generation systems. Even with its lower heat value, biomass can be substituted for fossil fuels. The performances of the cycles are assessed under the same conditions. The assessments show that the combined cycle has a higher efficiency at lower values of compressor pressure ratio but the steam injection plant is advantageous at higher pressure ratio values. The steam injection plant has a higher net power under the same conditions, while the exergy loss rate is higher for the combined cycle at all pressure ratios. But the exergy destruction rate is higher for the steam injection cycle at lower compressor pressure ratios, and for the combined cycle at higher pressure ratios.     

Dynamic simulation of a solar-driven carbon dioxide transcritical power system for small scale combined heat and power production

Carbon dioxide is an environmental benign natural working fluid and has been proposed as a working media for a solar-driven power system. In the current work, the dynamic performance of a small scale solar-driven carbon dioxide power system is analyzed by dynamic simulation tool TRNSYS 16 (Klein et al., 2004) and Engineering Equation Solver (EES) (Klein, 2004) using co-solving technique.Both daily performance and yearly performance of the proposed system have been simulated. Different system operating parameters, which will influence the system performance, have been discussed. Under the Swedish climatic condition, the maximum daily power production is about 12 kW h and the maximum monthly power production is about 215 kW h with the proposed system working conditions. Besides the power being produced, the system can also produce about 10 times much thermal energy, which can be used for space heating, domestic hot water supply or driving absorption chillers. The simulation results show that the proposed system is a promising and environmental benign alternative for conventional low-grade heat source utilization system.     

Exergy, exergoeconomic and environmental analyses and evolutionary algorithm based multi-objective optimization of combined cycle power plants

A comprehensive exergy, exergoeconomic and environmental impact analysis and optimization is reported of several combined cycle power plants (CCPPs). In the first part, thermodynamic analyses based on energy and exergy of the CCPPs are performed, and the effect of supplementary firing on the natural gas-fired CCPP is investigated. The latter step includes the effect of supplementary firing on the performance of bottoming cycle and CO₂ emissions, and utilizes the first and second laws of thermodynamics. In the second part, a multi-objective optimization is performed to determine the “best” design parameters, accounting for exergetic, economic and environmental factors. The optimization considers three objective functions: CCPP exergy efficiency, total cost rate of the system products and CO₂ emissions of the overall plant. The environmental impact in terms of CO₂ emissions is integrated with the exergoeconomic objective function as a new objective function. The results of both exergy and exergoeconomic analyses show that the largest exergy destructions occur in the CCPP combustion chamber, and that increasing the gas turbine inlet temperature decreases the CCPP cost of exergy destruction. The optimization results demonstrates that CO₂ emissions are reduced by selecting the best components and using a low fuel injection rate into the combustion chamber.     

Energy and exergy analyses of an externally fired gas turbine (EFGT) cycle integrated with biomass gasifier for distributed power generation

Biomass based decentralized power generation using externally fired gas turbine (EFGT) can be a technically feasible option. In this work, thermal performance and sizing of such plants have been analyzed at different cycle pressure ratio (r_p = 2−8), turbine inlet temperature (TIT = 1050–1350 K) and the heat exchanger cold end temperature difference (CETD = 200–300 K). It is found that the thermal efficiency of the EFGT plant reaches a maximum at an optimum pressure ratio depending upon the TIT and heat exchanger CETD. For a particular pressure ratio, thermal efficiency increases either with the increase in TIT or with the decrease in heat exchanger CETD. The specific air flow, associated with the size of the plant equipment, decreases with the increase in pressure ratio. This decrease is rapid at the lower end of the pressure ratio (r_p < 4) but levels-off at higher r_p values. An increase in the TIT reduces the specific air flow, while a change in the heat exchanger CETD has no influence on it. Based on this comparison, the performance of a 100 kW EFGT plant has been analyzed for three sets of operating parameters and a trade-off in the operating condition is reached.     

Exergy analysis of the woody biomass Stirling engine and PEM-FC combined system with exhaust heat reforming

The woody biomass Stirling engine (WB-SEG) is an external combustion engine that outputs high-temperature exhaust gases. It is necessary to improve the exergy efficiency of WB-SEG from the viewpoint of energy cascade utilization. So, a combined system that uses the exhaust heat of WB-SEG for the steam reforming of city gas and that supplies the produced reformed gas to a proton exchange membrane fuel cell (PEM-FC) is proposed. The energy flow and the exergy flow were analyzed for each WB-SEG, PEM-FC, and WB-SEG/PEM-FC combined system. Exhaust heat recovery to preheat fuel and combustion air was investigated in each system. As a result, (a) improvement of the heat exchange performance of the woody biomass combustion gas and engine is observed, (b) reduction in difference in the reaction temperature of each unit, and (c) removal of rapid temperature change of reformed gas are required in order to reduce exergy loss of the system. The exergy efficiency of the WB-SEG/PEM-FC combined system is superior to EM-FC.     

A preliminary study of the kalina power cycle in connection with a combined cycle system

Combined cycle systems have been recognized as efficient power systems in which exhaust gas from the topping cycle provides the available energy to the bottoming cycle. Since most heat sources available to the bottoming cycle are sensible-heat sources, there may be a better thermal match, and an increase thermodynamic efficiency, on reducing the entropy generation of the simple combined cycle. To increase the efficiency of the Rankine cycle working with sensible heat, two conventional methods have been proposed: one is to incorporate a multipressure boiler; the other is to implement a supercritical cycle. An alternative method is to use a multicomponent working fluid boiling at a variable temperature with a change in the liquid composition of the components, and yielding a better thermal match with the sensible-heat source than the constant temperature boiling process. The Kalina cycle is an implementation of this concept, where ammonia/water mixtures are used as the working fluid. The purpose of this study is to conduct a preliminary study of the Kalina power cycle system in connection with a combined cycle system, comparing the Kalina cycle and the Rankine cycle. This study is performed using new thermodynamic properties of ammonia/water mixtures developed by the authors.     

A study of an integrated land-fill and coppice power station

The use of methane from controlled landfill sites is well established as a method of generating usable energy from waste. However, the economics of this method are prejudiced by factors such as the restricted lifetime of the site and the initial capital costs in setting up the generating plant and the grid connection. Here we consider the benefits anticipated as a result of integrating wood fuels into the system and show that as well as the obvious shared capital costs and increased security of supply there is an increase in overall power output.     

Performance analysis of a heavy duty combined cycle power plant burning various syngas fuels

This paper presents a performance analysis of state of the art combined cycles power plants burning a number of syngas fuels. The first part of the analysis focuses on the effect of gas composition on the rated performance of the plant drawing two main conclusions. First, higher pressure ratio and lower firing temperature are found at turbine inlet. Second, the pressure at which fuel is supplied to the gas turbine plays an essential role in the power capacity of the engine. With respect to the steam cycle, no major effects are appreciated except for very low LHV fuels. In the second part of the work, the annual performance of the engine subjected to a typical load profile and real ambient and market conditions is studied. Differences in total incomes are appreciated depending on fuel composition and the concern about carbon emissions is highlighted.     

Performance comparison of three trigeneration systems using organic rankine cycles

In this paper, energetic performance comparison of three trigeneration systems is presented. The systems considered are SOFC-trigeneration, biomass-trigeneration, and solar-trigeneration systems. This study compares the performance of the systems considered when there is only electrical power and the efficiency improvement of these systems when there is trigeneration. Different key output parameters are examined: energy efficiency, net electrical power, electrical to heating and cooling ratios, and (GHG) GHG (greenhouse gas) emissions. This study shows that the SOFC-trigeneration system has the highest electrical efficiency among the three systems. Alternatively, when trigeneration is used, the efficiencies of all three systems considered increase considerably. The maximum trigeneration efficiency of the SOFC-trigeneration system is around 76% while it is around 90% for the biomass-trigeneration system. On the other hand, the maximum trigeneration efficiencies of the solar-trigeneration system is around 90% for the solar mode, 45% for storage and storage mode, and 41% for the storage mode. In addition, this study shows that the emissions of CO₂ in kg per MWh of electrical power are high for the biomass-trigeneration and SOFC-trigeneration systems. However, by considering the emissions per MWh of trigeneration, their values drop to less than one fourth.     

Strategy for the expansion of an existing steam rankine cycle to A combined cycle

A systematic procedure for designing an expansion of the steam Rankine cycle to a combined cycle is proposed. This paper discusses the approach from the point of view of overall thermodynamic efficiency. Practical limitations in design considerations are also addressed. The application of this approach is illustrated with a typical utility system design.     

Optimum conditions for a natural gas combined cycle power generation system based on available oxygen when using biomass as supplementary fuel

Due to the higher oxygen content and lower heating value, the amount of biomass required in a combined cycle, where it is used as supplementary fuel, to meet a given energy demand is such that the biomass consumes almost all of the oxygen remaining from gas turbine combustion process under certain conditions. This situation requires additional air for biomass combustion thus reducing the cycle efficiency and the net work output rate while increasing CO₂ emissions. Three conditions at which the oxygen is completely consumed are identified based on alterations in net fuel utilization. The first condition is linked to fuel utilization, which is observed to be significantly affected by variations in temperatures at three locations in the combined cycle (air temperature entering the gas turbine combustion chamber, gas turbine inlet temperature and HRSG inlet temperatures). The second condition relates to the characteristics of the feedstock (oxygen content of the biomass and heating value of natural gas). The heat loss due to combustion of natural gas and biomass is the third condition that affects oxygen availability. The current work assesses these conditions in order to identify the proper condition at which no additional air is required for supplementary firing of biomass.     

锅炉煤,气混烧方式下的热效率测试及经济性分析

涟钢热电厂变废为定,奖高炉煤气送入３５ｔ／ｈ抛煤机锅炉中燃烧发电,取得了显著的节能降耗效果。文中介绍了锅炉煤、气混合燃烧方式下的运行调整、热效率测试及计算方法,客观地分析了该项节能共作取得的经济效益。对同类企业实施节能改造有一定的指导作用。