Waste heat recovery from a landfill gas-fired power plant

Waste treatment and management is a certain challenge especially in areas with high population density. One of the options for waste treatment is landfilling, where the amount of municipal waste also produces landfill gas through anaerobic digestion. The heating value of the landfill gas is high enough to use it as a fuel in combustion processes, e.g. in internal combustion engines (ICEs) to produce electric power.In Ano Liosia, Athens (Greece) up to 6000 tons of waste are landfilled every day and the landfill gas is used in an ICE power station directly at the site of the landfill. The power station consists of 15 ICEs and has an installed capacity of 23.5 MW. The major advantages of using ICE for power generation are the high electrical efficiency of ICEs and their fast load response. However, more than 50% of the landfill gas energy content is still released to the atmosphere as engine waste heat (exhaust gas and engine cooling water).The aim of this paper is to study the possibilities of using this large amount of heat in order to increase the electricity production and efficiency of the Ano Liosia power station. Therefore, a thermodynamic and economic analysis of two different waste heat recovery (WHR) systems is conducted. The water/steam cycle and the Organic Rankine Cycle (ORC) are examined and evaluated by means of thermodynamic cycle simulation and by calculating their specific costs of power generation. Their advantages and disadvantages considering their application in landfillgas-fired ICE power stations are discussed under the consideration of maximal thermodynamic efficiency and minimal costs of power generation.     

Simulation analysis of cooling methods of an on‐board organic Rankine cycle exhaust heat recovery system

Energy saving and emission reduction of engines were taken seriously, especially for vehicular diesel engines. Exhaust heat recovery based on organic Rankine cycle (ORC) system has been considered as an effective approach for improving engine fuel economy. This article presents the investigation of water or air cooling method for an ORC exhaust heat recovery system on a heavy‐duty truck through simulations. The models of the truck engine and the ORC system were developed in GT suite, and the integration system model was developed in the Simulink environment. The validity of the models was verified experimentally. The performance of the vehicular engine with ORC system using water or air cooling method was comparatively analyzed. The simulation results indicated that the water cooling method is more suitable for the vehicular ORC system than air cooling method. The relation between benefit and penalty of the ORC system and cooling system was discussed. The operating condition of the cooling system was confirmed having significant effects on the combined system performance, especially the fan speed. The performance improvement of the engine with the use of ORC system was further evaluated under different engine operating conditions and ambient temperatures. Lower ambient temperature had positive effects on the engine fuel economy. The mass flow rate of exhaust gas for heat recovery should be regulated for better performance under high ambient temperature.     

Heat pump enhanced gas turbine cogeneration

A significant fraction of the gaseous fuel supplied to industry will be used in medium- and small-size cogeneration plants. In this paper, a gas turbine and a gas engine of about 800 kW power output are compared at full and part load operation. When low-temperature heat (e.g., for space heating) is produced, the higher exhaust losses of the gas turbine yield a lower system efficiency, particularly at part load. A scheme is proposed to recover the exhaust gas energy by cooling to a temperature near ambient. The system features a heat pump to raise the recovered heat temperature to a usable level and an organic Rankine cycle (ORC) engine to drive the heat pump. The ORC engine uses the high-temperature fraction of the heat recovered from the exhaust. The data for the ORC engine are derived from an actual experimental engine. The performance is calculated for the system at full load.     

Heat exchanger network design of an organic Rankine cycle integrated waste heat recovery system of a marine vessel using pinch point analysis

The coexistence of different kinds of waste heat sources on marine vessels with various temperature ranges increases the need for an optimal heat exchanger network (HEN) design for the heat collection process to reduce the unutilizable heat that needs to be discharged to overboard. The optimal HEN design has not been taken into consideration by using pinch point analysis in previous studies of marine organic Rankine cycle (ORC) systems that utilize from different kinds of waste heat sources. The objective of the study is to determine the optimal HEN design for an ORC integrated waste heat recovery system of a marine vessel by utilizing the pinch point analysis to improve the overall energy efficiency. Lubricating oil, high-temperature cooling water and scavenge air of the main engine, and the exhaust gas emitted from the boiler plant were identified as the major waste heat sources of a reference container ship. A heat collection stream, in which thermal oil is used as the heat transfer fluid that transfers the collected heat to an ORC system, was proposed. The pinch point analysis showed that the optimum waste heat recovery could be gained by separating the scavenge air cooler into three stages and the lubricating oil cooler into two stages. The results of the parametric study for the varying evaporator inlet pressure between 1000 and 3000 kPa showed that R1234ze(Z) yields the best performance among nine different organic working fluids with the thermal efficiency and exergy efficiency of 15.24% and 86.47% for the ORC system, respectively. For the proposed configuration, the unavailable waste heat that cannot be transferred to thermal oil was found as 23.71%, 16.56%, 13.17%, and 7.81% of the total waste heat produced by the heat sources, and also 8.24%, 9.80%, 11.55%, and 12.93% of the net power output produced by the main engine can be recovered for 25%, 50%, 76%, and 100% maximum continuous rating (MCR), respectively.     

Energetic and exergetic analysis of waste heat recovery from a microturbine using organic Rankine cycles

This article examines the exhaust waste heat recovery potential of a microturbine (MT) using an organic Rankine cycle (ORC). Possible improvements in electric and exergy efficiencies as well as specific emissions by recovering waste heat from the MT exhaust gases are determined. Different dry organic working fluids are considered during the evaluation (R113, R123, R245fa, and R236fa). In general, it has been found that the use of an ORC to recover waste heat from MTs improves the combined electric and exergy efficiencies for all the evaluated fluids, obtaining increases of an average of 27% when the ORC was operated using R113 as the working fluid. It has also been found that higher ORC evaporator effectiveness values correspond to lower pinch point temperature differences and higher exergy efficiencies. Three different MT sizes were evaluated, and the results indicate that the energetic and exergetic performance as well as the reduction of specific emissions of a combined MT‐ORC is better for small MT power outputs than for larger MTs. This article also shows how the electric efficiency can be used to ascertain under which circumstances the use of a combined MT‐ORC will result in better cost, primary energy consumption, or emission reduction when compared with buying electricity directly from electric utilities. Copyright © 2012 John Wiley & Sons, Ltd.     

基于有机朗肯循环的APU余热回收系统性能分析

为有效利用飞机辅助动力装置（Auxitlary Power Unit , APU）排气余热,基于有机朗肯循环（Organic Rankine Cycle, ORC）发电系统,构建了APU余热回收系统。系统以APU排气余热为输入,驱动ORC做功,输出电能,为机载设备提供二次能源。结合工程热力学原理,建立系统热力学模型,并通过Matlab编程对余热回收系统进行了仿真计算及性能分析。仿真结果表明,系统功率及效率随飞行马赫数增加而降低;APU余热回收系统在飞机低音速飞行时有良好的性能;马赫数小于1时,系统功率在12 kW以上,效率在11%以上,耗气率低于0.0262 kg/kJ。     

Stoichiometric H2ICE with water injection and exhaust and coolant heat recovery through organic Rankine cycles

High power density, stoichiometric, turbocharged, directly injected engines with water injection and a three way catalytic converter after treatment have been proposed as one of the most promising H₂ICE [1]. These throttle controlled engines have top brake efficiencies exceeding 40%, but large penalties in efficiency reducing the load with 1 bar BMEP values approaching 10%. Recovery of the large amount of fuel energy lost in the coolant especially at low loads as well as the fuel energy lost in the exhaust that is significant at high loads and speeds may push not only the top brake efficiencies to exceed the 45% mark, but also to dramatically increase the low load efficiency compromised by the throttling. In this paper, recovery of the waste heat from the exhaust gases and the coolant in a H₂ICE is performed with Organic Rankine Cycles (ORC). The engine without ORC has a maximum efficiency of 42% and an average efficiency over the map points of 32.7%. With the exhaust ORC, neglecting the possible back pressure increase due to the heat exchanger downstream of the catalytic converter the maximum efficiency increases to 45.6%, and the average efficiency rises to 35.3%. With the coolant ORC, neglecting the reduced mechanical efficiency for the coolant back pressure increment, the maximum efficiency increases to 43.4% and the average efficiency increases to 34.6%. Finally, combining the two ORC with same assumptions, the maximum efficiency increases to 46.9% and the average efficiency to 38%.     

Thermodynamic analysis of an LNG fuelled combined cycle power plant with waste heat recovery and utilization system

This paper has proposed an improved liquefied natural gas (LNG) fuelled combined cycle power plant with a waste heat recovery and utilization system. The proposed combined cycle, which provides power outputs and thermal energy, consists of the gas/steam combined cycle, the subsystem utilizing the latent heat of spent steam from the steam turbine to vaporize LNG, the subsystem that recovers both the sensible heat and the latent heat of water vapour in the exhaust gas from the heat recovery steam generator (HRSG) by installing a condensing heat exchanger, and the HRSG waste heat utilization subsystem. The conventional combined cycle and the proposed combined cycle are modelled, considering mass, energy and exergy balances for every component and both energy and exergy analyses are conducted. Parametric analyses are performed for the proposed combined cycle to evaluate the effects of several factors, such as the gas turbine inlet temperature (TIT), the condenser pressure, the pinch point temperature difference of the condensing heat exchanger and the fuel gas heating temperature on the performance of the proposed combined cycle through simulation calculations. The results show that the net electrical efficiency and the exergy efficiency of the proposed combined cycle can be increased by 1.6 and 2.84% than those of the conventional combined cycle, respectively. The heat recovery per kg of flue gas is equal to 86.27 kJ s^?1. One MW of electric power for operating sea water pumps can be saved. The net electrical efficiency and the heat recovery ratio increase as the condenser pressure decreases. The higher heat recovery from the HRSG exit flue gas is achieved at higher gas TIT and at lower pinch point temperature of the condensing heat exchanger. Copyright © 2006 John Wiley & Sons, Ltd.     

有机朗肯循环回收直接空冷机组排气余热系统的热力性能研究

空冷机组汽机排汽热损失巨大,而有机朗肯循环是利用中低温热源的重要技术之一。提出采用有机朗肯循环回收空冷机组汽轮机排汽余热的技术方案,建立空冷机组和有机朗肯循环的物理模型,编制有机朗肯循环回收空冷机组汽轮机排汽余热技术的模拟程序,并将模拟计算结果与厂家提供的某型号有机朗肯循环机组的性能数据进行对比。以内蒙古锡林郭勒盟某典型600 MW机组为对象,探究汽机乏汽温度、环境温度、ORC机组过热度等关键参数变化对系统热力性能的影响规律。结果表明,ORC机组净出功和ORC机组热效率随着汽机乏汽温度的升高而增大,而随着环境温度和ORC机组过热度的增大而减小。     

Thermo-economic analysis and optimization of a combined Organic Rankine Cycle (ORC) system with LNG cold energy and waste heat recovery of dual-fuel marine engine

A combined Organic Rankine Cycle (ORC) system with liquefied nature gas (LNG) cold energy and dual-fuel (DF) marine engine waste heat utilization was proposed. Engine exhaust gas and engine jacket cooling water were adopted as parallel heat sources. Thermo-economic analyses of the proposed system with 32 working fluids combinations were performed. Two objective functions covering thermal efficiencies and economic index were employed for performance evaluation. Afterward, the effects of operation pressure on the objective functions were investigated. Finally, the optimal conditions were obtained from the Pareto front with the Non-dominated Sorting Genetic Algorithm-II (NSGA-II) method. The results show that the proposed ORC system has better energy recovery performances than the parallel ORC system. R1150-R600a-R290, R1150-R601a-R600a, and R170-R601-R290 are determined as the three most promising working fluids combinations. Under optimized conditions, the output power range is 199.97 to 218.51 kW, the energy efficiency range is 13.64% to 15.62%, and the exergy efficiency range is 25.29% to 27.3%. The payback period ranges from 8.36 to 8.74 years. The working fluids selection helps to reduce the exergy destruction of intermediate heat exchanger, which could be up to 30.59%.     

利用烟气余热的有机朗肯循环与苦咸水淡化联合系统

针对沿海和西北内陆地区淡水紧缺和工业烟气余热的排放问题,设计了一种有机朗肯循环与苦咸水淡化的联合系统对工业烟气余热进行有效回收,以生产淡水和电能。该联合系统将闪蒸法与有机朗肯循环进行有机结合,通过变参数法计算采用戊烷作为工质的有机朗肯循环的循环效率,确定该系统运行的最佳参数,并与水工质朗肯循环进行对比,证明了联合系统的优越性。     

火电厂节能环保供热装置的设计及应用

排烟热损失是锅炉各项热损失中最大的一项,它直接影响锅炉效率及发电煤耗。一般情况下,排烟温度每升高10℃,煤耗将增加2 g/(kW·h)左右。因此,降低排烟温度、回收烟气热量对于节能降耗、提高经济效益具有重要的实际意义。对火电厂节能环保供热装置的设计及应用进行了探讨。该设备采用烟气余热回收技术,将高温排烟热量传递给空气,再进行城市及工业区供热,实现了热量的回收,节省了燃煤量,同时也减少了污染物的排放,还提高了锅炉效率,有利于城市及工业区的可持续发展。     

Energy system feasibility study of an Otto cycle/Stirling cycle hybrid automotive engine

The aim of this study was to investigate the feasibility of utilising a Stirling cycle engine as an exhaust gas waste heat recovery device for an Otto cycle internal combustion engine (ICE) in the context of an automotive power plant. The hybrid arrangement would produce increased brake power output for a given fuel consumption rate when compared to an ICE alone. The study was dealt with from an energy system perspective with design practicalities such as power train integration, location of auxiliaries, manufacture costs and other general plant design considerations neglected. The study necessitated work in two distinct areas: experimental assessment of the performance characteristics of an existing automotive Otto cycle ICE and mathematical modelling of the Stirling cycle engine based on the output parameters of the ICE. It was subsequently found to be feasible in principle to generate approximately further 30% useful power in addition to that created by the ICE by using a Stirling cycle engine to capture waste heat expelled from the ICE exhaust gases over the complete range of engine operating speeds.     

Progress in the development of solid–gas sorption refrigeration thermodynamic cycle driven by low-grade thermal energy

Heat-powered solid–gas sorption refrigeration technology has been regarded as one of the effective methods for reutilization of low-grade thermal energy such as industrial waste heat, renewable energy, and exhaust gases from engines. A number of advanced solid sorption refrigeration systems have been developed to improve energy efficiency by reducing the primary energy consumption as the recognition of energy saving. These advanced solid sorption refrigeration cycles mainly include heat recovery sorption cycle, mass recovery sorption cycle, mass and heat recovery sorption cycle, double/multi-effect sorption cycle, combined double-way sorption cycle, double-effect and double-way sorption cycle, two/multi-stage sorption cycle, etc. In this paper, the progress in the development of solid–gas sorption refrigeration thermodynamic cycle is reviewed. The operating principles of these advanced solid–gas sorption refrigeration cycles are introduced in detail, and the representative working performances of different sorption refrigeration cycles are presented and compared. Moreover, the key problems of advanced sorption refrigeration cycles are described and discussed. Finally, the future development of solid–gas sorption refrigeration cycle is also proposed.     

柴油机废热利用的ORC系统特性研究

以柴油发动机缸套水和尾气废热为热源,设计开发了有机郎肯循环ORC的热力循环系统及发电装置。在该系统中,采用R245fa作为循环工质,以板式蒸发器和冷凝器作为工质相变的换热元件,机械能与电能转化。ORC系统测试结果表明,在ORC系统和发动机长时间稳定运行,稳定发电量14.4kW,发电效率7.2%;净发电量12.45kW,净发电效率6.25%。在保持发动机稳定运行和冷却水全部进行大循环的前提下,发动机出水温度降低,有利于总发电量和净发电量的提升。     

A review and selection of engine waste heat recovery technologies using analytic hierarchy process and grey relational analysis

In this paper, a brief review and comparison of the engine waste heat recovery technologies have been made. These five technologies are electric turbocompounding systems (ETC), thermodynamic organic Rankine cycle (ORC), thermoelectric generators (TEG), hydrogen generation by using exhaust gas heat energy, and hybrid pneumatic power systems (HPPS). According to comparison results, the HPPS system can achieve the highest fuel economy improvement among the five technologies. Though there are their own benefits by utilizing these different technologies, their disadvantages prevent the application of these advanced technologies to different extent. Besides, a combined evaluation method consisting of grey relational analysis and analytic hierarchy process has been applied to assess the five new engine waste heat recovery technologies from the perspective of technical, economic, and environmental aspect. Based on the final results of the new evaluation method, the HPPS was found to be the most promising WHR technology for vehicle engines. But because of the emphasis on economic benefit, TEG was found to be more favorable for working conditions, like power plant and marine engine. What is more, as is shown in the sensibility analysis, the weighing of the environment relevant factors can prominently influence the comparison results between ETC and HPPS. Copyright © 2014 John Wiley & Sons, Ltd.     

Energy and exergy‐based working fluid selection for organic Rankine cycle recovering waste heat from high temperature solid oxide fuel cell and gas turbine hybrid systems

This paper performed a comparative analysis of organic Rankine cycle (ORC) using different working fluids, in order to recover waste heat from a solid oxide fuel cell‐gas turbine hybrid power cycle. Depending on operating parameters, criteria for the choice of the working fluid were identified. Results reveal that due to a significant temperature glide of the exhaust gas, the actual ORC cycle thermal efficiency strongly depends on the turbine inlet temperature, exhaust gas temperature, and fluid's critical point temperature. When exhaust gas temperature varies in the range of 500 K to 600 K, R123 is preferred among the nine dry typical organic fluids because of the highest and most stabilized mean thermal efficiency under wide operating conditions and its reasonable condensing pressure and turbine outlet specific volume, which in turn results in a feasible ORC cycle for practical concerns. Copyright © 2012 John Wiley & Sons, Ltd.     

蛋白粉尾气余热回收喷淋塔的热工特性研究

大豆蛋白粉干燥工艺过程产生的高温尾气中蕴含着大量显热和潜热,而无填料、垂直逆流喷淋塔可以深度回收尾气中的余热。对此建立了喷淋塔的数值模型,并通过实验验证其准确性;应用所建模型,分析喷淋高度、入口水温、喷淋密度、尾气流速和尾气入口湿球温度对喷淋塔热回收性能的影响规律,进而获得了喷淋塔在实验工况范围内的换热效率曲线及经验关联式,为尾气喷淋热回收塔的优化设计与工程应用提供了分析工具。     

Analysis of exhaust waste heat recovery from a dual fuel low temperature combustion engine using an Organic Rankine Cycle

This paper examines the exhaust waste heat recovery potential of a high-efficiency, low-emissions dual fuel low temperature combustion engine using an Organic Rankine Cycle (ORC). Potential improvements in fuel conversion efficiency (FCE) and specific emissions (NO_x and CO₂) with hot exhaust gas recirculation (EGR) and ORC turbocompounding were quantified over a range of injection timings and engine loads. With hot EGR and ORC turbocompounding, FCE improved by an average of 7 percentage points for all injection timings and loads while NO_x and CO₂ emissions recorded an 18 percent (average) decrease. From pinch-point analysis of the ORC evaporator, ORC heat exchanger effectiveness (?), percent EGR, and exhaust manifold pressure were identified as important design parameters. Higher pinch point temperature differences (PPTD) uniformly yielded greater exergy destruction in the ORC evaporator, irrespective of engine operating conditions. Increasing percent EGR yielded higher FCEs and stable engine operation but also increased exergy destruction in the ORC evaporator. It was observed that hot EGR can prevent water condensation in the ORC evaporator, thereby reducing corrosion potential in the exhaust piping. Higher ? values yielded lower PPTD and higher exergy efficiencies while lower ? values decreased post-evaporator exhaust temperatures below water condensation temperatures and reduced exergy efficiencies.     

水洗-凝露式烟气三回收工艺与集成设备

为了有效回收锅炉烟气中的热量、水分、硫分,本文提出了水洗-凝露式烟气三回收集成工艺.该工艺将气水接触式换热、烟气凝露式换热、水-水换热的高效换热方式集成,回收烟气中的热量的同时在喷淋塔内实现脱硫除尘,在凝结式换热器内实现水回收.介绍了工艺的热工设计原理及各关键部件的传热模型,总结了其计算方法与步骤,最后介绍了一个实例设计以供参考.该集成工艺与设备可有效地用于烟气热、水、硫的回收中.