Proposal and analysis of a novel ammonia–water cycle for power and refrigeration cogeneration

Cogeneration has improved sustainability as it can improve the energy utilization efficiency significantly. In this paper, a novel ammonia-water cycle is proposed for the cogeneration of power and refrigeration. In order to meet the different concentration requirements in the cycle heat addition process and the condensation process, a splitting /absorption unit is introduced and integrated with an ammonia–water Rankine cycle and an ammonia refrigeration cycle. This system can be driven by industrial waste heat or a gas turbine flue gas. The cycle performance was evaluated by the exergy efficiency, which is 58% for the base case system (with the turbine inlet parameters of 450 °C/11.1 MPa and the refrigeration temperature below −15 °C). It is found that there are certain split fractions which maximize the exergy efficiency for given basic working fluid concentration. Compared with the conventional separate generation system of power and refrigeration, the cogeneration system has an 18.2% reduction in energy consumption.     

Exergetic performance assessment of a pilot‐scale heat pump belt conveyor dryer

In this study, olive leaves were dried in a pilot‐scale heat pump (HP) belt conveyor dryer as a thin layer. Drying experiments were carried out at the drying air temperature range of 45–55°C with the drying air velocity range of 0.5–1.5 m s⁻¹. The performance of the system and the process was evaluated using exergy analysis method. The exergy loss and flow diagram (the so‐called Grassmann diagram) of the dryer system was presented to give quantitative information regarding the proportion of the exergy input that is dissipated in the various system components. Effects of the drying air temperature and the velocity on the performance of the drying process were discussed. The actual coefficient of performance values were obtained to be 2.37 for the HP unit and 2.31 for the overall system, respectively. The most important component of the system for improving the efficiency was determined to be the compressor. Exergetic efficiencies of the drying of olive leaves were in the range of 67.45–81.95%. It was obtained that they increased as the drying air temperature decreased and the drying air velocity increased. Copyright © 2009 John Wiley & Sons, Ltd.     

Experimental study of gas engine driven air to water heat pump in cooling mode

Nowadays a sustainable development for more efficient use of energy and protection of the environment is of increasing importance. Gas engine heat pumps represent one of the most practicable solutions which offer high energy efficiency and environmentally friendly for heating and cooling applications. In this paper, the performance characteristics of gas engine driven heat pump used in water cooling were investigated experimentally without engine heat recovery. The effects of several important factors (evaporator water inlet temperature, evaporator water volume flow rate, ambient air temperature, and engine speed) on the performance of gas engine driven heat pump were studied in a wide range of operating conditions. The results showed that primary energy ratio of the system increased by 22.5% as evaporator water inlet temperature increased from 13 °C to 24 °C. On the other hand, varying of engine speed from 1300 rpm to 1750 rpm led to decrease in system primary energy ratio by 13%. Maximum primary energy ratio has been estimated with a value of two over a wide range of operating conditions.     

Energy and exergy analyses of space heating in buildings

In the present study, energy and exergy analyses are presented for the whole process of space heating in buildings. This study is based on a pre-design analysis tool, which has been produced during ongoing work for the International Energy Agency (IEA) formed within the Energy Conservation in Buildings and Community Systems Programme (ECBCSP) Annex 37. Throughout this paper, in all of the calculations such as heat losses and gains were taken according to Turkish Standards Institution TSE, which is in accordance with the European Standard TS EN ISO 13789. In the analysis, heating load is taken account but cooling load is neglected and the calculations presented here are done using steady state conditions. The analysis is applied to an office in Izmir with a volume of 720 m³ and a net floor area of 240 m² as an example of application. Indoor and exterior air temperatures are 20 °C and 0 °C, respectively. It is assumed that the office is heated by a liquid natural gas (LNG) fired conventional boiler, an LNG condensing boiler and an external air–air heat pump. With this study, energy and exergy flows are investigated. Energy and exergy losses in the whole system are quantified and illustrated. The highest efficiency values in terms of energy and exergy were found to be 80.9% for external air–air heat pump and 8.69% for LNG condensing boiler, respectively.     

A comparative investigation of various greenhouse heating options using exergy analysis method

This study deals with modeling and analyzing the performance of greenhouses from the power plant through the heating system to the greenhouse envelope using exergy analysis method, the so-called low exergy or LowEx approach, which has been and still being successfully used in sustainable buildings design, for the first time to the best of the author’s knowledge. For the heating applications, three options are studied with (i) a solar assisted vertical ground-source heat pump greenhouse heating system, (ii) a wood biomass boiler, and (iii) a natural gas boiler, which are driven by renewable and non-renewable energy sources. In this regard, two various greenhouses, the so-called small greenhouse and large greenhouse, considered have heat load rates of 4.15 kW and 7.5 MW with net floor areas of 11.5 m² and 7.5 ha, respectively. The overall exergy efficiency values for Cases 1–3 (solar assisted vertical ground-source heat pump, natural gas boiler and wood biomass boiler) of the small greenhouse system decrease from 3.33% to 0.83%, 11.5% to 2.90% and 3.15% to 0.79% at varying reference state temperatures of 0 to 15 °C while those for Cases 1 and 2 (wood biomass and natural gas boilers) of the large greenhouse system decrease from 2.74% to 0.11% and 4.75% to 0.18% at varying reference state temperatures of −10% to 15 °C. The energetic renewability ratio values for Cases 1 and 3 of the small greenhouse as well as Case 1 of the large greenhouse are obtained to be 0.28, 0.69 and 0.39, while the corresponding exergetic renewability ratio values are found to be 0.02, 0.64 and 0.29, respectively.     

空气源单、双级燃气机热泵的应用及其效益分析

提出一种单、双级空气源燃气机热泵,并从多个角度上同传统的蒸汽压缩式热泵和单级燃气机热泵作了比较。结果表明,这种热泵在一次能源利用率、火用效率和经济性上有较大优势,它的推广使用将扩大热泵的适用范围和使用时间,尤其在三北地区。     

Evaluation of hydrogen production with iron-based chemical looping fed by different biomass

In this study, the iron-based chemical looping process driven by various biomasses for hydrogen production purposes is studied and evaluated thermodynamically through energy and exergy approaches. The overall system consists of some key units (combustor, reducers and oxidizer) a torrefier, a drying chamber, an air separation unit, a heat exchanger, and auxiliary units as well. The biomasses considered are first dried and torrified in the drying chamber and sent to reactors to produce hydrogen. The exergy and energy efficiencies of the iron based chemical looping facility are investigated comparatively for performance evaluation. The maximum exergy destruction and entropy production rates are calculated for the torrefaction process as 123.15 MW and 4926 kW/K respectively. Under the steady–state conditions, a total of 8 kg/s hydrogen is produced via chemical looping process. The highest energy efficiency is obtained in the looping of rice husk with 86% while the highest exergy efficiency is obtained in the looping using sugarcane bagasse with 91%, respectively.     

燃气机热泵的热力学分析

燃气机热泵是以燃气机作为动力来驱动的压缩式热泵。对燃气机热泵的热力学第一定律、Yong分析和能级平衡理论分析结果表明：其一次能源利用率可达1.76，Yong效率为0.291，能级平衡系数为0.394。与电动热泵等其他供热装置相比，燃气机热泵有着较高的热力学完善性，是一项高效节能技术。由于能级平衡理论分析考虑了Wu的作用，而热泵供暖时其性能系数的提高主要是利用了环境热量，所以建议采用能级平衡理论来分析评价热泵的性能。     

燃气机热泵变负荷特性的试验研究

燃气机热泵是一项高效节能技术，在试验条件下其一次能源利用率PER为1．13～1．79。为了解交负荷时燃气机热泵的性能，通过试验得到了燃气机热泵的发动机负荷特性、发动机余热回收和燃气机热泵的总体特性曲线。结果表明：随着发动机转速的增加，燃气机热泵的COP和PER是下降的，但下降的幅度较为平缓，且保持较高的数值。通过对IPL Vcop值的分析，发现燃气机热泵的IPL Vcop比热泵系统的大，这说明燃气机热泵的部分负荷性能好，可以很好地实现交负荷运行。     

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.     

Experimental study of combustion and emission characteristics of ethanol fuelled port injected homogeneous charge compression ignition (HCCI) combustion engine

The homogeneous charge compression ignition (HCCI) is an alternative combustion concept for in reciprocating engines. The HCCI combustion engine offers significant benefits in terms of its high efficiency and ultra low emissions. In this investigation, port injection technique is used for preparing homogeneous charge. The combustion and emission characteristics of a HCCI engine fuelled with ethanol were investigated on a modified two-cylinder, four-stroke engine. The experiment is conducted with varying intake air temperature (120–150 °C) and at different air–fuel ratios, for which stable HCCI combustion is achieved. In-cylinder pressure, heat release analysis and exhaust emission measurements were employed for combustion diagnostics. In this study, effect of intake air temperature on combustion parameters, thermal efficiency, combustion efficiency and emissions in HCCI combustion engine is analyzed and discussed in detail. The experimental results indicate that the air–fuel ratio and intake air temperature have significant effect on the maximum in-cylinder pressure and its position, gas exchange efficiency, thermal efficiency, combustion efficiency, maximum rate of pressure rise and the heat release rate. Results show that for all stable operation points, NO_x emissions are lower than 10 ppm however HC and CO emissions are higher.     

Techno-economic analysis of a novel hybrid heat pump system to recover waste heat and condensate from the low-temperature boiler exhaust gas

This paper is based on the proposal of a new waste heat recovery (WHR) system, which can be utilized to heat the boiler return water, boiler supply air, and building heating air. The system is the combination of an indirect contact condensing unit (IDCCU), a mechanical compression heat pump, and two air preheaters. The system is modeled on the basis of mass and energy balance and then thermodynamically analyzed. Improved performance results were obtained in the form of an increase in the boiler's energy efficiency of about 10.47%, with 4.87% increase in exergy efficiency. The coefficient of performance (COP) of the heat pump was increased from 1.23 to 1.45 by the addition of an air heater in the conventional heat pump. The exergy destruction in each component is calculated. Sensitivity analysis was performed to check the influence of different operating parameters on the performance of the WHR system and boiler. It can be observed from the results that for a specific refrigerant temperature and a calculated amount of mass, flow rate can maximize the condensation efficiency of IDCCU by decreasing the flue gas temperature, while the use of the air heater can further reduce the flue gas temperature, and a stream of hot air can be utilized for space heating. A comparison is made with the other system on a performance basis. The results shows a clear difference in efficiencies and profit earned.     

Exergetic evaluation of drying of laurel leaves in a vertical ground-source heat pump drying cabinet

This paper is concerned with the exergy analysis of the single layer drying process of laurel leaves in a ground-source heat pump drying cabinet, which was designed and constructed in the Solar Energy Institute, Ege University, Izmir, Turkey. The effects of drying air temperature on exergy losses, exergy efficiencies and exergetic improvement potential of the drying process are investigated. The results have indicated that exergy efficiencies of the dryer increase with rising the drying air temperature. Moreover, the laurel leaves are sufficiently dried at the temperatures ranging from 40 to 50°C with relative humidities varying from 16 to 19% and a drying air velocity of 0.5 m s⁻¹ during the drying period of 9 h. The exergy efficiency values are obtained to range from 81.35 to 87.48% based on the inflow, outflow and loss of exergy, and 9.11 to 15.48% based on the product/fuel basis between the same drying air temperatures with a drying air mass flow rate of 0.12 kg s⁻¹. Copyright © 2006 John Wiley & Sons, Ltd.     

Innovative concept for gasification for hydrogen based on the heat integration between water gas shift unit and coal–water–slurry gasification unit

In order to achieve the energy cascade utilization and improve the energy utilization efficiency of coal–water–slurry (CWS) gasification for hydrogen system, the heat integration scheme (HIS) between the water gas shift unit and the gasification unit is put forward. The effects of temperature change of CWS and oxygen on the gasification performance are investigated. Both the HIS and the non-heat integration scheme (NHIS) are analyzed by using gasification performance, energy conversion efficiency and exergy efficiency. The results show that the specific coal consumption and the specific oxygen consumption decrease by 2.7% and 6.5%, respectively, as the feedstock is preheated up to the temperature of 150 °C. The energy conversion efficiency of HIS and NHIS are nearly the same. The exergy efficiency of HIS (62.66%) is better than that of NHIS (62.02%). Therefore, the HIS is better than the NHIS by heat integration between the WGS unit and the gasification unit.     

Development and performance analysis of a new solar tower and high temperature steam electrolyzer hybrid integrated plant

In this article, an extensive thermodynamic performance assessment for the useful products from the solar tower and high-temperature steam electrolyzer assisted multigeneration system is performed, and also its sustainability index is also investigated. The system under study is considered for multi-purposes such as power, heating, cooling, drying productions, and also hydrogen generation and liquefaction. In this combined plant occurs of seven sub-systems; the solar tower, gas turbine cycle, high temperature steam electrolyzer, dryer process, heat pump, and absorption cooling system with single effect. In addition, the energy and exergy performance, irreversibility and sustainability index of multigeneration system are examined according to several factors, such as environment temperature, gas turbine input pressure, solar radiation and pinch point temperature of HRSG. Results of thermodynamic and sustainability assessments show that the total energetic and exergetic efficiency of suggested paper are calculated as 60.14%, 58.37%, respectively. The solar tower sub-system has the highest irreversibility with 18775 kW among the multigeneration system constituents. Solar radiation and pinch point temperature of HRSG are the most critical determinants affecting the system energetic and exergetic performances, and also hydrogen production rate. In addition, it has been concluded that, the sustainability index of multigeneration suggested study has changed between 2.2 and 3.05.     

Experimental study on combustion and emissions performance of a hybrid hydrogen–gasoline engine at lean burn limits

Lean combustion is an effective way for improving the spark-ignited (SI) engine performance. Unfortunately, due to the narrow flammability of gasoline, the pure gasoline-fueled engines sometimes suffer partial burning or misfire at very lean conditions. Hydrogen has many excellent combustion properties that can be used to extend the gasoline engine lean burn limit and improve the gasoline engine performance at lean conditions. In this paper, a 1.6 L port fuel injection gasoline engine was modified to be a hybrid hydrogen–gasoline engine (HHGE) fueled with the hydrogen–gasoline mixture by mounting an electronically controlled hydrogen injection system on the intake manifolds while keeping the original gasoline injection system unchanged. A self-developed hybrid electronic control unit (HECU) was used to flexibly adjust injection timings and durations of gasoline and hydrogen. Engine tests were conducted at 1400 rpm and a manifolds absolute pressure (MAP) of 61.5 kPa to investigate the performance of an HHGE at lean burn limits. Three hydrogen volume fractions in the total intake gas of 1%, 3% and 4.5% were adopted. For a specified hydrogen volume fraction, the gasoline flow rate was gradually reduced until the engine reached the lean burn limit at which the coefficient of variation in indicated mean effective pressure (COVimep) was 10%. The test results showed that COVimep at the same excess air ratio was obviously reduced with the increase of hydrogen enrichment level. The excess air ratio at the lean burn limit was extended from 1.45 of the original engine to 2.55 of the 4.5% HHGE. The engine brake thermal efficiency, CO, HC and NO_x emissions at lean burn limits were also improved for the HHGE.     

Effects of secondary combustion on efficiencies and emission reduction in the diesel engine exhaust heat recovery system

An experimental study on the effects of secondary combustion on efficiencies and emission reduction in the diesel engine exhaust heat recovery system has been undertaken. The co-generation concept is utilized in that the electric power is produced by the generator connected to the diesel engine, and heat is recovered from both combustion exhaust gases and the engine by the fin-and-tube and shell-and-tube heat exchangers, respectively. A specially designed secondary combustor is installed at the engine outlet in order to reburn the unburned fuel from the diesel engine, thereby improving the system’s efficiency as well as reducing air pollution caused by exhaust gases. The main components of the secondary combustor are coiled Nichrome wires heated by the electric current and diesel oxidation catalyst (DOC) housed inside a well insulated stainless steel shell. The performance tests were conducted at four water flow rates of 5, 10, 15 and 20 L/min and five electric power outputs of 3, 5, 7, 9 and 11 kW. The results show that at a water flow of 20 L/min and a power generation of 9 kW, the total efficiency (thermal efficiency plus electric power generation efficiency) of this system reaches a maximum 94.4% which is approximately 15–20% higher than that of the typical diesel engine exhaust heat recovery system. Besides, the use of the secondary combustor and heat exchangers results in 80%, 35% and 90% reduction of carbon monoxide (CO), nitrogen oxide (NO_x) and particulate matter (PM), respectively.     

α–h Diagram and principle of exergy coupling of GAX cycle

Ammonia absorption chiller systems of a single-stage cycle and a Generator Absorber heat exchanger cycle (GAX) were simulated and studied. At heat source temperatures of T_H = 120 °C, T_M = 25 °C and T_L = 5 °C, the coefficient of performances of the two cycles are 0.589 and 0.776, the GAX cycle is higher 31.8% than the single-stage cycle. And the exergy efficiencies of the two cycles are 15.4% and 27.4%, the GAX cycle is higher up to 77.9%. This paper proposes a new method that adopts the energy quality factor α as a evaluation criterion and also uses the α–h diagram as a thermodynamic analysis tool graphically, and a concept that divides absorption cycle to a heat pump subcycle and a heat engine subcycle. By means of the α–h diagram, the thermodynamic frameworks of the two cycles were illustrated. The comparison analysis indicates that the improvement of cycle performance depends on its thermodynamic perfectibility. In fact, the exergy demand of heat pump subcycle in the GAX cycle is as the same as that of the single-stage cycle, however, the energy cascading use and the exergy coupling framework of the heat engine subcycle in GAX cycle is retrofitted, so that the exergy consumption is reduced and the increased benefit is obtained from the overall cycle.     

Analysis on the heating performance of a gas engine driven air to water heat pump based on a steady-state model

In this study, the heating performance of a gas engine driven air to water heat pump was analyzed using a steady state model. The thermodynamic model of a natural gas engine is identified by the experimental data and the compressor model is created by several empirical equations. The heat exchanger models are developed by the theory of heat balance. The system model is validated by comparing the experimental and simulation data, which shows good agreement. To understand the heating characteristic in detail, the performance of the system is analyzed in a wide range of operating conditions, and especially the effect of engine waste heat on the heating performance is discussed. The results show that engine waste heat can provide about 1/3 of the total heating capacity in this gas engine driven air to water heat pump. The performance of the engine, heat pump and integral system are analyzed under variations of engine speed and ambient temperature. It shows that engine speed has remarkable effects on both the engine and heat pump, but ambient temperature has little influence on the engine’s performance. The system and component performances in variable speed operating conditions is also discussed at the end of the paper.     

Thermoeconomic assessment of an absorption refrigeration and hydrogen-fueled diesel power generator cogeneration system

The thermoeconomic assessment of a cogeneration application that uses a reciprocating diesel engine and an ammonia–water absorption refrigeration system for electrical power and cold production from hydrogen as fuel is presented. The purpose of the assessment is to get both exergetic and exergoeconomic costs of the cogeneration plant products at different load conditions and concentrations of hydrogen–diesel oil blends. The exhaust gas of the reciprocating diesel engine is used as an energy source for an ammonia–water absorption refrigeration system. The reciprocating diesel engine was simulated using the Gate Cycle™ software, and the ammonia–water absorption refrigeration system simulation and the thermoeconomic assessment were carried out using the Engineering Equation Solver software (EES). The results show that engine combustion is the process of higher exergy destruction in the cogeneration system. Increased hydrogen concentration in the fuel increases the system exergetic efficiency for all load conditions. Exergy destruction in the components of the ammonia–water absorption refrigeration system is increased with increasing load due to the rise of heat transfer. At intermediate and high loads energy efficiency is increased in the power system, and low values of unit exergetic cost and competitive specific exergoeconomic costs are noticed. The cogeneration system operation at intermediate and high engine loads was proven to be feasible.