Modeling and experimentation of a novel pressurized CHP system with water extraction

A novel cooling and power cycle is proposed, which combines a semi‐closed cycle gas turbine called the high‐pressure regenerative turbine engine (HPRTE) with a vapor absorption refrigeration system (VARS). This combined HPRTE/VARS cycle is capable of producing power, water and refrigeration effect for external loads. In a previous study, the combined cycle was modeled using zero‐dimensional steady‐state thermodynamics, with specified values of polytrophic efficiencies and pressure drops for the turbo‐machinery and heat exchangers. In this study, a modified version of the combined HPRTE/VARS cycle is experimentally investigated for the demonstration of the combined cycle concept and for the model validation. This modified HPRTE has two water‐cooled heat exchangers instead of the absorption refrigeration system. The model of the original combined HPRTE/VARS cycle was modified to simulate the performance of the modified HPRTE cycle. Temperatures, pressure, mass flow rates and other overall cycle parameters obtained from the computer model are compared with the corresponding experimental values of the modified cycle. The agreement between the values is found to be within acceptable limits. In addition, the uncertainty analysis of the experimental data is undertaken to find the uncertainty in the final output variables: thermal efficiency and non‐dimensional water extraction parameter. Copyright © 2008 John Wiley & Sons, Ltd.     

A novel pressurized CHP system with water extraction and refrigeration

A novel Cooling, Heat, and Power (CHP) system has been proposed that features a semi-closed Brayton cycle with pressurized recuperation, integrated with a Vapor Absorption Refrigeration System (VARS). The semi-closed Brayton cycle is called the High Pressure Regenerative Turbine Engine (HPRTE). The VARS interacts with the HPRTE power cycle through heat exchange in the generator and the evaporator. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration unit, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration in an amount which depends on ambient conditions. Water produced as a product of combustion is intentionally condensed in the evaporator of the VARS, which is designed to provide sufficient cooling for the inlet air to the high-pressure compressor, water extraction, and for an external cooling load. The computer model of the combined HPRTE/VARS cycle predicts that with steam blade cooling and a medium-sized engine, the cycle will have a thermal efficiency of 49% for a turbine inlet temperature of 1400 °C. This thermal efficiency is in addition to the large external cooling load generated in the combined cycle which is 13% of the net work output. In addition it also produces up to 1.4 kg of water for each kg of fuel consumed, depending upon the fuel type. When the combined HPRTE/VARS cycle is optimized for maximum thermal efficiency, the optimum occurs for a broad range of operating conditions. Details of the multivariate optimization procedure and results are presented in the paper.Previous studies have demonstrated the following attributes of the combined HPRTE/VARS cycle: attaining high part power efficiency in a compact package, threefold specific power increase over the state of the art, reduced IR signatures due to lower exhaust temperature, significant reduction of exhaust particulates and smoke, constant high-pressure compressor inlet temperature and order-of-magnitude reductions in emissions such as NO_x, CO and unburned hydrocarbons. The integrated nature of this system allows overall reduction in size and weight of approximately 50% relative to conventional equipment. The combination of positive attributes makes the HPRTE combined cycle engine attractive for future mobile power applications in terms of performance as well as life cycle cost.     

新型太阳能吸收式制冷循环的性能分析

在两级溴化锂吸收式制冷循环的基础上,提出了一种由太阳能驱动的新型吸收式制冷循环,并对其进行性能分析。通过大量计算,分析结果表明,在现有太阳能集热器所能提供的热水温度范围内,新型太阳能吸收式制冷循环有较高的热力系数。该循环系统的中间压力、中间浓度对系统的热力系数和热源可利用温差有较大影响。     

Cooling performance and energy saving of a compression–absorption refrigeration system driven by a gas engine

The prototype of combined vapour compression–absorption refrigeration system was set up, where a gas engine drove directly an open screw compressor in a vapour compression refrigeration chiller and waste heat from the gas engine was used to operate absorption refrigeration cycle. The experimental procedure and results showed that the combined refrigeration system was feasible. The cooling capacity of the prototype reached about 589 kW at the Chinese rated conditions of air conditioning (the inlet and outlet temperatures of chilled water are 12 and 7°C, the inlet and outlet temperatures of cooling water are 30 and 35°C, respectively). Primary energy rate (PER) and comparative primary energy saving were used to evaluate energy utilization efficiency of the combined refrigeration system. The calculated results showed that the PER of the prototype was about 1.81 and the prototype saved more than 25% of primary energy compared to a conventional electrically driven vapour compression refrigeration unit. Error analysis showed that the total error of the combined cooling system measurement was about 4.2% in this work. Copyright © 2006 John Wiley & Sons, Ltd.     

Design and development of a refrigeration system energized with hydrogen produced from scrap aluminum

Hydrogen holds out great promise as an energy source whose use does not pollute the environment. In this context, methods of hydrogen production which do not involve formation of carbon dioxide are especially attractive. The present work describes a cheap and versatile prototype of an alkaline hydrolyser which efficiently produces hydrogen from aluminum scrap and aqueous sodium hydroxide, the hydrogen produced being used directly to energize, by combustion, a refrigerator working on the ammonia–water principle, which was also designed and developed in our laboratory. A direct comparison of the system when energized by liquid-propane flame and by hydrogen flame shows a clearly better performance in the latter case, which produces a temperature of −20 °C after about 2 h of operation.     

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.     

Thermodynamic optimization of a solar system for cogeneration of water heating and absorption cooling

This paper presents a contribution to understanding the behavior of solar‐powered air conditioning and refrigeration systems with a view to determining the manner in which refrigeration rate, mass flows, heat transfer areas, and internal architecture are related. A cogeneration system consisting of a solar concentrator, a cavity‐type receiver, a gas burner, and a thermal storage reservoir is devised to simultaneously produce heat (hot water) and cooling (absorption refrigerator system). A simplified mathematical model, which combines fundamental and empirical correlations, and principles of classical thermodynamics, mass and heat transfer, is developed. The proposed model is then utilized to simulate numerically the system transient and steady‐state response under different operating and design conditions. A system global optimization for maximum performance (or minimum exergy destruction) in the search for minimum pull‐down and pull‐up times, and maximum system second law efficiency is performed with low computational time. Appropriate dimensionless groups are identified and the results are presented in normalized charts for general application. The numerical results show that the three‐way maximized system second law efficiency, η_{II,max,max,max}, occurs when three system characteristic mass flow rates are optimally selected in general terms as dimensionless heat capacity rates, i.e. (ψ_ss, ψ_wxwx, ψ_Hs)_opt=(0.335, 0.28, 0.2). The minimum pull‐down and pull‐up times, and maximum second law efficiencies found with respect to the optimized operating parameters are sharp and, therefore, important to be considered in actual design. As a result, the model is expected to be a useful tool for simulation, design, and optimization of solar energy systems in the context of distributed power generation. Copyright © 2008 John Wiley & Sons, Ltd.     

小型燃气制冷和采暖系统的研究

探索以燃气为能源的吸收循环式制冷和采暖系统,阐明了主要用于小型商业用户和居民用户燃气空调的技术指标、系统的设计、构造及试验方法.     

Exergy analysis of double effect vapor absorption refrigeration system

Energy and exergy analyses previously performed by the authors for a single effect absorption refrigeration system have been extended to double effect vapor absorption refrigeration system with the expectation of reducing energy supply as well as an interest in the diversification of the motive power employed by HVAC technologies. The total exergy destruction in the system as a percentage of the exergy input from a generator heating water over a range of operating temperatures is examined for a system operating on LiBr–H₂O solution. The exergy destruction in each component, the coefficient of performance (COP) and the exergetic COP of the system are determined. It is shown that exergy destructions occur significantly in generators, absorbers, evaporator2 and heat exchangers while the exergy destructions in condenser1, evaporator1, throttling valves, and expansion valves are relatively smaller within the range of 1–5%. The results further indicate that with an increase in the generator1 temperature the COP and ECOP increase, but there is a significant reduction in total exergy destruction of the system for the same. On the other hand, the COP and ECOP decrease with an increase in the absorber1 temperature while the total exergy destruction of the system increases significantly with a small increase in the absorber1 temperature. The results show that the exergy method can be used as an effective criterion in designing an irreversible double effect absorption refrigeration system and may be a good tool for the determination of the optimum working conditions of such systems. Copyright © 2007 John Wiley & Sons, Ltd.     

太阳能两级吸收式制冷机应用分析

在给定冷凝温度和吸收温度的情况下提出了利用太阳能做热源、地下水做冷源的两级吸收式制冷系统,COP可达1.4~1.7,高于其他形式吸收式热泵,节约了冷却水的用量。     

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.     

Ammonia–water absorption refrigeration systems with flooded evaporators

The harmful effects of water accumulation in the evaporator in ammonia–water absorption refrigeration systems (AARS) with flooded evaporators are a crucial issue. In this paper, the effects of the ammonia purification and the liquid entrainment and blow-down from the evaporator in AARS are analyzed. A mathematical model based on a single stage system with complete condensation has been developed. The ammonia purification is evaluated by means of the Murphree efficiencies of the stripping and rectifying sections of the distillation column. The entrainment and blow-down are taking into account considering the corresponding flow rates as a fraction of the dry vapour at the evaporator outlet. The influence of the distillation column components efficiency on the attainable distillate concentration and the effects of the distillate concentration and the liquid entrainment and blow-down on the system operating conditions and performance are analyzed and quantified. If no liquid entrainment or blow-down is considered, very high efficiencies in the distillation column are required. Small values of liquid entrainment or blow-down fractions increase significantly the operating range of the absorption system. If high values of the blow-down fraction are required, then a heat exchanger should be added to the system in order to recover the refrigeration capacity of the blow-down by additional subcooling of the liquid from the condenser. For a fixed value of the distillation column efficiency, an optimum value of the liquid blow-down fraction exists. Moreover, an optimum combination of generation temperature, reflux ratio and blow-down fraction can be found, which should be considered in designing and controlling an AARS.     

Modeling,numerical optimization,and irreversibility reduction of a triple-pressure reheat combined cycle

The main methods for improving the efficiency of the combined cycle are: increasing the inlet temperature of the gas turbine (TIT), reducing the irreversibility of the heat recovery steam generator (HRSG), and optimization. In this paper, modeling and optimization of the triple-pressure reheat combined cycle as well as irreversibility reduction of its HRSG are considered. Constraints were set on the minimum temperature difference for pinch points (PP_m), the temperature difference for superheat approach, the steam turbine inlet temperature and pressure, the stack temperature, and the dryness fraction at steam turbine outlet. The triple-pressure reheat combined cycle was optimized at 41 different maximum values of TIT using two different methods; the direct search and the variable metric. A feasible technique to reduce the irreversibility of the HRSG of the combined cycle was introduced. The optimized and the reduced-irreversibility triple-pressure reheat combined cycles were compared with the regularly designed triple-pressure reheat combined cycle, which is the typical design for a commercial combined cycle. The effects of varying the TIT on the performance of all cycles were presented and discussed. The results indicate that the optimized triple-pressure reheat combined cycle is up to 1.7% higher in efficiency than the reduced-irreversibility triple-pressure reheat combined cycle, which is 1.9–2.1% higher in efficiency than the regularly designed triple-pressure reheat combined cycle when all cycles are compared at the same values of TIT and PP_m. The optimized and reduced-irreversibility combined cycles were compared with the most efficient commercially available combined cycle at the same value of TIT.     

An experimental comparison between LPG and engine exhaust gas as energy source for an absorption refrigeration system

This paper presents an experimental analysis of an absorption refrigeration system, comparing two different energy sources. The exhaust gas from an internal combustion engine was evaluated against the original energy source, liquefied petroleum gas (LPG). The experiments were performed in a domestic refrigerator, monitoring the air temperature and humidity inside the equipment. A production engine was tested with 25% and wide‐open throttle valve (WOT), mounted on a bench dynamometer. The energy demand, cooling capacity and coefficient of performance (COP) were determined for both energy sources. The results showed that engine exhaust gas is a potential source for absorption refrigeration systems. When the engine exhaust gas was used as energy source, the energy available for the refrigerator was higher with 25% throttle valve opening. Copyright © 2011 John Wiley & Sons, Ltd.     

Proposal of a hybrid CHP system: SOFC/microturbine/absorption chiller

Distributed generation is becoming an attractive option for industrial and commercial scale customers. The main advantage of this on‐site power generation is that it offers a more efficient, reliable and cost‐effective power supply. In addition, waste heat can be used for local heating or cooling. This is known as cogeneration or combined heat and power (CHP). In the present work, a hybrid‐CHP system for a 230 kWe demand building is proposed and analyzed. The system considers the coupling of:

• A Solid Oxide Fuel Cell stack with an output of 200 kWe
• A Microturbine with an output of 30 kWe
• A single effect Absorption cooling system providing 55 kWt for air conditioning using water chillers

This plant would use natural gas as the primary fuel. The SOFC module is fed with the gas fuel and the whole stack generates the main power while acting as a combustor. The product gases exit the anode at a temperature of 900°C and are directly injected to the Micro Gas Turbine unit to produce additional power. Finally, the waste heat available at the turbine's exhaust fires a single effect Absorption Water‐Chiller to provide cooling for air conditioning in the building. This proposed system would generate up to 230 kWe and 55 kWt with high thermal efficiencies of around 70–75%. Currently, Hybrid SOFC/GT and Microturbine/CHP systems are being considered or tested at several facilities. However, a combination of both, which would yield to trigeneration, has not been considered yet. Here we present a conceptual model based on specific proposals and investigations done by other researchers. A theoretical analysis on the proposed model is conducted to evaluate the potential and possibilities of such Hybrid CHP system and further discussions based on the economical considerations is also presented. Copyright © 2009 John Wiley & Sons, Ltd.     

Modeling of an intermittent solar absorption refrigeration system operating with ammonia–lithium nitrate mixture

The theoretical performance of an intermittent absorption refrigeration system operating with ammonia–lithium nitrate mixture is presented. The analysis was done for representative days of each season of 2001. Meteorological data were taken from a local meteorological station installed in the Energy Research Centre of the National University of Mexico in Temixco, Morelos, Mexico. The system consists of a generator-absorber, a condenser, a valve and an evaporator. A compound parabolic concentrator (CPC) with a glass cover, operates as the generator-absorber of the cooling system. Since lithium nitrate does not evaporate during the generation, it is not necessary to use a rectifier. The theoretical efficiencies of the CPC varied from 0.78 to 0.33 depending on the time of the day and the season. Also, the results showed that with the proposed system it is possible to produce up to 11.8 kg of ice at generation temperatures around 120°C and condensation temperatures between 40°C and 44°C. These temperatures allow the system to be chilled with air or water. The overall efficiencies of the systems were between 0.15 and 0.4 depending on the generation and condenser temperatures. The efficiencies are satisfactory considering the simplicity of the system.     

Modeling, simulation and optimization of a solar collector driven water heating and absorption cooling plant

A cogeneration system consisting of a solar collector, a gas burner, a thermal storage reservoir, a hot water heat exchanger, and an absorption refrigerator is devised to simultaneously produce heating (hot water heat exchanger) and cooling (absorption refrigerator system). A simplified mathematical model, which combines fundamental and empirical correlations, and principles of classical thermodynamics, mass and heat transfer, is developed. The proposed model is then utilized to simulate numerically the system transient and steady state response under different operating and design conditions. A system global optimization for maximum performance (or minimum exergy destruction) in the search for minimum pull-down and pull-up times, and maximum system second law efficiency is performed with low computational time. Appropriate dimensionless groups are identified and the results presented in normalized charts for general application. The numerical results show that the three way maximized system second law efficiency, η_{II,max,max,max}, occurs when three system characteristic mass flow rates are optimally selected in general terms as dimensionless heat capacity rates, i.e., (ψ_sp,s,ψ_wx,wx,ψ_H,s)_opt≅(1.43,0.23,0.14). The minimum pull-down and pull-up times, and maximum second law efficiencies found with respect to the optimized operating parameters are sharp and, therefore important to be considered in actual design. As a result, the model is expected to be a useful tool for simulation, design, and optimization of solar collector based energy systems.     

Performance analysis on industrial refrigeration system integrated with encapsulated PCM‐based cool thermal energy storage system

Cool thermal energy storage (CTES) is an advanced energy technology that has recently attracted increasing interest for industrial refrigeration applications such as process cooling, food preservation and building air conditioning systems. An experimental investigation on the performance of an industrial refrigeration system integrated with encapsulated phase change material (PCM)‐based CTES system is carried out in the present work. In the experimental set‐up a vertical storage tank is integrated with the evaporator of the vapour compression refrigeration system. Effect of the inlet temperature of heat transfer fluid (HTF) on the temperature variation of the PCM and the HTF in the storage tank and the performance parameters namely average rate of charging, energy stored, specific energy consumption (SEC) of the chiller with and without storage system are studied in detail. The effect of porosity variation in the storage tank is also studied. A 1°C decrease in evaporator temperature results in about 3–4% increase in SEC and 1°C decrease in condensing temperature leads to 2.25–3.25% decrease in SEC. The range of HTF inlet temperature and porosity values for optimum performance is reported. Copyright © 2007 John Wiley & Sons, Ltd.     

Thermodynamic analysis of monomethylamine–water solutions in a single-stage solar absorption refrigeration cycle at low generator temperatures

A theoretical analysis of the coefficient of performance COP was undertaken to examine the efficiency characteristics of the monomethylamine–water solutions for a single-stage absorption refrigeration machine, using low generator temperatures (60–80°C), which allows the use of flat plate solar collectors. The thermodynamic analysis considers both, basic and refined cycles. The refined absorption cycle included a sensible heat recover exchanger (that is a solution heat exchanger). The thermal coefficients of performance COP_h for the basis cycle and COP_SHE for the refined cycle were calculated using the enthalpies at various combinations, at the operating temperatures and concentrations. The flow ratio F_R has been calculated as additional optimization parameter. Due to the relative low pressure and the high coefficients of performance, the monomethylamine–water solutions present interesting properties for their application in solar absorption cycles at moderate condenser and absorber temperatures (25–35°C), with temperatures in the evaporator from −10°C to 10°C which are highly usable for food product preservation and for air conditioning in rural areas.     

Energy and exergy analysis of novel solar bi‐ejector refrigeration system with injector

Energy and exergy balances were done on a novel solar bi‐ejector refrigeration system with R123, whose circulation pump is replaced by an injector. The analysis result of the novel system was compared with that of the original one. The effect of operation condition on system energy efficiency, exergy efficiency and exergy loss was analyzed, and the dynamic performance of a designed solar bi‐ejector refrigeration system was also studied. The comparative results indicate that under the same operating condition, the novel system and the original system have equal energy efficiency, exergy efficiency and exergy loss, and the only difference between them is the exergy losses of the generators and the added injector. The other conclusions mainly include: the solar collector has the largest exergy loss rate of over 90% and for the bi‐ejector refrigeration subcycle, the ejector has the largest exergy loss rate of about 5%; the total exergy loss changes inversely proportional to the evaporation temperature and positively proportional to the condensation temperature; when the other parameters are fixed, there exists an optimum generation temperature, at which the overall energy and exergy efficiencies are both the maximum and the total exergy loss is the minimum. The study points out the direction for optimizing the novel solar bi‐ejector refrigeration system. Copyright © 2009 John Wiley & Sons, Ltd.