Modeling of ammonia absorption chillers integration in energy systems of process plants

A mathematical programming approach is proposed to study the integration of absorption chillers in combined heat and power plants. The aim of this work is to determine the economic viability of the introduction of ammonia absorption chillers in energy systems instead of using the more conventional compression cycles. This procedure selects the best refrigeration alternative taking into account both absorption and compression cycles. To select the most suitable refrigeration cycle for a given refrigeration load, it is not only necessary to model the performance of each cycle, but also to take into account the interactions between the energy system and the considered cycles, optimizing the performance of the global plant. This approach has been implemented in the computer program XV, and tested in an energy plant in the petrochemical complex of Tarragona (Catalunya, Spain). The refrigeration demands to be met are at 0 and −20°C. The results highlighted the benefit obtained with the simultaneous presence of ammonia absorption cycles and a cogeneration based energy plant.     

Comparative study of cogeneration systems in a chemical industry

With the large penetration of the natural gas into the Brazilian energy structure, industries such as paper mills and chemical plants are analyzing the feasibility of implementing cogeneration schemes appropriate to this fuel. The analysis of the energy demand patterns of a chemical company from the photographic sector revealed the possibility of using combined cycles or diesel engine cogeneration schemes keeping the existing compression refrigeration units and steam or gas cycle cogeneration systems with absorption refrigeration units. In terms of economic attractiveness, an analysis based on the method of the internal rate of return was performed. The results indicated that the schemes composed by reciprocating engines and combined cycle with compression chillers, as well as the gas cycle scheme with absorption chiller, present return periods of up to 3 years, showing that the investment in cogeneration could be of interest for this plant.     

Integration of absorption cooling systems into micro gas turbine trigeneration systems using biogas: Case study of a sewage treatment plant

Absorption chillers can help to increase the performance of biogas-driven micro gas turbine (MGT) cogeneration plants. In this paper we analyse various integrated configurations of several types of commercially available absorption cooling chillers and MGT cogeneration systems driven by biogas. MGTs are fuelled with biogas and their waste heat is used to drive absorption chillers and other thermal energy users. The chillers considered in this study include single- and double-effect water/LiBr and ammonia/water chillers. The exhaust gas from the MGT can be used directly to drive the chiller or indirectly to produce hot water to drive the chiller. In this paper we conduct a case study for an existing sewage treatment plant. Chilled water is used to reduce humidity in the biogas pre-treatment process and cool the combustion air of the MGT. We identify the most interesting integrated configurations for trigeneration systems that use biogas and micro gas turbines. We analyse these configurations and compare them with conventional configurations using operational data from an existing sewage treatment plant. The best configurations are those that completely replace the existing system with a trigeneration plant that uses all the available biogas and additional natural gas to completely meet the heating demands of the sewage treatment plant.     

Modeling water/lithium bromide absorption chillers in ASPEN Plus

Absorption chillers are a viable option for providing waste heat-powered cooling or refrigeration in oil and gas processing plants, thereby improving energy efficiency. In this paper, single- and double-effect water/lithium bromide absorption chiller designs are numerically modeled using ASPEN. The modeling procedure is described and the results are compared to published modeling data to access prediction accuracy. Predictions for the single- and double-effect designs are within 3% and 5%, respectively of published data for all cycle parameters of interest. The absorption cycle models presented not only allow investigation into the benefits of using absorption chillers for waste heat utilization in the oil and gas industry, but are also generically applicable to a wide range of other applications.     

从热工学角度探讨国产吸收式制冷机的发展方向

该文从热工学角度探讨了目前我国溴化锂吸收式制冷机整机热力循环及各热质交换设备性能、结构等方面存在的问题;在整机循环方面,指出实现各设备的合匹配、发展新的结构流程及增加新品种、新规格的机组为进一步的发展方向;在各设备性能、结构方面提出应加强吸收机理研究以及表面活化剂、高效强化管的应用研究。     

用于太阳能空调的板型溴化锂吸收式制冷机

溴化锂吸收式制冷循环用于太阳能空调需要解决的主要问题是循环系统要适合集热器所能提供的热水温度范围，和提高溴冷机本身性能并降低其制造成本。板型(包括板壳式、板式、板翅式)换热器用于溴冷机具有效率高、结构紧凑、轻巧和成本较低等优点，已被本课题组研制的1台3kW板型单效溴冷机实验样机所证实。     

Experimental investigation of integrated refrigeration system (IRS) with gas engine,compression chiller and absorption chiller

An integrated refrigeration system (IRS) with a gas engine, a vapor-compression chiller and an absorption chiller is set up and tested. The vapor-compression refrigeration cycle is operated directly by the gas engine. The waste heat from the gas engine operates the absorption refrigeration cycle, which provides additional cooling. The performance of the IRS is described. The cooling capacity of the IRS is about 596 kW, and primary energy ratio (PER) reaches 1.84 at air-conditioning rated conditions. The refrigerating capacity of the prototype increased and PER of prototype decreased with the increase of the gas engine speed. The gas engine speed was preferably regulated at part load condition in order to operate the prototype at high-energy efficiency. The refrigerating capacity and PER of the prototype increased with the increase of the outlet temperature of chilled water or the decrease of the inlet temperature of cooling water. The integrated refrigeration chiller in this work saves running costs as compared to the conventional refrigeration system by using the waste heat.     

Residential solar air conditioning: Energy and exergy analyses of an ammonia–water absorption cooling system

Large scale heat-driven absorption cooling systems are available in the marketplace for industrial applications but the concept of a solar driven absorption chiller for air-conditioning applications is relatively new. Absorption chillers have a lower efficiency than compression refrigeration systems, when used for small scale applications and this restrains the absorption cooling system from air conditioning applications in residential buildings. The potential of a solar driven ammonia–water absorption chiller for residential air conditioning application is discussed and analyzed in this paper. A thermodynamic model has been developed based on a 10 kW air cooled ammonia–water absorption chiller driven by solar thermal energy. Both energy and exergy analyses have been conducted to evaluate the performance of this residential scale cooling system. The analyses uncovered that the absorber is where the most exergy loss occurs (63%) followed by the generator (13%) and the condenser (11%). Furthermore, the exergy loss of the condenser and absorber greatly increase with temperature, the generator less so, and the exergy loss in the evaporator is the least sensitive to increasing temperature.     

Simulation and Experimental Study of Metal Organic Frameworks Used in Adsorption Cooling

ABSTRACT

Metal-organic frameworks (MOFs) have recently attracted enormous interest over the past few years in energy storage and gas separation, yet there have been few reports for adsorption cooling applications. Adsorption cooling technology is an established alternative to mechanical vapor compression refrigeration systems and is an excellent alternative in industrial environments where waste heat is available. We explored the use of MOFs that have very high mass loading and relatively low heats of adsorption, with certain combinations of refrigerants to demonstrate a new type of highly efficient adsorption chiller. Computational fluid dynamics combined with a system level lumped-parameter model have been used to project size and performance for chillers with a cooling capacity ranging from a few kW to several thousand kW. These systems rely on stacked micro/mini-scale architectures to enhance heat and mass transfer. Recent computational studies of an adsorption chiller based on MOFs suggests that a thermally-driven coefficient of performance greater than one may be possible, which would represent a fundamental breakthrough in performance of adsorption chiller technology. Presented herein are computational and experimental results for hydrophyilic and fluorophilic MOFs.     

联产制冷的能效性能探讨

利用汽轮机抽汽作为吸收式制冷驱动热源的联产制冷，将供电、制冷有机结合在一起，不仅满足制冷要求也改善联产机组效率。通过引入抽汽yong增益概念，揭示了汽轮机抽汽特性规律，在此基础上从联产制冷目的yong效率角度比较了几种制冷方式，分析了汽轮机抽汽参数和相对内效率等因素对联产制冷能效性能影响规律，抽汽的yong增益比是联产制冷yong效率影响起决定作用的因素，所得结论对联产制冷吸收机的合理选用匹配提供有益的指导。     

Prediction of Chiller Power Consumption: An Entropy Generation Approach

ABSTRACT

Irreversibilities in each component of vapor compression chillers contribute to additional power consumption in chillers. In this study, chiller power consumption was predicted by computing the Carnot reversible work and entropy generated in every component of the chiller. Thermodynamic properties, namely, enthalpy and entropy of the entire refrigerant cycle were obtained by measuring the pressure and temperature at the inlet and outlet of each primary component of a 15-kW R22 water-cooled scroll chiller. Entropy generation of each component was then calculated using the first and second laws of thermodynamics. Good correlation was found between the measured and computed chiller power consumption. This irreversibility analysis can be also effectively used as a performance monitoring tool in vapor compression chillers, as higher entropy generation is anticipated during faulty operations.     

Trigeneration in the food industry

In the food industry cogeneration plants are widely introduced. Many industries use cogeneration plants with either gas engines or turbines to cover their steam, hot water and electrical demands. The combination of an absorption refrigeration with a cogeneration plant allows to use all generated heat for the production of cooling. Absorption refrigeration plants working with ammonia as refrigerant can be driven either by steam, pressurised hot water or directly with the exhaust gases. Examples of typical plants are illustrated on different sectors in the food industry.     

钢铁企业余热吸收制冷

调查和分析了钢铁企业余热利用的现状,得出余热制冷是钢铁企业余热利用的重要途径之一．以鞍钢为例介绍了吸收式制冷机组在钢铁企业的主要用途,具体分析了不同余热载体（蒸汽、热水、烟气）作为吸收制冷机组的驱动热源的应用情况,并介绍了国内外吸收式制冷最新研究情况,最后探讨了余热制冷在钢铁企业中经济性应用方案。     

Multi-pressure absorption cycles in solar refrigeration:: A technical and economical study

A technical and economical study of regenerative absorption chillers with multi-pressure cycle has been undertaken as solar operated refrigeration systems. Referred to as advanced absorption chillers they represent one of the new technology options that are under development. Advanced absorption cooling technology offers the possibility of chillers with thermal COPs of 1.5 or greater at driving temperatures of 140°C, which reduces the collector area and the heat rejection requirements compared to current absorption cooling technology. Two different absorption systems have been considered. The first is an advanced, double-effect regenerative absorption cooling system, driven at 140°C, whose efficiency is about 55% of the Carnot efficiency. The second is an ideal, single-effect regenerative absorption system that achieves 70% of the Carnot efficiency driven at 140°C or 200°C. To evaluate the solar performance of a thermally driven chiller requires a separate analysis of the solar availability for a given location compared to the required monthly average solar input. In this analysis different systems, including the vapour compression chillers, have been compared in terms of the thermal and electrical energy input. An effective electrical COP may be computed assuming that the ratio of electrical energy cost to thermal energy cost is four, which is typical of today’s fossil fuel costs. The effective electrical COPs of different technical options can then be compared. Those systems with higher electrical COPs will have lower energy costs. If solar is to be competitive, then the cost of delivered solar thermal energy should be less than the cost of delivered fossil thermal energy.     

Exergetic comparison of wind energy storage with ice making cycle versus mini-hydrogen economy cycle in off-grid district cooling

For the feasible and continuous utilization of intermittent wind and solar energy sources for electricity generation in district energy systems in hot-climates, where cooling loads are dominant, ice storage may be an option. In this study, the rationality of the ice storage system for wind energy was investigated using the Rational Exergy Management Model, REMM for two options and compared with a base scenario, which comprises a wind turbine system, grid connection, conventional chillers, and the district cooling system. The main objective is to minimize exergy destructions and thus to improve the exergy performance. The first ice storage option is composed of wind turbines, deep chillers for ice making, ice storage tanks, and the district cooling system. The second option is similar to the first option but it also includes a ground-source heat pump upstream the deep chiller. These options were also compared against a mini-hydrogen economy (District size) alternative, which encompasses a hydrogen-water cycle with excess renewable energy-powered PEM electrolysis unit, hydrogen tank, fuel cell, absorption chiller, gas compression chiller, and the district cooling system. These two options and the hydrogen-water cycle alternative were compared in terms of their REMM efficiency, First and Second-law efficiencies, and the primary energy ratio. A new Sustainability Performance Index, namely SPI was also defined. SPI is the product of the REMM efficiency, First-Law Efficiency, and the load coincidence factor, CF of wind energy. In order to establish a realistic application background for the comparisons, first a nearly-net-zero exergy farmland (nZEXF) utilizing biogas, cogeneration, solar photovoltaics, heat, absorption cycle, ground-source heat pump, Organic Rankine Cycle, and wind turbines was introduced as a model. The primary objective of this study is to determine the best option with the least avoidable CO₂ emissions responsibility of the systems considered in terms of the REMM efficiency in thermal or hydrogen storage systems. Results have been compared in terms of SPI with the base scenario and it has been concluded that the second option (SPI = 0.88) is better than the first option (SPI = 0.38). However, hydrogen storage is an even better alternative with an SPI value of 1.06. These figures according to REMM with the coincidence factor being considered, mean that the avoidable CO₂ emissions may be reduced by up to 54% compared to the base case. Hydrogen cycle option may also be used with the same effectiveness in district heating, while ice storage options are limited to district cooling only. This paper provides the relevant theory, shows the fundamental calculations about the option rankings based on a unit cooling load, makes recommendations for future district energy systems, and refers to a conceptual hydrogen economy driven city.     

Performance analysis of an irreversible cogeneration heat pump cycle

An irreversible heat engine-driven vapour compression and absorption heat pump system is considered as a cogeneration cycle. The effects of thermal resistances and internal irreversibilities on the coefficient of performance (COP) of this cogeneration cycle were investigated using finite-time thermodynamic approach. An improved equation for the COP of the system under consideration was obtained. The results obtained here may serve as a good guide for the evaluation of existing real cogeneration heat pumps or provide some theoretical bases for the optimal design of future cogeneration heat pumps. © 1998 John Wiley & Sons, Ltd.     

燃气—蒸汽联合循环机组轴系振动问题综述

本文对燃气—蒸汽联合循环机组轴系布置方案进行了详细研究,将其分为普通单轴布置轴系、带有SSS离合器(同步自动离合器)的单轴布置轴系、多轴布置中的燃气轮机轴系和汽轮机轴系4种类型。并且分析了4种类型与常规机组汽轮机轴系的区别,并通过对某联合循环电厂轴系的典型振动故障分析,讲述了此方面研究的重要性。本文从现场振动故障诊断和理论研究两个方面总结了近些年联合循环机组轴系振动的研究进展,提出带有SSS离合器的单轴布置轴系和多轴布置中带有SSS离合器的汽轮机轴系是今后的研究方向。     

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.     

Thermodynamic analysis of load-leveling hyper energy converting and utilization system

Load-leveling hyper energy converting and utilization system (LHECUS) is a hybrid cycle which utilizes ammonia–water mixture as the working fluid in a combined power generation and refrigeration cycle. The power generation cycle functions as a Kalina cycle and an absorption refrigeration cycle is combined with it as a bottoming cycle. LHECUS is designed to utilize the waste heat from industry to produce cooling and power simultaneously. The refrigeration effect can be either transported to end-use sectors by means of a solution transportation absorption chiller (STA) as solution concentration difference or stored for demand load leveling.     

Performance analysis of combined microgas turbines and gas fired water/LiBr absorption chillers with post-combustion

The integration of microgas turbines (MGT) and absorption chillers is an emerging technology that uses a wide range of fuels to produce electricity, cooling and heating simultaneously for small scale distributed generation in grid connected or isolated locations.This paper studies the performance of MGTs of different power capacities directly coupled to double-effect water–LiBr absorption chillers. In these systems the MGT exhaust gas is the heating medium to drive the chiller. Also post-combustion natural gas is used to increase the cooling capacity of the system. The paper analyses the effect of the post-combustion degree on the integrated system performance of four MGT power sizes. Two cases are considered. In the first, fresh air is added together with the post-combustion natural gas and in the second it is not added. In the latter case the oxygen necessary for the combustion reaction is extracted from the MGT exhaust gas stream. For the sake of comparison a study is also made of the performance of a more conventional system consisting of an MGT and a hot water heat exchanger to drive an absorption chiller. The main advantages of the new technology over this conventional system are that the COP of the chillers is higher because they are driven by higher temperatures, the production of electricity and chilled water is decoupled and there is a wider range of chilled water production capacity.