环周进汽型喷射器的火用效率分析

对环周进汽型喷射器的工作原理进行了深入分析,从可用能角度出发,建立了分析喷射器运行经济性的火用分析模型,计算得到了不同结构参数和运行参数下喷射器的火用效率,对喷射器火用效率的影响因素进行了分析,并将计算值与实验结果进行了对比。研究结果表明,喷射器的火用效率随入口水温、引射系数和升压比的升高而增大,随蒸汽压力的变化存在最小值,计算和实验得到的各参数对喷射器火用效率的影响规律基本一致,为环周进汽型喷射器的设计和应用提供了理论基础。     

有机朗肯循环膨胀机入口过热度实验

在给定热源条件下,探讨有机朗肯循环(ORC)膨胀机入口过热度对膨胀机性能和ORC系统性能的影响。建立了带前置泵的ORC实验系统,采用涡旋式膨胀机,R123为工质,在140℃热源下进行实验。通过改变膨胀机转矩调节系统蒸发压力,从而实现对膨胀机入口过热度的调节。实验获得最大膨胀机轴功和膨胀机实际运行效率分别为2.35kW和59.7%;ORC系统净输出功、热效率和(火用)效率分别为1.75kW、5.3%和21.8%。分析表明,随着膨胀机入口过热度递减,膨胀机机械效率递增,膨胀机等熵效率递减,膨胀机轴功和实际运行效率呈先增后减的变化趋势。膨胀机入口过热度为20℃左右时,有最大膨胀机轴功、最大系统净输出功、最高系统热效率和最高系统(火用)效率。此外,过热度影响系统的损失分布,随着膨胀机入口过热度减小,膨胀机(火用)损呈先增后减变化。     

机械蒸汽再压缩硫酸铵废水处理系统的分析

为全面反应机械蒸汽再压缩硫酸铵废水处理系统的用能情况,提高系统的效率,采用以热力学第二定律为基础的分析方法,对系统进行了分析。将硫酸铵废水视为实际溶液,建立了实际物流的分析模型,运用工厂实测数据对系统进行了分析计算,研究了参量:压缩比、蒸发温度和一效排出浓度对系统效率的影响并根据测算结果提出了改进建议。分析结果表明,该系统总的效率约为12.04%;各设备分析表明,换热器及压缩机是主要的损失部位,二者的损失约占总数的79.5%;参量分析表明,系统的效率随着压缩比的增大而减小,随着蒸发温度的升高而增大,在其他条件允许的情况下,应尽量采用压缩比小的压缩机和维持高的蒸发温度;在文中条件下,当一效排出质量分数为32%时系统的效率最大,应尽可能地维持在该质量分数下排料;消除进入加热器蒸汽的过热可以提高系统的效率。     

新型太阳能双喷射制冷系统的可用能效率分析

在特定工况下对新型的太阳能双喷射制冷系统进行了火用平衡分析,计算了火用效率、总火用损失及系统中各设备的火用损率和火用效率,探讨了发生器温度和蒸发温度对系统火用效率和火用损失的影响。结果表明,太阳能集热器的火用损最大,火用损率为91%,其次为气体喷射器,火用损率为5%。在其他条件一定时,系统存在一个最佳的发生器温度使系统的火用效率最高,总火用损失最小。当发生温度为75～120℃,蒸发温度为7～15℃,冷凝温度为35℃时,系统总能量效率为10%～18%,火用效率为0.3%～0.65%。     

Simulation and thermodynamic analysis of an integrated process with H2 membrane CPO reactor for pure H2 production

A one-dimensional steady-state heterogeneous model has been used to simulate the H₂ membrane reactor. The simulation work is the basis for the thermodynamic analysis of the integrated pure H₂ production process. The simulation and analysis also provide a quantitative tool for insight into and understanding the process.The simulation and thermodynamic analysis results indicate that increasing the inlet ratio H₂O/CH₄ cannot enhance the pure H₂ production rate. With increasing the inlet ratio H₂O/CH₄, the overall exergy efficiency of the process decreases, because a large amount of energy is required to obtain the steam.When the geometric parameters of membrane reactor and inlet temperature are given, there is a maximum feeding rate of methane for the integrated process. The pure hydrogen production rate increases with the inlet methane rate increasing, while the overall exergy efficiency decreases as inlet methane rate increases.For the same inlet rate of methane, operating the process at higher inlet temperature increases hydrogen production rate. Whereas, the overall exergy efficiency is lowered.Three suggestions are discussed to improve the overall exergy efficiency. All of them require more equipment investment. There will be an optimal point to balance equipment investment, pure hydrogen production rate and overall exergy efficiency. To find the optimum, thermo-economic analysis will be helpful.     

高压聚乙烯反应器的火用分析与优化

通过对高压聚乙烯反应系统进行Yong计算与分析,结果表明,由传热不可逆造成的内部Yong损为主要的Yong损。一、二、三段反应器的内部Yong损各占其总Yong损的97.78%、98.87%、85.44%。并提出了相应的节能措施和优化方案。     

回热器对双级压缩和复叠式压缩制冷系统影响的分析

为了研究回热器对双级压缩制冷系统和复叠式压缩制冷系统的影响,以R404A双级压缩制冷系统和R404A/R23复叠式压缩制冷系统为例,通过建立两种制冷系统的热力学模型和(火用)分析法,分析了回热器效率对压缩机排气温度、单位质量制冷量、制冷剂质量流量、系统制热能效比(COP)、系统总(火用)损、系统各部件(火用)损和系统(火用)效率的影响。结果表明,在双级压缩制冷系统中,当回热器效率ε 取0.1～0.9时,系统COP增大4.0%,系统的总(火用)损减少9.6%,而系统(火用)效率增大7.1%;在复叠式压缩制冷系统中,系统COP和系统(火用)效率随高温级回热器效率ε 增大而增大,随低温级回热器效率ε增大而减小,而系统总的(火用)损随高温级回热器效率ε 增大而减小,随低温级回热器效率ε 增大而增大。     

Exergoeconomic Analysis of a Combined Ammonia Based Solid Oxide Fuel Cell System

An exergoeconomic study of an ammonia‐fed solid oxide fuel cell (SOFC) based combined system for transportation applications is presented in this paper. The relations between capital costs and thermodynamic losses for the system components are investigated. The exergoeconomic analysis includes the SOFC stack and system components, including the compressor, microturbine, pressure regulator, and heat exchangers. A parametric study is also conducted to investigate the system performance and costs of the components, depending on the operating temperature, exhaust temperature, and fuel utilization ratio. A parametric study is performed to show how the ratio of the thermodynamic loss rate to capital cost changes with operating parameters. For the devices and the overall system, some practical correlations are introduced to relate the capital cost and total exergy loss. The ratio of exergy consumption to capital cost is found to be strongly dependent on the current density and stack temperature, but less affected by the fuel utilization ratio.     

油田集输子系统的热力学分析

油田采输系统是能源消耗的大户,为了评价油田集输系统的用能状况、找出用能薄弱环节,必须对油田采输系统进行热力学分析。以稠油的集输子系统为研究对象,建立了集输子系统的分析模型,并从热力学分析的角度对某油田集输子系统的热平衡和平衡进行计算。计算分析结果为:随着加热炉进风温度的提高,集输子系统的热效率和效率有所上升,将进风温度从20℃提高到110℃的情况下,集输子系统的热效率从0.95%提高到0.98%,效率从0.19%提高到0.2%;如果把分离出的污水中的能量回收利用起来,可使现行的效率从0.21%提高到1.09%。     

双压膨胀有机朗肯循环中低温余热发电系统的热力性能

基于热力学第一定律与第二定律分析法,结合动量定理与质量守恒定律构建一种双压膨胀有机朗肯循环（ORC）中低温余热发电系统热力性能的预测模型,研究热源温度、蒸发温度、夹点温差、闪蒸压力、循环倍率、喷射压缩器引射流体在混合室进口的马赫数、工质泵、向心透平及螺杆膨胀机的等熵效率对系统的净输出功率、热效率、余热利用率及(火用)效率等热力性能的影响。结果表明,系统的净输出功率与(火用)效率随着热源温度、蒸发温度、循环倍率及透平等熵效率的增大而升高,但随着夹点温差、闪蒸压力的增大而降低;系统的热效率随着蒸发温度、闪蒸压力及透平等熵效率的增大而升高;系统的余热利用率随着热源温度、循环倍率的增大而升高,但随着蒸发温度、夹点温差、闪蒸压力的增大而降低。当循环倍率k=2时系统的净输出功率、(火用)效率及余热利用率分别比常规单级ORC系统绝对提高了230.9kW、10.1%和17.9%。     

液化天然气冷能回收混合动力循环参数分析

提出了以氨水为工质的朗肯循环、燃气动力循环和液化天然气循环组成的混合动力循环系统,用于液化天然气冷能回收。建立了混合动力循环中换热和动力设备的能量平衡方程和可用能平衡方程,并以朗肯循环冷凝温度、朗肯循环透平进出口压力、液化天然气循环透平进出口压力为关键参数,分析了上述关键参数对混合动力循环热效率和可用能效率的影响。分析结果表明,混合动力循环热效率和可用能效率随朗肯循环冷凝温度升高、朗肯循环透平进口压力和液化天然气循环透平进口压力增大而提高,随朗肯循环透平出口压力和液化天然气循环透平出口压力增大而降低。     

Experimental study on performance of steam-water injector with central water nozzle arrangement

The steam-water injector (SI) is a simple mechanical device that has been widely used in industry. We did an experimental study to find the influence of physical and geometrical parameters on performance of the SI. The physical parameters studied were steam inlet pressure, water inlet pressure and water inlet temperature. Whereas, the geometrical parameters studied were steam nozzle area ratio, area ratio of steam nozzle to water nozzle and the mixing section converging angle. Pump head was introduced to evaluate the lifting-pressure performance of the SI under different operating and geometrical conditions. Optimal values of steam nozzle area ratio and mixing section converging angle were 1.3 and 11.6° respectively, for the present work, and optimal value of area ratio of steam nozzle to water nozzle increased with increasing water inlet pressure. Two head-capacity curves were introduced to highlight the effect of various physical and geometrical parameters on the performance of SI.     

真空闪蒸制取冰浆系统(火用)分析

采用已有的计算冷量以及损失的公式,对实验室用真空闪蒸制取冰浆系统进行了(火用)分析。利用EES软件,对真空闪蒸法冰浆制备系统中的4个关键环节(冷水冰水混合、真空室内喷雾闪蒸、捕水器内蒸汽凝结成霜、制冷机制备低温盐水)进行计算,得出各个环节(火用)损失以及整个系统的(火用)效率。结果表明:实验用真空室内喷雾闪蒸环节的(火用)效率较高,捕水器内蒸汽凝结成霜的(火用)效率较低,制冷机组制备低温盐水(火用)效率最低,(火用)损最大,导致整个系统的效率相对较低。为了改善真空闪蒸制取冰浆系统的能耗,应对低温盐水制备环节进行优化或采用其他方式替代该环节。     

三元制冷系统分析

乙烯装置产品分离过程需要在低温下进行,为此需配置压缩制冷系统为深冷分离提供冷量。三元压缩制冷由于能提供温位连续的制冷曲线,与工艺物流降温曲线更好地匹配,相比传统的复叠制冷具有热力学效率高、制冷能耗低的特点。为了分析三元压缩制冷的节能潜力,本文对某乙烯装置的三元制冷系统进行了(火用)分析。从(火用)总复合曲线(EGCC)图的分析可以得出该系统三元冷剂配置是比较合理的,(火用)损失较小。将该制冷系统划分为换热器、压缩机、节流阀、闪蒸罐等子系统,并分别计算了各子系统的(火用)损失。三元制冷系统的(火用)损失总计为24238.1kW,90%(火用)损失集中在换热器和压缩机两个子系统。然后将(火用)损失分为可避免的和不可避免的(火用)损失两类,其中不可避免的(火用)损失为13539.9kW,可避免的(火用)损失为10698.2kW,最后指出节能重点应该放在降低可避免的(火用)损失。     

有机朗肯循环发电系统变工况运行的实验研究

受余热热源及环境温度不稳定特性的制约,有机朗肯循环（ORC）发电系统在实际应用中需要有较强的变工况能力。本文以R245fa为工质,实验研究了在不同冷热源温度时,ORC系统在相同负载容量及膨胀机转速下的变工况运行特性及各部件实际性能。实验结果表明：热源温度主要决定了膨胀机的入口温度及过热度。随着热源温度的降低,膨胀机内部泄漏量变大,其等熵效率变低,单位质量工质做功能力变差,维持膨胀机做功状态的工质质量流量增加。由于工质在蒸发器内整体吸热量变小,系统发电效率随热源温度的降低而升高。在10℃冷源温度下,热源温度从115℃下降至100℃,机组的最大发电效率从5.03%升高至5.25%。改变冷源温度,主要作用于膨胀机的进出口压力,改变了膨胀机的做功状态。降低冷源温度,膨胀机压比升高,单位质量工质做功能力变强,维持膨胀机做功状态的工质质量流量减小。但由于膨胀机过膨胀运行带来的不可逆损失增加,膨胀机的等熵效率随冷源温度降低而减小。在115℃热源温度下,冷源温度从30℃下降至10℃,系统最大发电效率从6.08%升高至7.01%。     

Identification of optimum inter-stage pressure for two-stage transcritical carbon dioxide refrigeration cycles

The disadvantage of high discharge temperatures associated with transcritical CO₂ refrigeration cycles can be overcome by adopting two-stage compression with inter-cooling between the stages. This also helps in improving the overall volumetric efficiency and some power saving. This paper considers the criteria of minimum work of compression, equal discharge temperatures at the exit of each stage and minimum exergy loss during inter-stage and gas cooling for identifying inter-stage pressure. It is shown that the equality of stage discharge temperatures is a more useful criterion than the saving in power or improvement in COP because multi-staging has at best a marginal (<10%) effect on the latter. The criterion of minimal exergy loss in heat rejection also yields the same inter-stage pressures as the minimum work criterion. Optimum inter-stage pressure for each condition is identified for several evaporator and gas cooler outlet temperatures and expressed in terms of the inter-stage pressure index of the product of cycle operating pressure limits.     

Energy and exergy analyses of a lignite-fired power plant integrated with a steam dryer at rated and partial loads

Lignite is a reliable raw energy material with abundant supply worldwide. However, the efficient use of lignite to generate power remains challenging, because lignite exhibits undesirable characteristics, including low heating value and high moisture content. Despite these disadvantages, the efficiency of lignite-fired power plants can be increased by predrying lignite. In this study, a predried lignite-fired power plant, which uses steam extracted from steam turbines as a heat source to dry lignite, was simulated using Aspen Plus. This study then analyzed the performance of the predried lignite-fired power plant at rated and partial loads on the basis of the thermodynamics principles. This study also examined the influence of lignite predrying on the exergy losses and destructions of the power plant components. Results indicate that the exergy destructed the combustion process decreases significantly because of lignite predrying, by 5.78 percentage points. The plant thermal efficiency based on the lower heating value of raw lignite relatively increases by 4.35%. The efficiency improvement of the power plant reduces as the load ratio decreases, because exergy is destructed in the admission opening, which is used to control the pressure of the steam leading to the dryer. The integration of the dryer saves energy only when the load ratio is >50%.     

溶液除湿冷却系统的火用分析

基于热力学第二定律建立了针对溶液除湿系统的火用分析模型,重点分析了空气和溶液进口参数对溶液除湿器性能（除湿器火用效率）的影响,并且对采用LiCl的溶液除湿冷却系统进行了部件分析。结果表明：（1）除湿器的火用效率影响因素中,空气速度和空气湿度影响最大,其次是溶液的温度和浓度,而空气进口温度和溶液流速的影响基本可以忽略;（2）在整个系统中,溶液-热水换热器的火用损失最大,占24.5%,其次是溶液-溶液热回收器和冷水-溶液换热器,分别占24.4%和22.8%,可见减小换热器的火用损是提高系统火用效率的关键。此研究对于明确改进溶液除湿空调的方向有重要意义。     

Exergy analysis of humidification–dehumidification desalination systems using driving forces concept

In this paper, a new method for exergy analysis of humidification–dehumidification (HD) desalination systems is presented. It is based on the principle that there are exergy losses wherever the driving forces exist. A methodology was developed for investigating various parametric effects on exergy losses. The method involved developing a sink and source model as well as basic relations in the system. Results showed that the mass transfer phenomenon does not have any effect on the total exergy losses of the HD systems. Heater was the largest irreversibility resource. Flow rate of the Un-heated fluid and the maximum temperature of the system had key roles in the total exergy losses. An optimum point for the water-heated HD desalination system is also introduced. Finally, some comparisons are proposed between the water-heated and the air-heated HD desalination systems.     

Factorial design of experiment (DOE) for parametric exergetic investigation of a steam methane reforming process for hydrogen production

Hydrogen is expected to play a significant role in future energy systems. The efficient production of hydrogen at a minimum cost and in an environmentally acceptable manner is crucial for the development of a hydrogen-including economy. The exergy analysis is a powerful tool to quantify sustainable development potential. An important aspect of sustainable development is minimizing irreversibility. The purpose of this study is to perform the exergy analysis of a steam methane reforming (SMR) process for hydrogen production. As a first step, an exergy analysis of an existing process is shown to be an efficient tool to critically examine the process energy use and to test for possible savings in primary energy consumption. The results of this investigation prove that the exergetic efficiency of the SMR process is 65.47%, and the majority of destroyed exergy is localized in the reformer with a 65.81% contribution to the whole process destroyed exergy. Next, an exergetic parametric study of the SMR has been carried out with a factorial design of experiment (DOE) method. The influence of the reformer operating temperature and pressure and of the steam to carbon ratio (S/C) on the process exergetic efficiency has been studied. A second-order polynomial mathematical model has been obtained through correlating the exergetic efficiencies with the reformer operating parameters. The results of this study show that the rational choice of these parameters can improve the process exergetic performance.