A Steady-State Evaluation of Simple Organic Rankine Cycle (SORC) with Low-Temperature Grade Waste Heat Source

The low-grade heat source recovery is usually constrained by the physical characteristics of the hot fluid medium. The present work focuses on the importance of energy recovery from low-temperature waste energy sources and its conversion to useful electrical power. The thermal performance analysis is based on the utilization of R-123, R-134a, R-290, R-245fa, R-1234ze-E, and R-1233zd-E fluids in a simple organic Rankine cycle (SORC). A waste energy source from an industrial sector is suggested to be available at a temperature greater than 110 °C. A hypothetical organic Rankine cycle of 10 kW nominal heat recovery was implemented to evaluate the cycle performance. It operates at evaporation and condensation temperatures of 90 °C and 45 °C, respectively. The selected vapor superheat degree at the expander entrance was 5 °C - 15 °C, and the liquid was subcooled by 5 °C at the discharge port of condenser. The estimated first law cycle thermal efficiency fell in the range of 6.4% - 7.7%. The results showed that the thermal efficiencies of R-134a, R-123, R-245fa, R-1233zd-E, and R-1234ze-E were higher than that of R-290 by 10% - 14%, 11% - 12%, 9% - 12%, 4% - 7% and 1% - 3%, respectively. R-1233zd-E, R-1234ze-E, and R-290 showed close thermal efficiency values, and it fell in the range of 6.7% - 7% for the (SORC) at a superheat degree of 15 °C. At the same superheat degree, the corresponding range of thermal efficiency for R-134a, R-123 and R-245fa fell within 7.5% - 7.7%. R-134a possessed the highest net power output of the (SORC);it reached a value of 0.91 kW as predicted at 15 °C superheat degree. Increasing the expander volumetric efficiency value by 10% improved the cycle thermal efficiency by 10% - 12%.

Utilization and recycling of low-temperature waste heat of stainless steel continuous annealing furnace

Stainless steel continuous annealing furnace is mainly used for heat treatment of hot-rolled strip steel.The combustion air will be enabled to heat to 520℃by waste heat recovery system,but the discharge temperature is still up to about 300℃.Owing to with development of global emphasis on energy conservation energy saving and discharge reduction,it's significant to lower the discharge temperature to below 200℃, for the sake of achieving rational use of waste heat resource.Through the analysis of the existing heat recovery system by this study,it is proved that mixing low temperature with flue gas in high temperature standard will increase the capacity of the flue gas and deteriorate the quality of remaining heat resource.In stead of that,increasing the combustion air temperature to 600℃on the basis of stability temperature for the prerequisite of recuperator design,and giving priority to reducing fuel consumption are the better way.The recovery and recycle of low temperature gas are also be introduced.It is demonstrated by the way of setting a secondary recuperator at the exit of the primary recuperator,and using low temperature flue gas to heat the air used for drying the strip steel,the exhuast temperature of flue gas can be reduced to lower than 200℃.At the same time,the steam required for heating air is saved,the energy reserve as high as 2 300 t of standard coal per year.

Analysis of Temperature Profiles and Cycle Time in a Large-Scale Medical Waste Incinerator

Temperature profiles and cycle times in a large-scale medical waste incinerator installed in a referral hospital were used to assess the performance and functionality of incinerator. The study was conducted using data collected from 8 cycles per days for 67 days. For proper combustion and destruction of toxic components in the primary chamber and destruction of pollutants and toxic components in the flue gas, it is desired to reach the maximum temperature in the chambers faster and maintain this maximum temperature for an extended time interval. The primary and secondary temperatures T1 and T2, respectively, were recorded at an interval of one minute for different cycles. Different amounts of wastes with varying proportions of sharps and other wastes were loaded into the incinerator and temperature profiles recorded. The analysis shows that the incinerator works at primary temperature less than the required recommended by manufacturer while the secondary chamber operates between 600 and above 950℃, although higher temperatures up to 1020℃ were observed. The average load preparation time was observed to be 14.6 minutes, while the chamber preheating time before daily initial loading was 25.45 minutes. Both temperature profiles were observed to have similar shapes for all combustion cycles studied, except when incinerator malfunctioning occurred. The average cycle time was established to be 32.7 minutes and 28.97 minutes based on time to drop to 550℃ after the maximum temperature and loading time intervals, respectively, although longer cycle times were observed. Temperature drop in both combustion chambers as a result of waste charging was observed in the interval of 5 minutes. The chamber heating rate was observed to decrease exponentially with time during both preheating and incineration operation.

Modeling of Heat Transfers in Bioreactive Household Waste Storage Facilities: Spatial and Temporal Distributions

In order to enhance the production of biogas and to study the thermal behavior of waste, a numerical study of fluid flows and heat transfers within household waste was developed to predict the distributions of thermal fields. The mathematical model is based on the conservation of mass and energy equations. The resulting system of equations is discretized using the finite volume method and solved using the Thomas algorithm. The results of the model studied are compared with the numerical and site measurements results from other authors. The results have been found to be in good agreement. The results show that the mathematical model is able to reproduce the thermal behavior in anaerobic phase in landfills. The isotherms revealed that temperatures are lower in the upper part of the waste cell, very high in the core and decrease slightly in the bottom of the cell due to the biodegradation of waste.

Experiment and Analysis on Flue Gas Low Temperature Corrosion Monitoring

Thermal loss of exhaust flue gas accounts for the largest proportion of the total boiler thermal loss. Nowadays in China, the exhaust gas temperature in many thermal power plants is much higher than the designed value, thus, the recycle and reuse of the waste heat of tail flue gas is necessary. However, lower exhaust gas temperature will aggravate low temperature corrosion of the tail heating surface, which also causes huge economic losses. In order to solve this problem, this paper designs a monitoring experiment platform of flue gas low temperature corrosion, which can measure the corrosion condition of different materials by different flue gas compositions and temperature corrosion speeds. Besides, effects of low temperature corrosion factors are analyzed to find the best exhaust gas temperature and the surface material of tail heating surface.

Waste heat recovery from heavy-duty diesel engine exhaust gases by medium temperature ORC system

A medium-temperature waste-heat recovery system based on the organic Rankine cycle (ORC) is designed to recover the exhaust energy from a heavy-duty diesel engine. Analysis of the 1st law of thermodynamics for an ORC system is performed. This analysis contains two parts. The first part is an analysis with undefined heat exchangers to gain an understanding of the ORC and find out suitable organic fluid parameters for a better ORC efficiency. The second part of the analysis uses combined engine test results and two designs of heat exchangers. By comparing the two designs, an improved system of heat exchangers is described. This analysis also quantifies the effect of engine parameters on ORC system. The study concludes that the supercritical Rankine cycle is a better approach towards waste heat recovery. The ORC system is found to perform better under part-load conditions if the medium-high power condition rather than rated working point of the engine is used as the design parameter. The ORC system achieves the highest waste-heat recovery efficiency of up to 10-15% for the optimised heat ex-changer design.

Selection of organic Rankine cycle working fluids in the low-temperature waste heat utilization

In the current study, simulations based on the engineering equation solver （EES） software are performed to determine the suitable working fluid for the simple organic Rankine cYcle system in different temperature ranges. Under the condition of various temperatures and a constant thermal power of the flue gas, the influence of different organic working fluids on the efficiency of the subcritical organic Rankine cycle power generation system is studied, and its efficiency and other parameters are compared with those of the regenerator system. It is shown that the efficiency of the subcritical organic Rankine cycle system is the best when the parameters of the working fluid in the expander inlet are in the saturation state. And for the organic Rankine cycle, the R245fa is better than other working fluids and the efficiency of the system reaches up to 10.2% when the flammability, the toxicity, the ozone depletion, the greenhouse effect and other factors of the working fluids are considered. The R60 l a working fluid can be used for the high-temperature heat source, however, because of its high flammability, new working fluid should be investigated. Under the same condition, the efficiency of the organic Rankine cycle power generation system with an internal heat exchanger is higher than that of the simple system without the internal heat exchanger, but the efficiency is related to the properties of the working fluid and the temperature of the heat source.

Technical Measures and Selections for Reducing Flue Gas Heat Loss of Large Coal-Fired Boilers

The main technologies for reducing flue gas heat loss of pulverized coal-fired boilers are introduced, and the suitability of these technologies for boiler operation and the principles for selection of these technologies are explored. The main conclusions are： 1） the non-equilibrium control over flue gas flow rates at the inlet of the air heater and the reversal rotation of the air heater rotator should be popularized as regular technologies in large boilers; 2） increasing the area of the air heater to reduce the flue gas heat loss in pulverized coal-fired boilers should be the top option and increasing the area of the economizer be the next choice; 3） low- pressure economizer technology could save energy under special conditions and should be compared with the technology of increasing economizer area in terms of technical economics when the latter is feasible; 4） the hot primary air heater is only suitable to the pnlvefizing system with a large amount of cold air mixed.

大滑移温度CO_(2)非共沸工质余热回收热泵热水系统实验研究

通过热泵技术将生产/生活中的低品位余热提质增效具有广泛的应用潜力。其中,非共沸工质能够实现热泵循环换热过程中的温度匹配,实现余热资源的深度利用。基于水源热泵热水实验台对基于大滑移温度的CO_(2)/R1234yf、CO_(2)/R290、CO_(2)/R600a和CO_(2)/R32非共沸工质进行实验分析,并以R290工质作为对照,研究蒸发器与冷凝器同时满足大温差情况下的热泵性能表现。结果表明:非共沸工质充注量主要影响循环过冷度,进而影响系统COP,当CO_(2)/R1234yf的质量分数为15%/85%时,循环存在最优充注量,在实验工况(热源进水温度25℃,出水温度5℃;热汇进水温度15℃,出水温度45℃)下最优充注量对应的COP为7.66。同时,在实验工况下,相较于R290单工质,CO_(2)/R290工质对最优COP提升了75.2%,对应q v(单位容积制热量)提升了107.7%;CO_(2)/R1234yf工质对最优COP提升了27.7%,对应q v提升了92.0%;CO_(2)/R32工质对最优COP提升了15.0%;而CO_(2)/R600a工质对最优COP仅提升1.7%,应用潜力较低。

电渗热固结处理顶管废弃泥浆的减量化研究

针对顶管废弃泥浆渗透性差、含水率高、承载力低等特点,采用电渗热固结法对其进行减量化研究,并探究不同温度条件下电渗热固结的处理效果。选取EKG电极板作为电极,分析在40℃、60℃、80℃等不同加热温度下,泥浆固化过程中的排水量、排水速率、温度、电流等参数的变化趋势,对比电渗热固结前后泥浆的物理力学特性变化。结果表明:电渗热固结能够有效促进泥浆的排水,提高固结效率,降低含水率,增强固化泥浆的承载力和抗剪强度;在其加热到一定程度时,裂缝进展过快,泥浆导电性减弱,加热效率降低,且加热的温度越高,加热效率越低;电渗热固结对顶管废弃泥浆减量化应用具有一定的有效性与可行性。本文的研究成果可为其实际工程应用提供借鉴与参考。

低阻叉流板式换热器传热性能与热阻靶向调控研究

用于烟气余热回收的板式换热器存在温度分布不均的问题。为改善烟气温度分布均匀性,有效遏制换热器腐蚀,本文通过实验测试对比碳钢与铸铁材质低阻叉流板式换热器性能差异,运用数值仿真预测局部流动传热特性并开展热阻分析,采用局部热阻调控方法设计了非均匀翅片结构。实验结果表明,在450℃高温时碳钢与铸铁材质的叉流板式换热器总传热系数分别达到32.5 W/(m^(2)·K)与25.1 W/(m^(2)·K)。通过数值仿真研究发现,叉流传热方式导致烟气侧沿程截面温度分布极不均匀,在热侧出口与冷侧入口交叉区、热侧出口与冷侧出口交叉区的热阻大,极易导致局部烟气温度低于露点温度。基于热阻分析法开发非均匀翅片结构,实施局部热阻靶向调控,最终实现维持阻力几乎不变情况下,使出口截面平均温度方差由6.9℃降至1.1℃,换热器内流体温度分布均匀性得到显著提升。

驱动源及低温热源双向梯级利用热泵工艺研究

为提高一次能源利用效率,针对大庆油田吸收式热泵余热提取工艺进行了改进,采用驱动源和低温热源双向梯级利用热泵工艺,提高了能源利用效率。传统热泵工艺COP为1.7,采用双效梯级利用工艺COP达到2.7。双向梯级利用热泵工艺为耦合蒸汽直拖离心式热泵和蒸汽驱动吸收式热泵对余热余压梯级利用的工艺流程,利用中温中压蒸汽梯级驱动两级热泵,充分发挥了蒸汽的做功能力;同时梯级提取含油污水低温余热,使含油污水温度从35℃降至21℃,传统热泵工艺从35℃降至25℃。综合能源利用效率较传统热泵工艺提高了50%。

基于工业余热与可再生能源耦合的赤峰市低碳供热研究

以赤峰市大温差供热工程实践为例,介绍了赤峰市低碳供热方案的设计理念和实施步骤。从赤峰市供热热源紧缺,城区周边电厂乏汽余热、工业余热和弃风电力转化热量潜力估算,降低一次网回水温度必要性,大温差供热推进和分阶段实施过程,各阶段热平衡等5个方面进行了详细说明。根据规划,至2035年赤峰市中心城区供热热量来源于非供暖季储存弃风电力转化热量和工业余热,以及供暖季工业余热和燃煤调峰电厂热量,单位供热面积的二氧化碳排放强度是现状的1/30。

湿法脱硫后烟气和浆液余热回收技术研究进展

低品位余热高效深度利用是促进燃煤电站进一步节能减排的关键之一,湿法脱硫后的低温饱和湿烟气蕴含大量潜热和水资源,大量脱硫浆液吸收烟气热量后温度升高。烟气与浆液具有巨大的余热利用和水资源回收的潜力,若直接排放烟气,直接排出浆液,不但造成资源浪费,还容易引发“白色烟羽”污染环境。本文以湿法脱硫后饱和湿烟气和脱硫浆液为研究对象,针对目前湿法脱硫技术余热回收效率低、利用难以匹配冷源等困境,总结了国内外针对脱硫后烟气水热回收和浆液余热回收技术及发展方向,研究中针对浆液余热利用仍待发展。其中,直接冷凝烟气和浆液技术和热泵技术成熟,应用广泛;溶液吸收技术能源利用率高,烟气腐蚀性低;烟气膜分离技术、浆液闪蒸、热泵技术清洁环保,回收质量高。直接冷凝烟气、浆液技术和膜分离技术需要进一步提高抗腐蚀性和转换效率;浆液闪蒸、热泵技术能耗较高,吸收式热泵技术仍需寻找高效安全环保无毒的吸收溶液。最后,探讨了目前脱硫浆液余热利用的主要方式及存在问题,回收余热主要用于供暖和电厂内部热利用,以期进一步推动湿法脱硫后烟气与浆液余热回收利用,实现燃煤电站的深度节能减排。

脱硫废水低温烟气余热浓缩过程中组分变化及腐蚀风险

脱硫废水浓缩减量有利于降低旁路高温烟气蒸发工艺煤耗,但针对脱硫废水浓缩过程中的组分变化及腐蚀风险鲜有报道。利用低温烟气余热浓缩平台研究了脱硫废水浓缩过程中水质变化,并采用粒度分析仪及微观形貌表征手段分析了浓缩期间固体析出特征,并使用年腐蚀速率表征了不同金属材料在浓缩废水中的腐蚀风险。结果表明:随浓缩进行废水电导率持续增加,最高可达45 mS/cm,其pH最低可下降至1~2;浓缩过程中多数离子浓度呈线性增长趋势,但受结晶析出和共存离子影响,Ca^(2+)和SO_(4)^(2-)浓度存在波动;浓缩期间析出颗粒存在团聚现象,分布逐渐从单峰分布转变为双峰分布,峰值粒径从12μm上升至75μm;金属材料腐蚀速率与废水浓缩倍率及环境温度相关,当浓缩倍率为4.5倍,水浴温度40℃时,304不锈钢在浓缩脱硫废水中腐蚀速率(0.127 mm/a)低于20#碳钢(1.211 mm/a),耐腐蚀性能更好。

煤矿瓦斯抽采液环真空泵新型降温及余热利用方法研究

瓦斯抽采液环真空泵温度高是导致其运行效率低和使用寿命短的重要原因。基于液环泵无用功耗散理论,定量分析了泵的产热-散热机理,提出了基于低温热泵的瓦斯抽采泵智能降温及余热利用技术,并搭建了工程试验系统,研究了进液温度、工作液流量、环境温度等参数对系统降温效果的影响。以李村煤矿2BEC87型瓦斯抽采泵为试验对象,在吸气负压为-53 kPa、进液流量为10 m3/h时,进液温度可由35℃降至16℃,运行温度由54℃降至45℃,降温效果显著;抽采泵运行效率提高了7%以上。

工业低温余热回收利用研究进展

工业生产过程中产生的大量低温余热通过烟气、冷却介质等形式散发到环境中,将这些热能回收利用对提高能源利用率、促进实现“双碳”目标具有重要作用。文章通过详细回顾现有工厂利用低温余热的案例,对比不同热源条件下的换热方案及节能效果,得出低温余热具有余热制热、原材料预热及防冻、余热制冷、余热发电等广泛用途;指出在利用低温余热资源时,应重点关注热源的特点及工厂需求等方面,选择与企业适配的余热利用方式;并对低温余热在节能减排中发挥的重要作用提出展望。

烧结冷却烟气低温余热ORC系统建模与热经济性能

本文以烧结冷却烟气低温余热为有机朗肯循环(organic Rankine cycle,ORC)系统热源,建立超临界ORC系统热力和经济模型,并选取R134a为ORC工质,研究变温热源下膨胀机的进口温度和压力,以及工质冷凝温度对系统热经济性能的影响。研究结果表明:系统净输出功随膨胀机进口温度的增加而增加,随膨胀机进口压力和工质冷凝温度的增加而减小,但系统单位温度的传热量随之均减小。当系统热力参数一定时,热源进口温度越大,系统净输出功和单位温度的传热量越大。在实际操作过程中,存在适宜的热源进口温度和系统热力参数使得ORC系统获得较大的净输出功和较小的单位温度传热量。

DTDC的节能实践

为了降低大豆压榨厂中DTDC的蒸汽消耗量,对DTDC的结构和操作进行调整,并介绍了回收DT层热风余热、DC热风尾气余热及DTDC夹层余热的工艺技术。将DT气相温度由72~75℃下调至68~70℃,搅拌翅改为折弯式,各层的旋转阀配置变频电机,让物料呈悬浮状;DC热风层每层配一台风机,装变频电机,增加节能层。实践证明:经调整后的DTDC生产的成品豆粕外表呈金黄色,散发出浓香味,残溶在190~300 mg/kg;豆粕的KOH蛋白质溶解度大于80%;DTDC蒸汽消耗量得到有效降低。