Experiment Study on the Exhaust-Gas Heat Exchanger for Small and Medium-Sized Marine Diesel Engine

This paper aims to design a special exchanger to recover the exhaust gas heat of marine diesel engines used in small and medium-sized fishing vessels,which can then be used to heat water up to 55°C–85°C for membrane desalination devices to produce fresh water.A new exhaust-gas heat exchanger of fins and tube,with a reinforced heat transfer tube section,unequal spacing fins,a mixing zone between the fin groups and four routes tube bundle,was designed.Numerical simulations were also used to provide reference information for structural design.Experiments were carried out for exhaust gas waste heat recovery from a marine diesel engine in an engine test bench utilizing the heat exchanger.The experimental results show that the difference between heat absorption by water and heat reduction of exhaust gas is less than 6.5%.After the water flow rate was adjusted,the exhaust gas waste heat recovery efficiency was higher than 70%,and the exhaust-gas heat exchanger’s outlet water temperature was 55°C–85°C at different engine loads.This means that the heat recovery from the exhaust gas of a marine diesel engine meets the requirement to drive a membrane desalination device to produce fresh water for fishers working in small and medium-sized fishing vessels.

Gas Flow Development Through Tandem Heat Exchangers Inside Exhaust Nozzle by Using Porous Medium Model

A computational study on the flow development through tandem double-U-shaped-tubes compact heat exchangers inside exhaust nozzle is presented.In order to simplify the computational process on modeling the flow field,the compact heat exchanger is modeled as a porous matrix by using an isotropic porous medium assumption,which makes two-dimensional numerical simulation realistic.With the use of an existed quadratic relation which connects the pressure drop with the inlet velocity in the external part of the heat exchanger,the permeability and drag coefficient in the porous medium model are determined and a corresponding computational method validation is also made.Two schemes of tandem double-U-shaped-tubes compact heat exchangers are numerically analyzed.In relative to the baseline scheme,the modified scheme is improved by smoothing the nozzle expansion,varying heat exchanger mounting angle and installing boat-tail ramp at the trailing edge of the last heat exchanger.The results show that the pressure losses due to the existence of local recirculation zones and inappropriate distribution of the flow field are reduced in the modified scheme.The pressure loss coefficient is decreased from 1.7% under the baseline scheme to 1.2% under the modified scheme.

Optimization of Gas Turbine Exhaust Volute Flow Loss

The exhaust volute is a device that can change the exhaust direction of the ship’s gas turbine to reduce the flow loss of the high-temperature and high-speed turbine exhaust gas in the box-type exhaust volute,thereby improving its power output performance.This paper first investigates the internal flow field characteristics of the exhaust volute via numerical simulation and reveals the main source of the internal resistance loss of the volute.On the premise of not affecting the installation size of the volute and matching it with other components in the cabin,the design scheme of volute bottom shunt and volute chamfer are then optimized in accordance with the flow characteristics inside the volute.Numerical simulation results show that the partial flow structure at the bottom of the volute can effectively improve the low-velocity region and the vortex flow at the bottom of the volute,and the chamfered angle scheme can control the regular expansion and compression of the airflow.When the volute adopts the appropriate chamfer angle and the bottom split-flow structure,the total pressure loss can be reduced by 19.6%,and the static pressure recovery coefficient can be increased by 42.05%.

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.

Performance Optimization of Dual Pressure Heat Recovery Steam Generator (HRSG) in the Tropical Rainforest

This work evaluates the performance optimization of heat recovery steam generator system in Afam VI power plant, Rivers State. Nigeria. Steady state monitoring and direct collection of data from the plant was performed including logged data for a period of 12 months. The data were analysed using various energy equations. Hysys software was used to model the temperature across the heating surfaces, and MATLAB software was used to determine the heat transfer coefficient, heat duties, steam flow, effectiveness of the HRSG. The optimization technique was carried out by varying the exhaust gas flow, exhaust gas temperature, steam pressure and the theoretical introduction of duct burner for supplementary firing. The results show that between 490℃ and 526℃, the percentage increase in the overall heat absorbed in the HRSG is 37.39%. It also show that for an increase in the exhaust gas mass flow by 80 kg/s, the steam generation increase by 19.29% and 18.18% for the low and high pressure levels respectively. The overall result indicates an improvement in the HRSG energy efficiency and steam generation. As the exhaust gas mass flow and temperature increases, the steam generation and system effectiveness greatly improved under the various considerations, which satisfy the research objective.

Heat calculation and numerical simulation in steam mining of permafrost gas hydrate

Steam mining method was injecting hot steam into the borehole to heat the hydrate strata at the same time of depressurization mining,which could promote further decomposition and expand mining areas of gas hydrate. Steam heat calculation would provide the basis for the design of heating device and the choice of the field test parameters. There were piping heat loss in the process of mining. The heat transfer of steam flowing in the pipe was steady,so the heat loss could be obtained easily by formula calculation. The power of stratum heating should be determined by numerical simulation for the process of heating was dynamic and the equations were usually nonlinear. The selected mining conditions were 500-millimeter mining radius,10 centigrade mining temperature and 180 centigrade steam temperature. Heat loss and best heating power,obtained by formula calculation and numerical simulation,were 21. 35 W/m and 20 kW.

Delivery of inert gas through a vertical borehole using inert gas generator: A theoretical study

The delivery of the inert gas through a vertical borehole using inert gas generator or IGG is investigated.Potential limitations and/or transient effects are highlighted.During the analysis,the borehole diameter,borehole length,type of borehole and partial condensation prior to entering the borehole were varied.A choked flow will occur for a contraction exit or borehole of 0.3 m in diameter if no condensation prior to the contraction occurs.If partial condensation takes place,a borehole diameter of 0.3 m will be possible if almost 50%of the water vapour condensates.However,pressure losses along boreholes with a diameter of 0.3 or 0.4 m are significant and could pose a challenge if trying to mitigate the pressure losses.Adding a booster fan prior to the inlet of the 0.4 m lined borehole would still be a challenge.The corresponding case with a 0.5 m borehole presents much more favourable pressure losses.The 0.5 m diameter lined borehole should be regarded as the lower threshold.The rapid heating of the unlined borehole surface will increase the risk of thermal spallation and possibly imposing restrictions.Understanding the mechanisms during gas delivery will increase the likelihood of a successful inertisation.

基于CFD的垃圾焚烧锅炉二次风喷入角度优化研究

为研究二次风喷入角度对焚烧锅炉炉膛内温度、烟气速度、烟气停留时间、排烟热损失的影响以及二次风喷入角度与焚烧炉出口处NO_(x)浓度的关联性,采用UDF编译边界条件和Fluent耦合的方法,针对某600 t/d城市生活垃圾焚烧锅炉的前后墙二次风喷入角度进行数值模拟。模拟的前墙二次风喷入角度变化为68°~80°,后墙二次风喷入角度变化为61°~73°,二次风风速为42 m/s,二次风温度为301.15 K。结果表明:后墙二次风喷入角度不变时,随着前墙二次风喷入角度增加,NO_(x)浓度先升高后下降(最低为142.23 mg/m^(3),且焚烧炉排烟热损失降低(最小为7.12%);前墙二次风喷入角度不变时,随着后墙二次风喷入角度增加,NO_(x)浓度也呈现先升高后下降的趋势(最低为149.15 mg/m^(3),且焚烧炉排烟热损失先升高后降低(最小为7.46%);前后墙二次风喷入角度分别为80°和67°时,SNCR两层喷枪之间的平均温度为1229.59 K,停留时间为1.63 s,与其他工况相比更加接近SNCR脱硝的最佳反应温度和停留时间,第一烟道出口处的平均温度为1211.36 K且停留时间大于2 s,有助于抑制二噁英的生成。

循环流化床锅炉排烟温度高原因分析及应对措施

为了提高锅炉效率要从降低锅炉各项热损失中想办法,而锅炉各项损失中排烟热损失是锅炉热损失最大一项损失,所以从降低排烟热损失来提高锅炉效率。

Utilisation of waste heat from exhaust gases of drying process

Nowadays a lot of low-grade heat is wasted from the industry through the off- and flue-gasses with different compositions. These gases provide the sensitive heat with utilisation potential and latent heat with the components for condensation. In this paper, process integration methodology has been applied to the partly condensed streams. A hot composite curve that represents the gas mixture cooling according to equation of state for real gases was drawn to account the gas-liquid equilibrium. According to the pinch analysis methodology, the pinch point was specified and optimal minimal temperature difference was determined. The location of the point where gas and liquid phases can be split for better recuperation of heat energy within heat exchangers is estimated using the developed methodology. The industrial case study of tobacco drying process off-gasses is analysed for heat recovery. The mathematical model was developed by using MathCad software to minimise the total annualised cost using compact plate heat exchangers for waste heat utilisation. The obtained payback period for the required investments is less than six months. The presented method was validated by comparison with industrial test data.

An Experimental Study on Latent Heat Recovery of Exhaust Wet Flue Gas

The experiment was conducted to investigate the heat transfer performance of wet flue gas in a vertical tube. The factors influencing the convective condensation of wet flue gas were experimentally investigated. The measured results indicate that the convective heat transfer of bulk flow and condensation heat transfer of vapor have significant contribution to the total heat transfer and the dominant transport mechanism is dependent upon the vapor fraction in mixture.

燃天然气非冷凝锅炉排烟热损失简化及应用

【目的】简化燃天然气非冷凝锅炉排烟热损失的测试。【方法】以使用西气东输天然气燃料的非冷凝锅炉为研究对象,进行技术资料搜集,并结合目前非冷凝天然气锅炉能效测试报告计算方法。【结果】总结出一种适合河南省区域内非冷凝天然气锅炉排烟热损失测试方法,并结合实际测试过程对该方法进行验证。【结论】采用简化后的测试方法得出的数据与详细测试的原始数据进行对比,两者排烟热损失之差为+0.04%,只需测量排烟温度、入炉冷空气温度、烟气中的氧含量,测量项目少,降低测试成本,提高测试准确度,便于在实际工作中的应用。

660 MW超超临界褐煤锅炉烟气余热深度耦合系统设计及应用

针对660 MW超超临界褐煤锅炉排烟温度高、容积大、损失大的难题,对锅炉排烟损失的特征和汽轮机回热系统提高循环热效率的机理进行分析,打破锅炉、汽轮机热力系统的设计屏障,提出了锅炉烟气余热利用方案。该方案节煤效果明显、投资回收期短,可有效提高锅炉效率及汽轮机回热循环热效率。

烟气预干燥褐煤热经济性分析

将高温烟气滚筒干燥装置与机组锅炉系统耦合,建立了高温烟气干燥褐煤理论分析计算模型,提出了预干燥所需高温烟气流量与机组经济性评价方法。计算结果表明:采用烟气预干燥技术可将水分为38%的褐煤分别干燥到水分为27%,20%和14%,机组发电标准煤耗分别降低1.39,2.10,0.96g/(kW·h);烟气预干燥褐煤机组排烟温度每降低1℃,发电标准煤耗约减少1.3g/(kW·h);褐煤预干燥程度应结合锅炉排烟热损失与干燥机热损失综合考虑,以实现机组最佳经济性。

原油加热炉热效率分析模型

原油加热炉在变工况下运行会严重降低效率。以加热炉反平衡热效率为基础,通过进行变工况校核热力计算,用偏差分析法推导出加热炉排烟热损失预测模型。该预测模型定量分析了排烟温度、过量空气系数对热效率的综合影响,可帮助现场操作人员对变工况运行的结果进行提前预测,准确找出造成能量损失的部位,并合理调整运行参数,实现加热炉的安全、经济运行。

锅炉排烟热损失的精确计算方法研究

锅炉排烟热损失是衡量锅炉热经济性的重要指标,其准确计算对锅炉的能效评价具有重要意义。对比了锅炉排烟热损失2种常用算法计算结果,发现计算结果最大相差达0.552 4个百分点,分析获得了计算结果存在差异的原因:2种计算方法的基准温度不同,并且与燃料低位发热量测试的基准温度不统一。为此,通过对燃料的低位发热量进行修正,提出了排烟热损失的精确计算方法。

煤质变化对排烟热损失影响的计算与分析

在煤粉锅炉中,锅炉效率的高低对电厂热经济性的影响很大,而锅炉煤质的变化对锅炉效率的变化起着很大的作用。其中,影响锅炉效率最大的一项,是排烟热损失。针对排烟热损失的计算公式,推导出了煤质变化对排烟热损失影响的矩阵方程。通过与传统的计算方法进行对比,该矩阵方程可以直接计算出煤质中各种成分的变化对排烟热损失影响的大小。计算过程简单,累积误差小,计算结果能够满足工程精度的要求,对电厂锅炉经济性的分析,具有现实的意义。

浅谈锅炉烟气余热回收技术及其工程应用

随着能源价格日益高涨,空气污染日渐严重,降低能耗,减少污染物排放已成为重要议题。而现在工业锅炉的使用中普遍存在着热量利用率低下,排放烟气余热温度过高,以及烟气内污染环境气体含量过高等问题。因此,阐述了锅炉烟气余热回收技术和其优缺点,并详细介绍了热管技术和冷凝式锅炉的工程应用方案以及与其他系统的联合方案,然后以实际工程为例分析了锅炉烟气余热回收的效果,最后得出当前余热回收技术仍存在很大的问题,还有很长的路要走的结论。

添加石灰石脱硫对300MW循环流化床锅炉排烟热损失的研究

排烟热损失是锅炉最大的一项热损失,对锅炉效率影响很大。现在300MW循环流化床(CFB)锅炉已经成为电站锅炉的主要炉型,一般采用添加石灰石固硫。分析了CFB锅炉排烟热损失的影响因素,建立了CFB锅炉排烟热损失的数学模型,计算了我国首台CFBB在BECR工况时的排烟热损失,定量分析了各种因素的影响程度,提出了技术对策。

稠油集输系统加热炉节能技术研究

集输系统中的加热炉是油田耗能的主要设备,其热效率的高低直接影响油田的经济效益。文中分析了集输系统加热炉经济运行的主要影响因素:过剩空气系数、加热炉热负荷、排烟温度、加热炉燃烧效率等。利用加热炉反平衡效率测试法,对现场运行的加热炉进行效率测试,得到加热炉的散热损失率、排烟热损失率及燃料不完全燃烧率。利用测试数据计算出加热炉的热效率,根据计算结果分析了造成加热炉低效运行的原因。针对各加热炉的不同情况,提出实现经济运行的主要对策,为稠油集输系统加热炉的节能技术改造提供依据。