用天然气烟气废热作低温热源热泵循环的分析

用热力学理论和燃烧理论对天然气烟气的饱和含湿量、露点温度、水蒸气的冷凝率、烟气的焓和天然气的热利用率进行了理论分析和计算，并给出了关系图，可供实际工程参考。本文提出了一个换热器与三级热泵相结合利用天然气烟气废热的工艺，可以充分利用冷凝热，热泵的平均COP可达到3以上，采用本工艺后对排烟温度在100～200℃的天然气烟气，降低到20～30℃，对不同的过剩空气系数，可回收10～20％相当于天然气低热值的热量。     

填料塔中单乙醇胺吸收CO2的脱除率研究

在弹簧式玻璃填料的填料塔中模拟工业脱碳,用Monoethanolamine (MEA)溶液与模拟烟气反应.研究填料塔沿程上MEA溶液浓度、CO2分压、以及MEA溶液流量和烟气流量组合下对脱除率的影响.实验结果表明,脱除率会随着MEA浓度增加而升高;不同吸收液流量和烟气流量的组合对脱除效果影响明显,本质可能是反应物摩尔比对脱除过程的影响.当反应物摩尔比大于4时,CO2的脱除率接近90％.     

双接触液柱塔氨水吸收二氧化碳实验研究

对双接触式液柱塔的脱碳传质进行相关的实验研究。利用双接触式液柱塔开展氨水捕集CO_2的实验研究。研究了氨水浓度、入口CO_2浓度、烟气流量因素对脱除效率和单位体积吸收速率的影响。实验研究表明:随着氨水浓度的增大,CO_2的脱除效率和单位体积吸收速率都增大;增大CO_2入口浓度和烟气流量,CO_2的脱除效率都呈下降趋势,但其单位体积吸收速率升高。氨水浓度和烟气流量越大,反应达到平衡的时间就越短,但氨水浓度和烟气流量达到一定值时,氨水浓度和烟气流量对反应达到平衡的时间影响很小;CO_2入口浓度对反应达到平衡的时间的影响不大。     

循环流化床中糠醛渣与煤混燃特性的试验研究

在炉膛尺寸为150 mm×150 mm×2 500 mm的循环流化床燃烧试验台上进行糠醛渣与煤的混燃试验,研究其燃烧特性、尾部飞灰及烟气排放特性。研究表明:糠醛渣掺混质量比例为10%-50%的混合燃料在循环流化床中均可稳定燃烧;随着糠醛渣的掺混比例增加,炉膛上部温度升高,尾部飞灰含碳量下降,而颗粒排放浓度升高;随着流化风速增加,炉膛上部温度升高。密相区的温度升高,CO排放浓度下降,SO2、NOx排放浓度上升;糠醛渣的掺混比例增加,CO排放浓度上升,SO2、NOx排放浓度下降。     

钙基吸收剂脱碳的模型建立及参数研究

针对天然气联合循环(NGCC)电厂烟气CO_2脱除问题,对钙基吸收剂循环煅烧与碳酸化CO_2脱除法进行了研究.利用Matlab建立数学模型,并分析了碳酸化反应温度、碳酸化塔床料量、循环吸收剂摩尔流量以及补充吸收剂摩尔流量对CO_2捕集率的影响.结果表明:由于NGCC电厂烟气中CO_2摩尔分数较低,为达到90%CO_2捕集率(rcc),其碳酸化反应温度应为594℃,明显低于燃煤电厂的碳酸化反应温度(650℃);随着循环次数的增加,吸收剂的吸收能力明显下降;在补充吸收剂摩尔流量(F_0)一定时,r_(cc)随着单位发电量碳酸化塔床料量(W_(CaO))和循环吸收剂摩尔流量(F_R)的增加先大幅增加,后趋于稳定;在W_(CaO)一定时,rcc随着F_0和F_R的增加而增加,但当F_R增加到一定值时,碳酸化塔中床料量不足,使得进入其中的CaO颗粒转化率未全部达到最大平均转化率X_(ave),r_(cc)反而下降.     

不同长高比RQL燃烧室燃烧和排放特性研究

针对3种长高比富油/焠熄/贫油(RQL)燃烧室,保持头部旋流器入口空气和燃料体积流量不变,通过改变焠熄空气体积流量,研究了不同长高比燃烧室冷态流场、掺混不均匀度、轴向温度分布及排气温度分布均匀性和污染物排放变化。结果表明:相同工况下长高比越小,射流深度越大,上下射流相互干涉作用越强;长高比为3.75的燃烧室掺混不均匀度最小,掺混效果最好;随着长高比的增加,焠熄区最低温度降低;长高比为3.75时,排气温度不均匀度较好,长高比大于3.75时,排气温度不均匀度迅速增加;随着长高比增加,燃烧室NO_x排放质量浓度升高,随着焠熄空气体积流量减小,不同长高比燃烧室NO_x排放质量浓度均先升高后降低,且在高焠熄空气体积流量工况下,低长高比燃烧室的燃烧效率下降。     

褐煤旋风渣膜气化特性

在自主搭建的小型规模旋风渣膜煤气化装置上,开展了对褐煤气化特性的实验研究,重点研究了气化炉负荷、一次风氛围、氧煤比以及蒸汽煤比对粗煤气中有效组分含量、碳转化率以及冷煤气效率的影响.研究表明,随着气化炉运行负荷的增加,粗煤气中有效组分含量、碳转化率以及冷煤气效率均先增加后趋于稳定;用CO_2+O_2送粉相比于用空气送粉,粗煤气中有效组分含量增加、碳转化率以及冷煤气效率升高;随着氧煤比的增大,粗煤气中CO含量和冷煤气效率先增加后减少,当氧煤比为0.9时两者均达到最大值;随着蒸汽煤比的增加,粗煤气中CO含量、碳转化率、冷煤气效率均逐步减少.     

冷却边界下变孔隙多孔介质燃烧特性研究

针对天然气等高热值气体燃烧氮氧化物排放高和多孔介质烧蚀问题,设计开发了变孔隙多孔介质燃烧试验系统,研究了不同燃烧器内芯结构的孔隙排列方式及冷却空气流量对燃烧温度及污染物排放的影响。结果表明：积木式结构外环孔密度呈阶梯状排列比呈均匀型排列更有利于热量沿燃烧器径向传递;积木式结构的内芯孔密度呈阶梯状排列时,有利于提高燃烧室下游的温度;随着冷却空气流量的增大,冷却空气吸热量所占燃烧放热量的比例由23.62%增至70.87%,尾部烟气带走热量占燃烧放热量比例由71.65%降至21.63%,CO排放升高,NO排放最低降至3mg/m3。     

降低燃气锅炉排烟热损失方法探讨

燃用天然气的锅炉其排烟温度较高，除带走大量显热之外，烟气中还存在大量水蒸汽的潜热，若将这两部分热量充分回收，则将大幅度提高锅炉热效率。文章在对天然气的燃烧特性计算的基础上，分析燃气锅炉烟气潜热回收的效果和需要解决的问题。     

低排放塔式同轴分级旋流配比对燃烧流场的影响

以天然气-低排放塔式同轴分级燃烧室为研究对象，采用Realizablek-ε湍流模型和FGM燃烧模型研究了旋流器旋流数对热态流场的影响．结果表明：随着二级旋流数增加，中心级和一级流量增加，二级流量减少，燃料掺混均匀性提高，均匀指数最大提高0.061；压力损失小幅增加，而CO排放显著减少，燃烧效率提高且超过99%；模拟的各工况温度分布均匀，均形成稳定的回流区，燃烧稳定；对16种不同的旋流器方案进行筛选，选出0.7/0.8旋流器方案为最佳方案．     

低位烟气余热深度回收利用状况述评_新技术路线与回收条件改变的影响

提高能源的利用率来实现节能减排,是解决当前能源与环境问题的重要途径之一。通过对国内、外各行业窑炉与热能动力设备排烟温度的列举与分析,指出这类排烟的余温仍较高,提出在烟气余热回收热量传递过程中采取"质""量"分控的回收方式,利用烟气余热的"驱动力",即可实现烟气余热的深度利用,并对深度利用后烟气特性变化而引起的回收条件改变的影响进行了分析。     

Radiative and conductive transfer for a real gas in a cylindrical enclosure with gray walls

The purpose of this study is to examine the interaction of radiative and conductive transfer for a radiatively participating real gas stagnant in a cylindrical enclosure with gray diffuse walls. Consideration of reflecting boundaries represents an extension of previous black wall studies. Examination of radiative transfer was made by the zone method with gas radiative properties furnished by the weighted sum of gray gases model. Directed flux areas are expressed as the weighted sum of gray gas total exchange areas which are evaluated using the matrix formulation method from direct exchange areas. Axial and radial gas temperatures are examined along with wall heat flux or temperature for respective cases of either specified wall temperatures or heat fluxes. Emphasis is placed on examining results to show the effects of wall emittance and duct diameter. Results for heat generation within the gas are also presented.     

Numerical study of liquid film cooling in a rocket combustion chamber

A numerical study is reported to investigate the liquid film cooling in a rocket combustion chamber. Mass, momentum and heat transfer characteristics through the interface are considered in detail. A marching procedure is employed for solution of the respective governing equations for the liquid film and gas stream together. The standard turbulence k–ε model is used to simulate the turbulence gas flow and a modified van Driest model is adopted to simulate the turbulent liquid film flow. Radiation of gas stream is also considered and simulated with the flux model. Downstream of the liquid film the gaseous film cooling is numerically studied simultaneously. Results are presented for a mixed gases–water system under different condition. Various effects on the liquid film length are examined in detail. There is a good agreement between the numerical prediction and experimental result on the liquid film length.     

Mobile hydraulic power supply: Liquid piston Stirling engine pump

Conventional mobile hydraulic power supplies involve numerous kinematic connections and are limited by the efficiency, noise, and emissions of internal combustion engines. The Stirling cycle possesses numerous benefits such as the ability to operate from any heat source, quiet operation, and high theoretical efficiency. The Stirling engine has seen limited success due to poor heat transfer in the working chambers, difficulty sealing low-molecular weight gases at high pressure, and non-ideal piston displacement profiles. As a solution to these limitations, a liquid piston Stirling engine pump is proposed. The liquid pistons conform to irregular volumes, allowing increased heat transfer through geometry features on the interior of the working chambers. Creating near-isothermal operation eliminates the costly external heat exchangers and increases the engine efficiency through decreasing the engine dead space. The liquid pistons provide a positive gas seal and thermal transport to the working chambers. Controlling the flow of the liquid pistons with valves enables matching the ideal Stirling cycle and creates a direct hydraulic power supply. Using liquid hydrogen as a fuel source allows cooling the compression side of the engine before expanded the fuel into a gas and combusting it to heat the expansion side of the engine. Cooling the compression side not only increases the engine power, but also significantly increases the potential thermal efficiency of the engine. A high efficiency Stirling engine makes energy regeneration through reversing the Stirling cycle practical. When used for regeneration, the captured energy can be stored in thermal batteries, such as a molten salt. The liquid piston Stirling engine pump requires further research in numerous areas such as understanding the behavior of the liquid pistons, modeling and optimization of a full engine pump, and careful selection of materials for the extreme operating temperatures. Addressing these obtainable research quandaries will enable a transformative Stirling engine pump with the potential to excel in numerous applications.     

Fundamental Mechanisms That Influence the Estimate of Heat Transfer to Gas Turbine Blades

The quest for improved efficiency has motivated the elevation of turbine inlet temperatures in all types of advanced aircraft gas turbines. The accommodation of higher gas temperatures necessitates complex blade cooling schemes so as not to sacrifice structural integrity and operational life in advanced engine designs. Estimates of the heat transfer from the gas to stationary (vanes) or rotating blades poses a major uncertainty because of the complexity of the heat transfer processes. The gas flow through these blade rows is three-dimensional with complex secondary viscous flow patterns that interact with the end walls and blade surfaces. In addition, upstream disturbances, stagnation flow, curvature effects, and flow acceleration complicate the thermal transport mechanisms in the boundary layers. Some of these fundamental heat transfer effects will be discussed. The chief purpose of this paper is to acquaint those in the heat transfer community, who are not directly involved in gas turbines, with the seriousness of the problem and to recommend some basic research that would improve the predictions of gas-side heat transfer on turbine blades and vanes.     

Influence of thermal emittance on the performance of laminated solar control glazing

Influence of thermal emittance on the performance of laminated solar control glazing is presented. A transient one-dimensional mathematical model allowing the prediction of conductive heat transfer within the glazing and convective and radiative heat transfer from the glazing towards the interior and exterior are considered separately. A constant normal incidence of air mass 2 solar radiation of 750 W/m² was assumed. The redistribution of the component of the solar radiation absorbed by the laminated glass and the shading coefficient (SC) were calculated for solar transmittance, 0.05 to 0.35; thermal emittance of the inner surface of the glazing, 0.15 to 0.85; convective heat transfer coefficient for the exterior surface, 10–100 W/m² K and exterior ambient temperatures of 15°C, 32°C and 45°C. The results indicate that as the emittance decreases, the SC decreases by 10–20% for all cases of ambient temperatures considered. The contribution from the convective mechanisms to the heat transfer to the interior is always higher than that from radiative process in the range of ambient temperatures considered. The results presented in this paper would help to decide whether for a given location of interest, the incorporation of a heat mirror glazing would make a meaningful reduction in the cooling load in enclosures with single glazed windows.     

Effects of film evaporation on laminar mixed convection heat and mass transfer in a vertical channel

A numerical study of finite liquid film evaporation on laminar mixed convection heat and mass transfer in a vertical parallel plate channel is presented. The influences of the inlet liquid mass flow rate and the imposed wall heat flux on the film vaporization and the associated heat and mass transfer characteristics were examined for air-water and air-ethanol systems. Predicted results obtained by including transport in the liquid film are contrasted with those where liquid film transport is neglected, showing that the assumption of an extremely thin film made by Tsay and Yan (Wärme- und Stoffübertragung 26, 23–31 (1990)) is only valid for a system with a small liquid mass flow rate. Additionally, it is found that the heat transfer between the interface and gas stream is dominated by the transport of latent heat associated with film evaporation. The magnitude of the evaporative latent heat flux may be five times greater than that of sensible heat flux.     

Numerical study of heat transfer of hydrogen combustion in noble gases atmosphere in compression ignition engine

The high energy content of hydrogen and zero carbon emission from hydrogen combustion is very important for compression ignition engine development. Hydrogen requires a very high auto-ignition temperature, which encourages replacing nitrogen with noble gases with higher specific heat ratio during compression process. In noble gases-hydrogen combustion, higher combustion temperature potentially leading to a higher heat loss. This paper aims to investigate the effect of hydrogen combustion in various noble gases on heat distribution and heat transfer on the cylinder wall. Converge CFD software was used to simulate a Yanmar NF19SK direct injection compression ignition engine. The local heat flux was measured at different locations of cylinder wall and piston head. The heat transfer of hydrogen combustion in various noble gases at different intake temperatures was studied using the numerical approach. As a result, hydrogen combustion in light noble gases such as helium produces faster combustion progress and higher heat temperature. The hydrogen combustion that experienced detonation, which happened in neon at 340 K and argon at 380 K, recorded a very high local heat flux at the cylinder head and piston due to the rapid combustion, which should be avoided in the engine operation. At a higher intake temperature, the rate of heat transfer on the cylinder wall is increased. In conclusion, helium was found as the best working gas for controlling combustion and heat transfer. Overall, the heat transfer data gained in this paper can be used to construct the future engine hydrogen in noble gases.     

Non-gray radiative convective conductive modeling of a double glass window with a cavity filled with a mixture of absorbing gases

Coupled radiation and natural convection heat transfer occurs in vertical enclosures with walls at different temperatures filled with gas media. In glass window thermal insulation applications in hot climates, infrared absorbing gases appear as an alternative to improve their thermal performance. The thermal modeling of glass windows filled with non-gray absorbing gases is somewhat difficult due to the spectral variation of the absorption coefficients of the gases and the phenomena of natural convection. In this work, the cumulative wavenumber (CW) model is used to treat the spectral properties of mixtures of absorbing gases and the radiative transport equation is solved using CW model and the discrete ordinates method. Due to the range of temperature variation, the mixture of gases is considered as homogeneous. The absorption coefficients were obtained from the database HITRAN. First, the natural convection in a cavity with high aspect ratio is modeled using a CFD code and the local and global Nusselt numbers are computed and compared with available empirical correlations. Also, the flow pattern for different Rayleigh numbers is analyzed. Then, the heat transfer in the gas domain is approximated by a radiative conductive model with specified heat flux at boundaries which is equivalent to convective transport at the walls surroundings. The energy equation in its two-dimensional form is solved by the finite volume technique. Three types of gas mixtures, highly absorbing, medium and transparent are investigated, to determinate their effectiveness in reducing heat gain by the gas ambient. Reflective glasses are also considered. The numerical method to solve radiative heat transport equation in gray and non-gray participant media was validated previously. The temperatures distributions in the gas and the glass domain are computed and the thermal performance of the gas mixtures is evaluated and discussed. Also, comparison with pure radiative conductive model is shown.