可燃制冷剂的风险评估和降低风险措施

根据保护臭氧层的相关国际环境公约的要求,R22等制冷剂将会被逐步替代。目前可获得的制冷剂中,可燃制冷剂具有不破坏臭氧层、温室效应低等环保性能上的优势。然而,可燃性使得这些制冷剂的推广遇到了不少困难。出于安全角度考虑,在进行推广时必须要对制冷系统使用可燃制冷剂的风险进行评估,以便采取针对性的措施。本文对制冷剂常见的风险评估方法及提高制冷系统安全性能的方法进行了综述。     

T/CRAAS 1014—2022《使用可燃或高压制冷剂制冷空调设备维修培训场所及设施建设规范》解读

介绍了T/CRAAS 1014—2022《使用可燃或高压制冷剂制冷空调设备维修培训场所及设施建设规范》制定的背景及主要内容，同时就规范中实训室工位布置、实训室通风、主要设施操作注意事项以及教学人员和实训室管理人员理论及实践要求等方面进行了详细的解读，并提供了具体实施指南。     

Greencool制冷剂的特点及应用

本文介绍一种具有环保与节能效果的新型制冷剂-Greencool制冷剂,主要介绍这种制冷剂的特点并与传统的氟里昂制冷剂相比较.另外,本文还将介绍Greencool制冷剂的工程应用.     

制冷剂回收过程动态数学模型及仿真

通过对回收装置和被回收制冷剂系统建立数学模型及数值计算,模拟了制冷剂回收过程中的流量变化;得出了两种环境温度、两种不同状态下制冷剂回收时的流量变化特性,并对结果进行了分析,为制冷剂回收装置的设计和性能优化提供了参考.     

R32制冷剂泄漏位置对浓度分布与室内安全性的实验研究

本文通过实验研究的方法,对比分析了R32制冷剂在泄漏量为3.6 kg,不同泄漏位置时,R32气体在室内不同平面的浓度扩散规律,并通过典型平面首次达到可燃下限（LFL）的时间和可燃风险时间来分析室内的安全性影响。结果表明：随着泄漏位置高度的增加,制冷剂浓度扩散速率在沿高度方向上逐渐趋于一致,浓度上升速率和浓度下降速率分别保持在约0.5%/min和0.06%/min。当制冷剂气体从房间上部水平方向泄漏改变为垂直向下泄漏时,泄漏口附近平面处最大浓度及浓度扩散速率均减小约50%,可燃危险时间减少了约78%;房间下部的的可燃危险时间随泄漏位置高度的升高而逐渐增大。当泄漏位置位于房间上部和顶部时,房间底部区域最先达到LFL值,其余位置处泄漏口附近平面处最先达到LFL值。     

制冷剂替代技术研究进展及发展趋势

蒙特利尔议定书第19次缔约方会议通过了加速淘汰HCFCs制冷剂的调整案,给我国制冷行业带来了较大压力.根据联合国环境规划署“气候友好制冷剂之路”国际会议信息,介绍了制冷剂替代技术的国内外研究现状.欧盟正积极推进天然制冷剂的应用,美国杜邦公司等在开发和宣传化学合成制冷剂的优越性,而非洲、东南亚等发展中国家更关注制冷剂替代技术和替代资金的来源.我国在HCFCs替代方面,除了研究适合国情的R32等过渡制冷剂替代技术之外,还应该进一步研究CO2、R290等天然制冷剂的应用技术,同时开发GWP值较小但与HCFCs类制冷剂的物性更加接近的制冷剂.另外,这里还强调了HCFCs替代技术涉及到的相关标准的制订是行业发展的基础,应该受到特别关注.     

制冷剂回收再生的碳排放评估及经济性分析

我国已进入HCFCs制冷剂淘汰末期,并即将于2024年启动HFCs的产量和消费量削减。本文以制冷剂的回收再生过程为主要研究对象,基于LCCP气候性能模型,构建了制冷剂回收再生过程的碳排放量评估模型;分析了制冷剂回收再生的经济性;并对所构建模型,以汽车空调制冷剂R134a的回收再生为案例,计算其碳排放量及回收再生经济性。结果表明：本文案例中,对制冷剂进行回收再生处理可以减少当量CO2排放约42％,制冷剂回收再生的经济性能主要与再生后制冷剂单价及工人工资成本有关,工人工资按月最低工资标准时净化后制冷剂售价在11 元/kg（新制冷剂售价的50％）以上可在2年内开始盈利。     

碳氢制冷剂在小型商用冷柜上应用分析

碳氢制冷剂作为天然制冷剂的一种,因其热物理性质与环保性能(ODP为0,GWP极低)俱佳而受到国内外学者的广泛关注。本文从碳氢制冷剂的循环热力学性能出发,对碳氢制冷剂应用于小型商用冷柜的理论和实验进展进行论述,并介绍了压缩机、润滑油以及其他相关方面的研究进展。研究表明,相比于小型商用冷柜中使用的传统制冷剂,碳氢制冷剂的单位制冷量和性能系数较高,排气温度较低,实际运行时冷却速度和噪声水平都有较大改善。然而,碳氢类物质具有可燃性。虽然小型商用冷柜中碳氢制冷剂充注量较小,但要使得碳氢制冷剂在小型商用冷柜中大规模应用,需要做相应的泄漏燃爆实验。     

当前制冷剂替代品发展态势及我国制冷剂生产现状

我国是制冷剂生产和消费大国,目前制冷剂的替代已进入关键时期,如何有效地实现制冷剂的替代是我国制冷空调行业未来一段时期面临的严峻考验.本文介绍国际主要行业组织对制冷剂替代品评价和推荐情况,并概述我国制冷剂的生产及新一代制冷剂替代品的研发情况.     

新型混合制冷剂替代R12的性能研究

介绍了一种新型混合制冷剂的性能研究结果.这种新型混合制冷剂对臭氧层没有破坏作用,而且具有极低的全球变暖潜能值.研究结果表明,与R12相比,制冷量和输入功率均有所下降,但C0P值上升,压缩机的效率提高,寿命试验表明采用该制冷剂的压缩机具有良好的可靠性.     

工商制冷设备可燃性制冷剂相关安全标准的研究动态

简述了现有各类可燃性制冷剂相关安全标准,着重介绍了与工商制冷设备相关的可燃性制冷剂标准,分析并比较了这些标准中制冷剂命名、安全性分类以及制冷系统安全要求等差异,以期为制修订我国工商制冷空调设备使用可燃性制冷剂标准提供技术支持。     

易燃易爆商品安全管理现状及标准化初探

易燃易爆商品与我们的生活息息相关,且具有一定的火灾危险性.本文从人们日常使用的易燃易爆商品的概念、分类和火灾危险性入手,分析了当前易燃易爆商品安全管理的现状和存在的问题,并从通用名词术语和分类、火灾危险性分级、安全标签技术要求、安全管理标准等方面进行了标准化研究,为进一步加强人们对易燃易爆商品的安全意识以及商场超市安全地储存、经营易燃易爆商品提供了依据.     

Off-site ignition probability of flammable gases

A key step in the assessment of risk for installations where flammable liquids or gases are stored is the estimation of ignition probability. A review of current modelling and data confirmed that ignition probability values used in risk analyses tend to be based on extrapolation of limited incident data or, in many cases, on the judgement of those conducting the safety assessment. Existing models tend to assume that ignition probability is a function of release rate (or flammable gas cloud size) alone and they do not consider location, density or type of ignition source. An alternative mathematical framework for calculating ignition probability is outlined in which the approach used is to model the distribution of likely ignition sources and to calculate ignition probability by considering whether the flammable gas cloud will reach these sources. Data are collated on the properties of ignition sources within three generic land-use types: industrial, urban and rural. These data are then incorporated into a working model for ignition probability in a form capable of being implemented within risk analysis models. The sensitivity of the model results to assumptions made in deriving the ignition source properties is discussed and the model is compared with other available ignition probability methods.     

易燃易爆材料干式粉碎设备的研究

介绍了国内外有关易燃易爆干式粉碎四种类型设备,分析了各种类型设备的优缺点.重点研究了易燃易爆金属材料及无机材料进行超细化、或合金化、或超细与片状化的超细粉碎设备.研究表明了双(反)向旋转球磨粉碎机粉碎效果最好.由于内部设有高速反向连续搅拌装置,使沉积于底部并相互粘结、结块的粉体被打散,因而大大提高了对粉体的分散效果,有效地防止了粉体的团聚与反粉碎.因而可以在干燥状态下获得颗粒更细,分散性良好的干粉体.     

Interaction coefficients for 15 mixtures of flammable and non-flammable components

Bubble pressures were measured for 15 binary mixtures, each composed mainly of one flammable and one non-flammable component. The mixtures were trichlorofluoromethane + isopentane, pentafluoroethane + 1,1,1-trifluoroethane, 1,1-dichloro-2,2,2-trifluoroethane+{1,1-dichloro-1-fluoroethane or isopentane}, 1,1,1,2-tetrafluoroethane+{1,1-difluoroethane or propane or cyclopropane or isobutane}, difluoromethane +{pentafluoroethane or 1,1,1,2-tetrafluoroethane or 1,1-difluoroethane}. Also studied were mixtures of 1,1-difluoroethane+{cyclopropane or propane or butane or isobutane}, which comprise two flammable components. The measurements were made at approximately equimolar compositions using either a vapour-liquid equilibrium apparatus over a range of temperatures, or a static pressure measurement at 273.15K. The bubble pressures were used to determine interaction coefficients that characterize the non-ideal behaviour of these fluid mixtures. The interaction coefficients are used in equation-of-state models for the thermodynamic properties of refrigerant mixtures.     

Condensation heat transfer coefficients of flammable refrigerants

In this study, external condensation heat transfer coefficients (HTCs) of six flammable refrigerants of propylene (R1270), propane (R290), isobutane (R600a), butane (R600), dimethylether (RE170), and HFC32 were measured at the vapor temperature of 39 °C on a plain tube of 19.0 mm outside diameter with a wall subcooling of 3–8 °C under a heat flux of 7–23 kW m⁻². Test results showed a typical trend that external condensation HTCs decrease with the wall subcooling. No unusual behavior or phenomenon was observed for these flammable refrigerants during experiments. HFC32 and DME showed 28–44% higher HTCs than those of HCFC22 due to their excellent thermophysical properties. Propylene and butane showed the similar HTCs as those of HCFC22 while propane and isobutane showed 9% lower HTCs than those of HCFC22. Finally, a general correlation was made by modifying Nusselt's equation based upon the measured data of eleven fluids of various vapor pressures including halogenated refrigerants. The general equation showed an excellent agreement with all data exhibiting a deviation of less than 3%.     

Theoretical calculation of heat of formation and heat of combustion for several flammable gases

Heats of formation have been calculated by the Gaussian-2 (G2) and/or G2MP2 method for a number of flammable gases. As a result, it has been found that the calculated heat of formation for compounds containing, such atoms as fluorine and chlorine tends to deviate from the observed values more than calculations for other molecules do. A simple atom additivity correction (AAC) has been found effective to improve the quality of the heat of formation calculation from the G2 and G2MP2 theories for these molecules. The values of heat of formation thus obtained have been used to calculate the heat of combustion and related constants for evaluating the combustion hazard of flammable gases.     

A risk-based approach to flammable gas detector spacing

Flammable gas detectors allow an operating company to address leaks before they become serious, by automatically alarming and by initiating isolation and safe venting. Without effective gas detection, there is very limited defense against a flammable gas leak developing into a fire or explosion that could cause loss of life or escalate to cascading failures of nearby vessels, piping, and equipment. While it is commonly recognized that some gas detectors are needed in a process plant containing flammable gas or volatile liquids, there is usually a question of how many are needed. The areas that need protection can be determined by dispersion modeling from potential leak sites. Within the areas that must be protected, the spacing of detectors (or alternatively, number of detectors) should be based on risk. Detector design can be characterized by spacing criteria, which is convenient for design - or alternatively by number of detectors, which is convenient for cost reporting. The factors that influence the risk are site-specific, including process conditions, chemical composition, number of potential leak sites, piping design standards, arrangement of plant equipment and structures, design of isolation and depressurization systems, and frequency of detector testing. Site-specific factors such as those just mentioned affect the size of flammable gas cloud that must be detected (within a specified probability) by the gas detection system. A probability of detection must be specified that gives a design with a tolerable risk of fires and explosions. To determine the optimum spacing of detectors, it is important to consider the probability that a detector will fail at some time and be inoperative until replaced or repaired. A cost-effective approach is based on the combined risk from a representative selection of leakage scenarios, rather than a worst-case evaluation. This means that probability and severity of leak consequences must be evaluated together. In marine and offshore facilities, it is conventional to use computational fluid dynamics (CFD) modeling to determine the size of a flammable cloud that would result from a specific leak scenario. Simpler modeling methods can be used, but the results are not very accurate in the region near the release, especially where flow obstructions are present. The results from CFD analyses on several leak scenarios can be plotted to determine the size of a flammable cloud that could result in an explosion that would generate overpressure exceeding the strength of the mechanical design of the plant. A cloud of this size has the potential to produce a blast pressure or flying debris capable of causing a fatality or subsequent damage to vessels or piping containing hazardous material. In cases where the leak results in a fire, rather than explosion, CFD or other modeling methods can estimate the size of a leak that would cause a fire resulting in subsequent damage to the facility, or would prevent the safe escape of personnel. The gas detector system must be capable of detecting a gas release or vapor cloud, and initiating action to prevent the leak from reaching a size that could cause injury or severe damage upon ignition.     

Total flammable mass and volume within a vapor cloud produced by a continuous fuel-gas or volatile liquid-fuel release

The top-hat jet/plume model has recently been employed to obtain simple closed-form expressions for the mass of fuel in the flammable region of a vapor "cloud" produced by an axisymmetric (round) continuous-turbulent jet having positive or negative buoyancy [1]. The fuel release may be a gas or a volatile liquid. In this paper, the top-hat analysis is extended to obtain closed-form approximate expressions for the total mass (fuel+entrained air) and volume of the flammable region of a release cloud produced by either a round or a plane (two-dimensional) buoyant jet. These expressions lead to predicted average fuel concentrations in the flammable regions of the release clouds which, when compared with the stoichiometric concentration, serve as indicators of the potential severity of release cloud explosions. For a fixed release mass, the combustion overpressure following ignition of a hydrogen/air cloud is anticipated to be significantly lower than that due to ignition of a hydrocarbon/air cloud. The predicted average hydrogen concentration within the flammable region of the release cloud is below the lower detonability limit. The facility with which the expressions can be used for predictions of combustion overpressures is illustrated for propane releases and deflagrations in a closed compartment.