Development of heat transfer and evaporation model of LNG covered by Hi-Ex foam

Natural gas is a kind of clean, efficient green energy source, which is used widely. Liquefied natural gas (LNG) is produced by cooling natural gas to −161 °C, at which it becomes the liquid. Once LNG was released, fire or explosion would happen when ignition source existed nearby. The high expansion foam (Hi-Ex foam) is believed to quickly blanket on the top of LNG spillage pool and warm the LNG vapor to lower the vapor cloud density at the ground level and raising vapor buoyancy. To identify the physical structure after it contacted with LN₂ and to develop heat transfer model, the small-scale field test with liquid nitrogen (LN₂) was designed. In experiment, three layers including frozen ice layer, frozen Hi-Ex layer and soft layer of Hi-Ex foam were observed at the steady state. By characterizing physical structure of the foam, formulas for calculating the surface of single foam bubble and counting foam film thickness were deduced. The micro heat transfer and evaporation model between cryogenic liquid and Hi-Ex foam was established. Indicating the physical structure of the frozen ice layer, there were a certain number of icicles below it. The heat transfer and evaporation mathematical model between the frozen ice layer and LNG was derived. Combining models above with the heat transfer between LNG, ground and cofferdam, the heat transfer and evaporation mathematical model of LNG covered by Hi-Ex foam was developed eventually. Finally, LN₂ evaporation rate calculated by this model was compared with the measured evaporation rate. The calculated results are 1.2–2.1 times of experimental results, which were acceptable in engineering and proved the model was reliable.     

Pool evaporation: Experimental tests at medium-scale with gasoline

Pool evaporation is a major source of flammable vapour clouds. Predicting the evaporation rate of a liquid hydrocarbon pool is therefore a key issue of dispersion modelling for safety concerns. This paper presents small- and medium-scale experiments of pool evaporation carried out with liquid hydrocarbons (pentane, heptane), hydrocarbon “gasoline-like” mixtures and gasoline. Liquid mass loss was measured and the evaporation rate deduced with its evolution in time. Other observations are highlighted, regarding the evolution of liquid temperatures, mixture compositions, and scale effects like the influence of pool length on surface evaporation rate. Comparisons with well-known correlations are then shown. The authors finally suggest a new semi-empirical correlation with a set of parameters fitted on the performed experiments.     

蒸发-固化法处理垃圾渗滤液反渗透浓缩液的研究

采用蒸发-固化工艺处理垃圾渗滤液反渗透浓缩液。蒸发工艺可将反渗透浓缩液减量化,固化工艺可将蒸发残留液中的污染物稳定化。研究表明,蒸发残留液宜采用水泥和石灰混合料进行固化,混合料最佳水泥与石灰质量比约为1︰2,每100 mL蒸发残留液(质量约为120 g)最佳投加量为50 g。固化体含水率低于40%,抗压强度高于1.0 MPa,适合填埋处置,其浸出液污染物含量较低。采用硅酸钠和硫酸钙作为添加剂可加快固化速度,提高固化体的抗压强度。利用蒸发-固化工艺处理反渗透浓缩液可取得良好的经济和社会效益。     

高温热表面油液蒸发的时变性热质传递模型与实验研究

针对高温热表面油液蒸发热质传递过程的时变性,考虑这一过程中的对流传质传热,建立了热环境作用下油液蒸发的热质传递模型方程,通过无量纲变换,求得空间浓度分布和温度场随时间的变化规律。以庚烷为试验对象,对高温热表面油液蒸发过程进行了实验研究。理论分析与实验表明:庚烷蒸发过程中,刘易斯数大于1,传热速率大于传质速率;蒸发导致的质量损失与时间平方根的成正比,与液面的面积成正比,且与质量扩散系数的平方根成正比,饱和蒸气浓度越大,蒸发速率也越大。油液蒸发计算结果与试验结果基本一致,表明了模型的有效性。     

Graphical strategies for design of evaporation crystallization networks for environmental wastewater applications

This paper introduces graphical strategies for the design of an evaporation/crystallization network for ternary wastewater environmental applications. Sources, sinks and other streams are located on a ternary composition diagram. While a source is any wastewater stream that has the potential to be recycled, a sink is any unit in the process that can accept sources. The proposed methodology is extremely simple to understand and implement, as it only requires basic solid-liquid phase equilibria data and uses lever arm principles to generate alternative process designs. Geometric constructions are carried out on the ternary composition diagram and the respective lever arms are used to determine intermediate flow rates in the evaporation/crystallization network. The relative locations and flow rates of the sources and sinks under consideration, as well as the unique shape of the solid-liquid equilibrium, drive the design of the separation (via evaporation/crystallization) network. Some generic structures are proposed for a typical evaporation and crystallization network. Once the general problem statement has been defined, special cases consisting of a single source-single sink, single source-two sinks and two sources-single sink are described. These special cases are representative of commonly occurring industrial wastewater design problems. Several graphical insights are listed that allow one to represent evaporation and crystallization operations on a ternary triangular composition diagram and avoid mathematical complexity. The possibility of bypassing a part of the initial feed streams is also considered. Certain feasible composition regions are identified on the ternary composition diagram for cases dealing with multiple sources and sinks. The methodology is useful in pre-screening and eliminating certain sources/sinks and is readily applicable to cases with lower number of sources and sinks. A case study involving the ammonium nitrate manufacturing process is included to demonstrate the broad applicability and value of the proposed approach.     

Emissions of volatile hydrocarbons from floating roof tanks and their local dispersion: Considerations for normal operation and in case of damage

This work investigates the release and dispersion of volatile organic hydrocarbons, which may escape from external floating roof tanks (EFRT) during normal operation or in case of damage. The dispersion will be described using CFD simulations in close range of the EFRT where hazardous areas are assigned. The aim of this work is to investigate which events can lead to emissions in dangerous quantities and to estimate the corresponding likelihood with regard to explosion protection. An emission in hazardous amount is present if the lower explosion limit has been exceeded and if the extent of this emission is not too low. It is discussed in particular whether the used zoning of potentially explosive areas is conservative or over-conservative.     

The effect of turbulence on the rate of evaporation of LNG on water

The present study provides new measurements of the rate of evaporation of cryogenic liquids, liquefied natural gas (LNG) and liquid nitrogen (LN₂), floating on a water surface with different levels of turbulence intensity. The turbulent water surface is generated with an upward-pointing submerged jet with controlled jet velocity, an approach which has often been used in studies of free-surface turbulence. Direct measurements of the rate of evaporation were carried out for different pool thicknesses and turbulence intensities of the water surface. These tests reveal a strong dependence of the evaporation rate on the turbulence intensity, as well as a dependence on the thickness of the cryogenic liquid layer above the water surface. Models of LNG spills on water currently use a single rate of evaporation; these findings show that this approach is inadequate. Future models should incorporate the water turbulence intensity, and possibly the LNG spill thickness for improved accuracy.     

Investigation of oil vapor emission and its evaluation methods

In oil operations such as storage, loading, and unloading, there are many chances for oil vapor to be emitted from tanks, tankers or truck tanks into the air. Oil vapor emission (OVE), having serious harmful effects on people and the environment, is always an important research topic for scientists, engineers or managers engaged in the fields of oil production and transportation, fire prevention, and environmental protection. As the second greatest oil consuming country in the world, China has particular interests in investigating ways to better methods to realize and then control the OVE. In this paper, three evaluation methods for the OVE are introduced and summed up. In particular, a set of self-founded OVE’s appraisement methods, which work by theoretical deduced equations integrated with both a software PELES-2.0 and a simple correction method, was systematically investigated. This appraisement system can conveniently and accurately be applied to evaluate the OVE, and further it can also provide base references and/or guides for the law makers, enterprise managers and equipment developers in controlling OVEs.     

Experimental study of the evaporation of spreading liquid nitrogen

The investigation of cryogenic liquid pool spreading is an essential procedure to assess the hazard of cryogenic liquid usage. There is a wide range of models used to describe the spreading of a cryogenic liquid pool. Many of these models require the evaporation velocity, which has to be determined experimentally because the heat transfer process between the liquid pool and the surroundings is too complicated to be modeled. In this experimental study, to measure the evaporation velocity when the pool is spreading, liquid nitrogen was continuously released onto unconfined concrete ground. Almost all of the reported results are based on a non-spreading pool in which cryogenic liquid is instantaneously poured onto bounded ground for a very short period of time. For the precise measurement of pool spreading and evaporation weight with time, a cone-type funnel was designed to achieve a nearly constant liquid nitrogen release rate during discharge. Specifically, three nozzles with nominal flow rates of 3.4 × 10⁻² kg/s, 5.6 × 10⁻² kg/s and 9.0 × 10⁻² kg/s were used to investigate the effect of the release rate on the evaporation velocity. It is noted that information about the release rate is not necessary to measure the evaporation velocity in case of the non-spreading pool. A simultaneous measurement of the pool location using thermocouples and of the pool mass using a digital balance was carried out to measure the evaporation velocity and the pool radius. A greater release flow rate was found to result in a greater average evaporation velocity, and the evaporation velocity decreased with the spreading time and the pool radius.     

膜分离技术在油气回收中的应用

在油品储运、销售、应用过程中，存在着大量的油品蒸发损耗。可用膜分离技术来分离回收轻质油品蒸发排放出来的油气。介绍膜法油气回收的分离机理、应用实例和工艺设计数据，综合比较常用的吸收法、吸附法、冷凝法及膜法油气回收技术并获得各自的量化分值，认为膜法回收技术为目前较有可能及较容易取得突破成果的研究领域。最后指出今后的研究重点。