混合制冷剂制冷工艺在石油伴生气液化上的应用

小型天然气液化装置的制冷循环以带膨胀机的制冷循环和单级混合制冷剂循环为主,目前随着单级混合制冷剂流程研究的深入和使用的增多,装置越来越简单,投资越来越少,相对于膨胀循环流程的劣势很小,而能耗比膨胀循环更是要低40%左右,可有效降低系统的运行费用。石油伴生气的组份特点使得烃类制冷剂容易获得,应该优先采用单级混合制冷剂循环。在液化系统中设置分离塔,利用混合制冷剂本身就是混合物质的特点,不需要将各种冷剂提纯,就可以组合成多种冷剂配制方法,还可以根据不同的气源条件进行优化设计,解决了以往采用混合冷剂制冷循环的冷剂配比、采购、储运问题。     

单级混合制冷剂天然气液化流程动态特性模拟

研究天然气液化的工艺流程并进行模拟,对液化天然气装置的设计具有重要意义。本文运用AspenDynamics软件建立了单级混合制冷剂液化流程的动态模型,采用Peng—Rob状态方程计算工质的各热力学参数,动态过程的微分方程由欧拉隐式格式求解,在此基础上进行了动态模拟。原料天然气的各项参数发生变化时,所产生的扰动对整个液化系统的影响较小。通过调节入口天然气的流量,可使流程参数在较短时间内恢复到扰动前。     

天然气液化工艺的相平衡计算

天然气液化流程广泛采用的是丙烷预冷混合制冷剂液化流程.为了进一步优化流程,减少能源的消耗,需要对整个流程进行模拟,而模拟过程中热力学参数的计算便是整个流程计算的基础.使用两种状态方程（SRK和PR方程）对热力学参数进行相平衡计算,为后续计算焓、熵等参数提供相应的解决办法,并判断选择的状态方程是否符合要求.     

天然气物性的LKP方程求解

对于流程中的天然气和混合制冷剂,用LKP方程求解其焓熵等物性参数,对LKP方程的求解展开讨论,给出了一个收敛性极好的LKP方程求解方法,并计算了混合制冷剂天然气液化流程中天然气和混合制冷剂焓值与温度,压力和组分的关系,所给出的解法同样适用于其它类型的物质。     

液化天然气冷能回收发电的工艺流程模拟

根据勃雷登燃气动力循环和朗肯循环原理,提出一种液化天然气冷能回收发电的工艺流程,并利用ASPEN PLUS软件对该流程进行了模拟,获得了流程各物流的压力、温度、流量等状态参数,各热力过程的热功等过程参数,以及各循环热效率、总热效率等热力学性能参数,为建立高效的液化天然气冷能发电系统提供理论支持。     

边远油气田天然气回收利用流程模拟研究

针对边远地区油气田小气量天然气资源目前存在的回收难、效益低的问题,提出了一种采用N-CH4作为制冷剂,两级压缩的方式,可以实现小气量天然气的回收.通过对小型天然气液化装置流程模拟,分析和优化了各个节点的参数.该流程具有结构和操作简单、容易集成撬装化的优点.     

小型混合制冷剂天然气液化流程设计与分析

分析了IFP-Axens公司开发的混合制冷剂循环Liquefin工艺关键技术,在此基础上设计了一种全新的小型混合制冷剂液化流程。比较了三个流程的主要流程参数,综合分析了换热器冷热负荷曲线和温差曲线。结果表明,压缩机和换热器的损失是循环的主要损失,可以通过选用效率更高的压缩机,或者改变压缩系统结构减少损;提高返流轻组分节流后压力可有效降低换热温差,通过进一步优化制冷剂组成和运行压力,可使换热温差更加均匀,减少换热器损,提高流程的经济性。     

LKP方程在天然气相平衡计算中的应用

由于液化天然气(LNG)所具有的低温特性,其在储运中必然会发生相态的变化.目前,对于天然气相平衡的计算大多应用状态方程法,采用P-R方程和SRK方程进行计算.本文采用了LKP方程进行了气液相平衡的计算,通过与实验值的对比表明:应用LKP状态方程用于天然气及混合制冷剂的相平衡计算具有较好的精度,能够满足进一步天然气热物性...     

天然气/柴油双燃料发动机燃料喷射及着火特性

基于计算流体动力学(CFD)软件CONVERGE模拟了缸内高压直喷式柴油微引燃液化天然气(LNG)发动机的燃料喷射混合以及着火过程,校核和验证了湍流模型对模拟结果的影响,分析了天然气喷射正时、天然气喷射持续期及柴油与天然气射流中心轴线的夹角对缸内柴油和天然气射流发展、混合和着火的影响.结果表明:Smagorinsky大...     

生物质气化及其燃气的可替代性研究

文章采用下吸式固定床气化炉,对稻壳、麦秸和木屑3种典型生物质的气化过程进行了仿真模拟。通过对比可知,木屑原料的气化效果最好,稻壳次之。选取木屑为气化原料,得到了最佳工况下生物质气化气的体积分数和特性参数。利用A.G.A.多元指数法和德尔布法对生物质燃气进行互换性分析,结果表明,生物质燃气可以直接置换发生炉煤气,不能直接置换天然气、液化石油气、焦炉煤气和混合煤气。     

Design and analysis of liquefaction process for offshore associated gas resources

Liquefaction is the key section on floating platform. Some experts and designers selected mixed refrigerant process for floating platform, while some recommended expander cycle. However, few of them compared the two types of processes systemically before making a choice. In this paper, the liquefaction processes of propane pre-cooled mixed refrigerant cycle (C₃/MRC), mixed refrigerant cycle (MRC) and nitrogen expander cycle (N₂ expander) for the special offshore associated gases in South China Sea have been designed and studied. These processes have been analyzed and compared systematically considering the main factors including the performance parameters, economic performance, layout, sensitivity to motion, suitability to different gas resources, safety and operability, accounting for the features of the floating production, storage and offloading unit for liquefied natural gas (LNG-FPSO) in marine environment. The results indicated that N₂ expander has higher energy consumption and poorer economic performance, while it has much more advantages than C₃/MRC and MRC for offshore application because it is simpler and more compact and thus requiring less deck area, less sensitive to LNG-FPSO motion, has better suitability for other gas resources, has higher safety and is easier to operate. Therefore, N₂ expander is the most suitable offshore liquefaction process. In addition, the exergy analysis is conducted for N₂ expander and the results indicate that the compression equipments and after coolers, expanders and LNG heat exchangers are the main contribution to the total exergy losses. The measures to decrease the losses for these equipments are then discussed.     

Development of mobile miniature natural gas liquefiers

With increasing consumption of natural gas (NG), small NG reservoirs, such as coalbed methane and oil field associated gas, have recently drawn significant attention. Owing to their special characteristics (e.g., scattered distribution and small output), small-scale NG liquefiers are highly required. Similarly, the mixed refrigerant cycle (MRC) is suitable for small-scale liquefaction systems due to its moderate complexity and power consumption. In consideration of the above, this paper reviews the development of mobile miniature NG liquefiers in Technical Institute of Physics and Chemistry (TIPC), China. To effectively liquefy the scattered NG and overcome the drawbacks of existing technologies, three main improvements, i.e., low-pressure MRC process driven by oil-lubricated screw compressor, compact cold box with the new designed heat exchangers, and standardized equipment manufacturing and integrated process technology have been made. The development pattern of “rapid cluster application and flexible liquefaction center” has been eventually proposed. The small-scale NG liquefier developed by TIPC has reached a minimum liquefaction power consumption of about 0.35 kW·h/Nm³. It is suitable to exploit small remote gas reserves which can also be used in boil-off gas reliquefaction and distributed peak-shaving of pipe networks.     

Enhancement of APCI cycle efficiency with absorption chillers

Liquefied natural gas (LNG) plants consume a great amount of energy. In order to enhance the energy efficiency of the LNG plant, the potential energy efficiency enhancements of various options of utilizing the waste heat powered absorption chillers in the propane pre-cooled mixed refrigerant (APCI) liquefaction cycle were investigated in this study. After developing models of the LNG process, gas turbine and absorption chillers, eight options of gas turbine waste heat utilization were simulated. The simulation results show that by replacing 22 °C and 9 °C evaporators and cooling the condenser of propane cycle at 14 °C and inter-cooling the compressor of mixed refrigerant cycle with absorption chillers which are powered by waste heat from the gas turbine, both the compressor power and fuel consumption reduction can be achieved as much as 21.32%. This enhancement requires recovering at least 97% of gas turbine waste heat.     

Prediction of Refrigerant Gas Hydrates Formation Conditions

fat~ctionGas hydrates are solid clatbrate compounds that maybe formed when light hydrocwhons andlor some gasesand water come illtO contaCt under certain condihons oftemperatUre and pressure, In pAncular, hydrate Crystalscan form from fixtUres Of some gases, such as naturalgases (methane, ethane, PrOPane) and refugerants (CFCll, HFC-134a). Gas hydrates appear like ice, but theymay form at temperatore well above the ice-point.Refrigerant gas hydrates can be used for Phasechange materials …     

Refrigeration cycle for cryogenic separation of hydrogen from coke oven gas

Ten billion cubic meters of hydrogen are dissipated to the environment along with the emission of coke-oven gas every year in China. A novel cryogenic separation of hydrogen from coke oven gas is proposed to separate the hydrogen and liquefy it simultaneously, and the cooling capacity is supplied by two refrigeration cycles. The performance of the ideal vapor refrigeration cycle is analyzed with methane and nitrogen as refrigerant respectively. The results show that the coefficient of performance (COP) of methane refrigeration cycle is 2.7 times that of nitrogen refrigeration cycle, and the figure of merit (FOM) of methane refrigeration cycle is 1.6 times that of nitrogen refrigeration cycle. The performance of ideal gas refrigeration cycle is also analyzed with neon, hydrogen and helium as refrigerant respectively. The results show that both the coefficient of performance and figure of merit of neon refrigeration cycle is the highest. It is thermodynamically possible to arrange the refrigeration cycle with methane and neon as refrigerant, respectively. __________ Translated from Cryogenics and Superconductivity, 2007, 35(5): 387–390, 394 [译自: 低温与超导]     

The performance analysis of a two‐stage transcritical CO2 cooling cycle with various gas cooler pressures

A theoretical analysis of a two‐stage transcritical CO₂ cooling cycle is presented. The effect of a two‐stage cycle with intercooling process on the system coefficient of cooling performance is presented for various gas cooler pressures. However, the performance comparison between one‐stage and two‐stage cycles is presented for same operating conditions. Gas cooler pressure, compressor isentropic efficiency, gas cooler efficiency, intercooling quantity and refrigerant outlet temperature from the gas cooler are used as variable parameters in the analysis. It is concluded that the performance of the two‐stage transcritical CO₂ cycle is approximately 30% higher than that of the one‐stage transcritical CO₂ cycle. Hence, the two‐stage compression and intercooling processes can be assumed as valuable applications to improve the transcritical CO₂ cycle performance. Copyright © 2008 John Wiley & Sons, Ltd.     

Energy optimization for liquefaction process of natural gas in peak shaving plant

One of the most important sections in the gas peak shaving plant regarding the energy consumption is the liquefaction process of natural gas (NG). Thus, selection and development of this process with the lowest energy consumption, offer huge potential energy and cost benefits. Here, a single-stage mixed refrigerant (SMR) cryogenic cycle with two compression stages has been selected for producing Liquefied Natural Gas (LNG). Energy consumption of the process as an objective function is optimized by describing key variables of the design. The proposed process’s calculations of thermodynamic concepts and properties are applied in MATLAB software to generate the objective function; furthermore Genetic Algorithm (GA) is used as an optimization method. Concerning works done in this area, more key parameters – related directly to the objective function – are introduced in this paper. A low irreversibility is due to enhanced values of key parameters in the LNG heat exchanger observed under a low temperature difference between hot and cold composite curves. Finally, the exergy lost of equipments in the proposed process are evaluated and analyzed in details.     

Thermodynamic Analysis of Liquefied Natural Gas （LNG） Production Cycle in APCI Process

The appropriate production of liquefied natural gas(LNG)with least consuming energy and maximum efficiency is quite important.In this paper,LNG production cycle by means of APCI Process has been studied.Energy equilibrium equations and exergy equilibrium equations of each equipment in the APCI cycle were established.The equipments are described using rigorous thermodynamics and no significant simplification is assumed.Taken some operating parameters as key parameters,influences of these parameters on coefficient of performance(COP)and exergy efficiency of the cascading cycle were analyzed.The results indicate that COP and exergy efficiency will be improved with the increasing of the inlet pressure of MR(mixed refrigerant)compressors,the decreasing of the NG and MR after precooling process,outlet pressure of turbine,inlet temperature of MR compressor and NG temperature after cooling in main cryogenic heat exchanger(MCHE).The COP and exergy efficiency of the APCI cycle will be above 2% and 40%,respectively,after optimizing the key parameters.