Abstract:

The utilization of natural gas in marginal reservoirs is a great challenge and opportunity in China.A small-scale LNG plant in skid-mount packages is an economical method instead of pipe lines or a conventional plant.But with small and compact structure,clogging problem always occurs in the heat exchanger(HE),owning to its narrow channels for heat transfer.But heat pipe(HP)can overcome this drawback with its inherent high heat transfer coefficient and nearly isothermality of the wall.Thus the heat pipe heat exchanger(HPHE)can be an alternative choice to replace the traditional plate-fin heat exchanger in small-scale LNG plants.In order to study the heat transfer performance of a HPHE in its different temperature zones,a module of a six-row HPs with fins was manufactured and tested under specific temperature,in which each row of the HPs were connected together to flatten the temperature in the cross section.The cryogenic heat pipes(thermosyphons)were respectively charged with propane,ethane and methane under low temperature to ensure the safety.Nitrogen gas with adjustable temperature(-100-295 K)was applied as the heat sink,while electrical heating films wounded around the evaporators were used as heat source.Thus the whole module can reach a stable state in a specified temperature zone with the cooperation of the heat sink and heat source.Temperature distribution along each row of HPs was measured under stable states,while the temperature of nitrogen gas was recorded at the same time.The result shows that the whole effectiveness of the 414-row HPHE can reach to 99.68%,as the average effectiveness of each row in all the modules is about 43.28%,under a heat flux of 860 W·m^-2,which equals the thermal load of a small-scale LNG process with a flow rate of 50000 m³·d^-1.It is also identified that heat can be transferred very fast from the cold point to other area in the cross section of HPHE,with this characteristic the HPHE can prevent its channels from clogging when the working condition changes sharply.

Key words: cryogenic heat pipe, liquefied natural gas(LNG), heat exchanger, freeze out

摘要：

撬装式液化天然气(LNG)流程要求设备紧凑,而传统换热器在减小其换热通道尺寸时会产生冻堵问题。热管极高的传热系数和良好的温度均一性,可以有效克服这种缺陷。根据小型天然气液化流程参数,设计制造了低温工质(丙烷、乙烷、甲烷等)重力热管换热器模块。实验结果显示,低温热管换热器在热通量为860 W·m^-2时,每排热管的平均换热效率为43.28%,414排热管换热器总体换热效率可达到99.68%,换热量满足小型LNG液化流程50000 m³·d^-1的处理量要求。并且在工况突变时,能够迅速将局部冷量均匀分布至所在迎风截面,防止高凝固点的杂质在通道内冻堵。

关键词: 低温重力热管, 液化天然气(LNG), 换热器, 冻堵