Experimental study of two cascaded organic Rankine cycles with varying working fluids

Abbas Wameedh Khider Abbas; Linnemann Matthias; Baumhoegger Elmar; Vrabec Jadran

摘要

Organic Rankine cycles convert low-temperature heat from different sources, like solar, geothermal or biomass, into electricity and may thus help to meet the energy demand in an environmentally friendly way. While single ORC systems have been studied extensively, there are only very few experimental works on systems consisting of two cascaded organic Rankine cycles (two-ORC). In this work, an experimental study is carried out on the performance of a two-ORC system that consists of a high temperature (HT) cycle and a low temperature (LT) cycle. Each cycle is composed of the four significant components, i.e. expander, evaporator, condenser and pump, while the LT cycle is equipped with a throttle as expansion device. The HT cycle utilized heat from electrical heaters, while the LT cycle was driven by the waste heat from the HT cycle. The test rig utilizes Therminol 66 as a source that is heated up by electrical heaters with a power of 158 kW. Propane, butane, pentane and cyclopentane are chosen as working fluids for the present experiments. Parameter variations are carried out to study the thermodynamic characteristics of each cycle. The aim is to investigate the HT cycle performance considering turbine power output, thermal efficiency and exergy efficiency. The effect of the HT cycle on the LT cycle is examined by studying the heat transfer rate between the two cycles, characteristics of heat exchangers and pinch point temperature difference. A further goal is to explore the system performance under different conditions to maximize the exergetic utilization of the heat source. The results confirm that turbine power output and thermal efficiency increase with heat source temperature and turbine inlet pressure in the HT cycle. The maximum achieved thermal and exergy efficiencies are 5.5% and 20.2%, respectively, while the maximum turbine power output is 4.92 kW. Heat transfer measurements show that the maximum transferred heat flow from the HT cycle to the LT cycle is 23 kW when pentane is used as a working fluid. Temperature profiles and the pinch point temperature difference in the heat exchangers of both cycles are assessed under conditions where the highest turbine power is obtained. The experimental tests are promising and show that the two-ORC system is suitable to utilize heat sources in various temperature ranges.

机译：有机朗肯循环将低温热从不同来源，如太阳能，地热或生物量，进入电力，因此有助于以环保方式满足能源需求。虽然已经广泛研究了单副兽人系统，但在由两个级联的有机朗肯循环组成的系统上只有很少的实验工作，而是由两个级联的有机朗肯循环（两奥官）。在这项工作中，对两个兽人系统的性能进行了实验研究，该系统由高温（HT）循环和低温（LT）循环组成。每个循环由四个有效部件组成，即膨胀机，蒸发器，冷凝器和泵，而LT循环配有油门作为膨胀装置。 HT周期利用来自电加热器的热量，而LT循环由来自HT循环的废热驱动。试验台利用热量66作为电源加热的电源，电加热器具有158 kW。选择丙烷，丁烷，戊烷和环戊烷作为本实验的工作流体。执行参数变型以研究每个循环的热力学特性。目的是考虑涡轮机功率输出，热效率和高效率的HT循环性能。通过研究两个循环，热交换器特性和夹点温差之间的传热速率来检查HT周期对LT循环的影响。另一个目标是在不同条件下探讨系统性能，以最大限度地提高热源的横向利用。结果证实，涡轮机功率输出和热效率随HT周期中的热源温度和涡轮机入口压力而增加。最大达到的热和漏水效率分别为5.5％和20.2％，而最大涡轮功率输出为4.92千瓦。传热测量表明，当戊烷用作工作流体时，来自HT循环到LT循环的最大转移热流是23kW。在获得最高涡轮机动力的条件下评估两个循环的热交换器中的温度曲线和夹点温度差。实验测试是有前途的，并且表明两兽兽态系统适合于在各种温度范围内使用热源。

Experimental study of two cascaded organic Rankine cycles with varying working fluids

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