Energy and exergy recovery from exhaust hot water using organic Rankine cycle and a retrofitted configuration

工业过程中广泛存在着余热水,依附于余热水的热量经常被忽略而排放到环境中,造成了热量的散失和环境的污染。有机朗肯循环是一项从低温热载体中回收热量的技术,本文利用有机朗肯循环回收依附于余热水的热量。为了考察余热水的热回收和(火用)回收效果,建立数学模型并进行参数研究。以R245fa、R113和R123为工质,模拟余热水驱动的有机朗肯循环系统的热效率和(火用)效率。结果表明,余热水温度和蒸发温度对余热水驱动的有机朗肯循环系统的热效率和(火用)效率影响较大。在一定的余热水参数下,有一个对应于最高(火用)效率的最佳蒸发温度。为了对低温余热水进行深度回收,建立了一个联合闪蒸与有机朗肯循环的改进结构。对于本研究中的120°C和0.2 MPa的余热水,当闪蒸压力为0.088 MPa时,闪蒸–有机朗肯联合循环系统的最大(火用)效率为45.91%。余热水驱动的闪蒸–有机朗肯联合循环系统的(火用)效率优于纯闪蒸系统和简单朗肯循环系统。

Exhaust hot water （EHW） is widely used for various industrial processes. However, the excess heat carried by EHW is typically ignored and discharged into the environment, resulting in heat loss and heat pollution. An organic Rankine cycle （ORC） is an attractive technology to recycle heat from low-temperature energy carriers. Herein, ORC was used to recycle the heat carried by EHW. To investigate the energy and exergy recovery effects of EHW, a mathematical model was developed and a parametric study was conducted. The energy efficiency and exergy efficiency of the EHW-driven ORC system were modeled with R245fa, Rl13 and R123 as the working fluids. The results demonstrate that the EHW and evaporation temperatures have significant effects on the energy and exergy efficiencies of the EHW-driven ORC system. Under given EHW conditions, an optimum evaporation temperature exists corresponding to the highest exergy efficiency. To further use the low-temperature EHW, a configuration retrofitted to the ORC by combining with flash evaporation （FE） was conducted. For an EHW at 120 ~C and 0.2 MPa, the maximum exergy efficiency of the FE-ORC system is 45.91% at a flash pressure of 0.088 MPa. The FE-ORC performs better in exergy efficiency than the basic FE and basic EHW-driven ORC.