Economic Recovery of Low Value Stack Heat using Organic and Rankine Cycle Technology

Abstract

Demand of energy is increasing day by day while the resources used to generate this energy are limited. A major portion of the energy produced in the world is used by industrial sector. Major portion of this energy is lost in the form of waste heat streams that are at low temperature. Conventional waste heat recovery systems are not capable of recovering heat from these low temperature streams. This project assigned by Fauji Fertilizer Company aims to recover heat from stack gases of Primary Reformer Section at Ammonia Plant. Organic Rankine Cycle and Ammonia Rankine Cycle provide two solutions for recovering heat at low temperature efficiently. The temperature of the stack gases leaving the Primary reformer are at 260°C. Organic Rankine Cycle uses a low boiling working fluid that boils easily at low temperature making heat recovery system more efficient as compared to ordinary Steam Rankine cycle. Ammonia Rankine Cycle uses a solution of Ammonia and Water as working fluid. Both ORC and ARC technology are efficient but the operating parameters of these technologies are different. After analysing both cycles it was found that ORC with refrigerant R113 was most efficient. Depending upon refrigerant, 1787 kW energy could be recovered from the cycle. Economic analysis was performed and it was found that ORC based system was more economical.