Modeling and optimization of finless and finned tube heat recovery steam generators for cogeneration plants

Abstract

This article aims to model and optimize the fire tube Heat Recovery Steam Generator (HRSG) used in a gas microturbine cogeneration of heat and power system. Here, six cases including a finless and finned tube (solid and serrated) HRSGs with the inline and staggered arrangements are optimized and compared using techno-economic assessment. Optimization of HRSG was carried out by applying two objective functions of minimizing the total annual cost as well as maximizing the exergy efficiency. Nondominated Sorting Genetic Algorithm II is used to find out the optimal values of design variables. The TOPSIS decision-making process is employed to choose the optimum point of the Pareto front. A 600 kW gas microturbine cogeneration plant is considered as a case study. The results revealed that the finless tube HRSG with an inline arrangement has the lower pinch and approach temperatures (3.5 • C and 3.1 • C, respectively), the higher steam mass flow rate (12.7%), the lower total annual cost (64 096$/year), and the higher exergy efficiency (60.6%). It is also found that using the staggered arrangement tube banks along with the solid fins in HRSG leads the total annual cost, the steam mass flow rate, and exergy efficiency increase up to 41.6%, 100%, and 12.6%, respectively. This means that the thermodynamic performance improvement will compensate the total annual cost increment. Furthermore, it is demonstrated that HRSG with solid fins and staggered arrangement with total annual costs of (90 810$/year), exergy efficiency of (73.2%), and steam mass flow rate of (4680 kg/h) has the best performance in comparison with other finned tube cases. K E Y W O R D S cogeneration of heat and power systems, gas microturbine, genetic algorithm, heat recovery steam generator, inline and staggered arrangement, multiobjective optimization 1 INTRODUCTION In combined heat and power (CHP) systems, the prime mover waste heat is recovered to produce hot water/steam for heating or power generation. Heat recovery along with power generation, increases the efficiency of CHP systems up to This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.