Exergy, Economic, and Life-Cycle Assessment of ORC System for Waste Heat Recovery in a Natural Gas Internal Combustion Engine

Guillermo Valencia Ochoa,Jorge Duarte Forero,Javier Cárdenas Gutierrez

doi:10.3390/resources9010002

Abstract

In this article, an organic Rankine cycle (ORC) was integrated into a 2-MW natural gas engine to evaluate the possibility of generating electricity by recovering the engine’s exhaust heat. The operational and design variables with the greatest influence on the energy, economic, and environmental performance of the system were analyzed. Likewise, the components with greater exergy destruction were identified through the variety of different operating parameters. From the parametric results, it was found that the evaporation pressure has the greatest influence on the destruction of exergy. The highest fraction of exergy was obtained for the Shell and tube heat exchanger (ITC1) with 38% of the total exergy destruction of the system. It was also determined that the high value of the heat transfer area increases its acquisition costs and the levelized cost of energy (LCOE) of the thermal system. Therefore, these systems must have a turbine technology with an efficiency not exceeding 90% because, from this value, the LCOE of the system surpasses the LCOE of a gas turbine. Lastly, a life cycle analysis (LCA) was developed on the system operating under the selected organic working fluids. It was found that the component with the greatest environmental impact was the turbine, which reached a maximum value of 3013.65 Pts when the material was aluminum. Acetone was used as the organic working fluid.

Highlights

Due to the large consumption of coal, oil, natural gas, and other fossil fuels, energy production is increasingly unusual
This study found that substituting working fluids such as R245fa and R134a with low Global Warming Potentials (GWP) fluids such as R1233zd and
In the case of the increase of the condensing temperature from 55 ◦ C to 65 ◦ C, as shown in Figure 5b, there is an increase of the pinch point temperature in the condenser since the temperature of the cooling water is constant. This causes the heat transfer irreversibilities in the condenser to increase and, with it, the fraction of exergy destruction, which moves from 25% to 30%, while the exergy destruction in the evaporator decreases by 2.67% since the source temperature is limited by considerations of thermal stability of the thermal oil

Summary

Introduction

Due to the large consumption of coal, oil, natural gas, and other fossil fuels, energy production is increasingly unusual. The sustainability goal as well as the environmental and energy analysis had been conducted by some researchers in waste heat recovery systems based on ORC to convert the energy from renewable sources such as biofuels, biomass, solar energy, and geothermal values to electric energy [2]. One way to improve energy efficiency and potentially reduce pollution is by applying ORC technology as waste heat recovery devices [3,4]. Organic Rankine cycles (ORC) are an effective way of converting medium-low temperature heat into electricity that cannot be used for conventional high-temperature Rankine cycles, even though many studies have been conducted in recent decades. The use of ORC as an alternative to waste heat recovery has received relatively little industrial attention [5,6,7,8,9]

Methods

Results

Conclusion