Optimal Operation of Hydro-Olefin based Dual Mixed Refrigerant Lng Process

Abstract

With the increase in pollution level and increasing awareness of environmental concerns, the demand for clean energy production is also increasing. Currently, easiest and cheapest way to produce energy is from fossil fuels. However, their widespread usage is associated with many deleterious environmental consequences. Development and progression in non polluting, clean energy resources is vital not only for fulfilling increasing demand for clean energy but also for reducing pollution level caused by coal and liquid fuels. CO2 emission from coal and petroleum based liquid fuels is greater as compared to Natural Gas (NG). Therefore, NG is considered as environmentally and ecofriendly fossil fuel. But there is a mismatch in the location of natural gas reserves and end users; and is transported by pipelines within a country/region. However, the transportation method is not suitable for long distances due to high operational costs and geographic barriers. Therefore, transportation is carried out in liquid form. Liquefaction of NG is an energy demanding process. Different methods are used to convert NG into liquefied NG including single MR, dual MR process, N2-expander. All these methods have their own advantages and disadvantages. Selection of the process also depends on the location of reserves, whether onshore or offshore. The main theme behind the improvement in these technologies lies in the process thermodynamic efficiency. The process with more thermodynamic efficiency will be chosen. Among all the processes, Dual Mixed Refrigerant (DMR) has higher efficiency, however, it is a complex method with many design variables and mixed compositions of the refrigerants. Different researchers have worked on DMR process. In DMR process different loops with mixed refrigerants are used for NG liquefaction. The process of DMR is designed with Aspen HYSYS and optimization on the process is applied. Then the results are compared with the result of the process after doing optimization. The comparison represents that there is savings in energy and the efficiency of the process is increased. The key objective is to optimize DMR process by selecting optimal amounts of the refrigerants in Cold and warm loops; and the design variables to enhance thermodynamic efficiency. The efficiency improves when cold and hot xv composites curves matches better in LNG exchangers and entropy is reduced. In this work, an innovative hydro-fluoroolefin (HFO-1234yf) based MR is proposed by changing the composition to liquefy NG in an eco-friendly and energy-efficient manner with the lot of advantages, i.e. zero ozone depletion and minimal global warming potential. A cycle for liquefaction utilizing the HFO based MR is developed to fully gain its potential. The newly proposed composition of HFO based MR system gives an advanced solution/results to enhance ecological aspects and increase the process efficiency of liquefaction