Retrofit for a gas separation plant by pinch technology

Abstract

This study focuses on a retrofit applying pinch technology to the PTT (Thailand) gas separation plant 5. The prime objective is to maximize the energy recovery of the process via several tools including Problem Table Algorithm (PTA), Grand Composite Curve (GCC), Grid Diagram, and Column Grand Composite Curve (CGCC). The entire provess under study consists of two main parts; the distillation columns (the demethanizer, the deethanizer, and the depropanizer) and the heat exchanger networks (HENs). There are thirteen hot and six cold streams with fourteen heat exchangers in the HENs part. The current network is an unpinch process (or low temperature process) with Tmin lower than the threshold Tmin of 21C and the existing Tmin is observed of around 1.06C. The CGCCs of the deethanizer and the depropanizer reveal the scope of energy recovery via a side reboiling and a feed preheating, respectively. For the side reboiling of the deethanizer, the energy savings can be achieved by integrating hot process streams of the background process to the column. Six modification options (A, B, C, D, E, and F) for the gas separation plant were offered to reduce the energy consumption. The maximum energy savings can be obtained at approximately 11.69 MW or 13.32% from option F. This reduces the annual energy cost about 6.1 million US/yr. In order to achieve it, a capital investment is inecessary but the annual cost savings will be enough to recover the cost in less than one year.