Design and Control of Coal to Synthesis Natural Gas Process

Design and Control of Coal to Synthesis Natural Gas Process

Bor-Yi Yu¹, Ming-Lung Lee¹, Po-Hsien Lee¹, Yu-Lung Kao¹, Chung-Han Wu², Shih-En Hsu², Jeffrey D. Ward¹, Hao-Yeh Lee³, Yih-Hang Chen² and I-Lung Chien¹

1. Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan

2. Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan

3. Department of Chemical and Material Engineering, Tamkang University of Science and Technology, New Taipei City 25137, Taiwan

In this work, the steady state optimized process and the plantwide control structure of coal to synthesis natural gas (SNG) are developed. Natural gas has become one of the most important fuel candidates worldwide in pursuit of clean energy. In fact, above 90% of energy source in Taiwan, such as coal and natural gas, comes from imports. Before transportation, natural gas needs to be liquefied. This liquefied process results in a higher price of natural gas compared with that of coal. Therefore, our goal of this work is to develop a process that SNG can be produced from coal. The achievement of the goal is expected to be helpful for the energy supply and the industries in Taiwan.

SNG, which can be produced from coal or biomass, is mainly consisted of methane as well as other light hydrocarbons. It holds very similar composition to typical natural gas, and can be used as a replacement of natural gas in industries. The whole coal to SNG process can be divided into following main sub-process: air separation unit (ASU), gasification, sour water-gas shift reaction (SWGSR), acid gas removal (AGR), and methanation. Several key specifications for each sub-systems are stated as follows: The ASU sub-system will supply high-purity (>95 mol%) oxygen to gasifier. In AGR sub-system, 99.6% H₂S component and over 90% CO2 are captured to reach the environmental regulation. In methanation process, the conversion of CO is assumed to reach 98%.

In each sub-process, steady state optimized designs are developed based on minimizing energy consumption and then connected to a plantwide process. An improved heat-integration strategy is also presented in this work. Compared to the traditional pulverized coal (PC) power plant and integrating gasification combined cycle (IGCC) power plant, the overall energy conversion efficiency of coal to SNG process is higher.

After the steady state design, the dynamic control structures for each sub-system are developed. All the product specifications can be kept around the set point value under disturbances and loading changes.