Development and Analysis of an Integrated Mild/Partial Gasification Combined (IMPGC) Cycle: Part 1 — Development of a Baseline IMPGC System

Abstract

Around 50% of the world’s electrical power supply comes from the Rankine cycle, and the majority of existing Rankine cycle plants are driven by coal. Given how politically unattractive coal is as an energy resource in spite of its high energy content, it becomes necessary to find a way to utilize coal in a cleaner and more efficient manner. Designed as a potential retrofit option for existing Rankine cycle plants, the Integrated Mild/Partial Gasification Combined (IMPGC) Cycle is an attractive concept in cycle design that can greatly increase the efficiency of coal-based power plants, particularly for retrofitting an old Rankine cycle plant. Compared to the Integrated Gasification Combined Cycle (IGCC), IMPGC uses mild gasification to purposefully leave most of the volatile matters within the feedstock intact (hence, yielding more chemical energy) compared to full gasification and uses partial gasification to leave some of the remaining char un-gasified compared to complete gasification. The larger hydrocarbons left over from the mild gasification process grant the resulting syngas a higher volumetric heating value, leading to a more efficient overall cycle performance. This is made possible due to the invention of a warm gas cleanup process invented by Research Triangle Institute (RTI), called the High Temperature Desulfurization Process (HTDP), which was recently commercialized. The leftover char can then be burned in a conventional boiler to boost the steam output of the bottom cycle, further increasing the efficiency of the plant, capable of achieving a thermal efficiency of 47.9% (LHV). The first part of this paper will analyze the individual concepts used to create the baseline IMPGC model, including the mild and partial gasification processes themselves, the warm gas cleanup system, and the integration of the boiler with the heat recovery steam generator (HRSG). Part 2 will then compare this baseline case with four other common types of power plants, including subcritical and ultra-supercritical Rankine cycles, IGCC, and natural gas.