The Use of Integrated Mild/Partial Gasification Combined (IMPGC) Cycle Technology As a Potential Retrofit Option for Pulverized Coal Plants

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. Coal is also an abundant natural resource within the continental United States and numerous coal plants still operate within the U.S. as well as around the world today. The problem is that coal is very politically and environmentally unattractive, and many older pulverized coal (PC) plants are running at low efficiency and are at risk of being shut down. The newly conceptualized Integrated Mild/Partial Gasification Combined (IMPGC) Cycle is one promising new technology that has the potential to significantly augment the efficiencies of these older plants as well as help newer plants keep up with ever stricter environmental regulations. The key features of IMPGC are: it preserves volatiles with high energy density—about  3 times denser than fully-gasified syngas—so the size of the piping and the gas cleanup system can be reduced from a fully gasified system. In the meantime, since mild gasification is applied, the residence time is shorter than full gasificiation, and the product yield rate will be higher. This technology, which makes use of warm gas cleanup as well as mild and partial gasification, can conveniently and seamlessly convert a simple Rankine cycle to a combined cycle, greatly improving the efficiency of the plant without altering the base plant’s design. Furthermore, the mild-gasification system has a small foot print and can be easily incorporated into the existing compound of plant. In total, three different scenarios were simulated in addition to a simple subcritical baseline plant for comparison: (1) a case using the same fuel input as the original baseline, (2) a case with the same total maximum power output as the baseline, and (3) a case where the turbine with the highest steam pressure (HPST) has the same mass flow rate through it as the equivalent turbine from the baseline case. All cases use Illinois #6 coal as the input fuel. The results show that IMPGC can improve the efficiency of new subcritical Rankine cycles by up to nine (9) percentage points (or about 23%) and has the potential to augment total net power output by up to 2.5 times. For water consumption, retrofitting a Rankine cycle with an IMPGC system can reduce water usage by a minimum of 34%. This paper will analyze the specific challenges associated with retrofitting these plants and examine how the retrofit affects the plant performance and emissions.