DEVELOPMENT AND ANALYSIS OF AN INTEGRATED MILD/PARTIAL GASIFICATION COMBINED (IMPGC) CYCLE

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 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). This paper will first 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). This baseline will then be compared with four other common types of power plants, including subcritical and ultra-supercritical (USC) Rankine cycles, IGCC, and natural gas. The results show that IMPGC consistently outperforms all other forms of coal-based power. IMPGC is more efficient than the standard subcritical Rankine cycle by nine percentage points, more than a USC Rankine cycle by nearly four points, and more than IGCC by seven points.

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. The problem is that coal power plants are environmentally unfriendly; particularly, older plants have low thermal efficiency and poor emissions. In addition, the conventional and common practices for retrofitting those older plants can only provide incremental improvements for plant performance and emissions. This paper introduces the concept of the Integrated Mild/Partial Gasification Combined (IMPGC) Cycle as one promising new technology that has the potential to significantly increase the thermal efficiency of these older plants as well as reduce their emissions. In contrast to the conventional Integrated Gasification Combined Cycle (IGCC), IMPGC makes use of warm gas cleanup as well as mild and partial gasification to 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. Three different scenarios in total were simulated in addition to a simple subcritical Rankine cycle plant as a baseline 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. The results show that IMPGC can improve the efficiency of Rankine cycles by up to nine (9) points (or ∼23%) and has the potential to augment total net power output by up to 2.5 times. This paper will analyze the specific challenges associated with retrofitting these plants and examine how the retrofit affects the plant performance and emissions.

Performance of an Integrated Mild/Partial Gasification Combined (IMPGC) Cycle With Carbon Capture in Comparison With Other Power Systems

With rising concerns about potential CO2 emissions and the effects of which on climate change and ocean acidification, it becomes necessary to consider developing newer and cleaner power plant technologies, including carbon capture. A conceptual clean coal technology called the Integrated Mild/Partial Gasification Combined (IMPGC) cycle implemented with a post-combustion carbon capture process is introduced in this paper. The IMPGC cycle employs mild gasification to preserve the high energy volatile matters within the coal and partial gasification to supplement the steam bottom cycle with a purely char-fired PC plant boiler. The performance of this newly conceptualized model is compared to those of other types of power plants, including natural gas combined cycle (NGCC), integrated gasification combined cycle (IGCC), and pulverized coal (PC) Rankine cycle plants under the condition that all plants utilize carbon capture in some form so as to achieve the same overall CO2 emissions as a high-performing NGCC plant. The results show that, while natural gas is still the top-performing power plant, IMPGC with carbon capture has the highest performance of all coal plants studied (∼39.7%), able to achieve the same CO2 emissions as natural gas, but with the same efficiency as a top-of-the-line subcritical Rankine cycle plant without carbon capture. This is about 2.5 percentage points better than an IGCC plant with carbon capture, ∼8 percentage points better than an ultra-supercritical Rankine cycle plant with carbon capture, and over 9 points better than a subcritical plant with carbon capture. This high performance is achieved through the use of a warm gas cleanup process based on the technology developed by RTI with the support of the U.S. Department of Energy.