A Parametric Investigation of Integrated Gasification Combined Cycles with Carbon Capture

IGCC (Integrated Gasification Combined Cycle) technology is being developed to enable electricity to be generated at high efficiency and low emissions. Continuous improvement is essential to make IGCC reliable and costeffective. As environmental concerns over carbon emissions escalate, development of a practical carbon capture and storage (CCS) technology has become an important issue. Combining IGCC and CCS has become a promising technology to reduce the cost of CCS. This study investigates the pros and cons of different methods used to put together an approximately 250 MW IGCC plant with and without CCS by using the commercial software Thermoflow. Seven different IGCC plants have been designed with various parameters examined, including: oxygen-blown vs. air-blown, with/without integration, with/without CCS, sour vs. sweet water shift for carbon capture, and dryvs. slurry-fed. This study is based on technologies that are commercially available or close to commercialization. The results show that (a) integration between the gas turbine and the air separation unit (ASU) can boost the cycle efficiency about 4.5% (1.6 percentage points); (b) dry-feeding increases the CO content, the syngas heating value (19%), and the efficiency about 11% (4.7 percentage points); (c) carbon capture reduces the power output by 2.7% and efficiency by 10% (or 4.5 percentage points) and the slurry-fed system takes a heavier toll on power output and efficiency than the dry-fed system; (d) air-blown systems do away with the ASU, resulting in syngas with a 50% lower heating value and a small reduction in efficiency, but harvesting savings on reduced capital, operating, and maintenance costs; (e) for CO2, sweet water shift results in 5.5% (2 percentage points) higher cycle efficiency than sour shift. Acronyms ASU air separation unit BFW boiler feed water CCT clean coal technology CCS carbon capture and storage COS carbonyl sulfide CSC convective syngas cooler DGAN diluent nitrogen GHG green house gas GOX gaseous oxygen GT gas turbine HHV higher heating value HP high pressure HPGAN high pressure gaseous nitrogen HRSG heat recovery steam generator IGCC integrated gasification combined cycle IP intermediate pressure ITM ion transport membrane H total enthalpy LHV lower heating value LIN liquid nitrogen LP lower pressure LTGC lower temperature gas cooling MAC main air compressor MDEA methyl di-ethanol amine NGCC natural gas fired combined cycle PSA pressure swing absorption RSC radiant syngas cooler SAP sulfuric acid plant SGC syngas cooler ST steam turbine TSA temperature swing absorption WGS water gas shift 1.0 INTRODUCTION Around the world, coal has been used to generate a large portion of electricity. For example, coal generates 45% of the electricity in the United States and 70% in China. However, the conventional coal burning power plants are dirty and have relatively lower efficiency. To replace the direct coal combustion practice, gasification technology has been employed to gasify coal into synthesis gas (syngas,) which consists primarily of CO and H2 as fuel. After cleaning the ashes and sulfur, the syngas can be combusted in gas turbines with low emissions comparable to those of natural gas combustion. The technology of combing the gasification process with the combined cycle is called the Integrated Gasification Combined Cycle (IGCC) [1].