Process Intensification of Gasification and Reforming Technology for Enhanced Power Generation with Carbon Capture and Storage

Abstract

IGCC is a pre-combustion technique which represents higher thermal efficiency with large scale implementation of CO2 capture. On the other hand, NGCC power plants offers higher process performance compared to IGCC process with CCS technologies but the fluctuating and comparatively higher costs of natural gas limits its extensive implementation over coal based power generation systems. Therefore, process integration of coal gasification and natural gas reforming has been proposed to enhance the process performance while limiting the natural gas consumption. In this study, two IGCC based process models have been developed and evaluated in terms of both the process performance and economics with CO2 capture. Case 1 is taken as the conventional IGCC process, whereas, case 2 presents an idea of integrating methane reforming process with an IGCC technology. The high enthalpy steam generated during coal slurry gasification process in case 2 is used to assist the reforming process for H2 generation. The integration of IGCC with methane reforming process not only supplies the heat required for the endothermic reforming process but also increases the heating value of the resulting syngas. This concept also provides an opportunity for process intensification since shared water gas shift reactors and CO2 capture units will suffice the process needs. The net electricity generation capacity and efficiency for case 1 and case 2 is calculated as (375.08 MWe, 472.92 MWe) and (35.93%, 40.70%), respectively. While comparing the results, it has been seen that case 2 design offers nearly 4.7% higher efficiency compared case 1 design with CO2 capture. The process economics analysis showed that the case 2 design requires a higher CAPEX and O&M throughout the project life compared to the case 1 design. However, due to the higher power generation capacity of case 2 design, it has a potential to reduce the LCOE by 5.81% compared to the case 1 design. Moreover, case 2 design not only requires the less CO2 capture and avoidance costs compared to the case 1 but also exhibits higher rate of return on the investment with the less payback time. With the higher efficiency and least SECO2, case 2 has been considered as the most feasible option for electricity production at an economical price compared to the case 1 design. To complete the chain of power generation systems with the CO2 capture and storage, the CO2 injection system has been also studied in detail. The transport of CO2 for geological storage is economically feasible by ship when the storage site location is off-shore and installment of an off-shore pipeline requires a huge capital cost. Ship transportation requires the captured CO2 to be in liquid phase under pressurized thermodynamic conditions. The injection of liquid CO2 into the geological reservoir involves pressurization and heating in order to maintain the safe well head operating conditions. This study presents an improved design mechanism for CO2 injection that can utilize the cold energy available from the liquid CO2 to operate the two-stage NH3 rankine cycle. The results showed that the 2-stage rankine cycle design consume approximately 56% less power compared to that of the base case design. Moreover, the economic analysis also showed that the specific cost of CO2 injection can be reduced up to 6.2% using the improved design.Finally, a sensitivity analysis has been also performed in order to investigate the effect of some important variables on the process performance and economics.