(761d) Dynamics and Control of Air Separation Unit-Gas Turbine-Gasifier Integrated Power Cycle of Igcc Plants

Integrated coal gasification and combined cycle (IGCC) power plants have emerged as an attractive alternative to conventional pulverized coal (PC) plants for generating power from coal. If carbon dioxide capture and storage is required, IGCC is considered one of the most promising power generation technologies. In these plants, the subsections closely interact with each other, resulting in challenging operation and control problems. Examples of process interaction include: (i) the syngas fuel from gasifer serves as feed to the gas-turbine/compressor, (ii) pure oxygen from the air separation unit (ASU) serves as the oxidant for gasification, (iii) some of the compressed air from the gas compressor (which has a common shaft with the gas turbine) serves as feed to the ASU, and (iv) the nitrogen from the ASU is injected into the gas turbine's combustor. The substantial process integration, which is targeted to achieve lower emissions (cleaner coal) and increased efficiency, leads to higher investment costs, reduced operational flexibility and longer startup-shutdown time compared to PC plants.

This paper addresses control of ASU-GasTurbine-Gasifier power cycle by first detailing the development of an AspenDynamics model consisting of individual ASU, Gasifier and GasTurbine subsections. Thereafter these subsections are coupled to investigate feasibility, applicability and plant performance with varying coal quality and with changes in coal-feed quantity required to meet power demands which act as overall process disturbances. The operability characteristic of the integrated process is compared with that of the individual operating units. The process variables operating at different time scales are shown to be responsible for difficulties with commonly used PID-based control schemes. Further, we develop a model predictive control strategy that handles rate-of-change and multiple time-scale constraints imposed by the process design of the air separations, gas turbine/compressor and gasifier units. Finally we close with a discussion of future work on the simulation and control of an entire IGCC power plant.