(101c) IGCC Dynamic Model: H2S Absorption/Stripping, WGS Reactors, and CO2 Absorption/Stripping

Gasification is immerging as the premier unit operation in the energy and chemical industries. In the future, plants are predicted to be a hybrid between power and chemical with the ability to handle unavoidable swings in both power demand and biomass feed composition without a loss of efficiency. The coupling of a power plant with a chemical plant provides an additional control degree of freedom, which fundamentally improves the controllability of the process. The coupling of an Integrated Gasification Combined Cycle (IGCC) power plant with a methanol chemical plant handles swings in power demand by diverting hydrogen gas from a combustion turbine and syn gas from the gasifier to a methanol plant for the production of an easily-stored, hydrogen-consuming liquid product.

This paper presents an extension of the dynamic gasifier model, which uses a high-molecular weight hydrocarbon (with a 1:1 hydrogen to carbon ratio) as a pseudo biomass feed stock. Using this gasifier model, the downstream units of a typical IGCC can be modeled in the widely used process simulator Aspen Dynamics. Dynamic simulations of the H2S absorption/stripping unit, Water-gas Shift (WGS) reactors, and CO2 absorption/stripping unit are essential for the development of stable and agile plantwide control structures of this hybrid power/chemical plant.

Due to the high pressure of the system, hydrogen sulfide is removed by means of physical absorption. SELEXOL® (a mixture of the dimethyl ethers of polyethylene glycol) is used to achieve a gas purity of less than 5 ppm H2S. This desulfurized synthesis gas is sent to two water gas shift reactors that convert a total of 99% of carbon monoxide to hydrogen. Physical absorption of carbon dioxide with Selexol produces a hydrogen rich stream (90 mol% H2) to be fed into combustion turbines or to a methanol plant.

Steady-state economic designs and plantwide control structures are developed in this paper.