Gasification has been used in industry on a relatively limited scale for many years, but it is emerging as the premier unit operation in the energy and chemical industries. The switch from expensive and insecure petroleum to solid hydrocarbon sources (coal and biomass) is occurring due to the vast amount of domestic solid resources, national security, and global warming issues. Gasification (or partial oxidation) is a vital component of "clean coal" technology. Sulfur and nitrogen emissions can be reduced, overall energy efficiency is increased, and carbon dioxide recovery and sequestration are facilitated. Gasification units in an electric power generation plant produce a fuel gas for driving combustion turbines. Gasification units in a chemical plant generate synthesis gas, which can be used to produce a wide spectrum of chemical products. Future plants are predicted to be hybrid power/chemical plants with gasification as the key unit operation. The widely used process simulator Aspen Plus provides a library of models that can be used to develop an overall gasifier model that handles solids, so steady-state design and optimization studies of processes with gasifiers can be undertaken. However, at the present time, these models cannot be exported into Aspen Dynamics because the automatic export of models involving solids from Aspen Plus to Aspen Dynamics is not supported. Dynamic simulations are essential for the development of stable and agile plantwide control structures for energy and chemical processes. This paper presents a simple approximate method for achieving the objective of having a gasifier model that can be exported into Aspen Dynamics. The basic idea is to use a high molecular weight hydrocarbon that is present in the Aspen library as a pseudofuel. This component should have the same 1:1 hydrogento-carbon ratio that is found in coal and biomass. For many plantwide dynamic studies, a rigorous highfidelity dynamic model of the gasifier is not needed because its dynamics are very fast and the gasifier gas volume is a relatively small fraction of the total volume of the entire plant. The proposed approximate model captures the essential macroscale thermal, flow, composition, and pressure dynamics. This paper does not attempt to optimize the design or control of gasifiers but merely presents an idea of how to dynamically simulate coal gasification in an approximate way.

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Selection of "matched" areas for test marketing is an important undertaking if reliable comparisons among markets are to be made. This usually has been done on a rather arbitrary basis, largely because of the large number of market characteristics on which markets can be viewed as similar or different. The authors suggest a numerical procedure--cluster analysis--for matching prospective test markets on the basis of a large variety of characteristics which could affect test marketing results. In this way, markets can be pre-selected so as to reduce undesired variability among test areas.

Gasification could potentially emerge 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. Because of 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.

The coupling of an integrated gasification combined cycle (IGCC) electric power plant with a hydrogen-consuming chemical (methanol) plant can handle swings in electric power demand. Hydrogen gas from the combustion turbine and synthesis gas from the gasifier can be diverted to a methanol plant for the production of an easily stored, hydrogen-consuming liquid product. This paper extends previous work on dynamic studies of a gasifier and downstream units of an IGCC to explore the steady-state economic design, control, and successful turndown of the methanol plant. The plantwide control structure and interaction among units are also shown. The methanol plant is sized to reduce the power generation from an IGCC by 50%, producing a high-purity methanol stream of 99.5 mol %. Regulatory control structures are designed and play a significant role for the successful turndown of the methanol plant to 20% capacity. The exit temperature of the cooled tubular methanol reactor is controlled instead of a peak temperature within the reactor. During times of low capacity and minimum vapor rate within the distillation column, tray temperature is controlled by recycling a portion of the distillate and bottoms back upstream so that temperature can be effectively controlled by manipulating feed flow rate. The gasifier feed is held constant. The product hydrogen from the IGCC is fed to the combustion turbine as required by electric power demand. Synthesis gas fed into the methanol plant maintains pressure of the hydrogen stream. Make-up hydrogen is also fed to the methanol plant to maintain reaction stoichiometry by controlling the carbon monoxide composition of the recycle gas in the methanol plant.