Integrated Gasification Combined Cycle (IGCC) Plants - Technology / Performance/ Environment / Demand Trends

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Integrated Gasification Combined Cycle (IGCC) Plants - Technology / Performance/ Environment / Demand Trends

IGCC plants consist of three main sections: the "gas island" for conversion of coal and/or refinery residues (such as heavy fuel oil, vacuum residues or petroleum coke) including gasification and downstream gas purification (for removal of sulfur, alkali, and heavy metal compounds to meet required emissions levels and gas turbine fuel specifications), the air separation unit (ASU) and the combined cycle (CC) plant. The modular design (gas generation, gas turbine system, HRSG and the steam turbine system) offers the possibility of phased construction as well as retrofitting of CC plants with a gasification plant, thus replacing the "standard" gas turbine fuels (natural gas or fuel oil) by syngas produced from coal or refinery residues. IGCC is in principle a combination of two mature technologies.

IGCC Integration Concept Integration Options :

Non integrated (independent) ASU
Partially integrated ASU
Fully integrated ASU

Criteria for Selection of the Integration Concept :

Gasification process and waste heat recovery (syngas cooler, quench, cooler/saturation cycle)
ASU process
Fuel gas analysis (with or without nitrogen return)
Limits for NOx emissions
Overall plant efficiency
Investment costs
Operational aspects
Site-specific aspects
Necessary modifications of standard gas turbines
Available fuel flow

It may be noted that the environmental performance of IGCC plants in terms of reduced emissions is better than that of pulverized coal-fired steam power plants.

Depending on the degree of integration between the gas turbine and the air separation unit (ASU), either standard gas turbine/compressor configurations can be applied or in some cases only limited modifications are required to compensate for the mismatch between turbine and compressor mass flows which results from the use of gases with low heating values. Three principal options are available. Selection of the appropriate air and nitrogen integration concept depends on a number of factors to be considered on a case by case basis. The "fully integrated approach" which was selected for the European coal based demonstration plants results in the highest efficiency potential, but should be considered as highly sophisticated from the operational point of view.

The non integrated concept with a completely independent ASU is expected to have advantages with respect to simplified plant operation and possibly in achieving higher availability ratings. On the other hand, the loss in overall IGCC net plant efficiency compared with the fully integrated concept amounts to 1.5 to 2.5 percent. The non integrated concept is therefore primarily of interest in cases where efficiency is not the key factor (e.g. for the gasification of refinery residues). The concept of partial air side integration (Option 2) Is an interesting compromise solution, with only moderate loss in efficiency but improved plant flexibility compared with the fully integrated concept.

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