Integration of Gas Turbines Adapted for Syngas Fuel With Cryogenic and Membrane-Based Air Separation Units: Issues to Consider for System Studies

Abstract

The purpose of this paper is to aid systems analysts in the design, modeling, and assessment of advanced, gasification-based power generation systems featuring air separation units (ASUs) integrated with gas turbines adapted for syngas fuel. First, the fundamental issues associated with operating a gas turbine on syngas will be reviewed, along with the motivations for extracting air from the turbine-compressor and/or injecting nitrogen into the turbine expander. Configurations for nitrogen-only and air-nitrogen ASU integration will be described, including the benefits and drawbacks of each. Cryogenic ASU technology will be summarized for both low-pressure and elevated-pressure applications and key design and integration issues will be identified and discussed. Finally, membrane-based ASU technology will be described and contrasted with cryogenic technology in regard to system design and integration.

Feasibility analysis of gas turbine inlet air cooling by means of liquid nitrogen evaporation for IGCC power augmentation

“…The membrane operates at high temperature (800 C to 900 C). Pure oxygen emerges from the membrane at a very low pressure and can be removed by a stream of purge gas (usually steam) or by compressors [6]. Unlike cryogenic processes, which routinely recover nearly 100% of the oxygen from the feed air stream [7], ion transport membrane ASUs assure a much lower oxygen recovery rate (10% to 75% [6]).…”

“…Pure oxygen emerges from the membrane at a very low pressure and can be removed by a stream of purge gas (usually steam) or by compressors [6]. Unlike cryogenic processes, which routinely recover nearly 100% of the oxygen from the feed air stream [7], ion transport membrane ASUs assure a much lower oxygen recovery rate (10% to 75% [6]). Therefore, ion transport membrane ASUs require a much larger volume of feed air compared to cryogenic ASUs and this makes the integration with gas turbine more complicated.…”

“…Elevated-Pressure Cryogenic ASU. These cryogenic plants operate at much higher pressures (close to discharge pressures of gas turbine compressors) than the Low-Pressure Cryogenic ASU due to improvements in manufacturing technology that increase the maximum operating pressure rating of cryogenic heat exchangers [6]. Elevated-pressure ASUs are typically favored for systems that supply the ASU with air extracted from the gas turbine compressor.…”

“…Conventional cryogenic ASUs operate at low pressure, meaning that the feed air is compressed just enough to allow the nitrogen by-product to be discharged at atmospheric pressure. Depending on the oxygen purity specification and the extent of efficiency optimization, absolute air feed pressures to low-pressure cryogenic ASUs are typically 4.4 bar to 7.2 bar [6]. Product streams typically leave the ASU in gaseous form near ambient temperature and pressure.…”

“…An air separation unit is usually composed of a multi-column cryogenic distillation process and produces high-purity oxygen from compressed air (up to 99% v/v [6,7]). …”