Sampling and Analysis of Alkali in High-Temperature, High-Pressure Gasification Streams

This paper describes the experiences leading to successful sampling of hot, contaminated, coal-derived gas streams for alkali constituents using advanced spectrometers. This activity was integrated with a multi-phase, combustion test program which addressed the use of minimally treated, coal-derived fuel gas in gas turbines. Alkali contaminants in coal-derived fuels are a source of concern, as they may induce corrosion of and deposition on turbine components. Real-time measurement of alkali concentrations in gasifier output fuel gas streams is important in evaluating these effects on turbine performance. An automated, dual-channel, flame atomic emission spectrometer was used to obtain on-line measurements of total sodium and potassium mass loadings (vapors and particles) in two process streams at the General Electric fixed-bed coal gasifier and turbine combustor simulator facility in Schenectady, New York. Alkali measurements were taken on (1) slipstreams of high temperature, high pressure, minimally clean, low-Btu fuel gas containing entrained particles from the gasifier and (2) a slipstream of the exhaust gas from the combustor/turbine simulator. Alkali detection limits for the analyzer were found to be on the order of one part per billion. Providing a representative sample to the alkali analyzer at the limited flows required by the instrument was a major challenge of this activity. Several approaches and sampling hardware configurations were utilized with varying degrees of success during this testing campaign. The resulting information formed the basis for a second generation sampling system which has recently been successfully utilized to measure alkali concentrations in slipstreams from the described fixed-bed coal gasifier and turbine combustor simulator.