The Gas Turbine Heat Exchanger in the Fluidized Bed Combustor

Abstract

In a current research and development program a coal-fired atmospheric fluidized bed combustor is being designed to supply the heat to a closed cycle gas turbine cogeneration system. The major technical effort is directed towards the design of the in-bed heat exchanger, which is required to operate near bed temperature. This high temperature (850° C) exposes the heat exchanger tubes to potentially severe sulfidation. The corrosion behavior depends upon the intimate details of the bed environment and may be related to the occurrence of localized areas of low oxygen partial pressure and high sulfur partial pressure. This paper describes a series of measurements of oxygen partial pressure at various locations within a fluidized bed. The bed, containing densely packed heat exchanger tubes, was operated under various conditions to observe the effect of coal mixing and devolatilization on local oxygen activity. Substantial variations of oxygen partial pressure (below 10−14 atmospheres) were observed. It was noted that these locally severe variations could be substantially modified by changes in coal mixing (as through coal port design). The experiments with varying coal size suggest that rapid devolatilization is desirable and would reduce the extent of locally corrosive environments.

Experimental investigation of the two-phase theory in a fluidized-bed combustor

“…Some previous investigators (Holt et al, 1982;Boiarski et al, 1984;Li et al, 1984, Minchener et af., 1985 measured the oxygen partial pressure within FBC using zirconia sensors. The bimodal frequency distribution of oxygen concentration was sometimes attributed to different concentrations in bubble and particulate phases, but without direct experimental measurements of the phase location of the sensor.…”

Externally fired gas turbine technology: A review

“…6 shows the 18 by 18 inch combustion chamber with bed temperature in the range of 850-980°C [22]. Details of the experiment were described by Holt et al [20]. Details of corrosion test and Nickel-Chromium based metal alloys resistance against oxidization and sulfidation attacks were described by Wright and Minchener [21].…”

“…In the late 1970s, coal fired fluidized bed combustors (FBC) with HTHE submerged in the combustor bed was getting more attention in the USA for both steam-based and closed cycle EFGT-based power systems [19]. Several R&D test facilities were developed by the USA Department of Energy with elaborate examination of the HTHE performance in the FBC for the power range 5-50 MW e [20][21][22]. Trumpler [23] compared the steam-based and closed cycle EFGT-based FBC coal fired power plant and found that the latter can provide about 17% coal fuel savings with TIT of 927°C.…”

A model for volatiles release into a bubbling fluidized‐bed combustor

“…Similar in-bed oxygen probe signals have been obtained during coal combustion in fluidized-bed combustors, and two alternative interpretations have been suggested. The first interpretation was that the oxygen concentration was different in each of the two phases (bubble and particulate) within the bed (Holt et al, 1982;Saari and Davini, 1982;Li et al, 1984;Ljungstrom, 1985;Minchener et al, 1985).…”