ABSTRACT:

Gasifiers are high temperature, high pressure containment vessels used to convert carbon feedstock, such as coal or petcoke, into H2 and CO, called syngas. The syngas produced by gasification is used as a fuel in energy production or as a raw material feedstock for chemical synthesis. Slagging gasifiers used in gasification operate at temperature between 1325-1575oC and pressures between 2.1-6.9 MPa; and are lined with high chrome oxide refractory materials. Impurities exist in the carbon feedstock, which include Si, Fe, Ca, Al, Na, and S in coal; and include additional elements of Ni and V in petcoke. Depending on the feedstock source, the quantities of impurities generally range from one to over ten pct; leading to ash waste quantities reaching 100 tons/day or higher. At the operational temperatures of a slagging gasifier, the ash wastes liquefy and react with or penetrate within the refractory liner pores; leading to their wear and corrosion, and ultimately, premature brick failure. This paper will discuss interactions between slag components and the refractory liner that lead to lining failure.

INTRODUCTION:

Gasification as a modern high temperature, high pressure industrial process was first used by the oil industry in the 50's to process low value petroleum and by-products from petroleum refining into high value materials. Since that time, gasification has expanded to other uses; including power generation, the production of CO and H2 feedstock for use by the chemical industry (for applications from fertilizer to Fischer Tropsch liquids), and is a leading candidate for H2 production in a hydrogen based economy. As a process, gasification converts a carbon feedstock (typically methane, coal, or by-products from petroleum processing such as petcoke) into CO and H2 (called synthesis gas, which is shortened to syngas). The process of gasification occurs in a facility similar to the general flow sheet shown in Figure 1, with major downstream processing and uses/proposed uses for the syngas product shown. The process of gasification can occur using any of a number of types of gasifiers; including dry ash gasifiers (slag typically does not fuse due to the low temperature of operation), water cooled entrained bed slagging gasifiers (gasification occurs at temperatures that create a molten slag from ash that is contained by a water cooled refractory liner), and the air cooled entrained bed slagging gasifiers (these gasifiers operate at temperatures were ash liquefies into molten slag that flows on an air cooled refractory lined surfaces). Each gasifier design has advantages/disadvantages that center on the amount and type of carbon feedstock it can process and the syngas composition produced. The type, quantity, and amount of any minority gas or impurity are determined by the composition of the gasifier feedstock, the gasification temperature, and/or other factors such as temperature or O2 level. Depending on the application for the syngas, impurities are typically removed at the gasification facility (as shown in Figure 1), which is accomplished using a variety of chemical processing techniques downstream from the gasifier (see Figure 1).

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