Slag Behavior in Gasifiers. Part I: Influence of Coal Properties and Gasification Conditions

Abstract

Abstract:In the entrained-flow gasifiers used in integrated gasification combined cycle (IGCC) plants, the majority of mineral matter transforms to liquid slag on the wall of the gasifier and flows out the bottom. However, a small fraction of the mineral matter is entrained (as fly ash) with the raw syngas out of the gasifier to downstream processing. This molten/sticky fly ash could cause fouling of the syngas cooler. To improve gasification availability through better design and operation of the gasification process, a better understanding of slag behavior and the characteristics of the slagging process is needed. Char/ash properties, gas compositions in the gasifier, the gasifier wall structure, fluid dynamics, and plant operating conditions (mainly temperature and oxygen/carbon ratio) all affect slagging behavior. Because coal has varying ash content and composition, different operating conditions are required to maintain the slag flow and limit problems downstream. In Part I, we review the main types and the operating conditions of entrained-flow gasifiers and coal properties used in IGCC plants; we identify and discuss the key coal ash properties and the operating conditions impacting slag behavior; finally, we summarize the coal quality criteria and the operating conditions in entrained-flow gasifiers. In Part II, we discuss the constitutive modeling related to the rheological studies of slag flow.

A Critical Review of Mineral Matter Related Issues during Gasification of Coal in Fixed, Fluidized, and Entrained Flow Gasifiers

“…Besides corrosion, higher operating temperature can also increase the oxygen demand and consequently reduce the efficiency of the gasifier. Operating the entrained flow gasifier at relatively low temperature can increase the slag viscosity, which can affect the discharge of the slag by solidification [78]. Therefore, an optimum condition (1573-1773 K) should be maintained such that slag layer acts as thermal barrier coating for the refractory wall [78] not at the cost of overall efficiency.…”

Investigation on Coal Slagging Characteristics and Combustion Behaviour in Furnace

“…The seven parameters are the existing indices to predict slagging propensity. However, high softening temperature are required to maintain the 15 to 25 Pa.s viscosity to ensure slag is able to flow in the furnace else fluxing is required [9]. Coal-C performed fairly well as a sub-bituminous coal with the 950 o C to 1250 o C for 25 Pa.s viscosity for both good performing and low performing coals.…”

Effects of Design/Operating Parameters and Physical Properties on Slag Thickness and Heat Transfer during Coal Gasification

“…Many commercial coal gasification processes such as the Shell, Prenflo, Mitsubishi, Tsinghua and Siemens ones utilize entrained flow reactors feeding pulverized coal in dry or slurry forms [1][2][3]. Because the syngas temperature typically increases above the ash melting point, most of the coal ash is molten and deposits onto the gasifier wall to form slag layers.…”

“…Because of its importance in ash discharge, wall protection, and heat recovery, controlling the slag behavior is a crucial issue for the design and operation of entrained flow gasifiers [3,4]. The ash fusion temperature and slag viscosity are important properties in relation to the flowability and thickness of the liquid slag, which are determined by inherent properties such as the ash composition and chemistry, as well as external conditions such as the temperature and reaction atmosphere [5][6][7][8][9].…”