Date of Award

1-16-2001

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Energy Engineering

First Advisor

John Erjavec

Abstract

This research project studies the factors affecting the formation of ash agglomerates and deposits in advanced coal-fired power systems such as integrated gasification combined cycle (IGCC) and pressurized fluid-bed combustion (PFBC) systems. The formation of these ash agglomerates and deposits can adversely affect the performance of these advanced power systems. Significant factors include fuel and ash chemistry properties, gas/solid hydrodynamics, and operating conditions such as temperature, pressure, residence time, and atmosphere (reducing versus oxidizing). The methodology for this study was to compare the ash chemistry of the ash agglomerates and deposits of samples collected from various Energy & Environmental Research Center (EERC) advanced power systems to the starting mineralogical and ash properties of the starting fuels using advanced analytical techniques. These analytical methodologies include the utilization of computer-controlled scanning electron microscopy (CCSEM) and SEM point count (SEMPC) techniques that have been developed at the EERC. Samples from the transport reactor development unit (TRDU) located at the EERC were the primary source of the ash deposits and agglomerates examined in this work. The TRDU is a fast circulating fluidized bed system that can be operated either as a gasifier or a combustor. The ash formation mechanisms for the ash deposits and agglomerates formed in the TRDU have been inferred from the SEM analyses. The Facility for Analysis of Chemical Thermodynamics (FACT) is a thermochemical equilibrium code that has been acquired by the EERC to quantify chemical equilibria in various combustion and gasification systems. Historical operating data and the sample analyses were input to the FACT model, which was utilized to predict the temperatures and operating conditions at which the certain mineral and ash species can melt to form ash deposits and agglomerates, thereby becoming operating problems. The capability of the FACT code to successfully predict most of the ash deposition and agglomeration behavior as a function of operating conditions demonstrates its ability to predict the operating conditions to avoid for future pilot and commercial-scale tests utilizing various fuels.

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