(122g) Modeling Refractory Degradation Due to Slag Penetration in An Entrained-Flow Gasifier

Modeling Refractory Degradation due to Slag
Penetration in an Entrained-Flow Gasifier

Pratik Pednekar, PhD Student, West
Virginia University

Department of Chem. Eng., West Virginia University, Morgantown WV  26506

ppedneke@mix.wvu.edu

Debangsu Bhattacharyya, Assoc.
Professor, West Virginia University

Department of Chem. Eng., West Virginia
University, Morgantown WV  26506

Debangsu.Bhattacharyya@mail.wvu.edu

Tel: 3042939335, Fax: 3042934139

Richard Turton, Professor, West Virginia
University

Department of Chemical Engineering, WVU,
Morgantown, WV 26506

Richard.Turton@mail.wvu.edu

Tel: 3042939364, Fax 3042934139

Raghunathan Rengaswamy, Professor, Texas
Tech University

Department of Chemical Engineering, Texas
Tech University, Lubbock, TX 26507

Raghu.Rengasamy@ttu.edu

Tel: 8067421765, Fax 3042850903

Abstract

In
slagging gasifiers, molten slag flows down the inner refractory wall. The slag
can penetrate into the refractory causing thinning and spalling of the
refractory lining due to the build-up of stress. Replacement of the refractory
lining is required every 1-2 years and is very expensive. This also leads to
significant down-time lowering the overall availability of gasifier-based power
plants. Due to the harsh operating condition inside a slagging gasifier, an
in-situ measurement of the refractory degradation is not possible with the
current state of technology. Therefore, a mathematical model may be used to develop
a better understanding of the effects of various operating conditions and
physicochemical properties on the degradation characteristics. Such a model may
eventually lead to development of better monitoring and prevention techniques.

With
this motivation, first a slag submodel was developed to obtain the temperature
profile in the wall and the thickness profile of the slag along the gasifier
wall. A mechanistic model was developed by considering slag formation and
detachment from the char particles followed by transport and deposition of the
slag droplets onto the refractory wall. A model for the slag layer was then developed
by considering mass, momentum, and energy conservation equations. Due to the
temperature gradient that exists in the molten slag layer, a solid slag layer is
formed between the refractory and the molten slag layer. A model of the solid
slag layer was also developed using energy balance equations. Two
phenomenological models were then developed for refractory degradation - one
based on the tensile stress and the other based on the compressive force
developed due to thermal strains and shrinkage/swelling due to slag
penetration.

The
slag sub-model was integrated with a 1D steady-state model of a single-stage,
downward-firing, oxygen-blown, slurry-fed, entrained-flow gasifier developed
previously at WVU in the Aspen Custom Modeler® (ACM) environment. The gasifier
model included mass, momentum and energy balance equations for solid and gas
phases. The model also included a number of heterogeneous and homogeneous
chemical reactions along with devolatilization and evaporation of the slurry
feed. The presentation will include results that show the effects of gasifier
operating conditions on slag layer thickness, wall temperature profile, and
refractory degradation.