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.