ADVANCED COMBUSTION ENGINEERING RESEARCH CENTER

Fuel Minerals, Fouling and Slagging (Thrust Area 2)

John N. Harb, Chair

INTRODUCTION

Coal is a very heterogeneous material consisting of both organic and inorganic material. The portion of coal that is inorganic is usually small, but can and often does have a profound impact on the combustion system. This material greatly affects boiler design and has an impact on the flexibility the operator has to alter fuels sources and boiler operating procedures. The principal problem noted in combustion systems due to coal minerals is ash deposition, leading to reduced heat transfer and often reduced unit availability. In addition to ash deposition, mineral impacts are noted in a number of coal combustion processes, e.g., burnout and devolatilization. These impacts are greatly affected by the form of the inorganic material found in the coal.

The ACERC efforts in minerals behavior builds on the many activities currently underway at numerous university, government and industrial laboratories around the world. ACERC researchers have established collaborative relationships with several of the recognized expert groups and continue to expand these relationships. The ACERC focus is on fireside modeling. These cooperative relations will enable ACERC researchers to utilize the information and, in some cases, submodels developed by other researchers to accomplish its goal of describing minerals behavior during combustion.

OBJECTIVES AND APPROACH

The projects in Thrust Area 2 are designed to supplement efforts of researchers at other laboratories with the combined efforts leading to a clear understanding of minerals behavior during combustion. Items of concern include impacts of minerals on char burnout and devolatilization, as well as fouling and slagging. This program in minerals behavior attempts to provide necessary information related to model development. Work is underway on mineral matter characterization, catalysis, transformations and deposition. Key issues include:

1. Characterization of Minerals in Coal and Chars. Detailed information on concentrations, mineralogy, and local chemistry is needed for representative (ACERC) coals and chars.

2. Role of Inorganic Constituents in Devolatilization and Char Oxidation. Knowledge of the kinetics and mechanisms of catalytic reaction during pyrolysis and char oxidation during combustion is needed.

3. Transformation/Particle Formation. It is important to know the various phases present as ash moves through the system. In addition, the size and other physical characteristics such as the viscosity of the liquid phase and partitioning between solid, liquid, and vapor phases must be known.

4. Transport Processes. Ash only sticks to a surface if it arrives at the surface; thus the movement of all classes of material must be noted.

5. Sticking Behavior. Once the material reaches the surface, the combination of target (deposit surface) and incoming material must be such that the impinging material sticks. A basic understanding of the chemical/physical processes governing sticking behavior is needed.

6. Deposit Growth. The deposition of material on a heat transfer surface is a dynamic system. Reactions involving incoming material including ash particles, gas diffusion (SO2), and migration of mobile species may all affect the changing chemistry within the deposit. In addition, the momentum of impinging material may erode the developing surface under some circumstances or build up the deposit in different circumstances. A stationary deposit occurs when the build-up and erosion mechanisms come into balance. The time to balance may vary between one day and years. These mechanisms of growth and removal need to be understood and modeled.

The Advanced Combustion Engineering Research (ACERC) brings together a variety of researchers to examine many issues involved in the combustion of low-grade fuels. Industry has identified minerals behavior as a major problem area in coal combustion. Work in Thrust Area 2, both in understanding minerals behavior and its impact on key processes like ash deposition, devolatilization, and char burnout, as well as model development, are key to the Center's success. The eventual overall success of ACERC from an industrial perspective will depend, in large part on the ability of the 3-D code to predict the fate of mineral matter during combustion.

The successes of ACERC will be measured, in part, by the interaction of researchers representing the many aspects of the combustion process. Researchers in Thrust Area 2 are attempting to facilitate good communications with other researchers both within and outside of ACERC. Within ACERC, information developed on the impact of minerals on devolatilization and char burnout is being investigated in collaboration with researchers in Thrust Area 1. The compatibility of submodels requires considerable cooperation between submodel developers and researchers involved in Thrust Area 5, Comprehensive Code Development.

Collaboration with researchers outside ACERC is critical in successfully integrating minerals behavior into the ACERC codes under development. Working relationships exist with Pennsylvania State University, Sandia National Laboratory, Consolidation Coal Combustion Research Center and PSI. Additionally, collaboration exists with researchers at ABB-CE, Foster Wheeler Development Corporation, Riley Stoker, Shell Development and Texaco. Relationships also exist with numerous utilities firing coal. These relationships allow ACERC researchers to benefit from, as well as offer assistance to, other research efforts underway in the United States. Communication is also maintained with many foreign researchers.

ANTICIPATED PRODUCTS

Products anticipated from the efforts on Thrust Area 2 include:

1. Detailed understanding of the effects of coal minerals in char oxidation and devolatilization.

2. Detailed information on amount, size, form and juxtaposition of minerals in ACERC coals.

3. Fundamental information on key mineral transformation processes, both physical and chemical.

4. A submodel for fouling and slagging.

5. Integration of a slagging submodel into the 3D comprehensive code.

ACTIVE RESEARCH PROJECTS

No.	Project Title	Principal Investigator(s)	Univ.	Class.1
2E	Behavior of Mineral Matter in Coal Combustion Systems 4	John Harb	BYU	Fund., Foc.
2H	Char Minerals/Surface Properties 2	Calvin Bartholomew	BYU	Fund., Foc.
2K	Mineral Transform. & Ash Deposition During Staged Combustion	John Harb	BYU	Fund., Foc.

1 Fund.=Fundamental, App.=Applied 2 Initiated First Year 4 Initiated Third Year 6 Pending 8 Initiated Fifth Year 10 Initiated Eighth Year
Exp.=Exploratory, Foc.=Focused 3 Initiated Second Year 5 Initiated Fourth Year 7 Other Funding 9 Initiated Sixth Year 11 Initiated Ninth Year

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