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Fuel Preparation and Characterization

Relevant Publications

Fuel Preparation

Fuel Characterization

The CUC has the capability to characterize selective physical properties and complete chemical composition of solid and liquid fuels.

Reagent/Sorbent Characterization and Evaluation

The CUC has conducted several successful programs in characterizing and evaluating limestones as reagents in WFGD systems and as sorbents in FBC systems for reducing SO₂ emissions. The CUC has particular expertise in determining the qualities of limestones that make them attractive as a reagents/sorbents in a given system and the ability to evaluate limestones in a variety of on-site bench- to pilot-scale units. The CUC has conducted full-scale testing at a commercial FBC facility (30 MW_(e)) and is currently seeking to conduct testing at a utility-scale (1,800 MW_(e)) WFGD unit.

Limestone Characterization

Aspects Particular to Limestone Evaluation for SO₂ Reduction in:

Fluidized Bed Combustion

• Calcination/Sulfation Behavior
• Attrition Potential
• Development of Thermally-Induced Fractures during Heating

Wet Flue Gas Desulfurization

• Dissolution Behavior

A summary of project results for limestone evaluation for SO₂ reduction in FBC and WFGD systems is given in the section on Emissions Characterization and Reduction, SO₂ Control.

Combustion Systems Development

The CUC has been developing technologies for utilizing coal-water slurry fuels (CWSFs) and micronized coal in fuel oil-designed boilers. To evaluate the technical and economic viability of firing coal-based fuels in oil-designed, industrial watertube boilers, proof-of-concept demonstrations were conducted in our industrial-scale boiler. Technical aspects of these demonstrations included: coal storage (hoppers for micronized coal; tanks for CWSF) and handling (conveyors, screw feeders, weigh-belt feeders, and pneumatic transport for micronized coal; pumps and piping for CWSF) and integration with the burner; matching various burners with the boiler; combustion and boiler performance; ash deposition, accumulation, and erosion; emissions; and boiler derating.

• System Integration/Burner Development
• Pollution Control
• Boiler Retrofits

System Integration/Burner Development

As a consequence of the system integrations, the CUC identified special considerations for transporting, storing, and handling coal-based fuels that are being utilized in industrial boilers that have been designed for fuel oil. These are especially crucial in an one-burner boiler system.

A major element of the system integration was burner development. The CUC is actively involved in the development and evaluation of low-NOx burners for industrial boilers. This includes burner and boiler modeling, burner performance evaluation, and new burner development. Low-NOx burner evaluation and development activities have been conducted in conjunction with ABB Combustion Engineering (High Efficiency Advanced Coal Combustor and Radially Stratified Fuel Core burner) and Energy and Environmental Research Corporation (FlamemastEER^TM burner) using the Demonstration Boiler.

Another crucial component in the system integration is coal micronization and transport to the burner. The CUC works closely with TCS, Inc., a mill manufacturer for on-line micronization applications in industrial boilers.

The CUC also works closely with manufacturers of auxiliary components. CUC assisted ABB Air Preheater, Inc. in evaluating its heat pipe heat exchanger, which is installed on the demonstration boiler system, for use as a combustion air preheater. The results from this activity were used to assist in future preheater designs.

Pollution Control

The CUC assists in developing pollution control technologies. Currently, the CUC is demonstrating the removal of ultrafine particulate matter with increased particulate collection efficiency through the use of a ceramic filter. A ceramic filtering device is operated in parallel with the fabric filter baghouse to evaluate this new technology, contrast it with conventional filtration, and demonstrate a smaller, more efficient filtering device for boiler retrofit applications.

The CUC is actively participating in the identification/development of a NOx reduction catalyst that is compatible with the typical operating conditions and the economic constraints of industrial boilers. The catalyst is being developed for two applications -- as a monolith supported catalyst on the clean side of a conventional baghouse and as a coating on a ceramic filter. The CUC is collaborating with Englehard Corporation, CeraMem Corporation, and Babcock & Wilcox on this activity.

Boiler Retrofits

The viability of future oil-to-coal boiler retrofits has been assessed, starting with the conversion of two package boilers, 1,000 lb steam/h (research boiler located within The Combustion Laboratory) and 15,000 lb steam/h (industrial-scale boiler), from oil to CWSF and pulverized coal. The boilers were used to: determine the effect of boiler operating parameters (i.e., atomization quality, fuel particle size, level of combustion air preheat temperature) on combustion performance; automate the firing system, particularly with respect to start up and shutdown procedures but also to optimize boiler performance; evaluate fuels; determine the level of boiler derating (less than 15%); determine the maximum ash level (~5 wt.%) tolerable; and determine the ideal coal particle size distribution (D_(v,0.5) = ~18 µm).

The system and operating knowledge (e.g., level of combustion air and CWSF temperature, proper flow meters, gauges, and piping geometries, mixer types and tank dimensions, coal silo dimensions, and proper coal transport equipment) gained from the demonstration boiler was used to design the retrofit of an oil-designed boiler located on a military base to fire dry, micronized coal and CWSF. The conversion was engineered by the CUC and Energy and Environmental Research Corporation.

	Combustion Research

Determining combustion behavior is an intergal part of evaluating a fuel. This is especially true in the case of developing new alternative fuels. The CUC has years of experience in conducting combustion tests firing traditional fossil fuels and alternative fuels such as coal-water slurry fuel (CWSF) and emulsions in conjunction with other fuels. The CUC also has the capabilities to evaluate biomass-based fuels.

• Fluidized Bed Combustion
• Coal-Water Slurry Fuel Combustion
• Pulverized/Micronized Coal Combustion
• Stoker Combustion
• Evaluation of Emulsions

Fluidized Bed Combustion

The CUC assists the fluidized bed combustion industry by evaluating sorbent behavior for SO₂ capture, determining the influence of fuel properties on combustion performance and sulfur capture, assisting in materials handling issues, working with operators and regulatory agencies when developing new policies, and improving combustor operation by reducing bed agglomeration.

The majority of the CUC's activities in fluidized bed combustion focus on evaluating sorbent behavior for SO₂ control. A major program, that was recently completed, was conducted with The Combustion Laboratroy, the Pennsylvania Energy Development Authority, the Pennsylvania Aggregates and Concrete Association, Meckley's Limestone Products, The Pennsylvania Geological Survey, and Westwood Energy Limited Partnership to determine if low purity (low CaCO₃ content) limestones and dolostones can be utilized in fluidized-bed combustors as sorbents for SO₂ capture. Prior to this study, manufacturers of fluidized-bed combustors routinely specified the use of relatively high purity limestones (CaCO₃ content > 85 wt.%) for this purpose. Specific results from this work include:

• Each sorbent has an optimum temperature for sulfation, and that this temperature is residence time dependent;
• Sorbents with calcium carbonate contents ranging from 50 to 99.9 wt.% were effective in maintaining emissions compliance in Westwood's 30 MW(e) power plant;
• Finer particle size fractions had lower Ca/S molar ratios than coarser sizes in the bed ash and recycle ash of the power plant;
• For larger particles, the slow rate of SO₂ diffusion through the product layer limited the extent of sulfation;
• Hot-stage scanning electron microscopy and microprobe analysis of the sulfur distribution of sulfated sorbents indicated that some sorbents developed thermally-induced fractures (TIFs), while others with comparable CaCO₃ contents did not;
• The TIFs promoted SO₂ diffusion into the particle, and as a consequence, the sulfation behavior of such sorbents was less particle size dependent than was that for the sorbents which did not develop TIFs.

Specific results from additional activities include:

• Assisted Panther Creek Partners, in conjunction with Penn State's Material Research Laboratory, in identifying an efficient means for handling ash streams, specifically ways of minimizing dusting;
• Provided supporting information to the Anthracite Region Independent Power Producers Association and Foster Wheeler Power Systems, Inc. for the U.S. Environmental Protection Agency's study to classify fluidized bed ash for disposal;
• Produced ash samples for analysis for ash disposal permits, in conjunction with The Combustion Laboratory, for several developers of cogeneration facilities;
• Determined the sorbent performance of numerous limestones and dolostones, in conjunction with The Combustion Laboratory, for limestone producers, fluidized bed operators, and developers of cogeneration facilities;
• Evaluated coal/ash samples, for American Hydro Power Company, to verify sulfur retention in the ash and to determine the limestone addition rate necessary for the boiler to meet emissions standards; and
• Assisted Quaker State Corporation in identifying and remedying the cause for bed agglomeration in order to improve operation.

  More on the Use of Limestone in FBC for Reduction of SO₂ Emissions

Coal-Water Slurry Fuel Combustion

CWSF research and development have been an integral part of Penn State's activities since the early 1980's. The focus has been on establishing acceptable formulation and preparation procedures and obtaining satisfactory combustion performance in fuel oil-designed industrial boilers, and during cofiring with pulverized coal in utility boilers. Fundamental, pilot and demonstration scale activities have provided detailed understanding of the chemical and physical phenomena involved in CWSF rheology and stability, atomization and combustion, mineral matter transformations, atomizer tip and boiler tube erosion, ash settling and deposition, boiler derating, and emissions. Specific accomplishments include:

• Determined the status of commercially-available CWSF burners and atomizers in the U.S. as the first step in retrofitting two package, oil-designed boilers at Penn State, to CWSF;
• Converted a 1,000 lb steam/h, Cleaver Brooks package boiler from oil to CWSF in The Combustion Laboratory. This boiler was used to investigate: the effect of boiler operating parameters on combustion performance; automation of the firing system for slurry fuels, particularly with respect to start up and shutdown procedures but also to optimize boiler performance; screening candidate CWSFs; and providing the necessary research support and training prior to start up of a larger demonstration boiler (15,000 lb steam/h) converted to fire CWSF;
• Incorporated the system and operating knowledge gained from the 1,000 lb steam/h boiler into the retrofit design of the demonstration boiler (15,000 lb steam/h) and its shakedown for CWSF use. The technical and economic viability of firing CWSF in the retrofitted boiler were determined for CWSF cleaned to very low ash levels. This included performing natural gas baseline tests, developing a boiler performance model, conducting a parametric study of the effect of operating parameters on combustion and boiler performance, and performing a retrofit cost analysis.

Formulation and Preparation of CWSF

CWSF formulation and preparation have progressed from bench-scale (pound quantities) to pilot-scale (tons/h) and utility-scale production levels. Significant accomplishments include:

• Through programs with the U.S. Departments of Energy and Defense, and the Commonwealth of Pennsylvania, highly loaded and stable CWSFs have been prepared from deeply-cleaned coals for fuel oil substitution in industrial boilers;
• Through activities with Pennsylvania Electric Company, Tennessee Valley Authority, and the Homer City Coal Processing Corporation, low solids CWSFs have been prepared from fines from active cleaning plants and abandoned impoundments to cofire with pulverized coal in utility boilers;
• Formulation procedures have been documented, and potential problems and solutions in the preparation and handling of CWSF have been identified; and
• It has been found that oxidation of impounded coal fines had not occurred to an extent that affected CWSF formulation, and the same formulation, preparation, and utilization procedures could be used as for coal fines from active cleaning plants.

Fundamental Studies

Early studies at Penn State focused on increasing the combustion rate of CWSFs so that acceptable burnout could be achieved in the available residence time in retrofitted boilers. Significant accomplishments include:

• Oxygen enrichment of combustion air was found to improve the combustion efficiency by increasing the flame temperature and hence the char combustion rate. NOx emissions increased while SO₂ emissions were relatively unaffected;
• Secondary atomization of CWSF droplets due to explosive boiling required a heat flux in excess of that associated with conventional boilers, regardless of the additives used in the formulation;
• Combustion enhancement by imposing a high-intensity acoustic field to generate large and rapidly fluctuating gas velocities (relative to the CWSF droplets) was attributed to increased convective heat and mass transfer rates;
• Atomization quality, mineral matter size, and occurrence of mineral matter in coal particles affected the resulting ash particle size; and
• An erosion-corrosion model, based on accelerated erosion tests, indicated that significant boiler tube erosion does not occur if the flue gas velocity in the convective section is below the value required to keep the erosion in the oxide scale regime.

Cofiring CWSF and Coal in Utility Boilers

Interest in cofiring CWSF and pulverized coal stems mainly from its potential as a low cost NOx control technique. As a consequence, the CUC has been active in the development of this technology and has been working with the Pennsylvania Electric Company, Tennessee Valley Authority, Electric Power Research Institute's Upgraded Coal Interest Group, Central Illinois Public Service Company, and Southern Indiana Gas and Electric Company.

The CUC has visited numerous coal preparation facilities to evalute their coarse and fine coal refuse. Both active and inactive sites have been studied. Of particular importance is the history of the cleaning facility at the site.

Active Coal Preparation Facility with Reject Coarse and Fines in Foreground

Some sites are well documented regarding changes in the circuit design with time while other sites, particularity older inactive sites, are poorly documented. In the case of reclaimed sites, the reclamation plans can provide valuable information as to the volume of waste coal and geometry of the site.

Field evalation of a site usually involves a drilling program to evaluate the coal fines within the site to determine the extent of lateral and horizontal variation in quality and size. This is particularity important when dealing with a site that experienced numerous changes in the cleaning circuit, types of coal cleaned at the facility, end use of the cleaned product and changes in disposal techniques and plans over time.

CUC Field Sampling of Inactive Coal Pond Fines Site

• CWSFs produced from coal cleaning plant filter cake, and from impounded coal fines, were handled and cofired with pulverized coal in an utility boiler (Penelec's Seward Station); and
• Cofiring CWSF and pulverized coal in Penelec's Seward Station reduced NOx emissions by as much as 26.5% by the CWSF acting as a reburn fuel. The burner configuration increased the concentration, and changed the spatial distribution of hydrocarbon radicals within the combustor with the net effect of reburning the NOx produced in the pulverized coal flames to N₂.

Pulverized/Micronized Coal Combustion

A fuel oil-designed boiler was modified to fire dry, micronized coal. Major accomplishments, obtained in programs conducted for the U.S. Departments of Energy and Defense and ABB Combustion Engineering while developing three commercial burners (two ABB Combustion Engineering burners and one Energy and Fuels Research Corporation burner) were:

• Integrated the coal handling and micronizing systems with the burner;
• Conducted fundamental studies to determine the effect of the mineral matter on the boiler tube erosion and deposition;
• Determined that erosion was not significant in the convective pass;
• Quantified the extent of deposition during continuous operation;
• Computationally modeled the burners and boiler;
• Obtained targeted NOx emissions of < 0.6 lb/million Btu while maintaining combustion efficiencies of 98%; and
• Designed a compact, easy to retrofit burner with commercially acceptable combustion air pressure drop (< 8" W.C.).

Stoker Combustion

The CUC has experience in determining the combustion behavior of coals and blends on stokers. The CUC, in conjunction with The Combustion Laboratory, completed a program to evaluate the combustion behavior and determine the economics of firing various blends of anthracite with the bituminous coals used at the Jennison and Hickling generating stations of the New York State Electric & Gas Company (NYSEG). Results of the program include:

• Blends of anthracite and bituminous coals displayed better combustion behavior in a bench-scale stoker simulator than the bituminous coals alone, due to reduced caking of the bed and enhanced air flow through the bed;
• Tempering the bed with water was more effective than manipulating the initial particle size distribution for decreasing the bulk density of the bed and improving combustion performance; and
• Partly as a result of this program, NYSEG burned blends of 10-15% anthracite by-products with bituminous coals at their Jennison Station.

In a similar program, the CUC is assisting EFH Coal Company to reduce emissions from low stack boilers in the Krakow, Poland region. EFH Coal Company will be constructing and operating a coal washing and grading plant to improve the quality of coal (lower ash and properly sized) fed to these types of boilers. The CUC is supporting the program by performing combustion tests in the stoker simulator, and providing technical assistance during full-scale boiler demonstrations in Poland to evaluate the new feedstock prepared by EFH Coal Company.

Evaluation of Emulsions

The CUC has access to the facilities and has the capabilites for evaluating emulsions including fuel characterization, burning profiles, and combustion performance. For example, a program was conducted by the CUC, in conjunction with The Combustion Laboratory, to evaluate the combustion behavior of an emulsion of hydrocarbon and water, and compare it to No. 6 fuel oil for the Coastal States Management Corporation.

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