Fluidized Bed Combustion

The Energy Institute 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, improving combustor operation by reducing bed agglomeration, and evaluating combustion performance and emissions of alternative fuels.

The majority of the Energy Institute's initial activities in fluidized bed combustion focused on evaluating sorbent behavior for SO₂ control. A major program was conducted with 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.

Recent activities are focused on evaluating the combustion performance and emissions of biofuels. These fuels, tested in Penn State’s pilot-scale fluidized-bed combustor, are fired individually or cofired with coal or waste coal. Fuels that have been tested or currently being testing in the FBC include:

• bituminous coal
• bituminous coal wastes
• poultry litter
• poultry fat
• animal proteins including meat and bone meal, pork meal, blood meal, feather meal, poultry meal
• cow carcasses
• Specified Risk Materials
• sewage sludge
• waste foods
• switchgrass

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 for several developers of cogeneration facilities;
• Determined the sorbent performance of numerous limestones and dolostones 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