A 49.5 MW Non-cycling Circulating Fluid Bed Boiler

Application

A 49.5 MW non-cycling circulating fluid bed boiler producing a total 500,000 lbs/hr steam.

Optimization Potential

Stringent particulate requirements of 0.012 lbs/mm btu resulted in 0.006 gr/dscf @ 12% CO2 total particulate catch (front and back half of method 5). A spray dryer located upstream of a baghouse was considered in order to reduce back half catch (condensibles) and allow for a higher front half catch (solids).

Solution

A 12 compartment reverse air baghouse with GORE® membrane filter bags was chosen in order to provide the lowest possible front half (solid) catch. This increased the allowable condensible catch and eliminated the high capitol costs ($1.0 to $1.5 million) and high operating costs (lime consumption + power cost) associated with the spray dryer. Design airflow was 245,000 acfm with a net air-to-cloth ratio of 2.2 cfm/ft2.

Results

After the installation of GORE® membrane filter bags, testing revealed total particulate emissions averaging 0.007 lbs/MMBtu (0.00335 gr/dscf @ 12% CO2). Front half particulates averaged 0.0013 gr/dscf (0.0006 gr/acf). Particulate sizing testing of stack gases resulted in a total cascade impactor catch of 0.0002 gr/dscf @ 12% CO2 with 0.00003 gr/dscf @ 12% CO2 less than 10 µ (PM-10) using a six hour sampling. The low emission results were obtained despite several bags coming off thimbles (improperly seated snapbands) immediately prior to testing.

At full boiler load, the baghouse operates with a 2.0 - 4.0" DP, a 4-8 hour cleaning cycle and the reverse air fan is not used. Compartments clean solely by isolation. Tubesheet DP ranges from 0.25"-0.75" after cleaning to 2.0" before cleaning. Current experience with reverse air baghouses using conventional filter bags downstream of fluid bed boilers is limited to 1.6 cfm/ft2 A/C ratio. Substantial baghouse capitol savings were realized.