HOW TO SIZE WET ELECTROSTATIC PRECIPITATORS FOR BIOSOLIDS INCINERATORS
Abstract:The use of wet electrostatic precipitators (WESP) as secondary scrubbers for the removal of fine particle emissions from biosolids incinerators is increasing. Since 1990, fifteen (15) biosolids incinerators have been retrofitted with WESPs. In all of these applications WESPs have been installed downstream of the existing venturi scrubbers. The data from these installations show that the particulate matter and metal emissions from the biosolids incinerators can be significantly reduced with the installation of WESPs. The average particle emission rate from the biosolids incinerators equipped with WESPs is 0.19 lb/ton dry biosolids incinerated with a range of 0.02 to 0.27 lb/ton. The WESP metal removal efficiencies also show a wide range of performance. The significant factors affecting the collection efficiencies for particles and metals are the concentration of pollutants in the gas stream, secondary voltage and size of the WESP. Although, the WESP was a proven technology in other applications, there was no reliable data to size equipment for a desired performance for biosolids incinerators in the 1980's. In 1989, an extensive pilot test was conducted to develop the necessary data for sizing WESP at the City of Erie Wastewater Treatment Plant (CEWWTP). Based on this data the Erie Sewer Authority (ESA) has retrofitted two multiple hearth furnaces with WESPs for the reduction of particle and metal emissions. These WESPs have been extensively tested for the collection efficiencies for particles, various metals and condensable compounds.
This paper compares the results of the test data from the full scale WESP installation with the pilot test data. In the determination of the pilot and full scale WESP collection efficiencies, flue gases were simultaneously sampled at the inlet and outlet of the units for various pollutants. During the pilot tests the flue gas volume into the WESP was varied to determine the relationship between the specific collection area (SCA) and the collection efficiency for different compounds. The SCA is defined as the unit collection area in sq ft per 1000 actual cubic feet per minute (acfm) gas treated. From this data the effective migration velocity (EMV) for each compound was determined. The full scale WESP was sized for the required particle collection efficiency based on the EMV developed with the pilot test. The tests conducted at the EWWTP indicated that the data developed with a pilot WESP can be used in accurately sizing a full size WESP for a desired performance.
Document Type: Research Article
Publication date: January 1, 2000
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