Utilities Using DBA in Scrubbers Save Millions in Annual SO2 Compliance Costs

October 7, 2004
WICHITA, KS. October 7, 2004. - The use of organic diacid additives to Flue Gas Desulfurization (FGD) unit scrubbers can significantly reduce emissions control costs and put money in your pocket. It is well known that utilities burning high-sulfur coal can use diacids to help reduce SO2 emissions to allowance levels. However, what several utilities have discovered is that just getting into compliance may not be as economical as overscrubbing and selling emissions credits. With the current value of SO2 emission credits at over $400 per ton, the potential value of SO2 credits gained through efficiency improvements from organic diacid use can easily exceed $2 million annually.

"Utilities that burn high sulfur coal are being environmentally and operationally challenged by decreasing emissions limits and dramatically increased prices to purchase emissions allowances on the open market," says Kathleen O'Keefe, Regulatory Compliance Manager for INVISTATM Specialty Intermediates. "This year allowance prices have fluctuated from historical trading averages of about $200 per ton to upwards of $600 per ton and could go higher particularly if a proposed regulation, which further tightens the annual cap on emissions for certain eastern states, is approved."

Use of organic diacids in wet limestone scrubbers remarkably improves the SO2 removal efficiency in two ways. First, the diacids increase the dissolution rate of limestone into the liquid slurry feed to the scrubber. Second, the mass transfer rate of SO2 from the gas phase to the scrubber liquid, often a limiting factor in scrubber systems, is improved.

Use of organic diacids in wet limestone scrubbers has proven highly effective in significantly reducing SO2 emissions from coal-fired utility boilers. Utilities which have worked with INVISTATM Specialty Intermediates to install or retrofit scrubbers that utilize INVISTATM Dibasic Acids (DBA) have achieved impressive results. A recent trial at the AES Deepwater Plant, located in Pasadena, Texas, resulted in significant emissions reduction and cost savings. The introduction of DBA had an immediate and dramatic impact to the SO2 capture as the scrubber efficiency was increased by five percent. Additional savings were also realized through operational and maintenance improvements resulting from the use of DBA. According to Jacob Peter, Mechanical Engineer with AES, "Our experience was so positive that I don't know why any wet limestone scrubber would be run without a buffering additive addition such as DBA." The AES Deepwater Plant now regularly uses DBA and the nominal cost implementation was reasonably quick and trouble-free.

Depending on the specific operating strategy for controlling SO2 emissions, use of DBA can allow a utility to meet regulatory requirements while taking advantage of a variety of options to maximize potential savings. Lower operating costs can be achieved through reduced limestone consumption, switching to less expensive high-sulfur coal and reduced power usage. Maintenance costs can be reduced through less plugging, scaling and exit gas corrosion. Finally, the ability to over-scrub offers a utility the opportunity to develop a flexible compliance strategy and the option to sell excess allowances or bank them for future use.

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