6-26-08

Limestone Scrubber Design was the Hot Topic, June 26, 2008

Europe and the U.S. are both ratcheting down the emission limits for SO₂. This creates new demands on limestone scrubbers. Speakers from two continents reviewed the past and predicted the future. The biographies and pictures of the presenters are shown at bios and photos.

Jan Middelkamp of Kema summarized 25 years of FGD experience in the Netherlands, where 4,000 MW of coal-fired power plants are equipped with scrubbers. The demand for higher efficiency has resulted in some units switching to chalk. Co-firing of up to 10 percent biomass is now typical. Elimination of gas-to-gas reheaters has improved efficiency (no leakage of air). The present LCPD/Bees is a limit of 200 mg/m³ (0.15 lbs/MMBtu, but if biomass is co-fired the limits are lower.

Wastewater discharge requirements are stringent with mercury limits of 3 mg/m³. Three new pulverized coal-fired and one IGCC system power projects are planned. Emissions of SO₂ will be limited to 40 mg/m³. But carbon capture may dictate a combined maximum emission value of 10 ppm SO₂ and SO₃, so they are looking at advanced scrubbing plus WESPS.

Paul Croteau of Babcock Power showed a typical 600 MW FGD site. The absorber island is 120’ x 140’ and a common building for reagent size reduction and dewatering is 160’ x 80’. Limestone requirements are 35 t/h. Power requirements are 10-18 MW. Pressure drop across the system is 7-8 inches w.g.

Procurement is one of the biggest scheduling problems. It can take up to 18 months for delivery of ball mills and other critical components. Engineering takes six months, construction nine months, and commissioning two months. Everything considered, the utility should think in terms of four years from project inception to startup.

Anne Minga of Kuttner provided details on both lime and sodium as FGD reagents for dry systems. Sodium has advantages particularly with capital cost, as you eliminate the spray drier. A number of dry systems with recirculation of reagent have been supplied for European waste-to-energy and other plants.

Limestone scrubber decisions are impacted by Hg, CO₂, HCl and toxics capture plus implications of co-firing biomass. We are reporting elsewhere in this Alert the revised permit for Wise County which went from 3,300 tons of SO₂ to just 603 tpy. The CO₂ capture could lead to a requirement for greater than 99 percent SO₂ removal where the plant wants to be “CO₂ ready.”An analysis of tray, spray and sump scrubbers was provided by Bob McIlvaine and summarized below.

Parameter	Tray	Spray	Sump
Pump power	medium	High	low
Fan power	higher	lower	higher
Plugging potential	higher	lower	higher
Height	lower	higher	lower
Experience	2nd	1st	3rd
Suppliers	Babcock & Wilcox, Wheelabrator	Alstom Babcock Mitsubishi	Chiyoda Alstom
Particulate removal	higher	lower	higher
Biggest concern	Tray pluggage	Nozzle pluggage	Level control
Efficiency increase	2nd tray	More spray banks	Higher level differential