Hot Topic Hour on November 12 was Wet vs. Dry FGD

Mike Meadows of Black & Veatch spent two days talking about this subject in South Africa recently. So it was a challenge for all the speakers to condense the comparison into a two hour webinar. With the potential of new MACT rules, limits on FGD wastewater discharges and CO₂ capture cleanliness requirements, there is the big question as to whether the right choice for this year is the best choice for the longer term.

Terence Ake of Babcock Power said that the choice of scrubbing technology depends on whether the boiler is new, the age of the boiler, the space constraints, the availability of water, and other site specific facts.  It’s important to consider the use of the byproduct. The co-benefits of a technology to remove sulfur trioxide, mercury, and flyash may become important to answer the question of whether a boiler can be built or must be retired. Roosevelt Huggins and Mike Meadows (Black & Veatch) provided a good comparison between the two technologies. They cautioned that a retrofit situation can be different in terms of capital cost. If you already have a precipitator and are installing a wet scrubber, the cost may be lower than installing a fabric filter and dry scrubber.

Bob Nicolo of Hitachi Power compared the conventional technologies and then discussed the advanced venturi pre-scrubber which avoids ESP rebuilds, enhances gypsum purity and can provide salable hydrochloric acid. This technology is covered in Patent 5429808. In the discussion period it was pointed out that the mercury can be stripped from the acid bleed stream. This eliminates concern about metal contaminants in the gypsum or wastewater.

Pete Honeycutt of Kiewit Power discussed the Flash Dry Absorber (FDA or NID) design among others. This is available in modules of 100 MW. So you would need multiple units for large boilers. CFB scrubbers are now able to achieve up to 98 percent removal with inlet SO₂ as high as 6 lbs/MMBtu. They can use poor water quality sources for humidification.

Greg Carleton of Pollution Control Services pointed out basic differences for the two technologies in relationship to the operating parameters for existing coal-fired generators.   Understanding how numerous boiler modifications and fuel supply changes can either positively or negatively affect plant operational costs with both technologies is crucial. The two basic technologies need to be compared over the equipment life cycle because capital costs and O&M costs are considerably different. Since the rules are continuing to change the selection parameters will change as well.

Gordon Maller of URS Corporation took up the issue of SO₃ removal and pointed out that with SBS and other additives the wet scrubber can achieve high SO₃ removal. Previous speakers displayed the higher efficiency of the CFB scrubber on SO₃. Air toxics are divided into three classes which include those equally divided between the bottom ash and flyash, those that are enriched in the flyash, and those which pass through the particulate collector in a vapor phase. This includes selenium, HF, and HCl. Gordon stated that the wet scrubber would achieve higher removal efficiencies on this class of air toxic.

Emmett McDermott of Dedicated Transport explained that his company is delivering byproduct lime from municipal water plants to utilities for their FGD systems. This reduces pollutants at municipal water plants and provides a low cost source of reagents. Over 249,000 tons were delivered to FGD and waste-to-energy (WTE) systems in Florida last year

Bob McIlvaine stated that the Cement MACT rule which requires 2 ppm HCl will be the tail wagging the dog. It will likely also be the situation in coal-fired power plants. It is the reality in waste incineration plants where the HCl limit is only 27 ppm. You will reduce SO₂ by the same percentage as HCl, so an SO₂ limit becomes irrelevant. The wet vs. dry scrubbers for the SO₂ question may have to be replaced with the wet vs. dry scrubbers for 2 ppm HCl.

This again brings up the possibility of two stage scrubbers with the first stage concentrating hydrochloric acid as described by Hitachi. A number of waste-to-energy plants in Europe are selling 30 percent hydrochloric acid. They use ion exchange resins to take out the mercury. In light of the big potential in wastewater treatment for wet single stage FGD systems, this could be another justification for two stage scrubbers. On the wastewater treatment cost, this is a new development which could change the economics between wet and dry systems. On the other hand, maybe zero liquid discharge systems are a solution.

A dry system which would obtain the 2 ppm HCl plus the metal toxics along with NO_x and SO₂ is ReACT. Hamon Research Cottrell is going to be marketing it in the U.S. The comparative economics are now at least somewhat more attractive given MACT and wastewater rules. Sodium is another potential beneficiary. To obtain the 2 ppm HCl maybe a sodium spray drier is an answer.

With new rules on several fronts we are going to have to continually re-evaluate comparisons among the technologies.

The bios, abstracts and photos can be viewed as follows: November 12, 2009 - BIOS, PHOTOS, ABSTRACTS.htm

The individual slides for the “Wet vs. Dry FGD” recording are located in our FGD Decision Tree as follows:

Emmett McDermott – Dedicated Transport

FGD Continuing Decision Process For: Calcium

Lime Slurry Recycling Program - Water Treatment Plants, presented by Emmett McDermott, Dedicated Transport. Hot Topic Hour November 12, 2009.

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/Emmett McDermott - Dedicated Transport - 11-12.pdf

Terence Eke – Babcock Power

Greg Carleton – Pollution Control Services

Gordon Maller – URS

Robert Nicolo – Hitachi

Roosevelt Huggins and Mike Meadows – Black & Veatch

Pete Honeycutt - Kiewit

FGD Continuing Decision Process For: Calcium

Wet vs. Dry Hot Topic Hour Presenters

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/wet_vs._dry FGD.htm
 

Wet vs. Dry Flue Gas Desulfurization, presented by Terence Ake, Babcock Power. Hot Topic Hour November 12, 2009.
subscriber/Tree/DescriptionTextLinks/Terence Ake - Babcock Power 11-12-09.pdf

Current FGD Status, presented by Greg Carleton, Pollution Control Services. Hot Topic Hour November 12, 2009.
subscriber/Tree/DescriptionTextLinks/Greg Carleton - Pollution Control Services - 11-12-09.pdf

Comparison of Wet and Dry FGD, presented by Gordon Maller, URS. Hot Topic Hour November 12, 2009.
subscriber/Tree/DescriptionTextLinks/Gordon Maller - URS - 11-12-09.pdf

Wet vs. Dry FGD, presented by Robert Nicolo, Hitachi. Hot Topic Hour November 12, 2009.
subscriber/Tree/DescriptionTextLinks/Robert Nicolo - Hitachi - 11-12-09.pdf

Wet vs. Dry FGD Systems - Air Quality Control Systems, presented by Roosevelt Huggins and Mike Meadows, Black & Veatch. Hot Topic Hour November 12, 2009.
subscriber/Tree/DescriptionTextLinks/Roosevelt Huggins - Black & Veatch.pdf

CFB Scrubber History, presented by Pete Honeycutt - Kiewit. Hot Topic Hour November 12, 2009.
subscriber/Tree/DescriptionTextLinks/Pete Honeycutt - Kiewit.pdf