Many Mercury Sorbent Options discussed in Hot Topic Hour July 31


The webinar yesterday was based on presentations posted on a dedicated website:  Mercury Removal - Continuous Analyses.  The format was a discussion of important options. Some of the highlights are covered below. The recording captures the complete discussion. We will be posting this information to the website and are asking for additional input both from the participants and others.
 

·         World Outlook

Power plants in the U.S. emit about 40 tons of mercury/yr with an anticipated further reduction to less than 10 tons. World emissions are around 2,000 tons. The new regulations require existing coal-fired power plants in the U.S. to reduce emissions to the equivalent of 1.7-4 ug/m3.  This is low compared to the 30 ug/m3 limit for German and Chinese coal-fired power  plants. But the Chinese are tentatively looking at a reduction to 5 ug in 2015 and 3 ug in 2020.  Some individual plants in Europe have limits less than 3 ug/m3. (See presentation on website which is also a feature article in Air Pollution Control Magazine.)

 

·         Mercury removal from Natural Gas, CO2, Synfuels (huge Chinese Pipeline)

China will be making as much syngas from coal as the U.S. is extracting from shale. It will travel long distances by pipeline. What are the mercury reduction considerations?  No one volunteered to answer this one.

 

How do power plant requirements compare to those for removal of mercury from natural gas?

Richard Mimna, Calgon Carbon - In contrast to the electric utility sector where mercury control was driven by environmental legislation, mercury removal from natural gas was driven by the desire to protect process equipment.  Mercury naturally occurs in many natural gas fields around the world.  Mercury can damage a variety of alloys by a process known as liquid metal embrittlement in which penetration of a liquid metal into a solid metal leads to brittle fracture. This phenomenon has caused a number of catastrophic failures at natural gas processing plants over the years.

Back in the 1970s, activated carbon technology was developed to remove mercury from natural gas and other hydrocarbon streams. To this end, Calgon Carbon developed a product called HGR, a sulfur impregnated granular product.  In contrast to flue gas applications in which a powder carbon is injected into the duct, HGR is loaded into adsorber vessels that the natural gas is passed through. Also, the conditions are necessarily very different from coal-fired flue gas (higher pressure, much lower temperatures, very different composition).

Coincidentally, this is when copper sulfide (CuS) was also discovered as a possible mercury removal agent and it was first patented by the French Petroleum Institute back in 1978.  Rather than function as a true adsorbent, copper sulfide removes elemental mercury from gas streams by chemisorption via 2CuS + Hg -> Cu2S + HgS.  This is the same active component that others have tried to develop for non-carbon based sorbents for use in coal-fired flue gas today.

Activated Carbon

How do I determine whether I should use brominated PAC vs. non-brominated PAC?

John Miller of Albemarle observed that the value of brominated PAC is in proportion to the percentage of elemental as opposed to oxidized mercury in the flue gas.  Richard Mimna cited his posted presentation on the site that shows a combination of bromine fuel additive and non-brominated PAC was most economical in a plant burning PRB coal.

 

What are the temperature limitations of PAC?

 

Albemarle has a special high temperature PAC which extends the range but efficiency is reduced at higher temperatures. The problem is the release of captured mercury from the carbon at high temperatures.

 

What balance of plant effects have been observed with the use of ACI? 

Flyash salability is a major consideration and can be addressed with concrete friendly PAC

What are the most important considerations when storing PAC?

Some participants thought it was important to coat the brominated carbon storage silos.  Others have seen no corrosion. Stephen Potter of Duke said that the risk of shutting down to repair a silo leak even if negligible was justification for the small expenditure for coating.

 

What are the advantages and disadvantages of PAC injection before APHs?

 

The extended contact plus some build up of PAC on the air heater can increase mercury capture.  There is a downside, observed Stephen Potter. There is already a buildup problem in the air heaters due to ammonium bisulfate.  The safety and other risks of adding ACI to a heater which may plug should be avoided.

 

For brominated PAC, is there a minimum bromine content necessary for good mercury performance? 

 

Question was not addressed.

 

Activated Carbon Performance

 

Comments from Steve Otto, Minnesota Power

 

Lowering the operator entered carbon injection concentration from 1.2 to .25-.2 lb/MMacf results in the following:

 

o   10 lb/hr feed rate at lower loads appears to supply adequate activated carbon feed rate for mercury control.

 

      o   A drop to 25 lb/hr feed rate of activated carbon at high loads increases the CEM’s mercury.

 

Several participants had comments on this.

 

John Knotts of W.L. Gore questioned whether the problem has to do with leaks at the seams of the bags. This would cause the bleed of small carbon particles to the clean side of the bags. Gore makes a special seam to avoid this problem.

 

Definition of Impregnated Activated Carbon vs. Brominated

 

Albemarle:   Impregnated carbons only include activated carbon with bromide salts, our gas-phase bromination is not impregnated.  Possibly a better section would be brominated (which includes all types) vs. plain or non-brominated carbon.

 

Other Sorbents 


Non-carbon
Sorbents

How effective are the current non-carbon sorbents?

 

Steve Baloga of Novinda showed the economic advantages of amended silicates (bentonite). He also introduced a new product specifically designed to increase mercury oxidation in the flue gas and prevent re-emission in wet scrubbers (see presentation on the site).

Fixed sorbents such as gold amalgamation and the Gore membrane module.

 

(Not addressed)

 

UBC-unburned carbon in flyash can be effective if SO3 is reduced. 

Sterling Gray of URS showed how the use of SBS to reduce SO3 leads to inherent mercury capture by the unburned carbon in the flyash. 

What is the role of the SCR catalyst? 

 

Kyle Nedig of  MHPS cited high oxidation ratios for a special catalyst which also maintains low conversion of SO2 to SO3 but high conversion of NOx to N2 (see presentation on site)

 

 

THE 90 MINUTES EXPIRED WITHOUT DISCUSSION OF ANY OF THE FOLLOWING QUESTIONS:

 

System Integration Questions

 

How important is flyash salability and how does this affect the decision making?
 

What are injection considerations?
 

How is the best way to store, inject and distribute the carbon?  

 

Where should the carbon be injected?

If both an alkaline reagent and AC are injected, where are both injected?

If a precipitator rather than baghouse is in place, how much more carbon will be needed?  

 

Fuel Additives
 

When is it feasible to use a mercury oxidation technology, such as CaBr2 on the fuel, to assist in mercury control?

1.      Chemtura reports several cases where AC quantities are reduced with CaBR2 injection.

2.      Albemarle has experience.

Does ammonium in the flue gas affect mercury oxidation by bromides?

Other Relevant Questions:

How much selenium can be removed along with mercury?

How will mercury removal vary with site specific conditions?

Will there be an adequate supply of reagent?
 

Is there a benefit in adding sorbents in the WFGD?

Novinda is touting their sorbent for use with wet scrubbers and Evonik is using activated carbon in their German power plants to eliminate mercury re-emissions. Is this a good use for adsorbents?  Albemarle has experience with various injection with WFGDs.

 

Do these sorbents allow separation of captured mercury from the wastewater as well as preventing re-emissons?

 

 

 

Individual presentations follow:

Mercury Sorbent Options Webinar - Hot Topic Hour July 31, 2014

The webinar yesterday was based on presentations posted on a dedicated website: Mercury Removal - Continuous Analyses. The format was a discussion of important options.

Revision Date: 7/31/2014


MHPSA Hg Oxidation Catalyst by Kyle Nedig, Mitsubishi Hitachi Power Systems Americas - Hot Topic Hour July 31, 2014

Kyle Nedig of MHPS cited high oxidation ratios for a special catalyst which also maintains low conversion of SO2 to SO3 but high conversion of NOx to N2.

Revision Date: 7/31/2014


Strategy for Low-Cost Mercury Control: Using Native Unburned Carbon by Sterling Gray, URS Corp. - Hot Topic Hour July 31, 2014

Sterling Gray of URS showed how the use of SBS to reduce SO3 leads to inherent mercury capture by the unburned carbon in the flyash.

Revision Date: 7/31/2014


Mercury Sorbent Options by Steve Baloga - Hot Topic Hour July 31, 2014

Steve Baloga of Novinda showed the economic advantages of amended silicates (bentonite). He also introduced a new product specifically designed to increase mercury oxidation in the flue gas and prevent re-emission in wet scrubbers.

Revision Date: 7/31/2014


Market - Regulations - Mercury Reduction Status and Programs around the World by Bob McIlvaine, McIlvaine Company - Hot Topic Hour July 31, 2014

Mercury emissions and regulations in the U.S., China and Europe

Revision Date: 7/31/2014