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:
There is no apparent impact at low load unless high feed rates of activated
carbon at low load packs the bags with available carbon when we ramp to high
load.
o
10 lb/hr feed rate at lower loads appears to supply adequate activated carbon
feed rate for mercury control.
When the carbon injection concentration was dropped our CEM’s mercury
increased at high load.
There appears to be a relationship between carbon injection concentration, load and fabric filter pressure levels. – Can they comment on?
o As fabric filter inlet pressure increases, fabric filter outlet pressure increases and fabric filter dP increases; at full load CEMs mercury also appears to increase at full load settings.
o
At full load when the fabric filter outlet pressure drops below and stays
below -30 INWC we may pull more mercury thru the baghouse.
o There may be some relationship between coal types and/or mercury proxy with CEMs mercury. This needs to be further explored.
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
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
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
Mercury emissions and regulations in the U.S., China and Europe
Revision Date: 7/31/2014