February 15, 2007

Mercury Control is Commercial but Concerns Remain

On February 15, 56 people participated in a two hour session covering the state of the art of mercury control. The one consensus is that while the technology is commercial there are surprises ahead. The technology is commercial because there are companies making commercial guarantees and supplying systems. But as George Offen of EPRI pointed out, the fires in hoppers and dust handling problems were unanticipated. So what other surprises are out there?

It appears that the problems which have arisen to date have been solved or solutions are at hand. So this is positive. Nevertheless there are a number of site specific factors, some of which we have yet to understand.

Whereas in the September meeting there was extensive coverage of the technologies with semi- formal power point presentations, this discussion was primarily based on informal discussion of the issues with continuous reference to important displays in the Mercury Decision Tree.

The Mercury Decision Tree was enhanced with the inclusion of links to the NETL Mercury Conference held in December 2006. The papers from this conference are all posted on the NETL website.

McIlvaine conducted a number of audio interviews at the EUEC Conference. Two suppliers of activated carbon were interviewed. Both Rob Nebergall of Norit and Ward Rogers of Calgon Carbon confirmed that there will be adequate supplies of carbon available.

New Topics

Conveying and wetting mercury-laden carbon was the subject of the presentation by Kevin McDonough of UCC. Steve Derenne of We Energies also supplemented the presentation with the end user perspective. At about three pounds of carbon/MMacf the present rotary valve/pin mixer system works well. The dust is fed steadily into the mixer which wets the dust sufficiently for final disposal. Frequent evacuation of the hoppers has solved the problem with the fires but may have caused some bag plugging of the dust collector which is part of the handling system. The power points from the presentation are in the Mercury Decision Tree at

Mike Durham of ADA-ES presented a comprehensive set of graphs showing ACI performance under a number of conditions including various coal types, with and without SO₃ injection, along with co-injection of alkaline sorbents and also variations in the TOXECON II concept. In TOXECON II 99 percent of the ash is uncontaminated with PAC due to the fact that the injection is in the precipitator before the last field. The problem is obtaining proper distribution of the PAC; that is likely solved with longer lances and other physical means. The performance of carbons under various conditions is shown in the power points at

Joep Biermann of Minplus says that the Minplus sorbent actually enhances cement quality and will be available in sufficient quantities. It is a combination of clay and alkaline material. The clay does the job of capturing the mercury while the alkaline material prevents interference from SO₃. Major tests are underway and we will see whether the results support the company’s claims that more than 90 percent mercury capture is possible with all coals. His power points are displayed at 

(The company has been working with Mobotec. So the presentation is provided in this branch. As one of the attendees asked yesterday, is the material available directly? Joep was unclear on this subject.)

Updates from Previous Discussions with Remaining Issues

Chuck Miller of NETL addressed remaining technical/performance issues including: Coal Utilization Byproduct (CUB) impacts; mercury re-emissions across FGD scrubbers; increased particulate loading; acid gas/SO₃ interference with ACI; high temperature mercury capture; and baghouse impacts. Chuck indicated that mercury emission during gypsum processing is a problem. However, the present totals are less than one ton a year or two percent of national coal-fired power plant emissions. NETL funding for mercury will be minimal due to the latest budget constraints.

Tom Feeley’s NETL Mercury Conference power points were displayed as a basis for the discussion.

George Offen of EPRI addressed recent issues experienced: sorbent distribution - TOXECON II, long lances, short ducts, low turbulence; SO₃ impact on ACI - Solvable by alkali injection?; temperature sensitivity of halogenated sorbents; hopper fires and fugitive dust in TOXECON demo; Eastern bituminous plant with unusually low Hg²⁺; halogen injection at PRB unit doesn't produce Hg capture by SD/BH - May with SCR? Field sorbent tests often ≠ lab tests; normal variations mask/confuse analyses - e.g., normal PM variations ≥ increase by ACI.

George also addressed user challenges for commercial compliance applications. Limits are set at the level of best performers but data show range of performance: Reasons for site-to-site differences are often not understood or predictable; Guarantees appear to be site specific - not consistent with meeting one-size-fits-all limit. It is unclear how to assess Hg control capabilities under conditions not yet tested, e.g., for TX lignite. High Δ Hg requirements→very low Hg emissions. Can we measure these accurately? Hopper fires weren't expected. What else might happen?

The point of departure for his comments were his NETL Mercury Conference power points at

The meeting moved on to a listing of the remaining issues:

Site Specific Issues

Hot electrostatic precipitators

SO₃ conditioning

Poor performance of halogenated carbon when firing PRB coal and using Spray Drier/Baghouse

Commercial Issues

Availability of carbon

Carbon cost

Cost of higher performance carbons

Cost of flyash friendly sorbents

Lack of experience

Narrow guarantees

Meeting low mercury limits with high mercury in flue gas

Flyash salability impact

Review of Technical Issues

CUB impacts

Mercury re-emissions

Increased particulate

SO₃ interference

Baghouse impacts

Sorbent distribution

Temperature sensitivity of halogenated carbons

Hopper fires

PAC handling

Variability of mercury content in flue gas

The meeting ended with a brief discussion of the McIlvaine proposition that power plants should burn PVC scrap and make hydrochloric acid. Questions were raised about the dioxin emission potential. McIlvaine asserted that dioxins would be reduced rather than increased by burning the PVC in coal-fired boilers, as opposed to disposal in either incinerators or landfills. In fact environmentalists are waging a campaign against disposing of PVC in landfills because of the problems with landfill fires.

There is real resistance to considering treating a coal-fired boiler as part of an integrated processing facility. However, environmentalists are working toward eliminating coal-firing altogether. Presently TXU is waged in a big battle in Texas to defend its program to build new coal-fired power plants. If each of these plants were to make hydrochloric acid as a byproduct and to deliver its waste heat to make ethanol, there would be big environmental benefits and an easier road to permitting.