May 2015 - Air Filtration Insights 47

The Hot Gas Decisions session at AFS yesterday zeroed in on key issues and options relative to selection and operation of filters and precipitators to capture a range of pollutants. As Tom Hart of AEP pointed out to the attendees, power plants must evaluate mercury, water and solid waste impacts along with any decision to reduce particulate. Tom contributed additional power points on the regulatory maze. These have been incorporated into the PPAQ decision orchard. This service is free of charge to power plant personnel as explained in Power Plant Decisions

The first decision is whether to keep the existing precipitator or to replace it with a baghouse. The key factor is whether MATS particulate limits can be met where particulate is the surrogate for metal toxics. Mick Chambers of SEI presented a number of examples where precipitators are achieving efficiencies suitable to meet MATS.

A hot discussion was generated by the question of whether to use a precipitator or a baghouse for a new plant. Tom Hart unhesitatingly chose the baghouse. When challenged by Mick, Tom explained some of the operating problems he has seen at AEP plants. Maintaining efficiency in a baghouse is easier, in his opinion, due to the ability to easily replace bags. The same cannot be said for precipitator internals.

Steve Feeney of B&W said that the particulate decision is greatly influenced by the scrubber type selected. He believes that dry scrubbers are the better choice. Dry scrubber efficiency has improved over the years. This makes it a candidate for a range of coals. Steve also talked about successfully capturing and preventing re-emission of mercury in the wet scrubber. This also makes the wet scrubber option more attractive.

The scrubber now functions to capture a number of pollutants which results in what Tom Hart described as “scrubber soup”.

There was agreement regarding the difference between a 200 and a 500 SCA precipitator. The good news and bad news is as follows: the good news is that you can increase precipitator efficiency just by increasing the size. The bad news is that the cost rises proportionately. Also there is difficulty expanding the size of an existing precipitator.

This SCA sizing also impacts the capture of activated carbon laden with mercury. Some operators are finding higher mercury readings with sorbent traps than CEMS. The conclusion is that particulate mercury is captured in the sorbent trap but not measured by the CEMS. The further conclusion is that this could be a serious problem once EPA concludes that there is a big hole in the theory of just measuring gaseous mercury.

The opposite experience was communicated by Tom who says that their measurements may even show higher readings with CEMS than sorbent traps but acknowledged that they have large well operated precipitators with high total efficiency. But not all the power plants are operating in this highly efficient mode. As Tom, himself pointed out earlier, it is difficult to maintain precipitators except by shutting them down for repairs.

If a baghouse is chosen, a decision must be made on cleaning type. Reverse air and pulse jets are the options. Glass and synthetics are the common fiber options but ceramics and metals have suddenly joined the list.

Rich Miller of Solaft championed the use of extended surface area bags such as their star bag. He also recommended software to track bag life, predict change outs and manage operations. This was part of a theme addressed by many of the panel members. It is the maintenance and operation which determine performance. With the new continuous mass monitoring requirements the operator cannot operate for any length of time with broken bags without exceeding the limits.

The panel had proponents for membranes on glass and synthetics and proponents for non-woven felts including those with fiber blends by type and size e.g. nanofibers. Clint Scoble of Testori maintained that non-woven blends can meet MATS requirements. P84 fiber has a different shape than PPS. By blending the two the efficiency/pressure drop ratio can be improved.

Eddie Ricketts of Donaldson cited the efficiency and ease of cleaning associated with membranes. John McKenna of ETS agreed that membranes do provide the highest efficiency. Several of the panelists then discussed initial vs. long-term performance. If the membrane breaks, there is a problem. On the other hand, if the felt pressure drop builds up despite increased pulsing, there is also a problem.

John Eleftherakis of Filtration Group covered the extensive experience on glass furnaces, biomass boilers and incinerators with their ceramic hot gas element. When catalyst is embedded and dry sorbent injection is utilized results of less than 5 mg/Nm³, 90% SO₂ and even 90% NO_xremoval can be achieved.

Martin Schroter of Dürr provided insight into a unique combination of processes. Very finely powdered limestone is injected in the boiler with the fuel. A ceramic catalytic element follows the economizer. High SO₂ removal efficiency is obtained due to the contact time of the calcium particles on the filter element. The clean gas then enters a heat exchanger which can extract lots of valuable heat. Boiler efficiency is also enhanced by the lower volume of gas moved by the ID fan. This results in lower fan horsepower. Elimination of the rotary air heater also eliminates the extra flue gas volume created by air heater leakage.

John McKenna of ETS believes that combining nanofiber and catalyst technology could be a big step forward.

Pavlos Papadopoulos of Purolator displayed results showing that sintered metal fibers perform better than sintered powdered metal. Very high removal efficiencies are achieved at low pressure drop. Purolator has deep and varied experience on a range of applications including smelters. This technology may have some new uses in coal-fired boiler operation according to some new concepts offered by McIlvaine.

Coal flyash has been found to contain high percentages of rare earths in contrast to mined coal. China has concluded that flyash is, therefore, a top source for rare earth extraction. The process of capturing flyash is a beneficiation process. But what about refining this even further? What if there were two more particulate separation stages? If the rare earth percentage in one stage was much higher than in others, it could make the rare earth production from flyash even more attractive.

This hot gas session was a positive step toward improving the hot gas decisions program. We will keep updating the decision guide and the decision orchard.

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Startup Date	Location	Fuel Comment	Project Title
Unknown	Australia	or gas	Bayswater B expansion-Macquarie Generation
Unknown	Australia	local	Galilee power plant-Waratah Coal
Unknown	Australia	or gas	Mt. Piper expansion-TruEnergy
Unknown	Bangladesh	local	Barapukuria expansion (III)-CMC
Unknown	Bangladesh		Kalapara upazila ultra supercritical power plant-North West Power Generation
Unknown	Bangladesh		Mawa-Bangladesh Power Development Board/Orion
Unknown	Bangladesh	imported	Rampal (Friendship. Maitree) power plant-Power Development Board/NTPC
Unknown	Bangladesh		South Maheskhali power plant-Power Dev. Board/Tenega Nasional
Unknown	Belarus		Belarus cogeneration plant
Unknown	Bosnia		Kakanj addition
Unknown	Bosnia	lignite	Stanari--Energy Financing Team power plant
Unknown	Botswana		Mookane Project-Golden Concord Holdings/CIC Energy
Unknown	Brazil		Sul power project-MPX energia
Unknown	Brazil		UTE Porto do Acu power plant-MPX Energia/E.On
Unknown	Brazil		Porto do Pecem II power project-Energias do Brasil/MPX Energia
Unknown	Bulgaria		RWE project-Maritza Iztok
Unknown	Bulgaria		Maritsa Iztok 2 Units 9,10
Unknown	Cambodia		Koh Kong power plant-Ratchaburi Electricity Generating Holding
Unknown	Canada		Bow City Power Project-Bow City Power Ltd.
Unknown	Canada		Milner supercritical expansion-Maxim Power
Unknown	Chile		Codelco power project-Energia Minera
Unknown	Chile		Suez Energy-Infraestructura Energetica
Unknown	Chile		Rio Grande power project RG Generacion
Unknown	Chile		Patache power plant-Americas Energy Fund
Unknown	Chile		Pacifico power plant-South Cross Group
Unknown	Chile		Colbun Phase II-Complejo Termico Santa Maria de Coronel
Unknown	Chile		Los Robles power project-AES Gener
Unknown	CO		Colorado Springs possible power plant
Unknown	Colombia		Gecelca 2 and 3
Unknown	Czech Republic	brown	Czech Coal (Mostecka Uhelna) power plant
Unknown	Egypt		Jabal Al Mahghara power plant
Unknown	Egypt	imported	Safaga power plant on Red Sea-Orascom
Unknown	Germany		Buttel power plant-GETEC
Unknown	Germany		Dow power plant in Stade
Unknown	Germany	lignite	Niederaussem addition-RWE
Unknown	Greece	lignite	Ptolemais V power plant-Public Power Corp.
Unknown	Guinea		China Power Investment power plant
Unknown	India		Nellore district power plant-Kineta Power Pvt.
Unknown	India		Pipava power project-UROK
Unknown	India		Patratu block power plant-Jharkhand State Elect. Board/NTPC
Unknown	India		Parli TPP Stage III-Mahagenco
Unknown	India		Parikh Aluminex power project
Unknown	India	Jharkhand mines	Obra C-UP Thermal Power Generation Corp.
Unknown	India	imported	Pipavav coal-fired project-Gujarat Power Corp/Torrent Power
Unknown	India		Neulapoi power project-Calcutta Electric Supply Corp
Unknown	India		Rahim Yar Khan district power plant
Unknown	India	imported	Nayachar Island supercritical power plant
Unknown	India		Noida power plant-CESC
Unknown	India		Pipavav Energy/Larsen & Toubro/Videocon power plant
Unknown	India		Pitamohul power plant-KU Projects