MERCURY CONTROL WITH FABRIC FILTERSc.ymcdn.com/.../TechDiv/ICAC_Hg_Control_with_FF_Dra.docx · Web...

MERCURY CONTROL WITH FABRIC FILTERS FROM COAL-FIRED BOILERS

Technology Overview

Fabric filters are used as the primary particulate control device on about 30% of the coal fired power plants in the US. The combined use of fabric filters with sorbent injection systems has been utilized for many years in the municipal incinerator, as well as other industries as a way to enhance the removal of mercury and other pollutants such as dioxins, furans, and a wide range of heavy metals. In addition, sorbent injection has recently it has also been utilized in a large number of electric utility coal-fired boilers as a method to reduce mercury from the flue gas. Fabric filters, also known as baghouses, filter out the particles from the flue gas stream through a specialty tightly woven or felted fabric by sieving and other mechanisms. The dust cake which forms on the filter from the collected particulates can significantly increase particulate and mercury collection efficiency. With a carbon injection system upstream of the fabric filter, the carbon enriched dust cake on the fabric serves as a fixed bed reactor providing excellent contact (residence time) between the mercury laden flue gas and the reactive carbon. A fabric filter provides a relatively long residence time of several minutes compared to an electrostatic precipitator (ESP), which may only have 2-3 seconds of only in-flight exposure. This enhanced filter cake provides higher high inherent removal of mercury with much relatively lower low required sorbent injection rates, thus reducing providing comparatively lower the overall operation and maintenance (O&M) costs associated with sorbent injection for mercury control.

Types of Fabric Filter Systems Available

There are several types of fabric filters utilized today on electric utility coal-fired boilers including reverse gas (RGFF), pulse jets (PJFF), and combinations of ESP & PJFF (TOXECON/COHPAC). The primary difference between the various designs is the mechanism used to clean the dust cake from the filter bags.

All of these fabric filter designs can be utilized for mercury reduction with use of dry sorbents such as activated carbons. Fabric filters can also be utilized upstream of wet flue gas desulfurization (FGD) systems and downstream of dry FGD systems for SO2 control, particulate reduction, as well as mercury control.

Fabric filter technologies can be located in a multitude of locations, including being used as the primary particulate control device or downstream of an existing or new ESP collector in the COHPACTM /TOXECON configuration. Some designs can also place the fabric filter within the ESP casing as in the design of a full ESP conversion to a pulse jet fabric filter or even a partial conversion with the last few fields being converted to a high ratio pulse jet in the COHPAC II configuration.

Some basic differences between these various fabric filter technologies are as follows:

Reverse Gas Fabric Filters:

ICAC 1220 N. Fillmore Street NW, Suite 410, Arlington, VA 22201 703-812-4811 www.icac.com

jeanb, 05/11/10,

Need to confirm market percentage. I guessed.

http://www.icac.com/

Used on large coal-fired boilers for over 30 years Utilize woven fiberglass filter bags up to 36’ in length Designed at conservative air-to-cloth ratios (filtration rates) of 1.5 to 2.0 fpm Large real-estate requirements (40 to 50 percent larger than PJFF) Highest capital cost of all types of fabric filters (20-30 percent higher installed cost over

PJFF) Utilizes low pressure, reverse gas type centrifugal fans for fabric cleaning Gentle cleaning system provides longest bag life of any other fabric filter system as well as

lower O&M costs

Reverse Gas Fabric Filters

Pulse Jet Fabric Filters:

Current industry standard for new and retrofit fabric filter systems Utilizes synthetic felt fabrics such as PPS or P-84 felt with bag lengths up to 287’ in length May provide lower or compatible emission levels toover reverse gas designs because felt

fabrics are inherently more efficient than woven fabrics.. Higher filtration rates of 3.5 – 4.0 fpm greatly reduces the overall real estate requirements by

as much as 40-50 percent and capital cost by 20-30 percent



More aggressive fabric cleaning system requires use of either compressed air or low pressure positive displacement type blowers

Higher filtration rates combined with higher cleaning energies may result in reduction in bag life in comparison to reverse gas designs, although bag lives of 4-5 years is typical with this type of cleaning technology. O&M costs are therefore potentially higher over a 20-30 year life cycle.

Has proven to be highly effective in the conversion of older ESP casings into more efficient pulse jet fabric filters as shown below.

Standard Pulse Jet Fabric Filter ESP/Pulse Jet Conversion

COHPAC /TOXECON Technologies:

EPRI developed, patented and licensed technologies Combination of both ESP and pulse jet technologies PJFF is installed in series (Downstream) of existing or new ESP as a polishing device to

improve overall particulate control (COHPAC) or to remove mercury, SO2, or other air toxics by sorbent injection (TOXECON).

PJFF’s can be retrofitted within an existing ESP casing at standard air-to-cloth ratios or into the last few fields with higher air-to-cloth ratios (COHPAC II).

With the addition of sorbents, such as activated carbon for mercury control, COHPAC becomes TOXECON with the majority of the fly ash removed in the primary ESP and the activated carbon being injected between the two devices.

With the majority of fly ash collected in the primary ESP, the pulse jet filtration rates can be significantly increased to 5-6 fpm.

As the sorbent/carbon is collected in the fabric filter portion, fly ash sales are not impacted as the majority (>98 percent) of the uncontaminated ash remains in the ESP collector and the remaining carbon enriched ash stream is separated out for separate landfill or pond disposal.

Higher filtration rates reduce both required real-estate and capital costs.



CoalElectrostatic

Precipitatoror

PJFF

SorbentInjection

For existing power plants, this may be one of the lowest cost options for mercury and particulate control enhancement, especially in the case where an existing, poorly operating ESP may be present.

Typical COHPAC I/TOXECON Installation

TOXECON I TM SYSTEM ARRANGEMENT


COHPAC

98-99% of Ash Collected 1-2% of fly ash + Carbon


Commercial Activity

Sorbent injection technologies in combination with fabric filter systems are currently being offered and purchased by the electric utility industry for the control of mercury emissions from coal-fired boilers. Numerous commercial systems have been recently sold, many of which carry mercury reduction guarantees. Testing shows that fabric filters can achieve greater than 90 percent removal.

The first commercial sorbent injection system on a coal-fired boiler has been is in operation at the WE Energies Presque Isle Station as part of a DOE/NETL Clean Coal Program project since DecemberJanuary 20065 using a TOXECON type fabric filter system, and has been successful in achieving 90% mercury removal with activated carbon injection rates between 1.2 and 1.5 lb/MMacf..

The following are tables graph shows native mercury removal (No Sorbent Injection) with fabric filters on bituminous, sub-bituminous and lignite coals. These data were collected during the showing both baseline mercury data with fabric filters (No Sorbent Additives) from earlierpast ICR effort in 1999. testing results and graph of mercury reduction across a fabric filter system with sorbent injection. Additional ICR testing is currently underway on existing installations both with and without sorbent injection systems in operation.

The second graph presents a summary of expected mercury removal results with activated carbon with fabric filters and ESPs based on results from full-scale tests. These data show that high mercury removal can be achieved with relatively low activated carbon injection concentrations.


jeanb, 05/11/10,

Check dates of ICR, I think test were conducted 1999.

jeanb, 05/11/10,

WE started injection in January. December 2005 was shake down of the equipment.


ICR Data Base- Natural Hg Reduction Across Fabric Filters For Various Coals

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15

Injection Concentration (lb/MMacf)

Hg

Rem

oval

(%)

Low Sulfur Coal Western Coal ESPPolishing Baghouse

Dry Scrubber+ FF

LS Bit ESP

HS Bit ESP

Mercury Removal Comparisons Between ESP’s and FF’s With Sorbent Injection

[This graph above is seriously outdated. Now that new installations are injecting before the air preheaters, ESPs with subbituminous coal are seeing 90% at 2-3 lb/MMacf, not 6 or 7 (if they ever saw it there). The LS BIT curve is also much, much improved now. It is deceptive to have only a few points on a 2005/6 graph like this when we should have 40-or 50 today. We need an updated graph reflecting 2010 state-of-the-art performance. Perhaps the 2010 ICR data will provide it. – Sid] See above revised set of curves Jean Bustard submitted.

For Further Reference:

Operation and Maintenance of Fabric Collectors, 2002, ICAC F3 Technical Standard Types of Fabric Filters, 1991, ICAC F5 Technical Standard


Rich Miller, 05/12/10,

The above curve represents the addition of newer data from field studies. This does not include coal additives which is covered under a different FACT Sheet.


Baghouse Operation and Maintenance Log for Assessment of Stack Test Results, 1994, ICAC F6 Technical Standard

Fabric Filter Gas Flow Model Studies, 1996, ICAC F7 Technical Standard Structural Design Criteria for Fabric Filters, 2001, ICAC F8 Technical Standard EPRI Utility Baghouse Survey 2009



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