430F98086
United States
Environmental Protection Agency
Air and Radiation Draft
6202J April 1998
v>EPA
EPA Coalbed Methane Outreach Program Technical Options Series
CONVERSION OF COAL MINE VENTILATION AIR
INTO ENERGY USING OXIDATION TECHNOLOGIES
Regenerative thermal oxidizers recover heat energy by oxidizing low-concentration fuels
(Photo courtesy of Ship & Shore, Inc.)
USING COAL MINE VENTILATION AIR, OXIDIZERS CAN. ..
* Operate efficiently using gas with high air volume/low methane concentrations
typical of coal mine ventilation exhaust
4 Recover up to 75% of the heat energy they produce
+ Heat mine facilities and dry coal or slurry
* Produce thermal energy for use on-site at coal mines, or at nearby facilities such
as boilers, steam turbines or electricity generators
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Oxidation of coo/
mine ventilation air is
a new application of
a well-established
technology
Regenerative
oxidizers are self-
sustaining at methane
concentrations as
low as 0,1%
High heat recovered
(75%) is usable as
thermal energy
WHY CONSIDER USING MINE VENTILATION AIR IN OXIDIZERS?
For safety reasons, most coal mines worldwide dilute the methane liberated
during coal mining operations to a concentration of less than I %. At such
low concentrations, it is difficult to use this methane gas mixture as a fuel.
Oxidation technologies (which heat gases to their oxidation temperatures,
converting the vapors to CO2 and water) have long been used for the
treatment of volatile organic compound (VOC) emissions, and will soon be
tested with coal mine methane. Through high heat recovery, oxidizers provide
a way to use ventilation air as heat energy while reducing methane emissions.
There are two primary types of oxidation technologies that can effectively
oxidize methane: thermal and catalytic. Thermal oxidizers can utilize either a
regenerative heat exchanger (direct contact heat exchange on inert material
beds) or recuperative type (conventional, indirect heat exchangers) in their
processes. Both thermal and catalytic oxidizers can be operated under
unidirectional or reverse-flow conditions. Each type operates over a wide
range of air flow rates and dilute methane concentrations. The systems
produce excess thermal energy that mines could use for electricity generation,
heating, cooling, and drying processes.
The regenerative thermal oxidizer passes ventilation air through an inert bed
of high heat capacity material (i.e. silica gravel or ceramic material) to a
central combustion zone. Due to its stability, the methane molecule requires
temperatures in excess of 1,000°C to automatically oxidize in air. Thermal
energy resulting from this combustion heats up the media on the exhaust side
of the bed. The flow is reversed allowing preheating of the incoming ventilation
air. As a result, a relatively small amount of energy produces surplus heat,
which can be evacuated through heat transfer piping.
Operating at lower temperatures (500°C to 800°C), the catalytic oxidizer uses
a burner in addition to a chamber bed to promote the oxidation of methane.
Upon reaching a preheated temperature, the system reduces burner input to
maintain the required catalyst inlet and outlet temperatures. Usually, the
catalyst consists of a bed of metal or metal oxide substrate in the shape of
pellets, which can be replaced and/or regenerated periodically. It should be
noted that certain unidirectional catalytic oxidizers have difficulty oxidizing low
concentrations of methane, and may be unsuitable for mine ventilation air.
The reverse-flow catalytic oxidizer combines the processes of heat
exchange with the use of a catalyst. Storing heat in inert beds upstream and
downstream of the catalyst section ensure a full methane conversion, in
addition to promoting a high heat recovery rate. As a result, a coal mine can
choose a more economical catalyst to lower operating costs. Neill & Gunter
(Nova Scotia) Ltd. is currently co-operating with Natural Resources Canada and
others in the development of this technology. An industrial demonstration is
envisaged for the Spring of 1999.
While the above three methane oxidation technologies appear to be the most
promising for methane use to date, other types of methane oxidizers may
prove effective in the future.
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USING COAL MINE VENTILATION AIR WITH THERMAL OXIDIZERS
Off-Site
Use
1
/->__!
Loal
A
r
!,,(•_
Mine
i
Ventilation Air ^_
Thermal
Oxidizer
0 '• 1 07
Methane
Heat
Electricity
W
W
w
P
Misc. Operations
Coal Drying
Sludge Concentration
Steam Production
Ventilation Air Preheating
Power Plant
_
Turbine/Stecm Boiler
TYPICAL PARAMETERS OF METHANE OXIDATION SYSTEMS
Can operate at methane concentrations typical of coal mine ventilation air
(0.1-1.0% volume)
Primary heat recovery ranges from 50-75%
Recovers heat at temperatures between 500-900°C, depending on oxidizer type
Can operate on high air flow rates ranging from 30,000-200,000 set per minute
Approximate installed costs range from $US 800,000 -1,200,000 (depending on
the size of the facility)
Can produce 25-35 MW of thermal energy
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For More Information.
Coal mine operators and energy producers
have long sought a means of using the low
concentration methane contained in ventila-
tion air. Thermal and catalytic oxidizers
provide coal mines with several options for
converting ventilation air into usable energy
while reducing greenhouse gas emissions.
To obtain more information about using
oxidizers to convert coal mine ventilation air
into energy, contact:
Anoosheh Mostafaei
John Von Bargen
Ship & Shore, Inc.
2474 N. Palm Drive
Long Beach, CA 90806
(562) 997-0233
FOX: (562) 997-0667
Brian King
Neill And Gunter (Nova Scotia) Limited
PO Box 2190
East Dartmouth
Nova Scotia, Canada B2W3Y2
(902) 434-7331
Fax: (902)462-1660
Or contact EPA's Coalbed Methane Outreach Program for information about this and other
profitable uses for coal mine methane:
Coalbed Methane Outreach Program
U.S. EPA (6202J)
401 M Street, SW
Washington, DC 20460 USA
(202) 564-9468 or (202) 564-9481
Fax: (202) 565-2077
e-mail: fernandez.roger@epamail.epa.gov
schultz.karl@epamail.epa.gov
http ://www. epa. gov/coa I bed
METHANE
OUTREACH
1 R O G R A M
The mention of products or services in this case study does not constitute an endorsement by EPA.
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