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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