Technical aspects in detail
Methane is the main greenhouse gas that is related to coal production. The GWP (global warming potential) of methane is 21, which means that it traps 21times more heat in the atmosphere than CO2. Methane is produced from underground and surface mines, and results from postmining acivities including coal processing, storage and transportation. The energetic utilization of CMM contributes to the conservation of fossil fuels, to the diversification of energy resources and to the reduction of climate relevant emissions. Depending on the compostion and the amount of CMM (data delivered by a gas prognosis) and the kind of the mine (abandoned or acticve mine) different types of utilisation are possible. An overview of proved and tested utilisation technologies depending on the CH4- content are shown in the table below:
|Gas engines||(25) 30 - 100||proved and tested||Power, heat, emission reduction||since 1996 over 100 units in operation|
|Boilers / Burners - monovalent||(20) 25 - 100||proved and tested||Heat, emission reduction||since 1980th|
|Boilers / Burners - additional||(20) 25 - 100||proved and tested||Heat, emission reduction||since 1900 on mines|
|CMM flaring||20 - 100||proved||Emission reduction||used on landfills|
|Liquified Natural Gas - LNG||50 - 100||tested||LNG, emission reduction||660 Mio. m³ in 2006 (US-market)|
|VAM utilisation||0,2 - 1,2||demonstration||-||some are in operation|
|Gas turbines / mikro turbines||40 - 100||demonstration||-||-|
|Fuel Cells||30 - 100||pilot||-||-|
As the local conditions, methane concentration, pressure, dust, stable quality and quantity are different at each project site, the robustness of a technology is crucial for the project development. The following table shows the robustness of the proved technology against changing gas characteristics of concentration, gas pressure, moistness and dust.
|CMM flaring||(20) 25 - 100||++||++||++||+|
|Boilers / Burners - additional||(20) 25 - 100||++||+||++||+|
|Boilers / Burners - monovalent||(20) 25 - 100||+||o||+||+|
|Gas engines||(25) 30 - 100||o||-||-||-|
|Liquified Natural Gas - LNG||50 - 100||-||++*||++*||++*|
++* = with special gas treatment and compression necessary. The gas has to be free of moisture and dust.
In fact the local conditions have the highest impact on the chosen technology. Especially on active mines the quality of the degassing process is important for a high degree of utilisation. The methane use has not the highest priority for the operation of degassing system, which is mainly installed due to ensure the safety of the mine, but sensitive utilisation plants excuses only slow quality changes. High operational costs, short life time of the equipment and interrupts in the production are results and at the same time a very high risk of CMM projects.
Practical examples of the project
Thermal Power Plant
In this example (Russia) methane degassing from the gob coal seam "Breevsky" is used to operate a thermal power plant. The utilisation takes place for two gas composition: 1) gas with high (higher than 25%) and 2) low (lower 3.5%) methane concentration. For the extraction a dry compressor and a rotary pump are used by a extraction depression up to 100 mbar.
For the CMM utilisation two flare units and a thermal power plant is in opertation.
Two specific problems occured during the project:
1) Climate problems, as the winter temperature in the Kuzbass reached -55°C.
2) Intersection of powerlines and gas pipeline.
The first problem was solved using warm insulation at the important units of the plant and during extreme low temperatures in winter time the unit installation was paused.
For the second problem a transfer of power lines was a suitable solution.