Landfill Gas Practice

Introduction.
 

Raw LFG (Landfill Gas) cannot be used in Boilers for Central Heating nor in Gas Cookers or Ovens. The high concentration of carbondioxide makes the gas unsuitable for advanced burners.

So it has to be upgraded first before it can be used for household purposes. The methane concentration must be increased from ca 57% up to 88% and the carbon dioxide decreased to a maximum of 8%, due to the Specifications of the Dutch 'VEG-Gasinstituut'. (GASTEC, Apeldoorn, The Netherlands.)

For an optimal Flame-pattern it is prescribed that the Wobbe-index for SNG (Substitute Natural Gas) should accurately be regulated between 43.46 and 44.41 MJ/m³0. The Heat Value must meet that of NG (Natural Gas): 35 MJ/m³.

In practice there are three methods to grade-up biogases to specified Pipeline Gas.

 * Carbo-wash. Carbondioxide is washed-out in water under high pressure.
       After that the CO₂ is removed in an air stripper.
 * Pressure Swing Adsorption. Gas is adsorbed under pressure in a carbon
       bed. In depressing the bed, CH₄ and CO₂ release separately and by
       changing Valve actuators at the right times, separate flows of the
       gases are realized. In order to get a more-or-less constant flow of
       SNG, a Cascade system with sufficient buffering must be constructed.
 * Membrane Technology. Gases (or liquids) are separated by means of the
       permeability of polymers. A bundle with thousands of hollow fibres are
       fixed in a pressure vessel. The bottom side of the fibres is closed.
       Polymers have the property that carbondioxide diffuses through the
      membrane material while Methane is stopped. In this case a continuous  flow of methane-rich gas at high pressure is coming out of the lower connection and a low-pressure flow of carbondioxide-rich gas from the upper connection at the open side of the fibre-bundle. This gas still contains about 12% CH₄ and is flared-off.
Membrane technology has been developed by Monsanto(USA), Ube(Japan), Wafilin(NL) c.a.

Several techniques were investigated by the University Twente (prof. Smolders) and the University of Aachen in Germany (prof. Rautenbach). 
 

Activities on Membrane Utilization.
 

Centraal Overijsselse Nutsbedrijven 'COGAS' inc. at Almelo is the first company in the Netherlands that uses membrane modules for upgrading Bio-gas (Landfill Gas) to pipeline quality. Two Pilot plants are in operation very successful until now. At Vasse, a small village in the community of Tubbergen, a membrane set with a capacity of 200 m³/h of SNG was officially put in operation on May 7, 1992 and about one year later started the second plant at Collendoorn, community of Hardenberg.
The last mentioned delivers a quantity of 150 m³/h to the pipeline.
Quality of the SNG is under supervision of the Netherlands Institute for Gas Technology 'GASTEC'.
 

Although the period that both plants are in operation is too short to become sufficient records, the COGAS engineers are very enthusiastic. The installations run almost smoothly with a minimum of supervision.
With exception of the compressors there are no moving parts; so maintenance is in fact very simple.
Distance control is done via telephone-line by the COGAS head office in Almelo.

The COGAS Landfill Projects have international interest and are often visited by groups of students from developing countries in cooperation with the University of Twente.
 
  

      October 12, 1993.

You can reach me by e-mail at: lfgas@dvfaassen.demon.nl