The design and installation of the gas collection system

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Courtesy of Hofstetter BV

The designer of gas collection plants has the task to fulfill optimally the important criteria:

  • stability of gas quality
  • efficiency of collection
  • economic viability of the plant

The stabilisation of the gas quality helps to solve the problem between the uneven gas production of the landfill on the one side and the steady supply of gas to the utilisation plant, on the other. Only a carefully applied and readily adjustable active degassing, ensures the troublefree utilisation of the resulting landfill gas in gas engines or burner plants.

The efficiency of the gas collection i.e. the collection of as much gas as possible is vital: leaking gas pollutes the environment.

The economic viability of the whole plant in respect of adaptability and durability, maintenance and labour requirement for operation, justifies the considerable investment and makes the decision of the customer easier.

The 'organism' landfill
The landfill to be treated, is a living organism:

  • Methane bacteria work inside it: nevertheless working to an irregular timetable; the gas production fluctuates accordingly.
  • Internal temperatures of up to approx. 40 to 45 C and more, may prevail.
  • The biological decomposition and compaction brought about by the superimposed weight, lead to considerable settling of the landfill.
  • The differing composition of the waste, creates in the landfill, areas of variable reaction.
  • The generated gas is saturated with vapour, aggressive, and often enriched with problematical trace elements; even when slightly cooled down condensate results.
  • Contaminating leachate is present everywhere.
  • Atmospheric conditions influence the internal process of the landfill through humidity, temperature, pressure, etc.
  • Newly deposited waste raises the landfill, a new gas collection area must be developed.

In a slow motion take, the landfill would strike one as an effervescing mass; the gas collection system must accordingly be adaptable and robust.

Necessary features of the plant components
From this aspect there are a whole series of demands for which the components and the gas collection system are to be designed:

  • All gas transporting elements must be resistant to very aggressive substances and mechanical strain.
  • The choice of material must also conform to the relevent safety requirements.
  • Moving parts should be unaffected by dirt and moisture
  • The points for control, maintenance, measuring, regulation and collection of the relevant operating data, should be easily accessible and easily operated.
  • Shafts should be avoided for safety reasons; potentially explosive gas mixtures can form inside them.
  • The quantity governor inside the gas pipeline should allow a linear and fine adjustment, and should not impede the movement of any condensate (e.g. as do butterfly valves in well heads).

Necessary features of the system design
Each landfill has its own characteristic in respect of dimension, composition of waste, etc.

Once the question of dimensioning, well positioning, etc. is clarified by the usual preliminary tests, the design of the required system must incorporate the demands of the designer, in particular:

  • Ensuring a complete degassing of the landfill area, inhibiting gas migration.
  • Correct design of the pipeline layout in consideration of the gas and condensate flow. Prevention of the formation of deep points with water seals.
  • Adaptability of the gas collection system to the settling, shearing and possible growing
  • Compliance with the technical safety requirements in accordance with relevant directives and specifications.

Collection with separation system

Priorities: Measuring / Control / Regulation
The non-influencable, biological processes in the landfill, produce in the course of time, gas in variable compositions and quantities. The fluctuations must be regulated through active degassing with controllable intervention.

To this aim, the suction pressure is carefully regulated at each individual gas well head when putting into operation. If in the course of time, the gas production changes in individual landfill sectors, the relative gas well heads can individually, or collectively, be readjusted at the measuring and regulating points.

Much attention has to be given to the easy operation of the control elements: The responsible personnel should be able to carry out the regulating easily and safely, at as few as possible and well accessible locations. Therefore it is advantageous to group the suction pipelines in measuring stands with measuring and regulating units.

The increasingly required acquisition of relevant operating data of the landfill, results in centralisation of measuring. This requires the installation and operation of a measuring gas pipeline system from the measuring points to a central control.

Authorities, operating and technical safety requirements are putting a great deal of importance on 'measuring, control, regulating.' Gas collection systems logging the operational data are the future.

A perfected range of components to our own design
Hofstetter is one of the first manufacturers and suppliers of landfill gas collection equipment. The products are designed for vertical collection of landfill gas. This concept has established itself because of:

  • maximum effectiveness
  • efficiency also with horizontal, impermeable layers of covering
  • optimal adaptability to the growing landfill
  • elimination of shaft constructions
  • easy extension possibilities

It is possible with our range, together with the correlated gas collectors, regulating governors, measuring/regulating stands, to construct effective, easy to maintain gas collection plants.

From our range:

Gas well head GBA-1
A part of the gas collection for sealing the gas wells (bore hole) and connection piece to gas collection pipeline

With the GBA-1, it is possible to choose between serial or parallel connection to the gas wells.

Installation possibilities

Condensate discharge
The resulting condensate in the gas collection pipelines is continuously fed back to the landfill; independant of suction pressure, gas quantity, flow of condensate (with or against flow).

Measuring, regulation
All measuring and regulating points are operable at the head. This enables below ground construction with a very small protection box.

It is possible to measure all the relevant values in the gas wells as well as the gas pipelines. The suction quantity regulation is infinitely variable from 0 to 100 %. A particular advantage is the precise adjustment at small flow quantities (similar to MRV-valve).

Control and maintenance
The control opening of the GBA-1 always allows, after closing the valve for gas collection, entry to the inside of the well for:

  • Visual control
  • Checking water table level