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Biogas Treatment 

Although biogas can be used as a fuel, it must firstly be treated to ensure that it is delivered in a useable state. Depending on its source, biogas is a mixture of many elements, some of which are not much use in the generation of fuel and cannot be combusted. Organics provides a wide range of equipment for the treatment of biogas to ensure that, whatever the final destination, it is right for the job.

H2S Bioscrubbers

Biogas Chillers

Activated Air Controllers

Fuel Delivery Skids

Hydrogen Sulphide Bioscrubbers

What is Hydrogen Sulphide?

Hydrogen sulphide (H2S) is a gas that occurs naturally but can also be produced by human activity. H2S gas is colourless and flammable and can be both poisonous and corrosive but, as H2S is heavier than air, any uncontrolled release will stay low to the ground. In certain situations, H2S can be detected by its smell in concentrations as low as 0.6 parts per billion (ppb).

Its toxicity is similar to carbon monoxide and can prevent cellular respiration in organisms. In machinery, its corrosive properties can quickly render equipment inoperative. Monitoring and early detection of H2S could, therefore, mean the difference between life and death or catastrophic breakdown of valuable equipment. Biogas produced by anaerobic digestion is generally rich in H2S.

How is H2S produced?

Landfill sites can produce H2S in the presence of wastes plasterboard or other products that contain sulphur. It can also be present if there is the presence of gypsum (CaSo4.2H20).

In anaerobic digestion, H2S is produced by the microbial breakdown of organic material under anaerobic conditions and produces biogas that must be treated before using in vulnerable machinery.

What is the environmental impact of H2S?

In humans, prolonged exposure to high enough levels of H2S can cause unconsciousness and those affected may continue to experience headaches, reduced attention span and altered motor functions. Effects of H2S gas exposure may not become apparent for up to 72 hours following removal from the affected environment.

As H2S is heavier than air it usually accumulates in low lying areas of poorly ventilated spaces. During the production and collection of biogas in landfill sites or anaerobic digestion plant, H2S gas in the presence of air and moisture can form sulphuric acid which is capable of corroding metals within machinery that is often not seen.

How can H2S be treated?

There are several types of treatment system that involve high initial investment together with high ongoing costs of operation.

Organics has developed bio-scrubber technology, the main advantage of which is that, in most circumstances, no additional costs for chemical-additions are incurred. The bacteria involved in the process are ubiquitous and, as long as correct environmental conditions are maintained, the bacteria will function reliably and predictably in the removal of hydrogen sulphide from gas streams. The system is ideal for use with biogas producing projects that rely on anaerobic digestion such as bespoke AD projects or biogas generated in landfill sites.

Biogas Chillers

What is a gas chiller used for?

Gas chillers are used to reduces the moisture content of process gas streams. As well as reducing moisture, chillers will also reduce the concentration of chemical compounds such as ammonia and Volatile Organic Compounds (VOCs).

The process of extraction of landfill gas, or the recovery of biogas from anaerobic digestion, for power generation, results in the formation of condensate that can contain a wide range of potentially corrosive elements. If these elements are not removed from the gas flow, they can drop out of the condensate in the engine manifold or charge-cooler; a phenomenon that will eventually result in catastrophic engine failure. To avoid this happening, installation of a chiller unit will remove condensate prior to entry of the gas to the engine.

How does a chiller function?

A gas chiller can reduce the temperature of a biogas stream to around 2ºC. Temperatures below this can also be achieved but will result in freezing of the heat exchanger tubes. Where temperatures of less than zero are required it will be necessary to run tandem heat exchangers, switching the flow from one to the other as they become blocked with ice.

By reducing the temperature to close to freezing point the relative humidity of the gas can also be reduced, thus minimising the possibility of condensate formation in pipes down-stream of the chiller. The unit is usually placed before or after the booster unit on biogas collection systems either on landfill gas or bespoke anaerobic digesters. 

 

Size ranges

Chiller packages are, as with other items of purpose built process plant supplied by Organics, unlimited in practical size.

Flow rates of up to 10,000 Normal cubic metres per hour can be effectively “chilled” to the target levels.

Application

It is often the case that suppliers of certain types of equipment, such as internal combustion engines and gas turbines, will specify a maximum moisture content in the gas to be fed to their plant.

The options for dealing with such requirements are limited. Hydroscopic filters will reduce dew points by up to 6ºC but this may provide inadequate protection, especially as the dew point of the feed gas often varies significantly.

Where properly designed and built a packaged chiller will reliably ensure the target dew point is continuously met and the equipment is most effective on landfill biogas or biogas generated within AD plants.

Activated Air Odour Control Units

What is an Activated Air Unit?
The treatment and storage of waste material can often result in strong odours being generated that, if not treated, can cause problems for neighbours and workers on the site.

Deodorisation with an Activated Air unit is based upon high-speed oxidation. Molecules oxidised by this method cannot be detected by the human nose.

An Activated Air unit consists of a stainless steel cabinet containing wide-mesh UV-catalysts. Ambient air is passed through the unit, from atmosphere without any pre-treatment, and radiated.

How does it work?

By means of a high-voltage applied to an ultra-violet light generating, catalytic wire mesh, molecules in ambient air are split and energised, converting the moisture and air into a flow consisting of a mixture of unstable atoms, ions and radicals, with elevated electron activity levels. These Activated Air molecules may then be injected into a gas carrying target compounds. The result is the high-rate oxidation of odorous molecules.

Key Features
  • Highly efficient Odour Control by means of the high-rate oxidation of target substances,
  • No moving parts, mechanical wear,
  • No chemical additions required,
  • No water consumption and no waste products
  • Low energy requirements
Key data
Flow rates available: 2,000 to 20,000 cubic metres per hour of exhaust gas flow. Larger flows may be accommodated with multiple modules

Energy requirements: 5 kW hr per 1,000 cubic metres

Space requirements: The largest standard module occupies a space of 1.5 m wide x 1.0 metre deep x 2.4 metres high.

Front access is required for access to controls and for servicing

Gas Delivery Fuel Skids

Fuel-skids for power generation

The absolute requirement for a fuel skid for power generation is long-term reliability

Units designed, manufactured and supplied by Organics employ technology that has been tried and tested for pumping applications for landfill gas and biogas from AD where unnecessary downtime has immediate ramifications in terms of revenue generation and must be avoided.

Gas-pumping units manufactured and supplied by Organics have a well-established record in providing landfill gas to generators with up times in excess of 99%.

Biogas is a unique fuel

It is now well acknowledged that landfill biogas or biogas from AD plants can be employed as a unique fuel that does not normally require back-up from deisel or natural gas injection. However, biogas possesses characteristics that are not matched by any other similar fuel gas, such as natural gas.

For this reason, a biogas fuel skid must be built specifically for this application. Of particular note are the high-levels of moisture drop out and the possibility of a wide range of potentially corrosive trace gases. These range from halogens to ammonia and mercaptans.

Key features
  • High-reliability gas pumping sets
  • Optional air blast cooling and refrigerated chilling for dew-point management
    site-specific design
  • Automatic moisture removal systems for collected condensate
  • Integrated control systems with facilities to link into main control centre.
Key data
  • Flow rates available: 50 to 20,000 cubic metres per hour
  • Suction pressure head rarely needs to exceed 150 mbar. Deep-vacuum systems can also be considered for particular situations.
  • Delivery pressure head: 300 to 600 mbar g are normally achieved with twin-stage centrifugal blowers. Higher pressure heads may be achieved with screw compressors, rotary vane compressors and multi-stage reciprocating compressors.
  • Organics fuel skids have a well-established record in providing biogas to generators with up times in excess of 99%.
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