Bulk H2S Removal - Dehumidification - VOC Removal - Siloxane Removal - Residual H2S Removal

Outline process description

The package of equipment is designed to upgrade biogas produced by the digestion process to a quality required by a CHP generator. The biogas first passes through a 'biological' H2S Scrubber and on to a biogas dehumidifier for drying. The biogas is then pressure boosted through carbon filters for the removal of Siloxanes/VOC's and residual H2S. The biogas arrives at the CHP generator at the required quality and pressure.

Plant details

H2S Biological Scrubber

Biogas H2S scrubbers are used to reduce the content of hydrogen sulphide (H2S) in biogas and landfill gases providing a cleaner and less corrosive gas for engine combustion.

The content of H2S in the raw biogas can range from 1000ppm up to 50,000ppm and under combustion will convert into sulphuric acid leading to severe corrosion of the engine and a considerable reduction in its operational life. Income will be lost during overhauls and break downs which will also require substantial expenditures.

The leading gas engine manufacturers can specify a max. 250 ppm H2S in the biogas to enable full warranty's to be provided. The 'Biogasclean' biological H2S scrubber can meet these requirements and even better with any flow volume and H2S content of raw biogas.

The H2S scrubber will reduce H2S levels to an absolute minimum and is an essential part of the engine life providing operating stability, reliable and economical operation.

The H2S is removed from the biogas in a biological process, NO CHEMICALS ARE REQUIRED. The sulphur oxidation bacteria are of the Thiobacillus family and need the following:-

• Place to live and multiply (on a packed media inside a closed acid-proof tank)
• Sulphur (the H2S containing biogas)
• Oxygen (supply of atmospheric air)
• Moisture (soft water or gas condensate)
• Nutrients (liquid NPK nutrient or digested sludge liquors)
• Temperature between 25-60 deg C

Gas Dehumidifier

The plant is designed to dehumidify and dry biogas for use in CHP engines optimising combustion and reducing plant downtimes.

Dehumidification is carried out by cooling the gas to a preset temperature allowing moisture to condense and be removed.

The stand alone skid mounted package plant is weatherproof requiring only inlet and outlet gas connections and a power supply to be made. All wetted parts in contact with the gas are manufactured from stainless steel.

Gas flow cooling takes place in a water cooled tube bundle heat exchanger with accumulated condensate discharged via a condensate collection pot.

A closed circuit refrigeration/demistor plant provides and circulates the necessary cooling water and is automatic in operation.

The Relative Humidity of the gas is set by reheating through a recuperator (gas/gas heat exchanger) which uses the inlet gas to heat the cooled exit gas. This will prevent aggressive condensate precipitates reaching the CHP engine. Alternatively a hot water/gas heat exchanger can be provided.

Technical Data

Cold Water Set

Gas Compressor - ATEX compliant construction

Technical Data

Siloxanes and VOC's removal

1no CJC VOC195/170DB filter for the removal of VOC's and Siloxanes. 2 tonnes CJC Filtersorb AC64 Filter Medium (first fill)

1no VOC 195/170DB filter for the removal of residual H2S 2 tonnes CJC Filtersorb IAC68 Filter Medium (first fill)

3600 hours running time between carbon changes

The range of CJC™ Biogas Filters offers a cost-effective solution for the protection of internal combustion engines and turbines, using landfill gas, digester gas or sewage gas as fuel, against the damaging effects of contaminants such as siloxanes, mercaptans, halogenated and other volatile organic compounds.

Unlike natural gas, biogas contains varying quantities of siloxanes, sulphur and chlorine compounds. During combustion, siloxanes are converted to silicates, which build up as an off-white ash in combustion and exhaust areas, and, where moisture is present, H2S and other organic compounds, in particular, chlorines and fluorines, combine to form strong acids. The inevitable consequences include irreversible damage to valves, pistons, cylinder liners, bearings, turbochargers, catalytic converters and premature destruction of engine oil, highlighted by poor TBN/TAN values and high Oxidation, Si and Cl levels in oil analyses.

A CJC™ Biogas Filter, employing tried and tested filter medium technology, will successfully capture and retain more than 90% of contaminants in the biogas supply, thereby, increasing productivity and profitability by lowering operational running costs i.e., longer oil life, service and overhaul intervals.