Biogas Refining
Biogas produced in AD-plants or landfill sites is primarily composed of methane (CH4) and carbon dioxide (CO2) with smaller amounts of hydrogen sulphide (H2S) and ammonia (NH3). Trace amounts of hydrogen (H2), nitrogen (N2), carbon monoxide (CO), saturated or halogenated carbohydrates and oxygen (O2) are occasionally present in the biogas.
Usually, the mixed gas is saturated with water vapour and may contain dust particles and siloxanes.
For many applications the quality of biogas has to be improved. The main parameter that may require removal in an upgrading system are H2S, water, CO2 and halogenated compounds:
- Desulphurisation to prevent corrosion and avoid toxic H2S concentrations. When biogas is burned SO2/SO3 is emitted which is even more poisonous than H2S. At the same time SO2 lowers the dew point in the stack gas. The sulphurous acid formed (H2SO3) is highly corrosive.
- Removal of water because of potential accumulation of condensate in the gas line, the formation of a corrosive acidic solution when hydrogen sulphide is dissolved or to achieve low dew points when biogas is stored under elevated pressures in order to avoid condensation and freezing.
- Removal of CO2 will be required if the biogas needs to be upgraded to natural gas standards or vehicle fuel use
Biogas H2S scrubbers are used to reduce the content of hydrogen sulphide in raw biogas providing a cleaner and less corrosive gas for engine combustion.The content of H2S in raw biogas will typically be in the range of 1000 - 5000 ppm and depends on the type of feedstock being digested. Combustion of the raw biogas produces sulphuric acid and leads to severe corrosion of a CHP engine The engines operational life is greatly reduced and income will be lost during overhauls and breakdowns which also require substantial expenditures.
Leading CHP engine manufacturers specify maximum H2S limits of 250ppm in the biogas to enable full warranty's to be provided. Biogas H2S scrubbers can be designed for any biogas flow and H2S reduction requirements and are able to be retrofitted into existing biogas plants.
Gas drying optimises the combustion process in a CHP engine resulting in an increased engine efficiency and lower fuel gas consumption.
Reducing the contamination of engine oil with condensate will reduce the number of oil changes required and save costs. Hydrogen Sulphide and ammonia are also harmful substances and are naturally partially released along with the condensate.
Note – Condensate is an excellent fertiliser for a biological H2S Scrubber.
Main features:-
Inlet gas is initially cooled by passing it through an inlet/outlet gas heat exchanger and an air cooled liquid chiller further reduces the gas temperature. Using the outlet gas to cool the inlet gas negates the need for hot water for reheating.
The compact skid mounted design minimises installation costs and is suitable for indoor or outdoor location.
Containerised units can also be supplied.
Inbev Magor Brewery, Cardiff - Gas dehumidification, hot water/gas in-line heat exchanger and carbon filters
Raw biogas produced by anaerobic digestion is water saturated. As the biogas enters the pipework utilisation system cooling takes place and water drops out of the biogas. This water needs to be removed from the system to protect mechanical equipment and it is important that design consideration of the pipework layout includes correctly located condensate removal pots.
Biogas Products Ltd design and manufacture all sizes of stainless steel condensate pots for low and high pressure applications. We can offer trace heated insulated pots to protect against the common problem of freezing and simple ball floating outlet valves to stop carry through of water or sludge. Flushing points, level gauges and connections for instruments are all standard features.
Biogas Products Ltd design and manufacture biogas fine particle filters to protect your mechanical plant from particulate produced by raw biogas. We can provide porous ceramic cartridges down to 20 micron with a 2/3mbar pressure drop across the clean filters. Our filters are manufactured from inorganic ceramic compounds providing a high resistance to all biogas contaminants.
All this is contained and protected by bespoke filter housing manufactured in our own workshop from steel or stainless steel and finished to your requirements. Also incorporated into the design of the filter housing is an automatic condensate removal system and an additional feature to remove settled solids.
We also install pressure gauges on the inlet/oulet biogas connections to enable constant visibility of the pressure levels across the filter system.
Filter cartridges can easily be removed for cleaning or replacement via the top bolted cover resulted in quick and easily maintenance of the filter.
Single filter design is suitable for biogas flows of 50-6003/hr.
