正確的分子空氣過濾解決方案對沼氣生產行業的好處

Why you need proper filtration for biogas production? 

Biogas production is an important global industry and the third fastest growing renewable energy source in the world. Organic waste is used to replace non-sustainable fossil fuels for energy production. By using correct and dedicated molecular filtration the biogas can be purified, reducing engine corrosion and equipment abrasion while ensuring steady operations, profit and compliance to rules and regulations.  

The biogas process is critical as it releases heavily contaminated gasses that can cause engine corrosion and equipment abrasion, causing unscheduled downtime for maintenance and repair, which results in loss of output and profit. Luckily, there are several ways of solving molecular filtration in biogas plants with different types of filter media in deep beds. 

What are the risks in biogas production? 

Energy bearing biogas is a by-product of biowaste. When organic waste is digested in a rotting process without air (anaerobic), the resulting methane, which is the fuel for energy production, may be heavily contaminated with acidic hydrogen sulphide (H2S). H2S combustion leads to sulfur dioxide emissions, which have harmful environmental effects. Furthermore, if high concentrations of H2S reach the gas engine where the methane is combusted, the engine can suffer internal corrosion due to the combination of acidic gas and high temperatures. Engine corrosion requires unscheduled downtime for maintenance and repair and can also reduce the lifetime of the equipment by years, which results in loss of output and profit.  

Another risk for biogas engines comes from siloxanes and other volatile organic compounds (VOCs). These compounds are widely used in consumer products which reach land-fill disposal sites. Biogas generated at these facilities may be contaminated with siloxanes, that require special molecular media to purify properly. When siloxanes are combusted, they leave behind deposits of solid silica and silicates. These cause abrasion in moving parts and put engine components out of balance, all leading to loss of efficiency and unscheduled downtime. Special molecular media is required to properly purify biogas from siloxanes. 

Many anaerobic digesters (tanks) and biogas engines are located close to the feedstock of organic waste, i.e. on farms or waste processing sites. To optimize the efficiency of energy production, the biogas is fed to the engine at elevated pressures, typically up to 0.5 bar. Then the combustion phase begins and the energy from the gas becomes usable. 

The biogas or biomethane can also be converted into compressed biogas (CBG) or liquid biogas (LBG) and used as vehicle fuel.

The use of natural gas as car fuel can reduce carbon dioxide emissions.

Biogas driven cars are often quieter and produce less particulate matter, nitrogen oxide and sulfur dioxide emissions than cars driven by petrol or diesel. 

What is the ideal filtration solution to avoid the risks involved? 

Molecular filtration is the accepted method of removing hydrogen sulphide, siloxanes and VOCs from biogas prior to combustion. Molecular filtration will help to solve the biogas contamination and equipment challenges, as well as ensuring compliance with the strict rules and regulations for this industry, as there is also a very high focus on air quality & health and safety standards by the authorities. 

Molecular filters utilize a technique known as adsorption. In simple terms this means that the molecules adhere onto materials with extremely high surface areas. Molecular filters can use activated carbon or activated alumina as the active ingredient and are sometimes also impregnated to attract the target molecules. Molecular filters are also sometimes known as chemical filters or gas phase filters. 

There are many ways of solving molecular filtration in biogas applications. Activated carbon or alumina media are deployed as filter deep beds (>= 100 mm) between perforated metal sheets in a wide range of heavy-duty housings, and as single or multiple stages depending on concentration and flow requirements. 

The UL flammability rating of the media is important, as normal carbon is flammable, and that the media allows correct adsorption of the target gasses. 

The design and construction of horizontal deep bed (HDB) filters for biogas applications should take account of the system pressure. Biogas HDB filters must be constructed from heavier gauge material, have cylindrical shells and use dished ends. It is also crucial that flanged inlet and outlet connections and bosses for instrumentation are according to a recognized standard.  

For biogas production plants, the right molecular filtration solution can ensure steady operation, improved profit levels and compliance with rules and regulations.  

Sources: 

European Biogas Association 

Danish Technological Institute 

Co-author

Karl-Henrik Björkhem, Business Development Manager Northern Europe, Molecular Contamination Control, Camfil. With over 10 years of experience in renewable energy and environment sector focusing on air containment and filtration, Karl-Henrik has valuable insights on corrosion control, indoor air quality, molecular contamination and odor control.