Analysis of contaminants in biogas

Trace amounts of hydrogen, nitrogen, carbon monoxide, saturated and halogenated carbohydrates, sulphur gases and siloxanes are occasionally present in the biogas. Usually the mixed gas is saturated with water vapour and may contain dust particles.

The presence of contaminants in biogas for vehicles can harm the gas distributing system or the gas utilities or cause unwanted exhaust products. High quality is thus required in order to avoid performance disturbances.

As example, actual requirements in Sweden:

• Sum carbon dioxide, oxygen, nitrogen less than 5 %-vol
• Oxygen less than 1 %-vol
• Total sulphur less than 23 mg/ Nm3
• Ammonia less than 20 mg/ Nm3

SP provides in addition to the main components, methane, carbon dioxide etc. analyses of contaminants in biogas or any other gases via sampling in a gas-tight bag or by enrichment onto an adsorbent. The analyses are performed by gas chromatography (GC) together with a FID (flame ionisation detector) and MS (mass spectrometry) as well as ICP-MS (inductively coupled plasma - mass spectrometry). We can assist with the sampling directly at the facility or send equipment to perform the sampling if required.

With access to many different instruments of analyses, we can offer extensive gas analyses, all after requirement.

Siloxanes

During combustion, siloxanes are converted to silicon dioxide - SiO₂ (a white ash). Silicon dioxide accumulates on the heated surfaces in combustion equipment, especially in the cylinders, on the valve etc. Silicon dioxide is a solid compound and will remain in the engine and cause considerable damage.

Halogenated hydrocarbons

They cause corrosion in engines, in the combustion chamber, at spark plugs, valves, cylinder heads, etc.

Sulphur gases

Biogas and, especially, landfill gas can contain a variety of sulphur compounds, such as sulphides, disulphides and thiols. The sulphur-containing compounds may be oxidized to corrosive sulphates and sulphites in the presence of water. Sulphur gases are also known to be responsive for unpleasant odours already at very low concentrations. Moreover they are a well known poison for some fuelcells.

Example of analyses we can offer