BIOMETHANE
The biogas produced in the biogas plant can be purified to the quality of natural gas and convertible gas or replaceable gas. The convertible gas can be mixed with natural gas in any proportion, as it has the same parameters as natural gas. Replaceable gas, may only be added in a limited amount.
Biogas plants that inject purified biogas into the natural gas network have found widespread use, among others in Germany, Sweden, the Netherlands and Switzerland. The treatment methods used are pressure swing adsorption (PSA), water scrubber, Genosorb, Selexol, amine scrubber, membrane separation and cryogenic separation.
Biogas and natural gas
Due to its high toxicity and corrosive properties of biogas, the first stage of biogas treatment is the removal of hydrogen sulfide. Depending on the treatment process used, an additional desulfurization step may be necessary. To obtain biomethane of natural gas quality, it is necessary to purge it of CO2. In the last stage, the gas is odorized and its calorific value is adjusted (depending on the needs, it can be increased or decreased) to that of natural gas in a given network by adding LPG or air.
Comparison of the composition of biogas, biomethane and natural gas
| Parameter | Biogas | Biomethane | Natural gas |
|---|---|---|---|
| Methane | 45 – 75% | 94 – 99% | 93 – 98% |
| Carbon dioxide | 28 – 45% | 0,1 – 4% | 1% |
| Nitrogen | < 3% | < 3% | 1% |
| Oxygen | < 2% | < 1% | – |
| Hydrogen | trace amounts | trace amounts | – |
| Hydrogen sulfide | < 10ppm | <10ppm | – |
| Ammonia | trace amounts | trace amounts | – |
| Ethane | – | _ | < 3% |
| Propane | – | _ | < 2% |
| Caloric value | 5,5 – 7,7 kWh/m3 depending on the substrate | 10,2 – 10,9 kWh/m3 | 9 – 11 kWh/m3 |
Towards the future
The production of biomethane requires planning for the future and taking into account the regulations and trends that are in force in Poland and the European Union. For example, sustainable development policies and other needs pose further challenges, such as calculating the carbon footprint of a product, eliminating nitrogen, treating new types of bio-waste, compressing or liquefying biomethane.