Biogas contains carbon dioxide in the range of 35−45 vol %. Upgrading biogas to biomethane is primarily based on carbon dioxide removal. Biomethane is essentially purified biogas that contains at least 95 vol % methane and it can be either used as fuel for vehicles running on compressed natural gas (CNG) or injected into the natural gas grid. Nowadays, various techniques are used for CO 2 removal from biogas. Among the most commonly used technologies are adsorption, absorption, cryogenic separation, and membrane separation. Currently, in the Czech Republic, no units for biogas upgrading to biomethane are operating. In addition, during the summer months, there is heat overproduction from the co-generation units. In this work, a suitable unit for carbon dioxide separation is proposed. Carbon dioxide separation is possible using membrane separation. Along with carbon dioxide, minor compounds present in biogas such as hydrogen sulfide and water are also separated. The implementation of this unit makes it possible to obtain biomethane form biogas. Membrane separation was tested in a pilot scale using real biogas. All experimental tests were conducted at the Central Waste Water Treatment Plant in Prague. Experimental tests were performed using different types of membranes. For comparison purposes, the following membrane modules materials were chosen: polysulfone and polyimide fiber membranes. Separation of moisture and trace compounds present in biogas was tested for these two types of membrane materials. Other tests were performed using polyimide membranes. Parallel connection of membrane modules was the most effective to remove carbon dioxide from biogas. Purified biomethane contained at least 95 vol % of methane, as is required, even when the highest flow rate was applied of 7 m 3 h −1 of biomethane (measuring conditions: 0.6−0.8 MPa). This small membrane separation unit is recommended for biogas units in wastewater treatment plants.

Abstract. SiO 2 deposits which cause technical problems on combustion equipment are built by combustion of biogas containing siloxanes. Therefore, in these cases, the siloxanes must be removed from the biogas. For siloxane removal from biogas, its adsorption on activated carbon is often used. After saturation, the saturated adsorbent must be replaced. The adsorbent cost constitutes the main part of the operational costs of the purification equipment. Therefore it is necessary to find an adsorbent having high adsorption capacity for siloxane at a possible low price.Using laboratory apparatus and biogas produced from waste-water treatment sludge at the wastewater treatment plant Prague Bubeneč various activated carbons were tested for siloxane removal and their adsorption capacities for siloxanes were estimated, and the adsorbent cost relative to 1 kg of siloxanes removed from biogas were calculated. The lowest price for the removal of 1 kg of siloxanes was determined by Chezacarb, Sil Extra 40 AP and 4-60 adsorbents. Another important information obtained from the test is that the weakly adsorbed siloxane (OMCTS) is displaced by the larger molecule of DMCPCS during adsorption.

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Apart from burning, one of the possible uses of natural gas is as a fuel for motor vehicles. There are two types of fuel from natural gas — CNG (Compressed Natural Gas) or LNG (Liquefied Natural Gas). Liquefaction of natural gas is carried out for transport by tankers, which are an alternative to long-distance gas pipelines, as well as for transport over short distance, using LNG as a fuel for motor vehicles. A gas adjustment is necessary to get LNG. As an important part of the necessary adjustment of natural gas to get LNG, a reduction of CO₂ is needed. There is a danger of the carbon dioxide freezing during the gas cooling. This work deals with the testing of adsorption removal of CO2 from natural gas. The aim of these measurements was to find a suitable adsorbent for CO₂ removal from natural gas. Two different types of adsorbents were tested: activated carbon and molecular sieve. The adsorption properties of the selected adsorbents were tested and compared. The breakthrough curves for CO₂ for both adsorbents were measured. The conditions of the testing were estimated according to conditions at a gas regulation station — 4.0MPa pressure and 8 °C temperature. Natural gas was simulated by model gas mixture during the tests. The breakthrough volume was set as the gas volume passing through the adsorber up to the CO₂ concentration of 300 ml/m3 in the exhaust gas. The thermal and pressure desorption of CO₂ from saturated adsorbents were also tested after the adsorption.