Biogas Processing Plant Successful in Continuous Operation

For four years, biogas has been produced from maize, grass, and whole plant silage at the Laupheim site, about 30 km south of Ulm, Germany. The raw biogas is processed by Erdgas Südwest GmbH and made available to end customers in the form of biomethane over the own natural gas grid. In 2008, the first biogas processing plant was commissioned at the site. The pressure swing absorption of Schmack Carbotech processes about 600 standard m3 of raw biogas an hour. This amount is sufficient to continually supply about 2,000 four-person households with electricity.

To respond to the growing demand for biomethane, the operator decided to expand the production capacity. In view of the practical experience from the operation and the knowledge of the advantages of dry pressure swing adsorption, the operator opted for a biomethane system of ETW Energietechnik (Germany). One of the main reasons for this decision: The specialists from Moers, Germany, had the best solution for the challenge of integrating the new technology in the existing array.

Before the humid raw biogas enters the absorption tanks, hydrogen sulphide is removed and water is condensed out. The residual humidity is removed as a side effect of the pressure swing absorption. The smart control by means of which the absorption columns are connected ensures that the product gas purity reaches a stable methane content of 98 percent despite varying raw biogas compositions and quantities. Continual quality measurements guarantee short reaction times. Subsequently, the biomethane is forwarded to the feed-in station that serves as the interface to the natural gas grid with a pressure of about 6 bar.

For the first time, the plant in Laupheim generates biomethane with the PSA process control developed by ETW, which differs significantly from the established systems in Germany. The result is an extraordinarily high methane content in the product gas with minimal methane losses and rock-bottom power consumption. Thus, 98 percent of the supplied methane can be delivered to the natural gas grid. The methane loss of 2 percent is returned to the biological process of the biogas plant via an after-burning unit in the form of useful heat. Together with the recovery of the compression heat, a total heat output of 140 kW at 80 Grad Celsius can be separated from the gas processing.

With a power requirement of only 130 kW due to the optimised process technology and no need for additional supplies except active carbon for the desulphurisation, the operator benefits from a highly economic system.

The absence of self-inflicted problems such as heat requirements, fresh water requirements, winter conditioning, corrosion, sediments, channeling, and the handling of chemical substances makes for increased operational reliability and various ecological benefits.

The dry pressure swing adsorption of ETW Energietechnik will greatly stimulate the biomethane market. Especially as biomethane production is the only practicable method of storing renewable energy, it is up to the legislator to clearly define the role of biogas in the energy transition.