Streicher Anlagenbau GmbH & Co. KG, one of the largest constructors of biogas supply plants in Germany, has installed two Atlas Copco GG 90 compressors with variable speed drive (VSD) at a plant in Geislingen.
Biogas plant Compressor Installation
The two compressors, which have been specially designed for the biogas market, are used to compress the gas to 14 bar for distribution into the medium-pressure network of the local energy supply net.
Streicher Anlagenbau constructs biogas treatment and supply plants, among other facilities. Biogas treatment plants clean the raw biogas that comes from a producer's biogas plant and prepare the gas to be passed on to energy suppliers. Supply plants condition the biogas to be fed into the local gas network.
The processed gas must meet strict regulatory requirements before it is permitted to be fed into the natural gas grid. To do so, adjustments need to be made to the wobe index value and especially the pressure. "We receive the treated biogas at a pressure of around one bar," explains Thomas Kunze, Project Manager at Streicher Anlagenbau. "However, we have to supply it at a pressure of 10 to 14 bar."
Compressors meet high safety requirements
To bring the gas up to this higher pressure, Atlas Copco GG 90 VSD gas screw compressors are used in the supply plant. Atlas Copco entered the biogas market several years ago and has developed machines especially suited to this industry. The GG VSD series, is one example of these specially developed machines.
Equipment for gas compression must meet more stringent safety requirements than conventional compressors, such as being gas-tight and compliance with ATEX Zone 1 & 2. Furthermore, gas production continuously varies. The gas compressor therefore must continuously adjust to this changing inlet conditions yet keeping constant delivery pressure. This is achieved with variable speed compression.
The GG can take in gas at a pressure of 1.1 to 1.4 bar(a) and compress it up to a pressure of 16 bar(a). " explains Robert Liebl, biogas expert at Atlas Copco. "The GGs also operate reliably because the oil-lubricated screw element is very similar to its counterpart in the GA machines.
Reliability and redundancy necessary in plant operations
Energy suppliers generally demand an availability rate of 97% from the plant manufacturer as the biomethane production cannot be stopped. "To achieve and maintain this extremely high figure, all biogas supply plants are built with total redundancy," clarifies Thomas Kunze. Compressors, heaters, gas tanks, pressure regulator fittings, and measuring systems, among other things, are duplicated so that the failure of a system does not disrupt supply.
For this purpose, there are two speed-regulated GG compressors at the plant in Geislingen, each of which is capable of compressing 500 standard cubic meters of gas per hour. The compressors adapt to conditions by means of suction pressure control. "The expertise is in the control system," stresses Thomas Kunze. "All the components must be precisely attuned to each other."
The GG gas compressors feature a single-stage compression process and are water-cooled, speed-regulated and directly driven. This means that they also operate in a very energy-efficient manner.
This is the 2nd plant that Streicher has equipped with Atlas Copco gas compressors since September 2013. "We have had very good experiences with the GGs to date," says Kunze. "The machines are simply constructed, operate absolutely reliably and, therefore, guarantee the high level of availability that we need." Ultimately, the plants are intended to supply gas for at least 20 years.