Wärtsilä recently inaugurated its first commercial biogas liquefaction installation at a biogas plant in Norway. By converting household food waste into liquid biomethane, this novel facility at EGE Biogass is able to produce enough liquid fuel to run 135 buses in Oslo. The plant marks a breakthrough for Wärtsilä in developing liquefied biomethane (LBG) markets.
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The Finnish energy and marine technology major Wärtsilä Corporation recently inaugurated its first commercial biogas liquefaction installation.
Both the biogas plant and biogas liquefaction plant are co-located in Nes, Romerike, which is an agricultural region just northeast of Oslo, Norway.
Built adjacent to a former landfill site the plant produces biogas from household food waste. Further details about EGE Biogass plant can be found here.
The biogas is then upgraded, liquefied, and transported to a dispensing depot where it is used as biofuel for buses in Oslo. Liquefied natural gas/biogas (LNG/LBG) is gas that is condensed to liquid form by cooling it to a temperature of about -160°C for storage under pressure.
The plant marks a breakthrough for Wärtsilä in developing liquefied biomethane (LBG) markets.
Mixed refrigerant
The incoming raw biogas is supplied under pressure, 5.5 bar (gauge), to the LBG plant at a rate of anywhere between 0 – 140 Nm3 per hour.
Before the raw biogas can be liquefied it needs to undergo a pre-treatment or upgrading process to reduce the concentration of carbon dioxide (CO2) to 50 ppm and hydrogen sulfide or “rotten egg” gas (H2S) to 4 ppm. Furthermore, water needs to be removed to 1 ppm to avoid freeze-out in the liquefaction process.
At EGE the pre-treatment consists of two steps, a water scrubber, and a CO2 polishing unit.
The pre-treatment is the challenge as concentrations of unwanted gases vary and the pre-treatment technology used is dependent on the raw gas source, commented Tore Lunde explaining that different feed gas sources, such as biogas, landfill gas, and coal-bed methane, have different compositions.
From the pre-treatment, the biomethane is initially cooled by a glycol pre-chiller before entering the cold box where it is liquefied at around -160°C before being stored in a 180 m3 pressurized tank.
The tank has a 600 litre per minute pump capacity. The LBG plant has a capacity of 10 – 11 tonnes per day or about 4 200 tonnes per annum.
Modular and scalable
The core mixed refrigerant liquefaction technology developed by Wärtsilä is based on over 50 years of experience in the marine and oil and gas markets in particular the more recent experiences with small-scale, 20 000 – 84 000 tonnes per annum, land-based LNG projects in Norway and Finland.
A 2.6 tonne per day fully automated mixed refrigerant demo plant was developed in 2012 to conduct various operational testing.
The installation at EGE is the first commercial installation of this new mixed refrigerant technology. A single standard oil-type compressor and one aluminum plate-fin heat exchanger (PFX) are the main components of the system.
A standard glycol pre-cooling unit is incorporated to improve energy efficiency and to ensure the stable operation of the process.
According to Wärtsilä, the plant is fully automatic designed with unmanned operations in mind requiring only electricity as an energy supply. The technology is robust and designed to handle 0 – 100 percent raw biogas inlet loads.
Combined with modular containerized plug’n’play engineering this results in low investment costs and low OPEX due to low power consumption and simple unmanned operation.
Energy consumption, for the liquefaction unit exclusive pre-treatment, is given as 0.68 kWh per kg LBG. Furthermore, Wärtsilä says that the technology is scalable upwards to a capacity of at least 60 tonnes per day and already today the company offers standardization of capacities at 10, 17, and 25 tonnes per day.
Liquefying natural gas or biomethane reduces its volume to about one-six-hundredth of its volume in a gaseous state concentrating large quantities of energy into easily transportable volumes by specially designed ships, containers, or trailers. This makes LNG or LBG the best option in locations where pipelines are not available or viable, for instance when only limited volumes are needed. As demonstrated here at EGE, our mixed refrigerant technology enables the cost-effective satellite production of a transportable energy-rich biofuel, concluded Tore Lunde.
This article was first published in Bioenergy International No. 71, 2-2014.
