Articles & Case Studies

Sweden’s biomethane revolution continues with major new Schmack Carbotech plant

Posted: Wednesday 10th December 2014

Sweden’s leading role in bioenergy production is set to be further enhanced with the news that Schmack Carbotech has been awarded a contract to design and build a new 2000 Nm³/h processing plant just south of Stockholm.

A development that in early 2015 will see the Swedish capital increase its proportion of biomethane by 50 per cent, Schmack Carbotech’s innovative Pressure Swing Adsorption (PSA) principle will help produce biofuel in vehicles powered by natural gas. Part of the Viessmann Group, Schmack Carbotech is one of the key pioneers and market leaders in biogas purification with more than 30 years‘ experience in the development, engineering and manufacturing of turnkey gas upgrading plants. The company’s PSA principle distinguishes itself from other technologies because of its favourably low energy consumption, efficient heat extraction and high methane yield. Trace gases that are typically found in biogas made from wastewater and organic waste are also removed.

Utilising organic waste and waste kitchen oil as its feedstock, the plant, located in Sofielund, Huddinge will produce biogas with an annual energy yield of nearly 100 million kilowatt hours – enough to supply approximately 5,000 vehicles travelling an average of 20,000 km per year.

Setting new standards in biogas process efficiency, Sofielund’s new plant will be equipped with a CNG station, a Carbotech PSA plant, off-gas cleaning with high heat recovery system combined with a peak load boiler.

The PSA system offers specific power consumption that is the lowest available from pressurized upgrading technologies. The plant will also benefit from ultra-reliable VOC and Hydrogen Sulphide removal, making Carbotech’s robust technology ideal to produce biomethane from biogas, sewage gas and landfill gas for grid injection and CNG vehicle fuel.

‘Low energy yet high yield’

Eberhart Wusterhaus Gomez, Schmack Carbotech’s International Business Manager, commented: “As Sweden continues its advance to become the world’s first completely oil-free economy, we are very keen to play our part in delivering a low energy yet high yield technology that fits in with the government’s long-term thinking”.

Beyond the districts of Stockholm, the green-gas revolution has also caught on in many of Sweden’s more densely populated areas, for example in Skåne (Scania) in the far south. Here, there are already over 1,000 gas-powered buses, with a commitment to make the every bus fleet run on fossil-free biogas by 2020.

A figure approaching almost 50,000 CNG/LNG vehicles in Sweden, including refuse trucks, buses and light commercial vehicles are now powered by a combination of natural gas and biomethane. The biofuel is renewable and has an even CO2 balance.

To fully appreciate the sheer scale of this nation’s way of thinking about its future self-sufficiency, almost 90 million cubic metres of upgraded biogas were sold in 2013 – accounting for more than 61% of the total CNG consumption.

Key motivating factors introduced for those using Bio-CNG vehicles in Sweden include:

o Low fuel tax on biomethane (about 3 times less than petrol)

o Low fuel tax on CNG

o Five year exemption from vehicle tax for clean cars

o Financial support (normally up to 30 % of total investment) for some types of biomethane production units.

o Free municipal parking for Natural Gas Vehicles in many cities

o Priority lanes at airports, railway stations and ferry terminals for CNG taxi cabs.

More than 50 per cent of the biogas produced in Sweden is for fuel transportation, with 38 per cent for heating and less than 3 per cent for power generation (while the rest is produced by old landfills and can only be flared).

In addition to VOC and H2S, Schmack Carbotech’s Pressure Swing Adsorption (PSA) also removes siloxanes and BTEX (Benzene, Toluene, Ethylbenzene, and Xylene). The actual plant is largely pre-assembled and electrically-wired to allow for a functional test prior to delivery. As a result, installation time on site is greatly reduced, requiring just the positioning of the containers on existing foundations, plus the interconnection of mechanical and electrical interfaces.

The entire system consists of the following components:

· Raw biogas pre-cooling and compression

· Biogas drying

· VOC removal and desulphurization

· PSA methane enrichment

· Off-gas heat recovery unit and peak-load boiler

Biogas is delivered to the biogas upgrading plant, where first it will be cooled down and compressed to between 2-6 bar(g).

The biogas is then sent to the drying stage where it is gradually cooled to approximately 5°C to remove most of the moisture and condensable organic compounds.

After drying, VOC, BTEX and siloxanes will be adsorbed upstream of the desulphurisation stage. This is achieved by additional adsorption, consisting of high-grade activated carbon.

Subsequently, the biogas is directed to a Hydrogen Sulphide removal reactor with activated carbon, which absorbs the H2S – and with the presence of oxygen, breaks into basic sulphur and water.

‘Methane quality of more than 97 per cent’

For the removal of carbon dioxide, the conditioned biogas enters the pressure swing adsorption (PSA) unit. CO2, part of the O2/N2 load, plus the remaining moisture and other impurities are removed by adsorption on a Carbon Molecular Sieve (CMS). The product gas leaving the PSA will have a methane quality of more than 97 per cent.

The adsorbed components are removed from the CMS in a regeneration step by evacuation of the adsorber vessels. The off-gas, which is mainly composed of CO2, small fractions of O2, N2, H2O, traces of H2S and CH4, is sent to an off-gas combustion unit where all combustible components (mainly CH4) are decimated. The heat from the resulting off-gas is recovered in a waste heat boiler and used to heat the biogas plant.

Fine desulphurization and methane enrichment are processes that utilise activated carbon for an effective and reliable elimination of undesired components in the biogas. In the case of the H2S and VOC removal, the activated carbon must be changed at certain intervals. On the other hand, for the CO2 separation, the adsorption process is reversible, so the CMS is regenerated due to the pressure swing cycles, giving it a lifetime of several years and more. In fact, Schmack Carbotech still has plants operating that date back to the early 1990s.

The in-house Pressure Swing Adsorption (PSA) process developed by Schmack Carbotech is a tried and tested technology, with almost 70 successful and highly efficient industrial plant installations in Europe, where it provides the lowest utilities‘ consumption of its kind.

The inventive biogas upgrading process is based on the preferred adsorption of carbon dioxide compared to methane on the internal surface of a CMS. This separation effect is not only based on the better physical adsorption of CO2, but is also due to the different sizes of these molecules.

During the adsorption phase, biogas enters from the bottom into one of the adsorbers. When passing the adsorber vessel, CO2, as well as parts of O2 and N2 are kept on the internal surface of the adsorbent material so that enriched methane leaves the adsorber vessel at the top.

‘Continuous supply of methane’

Before the adsorbent material is completely saturated with the adsorbed gas components, the adsorption phase is stopped and switched to the next freshly regenerated adsorber vessel, thus guaranteeing a continuous supply of methane.

To achieve complete regeneration, the adsorber vessel is evacuated by a vacuum pump. After the evacuation step, the adsorbent material is completely regenerated and is ready for the next adsorption phase. The off-gas will be sent to the off-gas combustion unit and heat recovery system.

The off-gas is led through recuperative burners in a combustion chamber, where the complete oxidation of methane and other trace elements (e.g. VOC) takes place.

After oxidation in the combustion chamber, the hot flue gas exits through the recuperative burners where it passes a recovery heat boiler to generate hot water for heating purposes within the biogas plant.

As the heat from the off-gas heat recovery boiler does not quite cover the total heat demand of the biogas plant, an additional biogas-fired peak-load boiler provides the balance heat required.

Through this off-gas combustion, the total methane emissions to the atmosphere will be reduced to less than 0.1% of the incoming methane.

As well as being a specialist in upgrading biogas plants, the Viessmann Group is actively implementing complete biogas turnkey solutions worldwide. Installations include award-winning biological technology, with special wet fermentation (from Schmack Biogas) and batch-dry fermentation (BioFerm technology) now integral parts of more than 300 cogeneration and biomethane plants in Europe and beyond. This includes Europe’s largest dry-AD-from-organic-waste plant, located in Fife, Scotland.

The Viessmann Group is a leading international manufacturer of heating technology systems. Founded in 1917, the family company has around 11,400 employees with group sales of EUR 2.1 billion. Viessmann has an international presence with 27 production companies in 11 countries, sales companies and representations in 74 countries and 120 sales branches worldwide. 55 percent of sales are generated abroad.

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