German biomass equipment manufacturer WELtec BioPower is to install two biogas plants in France. The first is being built in Gruffy, a village in the French département Haute-Savoie in the Rhône-Alpes region (Figure 1), and will run a 104 kW combined heat and power plant with a 28 250 ft2 fermenter and separator. It is scheduled to be commissioned in May this year.

In this predominantly agricultural village, the fermenter will be fed with solid manure and cattle manure. Additionally, industrial waste from facilities in the region will be sent to the plant. Among other things bakery waste, vegetable leftovers, and other biomass residue will be used.

‘We are going to disperse the digestate on our farm’s growing area, thereby saving the cost of purchasing and transporting fertiliser’ said Marcel Domenge, who runs the farm where the unit is to be sited.

The plant will boast an efficiency of more than 75 %, as this CHP plant will supply part of the village with heat through an already installed local heat network.

In late January, WELtec BioPower received the order for the second farm plant, also in the Rhône-Alpes region at Esserts-Blay (Figure 2). Construction activities for the plant, which is based on a 46 260 ft2 fermenter, was scheduled to start during March, with commissioning to follow in the summer.

In Esserts-Blay, too, the biogas yield will be increased by adding co-ferments that are rich in nutrients and easily degradable. In addition to cattle manure and solid manure, the operator of the plant, Claude Mercier, will use whey from the farm’s own cheese dairy as substrate. Thanks to the use of the heat in the cheese dairy, this plant, too, will have an efficiency of about 75 %.

Feed-in effect

In France, the added efficiency mentioned above is valued; a premium of 3 c/kWh is added to the basic feed-in price of 9 c/kWh if the heat of a combined heat and power plant is used. And an increase in the number of orders from France is becoming evident especially in the case of small agricultural plants with waste co-fermentation. In this way, French farmers spread their risk, as other substances can also be fermented in the plant.

But in view of the fact that the agricultural growing area in France is larger than in Germany, and therefore resources are more readily available, this unfavourable contrast with the situation in Germany, where biomass enterprises are flourishing, is unexpected. According to information provided by the agricultural regeneration association Solagro, in Toulouse, at the end of January 2008 there were in France 100 plants that fermented industrial wastewater, six waste plants, 10 agricultural biogas plants, 60 sludge plants, and four landfill gas plants, with a total power output of 100 MW.

At least part of the explanation for France’s biogas plant population remaining so small may lie in the fact that although the country’s feed-in Act requires the state to purchase power from biogas plants at a guaranteed price, energy from renewable sources does not enjoy priority in the electricity network,

Fermenter construction

WELtec BioPower, which was founded in 2001, plans and produces complete biogas plants made from stainless steel to a modular design. Its industrial partners – Stallkamp and Weda – are both longer established firms but the three companies combine as a single source supplier. WELtec designs the biogas plants, and contracts out the production of all essential components to its partners.

These biogas plants are made from stainless steel because the biogas forming in the fermenter contains a proportion of hydrogen sulphide and ammonia, aggressive chemicals that attack unprotected components. Using SS V2A in the area of the fluid level and SS V4A in the areas contacting the gas ensures the quality and guarantees long service life of the entire system. Even after 20 years of operation, stainless steel still maintains a very high integrity.

How it works

The basic biogas plant technology is capable of fermenting a wide variety of different organic waste materials. More or less any kind of organic waste such as surplus food products, slaughterhouse waste or other organic residual material can be processed.

The biogas process itself is a WELtec innovation. The generated gas is upgraded to the quality of natural gas by means of proprietary procedures and fed into the existing natural gas network as biomethane. Using biomasses like liquid manure or corn offers impressive possible rates of return. The generated biogas can be directly transformed into usable energy that can be sold profitably.

Roughly, three process steps are needed for processing biological raw gas as the basis for feed-in to the natural gas network: biogas desulphurisation, gas drying, and methane enrichment through carbon dioxide separation (CO2). Various tried-and-tested procedures and technologies are available for these tasks. The selection and arrangement of the needed process technologies depends on project-related technical and economic framework conditions.

Amine treatment

The purpose of this chemical treatment is to bind the carbon dioxide contained in the biogas to the washing agent (usually an amine), thereby increasing the methane content in the biogas.

Pressure water scrubbing

During pressure water scrubbing, the carbon dioxide contained in the biogas is bound to the scrubbing agent (absorbed) by means of physical forces. Under the right conditions carbon dioxide is highly water-soluble; this effect is used to scrub the carbon dioxide from the gas flow. As a general rule, low temperatures and high operating pressures are conducive to the absorption of gases in liquids.

Pressure swing adsorption

Usually, pressure swing adsorption works as follows: the biological raw gas is compressed to about 4-7 bar; the compressed gas flows upwards through an adsorption column (zeolite, carbon molecular sieve), where the carbon dioxide is adsorbed (arrested). The product gas (biomethane) exits the adsorption unit continuously. If the adsorbent is saturated with the adsorbing component (in this case CO2), the flow is redirected to a newly regenerated adsorption unit. The switchover does not affect the continuity of biomethane production.