Biogas Production - Lessons Learned from Europe
On Monday August 21st a group organized by the Ontario Large Herd Operators left from Toronto Airport bound for Amsterdam. The next seven days would be spent traveling by bus through the Netherlands, Germany, and Denmark to study anaerobic digestion technology. The 32 participants were quite a diverse group, made up of dairy, beef, swine, vegetable and cash crop producers, research and extension people, waste haulers, industry people, plus a banker, a representative from Hydro One, and the Ontario Power Authority. Although a diverse group, they all had a common goal of seeing and learning as much as they could in seven short days. Or perhaps the group would say seven long days, as the tour started early every morning, and ended late every night.
Many hours where spent riding the bus, but each stop managed to give the group something new to talk about in between. The route went from Amsterdam, in the Netherlands to Ribe, Denmark in the North and then back again. We visited 16 anaerobic digester installations, or biogas plants, as they are more commonly referred to in Europe. Each stop had been carefully chosen because it was unique in some way - either by the technology at the facility, or because of the goals that the owners were trying to achieve.
There are other things in Europe to see besides biogas plants the first day started with a stop at the Aalsmeer Flower Auction. Aalsmeer is a co-operative where 3000 grower members market their floriculture products through a central marketplace using the Dutch Clock auction system. The group saw a lot more colour than the usual black and white many were used to. But after that, the rest of the European scenery and history was mostly enjoyed from the bus window, or from visiting the interesting towns the group stayed in each night.
The first biogas plant was located in the Netherlands at the Eissen Dairy. Here the group was introduced to the basics of how biogas is produced from manure. Manure from the dairy was pumped into an insulated above ground concrete manure tank. Hot water heating tubes wrapped around the tank kept the contents at about 40oC. At this temperature anaerobic bacteria in the manure are quite active, converting the organic matter in the manure into methane gas (CH4), more commonly referred to as biogas. The biogas was collected off the top of the digester and used to fuel two Jenbacher diesel engines running a pair of 625 kW electrical generators. Heat from the engines was collected and used to heat the hot water to keep the digester warm (Figure 2).
Before the biogas could be used in the engines, the hydrogen sulphide and moisture had to be removed. A small amount of oxygen was added in the head space of the digester to combine with the hydrogen sulphide to produce a precipitate, thus removing most of the hydrogen sulphide. The biogas was then transferred to the engines underground, so most of the moisture would condense out of the gas.
The majority of gas was removed in the anaerobic digester, and the remaining effluent was then transferred to a long term storage where the bacteria continued to work as the manure cooled off. This tank was also covered so the biogas could be collected and pumped to the engine.
The effluent in the long term storage was eventually applied on adjacent fields. Anaerobic digestion preserves the nutrient content of the manure, so that it can continue to be land applied as a fertilizer. Anaerobic digestion also greatly reduces both the pathogen content of the manure and the odour. This was most evident when the group visited the Futterkamp Research Station. While the group stood and viewed the digester, the long term storage tank 50 ft away was being agitated and manure was being hauled to the fields. There was no smell, other than what was coming from the cows in the barn!
The group quickly learned that a variety of other ingredients were added to the digesters to increase the output of biogas. The most notable ingredient was corn silage (Figure 3). Many digesters used a modified TMR mixer to meter corn silage into the mix to increase the
gas production. At one stop, a German engineer remarked that you had to "Love her like a cow", when referring to the digester. This helped the group to understand that you have to "feed" the digester very similar to how you would feed a cow. You need to concentrate on providing lots of energy feedstocks, and to make changes gradually when you introduce new feeds. The group also saw installations that were further processing the energy crops added to the digester to make the energy more available to the bacteria, in order to increase gas production. One company was also adding grain to the long term storage to try to keep the digestion process going after the effluent had left the main digester.
The biogas reactors which the group saw were basically of two types. The most common was the vertical totally mixed digester (Figure 4), while we also saw several horizontal digesters (Figure 1).
The horizontal digesters were usually used for feedstocks with higher dry matter content, like poultry litter. There did not seem to be a clear right or wrong, in terms of digester designs. The biogas companies would design the digester to meet the individual needs of the producer. The design would be based on feedstocks available, intended use for the biogas, alternate uses for heat, etc.
We saw several creative uses for the additional heat captured from the engine-generator sets or gen-sets. Most biogas plants were using excess heat to heat hot water for the barn or house, but three of the biogas plants were actually selling the heat for use by others. One plant in particular was using the excess heat to provide hot water heating to a nearby airport, and two others were supplying a portion of home heating requirements in adjacent villages, such as Jühnde.
Jühnde is a small German village where all the energy to the village is supplied by the adjacent biogas plant (Figure 5). The plant supplies the electricity from the diesel engines operating on biogas running generators, and then excess heat from the engines is used to heat hot water with is supplied to the villagers for water and heating needs. In the winter when excess heat from the gen-sets is not enough to provide the homes with heat, extra boilers are fired with wood chips. Plans are currently under way to dry the wood chips with extra heat that is available in the warm summer months.
Another unique stop was to a "gas" station that offered its customers the option of filling up with biogas (Figure 6). The biogas supplied to the gas station was produced at a nearby plant similar to the others, but it had been through an extensive refining process to concentrate the gas to a level that could be used in natural gas powered vehicles.
Most of the biogas plants visited with the tour had multiple partners. This allowed different feedstocks to be brought together for processing. For instance, there were several plants where the manure from cattle and hogs was mixed into the same digester. As well, at several sites, different food by-products were also added. Co-operatives ranged in size from two to three farmers up to one large plant that managed the manure from 300 farms in a 50 km radius from the plant. Here 20 tanker trucks were used to pick up the manure at the farms and transport it for processing at the centralized biogas plant. After processing, the treated manure would be stored in tanks in the area for land application, or spread directly onto fields depending on availability.
Not all biogas plants are large scale. If the group could have traveled south to Switzerland, Austria, and southern Germany more individual biogas plants would have been evident.
The group also had several opportunities to visit with technology suppliers, and leaders in the biogas industry. One leader from the German Biogas Association noted that, in Germany, direct benefits from the biogas sector include: 650 MW of installed electrical capacity, a reduction of 4 million tonnes/yr of CO2 emissions, $960 million spent in construction in 2005, and revenues of $500 million to farmers from electricity sales each year. He also noted that the anaerobic digestion/biogas sector in NW Europe is a mature industrial sector with over 200 businesses (8000 employees) offering services to farm-based, cooperative, and industrial biogas facilities. The vast majority of biogas facilities are farm-based systems.
The vast majority of the European farms visited were similar in many ways to what the producers had at home. So why don't we have a proliferation of biogas plants here in Ontario? There are two main factors that have made biogas generation in Europe wide-spread:
At present, the electrical prices in Ontario offered to farmers producing electricity from biogas are not sufficient in most cases to make it economically feasible. The Standard Offer Contract (SOC) program announced last March is one step in the right direction to having a biogas industry in Ontario. Hopefully this can be improved in the future to provide incentives to increase production of biogas by using energy crops in the mix, and to use excess heat recovered from the generator engines. And let's not forget that anaerobic digestion also greatly reduces the pathogen content of the manure, and greatly reduces the odour, both of which are societal benefits. Anaerobic digestion also gives an opportunity to use food by-products that are presently going to landfill sites.
The technology used by the biogas plants that the group visited in Europe would apply in Ontario as well. Many companies there are looking to partner with companies here, so if the electricity price paid for biogas improves, the technology is ready to go.
Biogas production in the future could provide farmers with an additional source of income, while providing society with an alternative use for food by-products, reduced pathogens, and reduced odours from manure. The potential exists for a "win-win" situation.
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