A small 7kW biogas plant to produce electricity, heat and biomethane – English subtitles


Welcome to Barrett’s Mill in Shropshire. This is the site of the Evergreen Gas pilot-prototype anaerobic digester, small-scale, which we’re using to test a new concept of anaerobic digestion which is below-ground plug-flow digestion compared with continuous stirred-tank reactor and here we’re able to use this site both for experimenting with different types of feedstock and also with different types of energy utilization. So, starting with the site, this is our reception hall where we receive feedstocks for the digester. The feedstocks are principally farm feedstocks, manures and grass silage and maize silage as well as poultry manure and we also put all the grass cuttings from this site through the biogas plant. The first stage of the process is an auger feeder with a hopper on top. The forklift picks up the plastic box, spins it 280 degrees and tips the contents into the auger feeder hopper. From this point there is a screw that goes gently down into the digester so the semi-solid feed stock is not pre-treated but simply fed straight into the digester. So moving outside, we’re able to have this feed mechanism because what we have here is two novel concepts. The first is the fact that its below ground which is unusual in the AD world at the moment, and the second one is it’s a plug flow, rather than being a cylindrical tank where everything is mixed up and you’re feeding it in and taking it out this plant there is a plug flow so the feedstock comes in at that end and it flows gently down through the digester and it comes out the other end. What you see there is a membrane roof to collect the biogas with a larger biogas storage at the back so we’ve got more flexibility for experimenting with different sorts of end utilization. The digester is heated up to a temperature of forty degrees by internal heat exchanges and it’s mixed by gas recirculation so there are no mechanical mixers or moving points within the digester. Within the digester, because the digestion process actually liquefies the material because solids are being digested we’re only able to take the material from the digester through a pump so that the macerator there is connected to the digester and it simply macerates the material through a pump and then into a screw press so we then have a screw press that separates the digestate into a nice compost-like nutrient-rich soil fertilizer, soil conditioner and also a liquid digester; that is the flow of the material. There are three other forms of energy utilization here with our experiments, the first is that there’s a pipeline here that just fuels the AGA cooker in the house. Number 2 is that we have a small engine which is a little Suzuki CHP unit for producing electricity from the biogas. At seven kilowatts it is tiny. Thirdly, we have a biogas boiler which is used to raise hot water from the biogas. Thanks Michael, so now that we’ve looked at BMAD and where the biogas comes from we’re going to talk a little bit about how the biogas is turned into vehicle fuel. So the biogas is compressed and it comes into this column here. Then there’s a flow of water that comes from the top of the column and the carbon dioxide and hydrogen sulphide dissolve into the water. Next, the cleaned-up gas goes off to be compressed. From the compressor it either goes into storage bottles or directly into a vehicle for using at a later date. The water which contains the carbon dioxide and the hydrogen sulphide passes into the top of the flash column where its partially depressurized and any methane that has dissolved into the water is recycled to the beginning of the process, the water then goes to the desorption column where it’s desorbed from the water and then is released to atmosphere leaving a flow of water which is recycled back to the beginning of the upgrading process. The important thing about this biogas upgrader is the scale; it has an inlet flow rate of ten cubic metres per hour of biogas and that is enough gas to produce vehicle fuels to take one of our caddies approximately nine hundred miles in a twenty-four-hour period.

8 Replies to “A small 7kW biogas plant to produce electricity, heat and biomethane – English subtitles”

  1. Why are these sort of systems not being used by waste water companies to provide a clean source of biofuel for cars? Would digested human waste gas such as methane be as calorific as useful as biogas developed from food waste feed?

  2. https://www.facebook.com/solarinverterindonesia/videos/pcb.631313160634813/631313057301490/?type=3&__tn__=HH-R&eid=ARAaPiCyFXYRuKK5cH6q1N1nouZGSOfJPv8DUrtLXhR0Itff8SULmXMUcowFXT2kcnUF7N7KXiT1ylNr

  3. Hi Michael. I’m impressed by your Evergreen biogas to Biomethane setup. I would like to ask if it’s possible to purchase a similar setup with complete Biogas scrubbing, compressor setup and storage storage system.
    The target is to have a Biogas upgrade system that processes Biogas generated from Biogas digester that uses large scale Pig farm manure and the feedstock.
    Did you build your own compressor and scrubber or did you purchase it ?
    Regards,
    Jesse

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