Small scale biogas plant

Guest blog by Linus Österdahl Wetterhag, MTK311 HT19

After receiving a phone call from my dear friend Mr Andersson asking me how he could increase the sustainability of his farm I was very excited. He provided me with some facts about his farm and his possible resources and at first I really had to analyze the prerequisites to figure out how he could best increase his sustainability. Of course I saw many possibilities but the one that made me most interested was that he paid a company to remove his manure which almost made me angry. Why pay someone to collect a resource that could increase your income. So the concept I proposed to Mr Andersson was simply to invest in a biogas plant.


Investing in a biogas plant for his farm would solve most of his problems. He could instead of paying a company to remove his manure, use the manure himself for production of biogas, which then could be used for heating his farm (of course this would require further investments), fuel his biogas car (might also need an extra investment), use the digestate to fertilize his feedstock and sell the excess biogas. This way Mr Andersson would solve a lot of problems in one go. His electricity bill would decrease, he would have to buy less fertilizer, he would also decrease his costs for fuel, earn money on his manure instead of paying someone to collect it and also get rid of some of that awful smell that is present at times when I visit him.


So how does it work? Well the concept of the process is explained in figure 1 where a flow chart of the whole system can be seen. The substrate in this figure is the manure from Mr Anderssons farm, the digester is the plant itself and the output of the digester is methane and carbon dioxide which is stored and then upgraded if the methane is to be used for fuel and the excess gas is used for heat and electricity production (Hansson & Christensson, 2006). The remaining digestate can be used as fertilizer.

Figure 1. Showing the working principle of farm based biogas plant. Figure taken from Ahlberg and Eliasson, 2018.

The more practical process consists of feeding the digester which is being stirred by a machine. The temperature has to be controlled to be within a specific range for the digestion to proceed as expected. The process is anaerobic, meaning that no oxygen is to be present in the digester. Depending on size the amount of days between switching substrate depends but for a smaller plant around 20-30 days of digestion is common (Hansson & Christensson, 2006). This also depends on what kind of substrate is used and what temperature is used. Overall the whole process is quite simple and does really seize otherwise wasted resources.


Now you are of course wondering what does all of this? This of course varies depending on manufacturer and size of the plant, but Biolectric Sweden AB (Biolectric, 2018) has a large variety of plant sizes 11kW, 22kW, 33kW and 44kW. The plant is operated via the cloud and the only thing the farmer has to do himself is to feed the plant with manure. Biolectric Sweden AB does not provide any prices but do state that the payback time is around 6 years for the investment. In (Nääs, 2010) the investments for a local plant is estimated between 2 to 15 million swedish crowns depending on size. According to (Bioenergiportalen, 2014) a smaller plant for only producing heat could cost around 600 000 swedish crowns but if it is to be upgraded to produce fuel as well, the cost beyond the first investment would be around 5 million swedish crowns. These numbers are more for one of a kind applications and a large scale product like Biolectric Sweden AB supplies could be very cost efficient for farmers (Wahlberg, 2015).


So is small scale biogas production something for farmers to invest in? I really think so, of course the investments has to be economically plausible. If they aren’t the politicians should really look into the possibility of subsidies for these kinds of investments and if they already are plausible, then more farmers should really invest!

References:


Wahlberg, Carolina (2015, August 15). De bygger sin egen småskaliga biogasanläggning. Retrievedfrom https://www.ja.se/artikel/48041/de-bygger-sin-egen-smaskaliga—-biogasanlaggning. html
Ahlberg Eliasson, Karin (2018). Swedish farm-scale biogas production. ( Doctoral Thesis, Uppsala University). Retrieved from https://pub.epsilon.slu.se/15821/8/ahlberg_eliasson_k_190107.pdf
Hansson, Anna & Christensson, Kjell (2006). Gårdsbaserad Biogasproduktion (Jordbruksverket) Retrieved from https://www2.jordbruksverket.se/webdav/files/SJV/trycksaker/Pdf_jo/JO06_1.pdf
Nääs, Charlotta (2010). Småskalig biogasproduktion: förutsättningar, hinder och lösningar (Mittuniversitetet). Retrieved from http://miun.diva-portal.org/smash/get/diva2:358626/FULLTEXT01.pdf
Biolectric (2018). “Vårt System”. Retrieved from
https://www.biolectric.be/sv/vart-system/
Bioenergiportalen (2014). Retrieved from
http://www.bioenergiportalen.se/?p=3368&m=1647&page=ekonomi

2 Comments on “Small scale biogas plant

  1. That’s good to know that the temperature would have to stay within a certain range to be able to use biogas safely. I like the idea of using biogas to provide energy since that sounds like a pretty clean, long-lasting form of energy. I’ll have to ask about temperature control if I decide to get a set up to help em use biogas, so I can make sure everything is safe.

    Liked by 1 person

    • Hi Tyler,
      The temperature is not so much a factor of safety but a prerequisite for the methane producing bacteria to be able to operate under optimal conditions. Are you planing to build a small scale biogas reactor?

      All the best,
      Patrik

      Like

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