Eva ten Velden
Meeting BOTALA energy solutions
Date: 1-12-2015
Duration: 16.00- 17.30
Participants:
- Job Seuren (team member)
- Yonis le Grand (team member)
- Steven Roerink (team member)
- Eva ten Velden (team member)
- Peet Steyn (founder of BOTALA)
- Stefanus? (intern of BOTALA and nephew of Peet)
Peet showed us his first build biogas plant at the farm of his father in law. His father in law ones horses and in the beginning the wanted to use the dung/manure of these horses for the digester. Only before actually trying they discovered that this dung/manure contains a lot of grass/straw and this is very difficult to digest. So they contacted the chicken farm next door and now they make biogas out of chicken manure. Every day there comes around 800 kg of chicken manure to the farm. Most of this manure comes from chickens which live in cages. The droppings can therefore be easily collected. In this case there is no sand that should be separated from the biomass. Peet does recommend to do this for our digester, because 30% of cow manure is sand and this can screw up the hole system. If you have a put in the beginning of your system the sand can sink to the bottom before you use the biomass for the digester. In this case you only have to clean out this put (500m3) one in a while instead of the digester itself.
For this digester there is only one operator necessary. In the morning this operator turn the generator on. Around noon he feeds the digester and during the evening he turns the generator off again. The system of this digester is a “flush for feeding” system. Before the manure is being fed to the plant the pump runs and extract water from the digester. The manure is than being fed to the plant and the pump flushes everything (water and manure) to the digester itself. In the digester the biomass is mixed by a propeller mixing system. The plant also contains an external boiler and spiral pipe heating system, but this was only used during the start-up period of the plant. The plant was build two years ago and Peet has concluded that you don’t need a heating system for a plant of this scale. The cost-benefit of a heating system turns out to have more cost than benefits. Also a CHP system was to expensive. A metabolic system was not worth it because the outcome was only 25% more and the costs were higher. The biogas than runs thru a pipe system in a water sealer. This water sealer keeps the gas from running back into the digester. After the water sealer there is another tube with we all don’t remember the name of (something with metallic shading) and the last tube is the scrubber which contains oxygen pallets. The scrubber has to be replaced but Peet has found that the smell of the gas is not changed yet so he concludes that the scrubber is still working fine. After this the gas runs thru the gas meter. If there is too much pressure in the gas dome on top of the digester the gas flows to the gasbag. This bag can contain 25 m2 gas and costs 5000 rand. Around the bag there is a cover which protects the gasbag from the sun and wind. The gas pump in the system deflates the bag and attracts gas from the digester to on the one hand the generator and on the other hand the demonstration chicken heater. The chicken heater needs 5 kPa of gas to produce a heat of 100 kWatt. (for example; if you want to heat 4000 chickens than you need two of these chicken heaters.) The generator produces 10 kWatt of energy. Peet had to import the pump and the generator from China (there are a lot of companies there, Peet mentioned NPT). The rest of the plant comes from South Africa. If it was a bigger plant he would import around 60% from China and 40% from Europe. Peet had to import the generator from China because there is no company which produces generator in South Africa. Only some companies which produce a generator on diesel instead of petrol and most of the time these generators are broken by the time they reach 6 months. Also a turbine was not the best option because there is no knowledge and skills about this in South Africa. When you have a turbine and it is broken you have to fly over a specialist from the US and let him stay for five days. This will cost the same amount of money of a new generator running on petrol imported from China. Thereby can you only use a turbine above the 10 MWatt and this is way more than we have.
The material of the outside of the digester is zinc sheets. The inside is made of isolation material and on top there is a plastic membrane. These materials were chosen because of the low prices and the small scale of the plant. A plant of a much larger scale will probably contain more concrete, but in this case that will give a seven times higher cost structure. The volume of this digester is around 100m3 but you can easily scale up to 500m3 before you have to change the design. The digester is built on a hill and that is why the half of it is buried in the slope of the hill. The foundation of the digester is barely something. The costs of a whole concrete floor where too high with less benefits. The only reason why you should have a foundation is because of the zinc of the digester. When zinc touches the earth the corrosion will be much faster. This is why Peet has chosen for a concrete ring under the zinc sheets. This is a much cheaper solution. The only thing that could happen is that the rest of the ground will flush away when there is, for example, lots of rain. If this happens, the digester contains a bag which is flexible enough to handle the changing bottom.
The digester of Botala has a lifetime of around ten years, after these years the corrosion on the outside of the digester will make it brake. The plastic pipes have a lifetime of around eight years, so they have to be replaced once in a while. The gasbag has to be replaced after five years. Peet has choosen for a “short life + short payback”. As mentioned before, it is all about cost-benefit and Peet has found this the best way to payback to costs he had made with this digester. His digester is cheap but has a short life, it is difficult to be efficient and economical at the same time.
The moister in the digester should be liquid enough to run thru the pipes. 95% water is the same as filter coffee and you definitely don’t want to run the plant on filter coffee. Peet has no idea what the moister content in his plant is, but he guesses around the 20% or more of solids.
The fertilizer of this plant is not being used. They just throw it on the land.
Because this is not a commercial biogas plant, you only have to get a notification of activity at NERSA and if you use more than 10 tons of waste per day you will need more licensing. Peet also didn’t get any funding. The owner of the plant did apply for the 1,2 MWatt Tronton and the IDC, but the qualifications were too difficult so they decided to withdraw. Only the DTI give them something, but after two years of finishing the project. According to Peet there are some fundings which are easy to get if you are black. But funding will not cover all the costs, it only helps to refund the payback period. But for example the IDC funds only if the funding will be more than 10 million rand. Because otherwise it will cost the IDC too much money. Peet also said something about normal banks. They will fund (give a loan) if you can show them you have the land and the equipment to get a biogas plant.
The feedstock of the plant of Peet contains only chicken manure but we asked him about his opinion about abattoir waste. He said that a feedstock should not contain more than 1/3 of raw proteins. Otherwise it will contain too much ammonia, so you have to add more grass or stomach contend. Furthermore the different components of a feedstock react each at their own time. Glycering takes only 10 hours to digest and raw proteins take around 8 days. If you use food in your biomass it will take 3 to 4 days of reaction time. Also you have to take into account the possibilities of bones in the food waste. These bones will react into calcium so they will become a sort of concrete at the bottom of your digester. In order to protect this from happening you need a grinder in the beginning of your system of the plant (again a cost-benefit analyse has to be made, a grinder cost R200000 according to Peet, and this could be a third of the hole plant. It this worth it?). When you change the feedstock it will take 20 days to actually see the change in the outcomes of the digester. Than it takes another 20 days to get stable and from that point you can increase the feedstock and thereby the outcome of the plant.
When you have decided what your feedstock is going to be, you have to make sure that it stays the same. For example if you have a feedstock with more than 10% fat and you suddenly run out of fat the digester will fall over. This means that the production of gas will be less and the digester will start foaming. At the end the digester will not function properly for at least two months. A way to do this is by adding a tube between the pump and the digester. In this tube, intake-mixing tank, the biomass can stabilize. There will be some fall to the bottom and there will be some float to the top. The useful biomass that will be brought to the digester will therefore stabilize in the middle of the tube (Bronkhorstspruit has this as well). 50% manure, 20% abattoir waste, 10% fat should be manageable.
Peet has said that all his customers have a biogas plant for self-use and also the people from the REIPPPP use the plants for self-use. This is because there is no payback for the electricity. Eskom sells their electricity for 70,9 cent per hour. If you want to sell to Eskom you have to sell the electricity for 95 cents per kWh otherwise it has not a reasonable payback, but normally someone sells electricity for 45 cents to Eskom. All these prices are to less to make the payback for electricity viable, so Peet recommend not to use the biogas/electricity for selling. Also if you want to transfer electricity back into the grid than it will cost you at least half of the money you will make with your plant. (cost is something around the 350 000 Rand). And just to give an idea; you need 60 tons of biomass to produce around 500 kWatt. (Bio2Watt has 320000 tons, but according to Peet BMW is only involved because of marketing and is not making money out of it.)
When we asked Peet about the plans of Takatso to let us design the plant and someone else built it. He said that it was possible. The building could be done by locals; local constructor, local plummer etc. This has to be done with a lot of supervising. So indirectly he answered that Botala will not build something that they didn’t design themselves.
After this we asked Peet about scaling. His digester has a volume of 100m3 and the design has to be changed if someone scales it up to more than 500m3. Because it is a small scale digester he chose a 3 kWatt pump. This is a small scale but fast pump. There is one important thing; you cannot scale down. Many systems which are great for large scale projects are not that great for small scale project. This has again something to do with cost-benefit. Peet mentioned also something about “wharsilla” we should visit their website. They have a whole other scale to be efficient.
There are a few things Peet should do different from the first time. At first he would not use a propeller as a mixing system. These propellers often break and you can mix the biomass also with a water mixing system. Second he would make the plant more beautiful. Last of all, if there is a possibility for larger scale projects he would use more concrete.
When Peet told us how he came by with the idea of biogas he told us about the fact that he wanted to start up a business. Energy is a good business, and especially green energy, in South Africa. Wind and solar had already great businesses so he wanted to come up with something new. That is why he choose for biogas, so he could deliver a unique service.