High yield from green mass
After CO2 removal or the upgrading of biogas, the resulting end-gas is an analog of natural gas. It's called biomethane, compressed biogas (CBG) or bio-compressed natural gas (bio-CNG). Though CBG and bio-CNG are commonly used terms in India, in Europe the word "biomethane" is more common. All words are correct. CBG consists of 98-99% methane, 1-2% carbon oxide, 0,2% oxygen, 0,2% nitrogen. Sulphur level is 0 ppm if good milty-stage purification is used.
In the tropics and subtropics, Napier grass is widespread. The other names are King grass, royal grass, Sudanese grass, perennial elephant grass. We did batch tests of Napier grass from India, Brazil, Indonesia, Kenya, the Philippines. The variety of the Napier grass is not so important for biogas. It's more important for agriculture. What is more important for biogas is the harvesting age. The young Napier grass, harvested in 30-45 days, has a lot of moisture. Solid content is just 15-18%. BioCNG output is just 45-65 kg per tonne grass. The older Napier grass, harvested in 80-100 days, had 33-37% solid and showed better yields 95-110 kg bioCNG per tonne grass.
To produce 10 tpd bioCNG it's required 120-150 tonnes Napier grass per day depending on moisture/solid content in the grass. The young grass gives little biogas because it has a lot of moisture. And the old grass gives also little because a lot of lignin. For farmers of course it is feasible to sell the young green grass because it's juicy and they are selling moisture to the biogas plant owners.
Between the young green grass and old brown straw there is a stage of green-yellowish grass. So between 18% solid in the young and 80% solid in the old grass there is an optimum harvested grass with 27-35% solid. You just need to harvest Napier grass when it's still greenesh-yellow or yellowish-green. But be careful, don't wait until the Napier grass becomes brown.
Before the biogas plant it is recommended to put Napier grass into a silage storage for several reasons. These reccomendations are general not only for our technology but for all kinds of biogas technologies.
(1) Fresh Napier grass has a lot of air. And because of the air Napier grass can abruptly go afloat in the reactors. It's not only difficult to mix the floating grass, but it is also dangerous. Floating grass may destroy the roof and clog the gas pipes. During silaging grass is pressed by vehilcles as tractors and air is removed.
(2) During silaging acidation and hydrolisis processes start and biogas yeilds are increased 5-10%. Grass is pre-fermented with the lacto-acid bacteria. The minimum silaging time is 35 days.
(3) Silage storage is also needed during the raining seasons when harvesting is not possible. Reactors must be fed constantly independently from the weather.
Feedstock preparation
High-load reactor (HLR) is the best bio-CNG technology for Napier grass. HLR reactor is 3 times smaller and cheaper than the conventional CSTR. For 10 tonnes bio-CNG per day a single HLR reactor 4000-5000 m3 is enough. At the same time, HLR is more relaible and consumes less electric energy for own needs than CSTR. Zorg Biogas implemented the world's largest project with HLR in the equivalent of 110 tonnes of clean bio-CNG per day. This project uses sorghum and maize. The same technology is suitable for Napier grass or sugar cane.
The smallest offered model of HLR is 5 tpd bioCNG. Technically it's possible to make smaller plants like 1-4 tpd bioCNG. But we consider it's not viable. For 1 or 5 tpd there will be 1 reactor anyway. You are very welcome to contact Zorg, If you want to build minimum 5 tpd bioCNG or more,
Proposal for a plant 5 tonnes Bio-CNG per day using Napier grass
Proposal for a plant 10 tonnes Bio-CNG per day using Napier grass
Proposal for a plant 20 tonnes Bio-CNG per day using Napier grass
Proposal for a plant 30 tonnes Bio-CNG per day using Napier grass
Teofipol-2
Bulgaria
TEOFIPOL-3 and -4. The biggest biogas plant in the world!
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