Bio-CNG plants
using Napier grass

Bio-CNG plants using Napier grass

Napier grass is the ideal substrate for biogas and bio-CNG. Biogas plant is the solution to satisfy the increasing demand for green energy and creating jobs in rural areas.

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High yield from green mass

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. What is more important is the age. The young Napier grass, harvested in 45-60 days, has a lot of moisture. Solid content is just 15-22%. BioCNG output is just 45-65 kg per tonne grass. The older Napier grass, harvested in 100-140 days, had 30-35% solid and showed better yields 85-95 kg bioCNG per tonne grass. There is a superstition that with 6 harvests every 60 days there would be more grass than with 3 harvests every 120 days. But in reality the amount of total solid per year per ha will not change. What changes is the amount of water in the grass. Water takes the useful volume of the reactor. The older Napier grass requires 2 times less volume of reactors.

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.

Construction features

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 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.

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

Zorg Biogas’s plants for this industry

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