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.


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 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. 

There is a superstition that with 9 harvests every 40 days there would be more grass than with 4 harvests every 90 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.

Also we hear often, that in certain countries Napier grass has high moisture and solid is 18% maximum. This is not true. Because between the young green grass and old brown straw (straw) there is a stage of green-yellowish grass. So between 18% solid in the young grass and 80% solid in the straw there is the optimum harvested grass with 33-35%. You just need to harvest it later. But be careful, don't wait until the 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 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 12,5 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 50 tonnes Bio-CNG per day using Napier grass

Zorg Biogas’s plants for this industry






TEOFIPOL-3 and -4. The biggest biogas plant in the world!

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