A mill of 45 tonnes per hour can supply enough biogas for a worthwhile plant: in one budgetary proposal, roughly 370 m³/day of effluent gave about 8,000 Nm³/day of methane. The key is that the numbers are budgetary and need confirming by a site visit and sampling.
The challenge: biogas for a port operator, without its own mill
The intended user was a coal port operator that wanted biomethane for its power plant and trucks, and so arranged to take gas from a neighbouring palm oil mill. The proposal covered the biogas plant at the mill only, up to a flange before the upgrading step.
The numbers
| Item | Figure |
|---|---|
| Fresh fruit bunches | 45 tonnes/h, 20 h/day |
| Effluent | 0.5 m³ per tonne, about 370 m³/day; peak 23 m³/h |
| COD | 75,000 mg/l, about 28 tonnes/day; 85% removal |
| Methane | About 8,256 Nm³/day |
| Biogas | About 15,000 Nm³/day, 625 Nm³/h |
The starred inputs (COD, operating hours and effluent ratio) were assumptions. A small change in the effluent ratio changes the gas output proportionally, which is why a sampling campaign precedes a firm price.
The plant
- Covered lagoon anaerobic reactor with pumps and pipework.
- Bioscrubber, dewatering unit and filtration.
- Flare, with seed material for the lagoon supplied by the client.
The design stresses recirculation and bottom feeding to reduce sludge, and a walk-on cover with sampling ports. Delivery takes about twelve months.
Where the uncertainty is
- Access to the site, soil conditions and land availability.
- Actual effluent flow and strength.
- Whether the gas will be upgraded or burned in engines.
What to consider
- Treat budgetary prices as ranges.
- Agree the interface point for gas.
- Secure a long-term gas supply agreement with the mill.
See the process chain from POME to compressed biomethane.
FAQ
How much gas per tonne of fruit?
Here, about 330 Nm³ of biogas per tonne of fruit processed (15,000 Nm³ ÷ 900 tonnes).
Who supplies the seed?
The client.
Are engines included?
No.
Can the plant be expanded?
Lagoons tolerate load increases.