Jenja vs fluidised bed gasification
Two ways to turn solid fuel into gas. One was built for large plants and clean fuels. The other was built for real waste, in a container.
Two reactors, two sets of rules
Fluidised bed
Air is blown up through a bed of hot sand. The sand and the fuel particles float and mix like a boiling liquid. The bed must stay below the temperature at which ash softens, typically around 800 to 900 °C, because sticky ash glues the sand together and the bed stops moving.
Jenja
A top-blown, single-stage fixed-bed converter. Prepared fuel enters at the top and moves down with the gas. Just below a thin fuel layer, the reactor runs at about 1,000 to 1,100 °C. At this temperature the ash melts into slag, and Jenja removes it mechanically while it runs: a poker from above, water-cooled rollers below. The gas passes through the hottest zone before it leaves.
The same job, different constraints
| Fluidised bed | Jenja | |
|---|---|---|
| Operating temperature | About 800–900 °C, kept below the ash softening point | About 1,000–1,100 °C in the reaction zone |
| Molten ash | A failure mode: it glues the bed and forces a shutdown | Expected and handled: slag is crushed and discharged while running |
| Bed material | Sand or mineral bed that wears, is carried out with the gas and must be topped up | None |
| High-ash fuels (sludge, digestate, household fines) | Difficult: ash and alkali salts raise the risk of bed agglomeration | Validated on fuels with up to 45% ash, including digestate from municipal waste fines, horse manure and sewage sludge |
| Fuel preparation | Sized particles that can be fluidised | Pellets or chips, below 15% moisture, prepared with the unit's own waste heat where possible |
| Dust in the raw gas | High: bed material and fine char are blown out; cyclones are needed | No bed material in the gas; it leaves at the bottom through a ceramic hot-gas filter |
| Size of one unit | Usually large, single plants of many megawatts | 150 kg/h of dry fuel per unit: 150–180 kWe plus 430–470 kWth in air mode (wood basis) |
| How it scales | Build a bigger plant | Add units. Ten Jenja units give 1.5–1.8 MW |
| Build and installation | Site-built, years from design to operation | Factory-built in 20-ft containers; installed in about a week, about 10–12 weeks from foundation to operation |
| If the project changes | The plant stays where it was built | The containers move to the next site |
| Gas uses | Power, heat, fuels | Power and heat (air mode); power and cooling; hydrogen-rich gas for methane and fuels (oxygen-steam mode) |
Four consequences of that choice
Running above the ash melting point turns the hardest fuels into an advantage instead of a shutdown risk. Validated on fuels with up to 45% ash.
No bed material to buy, replace or dispose of.
A unit at the wastewater plant, the farm or the island, instead of trucking waste to a central plant.
Factory-built, installed in about a week, and redeployable when a project changes.
Fluidised beds are proven at large scale and suit uniform fuels in big central plants. Jenja is built for the opposite case: mixed, high-ash waste, at the place it is produced, one container at a time.
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