How it works
- The idea — A greenhouse, a concrete floor, and a machine that turns the sludge over. The sun does the evaporating. Everything else in the building exists to make sure the water that leaves the cake actually leaves the building.
- What a square metre can do — Take the irradiation, keep the third to half of it that becomes evaporation rather than heating the structure, and divide by the 0.675 kWh it takes to evaporate a kilogram at around 30 °C. Two to five kilograms per square metre per day is the real band — and it sets the whole footprint.
- The turner is the machine — Without it the surface crusts over in a day and the bed goes anaerobic underneath. The turner breaks the crust, brings wet material up and keeps the pile aerobic. A greenhouse without one is a smell complaint, not a dryer.
- Weeks, not hours — A thermal dryer holds the cake for minutes. This holds it for weeks. That is a genuine cost in land and in working capital — but it is also storage, which on a works with seasonal disposal is worth having.
- The trade — Against a thermal dryer the energy saving is well over ninety per cent, because the only thing drawing power is the turner and the fans. What you pay instead is roughly half a hectare of building for a mid-sized works. Compare the two bars on the right.
- Ventilated greenhouse — The standard arrangement. Moving the saturated air off the bed is worth more than any amount of extra glazing. Fans and dampers on humidity.
- Size it on the worst month — Annual average irradiation gives a house that works beautifully for eight months and overflows for the other four — and sludge does not stop arriving because the sun went in. Pull the irradiation slider down to a winter figure and watch the area you would need.
Design parameters
The panel opposite runs the same correlations as the D-1310 design sheet, so the animation and the calculator cannot disagree. Every parameter below is live — drag one and the picture responds.
| Parameter | Unit | Default | Range |
|---|
| House |
|---|
| Greenhouse type | | Ventilated greenhouse | 4 options |
| What separates these is not the glazing but whether the saturated air sitting on the bed is taken away, and whether anything warms the floor. |
| Climate |
|---|
| Global horizontal irradiation | kWh/m²·day | 4.6 | 0.5 – 7 |
| Duty |
|---|
| Wet cake feed | t/day | 25 | 1 – 120 |
| Cake dry solids in | % DS | 22 | 12 – 40 |
| Product dry solids out | % DS | 75 | 50 – 90 |
| Layer depth | m | 0.25 | 0.1 – 0.5 |
| Thermal drying would use | kWh/kg water | 0.95 | 0.7 – 1.4 |
The full D-1310 design calculation — governing equations, accepted envelopes and the worked sizing — is in the design calculator workbook. Everything on this page stays free.