How does an evaporator perform in daily operation? Measured data from a food-waste AD plant
Updated: Oct 7
Short answer: On our reference plant, a food-waste AD plant in Switzerland, our 4-stage thermal vacuum evaporator (DV series) turns around 350 kW of CHP waste heat into around 40 m³ of distillate per day, or 4.5 to 4.7 litres per kWh. Over 51 complete operating days it was evaporating 82 % of the time, runs unattended at night and at weekends and needs about 1.5 hours of staff time per day. The heat transfer stayed stable from August to October, with a planned acid and alkaline CIP cleaning once a week.
The figures come from the plant control system: 10-minute values from 26 June to 3 October 2026, around 1,090 hours of evaporation in total. The plant has been in operation for more than 5 years.
The reference plant
Input: Digestate from food waste and residues from the food industry
Machine: DV evaporator, 4-stage thermal vacuum evaporator with vapour scrubber for ammonium sulphate solution (ASL)
Heat source: CHP waste heat, hot water at around 80 to 88 °C
Distillate: Collected and reused as process water in the de-packaging line
Concentrate and ASL: Taken over by a service provider as raw material for further fertiliser production
In operation: More than 5 years
This plant is reference 01 on our reference plants page.
How the heat moves through the evaporator
Only the first stage is heated. Hot water from the CHP (88 °C in, 64 °C out) heats an intermediate circuit at around 63 °C, which heats stage 1. Every further stage is heated by the vapour from the stage before. Each stage sits at a lower pressure, so the digestate boils at a lower temperature: 60 °C at 205 mbar in stage 1, down to 47 °C at 110 mbar in stage 4. The vapour from the last stage goes to the condenser.
This is why one kWh of heat produces several litres of distillate: the same heat is used four times.
"High heat efficiency, a sensible use of waste heat and water recycling: for the plant operator, that is a real gain." Michael Köhnlechner, MKR Cleanwater
The plant does not need 88 °C. On several days the supply temperature was around 80 °C, for example on 12 July: 378 kW, 4.6 l/kWh and 42 m³ of distillate.
What comes out per day
At 350 to 370 kW of heat the evaporator produced 39 to 42 m³ of distillate per day. The specific value at full load was 4.5 to 4.7 litres per kWh, above the design value of 4.3 for this machine.
The output follows the heat input. When the operator ran the plant at 300 kW, it produced around 35 m³ per day. The lower bars in the chart are days with a cleaning, a rinse or a stop on the plant side, not a drop in performance.
How the plant spends its time
Over all 51 complete days, the evaporator was evaporating 82 % of the time. Cleaning and rinsing took 4 %, start-up and shut-down 2 %, standby and other 12 %. In the three weeks shown in the chart (22 August to 12 September 2026), the period with the most continuous data, it was 89 %: cleaning and rinsing 5 %, start-up and shut-down 2 %, standby 5 %.
Three things stand out in the day-by-day view:
Nights and weekends are full. Across all complete days in the data, the plant was evaporating 92 % of the night hours (22:00 to 06:00) and 96 % of the weekend hours. Stops and cleanings happen in the day shift, when staff are on site.
Cleaning is planned. A complete CIP cycle runs once a week: pre-rinse, acid step, alkaline step, final rinse. In the period shown it took 8 and 11.5 hours. A short rinse in between takes less than one hour.
Start-up is quick. From vacuum and filling to evaporating takes around 50 minutes (median of 19 start-ups).
How much work is it for the operator?
Around 1.5 hours per day. The evaporator runs unattended at night and at weekends. If a fault occurs, the control sends an alarm to the on-call staff, who can operate the plant remotely. If needed, the control runs an automatic shut-down and safety routine.
Does the heat transfer stay stable?
The control calculates a heat transfer coefficient (k value) for each stage. If deposits built up on the heat exchangers, these values would fall over time.
At 350 to 370 kW the values stayed in a narrow band from August to October: 1,180 to 1,270 W/(m² K) from stage 1 to 2, 1,310 to 1,450 from stage 2 to 3 and 960 to 1,060 from stage 3 to 4. After the weekly CIP cleaning the values rise for about a day (stage 1 to 2 from around 1,210 to 1,350) and then settle back to the same level.
The values are compared at the same heat input only, because the k value rises with the load. The first 2 hours after a start-up are left out, as the plant runs on water first.
What this means for your project
Size the evaporator by the heat you have. As a rule of thumb from this plant: around 350 kW of waste heat at 80 to 90 °C gives around 40 m³ of distillate per day. The ratio scales: more waste heat, more distillate, with the machine size or the number of lines chosen to match.
Plan the cleaning into the week. A weekly CIP cleaning in the day shift keeps the heat transfer stable.
Test your own digestate first. Every project starts with a framework concept and a budget offer. Before the binding offer we run a trial evaporation with your digestate in our laboratory.
FAQ
How much distillate does a DV evaporator produce per kW of heat?
On this food-waste AD reference plant, 4.5 to 4.7 litres per kWh of heat at full load. At 350 kW that is around 40 m³ per day.
How often does the evaporator need cleaning?
Here, a complete CIP cycle once a week (pre-rinse, acid, alkaline, final rinse), taking 8 to 12 hours in the day shift, plus occasional short rinses.
Does the evaporator need staff at night or at weekends?
No. It runs unattended. Faults are sent as alarms to the on-call staff, who can operate the plant remotely. The daily staff time is around 1.5 hours.
What supply temperature does a DV evaporator need?
This plant runs on CHP hot water at around 80 to 88 °C. The stages boil between 60 °C and 47 °C under vacuum.
What happens to the distillate?
On this plant it is reused as process water in the de-packaging line. Whether it can be discharged depends on local limits and on the finishing steps after the evaporator.
How we evaluated the data
10-minute values from the plant control system, 26 June to 3 October 2026. Daily values are counted from 08:00 to 08:00; 51 days have complete data. Days with incomplete data transmission are not included. Distillate and heat input are measured values. The charts show 22 August to 12 September 2026, the longest period with nearly continuous data. The plant operator's name is not published.
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