The Oldenburger Fleischmehlfabrik GmbH, Kampe, Germany
On average around 70% of ABP is moisture and this is evaporated in the rendering process. Along with additional process and cleaning water around 1 tonne of water must be evaporated per tonne of ABP processed. This is an energy intensive process and maximising waste heat energy recovery is essential for minimising the carbon footprint of the process.
The Oldenburger Fleischmehlfabrik GmbH, Kampe, (OFK) operates five rendering lines processing around 230,000 tonnes of ABPs per year. The evaporated water from the ABP processing is condensed and cooled before treatment in OFK's wastewater treatment plant. Most of the waste heat available from condensation is used in evaporation or waste heat recovery systems at OFK. Nonetheless, considerable amounts of lower grade heat energy remains in the waste air stream after condensation which has a temperature of 70–100 °C. Unless recovered, this heat is lost into the atmosphere.
230K
Tonnes of ABP
Processed per year across five rendering lines
40K
Tonnes of Sludge
Thickened annually by the sludge drying plant
28.3
GWh Residual Heat
Used in sludge drying in 2020 — 25% of steam heat demand
80%
Heat from Waste
Residual heat provides 80% of sludge drier demand; 20% from direct solar
Sludge Drying in Action
Since 2008, residual heat from OFK has been used to dry sludge from their own wastewater treatment plant as well as sludge from local municipal sewage treatment plants. The heat energy is exchanged to a hot water heating circuit which heats the sludge drying plant.
The sludge drying plant thickens 40,000 tonnes of sludge per year, increasing the sludge dry matter content from 22% to 66%, enabling the dried sludge to be used as a biomass fuel in power stations.
The remaining 20% of drying energy comes from direct solar radiation in the glass halls where the drying takes place, as illustrated in Figure 1.
80% Waste Heat
Residual heat from condensation at 70–100 °C, exchanged via hot water heating circuit
20% Solar Energy
Direct solar radiation through glass hall roofs supplements the drying process
Figure 1 — Sludge Drying Chamber
The diagram illustrates the internal structure and airflow of a sludge drying chamber. Solar radiation enters through glass house roofs. Climate sensors, heat exchangers, and air sparging ventilators manage the drying environment. Air enters via an inlet on the left and exits through exhaust air ventilators on the right. The ELEKTRISCHES SCHWEIN® vehicle turns the sludge on the floor. Source: Thermo-System GmbH
OFK Thermal Energy Flow 2020 — Figure 2
This flowchart shows the thermal energy flow at OFK in 2020. Natural gas (Erdgas, ca. 136.8 GWh) enters the system, with 91% directed to the boiler plant (Kesselanlage) and 9% to the combined heat and power plant (BHKW).
Boiler Plant (91%)
Produces steam ca. 106.3 GWh → sent to Production
CHP Plant (9%)
Generates electricity ca. 4.4 GWh + heating water
Waste Heat Output
ca. 28.3 GWh redirected from Production to sludge drying