HoSt is building a demo and research plant for thermal pressure hydrolysis at Dutch water board Reest en Wieden. With this plant, the quantity of sludge that the water board has to transport will be lowered. The plant is part of the sludge digestion plant at the water treatment, also built by HoSt.
With the TPH-technique, sludge is pre-treated under high pressure and at a temperature of 160 °C. Through TPH, structures that are difficult to break down, such as lignin in plants and cells in sludge, can be broken down. Breaking down these structures makes the organic material more easily accessible for bacteria.
The sludge goes into the digester after the pre-treatment, and biogas is formed. Because of the pre-treatment more sludge will be broken down and a better dewatering of the digested sludge will be obtained.
Process Thermal pressure hydrolysis
|Temperature||140 – 180 °C|
|Retention time||0- 60 minutes|
|Regeneration||regeneration of energy through re-usage of flash vapour|
The cell structure is broken down with a TPH-treatment of approximately 30 minutes, so that more biogas can be formed. Furthermore, the requirements for sanitation will be met. The TPH-process is a batch process in which the material is heated by injection of steam. After the heat treatment the material is flashed, and the flash vapours are then used to pre-heat the material.
Effects of thermal pressure hydrolysis
- Increased biogas production
- Reduction of sludge: higher conversion and improved dewaterability
- Reduction of foaming
- Reduction of the viscosity of sludge. This allows for a larger pressure on the digester
- Positive energy balance: due to the increased biogas production and regeneration of the heat during the process of flashing, the energy production is higher than the energy costs (in case the heat from the CHP is used)
- The material is converted faster in the digester. This allows for using a smaller digester or an increase in input