Large sewage clarification plants, such as the urban drainage department of Stuttgart, recycle their sludge in mono-combustion plants. GEMÜ valves used in the plant design ensure the safety and reliability of processes when it comes to drying sludge.
In light of the amendments to German ordinances on fertiliser and sewage, an increasing number of sewage clarification plant operators are faced with the question of what to do with the sludge. Large sewage clarification plants have begun to invest in sewage incineration technology for the conversion of sludge into energy.
The Mühlhausen sewage clarification plant relies on GEMÜ valves in its modern sludge recycling system design.
GEMÜ valves are employed in the sludge drying step, assuring safe operation of the sludge conversion process. Currently, 150 tonnes of dried sludge are thermally recycled every day in the central combustion system.
Valves used in sludge drying processes not only need to withstand high operating temperatures. The body and seal materials must also be highly resistant to the substances contained in the vapour. Depending on the chemical composition of the sludge, the impurities in the vapour may vary and exhibit a range of corrosive properties.
Taking these operating parameters into account, the sewage clarification plant opted to use GEMÜ butterfly valves from the 490 series with PTFE sleeves in its plant.
Even plant faults that cause the system to reach temperatures above 100°C will not damage these valves, as the PTFE sleeves are sufficiently resistant to the substances contained in the vapour.
An electrically-actuated butterfly valve with spring force function is installed near the dryer for optimum safety. In the event of a power failure, this butterfly valve opens automatically. In such a case, steam pressure build-up due to residual heat will be released, avoiding damage to equipment and piplines.
Employing state of-the-art technology to optimise vapour condensation, the Mühlhausen sewage clarification plant is now able to process higher quantities of sludge. This optimises both the safety of the system in the event of faults, and the recovery of the heat. It has also allowed the plant to achieve its aim of minimising unpleasant smells.