Upgrade to near energy-neutral operation for sludge processing plant

Excellent engineering skills, perfect project management and close co-operation between the supplier and the customer were the key elements that enabled a successful installation of two steam boilers in an existing sewage sludge incinerator installation of SNB in Moerdijk, The Netherlands.

Sewage sludge is the end product of treatment installations that clean up the waste streams from sewage systems. This sewage sludge has to be incinerated in order to remove leftovers from medicines, hormonal material and toxic organic elements. The sewage of the close to 17 million inhabitants of The Netherlands results in some 1.5 million tonnes of sludge per year. SNB processes 30% of this sludge and this makes the facility the largest operating one of its kind in the world.

The incineration process is a combination of drying the sludge, burning it and cleaning up the exhaust gas. Until recently, the bulk of the electricity required for the pumps and ventilators in the process was supplied by the public electricity grid. However, closer analysis of the process revealed that the sludge contained sufficient energy to allow for the production of 60 bar steam instead of the 10 bar used initially for the drying process and ammonia removal. SNB decided to equip two of the four incinerators in parallel with such a high-pressure steam boiler. This would produce sufficient steam to drive a 3.5 MW steam turbine generator combination. This 3.5 MW would make the facility close to energy neutral.

The major challenge was to tie the two new boilers into the existing installation during a maximum time span of 70 days. SNB found an excellent partner in NEM, the world known boiler manufacturer with its headquarters based in Zoetermeer, The Netherlands. During the refurbishment, the facility had to continue operation since storing the total sludge flow was no option. Manufacturing a steam boiler is common practice for NEM, but here the big challenge was to match new elements with an installation of already 18 years old. Hands-on skills had to be combined with clever computer-based engineering and thorough understanding of the processes in a running installation.

On April 2, 2015, Marcel Lefferts, managing director of SNB and Gerard van Dijk, CEO of NEM, could lead the celebrations of a very successful project together with a happy team. Although at some occasions 250 people were working at the site, no accidents had happened and the 3.4 MW Siemens generator was running smoothly. The end result is a process requiring almost no external energy.

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