Sludge burning
The system for auto thermal combustion of sludge with high water content
The disposal of sewage sludge constitutes an ever increasing problem, as new requirements for the environmentally acceptable disposal are initiated.
Nowadays, when the environmental impact of sludge removal is assessed, emissions of transport vehicles are also considered or the mercury emissions of solar sludge drying in the open air has to be taken into account. The elimination of harmful substances from the food chain becomes increasingly important.
Municipalities and commercial enterprises charged with the duty of sludge disposal find themselves under financial pressure so that the disposal of sludge requires first class technology and at the same time has to be conducted at a minimum of investment-, operational- and maintenance costs. Therefore new, advanced systems for the sludge disposal are required.
On this background we have developed a cost effective, non complex system, which, without teh need for a thermal sludge dryer can incinerate sludge without the need for additional fuel, after it is mechanically dewatered. Therefore the incineration on the water treatment plant becomes a viable option.
By applying thermal disintegration of the sludge before the digester, the gas generation yield in the digester can be increased and so the electricity generation can be increased easily.
The advantages of this system can be summarized as follows:
- Mechanically dewatered sludge can be incinerated without the need of a sludge dryer or auxiliary fuel
- The plant is simple, cost effective and easy to maintain
- Because the flue gas volume is minimized, the flue gas cleaning plant is small.
- Disintegrated sludge from an optimised digester process can be used
- The system is also economical for medium size water works
Within our patented system, the sludge will be, after mechanical dewatering, pumped at high pressure to a mixer, where it will be mixed with hot, disintegrated sludge. As this whole system operates under pressure, the water in the sludge will not evaporate. Therefore raw sludge will be thermally disintegrated (hydrolysed) and the viscosity remains low. The sludge mixture is then heated by the flue gas of the combustion in a high pressure heat exchanger.
Some of the sludge is then injected into the fluidised bed incinerator and is burned there, and some sludge is recycled into teh mixer for teh thermal disintegration of the raw sludge.
To allow the combustion of sludge at high water content without the need for additional fuel, the plant is equipped with a flue gas air preheater. To meet the environmental requirements according to German legislation, the plant is equipped with a bag house filter including adsorbant injection for the removal of harmful substances.