Sludge drying and thermal sludge utilisation plant Tobl

Sludge drying (TRA)

The dewatered sewage sludge from our wastewater treatment plant [2] and from a further 13 wastewater treatment plants [1] is processed into dry granulate by the belt dryer [5]. While the dewatered sewage sludge still contains approx. 72 - 82% water, the dry granulate still contains approx. 4 - 5% water. We process 40 containers (á 12.5 tons) per week, of which 8 - 10 containers of dry granulate remain after drying. The weight reduction is approx. 75 - 80%. The dewatered sewage sludge is conveyed via screw conveyors to the dryer, where it is evenly distributed on a belt. Hot air (approx. 140°C), which is heated by the heat of the thermal recycling plant, is led to the belt via fans and the water in the dewatered sludge is evaporated.

The thermal sludge recycling plant (TVA)

The dried sewage sludge is mineralised in the thermal recycling plant (TVA) [6]. This closes the sludge circuit on the plant. Of the 24,000 tons (1,000 trucks with trailers) of dewatered sewage sludge treated, approx. 2,000 tons (80 trucks with trailers) of inert material [7] remains, which is recycled and reused for landfill covers. The recycling takes place in a rotary drum, in the first part of the drum the carbonization takes place at approx. 200 - 400°C, the carbonization gas reaches the afterburner chamber. In the 2nd part of the rotary drum the granulate is mineralised at 400 - 600°C.
The pyrolysis gas and the flue gas are burned in the afterburner chamber at 850°C. The afterburner chamber is equipped with a gas burner. The flue gas is cooled via the heat exchangers and then passes into the dry flue gas cleaning system (384 filter bags).
The continuous emission measurements guarantee a minimum environmental impact above the chimney.

The thermal sludge recycling plant (TVA)

rotary drum

Legend Function diagram


3) sludge receiving bunker

inert material

4) sludge stack

hot air

5) sludge drying plant (TRA)

1) foreign sludge

6) Thermal sludge recycling plant (TVA)

2) Sludge Tobl

7) inert material silo