In the exhaust gas pipe of a CHP, a t- piece is used after the sound absorber. A dual effect, failsafe exhaust flap installed there, guides the hot exhaust gas through a stainless pipe to the dryer. This mixes the approximately 1022°F (550°C) exhaust gasses to the desired dryer input temperature of 572°F (300°C).
If the exhaust gas energy of the biogas powered CHP is not sufficient to dry out the desired sewage sludge amount, an additional combustion chamber can be incorporated into the exhaust gas flow with a natural gas burner. The missing energy will be calculated by the process computer and the additional heat is supplied by the natural gas burner. The system can be configured to use a CHP or gas burner or both.
The hot exhaust gases are divided symmetrically into the individual drying chambers. Several temperature sensors monitor the process continually. The required mixed air volume is calculated continually and added to the exhaust gas flow. When the drying process begins, the failsafe valve is opened and hot exhaust gas is fed into the dryer. When the drying procedure ends, the exhaust gas valve closes the path to the dryer and the exhaust gases are conveyed through the normal exhaust system into the atmosphere.
Exhaust Air Treatment:
A filter chamber is integrated into the dryer. In the filter room of the 3 chamber dryer (STR12), there are many fine filter cartridges with a surface of over 2650 ft3 (75m3). The filters are made from fine needle-felted fabric. They have a special coating, are anti-static and water and oil resistant. They have a dust proof anchor due to the stitched-in tension ring with dual beading. The filter cartridges house a stainless steel support cage, which guarantees the full filter surface even when operating at low pressure.
The filter cartridges are connected together in a pipe frame. Using several pneumatic cylinders, the frame, and the connected filter, is vibrated and cleaned of adherent filter cake at defined intervals. A screw feeder beneath the filter conveys the filter dust into the holding chamber and mixes it with the dried sludge.
Exhaust fans can be found over the filter chamber. Pressure sensors are arranged in the drying chambers. The dryer is kept in a constant state of low pressure using the exhaust fans. If the fan output increases above a pre-set value, the vibrating procedure automatically begins and the filters are cleaned in the continual drying procedure. The filter media is effective at keeping the dust value of the exhaust gas below <1ppm. As a result, the dryer is 95% below the TA Luft (air) threshold.