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CONCEPT With highest efficiency the AQUEX® procedure achieves values of almost 95 % dry matters. The method is based on the conclusion, that various technologies and aggregates at different phases are necessary to dewater sludge most efficiently. In its efficiency unrivaled this procedure combines pre-dewatering, pressing and pelletizing followed by air-drying. Furthermore special aggregates were invented to optimize the proceeding results. The detailed steps can be combined separately or corporated and even adapted to traditional dewatering units.  |
APPLICATIONS
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| TECHNOLOGY
Tendencies of the past few years demonstrate, that sludge by dewatering shall be reduced to the most possible slender volume to achieve disposal status. Usually pre-dewatering is proceeded by centrifuges, belt band presses or chamber filter presses. Hereby dry substances in the range of 25 - 38 % DM are normally obtainable. The dewatered sludge is ought to be disposed or spread on agricultural fields. Sludge must have shear strength of 35 % DM to get disposal status. Many of the dewatering modules do not attain these values, so that in expensive back-admixing processes external dry matters such as lime or cinder are added. But this procedure even increases the volume and causes higher transport and disposal costs. Invaluable disposal volume is wasted. |
3-STEPS-PROCEDURE
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PRE-DEWATERING
The preliminary draining system consists of a round cylinder to which the flocculated and thickened sludge will be supplied from below. A slowly turning paddling machine is mixing the flocculent with the sludge. While the sludge is slowly rising in the cylinder, the flocks are created. At the height where there are flocks already, the cylinder barrel consists of a filter medium where the first batch of water flows off into a collecting collar. The sludge - fed with 3-4 % of dry matters and in case of sapropel with 12 -16 % of dry matters - is gliding to the second draining stage, the pre-thickening unit, on a chute. In fact, the pre-thickening unit consists of two telescoping cylinders, the internal one made of a filter medium, the external one constructed in closed form. Inside there is a slowly rotating screw which is turning the sludge from the inside to the outside and draining it. The sludge is gliding down at the screw blades, becomes dryer and dryer and is falling out with a dry matter of 24-28 % (municipal sapropel). This sludge is excellently suited for further pressing because the flock structure will not be destroyed during the preliminary draining process. Also more than 87% of water have been separated from a 25 % sludge by means of gravity. The presently known best draining units are chamber filter presses which achieve about 35 % of dry matters at a sludge which has been treated with an organic flocculent. This dry matter is not at all sufficient for pelletizing. Therefore it became necessary to develop a new type of press. With the rubber balloon press which we developed, the necessary high percentage of dry matters of 43-50 % can be reached. A once flocculated sludge must be handled like a raw egg. If the flocks are destroyed, sludge is mashed and can no longer be pressed. Therefore the rubber balloon press will be filled with gravity by locating the preliminary draining unit above the collecting hopper of the rubber balloon press. From there the drained sludge is falling directly into the press. |
PRESSING
The rubber balloon press consists of two telescoping pipes. The outer pipe consists of a filter medium and is fixed. The inner pipe can move up and down on a central guide. On top of the inner cylinder there is a rubber balloon which can be blown up with either air or water. The drained sludge will be pumped into the gap between the two cylinders and the pressing process blows up the balloon which presses the sludge against the outer wall, thus draining it. Even the inner side of the cake will be drained. The rubber balloon is covered by an elastic filter cloth which follows the movements of the rubber balloon. A drainage inside the balloon discharges the filtered water from the inside. At the completion of the pressing process, the pressure will be valved and the interior of the press with the tubular press cake will be lowered. A cutting technique crumbles the cake and throws the pieces into a basin where a carrier takes them to an ejection port for further transport. At the start-up of the press the inner and outer filters will be washed. Afterwards the inner part moves into the filling funnel and the press will be filled with drained sludge again. The press is operating discontinuously by using the principal of chamber filter presses. During the pressing process the filling funnel is filled with drained sludge. The preliminary draining unit is working continuously so that the complete process is more or less continuously. The rubber ballon press are available in two different sizes:
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PELLETIZING
The best form for drying is the round one, because this form offers - at the same volume - the largest drying surface. Small, evenly globules would be the best. But such globules are difficult to produce. We approach that ideal form by forming short pellets which can be produced by extruding the press cake. Extruding noodles with a dry matter of 41% become knotted and therefore can no longer be dried economically. When using sapropel with more than 50 % dry matters the noodles become so brittle that they break immediately behind the perforated plate and split into pellets. The round form is not only favorable because of its large surface, but also because the distance of steam diffusion out of the core is the same into all directions. Also the pellets are only piled tangentially as compared to cubes or discs of which the resting face will not dry. The dry material should always be kept moving so that all sides will be exposed to the dry air evenly. This pre-condition can be met best with pellets because they roll off one another easily. However, the dry material should be not only round, but also evenly big. If the pellets are uneven the smaller ones will block the gaps between the bigger ones. So it will be quite difficult to blow the dry air through these gaps. Also the drying process starts at the small particles which almost start burning while the bigger ones are still wet inside. |
DRYING
After the successful creation of trickling round pellets through mechanical high-grade draining of sludge, these pellets have to be dried fast and economically in an unconventional drying unit. The AQUEX Procedure applies tower trickling dryers which will be continuously filled with pellets from the top. The dry pellets will then be continuously discharged at the bottom of the dryer. So sludge will also be conducted through the dryer by gravitation. The tower trickling dryer consists of a large and two small lateral towers. In the large one drying is realized, the smaller ones are provided to feed the warm air respectively to suck off the exhaust air. Organic sludge is dried at temperatures of less than 100° C. As a drying medium any kind of heat can be used which will be fed through the horizontal channels of the dryer in form of hot air or fumes. These roof-type channels are open at their bottom side and installed in parallel and above each other in several rows. The front end of one row is open on the entrance side and closed on the other side, the next row is poled inversely. So the fetched hot air will be forced to emerge out of the channels downstream and can only be sucked off in channel rows which are located underneath or above. The hot air is thus penetrating the whole mass of pellets and drying it. The dryer is designed in such a way that the pellets are passing it for some previously determined hours. They will be deflected continuously by the heating flues and so turned to all directions. At this, a uniform drying is achieved. The heat source can come from the combustion fumes of primary energies (oil, natural gas), from the exhaust gas of block heating and power stations, from the combustion of methane gas or the waste heat of the industry, etc. The gases will be rarefied - if necessary - by adding fresh air until the required drying temperature has been reached. The fresh air will be taken off the pressuring room. In this way the vapors will be resorbed from the air of the sludge treating unit, too. |
A.C.S. AQUA-CARE-SYSTEMS GMBH
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