This invention relates to a method and devices for drying waste in a closed loop cyclic continuous process.
Wastes are separated as sludge from several waste streams among others: sludge from municipal waste water plants, industrial waste water, municipal solid waste [MSW], any kind of hazardous waste and manure from livestock production facilities. The wastes are wet, in most cases, have undesired smell and pollute the ground and ground water by leached water from them. The wastes may have nutrients good for agricultural crops, or other substances that may be recovered or recycled. The wastes need some biochemical and/or drying process to enable environmentally and economically disposal. The present disposal alternatives include among other spreading on agricultural fields, landfills and incineration. The organic wastes can be used as energy source, but need some biochemical and/or drying process to be used economically for that.
Several manufacturers are drying sludge by using belts and/or rollers to help in extracting the moisture out of the waste when the sludge is wet and exposing more surface area to the drying air at all stages of drying. Others utilize heated or unheated screws with or without the assistance of hot air.
One significant obstacle of the existing methods lays at the first drying stage, where wet sludge is bulky and tough to dry, resulting in economically inefficient process.
It is an object of the invention to provide a method and devices for drying the waste in a cyclic closed loop continuous process, while maintaining homogeneous sludge properties all over the sludge cavity, where wet sludge is continuously mixed with relatively large quantities of dry sludge, forming a mixture that is optimally dryable. Here lumps of the waste exposed to hot and dry air allowing large surface area of the waste in contact with the air. The mixture of dry and wet lumps together with large surface area enhances the drying process and makes it economically efficient.
The dry waste coming out of the process will be readily available for disposal. The dry waste has more environmental and economical benefits: a] while being spread in agricultural fields it will reduce soil and water pollution and increase its nutrient value as fertilizer b] in the event of waste used as energy source, it will require less heat in the energy generation process at a lower disposal cost.
The invention provides a method for drying the waste in a cyclic closed loop continuous process, while maintaining homogeneous sludge properties all over the sludge cavity. Wet sludge is diffused evenly over the surface of the dry sludge and consequently reduced in size and mixed with relatively large quantities of dry sludge. The resulting mixture of small size large surface dry and wet lumps is optimally dryable. Here lumps of the waste exposed to hot and dry air allowing large surface area of the waste in contact with the air. The mixture of dry and wet lumps together with large surface area enhances the drying process and makes it economically efficient the lumps undergo size reduction and mixing thus allowing maximization of the vapor transfer rate between the hot/dry air and the waste.
The wastes to be processed may be sludge from sewage treating facilities, municipal solid waste [MSW], industrial waste any kind of hazardous waste and manure from livestock production facilities. The process starts with pumping of the wet sludge to the sludge diffuser. On the way to the diffuser the sludge is heated and pressurized. The diffuser/ feeder feeds the chamber cavity with a continuous flow of lumps of wet or partly dried waste with maximal surface area, evenly spread over the drying layer of dry sludge. The pre water extraction process in the diffuser/feeder is done by pressurized heating the waste, resulting in flushing-like fast drying and granulating of the wet sludge while diffused to ambient pressure. The feeding flow rate of the dry sludge is designed to maintain constant volume of sludge at the cavity, so by nature it is always equal to the indeed rate of the wet sludge. The in feed capacity is set by the operator according to the intake sludge conditions and the discharge sludge requirements.
The size reduction mixing mechanism, with or without throwing forward, mix the wet lumps with the already dry lumps of waste and reduces the size of too large lumps, generating easy to dry homogeneous mixture with maximal surface area exposed to the drying air.
Drying air can be fed on top of the sludge layer and from any other direction as well as needed for further enhancement of the drying process. After being dried, the waste is being collected and conveyed to a transporting device or to an energy generator, using the dry waste as a source.
The continuous flow of waste according to the invention may be performed by at least one lumps diffuser/feeder above the floor.
The continuous lumps diffuser/feeder is a high pressure waste pump and high temperature heated pipes at the end of which is a granulating flush diffuser, providing small, high surface lumps. The intensive dewatering effect is made by steam flushing at the discharge of the diffuser.
In another embodiment, the continuous lumps feeder is a screw conveyor, cylindrical or conical, inside a perforated housing of the same shape, forcing the waste outside the holes while cutting them into individual lumps.
In another embodiment, the drying air circulates at high flows on to contact with the sludge and back to the heating zone.
In another embodiment, the drying air is heated by the residual heat from heating the diffuser/feeder.
In another embodiment, drying air is blown through nozzles located at the sides and or at the bottom of the sludge layer for further enhancement of the drying rate.
In another embodiment, the exhaust air flow rate is adjusted according the desired moisture content, as calculated to provide optimal drying.
In another embodiment, the exhaust air hood is located on top of the flushing steam coming out of the diffuser/feeder, resulting in lower exhaust air quantities.
In another embodiment, the at least one set of size reduction and mixing mechanism, based on rotating blades, moves through the stationary layer of waste forward while mixing the lumps at different depth.
In another embodiment, the residual dry waste discharged outside the cavity to the outside, by at least one top scraper supported by screw conveyor.
In another embodiment, the dry waste is collected by at least one top scraper without screw conveyor, out of the chamber.
In another embodiment, the cavity bottom rotates in circular cyclic manner. With lumps of waste while the feeding device; the size reduction and mixing mechanism and the discharge device are stationary.
In another embodiment, the rotating cavity bottom is composed of sections of a conveyor.
In another embodiment, the continuous cyclic drying of waste is performed by a stationary bottom while the feeding device; the size reduction and mixing mechanism and the discharge device are rotating.
The drying process according to the invention may be controlled by a computerized control system, using sensors to measure the different parameters like the temperatures of the waste and the air, at different points. The remote computer collects the processed data for analysis and optimization.
In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
The invention will now be described by referring to the following none limiting figures. Turning to
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Number | Date | Country | Kind |
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204790 | Mar 2010 | IL | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IL11/00277 | 3/27/2011 | WO | 00 | 9/28/2012 |