Abstract:
An enclosed drainage facility to dry municipal waste combustion ash has a plurality of spaced elongated channels to drain by gravity, water from piles of ash into a disposal or reclamation pool. The channels are sloping concrete ditches leading to a common trough or pipe to a covered storage basin. Steel plates pierced with a plurality of spaced slender slits abut each other to cover each channel. The atmosphere in the facility is changed by being pumped into one side of the facility and exhausted adjacent an opposite side. Also, a process for drying municipal waste combustion ash includes dewatering and drying of ash piles in an atmosphere of warm dry air for a period of time necessary to reduce the moisture to about 28%.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to the field of treatment and use of municipal waste; and more particularly, it relates to the drying of such waste material after it has been burned in a waste energy facility. 
     (2) Description of the Related Art 
     U.S. Pat. No. 5,992,776 issued on Nov. 30, 1999, describes a process for treating municipal waste combustion ash to recover the values of the combustion ash substantially free of unburned debris and metals, especially ferrous metals. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to a process and a facility for treating municipal waste combustion ash having a high moisture content to a drying operation and recovering an ash with a moisture content of not more than about 28%. The process includes draining water from wet masses of the raw ash spread out in rows on a floor in an enclosed dehumidified atmosphere for a time sufficient to reduce the moisture content to not more than about 28%. The enclosed atmosphere may be warmed to about 80-120° F. The facility for undertaking this process includes an underground covered water storage basin with a plurality of parallel drainage channels sloped to drain water by gravity to one side of the facility to a common gutter and thence to a covered storage basin for treatment and/or disposal. Each channel is covered with a removable metal plate having a plurality of spaced drainage slots for directing the drained water into the underground channels. The facility is closed to the atmosphere and equipped with sufficient dehumidification equipment to dry the interior atmosphere to accomplish the necessary drying of the ash in an appropriate time period. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which: 
     FIG. 1 is a top plan view of the drying enclosure as seen from above; 
     FIG. 2 is a cross-sectional view of one of the drainage channels in the drying enclosure taken at  2 — 2 ; 
     FIG. 3 is a cross-sectional view of one of the drainage channels in the drying enclosure taken at  3 — 3 ; 
     FIG. 4 is a cross-sectional view of one of the drainage channels in the drying enclosure taken at  4 — 4 ; 
     FIG. 5 is a top plan view of a drainage channel cover; and 
     FIG. 6 is an enlarged end elevational view of the drainage channel cover of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is directed to an enclosed facility  10  and to a process practiced in that facility for dewatering and drying municipal waste combustion ash so that it may be later processed with care to minimize contamination of the surrounding areas or the atmosphere. Normally the municipal waste is burned in a furnace after removal of large metal objects and chemical containers as feasible, and the resulting material remaining after combustion is removed from the furnace, quenched in a tank of water and piled up to cool prior to being removed to a landfill for disposal or to a recycling facility for processing. Such combustion ash normally has a moisture content of 35-55% by weight. The present invention involves delivery of the combustion ash to a covered and enclosed drainage area where free water from the ash is allowed to drain away by gravity. The ash usually is dumped in piles and is then spread out in rows over a larger area. The dumping area is generally a flat floor surface covering underground drainage channels that lead to a covered storage basin where it is treated as needed prior to discharge to a sanitary sewer. The flat upper surface is gently sloping in different directions so as to lead the drained water to the underground channels for processing and disposal. The atmosphere above the drainage surface is dehumidified to assist in the drying operation. FIG. 1 shows the general overall plan of the drainage building where the combustion ash is dried in accordance with this invention. The building is covered and enclosed so that the dehumidification part of the process may be effective in assisting in the drying of the ash. The building is preferably only one story high with head room high enough to accommodate dump chassis of delivery vehicles and earth-moving front loaders of small to moderate size; e.g., ceiling structures high enough to provide head space of about 35 to 40 ft. The floor area is fashioned with generally parallel drainage channels  13  spaced about 12-15 ft. apart, and each channel  13  is covered with a steel sheet cover  20  having slotted openings  23  therethrough to permit drainage water to pass through, but no large clumps of solid matter. The surrounding surface between channels  13  slope toward each of the adjacent channels so as to collect the drained moisture and conduct it away to disposal. Surfaces  18  slope downwardly to channels  13  which drain into collection trough or gutter  14  which lead to a collection site such as a covered storage basin  15 . An appropriate juncture of the sloping surfaces is generally depicted at  19 . 
     Trucks carrying combustion ash, dump their loads on surfaces  16  within the facility which slope gently toward drainage channels  13 . After the loads are dumped on surface  16 , they may be moved around by front end loaders to any selected location. In any event, the combustion ash is placed on the drainage surface  18  and allowed to drain its moisture into channels  13  where the collected water will drain away to collection channel  14  and thence to covered storage basin  15 . 
     So that the operators know how long the ash has been stored in the enclosed facility  10 , it should be large enough to at least accommodate a daily amount of ash in each row, i.e., generally corresponding to the number of drains  13 , and this permits the normal first in-first out for further processing. A minimum number of drains  13  accordingly, would be about fifteen and the maximum about twenty-five to assure some overly moist ash a sufficient time to become dewatered as well as some future increases in the amount of ash brought into facility  10 . 
     While the above-described drainage is occurring the air space in the building facility above the ash piles is subjected to dehumidified air by one or more dehumidifiers  24  to maintain a relative humidity of about 10-25%. Water from the dehumidifiers  24  may be discharged or may be added to the covered storage basin  15 , as shown by pipe broken lines  30 . Roof exhaust fans  29  are located generally at the opposite end of the facility  10  from the location of the dehumidifiers  24  to assure that the air in the facility is distributed throughout for proper drying of the surface portions of the ash piles. While two fans  29  are shown, the number may vary in that such fans should be operative to remove the volume of dehumidified air added to the drying area of facility  10  by dehumidifiers  24 . The combination of drainage and dehumidification will in about two weeks dry the combustion ash to a level of about 28% maximum. 
     Generally, the combustion ash that has been delivered from a waste-to-energy facility is very wet and has variable moisture contents in excess of 35% by weight. The first step in making the ash processable is to dry it out to a uniform moisture. At any moisture content above about 28% the ash tends to clump, adheres and clogs-up processing screens, sticks to conveyors, plugs chutes and hoppers, sticks to ferrous and non-ferrous metals, causes buildup in hammer mills and the like and causes spillage, cleanup chores and down time of the ash processing equipment. Thus, it is important to adjust the moisture content to be no more than 28% so that it may be processed to remove the ferrous and non-ferrous metals and unburned materials and use the processed aggregate for road or other building purposes. 
     It is well-known that municipal waste combustion ash having its usual history has a moisture content of about 25% to 55%. This ash must be dried to a maximum of 28% moisture to be acceptable for most processing purposes. Storing of raw ash in enclosed places for long periods of time will undoubtedly result in processable dry ash, but it requires very long periods of drying which are not economically acceptable because of the very large building required for storing the ash in a building for some two months or more. The process of this invention will minimize the size of the facility and adequately and economically dry the ash prior to processing same. The time for drying a pile of combustion ash that has withstood the weather of rain and sun in typical cycles may be a matter of several months, if no special treatments are employed. The process of the present invention is capable of transforming raw ash into acceptable processing material in about two weeks and therefore saves one or more months of dewatering treatment time, which is highly profitable to the operators of the ash processing plant. 
     FIGS. 2-4 depict cross-sectional views of the drainage channels  13  at three separate locations between the shallow end and the deep end of channel  13 . The cross-sections represent locations along lines  3 — 3 , and  4 — 4 , as shown on FIG.  1 . The drainage water from the ash collects in the channel  13  and flows by gravity from above the level-of section  2 — 2  down through level  3 — 3 , and on to level  4 — 4  as shown on FIG.  1  and there is emptied into collection channel  14  which is itself inclined downwardly to covered storage basin  15 . Insofar as this process is concerned the water in the covered storage basin  15  is available for treatment and recycle in any suitable manner; since it is not needed for the process of this invention. 
     FIGS. 5-6 are views of the drainage channel plates or cover  20  that covers channel  13 . Cover  20  is a steel plate of sufficient strength to allow equipment to cross over it without breaking. Generally, cover  20  is a sheet, for example, of T-1 steel, having a thickness of about 0.375 inch pierced with drainage slots  23  that are approximately 0.250 inch wide by about 6.0 inches long. Slots  25  are merely for removing and replacing channel covers  20  when needed for maintenance operations. The other slots  26  are about 0.25 inch by 2.0 inches in length and extend in the perpendicular direction with respect to slots  23  as shown in FIG. 6 so that water along the edges of the plate  20 , which are supported on the side walls of the channel  13 , may seep therethrough. The size and shape of the slots in covers  20  are intended to prevent, or at least minimize, the plugging of drainage channels  13  by clumps of ash that might fall into channels  13  and therefore require frequent cleaning, for example. 
     In addition to the drainage of water into channels  13 , the piles of ash are subjected to dehumidified air inside the building shown in FIG.  1 . Large volumes of dry warm air produced by dehumidifiers  24  are circulated over the drying combustion ash piles located in rows above surfaces  18  hasten the drying of the ash to a maximum level of about 28% moisture. This considerably shortens the treatment time from a couple of months to a couple of weeks, making the recycled use of municipal waste combuster ash into acceptable and economical products after processing and minimize placing same in landfills, and the like. Moisture-laden air is exhausted through fans  29  in the roof of the drying building  10  while dry air is blown into the building  10  from the dehumidifiers  24 . 
     The dried ash made by the process of this invention is admirably suited to be the starting material for the process of aforementioned U.S. Pat. No. 5,992,776 issued Nov. 30, 1999. 
     While the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. It is intended, therefore, by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.