2.description of the prior art
it is well know to from finely divided solid particles into pellets to faciliate handling use of the product .charcoal is formed into briquettoes use in backyard barbecues and metal ores are formed into pellets to be fed into smelting furnaces. Animal feeds are formed into pellets to minimize waste, and waste materials are pelletized to facilitate handling and disposal. other pelletizing operations too numerous to mention are well know.
In many commercial pelletizing operation ,the feed material is a product of a controlled manufacturing process and the composition is consistent so that pelletizing is easily controlled; in others, the feed composition varies so greatly that pelletizing must be carefully monitored and controlled. For example ,it is well know that variations in the amount of water or liquid in a feed material will have a marked effect both on the ability to form the material into pellets and on the strength integrity of the pellets formed. Commercial pelletizers may have feed blenders and mixers including means for the addition of water or liquids an necessary to enable the formation of competent pellets; however, such devices do not include dewatering systems for the removal of excess moisture.
Substantial effort has been and continues to be expended to economically recover and use products such as coal fines, biomass and waste products as fuels, but these efforts have met with limited success. As a result, industry is compelled to spend substantial sums to dispose of such waste product, and the disposal procedures have not always been satisfactory. For example, the large volumes of coal fines produced in the washing of mined coal have an excessively high water content for economic recovery and use despite their potential fuel value. Such coal fines, which normally have a particle size of about 1mm or less, are routinely collected in tailing ponds as waste. This practice is not only expensive but also harmful to the environment.
Similar problems plague other industries such as the paper and plastics industries where the substantial waste products are not easily disposed of. While furnaces have been designed to burn many such waste products as fuels, such furnace are expansive both to design and to operate. Specialized material handling equipment may be required and operation of the furnaces is erratic and difficult to control.
U.S. Pat. No. 5,743,924 discloses a pelletized fuel made from mixture of finely divided particles, paper making sludge waste, waste plastics and the waste paper, which products are mixed together and pelletized without the use of adhesives or binders. A commercial pelletized fuel plant constructed in accordance with this patent utilizes sludge from a paper making facility, in combination with finely divided coal and shredded plastic material, and is utilized by the paper making facility as fuel. This commercial facility not only realizes substantial savings on the cost of fuel over the previously used coal, but also saves the cost of disposal of the waste sludge. Further, substantial reductions in SO NO and particulate emissions are realized. Since the present invention is particularly useful in pelletized material of the type disclosed in pat. No. 5,743,924,the disclosure of this patent is incorporated hereby reference.