The present Invention relates to a eethod and apparatus for granulation and drying of organic/biological eaterlal such as, for example, sewage sludge or industrial waste sludge. Granules of a specific size are prepared without the use of additional granulation equipment affixed to the process after the drying is completed, and an indirect heat source is used for drying. The process input material has been previously seml-dewatered by other means, and is then granulated and dried by indirect contact, sterilised, and processed and stored as needed. The material can be used, for example, as a fertiliser, soil additive, landfill cover, fuel, bulking agent or an animal feed additive.

Biological and organic material and Industrial waste sludges are produced daily in a multitude of processes. This causes problems with regrad to adequate disposal options which are both cost effective, environmentaly safe and within the bounds set by the environmental protection authorities. These materials are currently disposed of in various ways: they are placed in landfills, composted, incinerated, dumped in the sea and/or heat dried.

The materials that are processed in the apparatus and by the method of the invention retain their nutrient content of, e.g., nitrogen, potassium, phosphorus and variable low levels of beneficial metals and minerals. The material may also contain pathogens, heavy metals, undesirable organic compounds and plastic, depending on the process by which the material is derived.

Current known methods for treating this material include spreading it over agricultural fields, mechanically dewatering it to a solids content in the range of 12% to 30% and applying it to a land area, dumping it in the sea or composting it. With heat drying of the material, a product is produced which is at least 90% dry. By employing indirect heat drying of this material, the disadvantages of other known methods are overcome.

After the material has been treated by the method of the invention, a pathogen free composition is obtained. The treated material has also been reduced in volume to an approximate ratio of 10:1 from its original liquid phase. The material is thus ready for use, and will occupy far less volume, thereby facilita¬ ting transport and further processing.

Waste materials that are not treated according to the invention will present an increased risk of contamination and pollution of lakes, landfills, ground water systems and agricultural areas.

US 5,069,801, US 5,215,670 and US 33,998 describe various syβt for treating waste sludge. A major difference between these US patents and the present invention is that in the present invention the granulation takes place exclusively in the blender and not in the dryer.

Known relevant treatment techniques also often use a system where there is direct contact between the material to be treated and the heating medium. Heated gases (air) are drawn over the material and the moisture is evaporated. In these processes the material comes into direct contact with the heating medium (heated air, gas), which is also used to transport the material. In this way the air required for carrying out the drying and transport process is contaminated. The gases that are used in such processes must then be treated in order to remove particles, moisture, odors and other contaminating material.

The method used in the present invention is an indirect contact drying. Here the organic material to be treated is brought into contact with rotating, concentric tubes that are filled with a heated medium such as, e.g., pressurized steam, hot air or heating oil. The method establishes a barrier between the material to be dried and the heated medium. In this manner one achieves an important separation between the material and the heated medium, since they do not come into direct contact with one another. This means that there are used smaller amounts of

heated medium, e.g. , air, than in methods employing direct drying. In addition, indirect drying is compatible with other systems. By employing steam from their processes, the present invention can utilize the steam in the Indirect dryer, dry the material and feed the product back to the other system.

The background and motivation in the present invention is to provide a system that treats sludge consisting of organic -saterial where the treated material Is envlron-sentally safe, clean and economically sound. By utilizing the apparatus according to the invention the material is converted without additional granulation equipment into a product of the proper size, shape and consistency, which may be treated in a simple manner with fertilizer blenders and other Industry without modifications to existing blending and packaging equipment. The method in the invention requires no addition of additives, which often Is necessary with known methods. The treated material may be epplied directly to the ground by employing existing spreader blenders. By the use of the treated material, a recycling of the resources is achieved.

A further objective of the Invention is to provide an odorless, non-polluting process for the treatment of sludge from industry and bio-organic sluge through an indirect heat drying method, by producing granules of a predetermined size, preferably from 1.5 to 4.0 mm. The existing organic starting material (sludge and industrial waste) may be coarsely divided into four fractions Including trash, oversized components, product and fine parti- cles. What is referred to as trash is any saterial that has passed through the system such as plastics or pebbles or unfll- tered products which were not removed during pretreatment before the material entered the apparatus of the present Invention. The oversized components are constituents which are not trash, but which have a size exceeding 4 mm in diameter. The product is that portion of the material which is of the proper size and density and which is ready for use. The fine particles are the remainder of the material which has passed through the vibrator

and which is not captured by the previous screens. This material, which is smaller than 1.5 mm, is conveyed back to mixer bin where it functions as "seed" material for the produc¬ tion of new granules.

It is another object of the present invention to exploit th benefits of using a horizontal, rotary steam heated indirec dryer such as the Kvsrner Eureka Multicoil dryer. This drye consists of a row of aligned concentric rings that conduct th heat medium. The rings rotate to provide good contact and hea ιe exchange with the material to be dried.

The invention will now be explained in more detail with referenc to Figure 1 showing a schematic illustration of the apparatus.

15

The system consists of a wet sludge bin 10 for intake and storag of organic material/sludge 11 from, e.g., Industry or purifica tion plants. The system also consists of a dry silo 20 fo storage of dried sludge 21. Wet sludge bin 10 and dry silo 2 are connected to mixer 30 via separate lines, or conveyors,

20 respectively lines 12 and 22. Mixer 30 is placed directly abov dryer 40 and is connected thereto via conveyor 31. Mixer 3 contains blender means that provide for efficient and precis production of granules of the correct size. Dryer 40 i horizontal and is preferably of the multicoil type. Granules o the proper size fall down into dryer 40 and are dried with th aid of rotation. The completely dried granules are conducted ou through conveyor 41 to the screen means 50, consisting of sieve 51 of a specific size. Screen means 50 has a conveyor 53 bac to dry silo 20, and another conveyor leading to a crusher/mil 60. From screen means 50 there is also a conveyor 52 fo transport of the finished product. The horizontal indirect drye 40 has a conveyor 42 for transport of particles to a cyclone 7 which separates out large particles and conducts these i conveyor 71 back to screen means 50. The smallest particles fro the cyclone separation are conducted further to a scrubber an a combustion furnage (not shown) via conveyor 72.

Raw sludge 11 in wet sludge bin 10 is mixed with dried sludge 21 in a specific ratio and is fed in continuous doses into mixer 30. In mixer 30 the dried sludge particles 21 function as "seeds" around which the moist sludge 11 attaches itself in a layer of about 0.5 mm. This forms uniform granules of a specific size, preferably from 1.5 to 5 mm. From the mixer the granules having a solids content of about 70% (about 65% to 72%) are fed into the dryer. The granules have attained their correct shape and size in mixer 30, and no further granulation will take place during the drying. In the indirect, horizontal dryer 30, preferably a multicoil type, the granules are dried by heat exchange with the heated medium circulating in the dryer. The completely dried granules are conducted in conveyor 41 to screen means 50, where the granule product is separated roughly into three fractions: dust, product and oversized clumps. The product is discharged in conveyor 52 for collection and storage. The large clumps are fed to a crusher/mill 60 for grinding/crushing. This milled and crushed material together with dust particles is fed in a conveyor back to dry silo 20 and used there as seed particles in the repeated granulation/drying process.

The use of the method and apparatus according to the Invention provides a process affording complete control over the odor that is produced, which often accompanies treatment of such waste materials. The method and apparatus of the invention is a closed system. First, the entire apparatus is placed under a vacuum so that there is no need for an air lock between dryer 40 and the rest of the system. Second, the building which houses the apparatus is maintained under negative pressure, which ensures that all air remains within the building until it is treated. All air used in the system is passed through a series of ducts which transport the process air through a cyclone 70 to separate out particles entrained within the air stream and passes on the process air into a direct contact condenser/scrubber. Effluent water from the plant is used as condensing water to further reduce the particle content in the air stream, while simultane¬ ously reducing any odorous constituent that may exist. Use of

effluent water from the plant means that no more water than necessary is used, and the plant's environmental profile is enhanced. The condenser also serves the purpose of removing the moisture from the air stream prior to its final treatment. The final treatment of the air takes place in a boiler combustion chamber. All air from the system as well as the air that transports the evaporate from the process and some air from the atmosphere is used as primary combustion air in the boiler for the production of steam. The final treatment of air removes the volatile organic compounds, fine particulate and noncondenβable gas from the process in the high temperature zone of the boiler furnace. It is also desirable to remove dry dust from the process to Improve the internal atmosphere of the building. All dust that is produced in the process from screening, crushing and transport is drawn through a dust collection means (bag house) 80. Dust that is captured in this device is transported by moans of an enclosed conveyor to the mixer 30 and combined there with wet sludge. Dust from the cyclone 70 is similarly transported to mixer 30. This provides a means of taking care of the dust as well as controlling the dust when moistening. The entire system is controlled by a computer, which ensures efficient and precise control of all parameters.

The solids flow through the system is also a closed system. The solids are reused until they have attained the desired size. Through precise direction and control of the formulation of the granules in the mixer, and subsequent separation by screening after drying, the present invention can create a product of the exact size desired depending on the particular need.