Device for drying loose and pasty materials and sludges

Background and summary of the invention

This invention deals with the device used for drying loose and pasty materials (such as wood sawdust, peat, draff, biomass, carbon dust etc.), and sludge. The device consists of drying chambers with worm conveyors through which the air is blown. The dried material passes through the worm conveyors.

Device of the above mentioned type, intended for drying the fish meal, is described e.g. In the patent GB 314 169. It consists of several cylindrical drying chambers disposed one under the another. In the chambers there are worm conveyors and stirring units that stir and move dried material through each cylindrical drying chamber to its end part. The material subsequently falls into the lower drying chamber and is conducted away from the drying device. The drying chambers contain, in at least one part, steam pipes for hot air or steam inlet (or the combination of both). The device is highly energy demanding and is suitable solely for drying fish meal.

The device of a similar type is also described in a published Czech patent application No. 1996 - 11005. It is intended mainly for drying particle toxic material, such as toxic sludges or organic residues from meat production. It also consists of several cylindrical drying chambers with worm conveyors. The drying chambers are set one under another with a gentle back fall, so that the material passes through from the top to the bottom in a zig-zag way. The ventilators force in the atmospheric air that blows away toxic evaporations. The air is consequently heated in the heating chamber by means of burners that to a large extent burn away dangerous aromatic compounds from air. Heated air is conveyed to the flues that adjoin and warm up the walls of the drying chambers from the outside. As the temperature rises, the process of drying inside the drying chambers becomes more effective.

The disadvantage of this device lies in its high energy intensity, because the gas burners in the heating chamber heat up the cool air brought from the outside to a relatively high temperature necessary for burning up the aggressive substances. The drying effect of the device is also rather low, as the outside air contains high amount of water. High temperature has a sterilizing effect, but this may prove as a disadvantage in case of organic materials (e.g. biomass) that needs to keep a range of its physiological values. High temperatures are dangerous in case of potentially explosive materials such as carbon dust.

Different devise, used mainly for drying sludge, clay, slurry, coal and lime sludge, is described in the patent GB 448 778. The material is dried in a cylindrical drying chamber that forms spiral conduit for drying gas, and is stirred by stirring particles. These particles are caught on the stirring lattice, while the dried material falls through and leaves the drying chamber. The disadvantage of this device lies in the fact that it is suitable only for drying thin pasty materials and can not be used e.g. for sawdust. Another disadvantage is its low production capacity.

Another device of a slightly different type is described in the patent GB 49 18 58. The device is used for gas modification (among others also e.g. drying) of fibrous particles. Large vertical drying chamber contains several rotary horizontal levels, where the material is stirred by worm conveyors, and blown through by the side ventilator. The material moves through the drying chamber from the top to the bottom. Its large size, as well as its investment cost and high energy intensity are the disadvantage of this device. This device is suitable mostly for drying loose materials consisting of light particles.

The main objective of the invention is to construct a drying device that could be used universally for drying loose and pasty materials, as well as sludges. Its operative temperature should be low enough to allow the material to keep its biological values even in its dried form. It is known that in case of drying e.g. wood sawdust lysine is released by temperatures higher than 120° C. Another objective is

to reduce energy consumption for the device operation, i.e. minimization of the energy intensity and its harmful emissions as low as possible, as well as the possibility to control and regulate the operation factor of the device during the processing of materials that are of various physical aspects, e.g. carbon dust and grains.

The drying device constructed according to this invention meets the requirements described above. The device includes a box with a charge hopper. The box contains a set of at least two drying chambers equipped with worm conveyors that are placed horizontally one under another and modified for consecutive flow of the dried material - horizontally in the upper drying chamber and vertically down to the lower drying chamber. It also contains a ventilation plant with a drying air distributor in at least one drying chamber, and a heating appliance attached to at least one heating unit for heating the drying chamber in at least a part of its sheath.

The principle of the device is based on the fact that at least one worm conveyor is equipped with stirring blades set on at least one side of the helicoid threads, and at least one drying chamber is constructed as a trough opened at the top, which is of the "U" shape in the cross section. On the side of the drying chamber there is at least one air directional diffuser, attached to the drying air distributor. The diffuser is adapted for the outlet into the drying chamber along the sidewall to its bottom. The top part of the box also contains at least one drying air exhaust that is by means of an exhaust pipe interconnected with the first input of the recuperative unit with the heat exchanger. The second inlet of the unit absorbs fresh air, and the drying air distributors are attached to its outlet. It is also significant that the heating appliance consists of two independent thermal circuits with heat-exchanging fluid (the temperature does not exceed 20CTC). The first thermal circuit is connected with the heat exchanger of the recuperative unit. The principle of the new solution is therefore based on the combination of heated drying chambers with the drying air distributor of a specific temperature. The air passes through the drying chambers to e.g. the axes

of the worm conveyors. Air recuperation is essential, because it reduces heat losses in the device.

It is advantageous when each drying chamber is placed in a separate supporting frame that is equipped with means for the connection with the upper and/or lower carry frame. The whole drying device is therefore adjustable in various size ranges, depending on the required capacity.

In the advantageous version of the invention the box is equipped with an exhaust flue that discharges the drying air from the drying chambers. The flue is placed on the side of the drying chambers, and is opposite to the side wall with the air directional diffuser. In the upper part of the box it leads into at least one exhaust. This exhaust flue works as a collector of the used drying air. In another advantageous version a dust barrier is set above the worm conveyor. The barrier catches dust particles from the dried material and sends them back to the drying chamber.

It is also advantageous when the drying air distributors are parallel to the side walls of the drying chambers and at the same time they are connected with at least two holes made in the side wall above the horizontal level of the worm conveyor axis, whereas the directional air diffusers are fixed with flanges around the holes to the sidewall inside the drying chamber. They are formed by closed tubular sections bent to the "L" shape that go to the bottom of the drying chamber and their end is equipped with a beveled exhaust. Such arrangement allows us to achieve the best parameters of the evenly drying airflow inside the drying chambers.

In another advantageous version, the stirring blades protrude in the axial direction alternately on both sides of the worm conveyor helicoid threads, and thus enable proper and continuous stirring of the dried material that flows through the drying chamber.

In another advantageous version the heating unit surrounds the bottom part of the drying chamber. The unit is formed by a set of conduits through which a heat- exchanging fluid flows. The conduits are attached to the second thermal circuit of the heating appliance. Low temperature of the drying air and heat-exchanging fluid allows the drying material to keep its biological values throughout the drying process.

The box is equipped with a heat insulation that prevents the heat dissipation, and keeps the drying air hot, so that it could also be used for recuperation.

It is also advantageous if the heating appliance is modified for distribution of the heating output between the first thermal circuit (used for heating the heat exchanger) and the second thermal circuit (for heating the heating unit in the ratio 80:20 with an optimal drying effect).

The final advantage is when the device contains humidity, heat and level sensors that are connected to the control and regulating unit for the output control. The unit is interconnected with the heating appliance, circulatory pumps in the first and second thermal circuit, worm conveyors drive, with ventilating and exhauster device for drying air distributor, and with the device for inlet and outlet of the dried material. Depending on the type of the dried material all propulsive, control and dispensing units can be set in order to achieve the optimal drying effect even with a large diversity of the dried material. The advantages of the drying device according to the invention are based mainly on the fact, that it is a universal device suitable for drying various types of material, e.g. sawdust, draff or coal sludge. The process of drying is safe, it is done under low temperatures and the dried material retains its biological values. The most significant advantage is minimal energy consumption as well as minimal steam emission from the dried material. The device is highly efficient and at the same time constructionally simple and reliable.

Brief description of the Drawings

The device will be illustrated in more detail by means of drawings, where Fig. 1 shows side view of the device, Fig. 2 shows the ground plan of the device, Fig. 3 shows perspective axonometric view of the drying chamber in the supporting frame, Fig. 4 shows perspective axonometric view of the worm conveyor helicoid, Fig. 5 shows in detail the view of the helicoid screw thread (with the stirring blades), Fig. 6 shows the front view of the drying chamber with the heating unit, Fig. 7 shows perspective view of the drying chamber with the heating unit, Fig. 8 shows the side view of drying chamber with the heating unit, Fig. 9 shows in detail the view of the directional air diffuser, Fig. 10 shows the perspective axonometric view of the drying chamber in the supporting frame with the dust barrier and the distance spacers for connecting the drying air distributor.

Detailed description of the preferred embodiments

It is understood that the below described and illustrated particular examples of the invention implementation are shown for illustration not as limitation of the invention implementation to the presented cases. Experts familiar with the existing prior art will be able to find out lower or higher number of equivalent to the specific implementations of the invention described here, by routine experimentation. Any of such equivalents will be also covered by the applicability of the following patent claims.

In the example of the implementation shown on Fig. 1 to Fig 9, the device is formed by the thermally insulated metal box 12 with a charging hopper 4, through which the material passes into the device. The box 12 consists of the supporting frame sheathing, which is formed by three separate cuboid-shaped supporting frames 3 welded together with metal profiles. The profiles are set one above another and joined together by screws in the joint flanges 28. The sets of supporting frames 3 may be of optional height, depending on the required capacity of the device. They

may also be set in more lines one next to another. Inside each supporting frame 3 a drying chamber 1 is placed, constructed as a metal trough made of stainless steel, in the "U" shape (in the cross section), with even side walls 9 and a semi-circled bottom 11. In the front parts 29 of the drying chamber 1 the recesses 30 are formed, through which the axis of the worm conveyor 2_ runs. The worm conveyor 2 is fulcrumed in the drying chamber 1 and its main function is to transport the dried material through the drying chamber 1 in the direction of its direct axis. The bottom IJ _. of each drying chamber 1 contains a discharger 31, through which the dried material falls (after it has passed through the drying chamber 1) into the lower drying chamber 1. Dischargers 3J _. are placed alternately on the opposite ends of the drying chambers 1, so that the dried material goes through the device in a zig-zag way from the top to the bottom. The last discharger 3J _. is connected with the pneumatic conveyance conduit (not shown on the illustration) that draws off and moves the dehydrated material to the storage tank for further processing, mostly pelletation. For easier stirring and spreading of the material during the drying process, the helicoid 8 screw threads of the worm conveyors 2 contain short rectangular stirring blades 7 protruding in axial direction alternately on both sides from the helicoid 8 screw threads of the worm conveyor 2.

During the process, the material is dried particularly due to hot drying air that is blown by ventilation plant through the drying air distributors 5 into the drying chambers 1, as well as by means of the heating units 6 with heat-exchanging fluid. The heating units 6 form a part of each drying chamber 1 bottom H and heat it up.

One heating appliance 19 is used for warming the drying air and the heat- exchange fluid. The unit can be formed by any known heating appliance suitable for heating up circular heat-exchange fluids. It may be advantageous to use the heating boiler for solid fuels, (e.g. for pellets - for their production dried material is used) as well as electric or gas boiler.

Heating appliance 19 contains two thermal circuits with the water temperature set to 120° C. The first thermal circuit 20 (that receives about 80% of the heating appliance 19 power output), is connected with the heat exchanger V7_ of the recuperative unit 16 where the used drying air mixes with fresh outside air. Passing through the heat exchanger 17, the air mixture heats up to 100 - 120° C, and then continues through the medium-pressure ventilator and the drying air distributor 5 back to the drying chambers 1 The second thermal circuit 2J _. (that receives about 20% of the heating appliance 19 power output) is connected with the heating units 6 that partially encircle the bottoms H of the drying chambers 1 The units are formed by the heat network of heating conduits 27.

Hot drying air is on the illustrated example of the implementation distributed into three drying air distributors 5, which run collaterally along the top edges of the drying chambers 1 side walls 9. Spacers 32 may be placed between the drying air distributors 5 and the drying chambers 1 Each drying chamber 1 contains in one of its side wall 9 four rectangular holes 22 (placed under the top edge), to which hot drying air distributors 5 are attached. Inside the drying chambers 1, air directional diffusers 10 are fixed around the rectangular holes 22 to the side wall 9 by means of the rectangular screwing flanges 25. The diffusers 10 direct the drying air flow along the side wall 9 to the bottom H of the drying chamber 1, so that the air passes across the drying chamber 1, dries the material vertically in the direction of its transportation by the worm conveyor 2 and leaves the trough of the drying chamber 1 along the opposite side wall 9. This method of drying proved itself as highly efficient even by keeping the temperature of the drying air low, in the range 100 - 200° C.

Air directional diffusers 10 consist of closed tubular metal sections. They are bent to the "L" shape along the side wall 9 to the bottom H of the drying chamber 1. The end part they have obliquely beveled exhaust 26.

To utilize the residual heat of the used drying air in the recuperative unit 16, it is necessary to dissipate it from the insulated box 12, so that it contains minimal

amount of dust particles from the dried material. For this purpose the exhaust outlet 23 is used, which runs vertically top-down along the drying chambers 1, on the side opposite to the side walls 9 with air directional diffusers 10.

The exhaust outlet 23 runs to the canopy upper part of the box 12 then leads into two cylindrical exhausts 13 placed above the upper drying chamber 1 approximately in the thirds of its length. Metal dust barriers 24 are placed in the drying chambers above the worm conveyors 2, so that the amount of dust particles flowing through the edges of the drying chambers 1 side walls 9 to the exhaust outlet 23, is reduced to minimum. Hot drying air that leaves the exhausts 13 is relatively clean, yet it is suitable to place a cyclone separator into the exhaust pipe, so that the air gets completely dust free before it gets into the recuperative unit 16.

The basic advantage of the recuperation in the recuperative unit _. 16 lies in the usage of the thermal energy of already heated air, but also in the fact, that the vapors from the dried material contained in the used drying air condensate with the cool fresh air in the recuperative unit 16 to the liquid condensate that can be filtered and safely impounded. Operation of the device therefore does not affect surrounding air in the sense of possible fumes escape and at the same time the efficiency of the recuperation in the recuperative unit is increased due to the process of condensation.

The whole box 1_2 is heat-insulated to prevent from unnecessary heat dissipation. The box 12 sheath consists of small two-shielded panels that are fixed to the supporting frames 3 by means of locks with position stops. After unlocking these locks and only when the device is shut down, the panel can be taken out, maintained and repaired.

The device contains humidity, heat and level sensors (not shown on the illustration), that are attached to the control and regulating unit for optimization of the device power output. This unit controls the heating appliance 19, circulatory pumps (not shown on the illustration) in the first 20 and the second 21 thermal circuit, worm

conveyors 2 drive with smooth regulation, ventilation and exhauster device for drying air distribution, and conveyors for inlet and outlet of dried material (not shown on the illustration).

Worm conveyors 2 drive and its speed control is arranged by the epicyclical gear case with an electric motor, regulated by frequency converter, drive gears, chain gears and tension pulleys. Worm conveyors 2 shafts are placed in the discharging bearings that resist high temperatures and that are sealed by a lip seal. Shaft entries through the drying chambers 1 are sealed with a brush segmental seal that must be regularly controlled and changed.

The device, according to the invention, may be applied for drying loose and pasty materials, such as wood sawdust, peat, draff, biomass, carbon dust, sludges etc. that may be subsequently used for other purposes or treatment, particularly for pelletation.

Overview of the positions used in the drawings

1 drying chamber

2 worm conveyor

3 supporting frame of the drying chamber

4 charging hopper

5 drying air distributor

6 heating unit

7 stirring blade

8 helicoid

9 drying chamber side wall

10 air directional diffuser

11 bottom of the drying chamber

12 box

13 exhaust

14 exhaust pipe

15 first input of the recuperative unit

16 recuperative unit

17 heat exchanger

18 second input of the recuperative unit

19 heating appliance

20 first thermal circuit for heating the heat exchanger

21 second thermal circuit for heating the heating unit

22 hole for diffuser

23 exhaust outlet

24 dust barrier

25 diffuser flange

26 beveled exhaust of the diffuser

27 conduit of the heating unit

28 joint flange of the supporting frame

29 front part of the drying chamber

recess in the front part of the drying chamber discharger on the bottom of the drying chamber spacer of the drying air distribution system