The invention relates to a drying apparatus for drying material, which drying apparatus includes a body, heating elements attached to it, between which the material to be dried is arranged to be transferred, and which are established in the body at a distance from each other and of elements attached in layers, between which the material being dried is arranged to be transferred, and one or more blower devices for removing humid air from the drying apparatus.

In drying apparatuses, material to be dried is fed on top of heating elements and, when drying, it is allowed to drop downwards onto a lower plane or it is collected onto the plane and dropped downwards. However, material being dried is not transferred in a totally controlled way and considering the degree of drying on different planes in drying apparatuses.

Heating plants burn fuels and produce heat for individual households or larger communities. As fuel, heating plants utilise e.g. wood in different forms or peat. Boilers of heating plants use wood which is usually processed into a form suitable for the purpose, such as e.g. into chips, briquets, pellets or some other form. Furthermore, it is possible to use wood materials created when processing wood, such as e.g. sawdust, chips and bits.

Material used in heating plants for burning are usually first dried outdoors, where it is partially dried. When wood material is processed into briquets, pellets or equivalents, it is of certain size, shape and has a certain humidity percentage. Burnable material is usually stored to storage spaces beside the burner, from where the material is transferred to the burner when required. Particularly chips can be relatively humid at this step. Additionally, particularly burnable material stored in cold conditions can be frozen. When such material is fed to the feed apparatus of the burner, the purpose is that it defreezes and heats up when travelling in the feed apparatus. If the material is frozen, its feeding can involve problems. These different factors can cause problems in the feed apparatus of the burner and the operation of the burner is then not optimal. Some heating plants include separate drying apparatuses where burnable material is dried before feeding it to the burner.

The efficiency of burners in heating plants is about 80-90%. There have been efforts to use lost heat created in heating in many ways but, in practice, at least part of it goes to waste. An object of the invention is to introduce a drying apparatus by means of which above problems are eliminated. A particular object of the invention is to introduce a drying apparatus used in connection with burners for drying burnable material and for processing it reliably, efficiently and quickly. A further object of the invention is to introduce a drying apparatus, which can utilise the lost heat of a heating plant.

The object of the invention is achieved with a drying apparatus, which is characterised by what is presented in the claims.

In the drying apparatus according to the invention, on the opposite sides of a heating element there are parts extending mainly perpendicularly outwards, the drying apparatus includes a rotating device for rotating the heating elements, adjacent parts of adjacent heating elements are in the immediate vicinity of each other when the drying apparatus is in the normal position. When using the apparatus, material being dried can be controllably transferred during drying and according to drying from one plane to another and the humidity of material can be monitored on different planes and the drying process controlled according to it. The material being dried can be e.g. for a certain time on each of the planes. The drying apparatus according to the invention is applicable for use in the drying of various dryable materials. It can be used for the drying and thawing e.g. of firewood, chopped wood, woodchips, bark, sawdust, peat and lake ore as well as peat ore and their mixtures and additionally of various cereal stems and grains, maizes, potatoes and other vegetables, berries, fruits, aromatic plants and many waste or other materials.

Material being dried in the drying apparatus is heated by means of medium circulating in the heating elements. In an advantageous embodiment of the invention, the heating elements are attached to each other by conductors to circulate the heatable medium in the heating elements. Then, the heating elements are provided with relatively uniform heat. However, heat is more intense at the beginning than at the end. The medium is most heated at the uppermost plane and somewhat cools down when transferring onto other planes. The material to be dried is fed onto the uppermost plane, whereby it has the best drying capacity. The material being dried is kept for a desired time on different planes and humidity is removed by means of blowers. This time depends on the material and its humidity. In some cases, it is possible to do vice versa and convey the heated medium first to the lower heating elements. In some cases, it is possible to omit blowers and to use the apparatus solely for thawing. In an embodiment of the invention, at least part of adjacent heating elements on the uppermost plane are at different points in the vertical direction. Then, the chopping property of a frozen chip cover or other frozen material is provided as the pieces of material diminish to such a dimension that they are able to fall onto the next plane. In an advantageous embodiment of the invention, the drying apparatus is particularly intended for drying burnable material and such a drying apparatus is characterised by having arranged the drying apparatus heatable by the lost heat of a heating plant. Then, the existing heat of a boiler is utilised and/or lost heat in the boiler space or exiting it efficiently in the drying apparatus. This so-called lost heat remains often totally unutilised.

In an advantageous embodiment of the invention, substitute air (drying air) is conveyed to the drying apparatus from the boiler room of the heating plant. The substitute air (suction air) of the drying apparatus is taken from the boiler room of the heating plant through a heat exchanger or a filter unit there and conveyed to the drying apparatus where it dries fuel efficiently and cost-effectively.

In an advantageous further embodiment of the invention, the drying apparatus is attached to the heat exchanger in the boiler room of the heating plant where heated liquid medium is arranged to be conveyed via a piping to the heating elements of the drying apparatus. Such a liquid medium can be even 120°C and, by conveying it to the heating elements, they can be efficiently heated. Dryable fuel dries very efficiently and cost-effectively in the drying apparatus according to the invention.

In an advantageous further embodiment of the invention, heat power from the lost heat of flue gases is conveyed to the drying apparatus by recovering heat by means of a heat exchanger via which the flue gases are conveyed. Then, the heat of flue gases, which would not otherwise be utilised, is employed.

Other different embodiments of the invention are presented in the other dependent claims.

The invention will now be described in more detail with reference to the accompanying drawing in which Fig. 1 shows an oblique front view of a drying apparatus according to the invention,

Fig. 2 shows a front view of the drying apparatus according to Fig. 1, Fig. 3 shows a rear view of the drying apparatus according to Fig. 1, Fig. 4 shows a top view of the drying apparatus according to Fig. 1, Fig. 5 shows a cross section B-B according to Fig. 4, and

Figs. 6-12 show a cross section A-A according to the figure when heating elements have been rotated to different positions.

The drying apparatus according to the figures includes a body 1 and heating elements 2-5 attached to it, which are established of tubular elements attached to the body at a distance from each other and in layers on a certain plane. Furthermore, adjacent heating elements 2a, 2b on the uppermost plane 2 are slightly at different points in the vertical direction on two planes.

In the figures, the drying apparatus is attached to a heat exchanger in the boiler room of a heating plant where heated liquid medium is arranged to be conveyed via a piping 7 to the heating elements of the drying apparatus. The piping 7 is attached to the edgemost heating element on the uppermost plane. The other end of this heating element is attached by a conductor 8 to the heating element adjacent it and so on, and the heating element being on the other edge of this plane is attached to the edgemost heating element on the lower plane and so on until a conductor 10 is arranged to transfer liquid medium back to the heat exchanger. Thus, the liquid medium can be circulated in all heating elements. It is also possible to use the drying apparatus according to the invention in some other place, whereby it has some other, conventional heat source.

The drying apparatus according to the figures includes between each plane 2-5 a blower device (not shown in the figures) and substitute air is conveyed to the drying apparatus from the heat exchanger in the boiler room of the heating plant or directly from the boiler room.

According to Figs. 6-12, on the opposite sides of the heating elements 2a-5 there are parts 9 extending mainly perpendicularly outwards, being parts of rib shape. The adjacent ribs 9 of adjacent heating elements are in the immediate vicinity of each other when the drying apparatus is in the normal position. They are so close to each other that, in the figures, they seem to be totally against each other, even though there can be a small gap between them. On the other hand, they can go partially on top of each other in some embodiments. The drying apparatus also includes rotating devices 6 for rotating the heating elements. In this embodiment, the rotating devices are hydraulic rotating devices and each plane of heating elements has its own rotating device which is attached to the heating elements on the plane in question by bars 11 shown in Fig. 2.

When using the drying apparatus, the heating elements are first in their normal position according to Fig. 6 i.e. all of the ribs of the heating elements in the horizontal position. Material to be dried is fed from above the drying apparatus to the drying apparatus and spread evenly. Then, the material spreads mainly on top of the heating elements 2a, 2b and their ribs on the uppermost plane. The material being dried is kept for a desired time on this plane and heated on the plane e.g. until frozen material starts to thaw. At the next step, the heating elements 2, 2b of the uppermost plane are rotated into positions according to Figs. 7 and 8, whereby their ribs 9 rotate into positions at different steps. The material being dried is possibly chopped into smaller bits and the material is able to drop on top of heating elements 3 on the lower plane. At the next step, the heating elements 2a, 2b on the upper plane are rotated back to their initial position. Some time having passed and the drying having continued, the heating elements 3 on the second plane are rotated into a position according to Fig. 9, whereby the ribs are in the vertical direction and the material being dried is able to drop on top of heating elements 4 on the next lower plane. In an equivalent way, the material being dried is kept for some time on this plane and dropped at the next step on top of heating elements 5 on the lowermost plane according to Fig. 10 and, lastly, on top of the lower plane of the drying apparatus. Fig. 12 shows a position where the heating elements on all planes are rotated away from their normal position. From the lower plane of the drying apparatus, the material is transferred onto a conveyor or in some other way out of the drying apparatus. This is repeated and the material being dried is transferred stepwise from one plane to another and stays for a certain time on each plane. The best drying result is provided when all planes have a layer of chips.

The drying apparatus includes on each plane or between the planes a suction flow blower or an axial blower depending on at which end the blower is installed. Another alternative is that e.g. suction pipes of the planes are combined to one suction blower unit and it is attached with a suction blower of adequate size (e.g. a radial blower) or with an axial blower to the output end. It is also possible to use other devices suitable for the purpose.

Between the planes, it is also possible to convey drying air directly from the boiler room of the heating plant or its heat exchanger unit. Then, the heated recirculation air also heats and dries the material and binds humidity and transports it away. The drying apparatus includes sensors for monitoring the relative humidity of air. The sensors are attached to a control unit of the blowers, which is arranged to monitor humidity and to control the power of the blower or blowers. The higher the humidity, the more the blower or blowers remove air from the drying apparatus. The outgoing air is recirculated via the heat exchanger back to the boiler room of the heating plant or in some cases directly outside. It is also possible to control the blower or blowers manually.

The drying apparatus described in this embodiment and shown in the figures can dry various materials, such as wood and peat. It is particularly suitable for drying wood chips, but it can be used for drying other materials. For instance, wood chips can be dried for the raw material of briquets or pellets when a transfer conveyor has been constructed on the lowest plane or after it for individual taking. An alternative is to construct a drying unit of sawdust utilising lost heat in the vicinity of the heating plant. It is also possible to dry readily chopped chips in a separate drying apparatus.

The drying apparatus according to the invention can be employed in various conditions and attached to different sources of heat. In different embodiments, the drying apparatus according to the invention can be used for drying various materials. These materials are not limited in any way here. The invention is not limited to the advantageous embodiment described, but it can vary within the scope of the inventive idea presented in the claims.