The invention relates to a cyclone dryer for plant biomass: chopped straw, oil sake, seaweed grown for energy purposes and other fibrous waste from agricultural production.

Combustion of biomass is considered better for environment than combustion of fossil fuels, mainly due to lower sulfur content and reduced amount of carbon dioxide, previously absorbed by plants. The efficiency of the combustion of biomass, in edition to homogenization and fragmentation, depends mainly to the degree of drying. Often used tumble dryers fired with liquid or gaseous fuels are characterized by very high - as far as the requirements for biomass are concerned - temperatures in burner zones, which imposes the need to cool exhaust gases by supplying additional air. There are also known fluid bed dryers for biomass, in which the receiving agent, which committees plant moisture from biomass which is entering a drying chamber, is air blown by fans and heaters located under the perforated bottoms of chambers. The air from the fluid bed is discharged by a discharge channel to a cyclone and to the atmosphere. Gas-tight screw feeders or cell feeders are used in these dryers. Such arrangements, among others, are shown in the description of the Polish patent PL 128251 and the utility model Ru 62261. A biomass dryer column known from the description of the international patent application WO2010052405 contains many coaxially positioned and vertically arranged cyclones with tapered cylindrical casings. In these cyclones agents flow in different manner than in the standard de-dusting system. Biomass pours down successively in coaxial channels between the outlet of the conical part of the upper cyclone and the inlet of the axis of the lid of the lower cyclone . Drying gas flows trough a channel having an inlet located within the axis of the upper cyclone , then the channel goes askew downwardly through the side surface of the cone and to the tangential inlet in the lid on the cylindrical part of the lower cyclone. Cold biomass and hot drying gas are fed into the upper cyclone and discharged from the lowest cyclone. The heat exchange in the case of the concurrent movement of the agents, however, are characterized by low efficiency.

The dryer according to the present invention, as in the above described embodiments, includes a pressure fan, an air heater, a biomass supply feeder, cyclones which are connected in series with gas outlet pipes, an exhauster which exhausts air to the atmosphere, and the gas-tight feeders of the biomass precipitated in cyclones. The flow of gas and particles in the cyclones is the same as in the de-dusting cyclones. The essence of the invention lies in the fact that the dryer has three cyclones, and that the cyclone receiving the dried biomass is connected by its outlet pipe to the inlet pipe of the middle cyclone, which in turn is connected by its outlet pipe to the upper cyclone ended with an exhauster. The biomass supply feeder is connected to the outlet pipe of the middle cyclone and the feeder of the upper cyclone is introduced into the outlet tube of the cyclone receiving biomass. The feeder of biomass precipitated in the middle cyclone is introduced into an air duct located between the air heater and the receiving cyclone.

The drying process in the dryer according to the invention is realized in three cyclones connected in series. Moist and cold biomass is introduced into the outlet pipe behind the middle cyclone. Biomass is previously precipitated in the middle cyclone and is already substantially mid-dried and heated when it is introduced into the receiving cyclone. The receiving cyclone is supplied with air at highest temperature. The described system of biomass circulation provides high efficiency of drying.

Dryer according to the invention in the embodiment is shown in a scheme.

The dryer has three cyclones connected in series in the flow of air: a receiving cyclone 9 which receives dry biomass, a middle cyclone 3 and a top cyclone 12 having an outlet pipe ended with an exhauster 13 which exhausters gases into atmosphere or into a de-dusting system. The outlet pipe of the receiving cyclone 9 is supplied with air from a pressure fan 14 through an air heater 6, an injector 5 and an air duct 7. Its outlet pipe 10 is connected to the inlet pipe of the middle cyclone 3. Wet biomass supply is realized by a screw supply feeder 1 connected to the outlet pipe 2 of the middle cyclone 3 and connected into the inlet pipe of the top cyclone 12. Biomass precipitated in the top cyclone 12 is supplied with a screw feeder 11 into the outlet pipe 10 of the receiving cyclone 9. Biomass precipitated in the middle cyclone 3 is supplied by a cell feeder 4 into the air duct 7 located between the air heater 6 and the receiving cyclone 9.

Wet biomass supplied to the dryer by the feeder 1 is lifted in a stream of hot air through the outlet pipe 2 into top cyclone 12. After vortexing, precipitated biomass in partly heated and partly dry condition is supplied by the feeder 11 into the outlet pipe 10. A stream of air at higher temperature flows through the pipe 10. Biomass is raised into the middle cyclone 3, and after precipitation it is supplied by the cell feeder 4 into the air duct 7 which is located directly behind the heater 6. An air stream at temperature 150 - 250°C blows through biomass, which is finally drying in the receiving cyclone 9. Dried biomass is derived out by a feeder 8. In each of the three stages of drying, which are set by the work of the cyclones, there are conditions for increasing the drying air temperature and in consequence for decreasing the humidity of the biomass— which ensures high efficiency of the process.