Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B25/00—Details of general application not covered by group F26B21/00 or F26B23/00
  • F26B25/005—Treatment of dryer exhaust gases
  • F26B25/007—Dust filtering; Exhaust dust filters
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B17/00—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement
  • F26B17/02—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by belts carrying the materials; with movement performed by belts or elements attached to endless belts or chains propelling the materials over stationary surfaces
  • F26B17/08—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by belts carrying the materials; with movement performed by belts or elements attached to endless belts or chains propelling the materials over stationary surfaces the belts being arranged in a sinuous or zig-zag path

Definitions

• the invention relates to a method and to a plant for drying bulk or free-flowing items to be dried, in particular wood chips or wood fibers, as described in the preamble of claims 1 and 8, respectively.
• Such a method and such a plant are known for drying wood chips, wood fibers or the like: (DE 35 17 433 B).
• a combustion chamber is arranged in front of the drying chamber, from which the hot combustion gases, which form the drying gas, are introduced into the drying chamber.
• the hot combustion gases which form the drying gas
• the exhaust gas generated here contains not only the moisture extracted from the wood, but also iron or wood tar fringes and wood dust. These pollutants, some of which are very sticky, are deposited in an undesirable manner on system parts and lead to problematic environmental pollution when the exhaust gas is introduced into the atmosphere through a chimney.
• the invention has for its object to reduce the pollution of the exhaust gas with pollutants and dust in a simple manner.
• GB 20 11 598 A has already disclosed a drying plant for pressed bodies (pellets) made of hops, in which two air-permeable belt conveyors are arranged one above the other in chambers separated by a horizontal intermediate wall, the material to be dried being fed to the upper belt conveyor, from which ⁇ sem reaches the lower belt conveyor and is transported to the Gutaus order.
• Warm drying air first rises through the material layer on the lower conveyor belt, is then passed out of the lower drying chamber into a laterally arranged intermediate heater, from which it then flows into the upper chamber and through the material to be dried on the upper belt conveyor.
• drying air is passed through the not yet dried material to be acted as a filter medium (filter layer), the pollutants or the dust which were taken up and carried during drying being removed again from the exhaust air.
• filter layer a filter medium
• Tests have confirmed that the exhaust gas can be effectively cleaned or pre-cleaned in this way.
• the separated particles do not interfere in the material to be further processed.
• sticky substances contained in the chips are even advantageous and lead to a reduction in the amount of binder to be added.
• Air can advantageously be used as the drying gas if waste heat is available for heating this air within an overall system, for example waste heat which is otherwise difficult to use in the low temperature range, such as that in the area of chipboard production in the range of approximately 60 ° Celsius to 70 ° Celsius can occur, for example from a washing system for exhaust air from production systems (dryers, presses, etc.).
• waste heat which is otherwise difficult to use in the low temperature range, such as that in the area of chipboard production in the range of approximately 60 ° Celsius to 70 ° Celsius can occur, for example from a washing system for exhaust air from production systems (dryers, presses, etc.).
• the heat of condensation of water vapor contained in such exhaust air can then be used and considerable energy savings can be achieved.
• this operating mode of the final dryer can be changed without loss of throughput so that the generation of emissions in the final dryer can be significantly reduced.
• the system shown has a drying chamber 1 which has a feed 2 with an inlet lock 3 for the material 4 to be dried. This runs inside the drying chamber 1 first over an upper belt conveyor 5 and then over a lower belt conveyor 6, the two belt conveyors 5 and 6 being high. arranged horizontally and one above the other and connected to each other by an intermediate lock 7. .A discharge end of the lower belt conveyor 6, a discharge 8 is provided with an outlet lock 9, which is followed by a discharge 10 for the dried material 4 to be dried. This flow path of the material to be dried through the drying chamber 1 is indicated by arrows.
• the two belt conveyors 5 and 6 each have a rotating conveyor belt 11 and 12, respectively, which is porous or air-permeable, but is suitable as its carrier, taking into account the particle size of the drying material 4.
• the upper run of the upper conveyor belt 11 forms a filter section 13, while the upper run of the lower conveyor belt 12 forms a drying section 14.
• the arrow 17 illustrates the supply of air which flows through the drying chamber 1 from bottom to top, as indicated by the sequence of vertical arrows.
• the air flows in from outside via an air filter 18.
• This air is heated in an air heater 19, which is operated by means of low-temperature waste heat, which is supplied, for example, with warm waste water through the heat exchanger line 20.
• the heated air flows upwards through the drying section 14 of the lower conveyor belt 12 and through the drying material 4 located in the drying zone 16. This is heated and dried, while the air is loaded with moisture and 4 dust-like particles from the drying material tears.
• the rising air penetrates the filter section 13 of the upper conveyor belt 11 and the drying material layer located in the filter zone 15, which acts as a filter center, so that particles carried along from the drying zone 16 are separated again in the filter zone 15.
• the exhaust air 21 cleaned in this way flows via the induced draft fan 22 to the chimney 23. As shown, this is provided with a control flap 24.
• the anteroom 25 below the lower belt conveyor 6 and the rear chamber 26 above the upper belt conveyor 5 are connected by a bypass line 27 to a control flap 28, so that heated air can be metered into the exhaust air 21, which is free of dust and Pollutants from the material to be dried
• Such an admixture of warm air can be particularly advantageous if, at low outside temperatures and without such an admixture of air, undesirable vapor vapor formation occurs as a result of the water vapor saturation of the exiting exhaust air.
• a circulation line 29 is provided with a control flap 30 for the exhaust air, which is connected to the chimney 23 between the suction fan 22 and the control flap 24 and opens into the space 31 between the air filter 18 and the air heater 19, so that the recirculated Exhaust air is also heated and, if necessary, mixes with outside air supplied according to arrow 17 in order to protect the air heater 19 and possibly also other parts of the system against the risk of frost at low outside temperatures.
• the extent to which the air flowing through the drying zone 16 entrains particles and is loaded with pollutants, and the extent to which these substances are separated in the filter zone 15 are dependent on several factors, in particular on the properties of the material 4 to be dried, its bulk height ( Layer thickness) and feed rate as well as the throughput or the flow rate of the air in the two zones 15 and 16. It is therefore provided that the corresponding values can be set or changed in order to adapt to the material to be treated 4 to get optimal results. In particular, different air flow speeds in the drying zone 16 and in the filter zone 15 are worked, for example by designing these zones with a corresponding air flow with different flow cross-sections or different lengths.
• the system could be built in a manner not shown, that in it by targeted airflow, such as through nozzles or in a fluidized bed or flight dryer, or by mechanical power such as e.g. in a vibration dryer, results in a movement of the material to be dried, which promotes rapid and / or even drying. With the goods to be moved in this way, there is an increased and normally disturbing or impermissible entrainment of small particles with the drying air.
• the drying air is cleaned again in the filter zone, in which a bed height adapted to the behavior of the material to be dried and the flow rate is selected such that the flow through the drying air is comparable to that of a deep bed fiber filter a separation of the particles carried in it results, in which they accumulate on the still moist drying material forming the filter layer. Therefore, the exhaust air can possibly be released into the atmosphere or used for other processes, for example also for recirculating air operation in the dryer, without additional exhaust air filters. In such a mode of operation, the system parts, in particular heat exchangers used for reheating, are no longer soiled to an extent that would only allow short operating times without complex cleaning devices.
• the described passage of the heated drying air through a filter layer formed from material to be dried has the additional advantage that the drying layer in the filter layer is warmed up well. It may well be that condensation of moisture from the drying air occurs on the cold material to be dried, which increases its filtering effect.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Drying Of Solid Materials (AREA)

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Publications (1)

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Cited By (1)

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Citations (8)

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• 1990
  • 1990-07-17 DE DE4022702A patent/DE4022702C1/de not_active Expired - Fee Related
• 1991
  • 1991-07-17 AU AU81817/91A patent/AU8181791A/en not_active Abandoned
  • 1991-07-17 WO PCT/EP1991/001338 patent/WO1992001896A1/de active IP Right Grant
  • 1991-07-17 DE DE91912501T patent/DE59101294D1/de not_active Expired - Fee Related
  • 1991-07-17 EP EP91912501A patent/EP0553089B1/de not_active Expired - Lifetime

Patent Citations (8)

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