DE10157596C1 - Fibrous substance preparation process involves diverting part flow into second heat exchanger before first heat exchanger in flow direction - Google Patents

Abstract

The preparation process comprises circulating a steam-gas mixture through the fibers in a circuit including a heat exchanger. Part (8) of the vapor flow is diverted into a second heat exchanger before the first heat exchanger in the direction of flow, where it is heated and then goes to the combustion chamber (11a) of a hot gas creator fired by solid fuel (12). At least one hot gas circuit is heated in this way.

Description

The invention relates to a method for processing fibrous substances, in particular special of wood fibers, which are dried in a dryer, by the in a substantially closed drying cycle a steam-gas Mixture as circulating gas (hereinafter "vapors") is carried out after passing through the dryer in a separator from the dried fibers and then into a first heat exchanger connected to the drying circuit is routed back.

Such a method can be found in EP 0 714 006 B1. Disclosed here is a process for drying a substance, especially wood chips NEN, in a tumble dryer, through which essentially closed in one a steam-gas heated in a first heat exchanger Mixture is performed, which after passing through the tumble dryer in the first heat exchanger is returned. It is used to heat the Steam-gas mixture the first heat exchanger in a combustion chamber Heated exhaust gas supplied to the burner. Part of the steam-gas mixture becomes  decoupled from the circuit before it is introduced into the first heat exchanger pelt passed through another heat exchanger and inserted into the combustion chamber leads in which the gases produced during drying are burned. Through the further heat exchanger mentioned, the combustion chamber Exhausted and heated exhaust gas before it is fed into the first heat rope sheared through, the decoupled part of the steam-gas mixture is heated.

The drum dryer used in this previously known method leaves one Use of fibrous materials with low bulk density and high inner Friction does not increase, because with such substances the transport mechanism inside the rotary tube does not work. A high proportion of accompanying steam (as a propellant steam) leads to an increased fuel in this previously known method consumption.

DE 196 54 043 A1 allows a thermal dryer for bulk goods such as z. B. Remove wood shavings. A rotary drum dryer and a own furnace to generate the necessary drying heat, but without that the combustion gases are fed directly to the rotary drum dryer. At least one gas / gas heat exchanger is provided, which the flue gas removes heat. A vapor cycle is also provided, which Drying apparatus and a recirculation for vapors emerging from this back to the point of entry, with a consequence of the vapor cycle the drying of the excess partial flow taking place in the drying apparatus the vapors are withdrawn and fed to the furnace as secondary air, where at Temperatures of at least 800 ° C the organic pollutants contained largely burned. The gas / gas heat exchanger arrangement above transfers the heat extracted from the combustion gases to that in the vapor cycle Vapors flowing in the dryer inlet, which then return to the drying Enter the apparatus and serve as a drying agent while cooling. Featured is also an air preheater, which after the combustion gases after  they have passed through the gas / gas heat exchanger for heating the vapor, extracts additional heat and transfers it to fresh air, which is drawn to the dryer leads. In the flow of the combustion exhaust gases is before the gas / gas heat exchanger Arrangement additionally arranged at least one heat exchanger as a heater, which flows through the cooling exhaust gases that cool down on the heating side is generated and thereby either steam on the cooling side or a cooling side flowing liquid heat transfer medium high volume specific Heat capacity heated, being in the drying apparatus for its additional loading heating after the vapor-heated drying section at least as a heating register a heat exchanger is arranged on its heating side with heat emission Steam condenses or a liquid heat transfer medium of high volume-specific cooling capacity. As a result, the dryer is on the cooling side in addition to the previous heating by vapors, additional heat is added leads, with the heater and heating register forming a heating medium circuit.

The invention is based, in particular energetically verbes the task to develop a special treatment process for fibrous substances.

According to the invention, this object is achieved by a method with the mark paint of claim 1.

In the hot gas generator, the solid fuel burns with conducted combustion air generates hot gas, which by the first gas-gas Heat exchanger flows and the vapors are heated. The heated brothers enter the preferably designed as a flow tube dryer in which the Gas flow wet wood fibers are added by the thermal energy of the gas stream are dried. This accumulates from the solid driven fluids as steam in the gas stream. This gas-vapor mixture will then together with the dried fibers in a dryer switched, preferably trained as a cyclone promoters where the  dried wood fibers separated by centrifugal force and out be removed from the process.

Some of the vapors in the circuit must be continuously removed because the drying process creates additional gas volume. The Coupled-off vapor partial flow is converted into a thermal vapor treatment Hot gas generator fed, in its combustion chamber the combustible ingredients fe of this vapor partial flow are burned. This thermally cleaned Gas, together with the combustion gases from the combustion of the hot gas Produced from a chimney as exhaust air into the atmosphere.

Solid fuels are waste materials, possibly from our own wood material production. The feeding of solid fuels into the The combustion chamber of the hot gas generator can be speed-controlled via a dosing screw regulates take place, whereby the hot gas by the fuel supply speed generation can be controlled.

It is expedient if the vapor partial stream to form a rotating one Flow is introduced tangentially into the combustion chamber. This will create a achieved intensive mixing with the hot gases, whereby the thermal loading action of the vapors and a high reduction rate are guaranteed. Therefore the secondary air is preferably introduced tangentially into the combustion chamber tet.

In addition, it can be advantageous if dust-like fuels are exposed Distance above the solid fuels tangentially into the combustion chamber blow and be burned here. It is useful if the dust mixed fuels with air before they are introduced into the combustion chamber become. The tangential injection creates a rotation in the combustion chamber current. Since the temperature here is above the ignition temperature, ver the dusty fuels burn when they enter the combustion chamber. The  this releases combustion energy is used to generate hot gas uses.

An intensive mixing of the hot gases with the vapors can be done by using be supported by flow control devices that also before the on occurs in the heat exchanger downstream of the hot gas generator provided be able to ensure its even exposure to flue gas to deliver.

That generated by the combustion of solids and possibly dust Hot gas is primarily used for the thermal treatment of the vapors. The Excess energy is extracted in the downstream heat exchanger.

According to the invention, it is advantageous if the outcoupled vapor partial flow before its heating in the second heat exchanger in a vapor condenser cooled and thus depleted and the resulting condensate expired be fed. The condensate trap particularly reduces energy consumption the reheating of the remaining vapors. The vapor is decoupled temperature-controlled according to the invention with the aim of optimal gas-gas Incineration and emission reduction. Through emission-related regulation of Temperature of the discharged vapors is possible in each Operating point to minimize the emission.

It is useful to lower the temperature level in the treatment process moderate if the first heat exchanger with the combustion exhaust gas from the fire heated hot gas in a first closed circuit is struck, and further if the second heat exchanger with from burning the combustion exhaust gas heated in a second closed circuit guided hot gas is applied.  

A short dwell time can be achieved by using a flow tube dryer of the fibers in the order of 2-10 seconds. This will the fiber material is dried in the flow tube dryer in the fluidized state and can't "bake". The process temperatures are in the tube dryer always above the water boiling point between 100 ° C and 350 ° C. The Drying with superheated steam reduces the risk of overdrying, as the company be moistened at the beginning. As a result, the heat transfer is ge increased compared to conventional drying; this has a shorter dry time in a row. In addition to the wet fibers, therefore, is according to the invention Propellant steam is fed into the flow tube dryer, which settles in the dryer Reali considerably higher temperature level compared to conventional processes can sieren.

The water required for fiber processing can then be increased if the condensate fed out of the vapor condensate is reduced Propellant steam generation turned into a refiner used for fiber production is set.

For fiber processing, it is useful if the drying cycle of excreted dried fibers in a downstream belei glue. It is advantageous if the dried fibers in a largely closed glue air circuit can be fed in, pass through a glue wetting zone and downstream in one of these Separators are separated from the circulating transport air.

By using the residual heat in the downstream gluing stage, the Energy consumption further reduced.

Exemplary embodiments for carrying out the invention are shown in the drawing Procedure shown. Show it

Figure 1 shows a system for low-emission drying of wood fibers in the cycle gas with subsequent gluing.

Fig. 2 shows a schematic representation of a hot gas generator for energetic waste use and thermal vapor treatment for a system according to Fig. 1 and

Fig. 3 is a cross section along the line III-III in Fig. 2.

In Fig. 1, the drying part of the plant is designated I and the plant part concerned with Belei with II.

The drying I comprises an essentially closed drying circuit 1 , through which a steam-gas mixture acted upon by a fan 2 circulates as circulating gas, which is referred to below as vapors. A section of this drying circuit 1 is designed as a flow tube dryer 3 , into which wet fibers 4 and motive steam in an order of magnitude of approximately 30-50% of the mass flow are fed. After passing through the flow tube dryer 3, the fibers are separated from the vapors in a separator 5 arranged downstream of the latter, which is preferably a cyclone separator, and discharged as dry fibers 6 . The vapors are fed back into a first heat exchanger 7 connected into the drying circuit 1 and passed through this, in order to then flow again through the flow tube dryer 3 .

A partial flow is seen in the flow direction of the drying circuit 1 before the first heat exchanger 7 is coupled out 8 of the vapor, cooled in a Brüden- capacitor 9 and thereby depleted reheated in a downstream second heat exchanger 10 and then introduced into the combustion chamber 11 a of a hot gas generator 11 and there burned. The combustion chamber 11 a has a connection for feeding in solid fuels 12 and a connection for feeding in combustion air 13 .

The resulting in the vapor condenser 9 condensate 14 is fed out of the condenser and z. B. for propellant steam generation in a refiner used for fiber generation and / or used as make-up water for fiber gluing.

In the combustion chamber 11 a combustion exhaust gases produced impinge on together with the thermally repurified vapor partial stream of a first hot gas circulation 15, which is guided through the first heat exchanger. 7 A second hot gas circuit 16 , which is guided through the second heat exchanger 10 , is also applied. Subsequently, the exhaust gas 17 cooled by the application of the two hot gas circuits 15 , 16 from a chimney 18 is passed into the atmosphere as exhaust air 19 .

The vapor extraction is temperature controlled. For this purpose, the vapor extraction and the reheating of the depleted vapor partial stream are controlled in a freely programmed manner, namely by a control valve 20 for the vapor partial stream 8 to be coupled out and controlled by a freely programmable control PLC and by a controlled control valve 21 in the inlet of the second heat exchanger 10 .

In the exemplary embodiment shown, the following process temperatures are entered: a temperature of 300-350 ° C. will occur at the inlet of the flow tube dryer 3 and a temperature of approximately 120-130 ° C. at the dryer outlet. The vapors circulated are thus heated in the first heat exchanger 7 from the low temperature mentioned to 300-350 ° C. The vapor partial stream 8 which is coupled out in front of the first heat exchanger 7 thus has a temperature of 120-130 ° C., is cooled in the vapor condenser 9 to approximately 40-60 ° C. and then in the second heat exchanger 10 again to a temperature of approximately 160 -300 ° C heated. The combustion exhaust gases of the combustion chamber 11 a reach a temperature of approx. 900 ° C. and then cool down to approx. 160 ° C. after the two hot gas circuits 15 , 16 have been charged.

The residence time of the fibers in the flow tube dryer 3 is about 2-10 seconds. During this time the fibers are dried to 2-4% dry.

The separated in the separator 5 dry fibers 6 are fed into a largely closed gluing air circuit 22 , pass through a glue wetting zone 23 , in which glue 27 is injected, and are separated in one of these downstream separators 24 from the circulating air transport. The glued fibers 25 emerging from the separator 24 , which is preferably a cyclone separator, are fed to a further processing device.

The transport speed of the glue wetting zone fibers 23 passing Fa is between 20 and 35 m / s, preferably at about 27 m / s. The temperature of the transport air is around 40-60 ° C.

The glue air circuit 22 is removed via an air discharge false air 26 and fed as additional combustion air into the combustion chamber 11 a of the hot gas generator 11 .

FIG. 2 shows an exemplary embodiment of a hot gas generator 11 , which is followed by a heat exchanger 28 for the first hot gas circuit 15 . The combustion chamber 11 a is closed at the bottom by a grate 29 , which serves to take up the solid fuels 12 fed via a metering screw 30 in a speed-controlled manner. The grate 29 serves as a holding system for the solid combustible fe 12 , which fall when burning as small particles through the grate 29 and from a z. B. discharge system 31 also formed by a dosing screw as ash 32 .

Above the dosing screw 30 there is a feed for the outcoupled vapor partial stream 8 , which can optionally be mixed with secondary air. In the clear distance above the solid fuels 12 , a feed for dusty fuels 33 is provided, the z. B. injected into the combustion chamber 11 a and burned here. Before the dusty fuels 33 z. B. mixes ge in a dust burner with secondary air.

Fig. 3 shows that the vapor portion of stream 8 is introduced tangentially to form a rotating flow in the combustion chamber 11 a. The combustion air 13 can be introduced tangentially into the combustion chamber 11 a. In order to achieve these rotating flows, additional flow guide devices can be used. In Fig. 2, a flow guide 34 is indicated, which should ensure a uniform application of the first hot gas circuit 15 with flue gas.

Claims (13)

1. A process for the preparation of fibrous substances, in particular wood fibers, which are dried in a dryer, through which a steam-gas mixture as circulating gas (hereinafter "vapors") is conducted in a substantially closed drying circuit ( 1 ) Passing through the dryer in a separator ( 5 ) separated from the dried fibers ( 6 ) and then passed back into a drying circuit ( 1 ) connected to the first heat exchanger ( 7 ), viewed in the flow direction of the drying circuit ( 1 ) before this a partial flow ( 8 ) of the vapors is decoupled from the first heat exchanger ( 7 ), heated in a second heat exchanger ( 10 ) and then introduced into the combustion chamber ( 11 a) of a hot gas generator ( 11 ) fired with solid fuels ( 12 ) in such a way that the decoupled one Vapor partial flow ( 8 ) mixes intensively with the hot gases and, after its combustion and heating, at least one hot gas circuit ( 15 , 16 ) from a chimney ( 18 ) as exhaust air ( 19 ) is passed into the atmosphere. 2. The method according to claim 1, characterized in that the vapor partial flow ( 8 ) is introduced tangentially into the combustion chamber ( 11 a) to form a rotating flow. 3. The method according to claim 1 or 2, characterized in that the secondary air ( 13 ) is introduced tangentially into the combustion chamber ( 11 a). 4. The method according to claim 1, 2 or 3, characterized in that dust-like fuels ( 33 ) at a clear distance above the solid fuels ( 12 ) are blown tangentially into the combustion chamber ( 11 a) and burned here. 5. The method according to claim 4, characterized in that the staubför shaped fuels ( 33 ) are mixed with air before they are introduced into the combustion chamber ( 11 a). 6. The method according to any one of the preceding claims, characterized by the use of flow control devices ( 34 ) for the intensive mixing of the vapor partial flow ( 8 ) with the hot gases and / or for a uniform application of the at least one hot gas circuit ( 15 ) with flue gas , 7. The method according to any one of the preceding claims, characterized in that the first heat exchanger ( 7 ) with the flue gas of the hot gas generator ( 11 ) heated, in a first closed circuit ( 15 ) guided hot gas is applied to heating the ge in the circuit vapors. 8. The method according to any one of the preceding claims, characterized in that the outcoupled vapor partial flow ( 8 ) before its heating in the second heat exchanger ( 10 ) in a vapor condenser ( 9 ) cooled and thereby depleted and the resulting condensate ( 14 ) be fed out. 9. The method according to claim 8, characterized in that the vapor Decoupled temperature controlled. 10. The method according to any one of the preceding claims, characterized in that the second heat exchanger ( 10 ) with the flue gas of the hot gas generator ( 11 ) heated, in a second closed circuit ( 16 ) guided hot gas is applied. 11. The method according to any one of the preceding claims, characterized by the use of a flow tube dryer ( 3 ), in which the wet fibers ( 4 ) are fed into the vapors flowing through it. 12. The method according to claim 11, characterized in that in addition to the wet fibers ( 4 ) motive steam is fed into the flow tube dryer ( 3 ). 13. The method according to any one of the preceding claims, characterized in that the solid fuels ( 12 ) via a metering screw ( 30 ) speed-controlled on a grate ( 29 ) of the combustion chamber ( 11 a) are fed.