EP2375152B1 - Device and method for generating hot gas with integrated heating of a heat distribution medium - Google Patents

Description

The invention relates to a device for hot gas production with integrated heating of a heat transfer medium comprising a bricked combustion chamber for hot gas production and arranged in the flow direction of the hot gas behind the combustion chamber and connected to the combustion chamber via a hot gas line boiler for heating the heat transfer medium. Furthermore, the invention relates to a method for hot gas generation with integrated heating of a heat transfer medium. Finally, the present invention relates to a drying device for drying lignocellulose-containing material, in particular wood and / or recyclable, wood-containing material.

Hot gas operated drying devices, which are regularly used, for example, in the woodworking industry for drying particulate substances, eg chips, are known from the prior art ( DE 20 2007 005 195 U1 ). The heat content of the hot gas is used not only for drying, but also for heating a heat transfer medium, for example water, steam or thermal oil, which in turn is used in various production processes, for example for heating hot presses for pressing chipboard.

A well known in the art apparatus for generating hot gas for a connected dryer with integrated thermal oil heating comprises a fully bricked Combustion chamber in which the hot gas is generated by a feed grate firing. The hot gas is withdrawn from the combustion chamber in a fully lined hot gas line, which branches off immediately after the combustion chamber. The main stream of the hot gas is then introduced into a hot gas cyclone, where in the hot gas still located fly ash is largely deposited. From the hot gas cyclone, the purified hot gas stream flows into a mixing chamber to set the desired dryer inlet temperature and from there into the dryer.

The partial flow of the hot gas branched off behind the combustion chamber flows into a thermal oil boiler having a radiant heat exchanger and a convection heat exchanger, where it delivers about two thirds of its heat energy to the thermal oil. Subsequently, the cooled partial stream before the mixing chamber is again introduced into the main stream purified in the hot gas cyclone and cools it down.

A disadvantage of this system is that the partial gas stream flowing into the thermal oil boiler, especially when using low-grade fuels, such as waste wood or waste wood, impregnated wood or production waste, leads to a continuous contamination of the thermal oil boiler. This is particularly problematic when due to increasing pollution, the hot gas temperature level in the thermal oil boiler in the region of the radiant heat exchanger increases, so that in the introduced into the thermal oil boiler part gas stream ash particles due to their at temperatures> about 700 ° C liquid or doughy consistency on the thermal oil Condensate heat exchanger flow through condense tube bundles. Also a partial return of emerging from the thermal oil boiler cooled partial gas flow in the thermal oil boiler to reduce the prevailing temperature levels there is associated with disadvantages, since this a higher fan power is required, and the higher hot gas volumes lead to increased erosion tendency in the convection heat exchanger of the thermal oil boiler.

Overall, the disadvantages described above lead to a reduced system availability, since at regular intervals cleaning work in the thermal oil boiler must be performed.

Another device for hot gas production is from the US Pat. No. 3,831,535 A1 known, from which the invention proceeds.

On this basis, the invention is based on the object to provide an apparatus and a method for hot gas production with integrated heating of a heat transfer medium, which is characterized by high system availability and compared to known from the prior art devices overall efficiency. Furthermore, the device and the method should ensure high reliability and longevity of the components used.

The object is achieved with a device according to claim 1.

In the apparatus according to the invention, the entire hot gas stream is freed from the fly ash flowing out of the combustion chamber with the hot gas by complete introduction of the hot gas stream emerging from the combustion chamber into the bricked hot gas cyclone. In this case, the hot gas stream is additionally strongly mixed, whereby a good burnout is achieved. As the Applicant's investigations have shown, there is an additional combustion of carbon monoxide in the hot gas cyclone, so that the energy content of the fuel burned in the combustion chamber can be used even more efficiently and the hot gas has a reduced pollutant content.

After flowing out of the purified hot gas stream from the hot gas cyclone, it is completely or partially passed into a boiler for heating a heat transfer medium, for example water, steam or thermal oil. As a result of the efficient particle separation in the hot gas cyclone upstream in the direction of flow of the hot gas, there is only a slight tendency to become soiled in the boiler, so that a system downtime is reduced as a result of an increased need for cleaning in the thermal oil boiler, thus increasing the overall system availability.

It is further provided that in the flow direction of the hot gas behind the hot gas cyclone branches off a bypass line from the hot gas line, so that the hot gas stream is divided after exiting the hot gas cyclone into a first and a second partial flow, wherein the second partial flow is introduced via the bypass line in the boiler for heating the heat transfer medium. By this division of the hot gas flow into a first and a second partial flow, it is possible to use the first partial gas flow as Main stream immediately to a corresponding use to be fed, for example, to introduce into a dryer, while the second partial flow is diverted to heat the heat transfer medium in the boiler. The respective volume flow of the first and second partial flow can be adjusted in a conventional manner by setting a corresponding induced draft or by control valves. With the aid of this particularly preferred embodiment, it is possible to clean the entire hot gas stream with only one hot gas cyclone even if the hot gas stream is split in the apparatus, on the one hand to heat a heat transfer medium in the boiler and, on the other hand, directly to an application, for example the heating of a hot gas Drying device to feed.

In one embodiment, which is not part of the invention, a first and a second hot gas cyclone may be provided. In turn, a bypass line branches off from the hot gas line, so that the hot gas stream is split into a first and a second partial flow, wherein in turn the second partial flow is introduced via the bypass line into the boiler for heating the heat transfer medium. In this embodiment, the first hot gas cyclone is arranged in the flow direction of the hot gas behind the branch of the bypass line in the hot gas line, while the second hot gas cyclone is arranged in the bypass line in the flow direction of the hot gas in front of the boiler for heating the heat transfer medium. This in turn ensures that the entire hot gas flow and in particular the branched off to the boiler partial flow is purified in a hot gas cyclone.

According to the invention, the outlet of the boiler and the combustion chamber are gas-conductively connected to one another, so that the cooled second partial stream leaving the boiler is at least partially, in particular completely, returned to the combustion chamber as cooling gas flow. By returning the cooled in the boiler second partial flow, the combustion chamber temperature is reduced and it needs less cooling air to be supplied. This reduces the power of the fresh air blower and the system operates with less excess air. In turn, a lower excess of air results in less fresh air being delivered to the system, thereby making the components, such as fans, air lines, flaps, etc., smaller. A lower excess air also means a lower O ₂ content and thus a more favorable conversion for emission measurements to a higher O ₂ reference content. At the same time, a re-introduction of the second partial stream cooled in the boiler into the first partial stream flowing through the hot gas line can be omitted, so that it remains at a very high temperature level and thus can be used more efficiently for a wide variety of applications, for example for drying.

Furthermore, the output of the boiler is also gas-conductively connected to the hot gas line, so that the cooled second partial flow emerging from the boiler can be mixed with it at least temporarily to regulate the hot gas temperature in the first partial flow.

In order to reduce the pollutant content in the hot gas, it can be provided according to a further advantageous embodiment of the invention that the device means for denitrification of the hot gas. The denitrification can be carried out for example by selective non-catalytic reduction (SNCR). For this purpose, at least one nozzle for introducing a reducing agent, in particular urea, may be provided in the hot gas line. Preferably, the at least one nozzle is arranged in the tangential inflow channel of the hot gas cyclone, since there prevails the temperature required for efficient denitrification of the hot gas. An efficient denitrification is also promoted by the intensive mixing of the hot gas in the cyclone, so that the urea consumption and the ammonia slip can be minimized.

According to a further advantageous embodiment of the invention, the boiler for heating the heat transfer medium to a first flow stage with a radiant heat exchanger and a second flow stage with a convection heat exchanger, wherein the first flow stage can be flowed through by the hot gas flow in the downward direction and wherein the second flow stage of the hot gas flow in Upstream is flowed through. In such a design of the boiler, the heat transfer to the heat transfer medium in the first flow section at very high hot gas temperatures corresponding in particular by thermal radiation, while after partial cooling already carried out the heat transfer in the second flow stage, in particular by convection.

In order to minimize contamination of the boiler by residual particles still present in the hot gas, according to a further embodiment of the invention it can be provided that the boiler has means for spraying a cleaning fluid, in particular water. By such a spray of a cleaning fluid can be a regular Cleaning the boiler during operation of the device done. If the boiler has a first and a second flow stage in the aforementioned manner, the means for spraying a cleaning fluid are preferably designed as at least one nozzle arranged in the first flow stage of the boiler. By means of this nozzle, the cleaning fluid can be injected at high pressure into the first flow section of the boiler, wherein the nozzle can be designed such that it performs a pendulum motion so as to apply the cleaning fluid to the entire heat exchanger surface in the first flow stage. The finely injected cleaning fluid causes thermal shock to break off adhering and sometimes hard deposits, which can prevent boiler stoppages. Furthermore, in this way an undesired temperature rise above 700 ° C. can be avoided in the first flow section, so that there is no longer any condensation of liquid or doughy ash particles in the vessel.

According to a further embodiment of the invention, the combustion chamber of the device comprises a grate firing, in particular a traveling grate firing, wherein solid, granular or fibrous fuel is burned on the flowed through by an ascending primary air flow grate through the combustion chamber. The combustion product is the hot gas which flows through the combustion chamber.

The continuous task of the fuel on the grid can be done by means of screw conveyor and a chute in the form of a chute, the chute is designed to be cooled by means of a water injection. This ensures that the chute in case of a Heat build-up, a blockage or a burn-back is protected by cooling and inerting. Furthermore, the projecting into the combustion chamber end of the chute is preferably bricked, so that there is no risk of deformation due to high thermal stress here.

In addition to grate firing, at least one radially oriented burner or at least two tangentially arranged burners for combustion of gaseous and pulverulent fuel can also be provided in the combustion chamber. Due to the performance of such a burner, it can be operated for hot gas generation in combination with grate firing or even alone. Due to the tangential two or more burner arrangement, a better gas mixing in the combustion chamber is achieved, whereby the carbon monoxide content in the hot gas can be significantly reduced by afterburning thereof.

A further aspect of the invention relates to a drying device for drying, in particular, wood products and / or waste with a device according to one of claims 1 to 9, wherein the hot gas flowing out of the hot gas cyclone hot gas at least partially in a dryer for drying in particular chopped wood, sawdust, Wood shavings, wood fibers, animal feed, cereals and the like. Is initiated. For the advantages of this drying device, the above applies accordingly.

The above-mentioned object is procedurally achieved with a method for hot gas production with integrated heating of a heat transfer medium according to claim 14.

The inventive method can be carried out with limited equipment and high reliability, with a reduced contamination due to the purification of the entire hot gas stream in the hot gas cyclone by deposition of fly ash a longer life of the system components is guaranteed. For the other advantages of the method according to the invention, reference is again made to the above.

The hot gas stream is divided after exiting the hot gas cyclone into a first and a second partial stream, wherein the second partial stream is passed via a bypass line into the boiler for heating the heat transfer medium.

According to an embodiment, which is not part of the invention, a first and a second hot gas cyclone may be provided. In this case, the hot gas flow is again divided into a first and a second partial flow, wherein in turn the second partial flow is introduced via the bypass line into the boiler for heating the heat transfer medium. In this embodiment, the first partial flow is purified in the first hot gas cyclone arranged in the direction of flow of the hot gas behind the branch of the bypass line in the hot gas line, while the second partial flow is cleaned in the arranged in the bypass line in the flow direction of the hot gas before the boiler for heating the heat transfer medium second hot gas cyclone becomes. This is again a complete cleaning of the hot gas stream, in particular the branched second partial stream ensured.

The first partial flow can be introduced into a drying device according to a further advantageous embodiment of the method. In any case, the cooled second partial stream emerging from the boiler is at least partially recirculated into the combustion chamber as a cooling gas stream.

To set a specific hot gas temperature in the first partial flow, it may also be necessary in exceptional cases that the cooled second partial flow exiting from the boiler is at least temporarily admixed with it for regulating the hot gas temperature in the first partial flow.

According to a further embodiment of the method, the boiler during operation at least temporarily by spraying a cleaning fluid, in particular water, to be cleaned. As a result, the formation of deposits can still be effectively suppressed by still in the hot gas flow fly ash already in operation.

According to a further embodiment of the method, the fuel input and the thus coupled supply of combustion air in the combustion chamber is controlled such that in the combustion chamber is a constant negative pressure. This means that the firing capacity of the combustion chamber is based on the hot gas power requirement of the respectively downstream application, for example a dryer and / or the boiler for heating the heat transfer medium. If a larger amount of hot gas is withdrawn and thus there is a greater need for hot gas, the negative pressure decreases in the combustion chamber and the power control promotes more fuel in the combustion chamber connected to a correspondingly increased air flow, whereby the total firing heat output increases in the desired manner.

The regulation of the fuel input preferably takes place steplessly by means of frequency-controlled screws.

In the following the invention will be explained in more detail with reference to an illustrative drawing.

Fig. 1

eine erste aus dem Stand der Technik bekannte Trocknungsanlage mit einer Vorrichtung zur Heißgaserzeugung mit integriertem Thermalölkessel und nachgeschaltetem Trockner in stark schematisierter Ansicht,

Fig. 2

eine zweite Trocknungsanlage mit einer Vorrichtung zur Heißgaserzeugung mit integriertem Thermalölkessel und nachgeschaltetem Trockner in stark schematisierter Ansicht und

Fig. 3

die Vorrichtung zur Heißgaserzeugung mit integriertem Thermalölkessel der Anlage aus Figur 2 in einer detaillierten Darstellung.

Show it:

Fig. 1

a first known from the prior art drying plant with a device for hot gas production with integrated thermal oil boiler and downstream dryer in a highly schematic view,

Fig. 2

a second drying plant with a device for hot gas production with integrated thermal oil boiler and downstream dryer in a highly schematic view and

Fig. 3

the apparatus for hot gas production with integrated thermal oil boiler of the plant FIG. 2 in a detailed presentation.

In Fig. 1 is a well-known from the prior art drying plant with a device for hot gas production with integrated thermal oil boiler and downstream dryer in a highly schematic view. Drying systems of this type serve, for example, the Drying of chopped wood, sawdust, wood shavings, wood fibers, animal feed, cereals, etc. With the dried material can then chip, fiber, OSB boards, wood pellets, grain concentrate pellets, etc. are produced. The heat carrier heated by the hot gas, in the present case thermal oil, is required for various processes, for example for pressing chipboard, fiber or OSB boards, for drying impregnated paper and pressing it onto support plates, for heating purposes etc.

The device for hot gas production of the plant Fig. 1 is executed with a fully lined combustion chamber 100. This in turn comprises a feed grate firing 101, but may also have a grate firing, fluidized bed firing, coal, gas, oil, dust firing, etc. as primary firing. Via a feed unit 102 solid or granular fuel is fed to the grate and burned by supplying primary air 103 below the grate and secondary air 104 above the grate, wherein the various combustion phases of drying, heating, gasification and combustion take place along the feed direction of the grate 101a , The ashes of the burnt fuel fall at the end of the grate into a wet stripper 160, which conveys the wet ash into a grate ash container 161 outside the boiler house.

To start the system are just above the grate 101a one or more Einblasfeuerungen 105 for fibrous and dusty waste which are equipped with a Gasstützflamme and thus bring the range of the fuel task to ignition temperature. Typically, another larger gas / dust combo burner 106 is located at the top of the combustor, which is not for starting the plant, but only for the sole combustion or recovery of accumulated fine wood dust can be used. The gas / dust combination burners 106 can be operated in parallel to the grate firing 101; their performance depends on the available dust supply.

The hot gas generated in the bricked combustion chamber 100, which has a high nitrogen oxide content (thermal NOx) due to the high combustion temperature of about 940 ° C is introduced via a preferably also fully lined hot gas line 107 in a hot gas cyclone 108, where it is largely of particulate impurities is cleaned. It is then fed to an external mixing chamber 130 and finally to the dryer 140.

A certain amount of the hot gases flows via a bypass strand 109 into a separate thermal oil boiler 110. The thermal oil boiler 110 here comprises a first flow stage in which the hot gas flows downwards (downstream part) and a part of its heat energy in a radiation heat exchanger 110a, in particular via radiation to the passing through the tubes of the first heat exchanger 110a flowing thermal oil. In the second flow stage, the already partially cooled hot gas flows upwards again (upward part) and releases at lower temperatures further heat energy in a convection heat exchanger 110b, in particular via convection to the thermal oil. In the first-stage radiant heat exchanger 110a, the hot gases are cooled to a temperature of <700 ° C before being overflowed into the second-stage convection heat exchanger 110b.

The deflection between radiant and convection heat exchangers 110a, 110b is presently designed as a large common (or alternatively) as two separate funnels, where the coarser ash content in the hot gas can settle due to gravity and double pendulum flap, feeder, screw, etc. (each not shown) dissipated and collected in the ash container 161.

As it flows through the thermal oil boiler 110, the hot gas cools and transfers the heat to the heat transfer medium, in this case thermal oil. This is heated, for example, from 255 ° C to 280 ° C. The cooled to about 350 ° C hot gas is withdrawn via a suction 113 in a line 112 and passed through a control valve 114 and a line 115 back to the hot gas main stream and cools it.

The hot gas main stream in turn is fed to a mixing chamber 130, in which the hot gas is controlled with cold air or with dryer air / dryer exhaust air to the necessary hot gas temperature before entering the dryer 140.

At the drying plant of Fig. 1 It has been found that in low-quality fuels such as waste wood and waste wood, impregnated wood, production waste, etc., the pollution of the radiant heat exchanger 110a increases sharply, resulting autgrund a deteriorated heat transfer results in an increase in the outlet temperature, which in turn the desired temperature value of approx. 700 ° C is clearly exceeded. As a result, the ash particles are not yet festkörnig, but liquid or doughy, resulting in a condensation on the cold pipes the convection heat exchanger 110b of the second stage leads and increases its pollution. Even with so-called soot blowers, the contaminants can not be removed after a certain period of operation, which leads to a strong limitation of the heat transfer performance and in extreme cases to the complete growth of whole Konvektionsrohrbündeln. In the case of the use of sootblowers their use interval must be steadily shortened. Here, the pipes must be subjected to high air pressure, which also greatly increases the erosion tendency.

To avoid this detrimental effect, in some plant concepts, the recirculation of cooled hot gas is provided via a conduit 115 with a control flap 117 so as to ensure a temperature of <700 ° C in front of the convection heat exchanger 110b. However, this disadvantageously requires a higher blower output, with the resulting increased amounts of flue gas in the convection heat exchanger also causing higher erosions.

Finally, the introduction of the cooled hot gas from the thermal oil boiler 110 into the hot gas stream cleaned in the hot gas cyclone 108 leads to a lowering of the temperature level in the hot gas and consequently to an undesirable reduction of the dryer efficiency because the disadvantage is associated with the introduction of the cooled hot gas into the purified hot gas stream is that less dryer air can be used and thus more exhaust air is produced, which is to be supplied to an exhaust air cleaning system 170. More exhaust air means more waste heat and thus a worse energetic dryer efficiency.

In Fig. 2 is now a second opposite of the plant Fig. 1 improved drying plant with a device for hot gas production with integrated thermal oil boiler and downstream dryer shown in a highly schematic view. The plant in turn comprises a combustion chamber 1 having a feed grate furnace 2 and a boiler 6 for heating a heat transfer medium, in the present case again thermal oil. The plant of Fig. 2 is characterized in that the entire hot gas stream is introduced after flowing out of the combustion chamber 1 in a bricked hot gas cyclone 4, whereby it is almost completely freed from the flowing with the hot gas from the combustion flue ash accordingly. In the hot gas cyclone 4, there is also a strong mixing of the hot gas, which leads to an improved burnout and in particular to an afterburning of carbon monoxide.

As in Fig. 2 recognizable, branches in the flow direction of the hot gas behind the hot gas cyclone 4 from a bypass line 10a from the hot gas line 10, so that the hot gas stream is divided after exiting the hot gas cyclone 4 in a first and a second partial flow, the second partial flow via the bypass line 10a in a Boiler 6 is initiated to heat the thermal oil. The boiler 6 is in to the system of Fig. 1 Comparably designed and includes a first flow stage with a radiant heat exchanger 6a and a second flow stage with a convection heat exchanger 6b. As can also be seen, the output of the boiler 6 is connected to the combustion chamber 1 via a hot gas line 12, so that the cooled hot gas stream emerging from the boiler can be returned to the combustion chamber 1 as a cooling gas stream. This allows the Combustion chamber temperature, which would be more than 2000 ° C with stoichiometric combustion and dry fuel assuming an adiabatic combustion process, effectively limited to, for example <940 ° C, without the combustion must be done with a high excess of air. In order to set a desired hot gas temperature, in exceptional cases, the cooled hot gas can be added to the hot gas main stream flowing through the hot gas line 10 via the control flap 9 before it flows into the mixing chamber 130. Likewise, a portion of the cooled hot gas via the control flap 13 of the exhaust air purification system can be supplied.

In Fig. 3 is the drying plant of Fig. 2 shown in a more detailed schematic drawing, for reasons of clarity, mixing chamber, dryer and the exhaust air / filter system are not shown. The drying plant is again designed for firing with solid, granulated and dust-like fuels. As a central plant components, the plant of the Fig. 3 in turn, a combustion chamber 1 with grate firing, arranged immediately behind the hot gas outlet completely lined hot gas cyclone 4 and a thermal oil boiler 6, in which a part of the produced in the combustion chamber 1 and in the Heißgaszykon 4 purified hot gas via a bypass line 10a and initiated there to heat the Thermal oil is used.

For fuel supply to the combustion chamber 1, the solid fuels via Zugböden 19, classifier (not shown) and 19 trough chain conveyor 19a via a distribution or - as in this case - via a distribution screw 21 and two gate valves 22 two dosing / supply bunkers 23 supplied. Of these, the fuel is metered via a total of six frequency-controlled screws 24 via a special fuel chute 29 in the form of a chute on a divided into two grate halves feed grate 2. The infinitely operable, frequency-controlled screws 24 make it possible to control the combustion in the combustion chamber 1 not only via burners but also via the fuel feed to the grate 2. As in Fig. 3 recognizable, the fuel chute 29 initially runs vertically and then passes the fuel through an oblique section directly to the grate 2. In the vertical section of the fuel falls in free fall down. In this area pneumatic horizontal slide 25 are arranged. Upon interruption of the furnace, boiler failure or failure of the screw 24 close the respective slide 25 - in the event of an interruption of the furnace or boiler failure and the slide 22 - abruptly. The fuel metering is thus separated from the combustion chamber 1 and best sealed to the outside.

At the fuel chute 29, a water injection 26 is provided, which is activated upon reaching a presettable temperature (for example 100 ° C) by opening a solenoid valve 26a, so that water can be finely atomized injected via a nozzle. As a result, the chute 29 is cooled and rendered inert. This may be necessary, for example, in the case of a heat backlog of clogging or burn-back. The combustion chamber-side end of the chute 29 is bricked, so that no metallic parts, which could deform in the long term under the action of the radiant heat, protrude into the combustion chamber 1. With the exception of this discontinuous water consumption by water injection and for the further below explained water spray 35 in the thermal oil boiler, the system has no water or cooling water needs.

In addition to solid fuels, granulate or fibrous fuels (recycling) can also be incinerated on the grate 2. These are in operation of the combustion chamber 1 of a storage silo 20 via its own discharge system (usually rotating discharge screw, slide frame, etc.) and a conveyor screw (not shown in detail) added to the trough chain conveyor 19a and so also on the feed chute on the feed grate. 2 given up. Not shown in Fig. 3 is the possibility to supply the fuel to a blowing furnace.

In the combustion chamber 1, the resulting ash falls at the end of the feed grate 2 via a shaft in a wet-Entschlacker 27 and is conveyed from there into a Rostaschecontainer 28. In the case of traveling grate firing, the ashes are drawn off dry by means of screws and conveyed via further screws in the Rostaschecontainer 28.

At the plant of Fig. 3 Dust-form fuels from dust silos are fed to a dust-dosing container and conveyed via dosing screws, feeder and conveying air to at least two tangentially arranged burners 3 for gas and dust-like fuels. For clarity, the fuel supply is in Fig. 3 not shown in detail. The tangential arrangement of the burner 3 improves the mixing and thus significantly reduces the CO value in the hot gas. The multifunctional burners 3 are arranged above a secondary air injection 18a, 18b, which will be explained in more detail below.

The burners 3 are started with gaseous fuel and can then be switched to a dusty fuel operation. The combustion in the combustion chamber 1 can thereby be operated exclusively with dust-like fuel, without having to install its own gas-fired starting torch. It may be provided that at least one of the burners 3 can be operated both with high-grade pulverulent fuel (for example, dust from the dry chip preparation or grinding dust from the grinding of chipboard, etc.) and with inferior pulverulent fuel (for example, from the extraction of a recycling wood preparation), so that the installation of its own Einblasfeuerung can be omitted. Due to the sole operation with the burners 3, a maximum amount of dust can be burned, so that accumulating dust peaks can thus be utilized in the best possible way. In addition, the burner 3 can be operated with minimal load to keep the system, for example, ready and hot.

Wood dust from the production of a wood processing plant is preferably used as fuel. Another fuel for the heat supply in the solid fuel burning plant are the internal wood and production residues as well as bark and residual wood from the wood storage yard. Similarly, externally delivered untreated woods are burned.

The fresh air flow required for the combustion in the combustion chamber 1 is fed to the combustion chamber 1 via a primary air blower 16 and a secondary air blower 17. The primary air is divided into several zones (windboxes) and flows in an ascending air flow in controlled amounts through the grate 2 and cools it. The secondary air 18 is blown above the grate 2 via a plurality of front nozzles 18a and rear nozzles 18b. The secondary air is used simultaneously as combustion air for the burner 3. The burners 3, in turn, have their own fully automatic air control, the air supplied being divided into primary, secondary and in part tertiary air.

The negative pressure in the combustion chamber 1 is through the Trocknersaugzug (see. FIG. 2 ) and arranged behind the thermal oil boiler 6 arranged frequency-controlled induced draft 8, which subtracts the hot gas in the required amount on the bricked hot gas line 10. The system is regulated in terms of fuel input and combustion air such that there is a constant negative pressure in the combustion chamber 1. The hot gas power of the combustion chamber 1 is thus always oriented to the hot gas power requirement of the dryer. If a higher hot gas output is demanded by the dryer or the thermal oil boiler 6 (more amount of hot gas is withdrawn), the negative pressure in the combustion chamber 1 decreases and the power control promotes more fuel in combination with additional combustion air into the combustion chamber 1 and thereby increases the firing heat output.

The emerging from the combustion chamber hot gas flows, as well as in the schematic view of Fig. 2 It is preferably subjected to denitrification in a selective noncatalytic reduction reaction (SNCR). Specifically, over a plurality of tangential Inlet duct of the cyclone 4 arranged nozzles 30 a suitable reducing agent, in this case urea, injected into the hot gas, since the temperature prevails here for the efficient denitrification of the hot gas. An efficient denitrification is also promoted by the intensive mixing of the hot gas in the cyclone 4, so that the urea consumption and the ammonia slip can be minimized.

In the hot gas cyclone 4, fly ash is separated up to a certain particle size (a grain with 50 μm is separated with about 50% probability). The hot gas is strongly mixed in the cyclone 4 by the special cyclone flow, with a good burnout is achieved with afterburning of carbon monoxide. The separated fly ash quantity in the cyclone 4 is fed via a double pendulum flap 14 and via a chute directly to a fly ash container 15 or the grate ash wet slagger 27 and discharged via this into the common ash container 28.

On the exit spiral of the cyclone 4 an emergency chimney 5 is arranged, which is opened in an emergency shutdown of the system, the hot gases are withdrawn by the natural train of the chimney from the combustion chamber 1. In case of malfunction in the thermal oil boiler 6 - for example, a pipe damage - cold air can also be sucked on the emergency chimney 5 after switching off the firing and thus the thermal oil boiler 6 effectively cooled.

As mentioned, a portion of the hot gas after leaving the hot gas cyclone 4 flows through a bypass line 10a in the Thermal oil boiler 6. This is related to Fig. 2 described manner constructed with a downwardly flowed first flow stage with a radiant heat exchanger 6a and an upwardly flowed through second flow stage with a convection heat exchanger 6b. Further, the thermal oil boiler 6 comprises, instead of a known in the prior art air circulation system in the first flow stage, a water spray 35, with the first flow stage depending on the pollution (temperature increase) during operation of the impurities can be cleaned so as to maintain the original heat transfer coefficients. The water spraying device 35 in the present case comprises a hose reel with a multi-hole nozzle at its free end, which descends with a longitudinal and rotating pendulum motion, the heat exchanger surface of the first flow stage and through the nozzle fine water jets are sprayed at high pressure on the contaminated pipe surfaces. The fine water jets lead by thermal shock to chipping the adhesive and sometimes hard deposits, which boiler stoppages due to required cleaning work can be avoided. In the second flow stage, soot blowers 40 are provided in a manner known per se from the prior art.

The two flow stages of the thermal oil boiler 6 are present and in contrast to Fig. 2 connected by a common ash funnel. About this, the ash can be removed via a double pendulum flap 14 in the closed fly ash container 15.

Behind the convective second flow stage of the thermal oil boiler 6 is the frequency-controlled induced draft 8 arranged, which draws a defined amount of hot gas through the boiler depending on the thermal oil power requirement.

The cooled in the thermal oil boiler 6 hot gas is recycled via a control valve 11 and a return air duct 12 of the combustion chamber 1 to reduce the adiabatic combustion chamber temperature as cooling air. Only in exceptional cases and to regulate a certain hot gas temperature is the cooled hot gas flowing through the bricked hot gas line 10 hot gas main stream through the control valve 9 in the direction of the dryer (see. Fig. 2 ) mixed.

In the following, the efficiency advantages of the above-described drying plant according to the Fig. 2 and 3 compared to the system known from the prior art according to Fig. 1 be presented briefly.

In the known system of Fig. 1 the fuel output is 38.59MW for a required 20MW target hot gas power and 16MW target thermal oil power. To maintain a certain hot gas minimum temperature of, for example, 750 ° C 2.41MW cooled hot gas can be passed into the hot gas main stream, while 5.33MW directly in the exhaust air purification system, such as a wet electrostatic precipitator 170, are disposed of. The oxygen content in the hot gas is 13.4% and the excess air λ = 2.8. The combustion air in this case is an exhaust air from a drying plant at 7.5 ° C and the introduced with the air volume heat output is 1.82MW over the primary air and 0.91MW via the secondary air.

In the case of the introduction of the entire cooled in the thermal oil hot gas amount in the hot gas main stream, deceive Ideally, the mixing temperature is only 533 ° C (in real terms, the heat losses are around 460 ° C). Accordingly, it would no longer be sensible to mix the dryer exhaust air with the hot gas and thus to operate the dryer efficiently in recirculation mode.

At the in Fig. 2 and 3 As shown, the fuel output is again only 34.41MW for 20MW nominal hot gas power and 16MW nominal thermal oil output, resulting in an efficiency increase of approx. 12%. In order to maintain the minimum hot gas temperature of 750 ° C in turn 2.41MW cooled hot gas can be passed into the main hot gas stream, while 5.33MW are recuperated to recover heat in the combustion chamber 1 for cooling. The oxygen content in the hot gas is in this case only 9.3% and the excess air λ = 1.8.

In the event that the 2.41MW heat output would not be introduced into the main hot gas flow, the hot gas temperature would theoretically remain at 920 ° C, which is ideal for overall dryer efficiency. In reality, temperature losses in the hot gas due to heat losses, false air, etc., and the temperature will fall by up to about 100 ° C. It can be seen that it makes sense to return the hot gas amount of the thermal oil boiler 6 as 100% as possible back to the combustion chamber.

Claims (15)

1. Device for producing hot gas with integrated heating of a heat transfer medium comprising a brick-lined combustion chamber (1) for producing hot gas and a boiler (6), which is arranged in the direction of flow of the hot gas downstream of the combustion chamber (1) and is connected to the combustion chamber (1) via a hot gas pipe (10), for heating the heat transfer medium, wherein at least one brick-lined hot gas cyclone (4) integrated with the hot gas pipe (10) is arranged between the combustion chamber (1) and the boiler (6), so that the hot gas flowing out of the combustion chamber (1) is completely directed through the at least one hot gas cyclone (4), characterised in that in the direction of flow of the hot gas downstream of the hot gas cyclone (4) a by-pass pipe (10a) branches off from the hot gas pipe (10), so that the hot gas flow after exiting the hot gas cyclone (4) is divided into a first and a second partial flow, wherein the second partial flow is fed via the bypass pipe (10a) into the boiler (6) for heating the heat transfer medium, in that the outlet of the boiler (6) is connected to the hot gas pipe (10) in a manner suitable for conducting gas, so that the cooled second partial flow exiting the boiler (6) can at least intermittently be mixed in with the first partial flow to regulate the hot gas temperature in the first partial flow, and in that the outlet of the boiler (6) and the combustion chamber (1) are connected to one another in a manner suitable for conducting gas, so that the cooled second partial flow exiting the boiler (6) can be at least partly, in particular fully, conveyed back as a cooling gas flow into the combustion chamber (1).
2. Device according to Claim 1, characterised in that the device has means for denitrifying the hot gas, wherein the means for denitrification are formed as at least one nozzle (30) for introducing a reducing agent, in particular urea, into the tangential inlet channel of the hot gas cyclone.
3. Device according to Claim 1 or 2, characterised in that boiler (6) has a first flow stage with a radiation heat exchanger (6a) and a second flow stage with a convection heat exchanger (6b), wherein the hot gas flow can flow through the first flow stage in the downward direction, and wherein the hot gas flow can subsequently flow through the second flow stage in the upward direction.
4. Device according to any one of Claims 1 to 3, characterised in that the boiler (6) has means for spraying a cleaning fluid, in particular water.
5. Device according to Claims 3 and 4, characterised in that the means are formed as at least one nozzle (35) arranged in the first flow stage of the boiler (6).
6. Device according to Claim 5, characterised in that the nozzle (35) is formed in such a way that it carries out an oscillating movement when spraying the cleaning liquid.
7. Device according to any one of Claims 1 to 6, characterised in that the combustion chamber (1) has a grate firing, in particular a travelling grate firing, wherein solid, granular or fibrous fuel on the grate (2) flowed through by a rising primary air flow is transported through the combustion chamber (1).
8. Device according to Claim 7, characterised in that the device has a screw conveyor (24) and a chute (29) in the form of a slide for continuously feeding the fuel to the grate (2), wherein the chute (29) is designed such that it can be cooled by means of a water injection (26).
9. Device according to any one of Claims 1 to 8, characterised in that at least two tangentially arranged burners (3) for burning gaseous and powdered fuel are provided in the combustion chamber (1).
10. Drying device for drying in particular wood products and/or wood waste with a device according to any one of Claims 1 to 9, wherein the hot gas flowing out of the hot gas cyclone (4) is at least partly fed into a dryer (140) for drying in particular chopped wood, sawdust, wood shavings, wood fibres, animal feed, cereals and suchlike.
11. Method for producing hot gas with integrated heating of a heat transfer medium, wherein the hot gas is produced in a brick-lined combustion chamber (1) and is directed into a boiler (6), which is arranged in the direction of flow of the hot gas downstream of the combustion chamber (1), for heating the heat transfer medium, and wherein the hot gas flow exiting the combustion chamber (1) is completely directed through at least one brick-lined hot gas cyclone (4) before entering the boiler (6), characterised in that the hot gas flow after exiting the hot gas cyclone (4) is divided into a first and a second partial flow, wherein the second partial flow is directed via a bypass pipe (10a) into the boiler (6) for heating the heat transfer medium, and in that the cooled second partial flow exiting the boiler (6) is at least partly conveyed back as a cooling gas flow into the combustion chamber (1).
12. Method according to Claim 11, characterised in that the first partial flow of the hot gas flow is fed into a drying device (140).
13. Method according to Claim 11 or 12, characterised in that the cooled second partial flow exiting the boiler (6) is at least intermittently mixed in with the first partial flow to regulate the hot gas temperature in the first partial flow.
14. Method according to any one of Claims 11 to 13, characterised in that the boiler (6) in operation is at least intermittently cleaned by spraying a cleaning fluid, in particular water.
15. Method according to any one of Claims 11 to 14, characterised in that the input of fuel and the supply of combustion air into the combustion chamber (1) is regulated in such a way that a constant negative pressure prevails in the combustion chamber (1).

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