AT14471U1 - furnace - Google Patents

Abstract

The invention relates to a combustion plant (2) having a combustion chamber (4), a heat exchanger (10) whose hot side is separated from its cold side by plates (32), a flue gas path from the combustion chamber (4) through the hot side of the heat exchanger (10). a cooling air path through the cold side of the heat exchanger (10) and a cooling air blower (16) for driving a cooling air flow (12) through the cooling air path. High reliability can be achieved if the plates (310) of the heat exchanger (32) are galvanized.

Description

Description: The invention relates to a furnace with a combustion chamber, a heat exchanger whose hot side is separated from the cold side by metal sheets, a flue gas path from the combustion chamber through the hot side of the heat exchanger, a cooling air path through the cold side of the heat exchanger and a cooling air blower for driving a Cooling air flow through the cooling air path.

A mobile solid fuel burning plant can be used for hay drying, for drying a building or for heating a tent or a building. For this purpose, the solid fuel firing system is driven to the site, parked there and put into operation. For operation, solid fuel is burned in the combustion chamber, the heat released in the flue gas is passed through a heat exchanger. For cooling the heat exchanger, it is flowed through by a cooling air flow, which dissipates the heat from the heat exchanger and is passed in an air flow into the building, the tent, a Heutrocknungsraum or the like.

In a firing system, the combustion chamber unfolds a large heat, so that the flue gas with I.OOO'C and above exits the combustion chamber and is led to the heat exchanger. Since the heat exchanger is cooled by the cooling air, which is blown, for example, with room temperature in the heat exchanger, the hot flue gas in the heat exchanger often cooled below a condensation temperature, so that the moisture present in the flue gas, especially in the increase in price of wood chips, condenses in the heat exchanger , The condensate runs down the sheets of the heat exchanger and collects in a designated place. This condensate is chemically very aggressive, so that the sheets of the heat exchanger must be protected from corrosion.

Due to the high flue gas temperatures comes as corrosion protection essentially only stainless stainless steel question, which must have the appropriate composition to achieve corrosion resistance.

It is an object of the present invention to provide a furnace, which can be operated very safe.

This object is achieved by a furnace of the type mentioned, in which the sheets of the heat exchanger are galvanized.

The invention is based on the consideration that the sheets of the heat exchanger are welded in the heat exchanger. The welding is done under inert gas to prevent the penetration of oxygen into the molten metal of the weld. If oxygen penetrates into the weld seam, the corrosion resistance is considerably reduced, so that there is a risk that the heat exchanger will corrode at these parts. In the case of corrosion, there is the considerable risk that an undesirable transfer of flue gas into the cooling air path takes place, with the consequence that the flue gas penetrates into the warm air. Especially in hay drying, this can have devastating consequences, as it may be that sparks in the flue gas present, which are then blown into the hay with unwanted transfer into the cooling air with the heated cooling air. The corrosion resistance of the welds is therefore a high priority.

By galvanizing and corrosion susceptible areas of the weld are covered or sealed by the zinc, so that the risk of the emergence of an opening between the cooling air path and the flue gas path is banned. If, for some reason, welds create areas that would corrode into the interior without galvanizing, they are obscured by the zinc, so that there is no danger of holes being formed.

Particularly advantageous is a hot dip galvanizing of the sheets of the heat exchanger. Hot-dip galvanizing is inexpensive and covers all or all desired areas of the plates or the heat exchanger reliable.

The firing system is suitably a solid fuel burning plant, as a result of which particularly large amounts of heat can be generated in a cost-effective manner. The combustion chamber is thus provided for burning solid fuel. Wood is particularly favorable as solid fuel, such as wood chips or pellets.

Particularly suitable, the invention is applicable to a furnace with a rated power of at least 40 kW, in particular of at least 100 kW. In such services, a high heat is associated with a high corrosion potential unfolds, which can be mastered by the galvanizing.

Next, the furnace is conveniently a mobile firing system, which is therefore intended to be transported by a vehicle to its site, to be operated there and later transported to another site and operated there.

The flue gas path extends from immediately above the flames in the combustion chamber through the heat exchanger to a flue gas outlet. The cooling air path extends from an inlet, which may be provided with a cooling air blower, to an outlet opening, at which the cooling air is available for removal at rated power. The outlet opening may be an opening of the furnace.

Advantageously, the sheets are stainless steel sheets. By combining the galvanizing with the stainless steel sheets of the heat exchanger corrosion can be prevented even with very aggressive flue gas and it can be a very high reliability of the heat exchanger can be achieved. Depending on the design, it may be sufficient if the areas of the welds are galvanized. It does not have to be galvanized the entire sheet, so that it is sufficient if the sheets of the heat exchanger are partially galvanized. Corrosion can be avoided very effectively and unwanted transfer of flue gas into the cooling air can be prevented.

In principle, the galvanizing is not limited to the use of stainless steel sheets, so that other temperature-resistant sheets can be used. Thus, the sheets of the heat exchanger are alternatively made of black plate, which get a zinc coating by the galvanizing, preferably with a thickness of at least 50 pm, in particular of at least 100 pm. By such a thick galvanizing high corrosion protection can be achieved even with black plate, which is suitable for particularly aggressive flue gases.

In view of the fact that a hot dip galvanizing is performed at about 450 ^ and the flue gas leaving the combustion chamber in furnaces with such a high rated power has a temperature of about 1,000 ° C, a certain contradiction arises between a hot-dip galvanizing and the application in a flue gas heat exchanger such a large plant. At a melting point of around 420 ° C and a boiling point of around 907 ° C, zinc is not in principle a suitable material for use in hot flue gas. By a flue gas cooling, which cools the flue gas before entering the heat exchanger, however, this problem is manageable.

In this case, the invention of the further consideration that the galvanized sheets of the heat exchanger are very good heat conductors, so that their temperature is set to about the average between the flue gas temperature and the ambient air or cooling air temperature. It is therefore sufficient and advantageous if the flue gas path in the flue gas stream before the heat exchanger has a cooling device for cooling the flue gas below 1.5 times the melting temperature of zinc.

Provided that the cooling air is tempered in a range between 30 ° C and 80 ° C, it is sufficient that the flue gas to TR = 2TBieCh - TLuft = 2 x 350 ° C - 80 ° C = 620 ° C. cool. At these parameters, a sheet temperature TBieCh of about 350 ° C will set, and even just under 400 ^ would still be acceptable. The flue gas does not have to be cooled down to 350 ° C or 400 ° C, but a cooling down to around 600 C to 700 ° C is sufficient.

A flue gas cooling can be achieved by several measures. Particularly expediently, a flue gas outlet is arranged in the flue gas path between the combustion chamber and the heat exchanger, which lies on the outside in the cooling air path. The flue gas enters from the combustion chamber and into the flue gas outlet, which is cooled from the outside by the passing cooling air. As a result, the flue gas is cooled before entering the heat exchanger, so that an acceptable temperature can be achieved.

Alternatively or additionally, the flue gas can be cooled by a arranged in the exhaust path flue gas recirculation into the combustion chamber. The cooled in the heat exchanger flue gas is partially returned by the flue gas recirculation into the combustion chamber, where it cools the hot flue gas. By adding cooled flue gas into the hot flue gas, the total temperature of the flue gas entering the heat exchanger can be lowered to 700 ° C or below.

Likewise, a cooling is useful when the recirculated flue gas is added to the fresh air for combustion. The recirculated and cooled flue gas is well mixed in the combustion process with the resulting flue gas in this way, so that high temperature gradients are avoided in running flue gas.

In a breakdown of the furnace, it may occur that the cooling air blower fails, but the fire in the combustion chamber continues to burn and generates flue gas at high temperature, which enters the heat exchanger and this damaged. To avoid this, it is proposed that the fresh air is drawn into the combustion chamber with a flue gas blower, which also draws the flue gases through the flue gas path. In the event of a power failure that disables the flue gas blower, both the flue gas flow through the heat exchanger and the secondary air supply into the combustion chamber will collapse because the fresh air is carried into the combustion chamber with the same blower. As a result, the fire in the combustion chamber collapses very quickly, so that the heat remains within reasonable limits. The flue gas also draws only very slowly through the heat exchanger, since the flow of fresh air is prevented and the exhaust gas flow is significantly impeded even in a possible chimney effect of the hot exhaust gas by the negative pressure in the combustion chamber. Overheating of the heat exchanger and destruction of the galvanizing are thereby reliably avoided.

A further advantageous embodiment of the invention provides that the sheets are arranged perpendicularly in the heat exchanger.

In the event that due to an operating error but once temperatures significantly above 400 ° C should occur in the material of the heat exchanger, it may occur that the zinc is partially liquefied. The zinc can now flow down to the sheets and this will flow around the lower welds and keep them tight.

A partial liquefaction of the zinc layer does not immediately lead to inoperability of the heat exchanger. Due to the high operating temperatures, the zinc forms an alloy with the sheet metal material, which develops a certain degree of corrosion protection. If, therefore, the overheating does not occur during the first operation, but only after a number of operating hours, the emergency layer can be built up and the heat exchanger can be adequately protected even in the event of a defect. Such an alloy layer may have a thickness of 100 .mu.m or more, so that it further prevents corrosion. Although the metal sheets are no longer so extensively protected, the corrosion protection can be sufficient for emergency operation up to a repair.

Conveniently, a liquid-tight trough is arranged under the sheets, into which also flows in on the outside of the heat exchanger down flowing zinc layer. In the event of a defect and overheating of the heat exchanger, a downflowing part of the zinc layer can be collected, so that destruction of other parts of the heat exchanger is avoided.

Particularly advantageous, the invention is applicable to a heat exchanger in which the sheets are welded to a foot. This is where large quantities of extremely chemically aggressive condensate form, which in conjunction with the welds can cause problematic spots. Especially in this application is a galvanizing of the sheets, in particular also of the sheet, with which the sheets are welded at the foot, such as a toe plate, which holds the heat exchanger plates together, particularly advantageous because corrosion-prone welding defects can be included.

Further, the invention is particularly advantageous applicable to a corrugated iron heat exchanger. Particularly large areas of corrugated iron can be effectively and inexpensively protected by galvanizing.

The previously given description of advantageous embodiments of the inventions contains numerous features that are given in the individual subclaims partially summarized in several. However, those skilled in the art will conveniently consider these features individually and summarize them to meaningful further combinations. In particular, these features can be combined individually and in any suitable combination with the firing system according to the invention.

The above-described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of an embodiment which will be explained in connection with the drawings. The embodiment is illustrative of the invention and does not limit the invention to the combination of features set forth therein. In addition, suitable features of the embodiment may also be considered explicitly isolated and combined with any of the claims.

[0032] FIG. 1 shows a mobile solid fuel firing plant with a combustion chamber and a heat exchanger, [0033] FIG. 2 shows the firing plant from FIG. 1 in a schematized plan view, and [0034] FIG. 3 shows a view of the heat exchanger of the solid fuel firing plant Figures 1 and 2.

1 shows a furnace 2 in the form of a mobile solid fuel burning plant, which is prepared for transport to several different sites. The furnace 2 comprises a combustion chamber 4 which is mounted in a frame 6 having at its lower end insertion openings 8 for inserting the fork of a forklift. In the schematic and greatly simplified illustration shown in FIG. 1, only the components essential to the invention are shown, and other essential elements have been omitted for the sake of clarity. The furnace 2 has a rated power of 150 kW in this embodiment and is fueled with solid fuel, such as wood chips, wood pellets and the like. For this purpose, it includes an unillustrated fuel storage and a supply of fuel to the combustion chamber 4, in which the fuel is burned.

The resulting from the combustion hot exhaust gases are discharged upward from the combustion chamber 4 and supplied in an exhaust gas stream 14 to a heat exchanger 10 of the furnace 2 from above. The exhaust gas is passed in a first train from top to bottom and then in a second train from bottom to top through the heat exchanger 10 and then blown upwards. To remove the combustion heat from the exhaust gas flow, a cooling air flow 12 is guided in a cooling air path in a countercurrent flow to the exhaust gas flow 14. The cooling air is sucked in as outside air by a cooling air blower 16 directly from the surroundings of the furnace 2 and blown through the two trains of the heat exchanger 10 in countercurrent to the exhaust stream 14. The heated in the heat exchanger 10 cooling air flow 12 then strikes the outer shell of the combustion chamber 4 and flows around the combustion chamber 4. On the other side of the combustion chamber 4, the air in this

Embodiment blown through an outlet port 18 from the furnace 2 and is there with the rated power of 150 kW available, e.g. for the heating of the building. The combustion chamber 4 is cooled by the cooling air flow 12 so that its outside temperature remains relatively cool and suitable for mobile use.

The heat exchanger 10 is a corrugated plate heat exchanger from a plurality of corrugated sheets, as explained in more detail to FIG 3. The individual sheets are indicated by vertical lines in FIG 1 and are each hot-dip galvanized sheets. In a first embodiment, the sheets are black steel sheets of plain steel that would rust in the air. In order to prevent corrosion from contact with aggressive condensate from the flue gas, the thickness of the zinc layer is at least 100 μm. For galvanizing the entire sheet metal body was immersed in a zinc bath.

In another embodiment, the sheets are stainless steel sheets that do not rust in the air, even in conjunction with water. In order to prevent corrosion of the welds of the sheets, the sheet metal body is galvanized only at the head and the foot, e.g. by hot dip galvanizing.

As shown in FIG 1, the cooling air flow 12 flows around not only the combustion chamber 4 per se, but also an exhaust passage 20 through which the exiting the combustion chamber 4 hot exhaust gas is fed into the heat exchanger 10. The arranged above the combustion chamber 4 part of the exhaust duct 20 is in this way an additional heat exchanger for transporting the heat of combustion in the cooling air or useful air for the heating. By this additional heat exchanger, the exhaust gas is cooled by at least 50 ° C.

In the exhaust duct 20, a flue gas fan 22 is arranged, which sucks the flue gas from the heat exchanger 10. This results in the heat exchanger 10, in the exhaust passage 20 between the combustion chamber 4 and the heat exchanger 10 and in the combustion chamber 4 itself a suppression of about 30 mbar. By this suppression prevents flue gas from the furnace 2 can escape to an undesirable location. In addition, this can be achieved in case of failure of the flue gas blower 22, an immediate interruption of the secondary air supply, as will be explained in connection with FIG 2 below.

2 shows the furnace 2 in a schematic plan view from above in the sectional plane ll-ll of FIG 1. It shows a flue gas recirculation 24 to the combustion chamber 4. The flue gas recirculation 24 branches off in the exhaust stream behind the flue gas fan 22 from the exhaust duct 20 from Thus, the flue gas removes behind the heat exchanger 10. The flue gas blown upwardly under pressure from the flue gas blower 22 is thus partially pressed into the flue gas recirculation 24, which leads the cooled flue gas back into the combustion chamber 4.

In addition, a secondary air supply 26 is shown, with the fresh air from outside the furnace 2 of the combustion chamber 4 is supplied. Both the flue gas recirculation 24 and the secondary air supply 26 are shown brought in FIG 2 only on one side to the combustion chamber 4. However, both flue gas and fresh air are inserted around the upper part of the combustion chamber 4 in this.

The cooled flue gas is thus pressed by the flue gas fan 22 to a switch, which directs most of the flue gas to the chimney 28. A smaller part is branched off and directed to the secondary air supply 26 of the combustion chamber. The secondary air supply 26 opens into the upper part of the combustion chamber 4 and comprises a number of arranged around the combustion chamber 4 openings, each with a tube through which fresh air is sucked from the outside by the negative pressure in the upper part of the combustion chamber 4. Outside the pipe, the cooled flue gas is directed into the upper part of the combustion chamber. For this purpose, an exhaust pipe is arranged around each fresh air pipe, as is schematically indicated in FIG 2 at a position of the combustion chamber 4. The fresh air is thus surrounded by the flue gas introduced into the combustion chamber 4. As a result, on the one hand, the fresh air is heated for better combustion and on the other hand, the flue gas is cooled further. In addition, a good mixing of the flue gas with the fresh air in the combustion process can be achieved by this process, so that the cooling of the newly formed exhaust gas in the combustion chamber 4 spatially very uniform happens because where the combustion takes place, is also cooled.

The flue gas-air mixture is conducted so abundantly in the upper part of the combustion chamber, that the entering into the corrugated iron heat exchanger flue gas at 620 ° C, a maximum of 700 ° C, cooled. For this purpose, in the exhaust duct 20 just before the heat exchanger 10 may be a temperature sensor which checks the temperature of the flue gas before entering the heat exchanger 10. By means of a flue gas control, the amount of flue gas recirculated into the combustion chamber 4 can be regulated upstream of the heat exchanger 10 as a function of the temperature of the flue gas.

By cooling the corrugated iron heat exchanger with ambient air through the cooling air flow 12, the metal temperature of the sheets of the heat exchanger 10 is approximately at mid-way between the cooling air temperature of 60 ° C at the outlet of the heat exchanger 10 and the flue gas temperature, which is a maximum of 700 ° C. , to a maximum of 380 ° C. At this temperature, the zinc of the heat exchanger 10 is indeed brown, but does not flow down on the sheets. In addition, evaporation of zinc at this temperature is excluded.

In a breakdown of the electrical system of the furnace 2 also ends the operation of the flue gas blower 22. The negative pressure in the combustion chamber 4 breaks down and the oxygen supply of the secondary air supply is stopped. The flames in the combustion chamber 4 decrease rapidly and there remains a heap of coals, whose heat radiation is low. Since the decrease in the heating power of the fire is very fast, the overheating of the flue gas is low. The flue gas rises only very slowly from the combustion chamber 4 and only very slowly reaches the heat exchanger 10, so that it can cool and does not overheat. For further safety, the flue gas fan 22 is also coupled to the cooling air blower 16 so that failure of the cooling air blower, e.g. in case of a motor failure, the flue gas fan stops, so that overheating of the heat exchanger 10 is prevented even in this case.

Further cooling of the flue gas is indicated in FIG. The cooling air flow 12 separates after exiting the heat exchanger 10 in a lower flow, which flows around the combustion chamber 4 and in an upper flow, which flows around the exhaust gas between combustion chamber 4 and heat exchanger 10. In particular, in a very flat configuration of the upper part of the exhaust duct 20, for example by a flat but very wide channel, a significant cooling effect can be achieved by the pressed with high speed and high volume through the heat exchanger 10 refrigerant gas. As a result, the flue gas is cooled before entering the heat exchanger 10, so that it does not overheat.

The heat exchanger 10, the additional heat exchanger on the exhaust duct 20 and the flue gas return together form a cooling device for cooling the flue gas below 1.5 times the melting temperature of zinc. This cooling device prevents melting of the zinc of the heat exchanger 10 and thus a defect of the heat exchanger 10 caused thereby.

3 shows a view of the heat exchanger 10, which is designed as a corrugated iron heat exchanger. You can see the two vertical trains through which the exhaust stream 14 is first performed from top to bottom and then from bottom to top. In its lower part, the heat exchanger 10 has a box 30 connecting the two trains.

Both trains are formed from corrugated sheets 32, which each pair a corrugated sheet 34 form. Each pair of corrugated sheets 34 forms between its two corrugated sheets 32 corrugated metal-shaped vertical tubes that form the hot gas side or flue gas side of the heat exchanger 10. In each case, a pair of corrugated sheets 34 forms a number of flue gas tubes, which are surrounded on both sides by a meandering cooling air duct, which is guided transversely to the orientation of the flue gas tubes. At the top of the sheets 32 are welded to a head plate 36 and the foot with a toe plate 38, the corrugated sheets 32 each hold together and separate the flue gas side of the cooling air side.

The toe plate 38 is the bottom of a tub whose four side walls are not shown for clarity. If zinc flows down from the galvanized corrugated sheets 32, the zinc falling down on the corrugated sheet metal pairs 34 collects in this tray and does not escape to the outside. The falling down inside of the corrugated iron pairs 34 zinc accumulates in the box 30, which forms a trough, and can not run out of there as well. REFERENCE LIST 2 Combustion system 4 Combustion chamber 6 Frame 8 Insertion opening 10 Heat exchanger 12 Cooling air flow 14 Exhaust gas flow 16 Cooling air blower 18 Outlet opening 20 Exhaust duct 22 Flue gas fan 24 Flue gas return 26 Secondary air supply 28 Chimney 30 Box 32 Corrugated sheet 34 Corrugated sheet pair 36 Head sheet 38 Foot plate

Claims (13)

Claims 1. A firing plant (2) having a combustion chamber (4), a heat exchanger (10) whose hot side is separated from its cold side by metal sheets (32), a flue gas path from the combustion chamber (4) through the hot side of the heat exchanger (10), a cooling air path through the cold side of the heat exchanger (10) and a cooling air blower (16) for driving a cooling air flow (12) through the cooling air path, characterized in that the sheets (32) of the heat exchanger (10) are galvanized. 2. Furnace (2) according to claim 1, characterized in that the sheets (32) are stainless steel sheets. 3. Furnace (2) according to claim 1, characterized in that the sheets (32) are black plates. 4. Furnace (2) according to one of the preceding claims, characterized in that the flue gas path has a cooling device for cooling the flue gas below 1.5 times the melting temperature of zinc. 5. Furnace (2) according to one of the preceding claims, characterized in that in the flue gas path between the combustion chamber (4) and the heat exchanger (10) a flue gas outlet (20) is arranged, which lies with its outside in the cooling air path. 6. Furnace (2) according to one of the preceding claims, characterized in that the flue gas path has a flue gas return (24) in the combustion chamber (4). 7. Furnace (2) according to claim 6, characterized in that the flue gas recirculation (24) branches off in the flue gas path to the heat exchanger (10). 8. Furnace (2) according to claim 6 or 7, characterized in that the flue gas recirculation (24) is designed such that during operation, the recirculated flue gas of the fresh air is mixed for combustion. 9. Furnace (2) according to any one of the preceding claims, characterized by a flue gas fan (22) which is prepared to suck during operation, the flue gases through the flue gas path and fresh air into the combustion chamber (4). 10. Furnace (2) according to one of the preceding claims, characterized in that the sheets (32) are arranged vertically in the heat exchanger (10). 11. Furnace (2) according to any one of the preceding claims, characterized in that below the sheets (32) is arranged a liquid-tight trough, in which also flows in on the outside of the heat exchanger (10) flowing down zinc layer. 12. Furnace (2) according to one of the preceding claims, characterized in that the sheets (32) are welded to a foot. 13. Furnace (2) according to one of the preceding claims, characterized in that the heat exchanger (10) is a corrugated iron heat exchanger. For this 2 sheets of drawings