WO2000025076A1

WO2000025076A1 - Method and device for saving energy in continuous annealing and processing lines

Info

Publication number: WO2000025076A1
Application number: PCT/DE1999/003429
Authority: WO
Inventors: Peter Vinz
Original assignee: Peter Vinz
Priority date: 1998-10-28
Filing date: 1999-10-27
Publication date: 2000-05-04
Also published as: AU1769900A; DE19849757A1

Abstract

The invention relates to a method and a device for saving energy in continuously operated continuous annealing and processing lines wherein the annealed material is subjected to forced convection cooling using gas quantities of the gas atmosphere of the furnace. According to the invention, heat transfer sections are arranged downstream of one another. In said heat transfer sections, a constant gas quantity of the furnace atmosphere is blown from both sides and in a perpendicular direction from above and below against the annealed material to be cooled which passes through the cooling line. The heated gas quantity is blown by way of blowers from section to section into the next section having a higher temperature. During this cascade-type passage of the cooling line the adapted gas quantity is heated up to such an extent that up to 70 % of the waste heat emitted by the annealed material can be used in a preheating line which is upstream of the furnace and which has a similar configuration as the cooling line. Said preheating line is used to preheat the material to be annealed which is received in a cold condition. The remaining waste heat is available for other heating purposes. The invention provides a means for reducing the energy consumption of such installations by up to 65 %.

Description

METHOD AND DEVICE FOR SAVING ENERGY ON CONTINUOUS GLOWING PLANTS

The invention relates to a method and a device for saving energy in continuously operated continuous annealing furnaces with a downstream cooling section and forced convection annealing cooling taking place therein. With this type of cooling, externally pre-cooled amounts of gas in the open atmosphere are blown in two or more areas from above and below or on both sides against the annealing material in one or more heat transfer segments of the cooling section and the heated gas amounts are drawn off on both sides or from above with blowers from the respective heat transfer segments, in heat exchangers recooled and blown back into the corresponding heat transfer segments of the cooling section.

Continuous annealing systems of this type are used, for example, as roller hearth or tunnel kiln systems in steel tube production for metallurgical heat treatment and / or bright annealing. For this purpose, hydrogen, nitrogen or a reaction gas mixture is used as the furnace gas atmosphere. Another application of this system technology with similar energy sales is given in the ceramic and brick production. Here air or flue gases are used as the furnace atmosphere. In both areas of application, the waste heat from the annealing material is predominantly dissipated to the environment via cooling devices or directly.

The use of waste heat is not very widespread in these areas of application because of its low cost-effectiveness. For example, it is only economically viable today in steel tube production if powerful and permanent waste heat users such as heated pickling baths in the vicinity of the furnace system have to be supplied with heating. The heat from the annealing material can only be used partially and temporarily for hot water generation systems or space heating. This waste heat component must also be dissipated to the environment when there is no need. So far, a general economic use of waste heat from these furnace systems has failed due to long heat transport paths, insufficient decoupling temperature levels or ultimately due to a lack of waste heat users with a corresponding heating output. The invention is therefore based on the object of using a considerable proportion of the heat from the annealing material, preferably in the furnace system itself, for the regenerative heating of the cold material being supplied and / or by opening up the decoupling temperature range to open up further economical uses.

The use of waste heat shown within the furnace system protects the environment, saves considerable energy costs and, in the event of capacity bottlenecks, enables an increase in the throughput of annealing material without changing the furnace part. The device according to the invention can be retrofitted to existing furnace systems. New systems can be manufactured in a shorter overall length and thus more cost-effectively than before.

The task is solved in two steps. The first step involves the convective cooling of the heat-treated annealing material in the cooling section downstream of the furnace by means of improved heat absorption of a gas stream from the furnace atmosphere, and the second step the convective heating of the heat-treated annealing material by means of the same gas stream and the same heat transfer method in a heating path upstream of the furnace. The amount of gas serves as a heat carrier and is conveyed past both parts of the system past the furnace part. The heating of the gas volume begins at the cold end of the cooling section and ends at the hot beginning of the cooling section, cooling begins at the hot end of the heating section and ends at the beginning of the cold heating section.

According to the first step and claim 1, a pre-cooled, constant partial gas quantity of the furnace atmosphere flows through the entire cooling section in a cascade manner, with constant heating. In this case, it flows through several heat transfer sections of the same design, arranged one behind the other in the cooling section. The amount of gas is blown in the form of a surface within each heat transfer section by means of a blower assigned to this section through nozzles from below and above or on both sides against the annealing material to be cooled, the heated amount of gas is sucked out of this section on both sides or from above and the same in the adjacent section with the following fan , blown higher temperature heat transfer section. This procedure is continued in the manner described until the hot cooling section begins. In this way, the annealed material cools continuously during the cooling section run to the required outlet temperature, and in countercurrent the constant amount of gas heats up to almost the furnace outlet temperature of the annealing material.

According to the second step of the object to be achieved and claim 2, the heated amount of gas is blown cascade through the heating section in the same way as in the cooling section with fans. The gas cooling begins in sections of the heat transfer at the higher temperature end of the heating section and ends at ambient temperature at the beginning of the heating section. The cooled amount of gas is then passed for cleaning through a filter device and for after-cooling through a heat exchanger and then blown into the first heat transfer section of the cooling section again with the first cooling section fan in the manner described.

The amount of gas circulating in this combined gas circuit is matched to the annealing material throughput of the furnace. It is adapted via speed-controlled blower drives. Several heat transfer sections through which flow in series form a cooling section or Heating section. As the number of heat transfer sections arranged in both sections increases, the amount of gas circulating in the circuit is reduced and its heating span increases, while the flow velocity onto the annealing material, which is important for heat transfer, remains constant. As a result, in the cascade-like gas circulation, the post-cooling heat exchanger and the filter device can be made geometrically smaller and thus less expensive than previously.

If, during the heat treatment of the annealing material, latent heat containing conversion points are passed over or the specific heat of the annealing material or the heat transfer gas changes significantly with the temperature, it is expedient according to claim 3 to split the previously described cascade-like gas cycle into a low-temperature and a high-temperature gas cycle and both cascade-like individual cycles in separate segments, each with adapted amounts of gas through the cooling section and the heating section of the furnace system. Only the low-temperature gas circulation is then equipped with a filter device and a post-cooling heat exchanger. With this method, up to 80% of the annealed waste heat can be removed be used regeneratively for heating the annealing material, while the remaining 20% are used for temporary room heating and hot water generation or are discharged to the environment.

According to claim 3, a particularly economical method is to use only the part of the annealing material waste heat of the high-temperature gas circulation for regenerative annealing material or heating, while the part of the low-temperature gas circulation is supplied to external consumers via a heat exchanger. In this way, up to 70% of the annealed waste heat can be reused in the furnace system with less additional technical effort. This reduces the energy consumption of an oven part that is indirectly fired with natural gas or electrically heated by 65%. The annealing material throughput can be more than doubled with this measure in furnace parts. As a result, investment costs for complete new systems can be saved in the event of throughput bottlenecks.

In special cases, when there are several external waste heat users with different temperature levels and sufficient heat requirements in the immediate vicinity of the furnace system, it can also be advantageous if the cascade-like individual circuits are only led through the cooling section and the heated gas quantities are passed through heat exchangers for cooling and the waste heat quantities are external Be fed to consumers. This means that the heating section in front of the furnace part can be dispensed with. This makes the furnace system shorter.

The penetration of atmospheric oxygen at the inlet and outlet ends of bright annealing plants is avoided, as in the prior art, with a continuous reaction gas replenishment in the furnace part. This also continuously regenerates the furnace gas atmosphere. It is advantageous if an additional reaction gas feed is arranged in the flow-reduced cooling zone outlet zone. The constant, cascade-like transport of the gas from the cooling section into the heating section and back then does not impair the quality of the annealed material to be heat-treated.

Further features of the cascade-like forced convective heat transfer according to the invention are disclosed in claims 1 to 8. The invention is explained in more detail below with reference to the partial solutions shown in simplified form in FIGS. 1 to 4. The figures show in detail;

Fig. 1: the cross section of a conventional cooling section or one of the novel heat transfer sections with forced convection annealing cooling, shown using the example of a roller hearth furnace,

2: the flow through a forced-convectionally cooled cooling section or heat transfer section,

3: the flow through a cascade-like cooling section segment, which is dimensioned according to the invention, and

4: the cascade-like gas circulation according to the invention, split into a low-temperature and a high-temperature gas circulation, shown using the example of a roller hearth furnace with regenerative annealing material heating.

The basic principle of forced convection annealing using a warming amount of furnace gas is shown in FIG. 1. The principle is not new and is used both in the prior art and in an adapted form in the solutions according to the invention.

Like the furnace part, the cooling section housing 1 contains driven transport rollers 2 on which the annealing material 3 is transported in the longitudinal direction through the cooling section segment. The transport space 4 is open at the front and is delimited at the top and bottom by the covers 6.1 and 6.2 equipped with inflow nozzles 5 in the transverse and longitudinal directions. The lateral boundary of the transport space 4 forms the wall of the cooling zone housing 1. Above and below the transport space 4, the covers 6.1 and 6.2 with the cooling zone housing 1 form gas calming chambers 7.1 and 7.2, which are closed at the front at the beginning and at the end of the cooling zone segment. The chambers 7.1 and 7.2 are supplied centrally with cooled furnace gas 10 via gas supply lines 8.1 and 8.2 by means of the fan 9. To even out the flat stream tion profile are opposite the central gas inlet openings 11.1 and 11.2 baffle plates 12.1 and 12.2. The gas 10 flows with excess pressure from the chambers 7.1 and 7.2 through the nozzles 5 and strikes the annealing material 2 vertically from above and below. Via openings 13.1 and 13.2 arranged on the longitudinal side in the cooling section housing wall 1, at the level of the annealing material 3, which extend to the longitudinal side , unilaterally closing collecting channels 14.1 and 14.2 are combined and the central discharge lines 15.1 and 15.2 flow the heated i

Gas quantity from the cooling section or from the relevant heat transfer section. By means of the blower 9, the gas flow rate and thus the vertical gas flow velocity within a heat transfer section can be adapted to the local heat transfer requirements.

The further improvements compared to the basic principle also concern heat transfer. Thus, by reducing the length of the heat transfer sections arranged one behind the other, through which one and the same amount of gas flows, the amount of gas can be reduced with a constant flow velocity, so that their heating-up span increases. For example, the section lengths at the cold cooling section end must be selected to be shorter than in the sections with higher temperatures.

The local heat transfer at higher temperatures is increased according to claim 6 by the additional utilization of the radiation portion by the nozzle-equipped upper and lower transport space covers of the heat transfer section in question being formed into hollow bodies and the gas to be discharged from the transport space flowing through them in the transverse and / or opposite direction before the gas transfers to the adjacent heat transfer section. For this purpose, the gas is supplied to the hollow bodies, for example via lateral flow gaps running on the inner wall of the transport space, and is removed centrally after the cross-flow at the warmer end of the hollow bodies. The hollow bodies can also be blackened on their side facing the annealing material in a temperature-resistant manner and resistant to the reaction gas with a chromium dioxide or silicon carbide coating. This measure proves to be advantageous in bright annealing plants.

When heat is given off to the material to be heated in the heating It is advantageous, for example, if the heated gas first flows through the nozzle-equipped hollow bodies and only then is it blown vertically through the nozzles against the annealing material.

FIG. 2a shows a conventional, cooling line segment 20 cooled by forced convection in its longitudinal direction. The segment 20 is traversed in the longitudinal direction by the annealing material 21. The annealed material enters the cooling section 20 at a temperature of 400 ° C. at the inlet 22 and exits at a temperature of 90 ° C. at the outlet 23. 2a schematically shows the same individual gas quantities 24 fed in over the segment length, which impinge on the continuous annealing material 21 in a fixed location and on the outlet side again accumulate over the length to the total amount of gas 25 circulating. The total amount of gas 25 is pressed by the blower 26 for cleaning by the filter device 27 and for cooling by the heat exchanger 28 and then blown back into the cooling section 20. The heating of the single gas streams, pre-cooled to 68 ° C, increases in the longitudinal direction. The mixing temperature of the total amount of gas 25 is 82 ° C at the segment outlet. The gas 25 is recooled in the heat exchanger 28 and the waste heat is transferred to the secondary medium 29.

2b shows the schematic temperature profiles (steel cooling and heating of the total gas flow) over the segment length. The total amount of gas circulating is determined by the heat transfer conditions at the cold end of the segment. A constant gas volume flow of 36,400 m ³ / h is required to be able to dissipate 236 kW of annealing material from the cooling section under the specified conditions. An electric blower output of 36 kW must be used for the gas circulation so that the waste heat can be used in the temperature range between 50 ° C and 70 ° C.

The principle of the cascade-shaped flow through the novel cooling section segment emerges from FIG. 3a. As in the case example according to FIG. 2b, the cooling zone segment 30 is traversed in the longitudinal direction by the same amount of annealing material 31 to be cooled, which likewise has a temperature of 400 ° C. at the inlet 32 and is to be cooled to 90 ° C. by the end of segment 33. A constant amount of gas 34 flows successively through a plurality of heat transfer sections 35.1 to 35. n arranged one behind the other. The heated gas quantities 36.1 to 36.n to be extracted from the sections 35.1 to 35.n are blown in with the blowers 37.1 to 37.n in each case into the adjacent, higher-temperature section, for example with the blower 37.2 from the section outlet 36.1 into the section inlet 38.2. The heated gas quantity 34 is conveyed after the segment outlet 36.n with the blower 37.1 for cleaning by the filter device 39 and for recooling through the heat exchanger 40 and then blown back into the heat transfer section 35.1 at the inlet 38.1. The flow through the sections 35.1 to 35. takes place in the same way as shown in Fig. 1.

Fig. 3b schematically shows the local temperature profiles of the annealing material and the gas along the cooling section segment 30. The temperature profile of the annealing material is the same as in Fig. 2b. A smaller amount of gas heats from 60 to 120 ° C, so that the same amount of waste heat can be extracted in a smaller heat exchanger than in the previous flow conditions. A total of only 12 kW of fan drive power has to be used for the circulation of the gas. In addition, the cooling section segment according to FIG. 3a is 20% shorter than the segment according to FIG. 2a.

4a shows the example of a roller hearth furnace system indirectly fired with natural gas, consisting of the furnace part 50, the cooling section part 51 with the flow-reduced outlet zone 52 and the heating section part 53 with the flow-reduced inlet zone 54. In the cooling section part 51 there are the cascade-like low-temperature cooling segment 55 and that also arranged in a cascade-like high-temperature cooling segment 56. Different amounts of furnace gas 57 and 58 flow through the cooling segments 55 and 56.

The low-temperature cooling segment 55, the filter 59 and the heat exchanger 60 are formed via connecting lines to a circuit 61 through which gas flows. The gas quantity 57 circulates through the circuit 61. The gas quantity 57 is circulated with the blowers 63.1 to 63. n assigned to the cooling segment sections 62.1 to 62.n. The entire low-temperature waste heat is transferred to a secondary medium 64 in the waste heat exchanger 60. An additional reaction gas feed 65 is arranged in the flow-reduced run-up zone 52. The high-temperature cooling segment 56 and the heating segment 66, which is also cascade-like and is arranged in the heating section 53, are formed via connecting lines to the gas circuit 67. The circulation of the gas quantity 58 is carried out with the blowers 70.1 to 70.m and 71.1 to 71.m assigned to the individual heat transfer sections 68.1 to 68.m and 69.1 to 69.m.

The annealing material 72 runs serially through the flow-reduced inlet zone 54, the heating segment 66, the indirectly heated furnace part 50, the high-temperature cooling segment 56, the low-temperature cooling segment 55 and the flow-reduced outlet zone 52.

4b shows the local temperature profiles of the annealing material 72 and the circulating gas quantities 57 and 58 within the furnace system. The annealing material 72 is moved into the furnace system at ambient temperature and preheated in the heating section 53 to 630 ° C., heated and held in the furnace part 50 to the heat treatment temperature of 930 ° C., cooled in the high-temperature cooling segment 56 from 930 ° C. to 380 ° C. aftercooled in the low-temperature cooling segment 55 of 380 ° C at 90 ^D C, with a temperature of about 85 ^D C leaves the annealing goods 72 the system. in gas-flow low-temperature cooling circuit 61, the amount of gas 57 heated in the cooling segment 55 of 60 ° C to 120 ° C., and the gas quantity 57 is recooled in the heat exchanger 60 to 60 ° C. In the high-temperature cooling circuit 67 through which the gas flows, the gas quantity 58 in the cooling segment 56 heats up from 230 ° C. to 780 ° C. and in the heating segment 66 it cools down to From 230 ° C.

A waste heat output of 560 kW is returned directly in the furnace system via the high-temperature cooling circuit 67. In continuous operation, the heating power of the furnace part 50 is reduced by this amount. In total, only 665 kW heating power need be supplied to the heated furnace part 50. This reduces the energy requirement from 1400 to 665 kW. In addition, the residual exhaust gas heat from the indirectly fired furnace part 50 can also be used and coupled out via an exhaust gas heat exchanger 73. The amount of useful heat to be removed from the furnace system is then 370 kW. This performance would have to be provided in the case of full utilization with a boiler. In this case, the total energy saving is 1145 kW with an annealing material throughput of 4.5 t / h of steel. xxx

Claims

claims

1.Method and device for saving energy in a continuously operated continuous annealing furnace with a downstream cooling section and forced-convective annealing cooling taking place therein, in which gas quantities of the furnace atmosphere cooled in one or more segments of the cooling section are blown flat against the annealing material from above and below or on both sides and the heated gas quantities drawn off from both sides or from above with gas blowers from the respective segments, recooled in heat exchangers and blown back into the corresponding segments of the cooling section, characterized in that forced convective annealing of the annealing material is carried out with a cascade-like gas flow, the heating of a defined, pre-cooled quantity of gas on the cold The end of the cooling section begins and ends at the hot beginning of the cooling section, the amount of gas under heating flows through several heat transfer sections of the same design, the amount of gas inside b of each heat transfer section is blown in a sheet-like manner from below and above or on both sides against the annealing material to be cooled by means of a blower assigned to this section, the heated gas quantity is drawn off from this section on both sides or from above with the follow-up fan and blown into the adjacent, higher-temperature heat transfer section in the same way is, so that the annealing material cools down continuously from the furnace outlet temperature to a value below the start-up temperature and, in a cascade-like countercurrent, heats the continuously flowing gas quantity from a value below the annealed material start-up temperature to almost the furnace outlet temperature of the annealed material.

2. The method and device according to claim 1, characterized in that the heated amount of gas flows in the same cascade as in the cooling section upstream of the furnace part, consisting of similar heat transfer sections heating section, the amount of gas supplied at the higher temperature end of the heating section and at the cold start of Heating section is discharged and flows through an emergency or post-cooling heat exchanger with or without further heat emission, so that the cold supplied annealing material heats up during the heating section run and is cascaded counterflow, the amount of gas cools to a temperature below the annealing material start-up temperature.

3. The method and device according to claim 1 and 2, characterized in that the cascade-like gas circulation is split into several cascade-like gas circulations and circulate different amounts of gas in the cascade-like split circulations for receiving and delivering the proportionate heat of annealing material.

4. The method and device according to claim 1, characterized in that the amount of gas flows through several external heat exchangers after the cooling section outlet and is recooled therein at different useful temperature levels.

5. The method and device according to claim 1 and 2, characterized in that a quantity of gas heated in a cooling section is blown directly for cooling through a heating section and from there back into the cooling section, several such separate gas circuits being thermally connected in series.

6. Apparatus for improving the heat transfer in the heat transfer sections of the cooling and heating section according to claim 1 and 2, characterized in that the upper and lower or lateral, with injection nozzles transport space boundaries formed in the direction of annealing material at the end closed cavity and this transverse and / or in are flowed through in the opposite direction to the nozzle flow from the amount of gas to be extracted.

7. The device according to claim 6, characterized in that the upper of the nozzle-equipped cavity body is adjustable in height, so that the flow gap can be adapted to the fixed lower flow gap according to the continuous annealing material dimensions.

8. The method and device according to one of claims 1 to 7, characterized in that the forced-convective cooling section is followed by a flow-calmed annealing discharge zone and a reaction gas feed is arranged in this.