WO2005035799A1

WO2005035799A1 - Method for heat-treating iron-containing materials

Info

Publication number: WO2005035799A1
Application number: PCT/EP2004/010951
Authority: WO
Inventors: Philippe Grognet; Hans-Peter Schmidt; Günter WAGENDORFER
Original assignee: Messer Austria Gmbh; Messer France S.A.; Air Liquide Deutschland Gmbh
Priority date: 2003-10-08
Filing date: 2004-10-01
Publication date: 2005-04-21
Also published as: DE502004010812D1; EP1673483B1; PL1673483T3; ES2341861T3; EP1673483B8; DE10347312B3; ATE458837T1; EP1673483A1

Abstract

The invention relates to a method for heat-treating, in a protective atmosphere from endothermic gas mixtures, iron-containing materials, especially for annealing tubes, profiles, wires, rods and sheets that consist of metal or steel, in a heat-treating installation that comprises a cooling tunnel and a heating chamber. According to the invention, pure endothermic gas or endothermic gas partially rarefied with nitrogen and additionally pure nitrogen are supplied separately and in different areas of the installation, thereby reducing the time and costs required for the heat treatment process, increasing product quality and allowing for a safe process conduction. The flow profile generated throughout the entire furnace preferably in the heating chamber feed direction considerably reduces the deposition of solids in the cooling tunnel and the heating chamber end.

Description

The invention relates to a method for heat treatment of iron materials, in particular for the annealing of pipes, profiles, wires, rods and sheets of metal or steel, in a heat treatment plant with a cooling tunnel and a boiler room under a protective gas atmosphere of endogas mixtures. When annealing pipes, profiles, wires, rods and sheets, exogas is often used as protective gas. This exogas is made from a hydrocarbon and air, for. B: CH4 + x (0.79 U2 + 0.21 O2) → CO + CO2 + H2 + H20 + N2 where x is> 2.41 and <9.64 (λ => 0.25 to. 1, 00). This protective gas is produced in exogas generators. For this purpose, the premixed natural gas / air gas stream is fed to a combustion chamber and reacted there. Since the CH4 / air ratio is greater than 2.41 (eg 6.5), there is no need for external heating of the gas mixture to the reaction temperature.

It is an exothermic reaction that generates excess thermal energy. The very moist exogas produced in this way is cooled to room temperature and fed to a dryer. The dew point of the dried gas is then about -30 ° C (0.10 vol .-% H2O).

A typical exogas has a composition of 7% H2, 7% CO, 7% CO2, 0.10% H2O, balance N2.

The gas mixture is then fed to a heat treatment plant and it turns in the boiler room - at a temperature of greater than 400 ° C - abruptly a moist furnace gas.

Boiler room reaction: C02 + H2 → CO + H20 (homogeneous water gas reaction) In the boiler room, at a temperature greater than 650 ° C, the carbon activity decreases to less than 1, thereby decarburizing the iron-carbon alloys during the heat treatment.

Because of the increasing quality demands on the finished products, however, decarburization is undesirable. There is even an increasing desire to recarburize decarburized iron-carbon alloys during heat treatment (annealing).

These quality requirements can not be realized with the use of Exogas as a protective gas in heat treatment furnaces, which is why endogas is also used as a protective gas in the heat treatment of iron materials.

The production of endogas takes place in endogas generators. For this purpose, the premixed natural gas / air mixture is fed to a heated retort with catalyst filling and reacted there.

Since the CH4 / air ratio is slightly greater than 2.41 (λ = 0.26-0.28), the catalyst retort must be heated and the gas mixture flowing through the retort be brought to the reaction temperature to react on the catalyst surface.

This is an endothermic reaction, i.e., part of the heating and total reaction enthalpy must be supplied to the system.

The endogas is made from a hydrocarbon and air, e.g. prepared according to the following reaction equation:

CH4 + 2.41 (0.79 N2 + 0.21 O2) → CO + 2 H2 + 0.79 N2 + traces H2O and CO2

The generated endogas is cooled to room temperature and is then ready for use.

The dew point of the endogas used in the heat treatment of iron materials as a protective gas is in the range of - 10 ° C and + 5 ° C with 0.30 to 0.86 Vol .-% H2O.

Endogenous gas commonly used in the conventional heat treatment of metals as inert gas has a composition of: 40% H2, 20% CO, 0.30% CO2, 0.86% H2O, balance N2.

This "pure" endogas is diluted with nitrogen and then fed to the heat treatment equipment, e.g., a roller hearth furnace.

With these shielding gas mixtures with 1 to 5% CO - due to the strong dilution with nitrogen - the dew point drops to values of -20 to -30 ° C, so that the use of an additional dryer, as in the Exogaserzeugung, is not necessary.

The invention is therefore based on the object to provide a method for heat treatment of iron materials available, with which can be improved and made safer by a targeted inert gas metering of the heat treatment process. The object is achieved by a method for heat treatment of iron materials with the features of claim 1. The features of the invention ausgestaltenden can be found in the dependent claims

According to the invention pure inert gas or partially diluted with nitrogen endogas and additionally pure nitrogen is fed separately as protective gas in different areas of the heat treatment plant.

Advantageously, the endogas is fed into the heating chamber end, ie in the end region of the heating chamber opposite the heating chamber inlet, transversely to the transport direction of the heat treatment material and additionally nitrogen in different regions of the cooling tunnel of the heat treatment plant by means of conventional nozzle devices.

The protective gas entry according to the invention into the heat treatment plant causes the formation of a flow profile oriented to the heating chamber inlet, whereby a high protective gas concentration in the heating chamber and a much lower inert gas concentration in the cooling tunnel of the heat treatment plant is present.

The endogas produced in an external endogas generator and fed into the heat treatment plant has a slightly higher dew point (+5 to +10 ° C) than the endogas used in the conventional procedure (dew point maximum +5 ° C).

The higher dew point temperature causes an increase in the service life of the catalyst and the retort of the heat treatment plant, since the risk of soot deposition in the catalyst bed is lower, thus preventing overheating of the catalyst in the necessary Rußabbrennen to regenerate the catalyst

The dosage of endogas required for the respective heat treatment process is set automatically by means of a metering valve as a function of the respective process conditions, whereby the excess amount of endogas can be minimized and moreover as little endogas as possible has to be flared.

The dosing time of the endogas and the nitrogen is detected in the usual way and used to calculate the actual oxygen and carbon activities during the heat treatment process.

In order to improve the convection of the endogases in the boiler room of the heat treatment plant, the endogas is mixed with a partial amount of nitrogen in an endomat arranged outside the heat treatment plant

For the fastest possible homogeneous gas mixture formation, the endogas with an overpressure of 40 to 60 bar by a, arranged in the nitrogen pipe, advantageously L-shaped tube formed in the regulated by means of a Feindruckreglers to an excess pressure of 20 to 30 mbar registered nitrogen an increased back pressure in the nitrogen endogas line, the metered amount of natural gas and air is changed so that the required dosage of endogas reduced and / or the natural gas / air ratio is changed, whereby the composition of the endogases is changed negatively. By changing the mixing ratio, soot can deposit in the catalyst, whereby the effectiveness of the catalyst is reduced. If the air supply is too high, the dew point rises unintentionally, so that overheating can occur at the beginning of the catalytic converter.

The entry of additional nitrogen in the cooling tunnel of the heat treatment plant by means of conventional nozzles, but advantageously by means of a conventional nozzle assembly.

Advantageously, the nitrogen is introduced into different regions of the cooling tunnel of the heat treatment plant, but particularly advantageously injected into the cooling tunnel region arranged in front of the heating chamber inlet and into the cooling tunnel region arranged upstream of the cooling tunnel outlet.

The protective gas entry according to the invention an optimal concentration profile of the protective gas in the heating and cooling chamber of the heat treatment plant is adjusted and at the same time prevents the unwanted influx of atmospheric oxygen into the cooling tunnel of the heat treatment plant.

Expediently, the heat treatment plant is equipped with a lambda probe arranged at the cooling tunnel outlet, by means of which the inflow of environmental pleasure, as well as the nitrogen feed, can be detected.

In order to obtain a protective gas flow directed towards the heating chamber inlet, the volatile constituents which are transported during the heat-treatment-dissipating layers (phosphates, borates, oxalates, etc.) and drawing agent residues of the heat treatment material are transported to the heating chamber inlet where they are flared.

The subsequent condensation of the evaporated components of the material to be treated on the cold walls of the water-cooled cooling registers, the cooling capacity is significantly reduced, so that the cooling devices must be cleaned at longer intervals. This is prevented or greatly reduced by the new gas technology.

Due to the invention, the time, personnel and financial expense in the heat treatment of ferrous materials is substantially reduced and a secure process management possible.

By introducing cryogenic liquid nitrogen into the cooling tunnel of the heat treatment plant, the cooling capacity of the cooling tunnel can be further increased. The liquid nitrogen having a temperature of -196 ° C. is advantageously introduced into the last third of the cooling tunnel, ie into the cooling tunnel area closest to the cooling tunnel outlet for lowering the outlet temperature of the heat treatment material transported from the heating room or into the first third of the cooling tunnel, ie nearest to the cooling tunnel inlet Cooling tunnel area entered to increase the cooling rate of the heat treatment material for hardening purposes. Due to the additional dosage of cryogenic liquid nitrogen in the heat treatment plant, the convection of the protective gas is significantly improved and also allows the heating enthalpy of the nitrogen, a faster cooling of the heat treatedππ workpieces. By a trained according to the particular application and appropriately arranged on the heat treatment system gas sampling device can - at each thermocouple located at the heat treatment plant - process gas is taken to determine the optimum concentration profile of shielding gas over the entire plant length.

The gas sampling device can also be equipped with a gas analyzer, a lambda probe or other measuring systems, whereby no additional gas sampling points are required at the heat treatment plant.

By means of a measuring system coupled to the gas sampling device, all measuring points are controlled (intermittently) and the current gas composition is measured.

The electronically determined measured values are used for the automatic protective gas control at a gas composition deviating from a predetermined nominal value.

Due to the protective gas metering according to the invention, the protective gas concentration in the heating chamber of the heat treatment plant is increased by about 50 to 60 percent, so that the entry amount of endogas can be reduced by about 30 to 40 percent.

In addition, it ensures that the sum of the concentration of carbon monoxide (CO) and hydrogen (H2) in the cooling tunnel end is less than 5% by volume, which is below the explosion limit of the protective gas. This is particularly important because the protective gas temperature in the outlet area of the heat treatment plant has approximately room temperature and thus far below the safety temperature of 750 ° C.

The protective gas entry according to the invention forms a reaction front, which flows counter to the heat treatment material, ie, the partially reacted endotherm escapes via the heating chamber inlet and thus only nitrogen-displaced endogas flows into the cooling tunnel, whereby the undesired oxidation of iron in the cooling tunnel of the heat treatment system is substantially reduced because the H2O / H2 ratio in the cooling tunnel is much lower than in the boiler room of the heat treatment plant.

The fact that the protective gas in the cooling tunnel has a significantly lower dew point (for example -7 degrees Celsius) than in the heating chamber (for example +10 degrees Celsius) prevents water condensation in the cooling tunnel of the heat treatment plant.

Due to the high concentration of endogas in the heating chamber of the heat treatment plant, the kinetics of carburizing or recarbonization during the heat treatment are greater, so that the residence time of the heat treatment material in the heating chamber is substantially reduced.

In addition, due to the high concentration of endogas in the heating chamber of the heat treatment plant, the kinetics of the reduction of iron oxide to hot-deformed iron alloys, such as wires, pipes, profiles, particularly large, so that their oxide layers are completely reduced. The oxide-free workpieces can then be processed with reduced effort, such as pickled, be and have the ever increasing expectations of surface quality. The endogas used according to the invention for heat treatment also has a much higher "reduction power" than conventionally used exogas, ie it can form and absorb more water and carbon dioxide without the reduction being stopped becomes.

The higher concentration of hydrogen (H2) and carbon monoxide (CO) in the boiler room of the heat treatment plant results in a higher heating rate of the heat treatment material than with conventional protective gas of exogas or monogas (N2 less than 5% H2).

The endogas and nitrogen feed according to the invention has the significant advantage that a concentration profile of the reactive components is advantageously established, whereby the risk of explosion is reduced and the reaction kinetics and heating rate are optimized.

The invention will be explained in more detail with reference to an exemplary embodiment.

Show it:

Fig. 1 Graphical representation of the controllability of the carbon activity of exogas and Endohn gas in the heat treatment of iron-carbon alloys;

Fig. 2 Graphical representation of the nitrogen concentration as a function of the Endogas endolm protective gas used in a heat treatment plant with Kuhltunnel.

In Fig. 1, the controllability of the carbon activity of exogas and endogas (Endolin) in the heat treatment of typical iron-carbon alloys is shown with a carbon content of 0.15 to 0.70% In such, in a temperature range of 400 to 900 ° C. The heat treatment is compared with the carbon activities a _c of a conventional protective gas (exogas) and of several protective gases (endogas in the form of endolin) with 1 to 5% CO. It can be seen from Fig. 1 that when using an endogase with 1% CO at a temperature of high 650 ° C and using a endogase with 5% CO, the carbon activity a _{c is} reduced to less than 1, in which the iron-carbon Alloys are decarburized during the heat treatment. It can also be seen from FIG. 1 that the carbon activity a _c of equal to / less than 1 caused in the temperature range 650 to 740 ° C. can be regulated via the mixing ratio endogas / nitrogen, such as, for example, 1 to 1: 3. Thus, by using protective gas mixtures of endogas and nitrogen recarbonization of decarburized iron-carbon alloys during the heat treatment is easy to implement. At temperatures of greater than 740 ° C, the nitrogen gas added endogenous gas must be added to the carbon activity a _c to the value of 1 gas, preferably propane, because of its significantly better reactivity with water and carbon dioxide. Furthermore, the carbon activity in the heating chamber gas can be increased by lowering the dew point in the generated endogenous gas at the endogenerator, since with decreasing water concentration in the endogas, the carbon activity increases in the mixed gas. Fig. 2 shows an oven (boiler room) with Kuhltunnel, wherein once endogas with a quantity of nitrogen premixed in the last third of the boiler room and the main amount of pure nitrogen in the middle / last third of the cooling tunnel are fed (variant 2). In variants 1 and 3, different amounts of endogas (10 and 30 m3 / h) are mixed with nitrogen externally of the furnace and fed completely into the feed point in the boiler room, ie the same concentrations of hydrogen and carbon monoxide prevail at each point in the boiler room and cooling tunnel For all 3 variants is the Total amount of gas always kept constant at 140 m3 / h. With variant 2 results in external complete mixture of endogas and nitrogen, a hydrogen concentration of 5.8 vol .-% H2, ie, the explosion limit of 5 vol .-% H2, CO is significantly exceeded. Dividing this total amount of variant 2, in endogas / N2 mixture and N2 and feeds the two streams at a suitable location, resulting in concentrations of hydrogen in the boiler room of 9 vol .-% H2 and in the cooling tunnel of 2.8 vol .-% H2, ie close to the required explosion limit. The hydrogen concentration is thus 40% higher in the boiler room and 40% lower in the cooling tunnel than the complete mixture of endogas and nitrogen. It has formed a directed gas flow of nitrogen from the cooling tunnel in the boiler room. Based on the measured concentrations of hydrogen, it can be seen that the nitrogen flows are directed to approximately two equal parts, so that the dilution in the cooling tunnel and concentration in the boiler room and gas removal to the boiler room inlet are optimal. Variant 3 illustrates that it is only possible with a small amount of endogas (10m3 / h) to realize the safety condition of less than 5% by volume H2, CO.

Variant 2 thus implements the aspects of safety and the highest possible H2, CO concentration in the boiler room.

Claims

1. A process for the heat treatment of iron materials, in particular for the annealing of pipes, profiles wires, rods and sheets of metal or steel, in a heat treatment plant with a cooling tunnel and a boiler room under a protective gas atmosphere of endogas mixtures, characterized in that pure endogas or partially diluted with nitrogen endogas and additional pure nitrogen separately from each other and in different plant areas are fed.

2. The method according to claim 1, characterized in that the endogas is entered directly into the boiler room of the heat treatment plant.

3. The method according to claim 1 or 2, characterized in that, preferably from carbon monoxide (CO), hydrogen (H2) and nitrogen (N2) existing endogas, preferably in the Heizraumende and is injected transversely to the transport direction of the heat treatment.

4. The method according to claim 1, characterized in that the nitrogen used in addition to the endogas is injected into different areas of the cooling tunnel of the heat treatment plant.

5. The method according to any one of claims 1 to 3, characterized in that the produced undiluted endogas has a dew point of +5 to + 15 ° C.

6. The method according to claim 5, characterized in that the endogas is fed by at least one automatic metering valve in the boiler room of the heat treatment plant.

7. The method according to any one of claims 1 to 6, characterized in that the metered amounts of endogas and nitrogen fed into the heat treatment plant are detected and used to determine the current oxygen and carbon activities during the heat treatment.

8. The method according to any one of the preceding claims, characterized in that for better convection of the endogases in the boiler room the endogas nitrogen is added outside the heat treatment plant.

9. The method according to any one of the preceding claims, characterized in that the required carbon activity of the gas phase is set in the boiler room of the heat treatment plant on the dew point of the pure endogases generated in the generator.

10. The method according to any one of the preceding claims, characterized in that the degassing gas, such as. As propane or natural gas, in which the boiler room of the heat treatment plant fed Endogasgemisch is metered and forms a homogeneous gas phase outside the gas feed.

1 1.Verfahren according to any one of the preceding claims, characterized in that at too high carbon activity, air in the boiler room of the Heat treatment plant fed Endogasgemisch is metered and forms a homogeneous gas phase outside the gas feed.

12. The method according to any one of the preceding claims, characterized in that the oxygen activity of the boiler room atmosphere is controlled in the propane or air is metered into the heating chamber supplied Endogasgemisch and forms a homogeneous gas phase outside the Gaseinspeisstelle and thereby avoided surface defects on the annealing become.

13. The method according to claim 8, characterized in that the endogas is introduced at an overpressure of 40 to 60 mbar, preferably by a arranged in the nitrogen pipe curved mixing tube in which an excess pressure of 20 to 30 mbar having nitrogen.

14. The method according to claim 8, characterized in that the endogas with an overpressure of up to 60 mbar, preferably by an injector, which sucks and mixes the endogas with the aid of the nitrogen stream and thereby generates a homogeneous diluted endogas, is registered.

15. The method according to any one of the preceding claims, characterized in that the metered amounts of natural gas and air and thus the metered amount of endogas depending on the ruling in the arranged at the heat treatment plant endogas-nitrogen pipe ram pressure can be controlled.

16. The method according to any one of the preceding claims, characterized in that the nitrogen is injected into the cooling tunnel with a first partial flow in the direction of the Heizraumeinlaufs and with a second partial flow in the direction of the Kühltunnelauslaufs the heat treatment plant.

17. The method according to claim 1 1, characterized in that the metered amount of nitrogen is regulated by means of a arranged in the outlet region of the heat treatment plant lambda probe.

18. The method according to any one of the preceding claims, characterized in that the evaporating from the boiler room of the heat treatment plant volatile components of the heat treatment material transported to the inlet of the heat treatment plant and flared and dissipated there.

19. The method according to any one of the preceding claims, characterized in that preferably liquid nitrogen is preferably fed into the first third of the Kühltunnelauslauf nearest cooling tunnel area or preferably in the last third of the Heizraumauslauf nearest cooling tunnel area of the heat treatment plant.

20. The method according to any one of the preceding claims, characterized in that the protective gas for determining its concentration profile during the heat treatment process over the entire length of the heat treatment plant by means of at least one arranged on the heat treatment plant gas sampling device removed from the heat treatment plant and after subsequent electronic processing for automatic control of Endogas and nitrogen supply in the heat treatment plant use place.

21.A method according to one of the preceding claims, characterized in that the sum of the concentrations of carbon monoxide (CO) and hydrogen (H2) at the end of the cooling tunnel of the heat treatment plant is less than 5% by volume.

22. The method according to any one of the preceding claims, characterized in that the dew point of the inert gas diluted with nitrogen in the cooling tunnel is lower than in the heating chamber of the heat treatment plant.