DE102009037370A1 - Plant for pickling of hot rolled steel strip and regeneration of the used pickling acid in a closed heating circuit, comprises heat exchangers, which circulate the fluid in venturi- and washer circulation - Google Patents

Abstract

The plant for pickling hot rolled steel strip and regeneration of the used pickling acid in a closed heating circuit, comprises heat exchangers, which circulate the fluid in venturi- and washer circulation. The fluid is in direct contact with the pickling good and the heat exchangers transmit the heat and start the pickling process in the first both short pickling containers. The additional cooling carries out the regeneration process to slight emission so that considerable steam quantities for the operation of the heat exchanger are saved.

Description

Problem:

It is known to be used for irritating steel strip acids. This is done in stimulating baths with temperatures of 80-85 ° C. Depending on the temperature of the incoming bands in these bands high amounts of heat are necessary, which are transmitted by means of steam in heat exchangers. Thereafter, the used pickling acid is passed into the tank farm and cooled off. During the subsequent regeneration process, the acid is heated in the oven to 650 ° C (spray roaster) or 900 ° C. Thereafter, in the Venturi, the exhaust gas temperature is reduced to 85 ° C. by the circulated acid concentrate. The rest of the waste heat is released through the chimney to the environment. This creates considerable energy costs in both separate systems.

Solution:

The advantages achieved by the invention are that the waste heat present in the regeneration and the pickle is sufficient to heat the tape to be pickled. Furthermore, the cooling of the exhaust gas results in lower emissions. Heat exchangers in the exhaust stream are not necessary, since the pickling tank act as a circulation tank for venturi and scrubber circuits.

Embodiment:

In the drawing of the summary is a combined pickling regeneration to see that has closed heat cycles to irritate the pickling.

Summary

1. Designation

Plant for the stimulation of hot-rolled steel strips and for the regeneration of the used pickling acid in a closed heat cycle

2nd short version

2.1 Technical problem of the invention

In the hot-rolled steel irritation, various acids are used to clean the hot strip surface of oxides, so-called scale.

• • Konzentration der Beizsäure in Bezug auf Gehalt an freier Säure, Gesamtsäure und Eisengehalt
• • Temperatur der Beizsäure in allen Beiztanks je nach Beizgut zwischen 60 und 85°C

In order to achieve a sufficient reactivity of the pickling acid and thus a quality-appropriate, scale-free hot strip surface for the further processing of the steel strip, the following parameters are to be regulated continuously:

• Concentration of pickling acid in terms of free acid content, total acidity and iron content
• • Pickling acid temperature in all pickling tanks between 60 and 85 ° C depending on pickling material

In particular, for heating the strip in pickling tank 1 considerable amounts of heat must be introduced. For this reason, steam-heated heat exchangers are installed for each pickling bath, and the pickling acid is pumped through these heat exchangers by means of circulating pumps. The reheated acid enters the pickling tubs in contact with the pickling material and thus heats the continuous steel strip. Usually, these heating circuits are dimensioned so that even at maximum pickling capacity and down to -5 ° C temperature of the incoming steel strip, the required temperature of 85 ° C can be achieved. This requires the installation of a heat exchanger capacity of 0.11 kcal / kg / K, which requires considerable initial cost with pumps, filters and heat exchangers. By and large, high maintenance costs for pumps and heat exchangers and high costs for the steam and power consumption of the pumps are constantly being incurred. For a pickling with an operating hourly output of 250 t this corresponds to a consumption of approx. 2000 Mcal / h. The installed capacity of all heating circuits can be up to 10,000 Mcal / h.

After the pickling process, the so-called pickling at a temperature of about 80 ° C flows into the tank farm of the hydrochloric acid regeneration. Here it is usually stored for a few hours and cooled to ambient temperature.

In the subsequent regeneration process, the cooled acid is first preconcentrated in the so-called Venturi cycle. Here it comes into direct contact with the hot exhaust gases of the reactor, the temperature of which is 400-450 or 850-950 ° C, depending on the regeneration process. The aim of the process is also to cool the roasting gases below 85 ° C. This is necessary, on the one hand to allow the absorption of hydrogen chloride gas to rinse water to regenerated hydrochloric acid and also to protect the components of the absorption column and in this case the column filling from thermal influence. Depending on the type of plant, 750 or 1000 kcal / l / h are required here, which corresponds to a consumption of 6750 Mcal / h for a 9000 l / h Sprühöster plant.

The roasting gases are then fed by means of an exhaust fan to a gas scrubber. Here, washing water is circulated in a washing column and also brought into contact in a column filling. The circulation water heats up to 50-65 ° C. It is later used in the absorption column to produce regenerated acid.

After the regeneration process, the regenerated acid is returned to the tank farm, where it cools to the outside temperature.

After the task of regenerated hydrochloric acid in the last pickling bath, this must of course be heated to the pickling bath temperature of about 80 ° C.

It can be seen that both the pickling acid and the exhaust gases change their temperature level several times. The heat available is largely released to the environment, while in the stain it is sometimes difficult to raise the temperature level or, as in Venturi, lower it.

A use of the waste heat of the regeneration process has been frequently suggested. However, this was based on the use of heat exchangers. However, this is not unproblematic in the Venturikreislaufes due to the medium and the high concentrations.

In the scrubber, on the other hand, a high amount of heat is available, but the temperature difference is very low at exhaust gas temperatures of 60-70 ° C. In addition, these heat exchangers would result in a considerable increase in investment.

2.2 Solution to the problem

The previously thermally countercurrent processes of pickling and regeneration are now linked together so that there is a direct contact of the circulating fluids both with the exhaust air, as well as the tape to be picked. In detail, the following circuits are provided. (See charge 1)

Exhaust scrubber 1 in regeneration

• • Durch das durch die Bandaufheizung abgekühlter Umwalzwasser ergibt sich eine bessere Abscheidung von HCl-Gas, im Wäscher. Die Emissionen werden verringert, zusätzlicher Verbrauch von Wasser oder Neutralisationsmittel kann vermieden werden.
• • Durch das säurehaltige Spülwasser werden die in der Zunderoberfläche befindlichen Risse und Fehlstellen bereits mit Flüssigkeit gefüllt. Der Säureaustausch im darauf folgenden Beizbad 0 erfolgt schneller, da die Säure direkt die Bandoberfläche erreichen kann und nicht erst die in den Fehlstellen befindliche Luft verdrängt werden muss.

The scrubber recirculation pump ( 1 ) with a capacity of 80-140 m ³ / h acts on the exhaust gas scrubber 1 ( 2 ) with circulating water. As a storage container serves for this purpose directly the heating tank ( 3 ) or a circulation container ( 4 ). The water heats up to 60-70 ° C. It then flows back into the heating tank 1 through which the tape is passed. With a bath length of 12 m and a pickling speed of 180 m / min results in a residence time of 4 seconds, which already leads to a warming of the band. Depending on the outside temperature, the belt leaves the heating tank at a temperature of 50-60 ° C. The heating container collects both circulated water from exhaust scrubber 1 ( 2 ) and the gas scrubber of the pickling as well as the 85 ° C hot water from the rinse tank 1 ( 5 ). The following additional effects are achieved:

• • By the Umwalzwasser cooled by the belt heating results in a better separation of HCl gas, in the scrubber. The emissions are reduced, additional consumption of water or neutralizing agent can be avoided.
• • The acidic rinse water already fills the cracks and flaws in the scale surface with liquid. The acid exchange in the subsequent Beizbad 0 is faster because the acid can directly reach the surface of the strip and not only the air in the flaws must be displaced.

Venturi cycle

The Venturi ( 6 ) is by means of a circulation pump ( 7 ) applied with a circulation rate of 100-130m ³ / h so-called concentrate.

• • Das Beizgut wird ohne jede zusätzliche Temperaturzufuhr auf 85°C erwärmt, es ist keinerlei Dampf zur Badaufheizung notwendig.
• • Die freie Säure im Venturikonzentrat ermöglicht bereits hier einen schnellen und effizienten Beizprozess, die darauffolgenden Beizbäder können entsprechend der Anlagenleistung verkürzt werden.
• • Eine zusätzliche Umwälzung der Beizsäure ist nicht notwendig, auf diverse Pumpen, Wärmetauscher und den kontinuierlichen Energieverbrauch der Pumpen kann verzichtet werden.
• • Für einen separaten Betrieb des Beiz- und des Regenerationsteiles mit eingeschränkter Anlagenleistung (z. B. nach Wartungsstillständen) können kleinere Pumpen und Wärmetauscher installiert werden, so dass nur ein Bruchteil der Installationskosten für herkömmliche Aufheizkreisläufe entsteht.
• • Konzentrationsänderungen und andere negative Einflüsse im Venturikreislauf werden vermieden, da sich bei gleicher Beizleistung eine gleiche Eisenbelastung des Konzentrates ergibt.

The return of the Venturikonzentrates takes place in the composite system directly into the pickling tank 0 or its storage container ( 9 ). The 85 ° C warm concentrate has direct contact with the pickling material. From the pickling bath 0, the concentrate becomes the Venturi ( 6 ) pumped. This leads to the following effects:

• • The material to be treated is heated to 85 ° C without any additional temperature supply; no steam is needed to heat the bath.
• • The free acid in the Venturi concentrate already enables a fast and efficient pickling process here, the subsequent pickling baths can be shortened according to the plant's performance.
• • An additional circulation of the pickling acid is not necessary, various pumps, heat exchangers and the continuous energy consumption of the pumps can be dispensed with.
• • For separate operation of the pickling and regeneration parts with limited system performance (eg after maintenance shutdowns), smaller pumps and heat exchangers can be installed, resulting in only a fraction of the installation costs for conventional heating circuits.
• • Concentration changes and other negative influences in the Venturi cycle are avoided, since the same pickling power results in the same iron load on the concentrate.

absorption column

In the absorption column ( 10 ), the roasted gases cooled to 85 ° C are treated with rinsing water. This in turn produces hydrochloric acid, which flows to the tank farm as so-called regenerated acid and is later returned to the pickling process. The rinse water can be taken directly from the heating container ( 4 ). Furthermore, from this container, the Venturi circuit can be acted upon with rinse water for density control of the concentrate.

The reflux from the absorption column can directly into the last pickling tank ( 11 ), so that the 85 ° C hot rain rate also contributes to energy savings. Only surplus quantities are discharged into the tank farm in a regulated manner.

2.3 Application

The invention is applicable to cold rolling mills which have strip pickling systems for descaling hot-rolled coils. It is particularly useful if a workup (regeneration) of the spent pickling acid takes place at the same site. Additional effects arise in cold rolling mills that are not located in integrated smelting works. In these cases, the steam must be generated to heat the pickling acid and can not be taken from the energy network of the plant.

The invention is applicable to new plants or for the modernization of existing plants.

• • Reduzierung der zum Aufheizen des Bandes notwendigen Energie um bis zu 100%, verglichen mit konventionellen Anlagen
• • Schnellerer und effektiverer Beizprozess durch schnellere Bandaufheizung und günstigerer Säurewerte
• • Reduzierung entstehender Abwasser und entfallende Neutralisationskosten
• • Bessere Abgaswerte in der Regeneration durch kühlere Umwälzkreisläufe und somit besserer Abscheidung von Aerosolen
• • Anwendung ist in Verbindung mit Sprühröst- und Fließbettregenerationen möglich.
• • Geringerer Investitionsbedarf im Bereich der Beizanlage durch fehlende Aufheizkreisläufe
• • Wegfall der Umwälzungen im Normalbetrieb der Beizanlage und dadurch Wegfall des Energieverbrauchs für die Pumpen
• • Bessere Produktqualität durch effektiven und schnellen Beizprozess.

By combining previously thermally countercurrent processes in the closed material cycle between a pickling plant and a hydrochloric acid regeneration, the following advantages can be achieved:

• • Reduce the energy required to heat the belt by up to 100% compared to conventional systems
• • Faster and more effective pickling process with faster strip heating and lower acidity
• • Reduction of emerging wastewater and negligible neutralization costs
• • Better exhaust emissions in regeneration due to cooler recirculation cycles and thus better separation of aerosols
• • Application is possible in conjunction with spray roast and fluid bed regeneration.
• • Lower investment requirements in the area of the pickling plant due to the lack of heating circuits
• • Elimination of the circulation during normal operation of the pickling plant and thus the elimination of energy consumption for the pumps
• • Better product quality through effective and fast pickling process.

Claims (1)

Both systems are combined so that a direct combination of the pickling and the regeneration process takes place. For heat exchange, no heat exchangers are used, but the circulation fluids in venturi and scrubber cycle. The liquids come into direct contact with the pickling material, transfer the heat and start the pickling process in the first two short pickling tanks. The additional cooling of the regeneration process leads to lower emissions. Considerable amounts of steam For the operation of the heat exchangers can be saved.

Images