JP2009074116A - Method for cooling skid pipe in heating furnace, and method for manufacturing metal plate using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for cooling a skid pipe in a heating furnace, which prevents Langelier index from being poorly adjusted because of cooling water having a high temperature in the heating furnace, and can surely prevent the skid pipe from being plugged, and to provide a method for manufacturing a metal plate using the same. <P>SOLUTION: This cooling method comprises the steps of: embedding a thermocouple 105 in skid pipes of a fixed skid 103 and a moving skid 104 in the heating furnace 10, and measuring the temperature of the cooling water in the skid pipe (203); calculating correction values of M-alkalinity and pH due to the movement of the equilibrium of a bicarbonate ion from a difference between the measured temperature of the cooling water and the temperature of the cooling water in a water supply position 222 (204); calculating the Langelier index of the cooling water in the skid pipe from thus determined temperature and correction values of M-alkalinity and pH (201); calculating an amount of an alkali agent to be charged (219); and charging the alkali agent from a charging device 214 on the basis of the result. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for cooling a skid pipe of a heating furnace for heating a metal piece, and more particularly to a method for preventing the skid pipe of a walking beam type continuous heating furnace from being blocked.

  As an example, the case of the heating furnace 10 of the hot rolling line 100 of the steel strip as shown in FIG. 2 is taken as an example.

  Hot rolling is generally a slab-like metal material produced by continuous casting, ingot-making, or ingoting, heated in a heating furnace to several hundred to several hundreds of degrees Celsius, and then placed on a hot rolling line. It is a series of processes of extracting and winding thinly and winding it into a coil shape by rotating the roll while pinching with a pair or a plurality of pairs of rolls.

  A metal material 8 having a thickness of 150 to 300 mm (hereinafter referred to as a material to be rolled) heated to several hundred to several hundreds of degrees Celsius by the heating furnace 10 is rolled to a thickness of 0.8 to 25 mm by a roughing mill 12 and a finishing mill 18. After being thinly extended into a metal plate (metal strip) shape and cooled by the cooling-related equipment 26, the coiler 24 takes up the coil.

  7 is a table roll, 23 is a run-out table, 14 is a crop shear, and 16 is a descaling device. In addition, various sensors for measuring the temperature, dimensions (thickness, width), shape, and the like of the material 8 to be rolled are installed at various locations on the hot rolling line 100.

  50 is a control device, 70 is a process computer, and 90 is a business computer.

  As an example of the heating furnace 10, a case of a walking beam type continuous heating furnace as shown in FIG. 3 will be described as an example.

  101 is a burner, 102 is a furnace wall, 103 is a fixed skid, and 104 is a moving skid.

  In most cases, the temperature in the heating furnace 10 is 1100 ° C. or higher, and may reach 1300 ° C. depending on the material of the material 8 to be rolled. Therefore, the fixed skid 103 and the moving skid 104 that support the steel slab from below in the heating furnace 10. The inside is water cooled.

  A path through which the cooling water for water cooling passes is a skid pipe, and the inside of the skid pipe is cooled by circulating cooling water.

  When the inside of the skid pipe is water-cooled under such conditions, an oxidation reaction occurs between dissolved oxygen in the cooling water and iron on the inner surface of the skid pipe, and corrosion progresses over time.

  In particular, when the system of circulating the circulating cooling water is an open circulation system, oxygen in the atmosphere is absorbed, so that the above-described oxidation reaction and accompanying corrosion are further promoted.

  Further, in the case of circulating cooling water, substances such as chlorine ions and sulfate ions in the cooling water are likely to be concentrated with the evaporation of water due to cooling, and corrosion is easily promoted accordingly.

  Oxidation products produced by corrosion accumulate throughout the system circulating the cooling water or become layered, but if left untreated, this is particularly noticeable in the case of the above-mentioned skid pipes. This may cause a blockage of the water path and the associated heat transfer failure, leading to serious equipment troubles.

  On the other hand, when the calcium hardness and pH in the cooling water are high, when the temperature of the cooling water rises, carbonate ions and calcium ions in the cooling water are saturated, and the route of the cooling water as calcium carbonate and the devices on the route Precipitate on the surface.

  If calcium carbonate is excessively precipitated, the oxidation water product caused by corrosion may cause a blockage of the passage through which the cooling water passes and a heat transfer failure associated therewith, resulting in a serious equipment trouble.

  It is an index that shows the corrosiveness of cooling water and calcium carbonate precipitation for the problem of corrosion and blockage of each device on the path due to the water quality of the cooling water as described above. There is a method of water quality management using the Langeria index.

  That is, for the purpose of adjusting the Langeria index to be within the appropriate range, by introducing a chemical such as an alkaline agent into the cooling water, the water quality can be improved to a low corrosive property or a low calcium carbonate precipitation property. Is used as cooling water.

  As a method using the Langeria index as a corrosive index, there is a method in which a pH adjusting agent typified by an alkaline agent is added to cooling water.

  The method described in Patent Document 1 attempts to reduce the corrosiveness of water in order to prevent corrosion of various water or drainage pipes, and has a low Langerian index and calcium salt in highly corrosive water. In addition, one or both of the alkaline agent and the alkaline agent are injected to reduce the corrosiveness of the service water.

  In addition, the method described in Patent Document 2 adjusts pH and Langeria index by injecting calcium chloride and sodium bicarbonate after reducing pH to 7 or less as a method for reducing the corrosivity of fresh water, This is a method of reducing the corrosiveness.

  All of these methods attempt to improve the water quality by quantifying the corrosiveness of the cooling water using the Langeria index and introducing an alkaline agent.

  As shown in FIG. 4, the method described in Patent Document 3 has a position where water is to be supplied (water supply position) that is open to the atmosphere after the sand filtration pond 212 or the water purification pond 215. The pH, temperature, turbidity, chromaticity, and conductivity are measured to estimate M alkalinity and calcium hardness, and to obtain the Langeria index.

  A conventional method for cooling a skid pipe of a heating furnace is substantially the same as that of Patent Document 3.

As shown in FIG. 5, the cooling water from which impurities have been removed in the sedimentation basin (sand filter basin in Patent Document 3) 212 is lowered in temperature in a cooling tower 220 that is not in Patent Document 3, and then the Patent Document The water is pumped up to an elevated water tank 221 not included in 3 and supplied to the skids 104 and 105 of the heating furnace 10, but the pH, temperature, and M alkalinity are measured at the water supply position 222 (in Patent Document 3, the water quality meter 202 is used). Based on this, the Langeria index is obtained (L1 measurement and calculation device 201 in Patent Document 3), and the amount of alkali agent charged is calculated based on the obtained Langelia index (pH control device 219 in Patent Document 3) and charged. It is the same as that in Patent Document 3 in that an alkali agent is introduced into the cooling water from the device (post-alkali injection in Patent Document 3) 214. .
Japanese Patent Laid-Open No. 06-287777 JP 2004-034001 A Japanese Patent No. 3385767

  However, in an environment that reaches as high as 1300 ° C. as in a heating furnace, the temperature of the cooling water also rises considerably, so that the first dissociation constant and the second dissociation constant of the carbon dioxide species determined by the temperature change. As the chemical equilibrium moves in the direction of decreasing bicarbonate ion concentration and increasing carbonate ion concentration, the hydrogen ion concentration increases and the pH decreases.

  On the other hand, the solubility product of carbonate ions and calcium ions decreases with increasing temperature.

  Overall, due to such changes, the allowable saturation of calcium carbonate decreases as the temperature increases, and calcium carbonate tends to precipitate.

  Therefore, as in the conventional case, when the Langerian index is obtained based on the temperature measurement result of the cooling water at the water supply position, and the alkali agent is added and adjusted based on the result, the inside of the heating furnace skid pipe Then, since the temperature of the cooling water rises more and calcium carbonate tends to precipitate, there is a problem that the skid pipe is likely to be blocked.

  The present invention has been made to solve such problems as in the prior art, and prevents misalignment of the Langeria index resulting from the high temperature of the cooling water in the heating furnace, and reliably blocks the skid pipe. An object of the present invention is to provide a method of cooling a skid pipe of a heating furnace and a method of manufacturing a metal plate using the same.

  That is, the present invention measures the temperature of the cooling water in the skid pipe of the heating furnace, calculates the M alkalinity and pH of the cooling water based on the temperature measurement result, and calculates the M alkalinity and the pH. Using the calculation result, the Langelia index in the skid pipe is calculated, and the amount of alkaline agent input is determined based on the calculation result of the Langeria index.

  As a suitable form, a thermocouple is embedded in the skid pipe of the heating furnace, the temperature of the cooling water in the skid pipe is measured, and the equilibrium transfer of bicarbonate ions from the difference from the temperature of the cooling water measured at the water supply position The correction value of M alkalinity and the correction value of pH are calculated, and the cooling water in the skid pipe is calculated from the temperature of cooling water in the skid pipe, the correction value of M alkalinity, and the correction value of pH. A Langeria index is calculated, an alkaline agent charging amount is calculated based on the Langeria index, and an alkaline agent is charged from a charging device based on the calculation result of the alkaline agent charging amount.

  According to the present invention, a method for cooling a skid pipe in a heating furnace, which can prevent a misalignment of the Langeria index resulting from the high temperature of the cooling water in the heating furnace, and can reliably prevent the clogging of the skid pipe, and uses the same. A method for manufacturing a metal plate can be provided.

The inventors measure the temperature of the cooling water in the skid pipe of the heating furnace, calculate the M alkalinity and pH of the cooling water based on the temperature measurement result, and calculate the M alkalinity and the pH. Using the results, calculate the Langelia index in the skid pipe, and determine the amount of alkaline agent input based on the calculation result of the Langeria index, and found that calcium carbonate precipitation and resulting skid pipe blockage can be prevented. It was.

  FIG. 1 shows an example of an embodiment of the present invention.

  A thermocouple 105 is embedded in the skid pipe, and a unit (203) for measuring the temperature of the cooling water in the skid pipe is newly installed.

  Also, a correction value for M alkalinity and pH due to the equilibrium movement of bicarbonate ions is calculated from the difference between the measured temperature of the cooling water and the temperature of the cooling water at the water supply position (204).

  From the corrected values of temperature, M alkalinity, and pH determined in this manner, a Langelier index of the cooling water in the skid pipe is calculated (201), and the amount of alkali agent charged is calculated based on the Langeria index ( 219).

  Based on the result, an alkaline agent is charged from the charging device 214.

  A thermocouple 105 having both heat resistance and waterproofness is used. The thermocouple 105 is wired along the inner surface of the skid pipe, but the wiring needs to be sufficiently insulated and waterproof. From the viewpoint of ensuring reliability, the thermocouple 105 is preferably attached to three or more locations, and the average voltage thereof is converted into temperature.

  In addition, although heat insulating material is arranged outside the skid pipe, it is difficult to quantitatively grasp the effect of the heat insulating material, and the heat insulating material may partially fall off or be thinned. is there.

  However, as in the present invention, if the Langelia index is obtained based on the measurement result of the temperature of the cooling water in the skid pipe, and further adjusted by adding an alkali agent based on the Langelia index, poor adjustment of the Langeria index can be achieved. This eliminates the possibility of blocking the skid pipe.

  A unit (204) that calculates and outputs correction values for M alkalinity and pH based on the difference between the temperature of the cooling water at the water supply position 222 and the temperature of the cooling water in the skid pipe is also installed.

  Further, the temperature of the cooling water at the water supply position 222 is measured in the same manner as before, but a unit (205) for calculating and outputting the difference from the temperature of the cooling water in the skid pipe is also newly installed. .

  The calculation is performed by referring to a table separately created based on data obtained by experiment in advance, and the calculated M alkalinity and pH correction values are output.

  The M alkalinity and pH at the water supply position 222 are measured in the same manner as in the past. However, these values reflect the calculated correction value, and the M alkalinity and pH of the cooling water in the skid pipe are as follows. Output.

  Using the M alkalinity, pH, and temperature in the skid pipe calculated and output as described above as input, the Langelia index of the cooling water in the skid pipe is calculated (201). The calculation is based on the simple calculation method of Langeria index by the Nodel method.

The Nodel method is commonly used to conveniently calculate the Langeria index,
Langeria index = pH value of water-pHs value
= PH value of water-{(9.3 + A value + B value)-(C value + D value)}
... Formula (1)
The Langeria index can be calculated by the equation (1) given by

  Here, the A value to the D value are shown in Tables 1, 2, 3, and 4 based on the measured amounts of evaporation residue, water temperature, calcium hardness, and M alkalinity remaining after evaporation of water as the test solution. It is a value obtained from the correspondence relationship.

  The amount of alkali agent charged is calculated from the obtained Langeria index (219). The calculation is performed by referring to a table created separately based on data obtained by experiment in advance.

  These measurements and calculations are performed to determine the amount of alkaline agent input, but each measured value and calculation result should be constantly monitored by a computer terminal or the like to ensure maintainability. Is desirable.

As shown in Table 5, when the present invention is applied to the operation of the hot rolling line 100 of steel strip for one year (example of the present invention), the Langeria index is not adjusted at all (no water quality adjustment), or Patent Document 3 It can be seen that, compared with the case where the above method is applied as it is to the cooling of the skid pipe of the heating furnace (conventional example), poor adjustment of the Langeria index can be prevented, and the blocking of the skid pipe can be surely prevented.

The alkali agent may be sodium hydroxide or calcium hydroxide, but here, sodium hydroxide is used.

  The present invention can be applied not only to the hot rolling line 100 for strip steel, but also to a heating furnace for a production line for various metal plates other than steel, as well as a thick plate rolling line equipped with a heating furnace. Needless to say.

Diagram for explaining an example of an embodiment of the present invention Diagram for explaining an example of a hot rolling line Diagram for explaining an example of a heating furnace Diagram for explaining the prior art Diagram for explaining the prior art

Explanation of symbols

7 Table roll 8 Rolled material 9 Width press 10 Heating furnace 12 Rough rolling mill 135 Edger roll 14 Crop shear 15 Finishing side thermometer 16 Finishing scale 18 Finishing rolling mill 19 Work roll 19A Backup roll 20 Looper 21 Finishing side Thermometer 22 Finishing side thickness gauge 23 Runout table 24 Coiler 25 Coiler inlet side thermometer 50 Controller 70 Process computer 90 Business computer 100 Hot rolling line 101 Burner 102 Furnace wall 103 Fixed skid 104 Moving skid 105 Thermocouple 201 L1 measurement , Arithmetic device 202 water quality meter 203 skid pipe cooling water temperature measurement unit 204 correction value arithmetic unit 205 arithmetic unit 211 sedimentation water 212 sedimentation basin (sand filtration basin)
213 Filtered water 214 After alkali injection 215 Water purification tank 216 Water purification 217 Water distribution tank 219 pH control device 220 Cooling tower 221 Elevated water tank 222 Water supply position A Transport direction

Claims (3)

The temperature of the cooling water in the skid pipe of the heating furnace is measured, the M alkalinity and pH of the cooling water are calculated based on the temperature measurement result, and the skid is calculated using the calculation result of the M alkalinity and the pH A method for cooling a skid pipe in a heating furnace, comprising: calculating a Langelia index in a pipe and determining an input amount of an alkaline agent based on a calculation result of the Langeria index. A thermocouple is embedded in the skid pipe of the heating furnace, and the temperature of the cooling water in the skid pipe is measured. From the difference from the temperature of the cooling water measured at the water supply position, Calculating a correction value, a correction value of pH, and calculating a Langeria index of the cooling water in the skid pipe from the temperature of the cooling water in the skid pipe, the correction value of the M alkalinity, and the correction value of the pH; A method for cooling a skid pipe in a heating furnace, wherein an alkali agent input amount is calculated based on the Langelier index, and an alkali agent is charged from a charging device based on a calculation result of the alkali agent input amount. A method for producing a metal plate using the method for cooling a skid pipe of a heating furnace according to claim 1 or 2.

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