JPS5980730A - Method for recovering sensible heat from steel strip coil - Google Patents

Abstract

PURPOSE:To recover the sensible heat possessed by a steel strip of a high temp. in a utilizable form with a molten salt as a heat medium by putting the coil of a hot-rolled steel strip or the coil of a cold-rolled steel strip subjected to a heat treatment in a molten salt tank, putting the molten salt in the tank, and heating the same with the coil then circulating the salt between a heat exchanger and the tank. CONSTITUTION:A high temp. coil 3 of a hot-rolled steel strip or cold-rolled steel strip subjected to an annealing treatment is put into a molten salt tank 2 contg. a molten salt 1 consisting of KNO3, NaNO3, NaNO2 and the molten salt is heated by the sensible heat possessed by the coil 3 and is pumped 4 to a heat exchanger 5. The water 6 of the heat medium is heated by the exchanger 5 to steam 7 of a high temp. which is removed from the exchanger and is utilized. The molten salt cooled in the exchanger 5 returns to the tank 2 where the salt is again heated by the coil 3 and runs in the circulation route toward the exchanger 5. If the heat transmission pipe part 27 of the heat exchanger or a boiler is disposed in a molten salt bath 25, the need for the piping for circulating the molten salt is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering sensible heat possessed by a steel strip coil.

Steel strips manufactured by hot rolling mills and cold rolled steel strips treated in heat treatment furnaces are wound into coils, and the temperature is 4.
00°C to 800°C. This sensible heat is currently not utilized at all and is dissipated by air or water cooling.

As a method of recovering this heat, a process has been proposed in which the coil is immersed in a water bath and the sensible heat of the coil is recovered as hot water of 70°C to 100°C, but the thermal potential of the hot water obtained is small and the use of hot water is difficult. Since there are only a few points, there are many practical applications. In this case, if operated under pressure, the temperature will rise to 100°C.
Although it is possible to obtain hot water or steam of the above amount, it is difficult to realize because it involves difficulties in equipment technology.

The present invention recovers high potential heat by operating under normal pressure by using molten salt as a heat medium when recovering sensible heat from a steel strip coil.

The gist of the present invention is to heat the strip steel into a coil once from 0°C to 4°C.
A molten salt tank at 00°C≦2 is charged, the sensible heat of the coil is transferred to the molten salt, and the molten salt is introduced into a boiler or a heat exchanger to generate steam or heat a heat medium. Since the molten salt at this temperature is liquid under normal pressure and does not boil, the molten salt tank into which the steel strip coil is charged can be operated while being open to atmospheric pressure. The equipment required to implement this method is a molten salt tank, a molten salt transfer piping system, a heat exchanger (or boiler), and some incidental equipment, and heat recovery can be performed with a simple equipment configuration. be.

Conventionally, methods have been proposed in which the metal strip is unwound and immersed in a molten salt bath sequentially from the tip to perform heat recovery. It has the disadvantage that it requires a lot of complicated equipment such as guide rolls, roll drives, boilers, etc.

In the present invention, since heat recovery is performed without unwinding the coil, the necessary equipment can be achieved with the simple equipment described above.

The present invention will be specifically described below based on embodiments shown in the drawings.

FIG. 1 shows the basic configuration of the present invention.

Molten salt tank 2 (2 is filled with molten salt 1, which is circulated between molten salt tank 2 and heat exchanger 5 by pump 4. A plurality of these tanks and devices may be provided. The coil 3 is charged into the molten salt tank 2 using tongs not shown in the figure.The molten salt 1 is heated by the sensible heat of the coil 3, and the molten salt 1 is transferred to a heat exchanger or boiler 5 (hereinafter referred to as a heat exchanger etc.). ), water supply or heat medium 6 (hereinafter referred to as water supply, etc.)
is heated to generate steam or high temperature heat medium 7 (hereinafter referred to as steam etc.). This steam etc. is used for heating and other purposes. When heat recovery is complete, the coil is removed by tongs (not shown) and a new coil is inserted.

FIG. 2 shows another embodiment of the invention. The molten salt tanks 14 and 15 are filled with a molten base cylinder, 21, and a pump 16.1
It is circulating by 7. The hot steel strip coil 18 is introduced into the tank 14 by means of tongs (not shown). Approximately half of the sensible heat is recovered in the tank 14, and the coil whose temperature has decreased slightly is transferred to the tank 15, where the remaining sensible heat is recovered. In this way, the melting base cylinder in the tank 14 becomes high temperature, and the melting base cylinder in the tank 14 becomes hot.
The molten salt in 5 has a lower temperature C2. Below tank 1
4 is called a high temperature tank, and tank 15 is called a medium temperature tank.

The feed water etc. 9 is preheated by a heat exchanger etc. 13 and further heated to a high temperature by a heat exchanger etc. 12 to become steam etc. 11. With this method, higher temperature steam etc. can be obtained compared to the above method.

In FIG. 2, the tank has two stages, but it may have three or more stages. Furthermore, instead of a multistage tank, a single long tank may be used, and the molten salt may be continuously flowed from the low temperature section to the high temperature section, and the coil may be continuously transferred from the high temperature section to the low temperature section. In that case, the configuration is as illustrated in FIG.

A partition wall may be installed in this long single tank to prevent mixing of the molten salt in the low temperature section and the high temperature section. In FIG. 4, A is a conveyor for transferring coils.

Note that the heat exchanger etc. 13 in FIG. 2 may be omitted.

In that case, the pump 17 may be omitted and a gutter or a communication pipe may be provided between the tanks 15 and 14 to allow natural flow of the molten salt.

FIG. 3 shows yet another embodiment. In the molten salt bath 5 a heat exchanger or heat exchanger tube section n of a boiler is arranged. In this method, it is not necessary to install a molten salt circulation piping system.

The present inventors tested a 600°C steel strip coil in a molten salt bath for 30°C.
A test was conducted to cool down to 0°C and recover sensible heat corresponding to the temperature difference during this time.

The molten salt used was a mixed salt of 53% potassium nitrate, 7% sodium nitrate, and 40% sodium nitrite.

The melting point of this mixed salt is 140°C, and it can be handled as a normal liquid at temperatures above 160°C. In this example, it was used at 200°C.

Heat was recovered from 600°C to 300°C using a hot rolled steel strip coil. The time required for one coil is 3 hours. The amount of sensible heat recovered is 180 M, T per coil 1.
and the sensible heat of the coil at 600°C is 350 M, T/
This means that 51 pieces of t have been collected.

As described above, the present invention is a highly practical sensible heat recovery method that can recover sensible heat from a steel strip coil with simple equipment. In addition, in this method (2), the molten salt plays the role of a heat storage material, so even if the production of steel strip coils is carried out intermittently, steam or high-temperature heat transfer medium can be continuously generated. In this sense as well, it is an excellent method for recovering waste heat.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the basic configuration of the present invention, FIG. 2 is an explanatory diagram of another embodiment of the invention, FIG. 3 is an explanatory diagram of still another embodiment of the invention, and FIG. 4 is an explanatory diagram of another embodiment of the invention. FIG. 2 is an explanatory diagram of a modification of the embodiment shown in FIG. 2; 1; Molten salt 2; Molten salt tank 3; Steel strip coil 4
;Pump 5;Heat exchanger (or boiler) 6:
Water supply (or heat medium) 7; Steam (or high temperature heat medium)
8: Valve 9; Water supply (or heat medium) 10; Medium temperature water (
or steam or heat medium) 11; steam (or high temperature heat medium) 12; heat exchanger (or boiler) 13: heat exchanger (or boiler) 14.15; molten salt tank 16
．． 17; Pump 18.19; Steel strip coil added, 21;
Molten salt 22: Water supply (or heat medium) 23; Steam (or high temperature heat medium) 24; Molten salt B: Molten salt tank 26
;Strip coil n;Between heat transfer tubes;Conveyor No. 1 @ Rod 2" 3rd issue Fig. 4

Claims (1)

[Scope of Claims] 1. A strip characterized in that a steel strip is immersed in the form of a coil in a molten salt bath, the sensible heat of the steel strip coil is transferred to the molten salt, and the heat retained in the molten salt is recovered. Sensible heat recovery method for steel coils. 2. Sequentially immerse the steel strip in the form of a coil in the higher temperature molten salt section of a plurality of molten salt tanks or a long single molten tank, and then transfer the coil to a lower temperature molten salt section, or A method for recovering sensible heat from a steel strip coil, comprising transferring salt to a higher temperature molten salt side to obtain a higher temperature molten salt, and then recovering the heat retained in the molten salt. 3. A method for recovering sensible heat from a steel strip coil according to claim 1 or 2, wherein the heat recovery means is a boiler or a heat exchanger. 4. The sensible heat recovery method for a steel strip coil according to claim 1 or 2, wherein the heat recovery means is a molten salt tank C; a high temperature heat medium is obtained by the disposed heat transfer tubes.