GB2117105A

GB2117105A - Heat exchanger for recovering thermal energy from highly corrosive fluid substances

Info

Publication number: GB2117105A
Application number: GB08207289A
Authority: GB
Inventors: Masayuki Kosaka
Original assignee: Mitsui Mining and Smelting Co Ltd
Current assignee: Mitsui Mining and Smelting Co Ltd
Priority date: 1982-03-10
Filing date: 1982-03-12
Publication date: 1983-10-05
Also published as: FR2523289B1; AU555447B2; DE3208665A1; FR2523289A1; GB2117105B; AU8135282A

Abstract

A heat exchanger is characterized in that a low melting point alloy 9 having a high thermal conductivity, a high boiling point and a low vapour pressure at high temperatures is filled inside a box 1 which comes in contact with corrosive fluid substance, or the heat source, and that a pipe 7a, 8 through which water and steam used as a heat transmitting medium circulates is arranged in the low melting point alloy in heat exchange therewith directly or (as shown) via a heat transmission panel 7. <IMAGE>

Description

SPECIFICATION Heat exchanger for recovering thermal energy from highly corrosive fluid substances The present invention relates to a heat exchanger for recovering thermal energy from highly corrosive fluid substances in a safe and effective manner.

A large amount of thermal energy is contained in corrosive substances exhausted from biastfurnace sintering device, distillation furnace, vaporization furnace, boiler and the like (for smelting nonferrous metals) such as gasses containing SOx, gasses containing chlorine, flourine, etc. or zinc or molten metal containing zinc, molten matte, molten slag, and the like and it is of great significance to effectively recover such thermal energy.

There is generally known a method for recovering such thermal energy from corrosive fluid substances by introducing corrosive fluid substances of a high temperature generated in a blast-furnace, sintering device and the like into a heat exchanger 01, as shown in Fig. 1, and by contrasting it with a heat transmission pipe 02 inside of which water circulates so that the thermal energy may be recovered by changing the water into hot water or vapor through heat transmission. In the drawings, the reference number 03 denotes a water tank, 04 water, 05 a water supply pump, 06 and 07 water pipes and 08 a radiator. The reference character denotes the flow of the corrosive fluid substance.

In this method, it is necessary to maintain the temperature and pressure of the obtained vapor as high as possible in order to utilize the recovered thermal energy to the fullest extent. Under the conditions observed in the method, however, usual materials for a heat exchanger such as steel, copper, copper alloy or the like are easily corroded by said fluid substances. As a result, the heat exchanger is broken and water and vapor of high temperature and high pressure leak into said fluid substance, which in some cases might lead to a grave accident like explosion.

Use of silicon carbide bricks, graphite bricks and the like which have corrosion resistance against said fluid substances and higher thermal conductivity is conceivable as the materials for the heat exchanger in order to avoid the danger described above. Such materials are, however, inferior in the strength as compared with the conventional materials mentioned above, and it is difficult even to design a structure which can withstand the steam pressure of about 7 kg/cm2G which is commonly employed in heating of a plant, etc. Moreover, since they are vulnerable to thermal shocks at the time of radically heating or cooling and other impacts, it is therefore difficult to construct a heat exchanger of high safety.

Thus the temperature of water at the discharge port was at best 60-700C in the conventional heat exchanger, and the exhaust heat was partly utilized within its limited temperature range in hot-water heating, or otherwise left totally unused.

The present invention aims to provide a heat exchanger for recovering thermal energy from corrosive fluid substances which can overcome the defects as mentioned above in the conventional heat exchangers and which can achieve safe and effective recovery of the thermal energy. In order to achieve the object, the present invention is characterized in gist by the use of a low melting point alloy to be filled inside a box which comes in contact with the corrosive fluid substance, or the heat source, the molten alloy having a higher thermal conductivity, a higher boiling point and a lower vapour pressure at a higher temperature and by the use of pipe system inside of which heat transmission medium circulates and is arranged directly or by way of a heat transmission panel in the molten alloy.

The present invention will now be described with reference to the embodiments as shown in the attached drawings, by way of example, in which: Fig. 1 shows schematically a conventional device for recovering thermal energy.

Fig. 2 shows an embodiment of the heat exchanger according to the present invention in section.

Fig. 3 shows the embodiment of Fig. 2 sectioned in the direction of arrows Ill-Ill.

Fig. 4 is a sectional view of another embodiment.

Fig. 5 is a sectional view of Fig. 4 along the arrows V-V.

Fig. 6 is a diagram of a device for recovering thermal energy using the heat exchanger according to the present invention as the heat exchanger and superheater.

Sectional views of an embodiment are shown in Figs. 2 and 3. An outer box 1 is a rectangular parallelepiped and an opening 2 is projected from its top at the center. The outer box 1 which comes in contact with the high temperature corrosive fluid substances is at its exterior surface provided with a linging of corrosion resistant member 3 such as silicon carbide bricks, graphite bricks and the like having a higher thermal conductivity. An inner box 4 is housed in the outer box 1 with a space from the interior surface of the box 1.

Openings 5 and 6 are projecting from the upper both ends of the inner box 4 and penetrating the outer box 1. The outer surfaces of these openings 5 and 6 are also provided with a iining of corrosion resistant member 3 such as silicon carbide bricks, graphite bricks and the like having higher thermal conductivity. A heat transmission panel 7 provided with a plurality of throughholes 7a and made of a material having a higher thermal conductivity such as low-carbon steel, copper and the like is fixed in the inner box 4. Pipes 8 are welded on the heat transmission panel 7 connecting all the throughholes 7a. The pipe 8 which circulates a heat medium such as water inside the holes 7a comes in from one of the openings 5 of the inner box 4 and comes out from the other opening 6. Said space between the outer box 1 and the inner box 4 is filled with a low melting point alloy 9.The low melting point alloy consists mainly of bismuth and lead and it is possible to maintain its melting point at about 600 C, if necessary, by adding such metals as tin, cadmium and the like. On the other hand, since bismuth and lead respectively have a high boiling point of 1 50O0C or higher, the low melting point alloy 9 can maintain the molten state over a wide range from a temperature as low as 600C to a temperature as high as 1 5000C. In other words, heat exchange can be carried out over an extremely wide temperature range of lower than 1 000C and higher than 1 5000C with the low melting point alloy 0 in molten state.

Let us now consider the heat transmission in the present heat exchanger. The heat transmitted to the corrosion resistant member 3 in direct contact with the heat source will be transmitted to water or the heat transmitting medium in the holes 7a of the heat transmission panel 7 via the outer box 1, the low melting point alloy 9, the inner box 4 and the heat transmission panel 7. In other words, as all of the heat transmitted from the corrosion resistant member 3 to the heat transmission panel 7 is made to pass through the substances having good thermal conductivity, highly effective heat exchange can be achieved even by the device of such a dual structure.

A low melting point alloy 9 mainly consisting of bismuth lead, etc. is used, as mentioned above, for filling the space between the outer box 1 and the inner box 4. This low melting point alloy 9 maintains its steam pressure extremely low when the temperature is as high as 10000C and there is hardly any loss on account of vaporization.

Since the vapour pressure of the low melting point alloy at higher temperature is low and that the vapour pressure can be released in the atmosphere, there is substantially no need to consider the strength of the outer box 1. Materials such as silicon carbide bricks, graphite bricks and the like which have not very high strength but have higher thermal conductivity and corrosion resistance, therefore, can be utilized.

In order to detect leakage of the low melting point alloy 9 due to damages of the outer box 1 or the inner box 4, a level detector 10 for detecting the level of the low melting point alloy is provided in the opening 2 of the outer box 1 and a leakage detector 11 at the bottom of the inner box 4. If by any chance the outer box 1 is broken to cause the low melting point alloy 9 to leak out, the level of the alloy 9 filled in the space between the outer box 1 and the inner box 4 drops to activate the level detector 10 so as to indicate accidents on the outer box 1 and, thereby, enables the operator to easily replace or repair the outer box 1 before the inner box 4 is damaged.The level of the low melting point alloy 9 would also drop when the inner box 4 is damaged but the low melting point alloy 9 in this case would flow into the inner box 4, and the leakage detector 11 detects the abnormal situation.

Figs. 4 and 5 show another embodiment. The heat exchanger comprises a box 1' which opens at its upper portion, heat transmitting pipe 8' which is arranged inside said box 1' in a repeating pattern and a low melting point alloy 9 which is filled inside said box 1' and has a higher thermal conductivity, a higher boiling point and a low vapour pressure at higher temperatures. In Figs. 4 and 5 members identical with those shown in Figs. 2 and 3 have identical reference numbers.

The heat exchanger of this structure is easier to construct and is economically more advantageous as compared with the embodiment described before.

Use of the heat exchanger according to the present invention in place of a conventional heat exchanger enables safe and effective heat exchange even if the temperature of corrosive fluid substances is relatively low at about 3500C.

Saturated vapor of about 7 kg/cm2 G can therefore be easily generated by additional use of vapor/water separator. Further, when an excessively large amount of vapor is recovered in a calory that can not be fully consumed by any ordinary ways such as in heating, the heat exchanger of the present invention can be additionally attached as a superheater as shown in Fig. 6 for generating superheated vapor of high temperature and high pressure which can be effectively utilized, for example, for generating electricity. In Fig. 6 corrosive fluid substance exhausted from blast furnace, sintering device, distillation furnace, vaporization furnace, boiler, etc. such as gasses containing SOx, gasses containing chlorine, flourine, etc., zinc and molten metals containing zinc etc., molten matte, molten slag, etc. is introduced into a heat exchange chamber 12 as indicated by the arrow A.The heat exchange chamber 12 is provided with a heat exchanger 1 3 and a superheater 14 of the structure shown in Figs. 2 and 3. A water pipe 15 is connected to the heat transmission pipe 8 at the inlet port of the heat exchanger 13 and a vapor/water separator 1 6 is connected to said pipe 8 at the discharge port. The steam pipe 1 7 from the vapor/water separater 1 6 connects with the inlet port of the heat transmission pipe 8 of the superheater 14 and the superheated steam pipe 1 8 with the discharge port. In the drawings, the reference number 19 denotes a water tank, 20 water, 21 a water supply pump and 22 a drain pipe.

As has been described above, the heat exchanger according to the present invention enables economical heat recovery by effectively and safely causing highly corrosive fluid substance to generate useful steam.

Claims

1. A heat exchanger characterized in that a low melting point alloy having a higher thermal conductivity, a higher boiling point and a low vapour pressure at higher temperatures is filled inside a box which comes in contact with corrosive fluid substance, or the heat source, and that a pipe through which water and steam used as a heat transmitting medium circulates is arranged in the low melting point alloy directly or via a heat transmission panel.

2. A heat exchanger as claimed in Claim 1 substantially as hereinbefore described with reference to and as illustrated in either Figures 2, 3 and 6 or Figures 4 and 5 of the accompanying drawings.

3. A process for exchanging heat with a corrosive fluid substance which comprises supplying the substance to a heat exchanger as claimed in Claim 1 or Claim 2, and supplying a heat transmitting medium also to the exchanger.

4. A process as claimed in Claim 3 substantially as hereinbefore described.