FR2523289A1 - HEAT EXCHANGER FOR RECOVERING THERMAL ENERGY FROM HIGHLY CORROSIVE FLUID SUBSTANCES - Google Patents

Abstract

THE OBJECT OF THE INVENTION IS A HEAT EXCHANGER FOR RECOVERING THE THERMAL ENERGY FROM CORROSIVE FLUID SUBSTANCE IN A SAFE AND EFFICIENT MODE. THE INTERIOR OF A BOX 1 COMING IN CONTACT WITH THE CORROSIVE FLUID SUBSTANCES, IS FILLED WITH A LOW MELTING POINT ALLOY 9 HAVING GREATER THERMAL CONDUCTIVITY, A HIGH BOILING POINT AND LOW VAPOR VOLTAGE AT TEMPERATURES HIGH, A DUCT 8 FOR THE CIRCULATION OF THE HEAT TRANSMISSION FLUID BEING ARRANGED DIRECTLY IN THEIT ALLOY 9.

Description

The present invention relates to a heat exchanger for

  recovering, in a suave and efficient way, the thermal energy from

  highly corrosive fluids.

  A large amount of thermal energy is contained in corrosive substances that escape from blast furnace sintering devices, distillation furnaces, steam ovens, boilers or similar devices (for non-ferrous metal smelting ) as, for example, gases containing SO, gases containing chlorine, fluorine, etc., zinc or a molten metal containing zinc, molten matte, molten slag and the like, and this energy has a large

  interest if we can recover it effectively as thermal energy.

  There is generally known a method of recovering a

  such energy from corrosive fluid substances, consisting in introducing

  the high temperature corrosive fluid generated in a blast furnace, sintering device or similar apparatus in a heat exchanger (01 in Figure 1) and contacting it with a heat transmission line ( 02 in Figure 1) on the inside

  from which water circulates so that thermal energy can be recovered.

  that by transforming the water into hot water or steam by transmitting

  Always in this same figure 1, the reference 03 designates a reservoir

  see water, 04 represents the water itself, 05 is a water supply pump, o 6 and 07 designate water pipes and o 8 is a radiator Finally the

  reference A symbolizes the circulation of the corrosive fluid substance.

  In this process, the temperature and the voltage of the steam obtained must be kept as high as possible in order to make maximum use of the thermal energy recovered. Under the conditions observed in this process, the usual materials used for the construction of the heat exchangers heat, such as steel, copper, copper alloys,

  etc., however, are easily corroded by said fluid substances.

  As a result, the heat exchanger breaks down and the water and the steam at high temperature and under high voltage infiltrate into the fluid substance, which can sometimes cause serious accidents such as

than an explosion.

  The use of silicon carbide bricks, graphite bricks and similar materials having some resistance to corrosion caused by fluids and having

  higher thermal conductivity, is perfectly conceivable for

  heat exchangers in order to avoid the disadvantages

  These materials, however, are inferior in mechanical strength to conventional materials of which it has been

  question and it is even difficult to achieve a structure capable of

  have a vapor pressure of about 7 105 Pa, commonly used for heating a workshop and for similar purposes Furthermore, because of the susceptibility to heat shock during sudden heating or cooling or other impact, he was so far

  difficult to build a heat exchanger with high security.

  So the temperature of the water at the exit was at best 60-

  700 C in a conventional heat exchanger and the exhausted heat was partially used in its limited temperature range, for the

  heating of the water or this heat remained totally unused.

  The present invention aims to provide a heat exchanger for recovering thermal energy from corrosive fluid substances, to overcome the aforementioned drawbacks of conventional exchangers

  and can ensure a safe and efficient recovery of thermal energy.

  To achieve this objective, the invention is characterized in its essence

  by the use of an alloy having a low melting point and with which

  folds a box that comes in contact with the corrosive fluid substance or

  the heat source, said molten alloy having a thermal conductivity

  high, high boiling point and low vapor pressure at elevated temperatures, with the use of piping within which a heat transfer fluid can circulate, wherein the pipetting is disposed directly into the molten alloy or put in cooperation with this

  last through a heat transmission panel.

  Other objects, features and advantages of the invention are

  will come out of the detailed description which will follow next to the drawings

  in which: FIG. 1 schematically represents a conventional energy recovery device; Figure 2 shows a sectional view of an embodiment of the heat exchanger according to the invention; FIG. 3 represents a sectional view taken along line III III of the embodiment of FIG. 2; Figure 4 is a sectional view of another embodiment; Figure 5 is a sectional view taken along the line V V of the embodiment of Figure 4;

  FIG. 6 is a diagram of an energy recovery device.

  thermal unit using the heat exchanger according to the invention in

  heat exchanger and an overheating device.

  FIGS. 2 and 3 show in section a mode of embodiment

  DESCRIPTION OF THE INVENTION An outer casing 1 in the shape of a parallelepiped

  rectangle is provided with a central opening 2 overlooking its upper face.

  This outer casing 1 which comes into contact with fluid substances cor-

  high temperature rosies having on its outer surface a coating of a corrosion resistant material 3 such as silicon carbide bricks, graphite bricks or similar materials having high thermal conductivity An inner casing 4 is housed in the casing outside 1, a space being provided between this box 4 and the inner surface of the box 1 The box 4 is provided with two openings 5,6 located at both ends of its upper face and overlooking the latter; these two

  openings 5,6 opening out into the outer casing 1

  external faces of the openings 5 and 6 also bear a coating made of a corrosion-resistant material 3, for example carbide bricks,

  silicon, graphite bricks or similar materials having a conductivity

  high thermal conductivity A heat transmission panel 7 having a series of holes Ta extending right through said panel and constructed of a material having a high thermal conductivity, for example a low carbon steel, copper or the like metal , is fixed in the inner casing 4 Pipes 8 are welded to the heat transmission panel 7 so as to ensure the connection of all the holes 7 to the pipe 8, which brings a heating fluid such as water, in the bores

  7a, penetrates into the casing 4 by one of the openings 5 of said inner casing

  4 the space between the outer casing 1 and the inner casing 4 is filled with an alloy 9 having a low melting point. This low-melting alloy comprises mainly bismuth and lead and can maintain its melting point at about 600 C, if necessary, by adding metals such as tin, cadmium or similar On the other hand, since bismuth and lead respectively have a With a high boiling point of about 15,000 C or higher, low-melting alloy 9 can maintain its molten state over a wide range of temperatures from as low as 600 C to such a high temperature In other words, the heat exchange can be carried out in a very wide range of temperatures from less than 100 ° C up to more than 15,000 C, using

  the alloy 9 still in the molten state.

  We will now study the heat transfer in the sample.

  According to the invention, the heat exchanger coating 3, which is resistant to corrosion and is in direct contact with the heat source, is transmitted to the water or to another heat transfer fluid at the bores Ta transmission panel 7, via the outer casing 1, the low-melting alloy 9, the inner casing 4 and the heat-transmitting panel 7 In other words, since all of the heat transmitted from from the corrosion resistant element 3 to the heat transmission panel 7 passes through substances having good thermal conductivity, highly heat exchange can be achieved.

  effective even with a device having such a dual structure.

  A low melting alloy 9 is used, consisting mainly of

  bismuth, lead, etc., as has been said, to fill the space between the outer casing 1 and the inner casing 4 This low-melting alloy 9 maintains its vapor pressure at an extremely low value when the temperature is as high as 10000 C and one observes practically

no loss by vaporization.

  Since the vapor pressure of the low melting alloy at elevated temperature is low and since this vapor pressure can be exhausted to the atmosphere, it is practically useless to take into consideration the resistance of the outer casing 1

  materials such as silicon carbide bricks, gravel bricks,

  phite, etc., which do not have a very high mechanical strength but have a very good thermal conductivity and a very high resistance to

  corrosion, can therefore be used for this purpose.

  To detect a leak of the low-melting alloy 9 following damage to the outer casing 1 or the inner casing 4, a level detector 10 for detecting the level of the low-melting point alloy is disposed in the opening 2 of the outer casing 1 and a leak detector 11 is disposed in the bottom of the inner casing 4 If the outer casing was broken by any accident causing an outward escape of the alloy to low melting point, the level of the alloy 9 in the space between the outer box 1 and the inner box 4 would be lowered to operate the level detector 10 and thus indicate an accident of the structure of the box 1, to allow the operator to replace or repair without difficulty the outer casing 1 before any damage to the inner casing 4 The level of the alloy with low melting point 9 also drops during a damage of the casing i 4, but in this case, the low-melting alloy 9 escapes into the inner chamber 4 and this anomaly is detected by the detector

leak 11.

  FIGS. 4 and 5 show another embodiment of the invention. The heat exchanger comprises a box 1 'open at its upper part, a heat transmission line 8' disposed inside the box 1 'on a box. recurring mode and a low melting point alloy 9 which fills the chamber 1 'and which has a high thermal conductivity, a high boiling point and a low vapor pressure at high temperatures In FIGS. 4 and 5, the identical elements to those described in

  Figures 2 and 3 bear the same numerical references.

  heat of this structure is easier to build and is more

  economically advantageous that the exchanger of the first mode of

tion.

  The use of a heat exchanger according to the invention to replace a conventional exchanger allows a safe and effective heat exchange even if the temperature of the corrosive fluid substances is relatively low (about 3500 C) Saturated steam under a pressure of 100.degree. approximately 7 105 Pa can easily be produced by the additional use of a steam / water separator. On the other hand, if an excessively large quantity of steam is recovered and the calorific value can not be entirely used for ordinary purposes. for example for heating, the heat exchanger according to the invention can be further mounted as an overheating apparatus (see Fig. 6) for generating steam

  superheated at high temperature and high pressure that can be used ef-

  for example, to produce electricity In Figure 6 the corrosive fluid that escapes from a blast furnace, an appliance

  sintering furnace, a distillation furnace, an evaporation furnace, a furnace

  etc., for example gases containing S Ox, gases containing chlorine,

  fluoride, etc., zinc and molten metals containing zinc, the matte

  due, the melted slag, etc., is introduced into a heat exchange chamber 12, as indicated by the arrow A This heat exchange chamber 12 comprises a heat exchanger 13 and an overheating apparatus 14 whose structure is like that shown in Figures 2 and 3 A water pipe 15 is connected to the heat transmission pipe 8 to

  level of the inlet port of the heat exchanger 13 while a separator

  The steam / water reactor 16 is connected to line 8 at the outlet port.

  The steam pipe 17 which leaves the separator 16 is connected to the pipe

  8 at the inlet of the overheating device

  FIG. 14, while the superheated steam line 18 communicates with the ori-

  In the drawings, the reference 19 denotes a water tank, the reference 20 designates the water, 21 is a water supply pump and 22 is a

exhaust pipe.

  As has been said, the heat exchanger according to the invention allows

  economic heat recovery by efficiently and safely

  to a highly corrosive fluid to generate steam

possessing great utility.

FVFçNDTCATTONS

  Heat exchanger characterized in that it comprises a low-melting alloy (9) having a high thermal conductivity, a high boiling point and a low vapor pressure at high temperatures which fills the interior of a box (1,1 ') which comes into contact with the corrosive fluid substance or the heat sourcea conduit (8,8') in which the water circulates and the steam serving as heat transfer fluid being arranged directly in the alloy low melting point (9) or placed in cooperation with the latter by means of a panel of

heat transmission (7).