WO2021185388A1

WO2021185388A1 - Screw heat exchanger, in particular for bulk materials

Info

Publication number: WO2021185388A1
Application number: PCT/CZ2020/000056
Authority: WO
Inventors: Bohumír Čech; Zbyszek Szeliga; Pavel DVOŘÁK; Radim Fojtů
Original assignee: Vysoká Škola Báňská - Technická Univerzita Ostrava
Priority date: 2020-03-17
Filing date: 2020-12-29
Publication date: 2021-09-23
Also published as: CZ308768B6; CZ2020146A3

Abstract

The invention relates to a screw heat exchanger, in particular for bulk materials, made of a tubular casing (1), in which a driven hollow shaft (4) is rotatably mounted that forms a heat transfer surface and has openings (5) at both ends, wherein the outer surface of the shaft is welded to an outer spiral belt (8) for conveying a material through a gap (7) between the shaft (4) and the casing (1), and the inner surface of said shaft is welded to an inner spiral belt (8) for conveying a material with a sensible heat which is to be transferred, said belts (6, 7) being wound in opposite winding directions.

Description

Screw heat exchangers, in particular for bulk materials

The invention relates to the construction of a helical heat exchanger for the transfer of heat between two pourable materials, which can be used in particular in the production of building materials and in energy technology.

The SNCR method (selective non-catalytic reduction) is a method for reducing the nitrogen content in emissions from power plants that burn coal, biomass or waste. Ammonia water or urea is injected into the furnace of the boiler, whereby the flue gases react with nitrogen oxides at temperatures of 760 ° C to 1000 ° C. The end products of this reaction are nitrogen, carbon oxide and water. In addition to the denitrification reaction, undesired ammonia compounds are formed, which condense on the surface of the fly ash at lower temperatures and form ammonia salts. The salts limit the use of the ashes in construction, because when water or any other alkali, e.g. calcium, is added, ammonia salts dissolve, which results in an unpleasant odor in the building material.

This problem can be solved by displacing the ammonia salts with chemicals. However, this impairs the required properties of the ash, in particular the cement formation. Another solution to this problem is the thermal displacement of the ammonium salts through their sublimation at temperatures of 200 ° C to 400 ° C. In this process, the ash retains the properties that are important for the construction industry, but the process has a high energy consumption as a disadvantage. The ash is to be heated to temperatures of 200 ° C to 400 ° C and then cooled to a temperature suitable for storage and subsequent manipulation.

Similar problems arise in the production of any crumbly building materials, such as cement, lime or gypsum stone, which have high temperatures at the end of the production process. The temperature should be reduced to a safe level. The sensible heat that is transferred to the product, for example by means of Cooling water is withdrawn, is then discharged into the environment without further use.

The RU 2616630 presents a system for the use of municipal waste, in which the material is transported with a screw conveyor through a cylindrical pyrolysis chamber. A heating medium flows through a hollow shell of the chamber - in addition, exhaust gases from a combined heat and power unit heated to a temperature of 1100 ° C. It is a screw heat exchanger, but its construction does not allow heat transfer between bulk materials of different temperatures.

From DE 3012829 a fermentation device is known which is formed by a cylindrical container, in the vertical axis of which a screw mixer is attached, a spiral band being welded to the inner wall of the container. This arrangement only serves to completely mix the liquid contents of the container.

The invention is based on the object of designing a construction of a heat exchanger which enables the sensible heat contained in a bulk material to be used to preheat another bulk material at temperatures of up to 400.degree.

According to the invention, this object is achieved by the heat exchanger having the features of claim 1.

The screw heat exchanger according to the invention is formed by a tubular jacket in which a driven hollow, heat transfer surface forming shaft is rotatably mounted, which has openings at both ends, on the outer surface of which an outer spiral belt for conveying a material through a gap between the shaft and the Sheath is welded and on the inner surface of which an inner spiral-shaped belt is welded for the conveyance of a material to be transferred to its sensible heat, the belts being wound in the reverse direction of winding. In one embodiment of the heat exchanger, there is an entry for the material into the gap between the jacket and the hollow shaft and an exit for the material from the cavity of the shaft at one end of the heat exchanger, the gap at the other end of the heat exchanger with the cavity the shaft is connected and wherein the heat exchanger is provided at the other end with means for heating the material.

In another embodiment, the heat exchanger is provided at one end with an inlet for the material to be heated into the gap between the jacket and the hollow shaft, as well as with an outlet for the material to be transferred from the cavity of the shaft, whereby it is provided at the other end with the outlet for the heated material, and wherein the cavity of the shaft is connected at the other end to a supply of its sensible heat to be transferred material.

The inner spiral belt can preferably protrude from the cavity of the shaft at the other end of the heat exchanger so that it engages the material or building material that is located in the space connecting the cavity and the gap or in the material supply.

The gap between the jacket and the hollow shaft is provided with air channels for the discharge of gaseous products.

The bearings of the hollow shaft are provided with feed lines for sealing air.

Both edges of the gap between the jacket and the hollow shaft are preferably provided with pairs of circular rings for a supply of the separating air.

The spiral belts on the outer and inner surfaces of the hollow shaft are interrupted in another embodiment of the heat exchanger, and in this case the belt sections can be bent at their rear ends against the sense of the rotations of the shaft or provided with openings in the contact lines with the shaft be. The invention thus represents the construction of a continuously operating heat exchanger which enables the transfer of heat between bulk materials at different temperatures. In contrast to the known heat exchangers for bulk masses, the heat transfer takes place directly between the masses, with no heat transfer medium being necessary.

The principle of the heat exchanger according to the invention thus consists in a pair of spiral-shaped reversely wound belts which are welded to the inner or outer wall of a rotating hollow shaft and which convey the material along the wall of the shaft in reverse directions. The heat is transferred from one material to another at different temperatures through the wall of the hollow shaft. The materials move in countercurrent, which contributes to the high efficiency of the heat exchanger.

The preferred exemplary embodiments of the invention are shown schematically in the drawings and are described in more detail below. Show it

Fig. 1 is a longitudinal section through a screw heat exchanger in which the

Bulk material is first heated by means of an external heat source until it has reached the temperature required for the unwanted accompanying substance to flow out, and then the sensible heat acquired in the heated material is used to preheat the incoming material,

Fig. 2 is a longitudinal section through another embodiment of the

Screw heat exchanger designed to cool a hot, pourable end product, e.g. in the production of cement, lime or gypsum, and to simultaneously transfer its sensible heat to the incoming material,

3 to 5 different versions of the hollow shaft with the interrupted outer belt, or with sections of the outer belt,

Fig. 4 belt sections with curved rear ends Fig. 5 belt sections which are provided with openings in the contact lines with the shaft.

The screw heat exchanger according to FIGS. 1 and 2 is formed by a tubular jacket 1 in which a rotatably mounted, driven hollow shaft 4 is mounted, which forms a heat transfer surface and is provided with openings 5 at both ends. An outer spiral-shaped belt 6 is welded to the outer surface of the hollow shaft 4 and, when the shaft 4 rotates, conveys a material to be heated through a gap 7 between the jacket 1 and the shaft 4 to the left. An inner spiral-shaped belt 8 is welded to the inner surface of the hollow shaft 4, which, when the shaft 4 rotates, conveys the material to be cooled and its sensible heat to be transferred through the inner space of the shaft 4 to the right. The belts 6, 8, which actually represent two screw conveyors, are wound in the opposite direction of winding.

The heat exchanger according to FIG. 1 is intended for the temporary heating of the material and its subsequent cooling. An inlet 9 for the material to be heated into the gap 7 between the jacket 1 and the shaft 4 and an outlet 10 for the cooled material from the inner space of the shaft 4 are located here at the right end of the heat exchanger. At the left end of the heat exchanger between the jacket 1 and the shaft 4, a gap 11 is formed which connects the gap 7 with the inner space of the shaft 4. At the left end of the heat exchanger is provided with an external heat source 12, which is used to reheat the material. This can be, for example, a gas or oil burner or a heat exchanger that uses waste heat.

The heat exchanger according to FIG. 2 is intended to use the sensible heat of a freshly burned building material. The inlet 9 for the material to be heated into the gap 7 between the jacket 1 and the shaft 4 and the outlet 10 for the cooled building material from the inner space of the shaft 4 are located here at the right end of the heat exchanger. At the left end of the heat exchanger there is an outlet 13 for the heated material from the gap 7. At this end, the inner space of the shaft 4 is connected to a supply 14 of a hot building material, for example a clinker from a cement kiln, which is supposed to transfer its sensible heat.

In both versions, the inner spiral belt 8 protrudes from the cavity of the shaft 4 at the other end of the heat exchanger and thus engages in the material that is in the gap 11 or in the feed 14 of the building material is located. In this way, the supply of material into the inner space of the shaft 4 is supported.

In the embodiment according to FIG. 1, the gap 7 between the jacket 1 and the hollow shaft 4 is provided with air ducts 15 for the removal of gas products.

In both versions of the heat exchanger, shaft bearings 2 are provided with feed lines 16 for the sealing air, and the edges of the gap 7 between the jacket 1 and the shaft 4 are provided with pairs of circular rings for the supply 17 of separating air.

In other embodiments, the outer belt 6 attached to the outer surface of the shaft 4 is separated into sections - see Figs. 3 to 5. These sections can then be bent at their rear ends against the sense of the rotations of the shaft 4 - see Fig. 4, optionally provided with openings in the contact lines with the shaft 4 - see Fig. 5.

For the embodiment according to Fig. 1:

The material intended for heating is fed through the inlet 9 into the gap 7 between the jacket 1 and the hollow shaft 4, in which the spiral-shaped outer belt 6 welded to the shaft 4 rotates, which moves the material through the unheated section of the gap 7 pushes to the left. The material is heated to the target temperature in the end section which is provided with the external heat source 12. At the left end of the heat exchanger, the material fills the gap 11 and enters the inner space of the shaft 4, where the inner belt 8, which is wound in the opposite direction, pushes it to the right to the outlet 10. The material transfers the assumed sensible heat through the wall of the shaft 4 to the material moving through the gap 7. At the same time, the sublimed component, such as ammonia and its compounds, is discharged through air channels 15 discharged from the material for neutralization. The material then falls through the opening 5 into the outlet 10 at the right end of the heat exchanger. In order to reduce the dust in the system, a small amount of sealing air is fed to the bearings at both ends of the heat exchanger through the supply lines 16. At the same time, a small amount of separating air is fed in between the circular rings which separate the gap 7 from the exit space. The heat exchanger is provided with thermal insulation 18.

For the embodiment according to Fig. 2:

In this heat exchanger, too, the media move in countercurrent. The building material of high temperature passes through the feed 14 for the hot building material into the heat exchanger and is drawn into this space by means of the inner belt 8, which protrudes from the inner space of the shaft 4. The building material is then pushed from left to right by means of the inner belt 8 when the shaft 4 rotates, transfers its sensible heat via the wall of the shaft 4, its temperature drops and it falls at the end of the shaft 4 through the opening 5 into the heat exchanger outlet 10 The cold pourable material (charge) is fed through the inlet 9 to the gap 7 and pushed through it to the left. The preheated material then exits the heat exchanger through outlet 13. In order to reduce the dust in the system, a small amount of sealing air is fed to the bearings at both ends of the heat exchanger through the supply lines 16. At the same time, a small amount of separation air is supplied between the circular rings, which separate the gap 7 from the supply 14 for the hot building material or from the outlet space. The heat exchanger is also provided with thermal insulation 18.

In order to increase the heat transfer, the spiral belts 6, 8 can be interrupted - see Figures 3 to 5 - and their belt sections welded to the inner surface of the hollow shaft 4 at a suitable angle can be shaped. At their rear ends they can be bent against the direction of the rotation of the shaft 4 - see FIG. 4, or provided with openings in the contact lines with the shaft 4 for the purpose of shaking the material - see FIG. 5. Shaking the material on the wall of the shaft 4 increases the heat transfer via the shaft wall and thereby the efficiency of the heat exchanger. The heat exchanger must be operated at temperatures above the condensation point.

The heat exchanger according to the invention was designed in two variants:

In the embodiment according to FIG. 1, it is used to heat bulk material by an external heat source for a certain time required and then to reuse the sensible heat in the material to be cooled to heat the incoming material.

In the embodiment according to FIG. 2, the heat exchanger is used to use the sensible heat of a hot, pourable building material emerging from a production process, and to preheat a raw material that enters the process. The system can be used in the cement industry, where it is necessary to cool the escaping building material from a high temperature to a safe level.

The heat exchanger according to the invention shows its advantages particularly in companies where work is carried out continuously with larger amounts of material. Such a case are in particular heat exchangers for carrying out denitrification methods in which it is necessary to remove ammonium salts in a thermal manner from the ash leaving the combustion process.

Claims

1. Screw heat exchanger, especially for bulk materials, characterized in that it is formed by a tubular jacket (1) in which a driven hollow, heat transfer surface forming shaft (4) is rotatably mounted, which has openings (5) at both ends the outer surface of which is welded an outer spiral-shaped belt (6) for conveying a material through a gap (7) between the shaft (4) and the jacket (1) and to the inner surface of which an inner spiral-shaped belt (8) for conveying one of its sensible heat is welded to the material to be transferred, the belts (6, 8) being wound in the opposite direction of winding.

2. The heat exchanger according to claim 1, characterized in that at one end there is an inlet (9) for the material in the gap (7) between the jacket (1) and the hollow shaft (4), as well as an outlet (10 ) for the material from the cavity of the shaft (4), the gap (7) being connected to the cavity of the shaft (4) at the other end of the heat exchanger and the heat exchanger at the other end being provided with means for heating the material .

3. The heat exchanger according to claim 1, characterized in that it is at one end with an inlet (9) for the material to be heated in the gap (7) between the jacket (7) and the hollow shaft (4), as well as with an outlet (10) for a material transferred to the sensible heat from the cavity of the shaft (4), wherein it is provided at its other end with an outlet (13) for the heated material, and wherein the cavity of the shaft (4 ) is connected at the other end to a supply (14) of a material to be transferred to the sensible heat.

4. The heat exchanger according to one of the preceding claims, characterized in that the inner spiral belt (8) protrudes from the cavity of the shaft (4) at the other end of the heat exchanger.

5. The heat exchanger according to claim 2, characterized in that the gap (9) between the jacket (1) and the hollow shaft (4) is provided with air ducts (15) for discharging gaseous products.

6. The heat exchanger according to one of the preceding claims, characterized in that the bearings of the hollow shaft (4) are provided with feed lines (16) of the sealing air.

7. The heat exchanger according to one of the preceding claims, characterized in that both edges of the gap (7) between the jacket (1) and the hollow shaft (4) are provided with pairs of circular rings to a supply (17) of the separating air.

8. The heat exchanger according to one of the preceding claims, characterized in that the spiral belts (6, 8) are interrupted on the outer and inner surfaces of the hollow shaft (4).

9. The heat exchanger according to claim 8, characterized in that the belt sections are bent at their rear ends against the sense of the rotations of the shaft (4).

10. The heat exchanger according to claim 8, characterized in that the belt sections are provided with openings in the contact lines with the shaft (4).