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INVENTION
Patent of the Russian Federation RU2280821
METHOD OF HEATING AIR FLOW AND DEVICE
The name of the inventor: Semenov Anatoly Leonidovich (RU); Belykh Sergey Anatolievich (RU); Belyanin Nikolay Mikhailovich (RU); Kotelnikov Yuri Leonidovich (RU)
The name of the patent holder: Federal State Unitary Enterprise "Central Institute of Aviation Motors named after PI Baranov" (RU)
Address for correspondence: 111116, Moscow, ul. Aviamotornaya, 2, FSUE "CIAM named after PI Baranova", department of intellectual property
Date of commencement of the patent: 2004.12.22
The invention relates to the heating of industrial gases, including air, at high flow rates by the electrothermal method. The method for heating the air flow to a temperature above 500 ° C at a mass flow rate of more than 0.5 kg / s includes heating the heating element with an electric current and heat transfer to the heated air stream of Joule heat, while the heated air flow is passed inside the heating element by symmetrical flows directed towards each other To a friend, and form a common stream of heated air by merging counterflows, selecting a common heated stream into space along a central centerline between the heating elements. The device for heating the air flow to a temperature above 500 ° C. at a mass flow rate of more than 0.5 kg / s comprises a three-phase electrical supply source, hollow heating elements each connected to a single phase of a three-phase electrical supply, manifolds for supply and discharge of air, To which the ends of the hollow heating elements are connected, the air supply manifold being configured as at least two symmetrical risers, to each of which a cavity of the hollow heating element is connected, and each hollow heating element is divided into at least two identical sections Located along a common longitudinal axis and connected at opposite ends to a respective riser of the air intake manifold which is the input flow for each hollow heating element and to an outlet manifold located along the central axis of the device symmetrically with respect to risers of the inlet manifold and both sections of each heating element Electrically connected to each other in series and electrically isolated from the inlet and outlet manifolds by insulators, fixed on each hollow heating element. The technical result of the proposed invention is to reduce the inlet pressure of the air stream supplied for heating by reducing the pressure loss along the length of the heating element.
DESCRIPTION OF THE INVENTION
The invention relates to the heating of industrial gases, including air, and more particularly means for high-temperature heating of air and / or industrial gases (hereinafter - air) at high flow rates by electrothermy.
The invention can be used for heating air and its further use in various industrial installations, including in air conditioning systems, in stationary furnaces, in drying systems. It can be used for research purposes, for example, in wind tunnels.
Known devices for heating air using electricity.
Known ohmic air heaters of flow type (electric heaters).
The heating of air (or other fluid) in such heaters is carried out at the expense of Joule heat when the air flow is removed by heating (heating) elements-conductors with a relatively high electrical resistance, through which an electric current passes.
Electric heaters are known in which plate heating elements, spirals, tubes, grids, etc. are used as a heating element.
Electric fluid heaters are known, where tubes are used as heating elements in the form of a corridor bundle of tubes, a chess bundle of tubes with transverse or longitudinal air flow.
An electrical fluid heater is known which includes current-heated pipes connected at their ends to collectors and current-carrying buses ( Aut.No.117394, MKI F 24 N 3/04, published in 1958 ).
A method for heating an air stream to a temperature above 500 ° C is known, which includes heating the heating element with an electric current and heat transfer to the heated air stream of Joule heat, while the heated air stream is passed inside the heating element ( autorid No. 1776930, MCI F 24 N 3/04 , Published in 1992 ).
A gas heater is known (autorid No. 1776930, MKI F 24 N 3/04, published 1992) , which contains hollow tubular heaters connected to the collector, connected to busbars located on the heaters with displacement relative to the collector, while current carrying Tires are made in the form of a shunt connecting tubular heaters, whose electrical resistance is 5-10 times less than the electrical resistance of the heaters on the shunt section.
The known method for heating the air flow and the electric heater may be used advantageously in testing installations, for example, wind tunnels, for testing and research purposes.
It is the object of the invention to provide a method and apparatus for heating an air stream to a temperature above 500 ° C. at a mass flow rate of more than 0.5 kg / s for use in industrial environments in industrial installations. Another task was the creation of an economical heating of such a flow of air.
The complexity of the solution of the problem is that for high-temperature heating of the air flow of a large mass flow, such as these values, a high heat transfer rate is required, which is ensured by an increase in the flow velocity, but this causes a strong increase in the aerodynamic resistance, which is proportional to the square of the flow velocity In the heating element. When the air flow is heated at a mass flow rate of 0.3 kg / s, for example from the phase of a three-phase electric current, in a hollow heating element to a temperature of 700 ° C, the pressure loss is from 35 to 40 atm, which requires an air inlet to the heating element Flow with operating pressure above 40 atm. Providing the process of heating and moving air flow through the hollow heating element in this case should be provided by the presence of an external source of compressed air. Such a source of compressed air in industrial conditions is usually a compressor plant. In industrial conditions, according to economic and technological requirements, it is usually not advisable to use (and not apply) compressor units with pressures above 20 atm. The need for high inlet pressure for high-temperature and high-speed air flow heating does not allow the use of known inventions in industrial conditions in industrial installations, and a large loss of pressure in this case additionally causes the uneconomical nature of such heating.
The authors found that with such a method of supplying air to the heater, by dividing the flow of heated air, for example, into "n" symmetrical flows, the flow rate in the heating element decreases "n" times, the pressure loss, while proportional to the square of the velocity, Is reduced by "n 2 " times, while heating of the present invention achieves heating of the entire mass flow up to the maximum design heating temperature
The technical result of the proposed invention is to reduce the inlet pressure of the air stream supplied for heating by reducing the pressure loss along the length of the heating element.
This object is achieved in that the method for heating the air flow to a temperature above 500 ° C. at a mass flow rate of more than 0.5 kg / s, comprising heating the heating element with an electric current and heat transfer to the heated air stream of Joule heat, the heated air stream being passed inside Of the heating element according to the invention, the heated air is supplied to the heating element by symmetrical flows directed towards each other and forms a common flow of heated air by merging counterflows, taking the total heated flow into space along the central center line between the heating elements.
The heating of the heating element can be carried out by an electric current phase with a power of over 0.3 MW.
It is advisable that the electric current is output to the maximum power position in less than 20 seconds.
The above object is achieved by the fact that in a device for heating the air flow to a temperature above 500 ° C at a mass flow rate of more than 0.5 kg / s containing a source of three-phase electrical power, hollow heating elements, each of which is connected to one phase of a three-phase electric Supply manifolds to which the ends of the hollow heating elements are connected, according to the invention, the air supply manifold is designed in the form of at least two symmetrical risers, to each of which a cavity of the hollow heating element is connected, and each hollow heating element is divided into At least two identical sections along a common longitudinal axis and connected at opposite ends to a respective riser of the air intake manifold which is the input flow for each hollow heating element and to an outlet manifold located along the central axis of the device symmetrically with respect to the risers of the inlet manifold, And both sections of each heating element are electrically connected to each other in series and electrically isolated from the inlet and outlet manifolds by insulators fixed to each hollow heating element.
It is advisable that the insulators be fixed on each hollow heating element without a gap.
It is advisable and that each insulator be made of a composite fabric material based on silica.
In addition, it is expedient that each hollow heating element be made of a metal conductive material based on stainless steel.
Each hollow heating element can have a length of 5 to 10 meters.
It is expedient that the outer diameter of each hollow heating element is 11 to 20 mm.
It is also advisable that the inner diameter of each hollow heating element is 10 to 18 mm.
Advantageously, as a source of three-phase electrical power supply, a source with a power of above 0.9 MW and a current strength of above 1000 A.
It is advantageous and that the electric current be output to the maximum power position in less than 20 seconds.
In the following, the proposed invention is explained by the description of examples of its implementation and the attached drawings, in which:
FIG. 1 is a schematic diagram of an apparatus for heating an air flow according to the invention
FIG. 2 is a view of an installation for heating the airflow according to the invention, according to the arrow A of FIG. 1
3 is a view of an installation for heating the airflow according to the invention (variant)
FIG. 4 is a sectional view of arrow B in FIG. 3. FIG.
A method for heating an air stream to a temperature above 500 ° C. at a mass flow rate of more than 0.5 kg / s is carried out as follows.
The hollow heating element is heated with the flow of air introduced into this heating element, the phase of the electric current. The heating of the heating element can be carried out by an electric current phase with a power of over 0.3 MW.
The electric current is output to the maximum power position in less than 20 seconds. The process of entering the operating mode of a heating element with an air flow inward is less than 40 seconds.
In this case, according to the invention, the heated air is supplied to the heating element by symmetrical flows directed towards each other. As the air passes through the heating element, the Joule heat is heated to the heated air stream, thereby increasing its temperature at the outlet of the heating element from above 500 ° C. Counter-streams of heated air are poured into a common heated stream, taking the total heated stream into space along the central center line between the heating elements.
The device for heating the air flow to a temperature above 500 ° C. at a mass flow rate of more than 0.5 kg / s (FIG. 1) according to the invention comprises a three-phase electrical supply source 1, hollow heating elements 2, each of which is connected to a single phase of a three-phase source Power supply. Each hollow heating element 2 is divided into at least two identical sections 3 and 4 arranged symmetrically along a common longitudinal axis (not shown). However, as an option, it is possible to arrange the sections 3 and 4 symmetrically with a slope. As shown in FIG. 2, the heating element 2 is divided into two sections - a section 3 and a section 4, the sections being arcuate. The heating element 2 can be divided into several sections more than two. (As shown in FIG. 3, the heating element 2 is divided into 4 sections.) Each section of the heating element-section 3 and section 4-is connected by a busbar 5 and 5 1 with one phase of a three-phase electrical supply 1. The busbar 5 1 is shown in FIG. .1 schematically. In kind, its role is played by the flange 10 (FIG. 2). The device also includes an air intake manifold 6 which is made in the form of two risers 7, to each of which a cavity of hollow heating elements 2 is connected and each of which is an input stream for each hollow heating element 2, an outlet manifold 8 disposed along the central axis Devices for removing heated air, symmetrical with respect to the risers 7 of the intake manifold 6 for supplying air. The sections of each hollow heating element - section 3 and section 4 - are electrically connected in series and electrically isolated from the inlet and outlet manifolds by insulators 9 fixed to each hollow heating element 2.
As shown in FIG. 4, the insulators 9 are fixed on each hollow heating element 2 without a gap and are fixed by a flange 10. As a material for the manufacture of the insulators 9, a composite fabric material based on silica is used.
Each hollow heating element 2 is made of a metal conductive material based on stainless steel. The internal diameter of each hollow heating element is from 10 to 18 mm, and the outer diameter is from 11 to 20 mm, and the length is from 5 to 10 m.
The device operates as follows and operates the method according to the invention.
The electric current is supplied to the heating element 2 from the three-phase electrical supply phase 1, which heats the heating element to the design temperature.
The air flow enters the collector 6, is divided into symmetrical flows entering the risers 7, in which it is further divided into symmetrical flows entering the cavities of the sections 3 and 4 of the heating element 2. As the air passes through the heating element, heat transfer to the heated air stream causes the Joule Heat, due to which, at the outlet of the heating element, its temperature becomes higher than 500 ° C. The flows of heated air from sections 3 and 4 are merged into a common heated stream into the outlet manifold 8, from where the heated air is withdrawn and then can be used in industrial conditions in industrial installations.
For the operation of the device it is important to ensure the symmetry of the flows directed towards each other in order to ensure uniformity of the field of mass velocity in the cross sections of the cavities of the heating element. For heating elements according to the invention, the specific heat generation, for example per unit volume, can be considered practically constant for a given section, and therefore the unevenness of the mass velocity inevitably leads to uneven temperature fields and heat transfer coefficients, resulting in uneven temperature of the heating element - local overheating, which is capable of Lead to its destruction.
Exemplary embodiments of the method using the device of the invention in FIG.
EXAMPLE 1 An electric current of more than 0.3 MW is supplied to each heating element 2 from a phase of a three-phase power supply source 1, a power of 1 MW and a current of 1000 A, and simultaneously a collector 6 is fed with a flow of heated air at a mass flow rate of 1 kg / s . The airflow pressure at the collector inlet is 6-55 bar, the temperature is 20 ° C. At the outlet of the collector 6, the heated air stream is divided into two symmetrical flows, each of which (0.5 kg / s) enters the corresponding riser 7, where it is divided into three more streams, each of which (at 0.167 kg / s) is supplied To the input of the respective sections 3 and 4. As the air passes through the heating element, heat is transferred to the heated air stream of Joule heat and its temperature at the inlet to the collector 8 is 680 ° C, the pressure is 50 bar.
An electric current of 1000 A is output to the maximum power position in 19 seconds. The process of reaching the operating mode of the device with a mass flow of 1 kg / s flowing into its heating elements is 38 seconds.
Examples 2-4. The process is carried out on the device according to the invention under the conditions of Example 1, but this is varied by the incoming mass flow rate and the pressure at the inlet of the air stream.
The experimental data relating to Examples 2-4 are given in the table.
Thus, the method for heating the air flow and the device according to the invention made it possible to carry out a high-temperature and high-speed heating of the stream at an operating pressure below 20 bar. The pressure losses in this case are on the order of 8-10% of the inlet pressure, which allows to reduce the energy and operating costs and widely use the proposed invention in industrial conditions in industrial installations.
CLAIM
A method for heating an air stream to a temperature above 500 ° C at a mass flow rate of greater than 0.5 kg / s, comprising heating the heating element with an electric current and heat transfer to the heated air stream of Joule heat, the heated air stream being passed inside the heating element, , That the heated air is supplied to the heating element by symmetrical flows facing each other and forms a common flow of heated air by merging counterflows, taking the total heated flow into space along the central center line between the heating elements.
2. A method according to claim 1, characterized in that heating of the heating element is carried out by an electric current phase with a power of above 0.3 MW.
3. The method of claim 1, wherein the electric current is output to a maximum power position in less than 20 seconds.
4. A device for heating the air flow to a temperature above 500 ° C at a mass flow rate of more than 0.5 kg / s, comprising a source of three-phase electrical power, hollow heating elements, each of which is connected to a single phase of a three-phase electrical supply, Of the air outlet to which the ends of the hollow heating elements are connected, characterized in that the air supply manifold is made in the form of at least two symmetrical risers, to each of which a cavity of the hollow heating element is connected, and each hollow heating element is divided, at least At least two identical sections located along a common longitudinal axis and connected at opposite ends to a respective riser of an air intake manifold which is the input flow for each hollow heating element and to an outlet manifold located along the central axis of the device symmetrically with respect to risers of the inlet manifold, And both sections of each heating element are electrically connected to each other in series and electrically isolated from the inlet and outlet manifolds by insulators fixed to each hollow heating element.
5. The device according to claim 4, characterized in that the insulators are fixed on each hollow heating element without a gap.
6. Apparatus according to claim 5, characterized in that each insulator is made of a composite fabric material based on silica.
7. Apparatus according to claim 4, characterized in that each hollow heating element is made of a metal conductive material based on stainless steel.
8. Apparatus according to claim 4, characterized in that each hollow element has a length of less than 10 m.
9. Apparatus according to claim 4, characterized in that the outer diameter of each hollow heating element is 11 to 20 mm.
10. Apparatus according to claim 4, characterized in that the inner diameter of each hollow heating element is 10 to 18 mm.
11. The device according to claim 4, characterized in that a source of three-phase electric power supply is a source with a power of above 0.9 MW and a current strength higher than 1000 A.
12. The device of claim 4, wherein the electric current is output to a maximum power position in less than 20 seconds.
print version
Date of publication 07.12.2006гг
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