GB1593473A

GB1593473A - Process and apparatus for heating gases or vapours

Info

Publication number: GB1593473A
Application number: GB9903/78A
Authority: GB
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1977-03-23
Filing date: 1978-03-13
Publication date: 1981-07-15
Also published as: PL205351A1; DE2712728A1; ZA781067B; PL108978B2

Description

(54) PROCESS AND APPARATUS FOR HEATING GASES OR VAPOURS (71) We, METALLGESELLSCHAFT AKTIENGESELLSCHAFT, a body corporate organised under the laws of the German Federal Republic, of Reuterweg 14, 6000 Frankfurt am Main, German Federal Republic, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to apparatus for heating a gas or vapour and to a process for heating a gas or vapour by direct heat exchange with a heated surface using such apparatus.

Previously proposed electric gas heaters have the disadvantage that large, expensive structures are required to accommodate the heat exchange surface area which is needed for heating a gas or vapour.

According to one aspect of the present invention there is provided apparatus for heating a gas or vapour, wherein a tube which is electrically non-conducting or of low electrical conductivity contains a stationary gas-permeable packing of electrically conducting elements and is surrounded by the primary coil of an induction heater arranged to heat said elements by electromagnetic induction, the tube having an inlet end for a gas to be heated and an outlet end for heated gas, and wherein a pressure housing surrounds said tube and coil, there being an inlet to said housing through which the space between the housing and the tube can be filled with gas under pressure and there being electrically conducting connections for supplying electric current to said coil leading through said housing.

According to another aspect of the present invention there is provided a process for heating a gas or vapour, wherein the gas or vapour is passed under pressure through the tube of the apparatus just indicated while said coil is connected to a source of alternating current of a frequency of 50 to 20,000 Hz and while said space is maintained under pressure by gas supplied through said inlet.

With this process, it is possible to heat gases or vapours quickly up to high temperatures in a minimum of space.

The electrically conducting elements may be made, e.g. from metal or graphite. A noncontacting transfer of energy to the packing is conveniently effected from the aforesaid primary coil, which conducts an alternating current of which the frequencies may be in the range from 50 to 20,000 Hz, preferably from 1000 to 10,000 Hz. Usually, the larger the dimensions of the elements, the lower are the frequencies which are employed.

The elements of the packing preferably have a largest dimension of 3 to 50 mm. and good results are obtained with a packing of spherical elements, a packing consisting of balls which are substantially equal in size and differ in diameter by not more than 10% being preferred. Balls which are approximately equal in size are in substantially uniform contact with each other so that the soaking of the packing with heat is improved. The heat conduction from ball to ball is also significant. A packing of balls also improves the conditions for the flow of the gas to be heated, high film coefficients of heat transfer being obtained in conjunction with a low pressure loss.

In selecting the material of which the elements or balls are made, consideration must be given to the chemical behaviour of the material in contact with the gas to be heated.

When the elements are heated to a high temperature, that temperature must be adequately below their melting point, the elements or balls preferably being heated to a temperature which is at least 300"C. below their melting point. Gases can be heated to the following temperatures by heated elements of the following metals: Up to 1100 C. by means of nickel elements, up to 1600 C. by means of chromium elements, and up to 2300"C. by means of molybdenum elements.

The packing is conveniently accommodated in a tube or container which has a perforated bottom and consists of a material which is electrically non-conducting or has a low electrical conductivity. Ceramic material or glass, e.g., may be used for this purpose.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawing, which illustrates diagrammatically and by way of example an embodiment thereof, and which is a longitudinal sectional view of apparatus for heating a gas or vapour.

Referring now to the drawing there is shown a gas heater in the form of a tube 2 extending through a pressure housing 1. The tube 2 is provided with a perforated plate or grid 3 supporting a packing 4 of electrically conducting balls. The balls of the packing contact each other and are indicated by dots on the drawing.

The primary coil 5 of an induction heater surrounds that portion of the tube which contains the packing 4, the packing constituting the secondary coil.

The primary coil 5 consists of convolutions of copper tubing, which conducts alternating current as well as a cooling liquid, e.g., water.

Copper tubes 6 and 7 lead from the coil 5 out of the pressure vessel. That portion of the tube 7 which extends through the housing 1 coaxially surrounds the other tube 6. Cooling liquid is supplied to the tube 6 from the outside and is withdrawn through the tube 7.

The two tubes 6 and 7 are connected to an a.c. generator 8, which supplies electric current to the coil 5.

In the pressure vessel 1, the tube 2 consists of non-conducting material, e.g., glass or ceramic material, so that losses due to induced currents are avoided. The tube, however, consists of steel at the gas inlet 10 and the gas outlet 11. A reaction zone 12 is indicated in the tube 2 within the housing 1, the gases heated in the packing 4 being reacted in the reaction zone. The reaction zone 12 may contain, e.g., a catalyst for initiating a reaction between the components of the gas. Product gas is withdrawn through the gas outlet 11. When the gas flowing through the tube 2 is at superatmospheric pressure, the superatmospheric pressure can be compensated by a pressure in the vessel 1, protective gas being forced into the vessel 1 by a compressor 13 through a conduit 14 in order to maintain the desired pressure in the housing 1 and to avoid overloading of the tube 2.

The relatively cold gas which has flowed from the gas inlet 10 into the packing 4 is progressively heated as it flows through the packing 4. For this reason it may be desirable to transfer less energy to the packing near the perforated support 3 so that overheating of the balls or other electrically conducting elements is avoided. When it is desired to transfer less energy in that region, this may be accomplished, e.g., as has been shown on the drawing, in that the spacing of the convolutions of the coil is greater near the perforated support than where the gas is still relatively cold.

The invention will now be further illustrated by the following Examples.

Example 1.

Hydrogen at a rate of 50 standard m.3/h. is heated from 20"C. to 1000 C. on a laboratory scale. The heat rate to be transferred is about 18 kW. When this is accomplished by passing the hydrogen internally through a conventional heating tube system which is heated by electric resistance heating, two tubes of "Nicrofer" steel are required, which are 12 mm. in diameter and have a wall thickness of 2 mm. and a length of 4 metres each. The calculation of the tube length is based on a temperature difference of 100 C. between the tube wall and the gas.

A heater operating in accordance with the invention and used for the same purpose comprises a ceramic or glass tube which is 70 mm.

in diameter and has a height of about 20 cm.

The tube has a perforated support and contains a packing which has a height of 30 mm. and consists of nickel balls, which are uniformly 5 mm. in diameter. The primary coil has 8 turns and is supplied with electric current from a 10,000 Hz-generator. A temperature difference of at least 300zC. is maintained between the packing and the gas.

Example 2.

To heat air at a rate of 50 standard m.3/h.

from 20"C. to 1000 C. in an operation which is analogous to that of Example 1, about 19 kW of electrically generated heat must be transferred. Four tubes having a length of 4.3 m. each are required in the conventional tube system explained in Example 1. When a glass tube which contains a packing of balls and has been described in Example 1 is employed, a packing having a height of 110 mm.

is sufficient.

WHAT WE CLAIM IS:- 1. Apparatus for heating a gas or vapour, wherein a tube which is electrically nonconducting or of low electrical conductivity contains a stationary gas-permeable packing of electrically conducting elements and is surrounded by the primary coil of an induction heater aranged to heat said elements by electromagnetic induction, the tube having an inlet end for a gas to be heated and an outlet end for heated gas, and wherein a pressure housing surrounds said tube and coil, there being an inlet to said housing through which the space between the housing and the tube can be filled

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. temperatures by heated elements of the following metals: Up to 1100 C. by means of nickel elements, up to 1600 C. by means of chromium elements, and up to 2300"C. by means of molybdenum elements. The packing is conveniently accommodated in a tube or container which has a perforated bottom and consists of a material which is electrically non-conducting or has a low electrical conductivity. Ceramic material or glass, e.g., may be used for this purpose. In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawing, which illustrates diagrammatically and by way of example an embodiment thereof, and which is a longitudinal sectional view of apparatus for heating a gas or vapour. Referring now to the drawing there is shown a gas heater in the form of a tube 2 extending through a pressure housing 1. The tube 2 is provided with a perforated plate or grid 3 supporting a packing 4 of electrically conducting balls. The balls of the packing contact each other and are indicated by dots on the drawing. The primary coil 5 of an induction heater surrounds that portion of the tube which contains the packing 4, the packing constituting the secondary coil. The primary coil 5 consists of convolutions of copper tubing, which conducts alternating current as well as a cooling liquid, e.g., water. Copper tubes 6 and 7 lead from the coil 5 out of the pressure vessel. That portion of the tube 7 which extends through the housing 1 coaxially surrounds the other tube 6. Cooling liquid is supplied to the tube 6 from the outside and is withdrawn through the tube 7. The two tubes 6 and 7 are connected to an a.c. generator 8, which supplies electric current to the coil 5. In the pressure vessel 1, the tube 2 consists of non-conducting material, e.g., glass or ceramic material, so that losses due to induced currents are avoided. The tube, however, consists of steel at the gas inlet 10 and the gas outlet 11. A reaction zone 12 is indicated in the tube 2 within the housing 1, the gases heated in the packing 4 being reacted in the reaction zone. The reaction zone 12 may contain, e.g., a catalyst for initiating a reaction between the components of the gas. Product gas is withdrawn through the gas outlet 11. When the gas flowing through the tube 2 is at superatmospheric pressure, the superatmospheric pressure can be compensated by a pressure in the vessel 1, protective gas being forced into the vessel 1 by a compressor 13 through a conduit 14 in order to maintain the desired pressure in the housing 1 and to avoid overloading of the tube 2. The relatively cold gas which has flowed from the gas inlet 10 into the packing 4 is progressively heated as it flows through the packing 4. For this reason it may be desirable to transfer less energy to the packing near the perforated support 3 so that overheating of the balls or other electrically conducting elements is avoided. When it is desired to transfer less energy in that region, this may be accomplished, e.g., as has been shown on the drawing, in that the spacing of the convolutions of the coil is greater near the perforated support than where the gas is still relatively cold. The invention will now be further illustrated by the following Examples. Example 1. Hydrogen at a rate of 50 standard m.3/h. is heated from 20"C. to 1000 C. on a laboratory scale. The heat rate to be transferred is about 18 kW. When this is accomplished by passing the hydrogen internally through a conventional heating tube system which is heated by electric resistance heating, two tubes of "Nicrofer" steel are required, which are 12 mm. in diameter and have a wall thickness of 2 mm. and a length of 4 metres each. The calculation of the tube length is based on a temperature difference of 100 C. between the tube wall and the gas. A heater operating in accordance with the invention and used for the same purpose comprises a ceramic or glass tube which is 70 mm. in diameter and has a height of about 20 cm. The tube has a perforated support and contains a packing which has a height of 30 mm. and consists of nickel balls, which are uniformly 5 mm. in diameter. The primary coil has 8 turns and is supplied with electric current from a 10,000 Hz-generator. A temperature difference of at least 300zC. is maintained between the packing and the gas. Example 2. To heat air at a rate of 50 standard m.3/h. from 20"C. to 1000 C. in an operation which is analogous to that of Example 1, about 19 kW of electrically generated heat must be transferred. Four tubes having a length of 4.3 m. each are required in the conventional tube system explained in Example 1. When a glass tube which contains a packing of balls and has been described in Example 1 is employed, a packing having a height of 110 mm. is sufficient. WHAT WE CLAIM IS:-

1. Apparatus for heating a gas or vapour, wherein a tube which is electrically nonconducting or of low electrical conductivity contains a stationary gas-permeable packing of electrically conducting elements and is surrounded by the primary coil of an induction heater aranged to heat said elements by electromagnetic induction, the tube having an inlet end for a gas to be heated and an outlet end for heated gas, and wherein a pressure housing surrounds said tube and coil, there being an inlet to said housing through which the space between the housing and the tube can be filled

with gas under pressure and there being electrically conducting connections for supplying electric current to said coil leading through said housing.

2. Apparatus as claimed in claim 1, wherein the tube has a gas-permeable support for said packing.

3. Apparatus as claimed in claim 1 or 2, wherein the spacing of the convolutions of the primary coil of the induction heater is greater near the outlet end of the tube than near the inlet end of the tube.

4. Apparatus as claimed in any one of the claims 1 to 3, wherein the elements of the packing have a largest dimension of 3 to 50 mm.

5. Apparatus as claimed in any one of claims 1 to 4, wherein the elements of the packing are substantially spherical and differ in diameter by not more than 10%.

6. Apparatus as claimed in any one of claims 1 to 5, wherein the electrically conducting connections are in the form of tube elements passing coaxially through said housing for supplying cooling liquid to and withdrawing it from the coil which is of hollow tubular construction.

7. Apparatus for heating a gas or vapour substantially as hereinbefore described with reference to the accompanying drawing alone or in conjunction with either of the foregoing Examples.

8. A process for heating a gas or vapour, wherein the gas or vapour is passed under pressure through the tube of the apparatus claimed in any preceding claim while said coil is connected to a source of alternating current of a frequency of 50 to 20,000 Hz and while said space is maintained under pressure by gas supplied through said inlet.

9. A process as claimed in claim 8, wherein the frequency of said alternating current is 1000 to 10,000 Hz.

10. A process as claimed in claim 8 or 9, wherein a cooling liquid is passed through said coil, being supplied through one tube element and withdrawn through the other.