GB1568706A - Furnace - Google Patents

Description

(54) FURNACE (71) We, ROLLS-ROYCE LIMITED, a British Company, of 65 Buckingham Gate, London SW1E 6AT, formerly ROLLS ROTcE (1971) LIMITED, a British Company, of Norfolk House, St. James's Square, London SW17 4JR, 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 particu larly described in and by the following statement: This invention relates to a furnace.

It is a normal requirement for furnaces that they should have an internal tempera ture which is substantially constant, or at least lies within specified limits over the en tire working area of the furnace, and in order to achieve this in the past fans have been used to circulate the atmosphere with in the furnace. However, such fans tend to be bulky and require the provision of a supply of electricity, and since they have rotating components, it is sometimes diffi cult to arrange that they operate satisfac torily in special atmospheres such as for instance as are used in hydriding furnaces.

The present invention provides a fur nace within -which circulation of the atmos phere is effected in a simple manner.

According to the present invention a fur nace comprises a vessel, heating means within the vessel, a plurality of ejector pomps mounted within the vessel, and fluid supply means adapted to supply com pressed fluid to the pumps, the pumps being arranged to entrain as a secondary flow the -atmosphere within the vessel and thus to promote cirction of the atmosphere within the vessel.

Throughout this specification the term ejector pump is to be taken to refer to a pump within which a primary flow of compressed fluid entrains a greater quan tity of the same br a different fluid thus forming a secondary flow which is the pumped flow.

Preferaw a feed d -eoanpIe'ed gas which is the ianie as that- mating up the atmosphere of the vessel is supplied to the ejector pump, and in one embodiment this feed comprises a portion of this atmos phere which is compressed by a separate pump. In this case we prefer to carry the atmosphere to a remote location where it is cooled and compressed before returning to the vessel to power the ejector pump.

We prefer to use the type of pump in which flow takes place from an annulus along the surface of a venturi, the secon dary flow being entrained through the venturi.

The invention will now be particularly described, merely by way of example, with reference to the accompanying drawings in which: Fig. l is a schematic diagram of a fur nace in accordance with the invention, and Fig. 2 is a cross-section through one of the ejector pumps used in Fig. 1.

In Fig. 1 there is shown a furnace com prising a pressure vessel 10 within which are mounted heating elements 11 positioned adjacent the walls of the vessel. The ele ments 11 in this instance are electrical re sistance heating elements although they could be other types as desired. A heat shield 12 protects the major area of the furnace from the effect of heat radiated directly from the heating elements so that the transfer of heat to workpieces within the furnace is mainly effected from the hot atmosphere of the furnace. Mounted be tween the heat shield and the wall of the furnace are a plurality (in this case six) of ejector pumps 13, these pumps being pro vided with a primary flow by way of pipes 14.

In order to provide this primary flow, the atmosphere from the furnace, which in this case comprises hydrogen, is removed from the furnace through a duct 15 and flows to a heat exchanger 16. The heat exchanger 16 is provided with a flow of cooling water through passages- 17 and in the exchanger the temperature of the hot. hydrogen is re duced to a level at which it may be more easily handled. From the heat exchanger 16 the gas flows through a valve 18 to a mechanically operated pump 19. The pump 19 may be any convenient form of pump but in this case it comprises a pump driven by an electric motor.

The compressed gas then passes through a second valve 20 into a reservoir 21 which is used to smooth out fluctuations in the output from the pump, and it flows from the reservoir through a regulator 22 and filter 23 to an isolation valve 24 at which point it connects with the pins 14. A pres sure gauge 25 and flow meter 26 are pro vided to monitor the pressure and flow of the gas downstream of the filter 23.

Operation of this system is quite straight- forward in that a proportion of the furnace atmosphere is drawn off through the pipe 15 and is cooled in the heat exchanger.

The pump raises it to a higher pressure suitable for driving the ejector pumps 13 and the compressed gas is then returned through the regulator, filter and isolation valve to -drive the pumps. A number of valves are provided to meet special condi tions of operation; thus the valves 18 and 20 may be used to protect the pump 19 against atmospheres within the furnace which might otherwise damage it. For instance, it may sometimes be necessary to evacuate the furnace and the pump might be dam aged by this procedure. The valve 24 enables operation of the ejector pumps to be stopped and started at will.

Fig. 2 shows in detail the operation of the ejector pumps themselves. The pri mary flow of fluid enters from the pipe 14 through a connection 30 and into an annu lar chamber 31 from where it exhausts through an annular slot 32 formed at the entrance of a venturi 33. The slot is ar ranged so that it directs the gas along the surface of the venturi, and because of the Coanda effect the primary flow sticks to the wall until it reaches the end of the ven turi. In flowing through the venturi the primary flow entrains a considerably larger flow of secondary fluid which also flows through the venturi as shown by the arrows 34. At the open end 35 of the venturi the primary flow detaches from the surface and together with the secondary flow discharges, at the same time entraining still more fluid which flows round the outside of the venturi as shown by the arrows 36.

In this way the ejector pump is enabled to move a- volume of gas which may be thirty times as great as that of the primary flow, although it will be appreciated that the .primary flow is at high pressure.

b will be understood that although the form of ejector pump described above is particularly convenient, there are a variety of different designs of such pumps which could be used.

It will be seen that the system described above enables even atmospheres of gases which are difficult to - handle to be circulated within the furnace by apparatus requiring very little space and very little modification to the furnace vessel itself, which may be important where this is a pressure vessel for operation at elevated or reduced pressures. Because the external pump works on cold gas it does not have such arduous conditions as it would if it were within the furnace, and it is very easily accessible for maintenance.

WHAT WE CLAIM IS: - 1. A furnace comprising a vessel, heating means within the vessel, a plurality of ejector pumps mounted within the vessel and fluid supply means adapted to supr compressed fluid to the pumps, the pumps being arranged to entrain as a secondary flow the atmosphere within the vessel and thus to promote circulation of said atmosphere.

2. A furnace as claimed in claim I and in which the motive fluid of the ejector pump comprises the same gas which makes up the atmosphere within the furnace.

3. A furnace as claimed in claim 2 and comprising a separate pump which is fed with a portion of the atmosphere within the vessel, compresses this portion and returns it through said fluid supply means to power said ejector pump.

4. A furnace as claimed in claim 3 and comprising cooling means adapted to cool said portion of the atmosphere before it is compressed by said separate pump.

5. A furnace as claimed in any preceding claim and in which each said ejector pump comprises a body within which is formed a venturi, the primary flow of the pump taking place from an annulus up stream of the venturi and the secondary flow being entrained through the venturi.

6. A furnace as claimed in any preceding claim and in which said vessel comprises heater elements spaced about its walls and a radiation shield interposed between the heater elements and the working volume, said ejector pumps being mounted between the walls and the radiation shield.

7. A furnace substantially as particularly hereinbefore described with reference to the accompanying drawings.

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

Claims (7)

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

   easily handled. From the heat exchanger

   16 the gas flows through a valve 18 to a mechanically operated pump 19. The pump 19 may be any convenient form of pump but in this case it comprises a pump driven by an electric motor.

   The compressed gas then passes through a second valve 20 into a reservoir 21 which is used to smooth out fluctuations in the output from the pump, and it flows from the reservoir through a regulator 22 and filter 23 to an isolation valve 24 at which point it connects with the pins 14. A pres sure gauge 25 and flow meter 26 are pro vided to monitor the pressure and flow of the gas downstream of the filter 23.

   Operation of this system is quite straight- forward in that a proportion of the furnace atmosphere is drawn off through the pipe

   15 and is cooled in the heat exchanger.

   The pump raises it to a higher pressure suitable for driving the ejector pumps 13 and the compressed gas is then returned through the regulator, filter and isolation valve to -drive the pumps. A number of valves are provided to meet special condi tions of operation; thus the valves 18 and 20 may be used to protect the pump 19 against atmospheres within the furnace which might otherwise damage it. For instance, it may sometimes be necessary to evacuate the furnace and the pump might be dam aged by this procedure. The valve 24 enables operation of the ejector pumps to be stopped and started at will.

   Fig. 2 shows in detail the operation of the ejector pumps themselves. The pri mary flow of fluid enters from the pipe 14 through a connection 30 and into an annu lar chamber 31 from where it exhausts through an annular slot 32 formed at the entrance of a venturi 33. The slot is ar ranged so that it directs the gas along the surface of the venturi, and because of the Coanda effect the primary flow sticks to the wall until it reaches the end of the ven turi. In flowing through the venturi the primary flow entrains a considerably larger flow of secondary fluid which also flows through the venturi as shown by the arrows 34. At the open end 35 of the venturi the primary flow detaches from the surface and together with the secondary flow discharges, at the same time entraining still more fluid which flows round the outside of the venturi as shown by the arrows 36.

   In this way the ejector pump is enabled to move a- volume of gas which may be thirty times as great as that of the primary flow, although it will be appreciated that the .primary flow is at high pressure.

   b will be understood that although the form of ejector pump described above is particularly convenient, there are a variety of different designs of such pumps which could be used.

   It will be seen that the system described above enables even atmospheres of gases which are difficult to - handle to be circulated within the furnace by apparatus requiring very little space and very little modification to the furnace vessel itself, which may be important where this is a pressure vessel for operation at elevated or reduced pressures. Because the external pump works on cold gas it does not have such arduous conditions as it would if it were within the furnace, and it is very easily accessible for maintenance.

   WHAT WE CLAIM IS: - 1. A furnace comprising a vessel, heating means within the vessel, a plurality of ejector pumps mounted within the vessel and fluid supply means adapted to supr compressed fluid to the pumps, the pumps being arranged to entrain as a secondary flow the atmosphere within the vessel and thus to promote circulation of said atmosphere.
2. 2. A furnace as claimed in claim I and in which the motive fluid of the ejector pump comprises the same gas which makes up the atmosphere within the furnace.
3. 3. A furnace as claimed in claim 2 and comprising a separate pump which is fed with a portion of the atmosphere within the vessel, compresses this portion and returns it through said fluid supply means to power said ejector pump.
4. 4. A furnace as claimed in claim 3 and comprising cooling means adapted to cool said portion of the atmosphere before it is compressed by said separate pump.
5. 5. A furnace as claimed in any preceding claim and in which each said ejector pump comprises a body within which is formed a venturi, the primary flow of the pump taking place from an annulus up stream of the venturi and the secondary flow being entrained through the venturi.
6. 6. A furnace as claimed in any preceding claim and in which said vessel comprises heater elements spaced about its walls and a radiation shield interposed between the heater elements and the working volume, said ejector pumps being mounted between the walls and the radiation shield.
7. 7. A furnace substantially as particularly hereinbefore described with reference to the accompanying drawings.