GB1579772A - Furnace control - Google Patents

Description

(54) IMPROVEMENTS IN FURNACE CONTROL (71) We, BRITISH STEEL CORPORA TION, a Corporation incorporated and existing under the Iron and Steel Act 1967 whose principal office is at 33 Grosvenor Place, London, S.W.1 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 fuel-fired furnaces and more particularly relates to an improvement in or modification of the invention in our U.K. Patent No. 1 487 385.

In that case there is provided a fuel-fired furnace of generally rectangular section having at one end a main fuel burner located above an exhaust flue system and directed towards the other end of the furnace, whereby the heat flow pattern executes a U-shaped path, and an auxiliary burner located below the main burner in the said one end supplementing the heat flow and heat transfer therefrom.

The present invention provides a furnace in accordance with the preceding paragraph further including means for sensing the temperatures at both the one and the other ends of the furnace and control means for controlling the thrust ratio between the main and auxiliary burners in dependence on any end to end temperature difference whereby to reduce said difference to zero or a selected small value.

The temperature at the one and other ends may be preset to exhibit the same value (or the said selected small value) the control means including separate control links to govern the main burner in dependence on the 'other' end temperature and the auxiliary burner in dependence on the 'one' end.

Alternatively however, and preferably the control means comprises a comparator for comparing the temperatures sensed at the one and other ends and is effective to control the thrust of the auxiliary burner only, the control being effective on the fuel or the fuel and the air flow rate; if the air flow rate only is controlled directly the fuel flow rate may be automatically proportioned thereto. In all these cases of course the main burner will be governed by a separate temperature sensor at the other (far) end as in conventional U-fired furnaces.

The temperature sensors may be thermocouples.

In accordance with this invention then, end to end temperature difference in a furnace, e.g. a soaking pit, is controlled automatically whereby the temperature at both ends of the furnace is simultaneously raised to, and maintained at, the level(s) desired, giving even greater uniformity in the ingot temperatures than that achieved in our earlier case referred to.

In order that the invention may be fully understood an embodiment thereof will now be described with reference to the accompanying drawings, in which: Figure 1 is a sectional side elevation through a soaking pit in accordance with this invention, and Figure 2 is a schematic illustration of the control means by which end temperature difference is governed.

Referring now to Figure 1 the soaking pit shown is essentially the same as that illustrated in the earlier case and the reference numerals identified represent the same elements as those described, and depicted by the corresponding numerals, in the earlier case. Essentially a main (3) and an auxiliary (4) burner are sited in one end wall 13 their flame jets being directed towards the opposite end wall 14. They may be fired by a gaseous or a liquid fuel and indeed the two burners may use different fuels from one another.

Pyrometers 15, 16 are mounted in the walls 13 and 14, respectively, and each comprises a thermocouple housed in a refractory sheath 17, 18.

In operation, the thrusts of the main and auxiliary burners are adjusted so that the jet from the auxiliary burner reaches the end wall but with insufficient momentum flux to deflect the jet from the main burner upon to the roof (2). Hitherto, the normal pit control thermocouple (not shown) in the wall 14 has been operative in controlling the fuel input to the burners for governing the temperature of the furnace and the thrust ratio and thermal power ratio between the two burners have been manually adjusted to gain the required temperature distribution.

An increase in the thrust from the auxiliary burner has been found to provide a change from a far end hot condition to a burner (near) end hot condition. This feature has been utilised here, namely, automatically to control the auxiliary burner thrust so as to maintain the end-to-end temperature difference at zero or a small predetermined value.

Referring now to Figure 2, the outputs from the thermocouples 15, 16 usually of the order of millivolts, are amplified by amplifiers 19, 20 and fed into a comparator 21.

The difference (error) signal output from this unit is applied to a controller 22 which converts the electrical input to a mechanical, hydraulic or pneumatic medium for controlling the fuel supply to the auxiliary burner via 23. The control is such as to adjust the thrust in a sense to reduce the temperature difference to zero or a small selected value as dcscribed--the latter value may be desired to compensate for the sequence in which the ingots are removed from the pit.

Additionally, the air supply to the auxiliary burner may be adjusted via 24 by the output from the controller.

Although the invention has been described with reference to the particular embodiment illustrated it is to be understood that various modifications may be made without departing from the scope of this invention. For example thermocouples are just one form of pyrometer suited to this application, other forms could equally well be used. Further, the disposition of these thermocouples is not critical and the thermocouples 16 conveniently be housed in the same sheath as that in which the pit control thermocouple (not shown) is housed for governing the main burner in the conventional manner. The auxiliary burner has been shown to be a tunnel burner, but any other form of burner could alternatively be adopted, the principal requirement being that of having a high thrust/mass ratio.

Further, the simpler alternative system involving preset temperature settings for the main and auxiliary burners utilises only thermocouples, one governing the main burner as in the conventional manner and the other governing the auxiliary burner. With this direct and discrete form of control a comparator is of course not utilised but the drawback with this system as compared with the principal embodiment described is that end to end temperature difference is not necessarily minimised as the furnace is being brought up to its operating temperature, although of course the two temperature settings are ultimately realised and maintained.

WHAT WE CLAIM IS: 1. A fuel-fired furnace of generally rectangular section having at one end a main fuel burner located above an exhaust flue system and directed towards the other end of the furnace, whereby the heat flow pattern executes a U-shaped path, an auxiliary burner located below the main burner in the said one end supplementing the heat flow and heat transfer therefrom, sensors for sensing the temperatures at both the one end and the other ends of the furnace and control means for controlling the thrust ratio between the main and the auxiliary burners in dependence on any end to end temperature difference whereby to reduce said difference to zero or a selected small value.

2. A furnace according to claim 1, wherein the control means includes a comparator for comparing the temperatures sensed in the one and the other and is effective to control the auxiliary burner only.

3. A furnace according to claim 2, wherein the thrust of the auxiliary burner is controlled.

4. A furnace according to claim 2 or claim 3, wherein the fuel flow rate only, or both the fuel and the air flow rate to the auxiliary burner are controlled.

5. A furnace according to claim 1, wherein the temperatures at the said one and other ends are preset to exhibit the same value, or the said small value difference, and the control means includes two control links separately governing the thrusts of the main and auxiliary burners.

6. A furnace according to any one of claims 1 to 5, wherein the temperature sensors are thermocouples.

7. A fuel-fired furnace substantially as herein described and/or as illustrated in the accompanying drawings.

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

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. sheath 17, 18. In operation, the thrusts of the main and auxiliary burners are adjusted so that the jet from the auxiliary burner reaches the end wall but with insufficient momentum flux to deflect the jet from the main burner upon to the roof (2). Hitherto, the normal pit control thermocouple (not shown) in the wall 14 has been operative in controlling the fuel input to the burners for governing the temperature of the furnace and the thrust ratio and thermal power ratio between the two burners have been manually adjusted to gain the required temperature distribution. An increase in the thrust from the auxiliary burner has been found to provide a change from a far end hot condition to a burner (near) end hot condition. This feature has been utilised here, namely, automatically to control the auxiliary burner thrust so as to maintain the end-to-end temperature difference at zero or a small predetermined value. Referring now to Figure 2, the outputs from the thermocouples 15, 16 usually of the order of millivolts, are amplified by amplifiers 19, 20 and fed into a comparator 21. The difference (error) signal output from this unit is applied to a controller 22 which converts the electrical input to a mechanical, hydraulic or pneumatic medium for controlling the fuel supply to the auxiliary burner via 23. The control is such as to adjust the thrust in a sense to reduce the temperature difference to zero or a small selected value as dcscribed--the latter value may be desired to compensate for the sequence in which the ingots are removed from the pit. Additionally, the air supply to the auxiliary burner may be adjusted via 24 by the output from the controller. Although the invention has been described with reference to the particular embodiment illustrated it is to be understood that various modifications may be made without departing from the scope of this invention. For example thermocouples are just one form of pyrometer suited to this application, other forms could equally well be used. Further, the disposition of these thermocouples is not critical and the thermocouples 16 conveniently be housed in the same sheath as that in which the pit control thermocouple (not shown) is housed for governing the main burner in the conventional manner. The auxiliary burner has been shown to be a tunnel burner, but any other form of burner could alternatively be adopted, the principal requirement being that of having a high thrust/mass ratio. Further, the simpler alternative system involving preset temperature settings for the main and auxiliary burners utilises only thermocouples, one governing the main burner as in the conventional manner and the other governing the auxiliary burner. With this direct and discrete form of control a comparator is of course not utilised but the drawback with this system as compared with the principal embodiment described is that end to end temperature difference is not necessarily minimised as the furnace is being brought up to its operating temperature, although of course the two temperature settings are ultimately realised and maintained. WHAT WE CLAIM IS:

1. A fuel-fired furnace of generally rectangular section having at one end a main fuel burner located above an exhaust flue system and directed towards the other end of the furnace, whereby the heat flow pattern executes a U-shaped path, an auxiliary burner located below the main burner in the said one end supplementing the heat flow and heat transfer therefrom, sensors for sensing the temperatures at both the one end and the other ends of the furnace and control means for controlling the thrust ratio between the main and the auxiliary burners in dependence on any end to end temperature difference whereby to reduce said difference to zero or a selected small value.

2. A furnace according to claim 1, wherein the control means includes a comparator for comparing the temperatures sensed in the one and the other and is effective to control the auxiliary burner only.

3. A furnace according to claim 2, wherein the thrust of the auxiliary burner is controlled.

4. A furnace according to claim 2 or claim 3, wherein the fuel flow rate only, or both the fuel and the air flow rate to the auxiliary burner are controlled.

5. A furnace according to claim 1, wherein the temperatures at the said one and other ends are preset to exhibit the same value, or the said small value difference, and the control means includes two control links separately governing the thrusts of the main and auxiliary burners.

6. A furnace according to any one of claims 1 to 5, wherein the temperature sensors are thermocouples.

7. A fuel-fired furnace substantially as herein described and/or as illustrated in the accompanying drawings.