Method And Apparatus For Controlling A Metallurgical Furnace Turbo Compressor

Abstract

The blade angle of the stator blades in the turbocompressor is adjusted in order to control the amount of compressed air delivered by the turbocompressor. The blade angle is adjusted in dependence on the speed of the turbomachinery shaft and the amount of compressed air delivered by the turbocompressor can be divided between the compressed air line to the plant and a branch line to a reduced pressure zone so as to prevent pumping of the turbocompressor.

Description

This invention relates to an apparatus for controlling a furnace plant, and particularly, a furnace plant for the heat treatment of metals.

Heretofore, furnace plants have been known in which compressed air necessary to support combustion has been supplied over a compressed-air line to a furnace in which combustion has taken place at elevated pressure. These plants have usually exhausted the combustion gases from the furnaces at elevated pressures to a turbine which, in turn, has driven a turbocompressor delivering compressed air to the compressed-air line. In order to control the turbocompressor sections of these plants, it has been the usual practice to act on the turbine input gas flow. Unfortunately, the possibilities of adaptation of this kind of control to the special features of the furnace have been limited because only some of the gas can then be supplied to the turbine while the remainder must be discharged elsewhere as a reserve supply for control purposes. As a result, the available gases cannot be utilized economically enough.

Accordingly, it is an object of this invention to economically utilize the waste gas flow of a furnace plant.

It is another object of the invention to eliminate any need to act on the turbine input gas flow in order to control a furnace plant.

Briefly, the invention provides a furnace plant which has a compressed-air supply line, a furnace receiving compressed air from the supply line, a turbine for receiving the waste gas exhausted from the furnace and a turbocompressor for delivering compressed air to the supply line with a speed controller in the section of the plant containing the turbine and turbocompressor. This speed controller is used to adjust an adjustable stator blade system in the turbocompressor while the flow of gas to the turbine is unaffected. In this way, by shifting the control from the turbine to the turbocompressor, it is possible for the turbine to receive the entire waste gas output from the furnace substantially at all times. Full use is thus made of the turbine output.

The speed control is also provided with a means for adjusting the speed set value. This adjusting means can be adjusted, e.g. in dependence upon the pressure in the compressed-air line. As a result, the compressor operation can always be controlled so as to deliver in optimum circumstances the quantity of air corresponding to the available power.

In addition, the turbocompressor delivery line is connected to a branch line which leads to a reduced-pressure zone. This branch line includes a control system which is adjusted by a senser which measures the air delivery of the turbocompressor. This metering system serves to control a means for adjusting the air quantity set value at which a regulating element in the branch line begins to open.

The means for adjusting the air quantity set value is itself adjusted by the pressure in the turbocompressor delivery line. This prevents the turbocompressor from operating near its pumping limit. When little air is being taken from the compressed-air line, the quantity of air which prevents the compressor from starting to be pumpted discharges through the branch line. Any return of air from the compressed-air line to the compressor or into the branch line is prevented by the provision of a check valve in the delivery line, a feature which may be particularly useful when air has to be bled through the branch line to prevent pumping of the turbocompressor.

The turbine feed line also has a stop member which is closed under the control of a quick-acting controller when the turbocompressor reaches maximum permissible speed. This case might occur if the turbocompressor should suddenly prove unable to absorb the power from the turbine, the result of which might cause the turbo-machinery to race. It is also recommended, in this case, that a branch line which has a straight-through valve and which extends to an area of reduced pressure be connected to the turbine feed line at a place upstream of the straight-through member, and to have the straight-through valve opened under the control of a quick-acting controller when the turbocompressor reaches maximum permissible speed.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 diagrammatically illustrates a view of a furnace plant controlled in accordance with the invention, and

FIG. 2 is a PV diagram of the turbocompressor.

Referring to FIG. 1, a metallurgical or blast furnace 1 is supplied through a supply line 2 with combustion-supporting air at elevated pressure. The waste gases of combustion leave the blast furnace 1, at a pressure which, although reduced by the pressure drop in the blast furnace 1, is still considerable, through a line 3 and pass to a gas turbine 4. The turbine 4 drives, via a coupling 5, a turbocompressor 6 having at least one row or ring of rotatable adjustable stator blades 7 (only one of which is shown). The compressor 6 intakes air from atmosphere through a line 8 and delivers compressed air through a delivery line 9 to a compressed-air line 10 which in turn is connected to at least the blast furnace air supply line 2. Other lines for supplying combustion-supporting air to other furnace plants can also be connected to the line 10. A separately driven compressor (not shown) will also be needed, as a rule, to supply the line 10 with the quantity of air which the turbocompressor 6 cannot supply. In operation, therefore, it is essential to maintain a constant pressure, e.g. the pressure P1, in the compressed-air line 10 by appropriate control of the quantity of air delivered by the added compressor.

In order to control the operation of the turbocompressor 6, a speed controller 11 driven by the turbomachinery shaft acts through the agency of a servomotor 12 on the ring of adjustable blades 7 so that the compressor efficiency decreases as speed decreases and increases as speed increases. Through the agency of a set-value adjustment system 13, as is known, the required set value of the turbomachine can be determined in accordance with the pressure P1 in the line 10. However, since the pressure therein is maintained constant, the speed too remains constant unless the pressure in the line 10 changes.

In order to prevent pumping of the turbocompressor 6, a branch line 14 comprising a regulator valve 15 is connected to the turbocompressor delivery line 9. The line 14 extends to an area at a reduced pressure, such as a discharge line through which air delivered in excess can discharge to atmosphere above the roof (not shown) of the plant. The regulator valve 15 is actuated by a servomotor 16 which is controlled by a senser 17 of conventional structure which, in turn, is controlled by the quantity of air flowing through line 9 to line 10. The regulator valve 15 starts to open when the quantity of air entering line 10 becomes so small that the turbocompressor 6 is near the critical level at which pumping begins. The resulting increase in air delivery from the turbocompressor 6 precludes any pumping thereof as the turbocompressor 6 acts only against a small pressure. Since the critical level for pumping also changes when the delivery pressure is low, a senser 18 responsive to the pressure in the delivery line 9 adjusts the air quantity set value at which the servomotor 16 opens the valve 15. Consequently, whatever the operating condition may be, as much compressed air can always be supplied to the line 10 as the same can absorb without any pressure increase, and air need be discharged only in the amount necessary to prevent pumping of the compressor. A check valve 25 in line 9 prevents a flowback of air from line 10 to compressor 6 or to line 14 in such cases.

In order to prevent the turbomachinery from racing under an excess flow of waste gas, a quick-acting shut-off element 19 under the control of a quick-acting shut-off controller 20 is interposed in the line 3. If speed becomes excessive, the element 19 closes to prevent the turbomachinery from racing. Also, a branch line comprising a straight-through valve 22 is connected to the line 3 upstream of the element 19. The valve 22 is also controlled by the controller 20 as is known, so that upon closure of the element 19, the blast furnace waste gas passes through the line 21 to a lower-pressure area. This feature ensures that a rapid shutdown of the turbomachinery does not disturb the blast furnace operation.

The compressor 6 shown is an axial-flow machine wherein either the inlet stator blades, e.g., a ring preceding the first stage or inter-stage rings or a final ring after the final stage can be adjusted. If required, however, radial-flow compressors can be used, in which event appropriate inlet turbulence devices or turbulence devices in the diffusers are used. In special cases, it might be possible for rotor rings of axial-flow compressors to be adjustable.

The nature of the control provided can be gathered from the PV diagram shown in FIG. 2. P1 denotes the delivery pressure in the line 10 in FIG. 1. A denotes the pumping limit for various operating conditions, and B denotes a level which the compressor must not pass through if pumping is not to occur. Curves W1, W2 and W3 represent zones of equal efficiency (86, 84 and 80 percent).

The normal operating condition is at point F on the line P1, the compressor having a particular performance N at a speed R. The adjustable blades 7 are at a blade angle B. When the turbine output decreases, e.g. because either the quantity of gas or the pressure or the temperature decreases, the operating point shifts from point F to point F', the blade angle B changing. The control adjusts the blade, for instance, to the blade angle B' at the point F'. If there still is a tendency to shift towards the critical pumping level A, the metering control system 15, 16, 17 then opens the regulator valve 15 so that air can discharge through the line 14 and the total delivery of the compressor 6 increases, operation shifting back towards the point F' so that the pumping zone above the curve A is not reached.

When the output from the turbine to the turbocompressor increases, operation shifts from the point F towards the point F". The control then acts to adjust the adjustable blades to the blade angle B". More air is therefore supplied to the line 10 and so the work done by the turbine is absorbed. If the turbine output were to increase further, compression would be controlled out and operation would follow the curve B". The turbocompressor would then deliver a smaller volume of air but at high pressure and thus absorb the increased turbine output, although at increased speed.

Speed could become excessive only in exceptional circumstances in which the compressor ceased to be able to absorb the power supplied thereto. In such cases, the quick-acting controller 20 would operate and in all cases close the quick-acting element 19, and, if required, open the discharge valve 22 so that the turbine plant would stop.

Since waste gases from blast furnaces usually contain appreciable proportions of finely divided impurities, with the consequent risk of deposits being formed in lines and difficult bends, accumulations of this kind may build up in quite a short period of operation to such an extent that the flow cross-sections are reduced to a disturbing extent and any moving parts present may jam. The places most at risk are tube elbows and, in particular, control equipment, such as the turbine control valves. However, at the high flow velocities in the turbine, the blade shaping according to the invention so directs the flow that either accumulations are completely obviated or small accumulations are at least prevented from getting any bigger. The invention thus allows the placement of the all important control equipment elsewhere than in the turbine gas flow so that the turbine can operate without disturbance despite the high dust contents of the turbine-operating gas.

Claims

What is claimed is:

1. An apparatus for controlling a metallurgical furnace plant having at least one furnace, a compressed-air line connected to said furnace to supply compressed air thereto, a turbine connected to said furnace to receive combustion gas therefrom and a turbocompressor drivingly connected to said turbine to be driven thereby and connected to said compressed air line to deliver compressed air thereto, said turbocompressor having an adjustable blade system therein; said apparatus comprising a speed controller connected to said turbocompressor to be driven thereby and to said adjustable blade system for changing the blade angle of said system to vary the efficiency of said turbocompressor while maintaining a constant turbocompressor speed and to maintain a constant pressure in said compressed-air line, said speed controller having a predetermined speed set value and means for adjusting said speed set value, said means being adjusted in dependence upon the pressure in said compressed-air line as created therein by a separately driven compressor.

2. An apparatus as set forth in claim 1 which further comprises a supply line connected between said furnace and said turbine for delivering the combustion gas to said turbine, a shut-off element in said supply line for selectively closing off the flow of gas through said supply line to said turbine, and a quick-acting controller connected between said turbine and said element for actuating said element to close off the flow of gas to said turbine in response to a measurement of a predetermined speed of said turbine.

3. An apparatus for controlling a furnace plant having at least one furnace, a compressed-air line connected to said furnace to supply compressed air thereto, a turbine connected to said furnace to receive combustion gas therefrom and a turbocompressor drivingly connected to said turbine to be driven thereby and connected to said compressed air line to deliver compressed air thereto, said turbocompressor having an adjustable blade system therein; said apparatus comprising a speed controller connected to said turbocompressor to be driven thereby and to said adjustable blade system for changing the blade angle of said system to vary the efficiency of said turbocompressor while maintaining a constant turbocompressor speed and to maintain a constant pressure in said compressed-air line, as created therein by a separately driven compressor, a delivery line between said turbocompressor and said compressed-air line, a branch line connected between said delivery line and a reduced pressure zone, and a control system in said branch line for controlling a flow of compressed air through said branch line, said control system including means in said delivery line for measuring the air delivery of said turbocompressor and for actuating said control system in dependence on the measured air delivery pressure falling below a preset value.

4. An apparatus as set forth in claim 3 wherein said speed controller has a predetermined speed set value and which further comprises means for adjusting said speed set value.

5. An apparatus as set forth in claim 4 wherein said means is adjusted in dependence upon the pressure in said compressed-air line.

6. An apparatus as set forth in claim 3 wherein said control system includes a regulating valve in said branch line responsive to an air quantity set value in said system for opening thereof, and means responsive to the pressure in said delivery line for adjusting said air quantity set value.

7. An apparatus as set forth in claim 3 which further comprises a check value in said delivery line between said branch line and said compressed-air line for preventing a back flow of air from said compressed-air line to said branch line and said turbocompressor.

8. In combination with a metallurgical furnace plant having at least one furnace producing a flow of combustion gas, a compressed-air line connected to said furnace to supply compressed air thereto at a constant pressure, a turbine connected to said furnace to receive the flow of combustion gas therefrom and to be driven thereby, and a turbocompressor drivingly connected to said turbine to be driven thereby and connected to said compressed air line to deliver compressed air thereto at constant pressure, said turbocompressor having an adjustable blade system therein; an apparatus for controlling said plant comprising a speed controller connected to said turbocompressor to be driven thereby and to said adjustable blade system for changing the blade angle of said blade system to vary the efficiency of said turbocompressor while maintaining a constant turbocompressor speed to maintain a constant air pressure in said compressed-air line, said speed controller having a predetermined speed set value and means for adjusting said speed set value, said means being connected to said compressed air line for adjustment in dependence upon the pressure in said compressed-air line as created therein by a separately driven compressor.

9. A method of controlling a metallurgical furnace plant having at least one furnace producing a flow of combustion gas, a compressed-air line connected to said furnace to supply compressed air thereto at a constant pressure, a turbine connected to said furnace to receive combustion gas therefrom and to be driven thereby and a turbocompressor drivingly connected to said turbine to be driven thereby and connected to said compressed air line to deliver compressed air thereto at a constant pressure, said turbocompressor having an adjustable blade system therein; said method including the steps of

setting a set-value for the speed of said turbocompressor in dependence on the pressure in said compressed-air line said pressure created therein by a separately driven compressor;

determining a difference between the speed of said turbocompressor and said set-value; and

changing the blade angle of said blade system in response to occurrence of a said difference to vary the efficiency of said turbocompressor while maintaining a constant turbocompressor speed and a constant pressure in said compressed-air line.

10. An apparatus as set forth in claim 2 which further comprises a branch line connected to said supply line upstream of said shut-off element and to a reduced pressure area, and a straight-through valve in said branch line connected to said controller for actuation thereby to open said branch line to a flow of gas in response to the measurement of said predetermined speed of said turbine.

11. An apparatus as set forth in claim 1 which further comprises a check valve between said turbocompressor and said compressed-air line for preventing a flow back of air from said line to said turbocompressor.