US2806684A - Output control for hot air gas turbine plant - Google Patents

Description

p 7 9 .c. GREY 2,806,684

OUTPUT CONTROL FOR HOT AIR GAS TURBINE PLANT 4 Sheets-Sheet 1 Filed April 30, 1956 Fmal so v I I I lo so 40 so so 90, I00 no :20 I30 no I50 Inventor ymmm,m

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J. C. GREY ou'rP u'r doNTR L. FOR 501 AIR GAS TURBINE PLANT Filed April so, 195

Sept17, 1957 J. c. GREY v v om urfcomomoa nor AIR GAS TURBIJNE PLANT Filed April so; 1956 l 4 Sheets-Sheet s v .I A

. voLuma SELECTOR PRESSURE Sucronpv lnven'l'or Sept 17; 1957 J. c. GREYY v OUTPUT CONTROL FOR HOT AIR GAS TURBINE PLANT Filed April so; 1956 4 Shasta-Sheet 4 WWW ' ATTORNEYS ,.U/ M ,mm 1 M o R n M 1 4 O 1 M J f m H o N m. m E s c E F W W m m Unite States OUTPUT CONTROL FDRHOT AIR GAS TURBINE PLANT John Constantine Grey, Isleworth, England, assignor to Power Jets (Research & Development) Limited, London, England, a British company Application April .30, 1956, Serial No. 581,652 Claims priority, application Great Britain June 1, 1951 12 Claims. (Cl. 26319) furnace; first, because resistance to air flow is produced by a mass of porous material, and second, the aerodynamic properties cannot be accurately predicted. Thus, whereas at a given instant it may be broadly true that an increase in volume requires an increase in pressure, their numerical relationship may vary from day to day, according to the state of the furnace charge. The actual required values of the pressure, volume and temperature are dictated by experience and the engineer in charge needs control over each one, independently of the other two.

While aiming at as much measure of independence as possible, it is clear that of the three variables, only the temperature can be really independent, whereas the pressure and volume are related to each other by the blast furnace characteristics. Thus operation at constant pressure involves large variations of volume flow and, conversely, operation at constant volume (or mass flow) necessitates considerable variation in blast pressure.

An object of the invention is to provide control of the blast air supply to a blast furnace either for constant pressure or constant mass flow conditions, which control is automatically effected in normal operation, over-riding manual supervision being able to be introduced without delay for controlling abnormal operations.

It has previously been proposed to provide the blast air supply from a gas turbine plant. Moreover it has also been suggested that an easily adjustable arrangement will comprise an open cycle single-shaft plant with two turbines one of which has a throttled stream of working fluid and which gives supplementary power to maintain the plant self-driving. In one such plant a by-pass duct leads a portion only of the main air stream to be expanded in the throttled turbine. Another part of the stream forms the blast supply. More than one cycle arrangement of this nature is possible. In one described below division of the air stream follows after it has been passed wholly through one of the turbines. In another cycle the air stream is split immediately downstream of the compressor, neither turbine receiving the whole stream. Reheating arrangements before the throttled turbine are preferably incorporated.

It is proposed to unite together gas turbine blast furnace air supply plant with an arrangement for effecting the desired control mentioned above.

Patented Sept. 17, 1957 'ice means for controlling the air pressure at the delivery point of the compression stage of the plant in accordance with the mass flow of air supplied to the furnace and with the blast air-supply pressure acquired by the furnace.

The control arrangement may be operated so as to provide in normal operation a .blast air supply either of constant mass flow or at constant pressure. Preferably the control is effected via a throttle fitted in the lowpressure outlet duct of'an auxiliary turbine incorporated for the reasons specified above. In this case variation in work done by the auxiliary turbine adjusts the compressor delivery pressure. The control arrangement may comprise mechanical servo-mechanisms. Alternatively, electrical remote control'may be employed.

The invention also provides a control arrangement for a gas turbineblast furnace blower plant which plant comprises a rotary air compressor, two turbines each provid ing' drivin'g torque for the compressor with a part only of the air stream through the plant being expanded through one of theturbines, another part being delivered as the blast supply and heat input means, the control arrangement comprising means for varying the power outputof said one turbine thereby varying the delivery pressure of the compressor and differential means automatically responsive to the monitored compressor delivery pressure, to the monitored air mass flow supplied to the furnace and to a predetermined setting of blast pressure required to control the power varying means.

"lhe invention will nowbe described with reference to one embodiment thereof shown in the accompanying drawings in which:

Figures 1, 2 and 3 are graphs showing the operating characteristics of gas turbine air blower equipment in relation to an associated blast furnace.

Figure 4 is a general schematic diagram of an arrangement forming the embodiment of the invention to be described.

Figure 5 is a more detailed view of the mechanical differential control outlined in Figure 4.

Figure dis a side view of a cam seen in Figure 5.

Figure 7 is a detailed view of the control box which is shown schematically in Figure S.

Figure 8 is a detailed view of the mass flow monitoring equipment shown schematically in Figure 5.

Figure 9 is a schematic of an alternative electrically operated control circuit.

The required operating characteristics of a control arrangement according to the invention will be appreciated by reference to Figures l-3.

References used in the following argument are as follows:

PT=Main turbine inlet pressure t'r=--Main turbine inlet temperature Pb Blast pressure M=Airmass flow to blast furnace t =Blast temperature Figures 1 and 2 show the characteristics of the air turbirre blower, i, e. the main turbine inlet pressure (which is approximately the same as the compressor delivery pressure in the arrangement of Figure 4 described below and is here plotted as such) and temperature respectively that are required in order to sustain given blast pressures and mass flows. (The mass flow is shown as percent of maximum continuous flow at the blast pressure of 20 p. s. i. g.) Thus, if the blast furnace will accept M =70% at Pb=10 p. s. i. g., the turbine inlet conditions have to be P ==68 p. s. i. .g. and t =55O C. as denoted by points Aand A; In Figures 1 and 2 respectively, an increase l l l of mass flow at constant 'blast pressure requires an increase of turbine pressure as shown in Figure 1 but constant turbine temperature is maintained as Figure 2 shows. The changes are indicated by arrows (a). In another case, an increase of blast pressure at constant mass flow requires an increase of both turbine pressure and temperature as indicated by arrows (b) in the two figures. In practice, an increase of blast pressure would probably be accompanied by some increase of mass flow as indicated by arrows (c). The linear blast pressure/mass flow relationship is shown in Figure 3.

Assuming that the turbine is delivering steadily at the operating point A, any deliberate departure from this point, say an increase of mass flow and/ or blast pressure, must be initiated by an increase in turbine speed. In the arrangement of Figure 4, this may theoretically be obtained either by an increase in turbine inlet temperature or by in increase in power output from the auxiliary turbine. The latter method is adopted because of the slow response to attempts to adjust turbine temperature.

The general layout of the blast air supply plant will be appreciated from Figure 4. In this control apparatus and connections are shown in heavy print. The cycle diagram is drawn more faintly. The turbine plant consists of an air compressor CP, a main air turbine MT and an auxiliary air turbine AT, all mounted on the same shaft. There are indirect heaters AH and BH, the former being primarily the turbine heater and the latter the blast heater. It will be seen that some of the output stream from the main turbine MT after passing through the blast heater 81-1 is by-passed to provide working fluid for expansion in the auxiliary turbine AT. The main airstream is taken direct to the blast furnace shown at BF. In the outlet duct of the auxiliary turbine there is a throttle T by means of which the power delivered to the shaft by this turbine may be adjusted.

There are two main control arrangements associated with the plant, one of which i the temperature control of the air heaters and therefore also of the inlet air to the main turbine and of the blast air. This is exercised by the adjustment of the combustion regulator P, by means of which the quantity of fuel burned in the air heater may be adjusted in known manner. The heaters AH and EH are fired in the same way as gas fired boilers; they are blown by electrically driven fan and their control does not involve any new problems and so forms no new part of the invention. The control of the blast temperature is entirely independent of the operation of the air supply plant and may be selected in advance and varied as required. The other control arrangement, to which the invention particularly relates, is concerned with the regulation of a gas turbine air blower equipment. In one form it comprises a mechanical arrangement as indicated in Figure 4 to 7. A mass flow monitor FM is inserted in the blast airstream being delivered to the furnace and its reactions are communicated to the control box 51. Mass flow monitors are themselves known and the most accurate kind are those which comprise a venturi restriction in the duct with means for measuring venturi head, absolute pressure and temperature. These measurements may be combined to give a movement of a control lever which is a close approximation to changes in the actual flow valve. In Figures 4 and 5 the flow monitor FM has been diagrammatically shown, and the dotted line between the monitor and the control box S1 represents the transmission of a shaft movement directly proportional to mass flow. In Figure 8 is represented a known type of flow monitor which indicates the mass flow through a venturi in a duct D at any moment by the position of a link L. The volume flow through the venturi V depends upon the difference in pressure upstream and downstream of the venturi. These upstream and downstream pressures are effective through pipes P1 and P2 respectively, and act on the inner and outer surfaces respectively of a bell BL partially submerged .in a liquid as shown. A pressure acting within the bell sutficiently greater than that acting without, will cause the bell to rise, and the lever R and steadying link LS to move about their pivots. This causes a downward movement of the vertical rod RV, which is translated to a horizontal movement of the link L by means of a bell-crank BC. The bell BL is constructed and shaped in such a manner that its movement, and consequently that of the link L, i linearly related to the rate of flow in the duct D. Compensation for different temperature and pressure conditions within the flow is made by varying the effective length of the lever R between its pivot and its point of attachment to the rod RV, a slot beingprovided in the lever R for this purpose. Variation in the position of the rod RV along the slot will therefore influence movement of the link L, and thi variation is made dependent upon variations of pressure and temperature within the duct by means of Bourdon tubes p and t respective-1y, connected to the duct D downstream of the venturi V by means of pipes P4 and P3. Such variations in pressure and temperature will cause movement of the free ends of the tubes 2 and t, and of the floating beam FB attached thereto. Any horizontal movement of the central point of the beam FE a shown will depend upon the combined effect of temperature and pressure, and will be conveyed by the rod RX, lever LX and rod RY to the upper end of the rod RV, thus controlling the movement of the rod RV in the slotted end of lever R, and influencing the movement of the link L as described. The action of the link L is conveyed to the control box S1, and may be supplemented by a conventional servo mechanism if required. This control box S1, which is more fully described in Figure 7, adjusts a cam PVC whose follower is connected to the differential control C. This control is also responsive to the main turbine inlet pressure, an air connection being taken from the inlet duct for this purpose. The differential control acts via mechanical transmission and a servo-motor S2 to regulate the throttle T in the downstream duct of the auxiliary turbine AT.

The control arrangement outlined above may be more fully seen in Figures 5 to 7 and the actual operation of the plant will be described from these figures. Referring first to Figure 5, it will be'noticed that there are two handwheels for manual adjustment of the control arrangement, one is for selection of mass flow or volume of the blast air supply and the other i a blast air pressure selector. The volume selection handwheel is connected to the control box S1 and that in turn moves a rack RE. The internal arrangement of the control box is indicated in Figure 7.

The link L in Figure 7 transmits to the control box the mass flow monitors indications. The movements are transferred to one end of a swinging link reversing mechanism RM the purpose of which will be apparent later. The swinging link itself SL has a handle RL on it which extends outside of the box and enables reversal to be accomplished. The movement of the link L is transmitted directly, or in reverse as the case may be, to the guided rod FL. To the end of the rod FL there is fitted a piston FF which is a friction fit in the cylinder FC. Normally the movements of FL, following those of the link L, are directly passed on to the rack RE which is connected to the cylinder FC. To the side of the cylinder FC is attached a rack VR which is engageable by the pinion VP on the shaft of the volume selection handwheel. The relative positions of the cylinder FC and the piston F? can therefore be adjusted by manual operation of the handwheel overcoming the friction drive. According to the handwhecl operation so is the rack first positioned; thereafter that rack follows the mass flow monitors responses. In the description of the operation of the control arrangement, it will be assumed that the engineer in charge of the blast furnace has been ordered to maintain a constant blast pressure. The action needing to be taken is discussed below.

Reference to the curves of Figures 1 and 2 shows that the mass flow may be varied widely at any given blast pressure providing that the turbine temperature follows the appropriate line in Figure 2 and the turbine inlet pressure and compressor delivery pressure follow the appropriate line in Figure 1. Thus, at a blast pressure of p. s. i. g. in order to increase the mass flow from 70% (point A) to 100% (point B), the turbine temperature must remain substantially constant but the turbine pressure must be increased from 68 p. s. i. a. to 87 p. s. i. a., i. e. the turbine speed must be raised.

The increase of speed from vA to B can only be obtained by increasing the turbine power during the transition from A m3, and in the absence of other means, this would normally be achieved by a temporary increase in turbine temperature so that the operating point would travel in the direction of arrow (0) before settling on point B. The disadvantage of this method is that, due to the thermal inertia of the air heater AH, the increase in turbine temperature is a relatively slow operation (a question of minutes) and the control here provided over the throttle valve T downstream of the auxiliary turbine provides a considerable speeding up ofadjustment. This auxiliary turbine is normally designed to operate against a pressure somewhat above atmospheric so that, when an acceleration is required from the unit, it may be obtained at practically constant turbine temperature simply by opening throttle T, thereby increasing the work output of the auxiliary turbine. Under these circumstances, the rapidity of response is almost instantaneous (a question of seconds). It should be noted that the opening of throttle T is of a transient character so that when the operating point reaches B, the valve T will be closed slightly in order to restore to the auxiliary turbine approximately its original pressure ratio, i. e. the pressure ratio when operation was at point A.

Assuming now that the control gear has been manually adjusted so that Pb=10 p. s. i. g., the rack RA having been positioned correspondingly as a result. Assume also that a mass flow has been obtained giving tr=550 C. in accordance with Figure 2. These handwheel movements effect both axial and angular motion of the cam PVC. The pressure selecting wheel rotates a pinion on a rack RA which is integral with the shaft CS on which the cam is mounted. Hence longitudinal movement is imparted to the cam with a result on its follower CF which can best be seen from the cam side View, Figure 6. The mass flow or volume selecting handwheel moves the rack RB with which a pinion fixed to shaft CS engages. This pinion is, of course, of sufficient width to accommodate longitudinal movements of shaft CS without disengagement from the rack RB. Hence angular motion of the cam PVC is obtained. It will be recalled that rotation of PVC is also obtainable by driving the rack RB directly from the mass flow monitor FM.

The cam follower CF is extended to form part of the differential control C. The latter consists essentially of a spring-extended capsule or bellows within a sealed casing. The spring is normally compressed and additional spring force is exerted whenever the cam follower rides up. The skirt of the bellows is attached to the casing and the outside of the bellows is subject to the pressure PT communicated via the connection from the turbine inlet.

The spring pressure exerted in the differential control depends on the position of the cam follower CF. The profile of PVC is therefore so shaped that for any given mass flow the spring pressure balances the appropriate P1 in accordance with Figure 1. Thus a steady condition such as has been assumed results in the extension of the bellows remaining constant. Lack of balance causes the bellows to expand or contract and the bellows follower F, which has a limited travel, is raised or lowered. This movement is communicated to the servo-motor S2 which in turn regulates the auxiliary turbine throttle T,

6 openingit when F moves upwards and shuttingit when F moves downwards.

With this interaction of parts it follows that clockwise rotation and movement axially to the right (as seen in Figure 6) of PVC lowers the cam follower CF. Hence the spring pressure .in the differential control is reduced, the bellows are compressed by the air pressure PT, the follower F .drops and S2 closes the throttle T. This causes the .power developed by the auxiliary turbine to be decreased and the shaft speed falls. The compression ratio of the compressor CP (Figure 4) is lowered and at a new smaller valueof PT equilibrium is again established in the differential control, the throttle T condition "beingautomatically readjusted to a new position.

Anticlockwise rotation and/ or movement axially to the left (as seen in Figure 6) of PVC raises CF. By a similar chain of causation a new increased balancing value of PT is obtained and a new higher shaft speed obtained.

All these parts are brought into play during a manual operation of the control arrangement. Automatic adjustment is provided for by the introduction of the control box'Sl which is responsive to the mass flow monitoring unit, diagrammatically indicated at FM. If the mass flow changes, the control box Si moves the rack RB correspondingly and so rotates PVC. The direction of rotation is made dependent on Whether constant pressure or constantvolume Working is required. In the former case, which has been assumed above, a reduction in flow is caused to effect clockwise rotation of PVC and vice versa. Hence, ifthe mass flow through the blast furnace diminishes, say, due toa stiffening charge in the furnace, the controlibox S1 will rotate the cam clockwise until the turbine inlet pressure is lowered and equilibrium is restored.

In order to achieve automatic constant volume working the onlyv change that has to be made to the equip- 'ment is that a reduction'in flow now effects anticlockwise rotation of PVC. This isachieved by reversing the swinging link SL by means of the handle RL.

For example, assume that the plant is operating steadily at point A (see Figures 1 and 2) and that, as a result of a stiifening charge in the blast furnace, the mass flow diminishes (incidentally with a slight transient increase in blast pressure). Under the response of the mass flow sensitive control box S1, the cam PVC will be rotated anticlockwise. This produces a higher turbine inlet pressure and in the manner described above. In Figure l the operation can be seen first as a mass flow reduction, arrow a, and then as an increase of PT and restoration of M, arrow e. This process will go on tending to restore the original equilibrium position. Failure to do so completely is an indication to the operatorthat the selected blast pressure is too low to achieve the desired mass flow. He then selects a progressively higher blast pressure until the mass flow indicator reading is restored.

v The mechanical control arrangement shown in Figures 4 to 7 may be replacedby anequivalent electrical controlling circuit. Such a circuit is shown schematically in Figure 9. A five-position switch BPS, in accordance with its positioning, taps off a corresponding potential difference from the potentiometer PR. This voltage is a measure of the blast pressure setting required and it is furtheradjustable by the potentiometer MS to a final value dependent also on the mass flow setting required. The supply, voltage thus developed provides current via a rheostat MC and a change-over-switch PVS through one side of a difierential relay DR. The balancing current through the other side of the relay DR is developed from a pressure sensitive supply PTM, monitoring the turbine inlet pressure. In equilibrium conditions these balance and the relay movable arm makes contact with neither of the fixed stops 1 or 2. If, however, the relay is unbalanced one or other of these contacts is made and a circuit is completed to the control TC for the throttle T, either opening or shutting thelatter.

The operation of the electrical circuit is exactly equivalent to the mechanical control already described. The higher the blast pressure setting the greater the current that flows through the left hand winding of relay DR; to restore equilibrium greater current has also to flow through the right hand winding, this follows from an increase in PT brought about by operation of TC to open the throttle. Larger or smaller currents in the controlling (left hand) winding are obtained by variation of the potentiometer MS in response to manual adjustments of mass flow.

The automatic control, as before, follows the indications of the flow monitor FM, which is arranged to position the rheostat MC accordingly, thereby altering the controlling current. As shown in Figure 6 assuming that reduction in mass flow causes the sliding contact of MC to move to the right, the circuit is arranged for constant volume working. Change over of the switch PVS automatically alters the control arrangement for constant pressure working.

Although in the above description the throttle T has been positioned on the downstream side of the auxiliary turbine AT, which positioning is preferred, it is possible for it to be situated upstream of AT, as shown at T in Figure 5.

Although over-riding controls have not been shown in the drawings it is intended that they should be incorporated. These controls automatically ensure that ceiling turbine temperature and speed are not exceeded. There is also included automatic antisurge gear which operates across the intake and delivery of the compressor so that at any given speed it is impossible to reduce the compressor mass flow below the surge limit. The plant incorporates overspeed and overheat controls set to trip the unit to a standstill in the event of either the speed or temperatures reaching a predetermined value beyond the limit set by the over-riding controls. The stopping of the unit is justified by the possibility of a major breakdown that would result by the continued operation under such conditions.

By manually overriding the automatic operation of the control box S1 in the mechanical arrangement and fixing MC in a home position in the electrical arrangement the control becomes fully responsive to manual adjustment. Such a return to hand operation is easily and quickly performed.

An automatic control system has been described which is capable, by means of simple operations, of maintaining the supply of blast air either at constant pressure with varying mass flow or at constant mass flow at varying pressure. The arrangement is such that changes of load are effected rapidly, the response being independent of the thermal capacity of the air heaters.

What I claim is:

l. A control arrangement for a gas turbine blast furnace blower plant having means for compressing, heating and delivering an air supply into a duct leading to a last furnace, which arrangement comprises differential means responsive on one hand to the air pressure de veloped by said compression means and on the other hand to air mass flow in said duct, means operable to adjust the pressure ratio of said air compression means and a connection between said differential means and said pressure ratio adjusting means enabling said pressure ratio to be altered in accordance with the relationship between said air pressure and said mass flow.

2. A control arrangement for a gas turbine blast furnace blower plant having means for compressing, heating and delivering an air supply into a duct leading to a blast furnace, which arrangement comprises means for positioning a device in accordance with air mass flow in said duct, means for altering the effect of said positioning in accordance with manual adjustment of desired pressure for said blast air supply, further means for altering the effect of said positioning in accordance with a manual adjustment of desired air mass flow in said duct, differential means responsive on the one hand to the eifect of positioning said device and on the other hand to the air pressure developed by said compression means, means operable to adjust the pressure ratio of said air compression means and a connection between said differential means and said pressure ratio adjusting means enabling said pressure ratio to be altered in accordance with the relationship between the effect of positioning said device and said air pressure.

3. A control arrangement for a gas turbine blast furnace blower plant having turbine-driven compressing means and indirect heating means for an air supply delivered into a duct leading to a blast furnace comprising means for adjusting the turbine power input to said compression means independently of any adjustment of said indirect heating means a mechanism whose motion is responsive to air mass flow in said duct equipment for producing pressures corresponding to said motion and differential pressure means operable to control said adjustment means in accordance with the state of balance between said motion representative pressure and turbine inlet pressure communicated thereto.

4. A control arrangement for a gas turbine blast furnace blower plant having rotary air compression means, a main turbine and an auxiliary turbine, together driving said compression means, indirect heating means for an air supply compressed by said compression means and a duct leading to said blast furnace into which is delivered at least part of said air supply, the arrangement comprising a throttle for the flow of working fluid through said auxiliary turbine, means for deriving a first response indicative by its magnitude of outlet pressure from said compression means, means for deriving a second response whose magnitude is based upon the air mass flow in said duct, means for comparing said first and second responses and controlling said throttle in accordance with the difference therebetween.

5. A control arrangement as claimed in claim 4 further comprising means for manual adjustment of the magnitude of said second response in correspondence with desired air mass flow in said duct.

6. A control arrangement as claimed in claim 4 further comprising means for manual adjustment of the magnitude of said second response in correspondence with desired air pressure in said duct.

7. A control arrangement as claimed in claim 4 in which said second response derivation means incorporates a three dimensional cam and a follower thereof whose movement is transmitted to said comparison and controlling means.

8. A control arrangement as claimed in'claim 7 in which said comparison and controlling means comprises a spring loaded diaphragm whose extension depends upon transmitted movement of said follower and a connection through which air pressure constituting said first response is communicated to said diaphragm to oppose extension thereof.

9. A control arrangement as claimed in claim 4 in which both of said response derivation means produce electrical current responses and in which said comparison and controlling means comprises a differential electrical relay.

10. A control arrangement for a gas turbine blast furnace blower plant having rotary air compression means, a main turbine and an auxiliary turbine, together driving said compression means, indirect heating means for an air supply compressed by said compression means and a duct leading to said blast furnace into which is delivered at least part of said air supply, the arrangement comprising a throttle for the flow of working fluid through said auxiliary turbine, a three dimensional cam, a manually adjustable mechanism for positioning said cam in one direction of motion thereof, another manually adjustable mechanism for positioning said cam in a second direction of motion at right angles to said one direction, automatic adjustment means for positioning said cam in said second direction in accordance with measurements of air mass flow in said duct, a differential pressure device, a connection conveying main turbine inlet air pressure to one side of said device, a follower on said cam, means for producing a pressure in said device proportional to movement of said follower and opposing said turbine inlet pressure and a connection between said device and said throttle so that the pressure balance state in the former controls the latter.

11. A control arrangement as claimed in claim 10 in which said throttle is positioned downstream thereof in the direction of flow of its working fluid.

10 12. A control arrangement as claimed in claim 10 further comprising means for reversing said automatic adjustment means so that the same changes in said air mass flow may have positioning eflFect upon said cam in opposite senses.

References Cited in the file of this patent UNITED STATES PATENTS 2,253,809 Pfenninger Aug. 26, 1941 FOREIGN PATENTS 531,997 Great Britain Jan. 15, 1941 724,742 Germany Sept. 5, 1942

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