US1921903A

US1921903A - Elastic fluid turbine

Info

Publication number: US1921903A
Application number: US475016A
Authority: US
Inventors: Oliver D H Bentley
Original assignee: BF Sturtevant Co
Current assignee: BF Sturtevant Co
Priority date: 1930-08-13
Filing date: 1930-08-13
Publication date: 1933-08-08
Anticipated expiration: 1950-08-08

Description

o. D. H. BENTLEY 1,921,903

ELASTIC FLUID IJIJRBINEI Filed Aug. 13, 1930 Patented Aug. 8, 1933 UNITED STATES ELASTIC FLUID TURBINE Oliver D. H. Bentley, Norfolk, Mass, assignor to B. F. Sturtevant Company, Hyde Park, Mass, a Corporation of Massachusetts Application August 13, 1930. Serial No. 475,016

3 Claims. ((31. 25356) The present invention relates to elastic fluid turbines and more particularly to control means therefor.

One object of the present invention is to provide a turbine adapted particularly for driving the mechanical draft apparatus of a power plant and having means for controlling the power and speed in accordance with the demand placed upon the plant.

Another object of the invention is to provide in a mechanical draft turbine a control means, the movements or changes whereof produce proportionate changes in the volume of air handled by the draft apparatus.

With these objects in view, the present invention consists of the turbine and associated apparatus hereinafter described and particularly defined in the claims.

In the accompanying drawing, Fig. 1 is a diagrammatic elevation of the preferred form of the present invention; Fig. 2 is a section on line 2-2 of Fig. 1; Fig. 3 is a development of the valve actuating cams; and Fig. 4 is an enlarged sectional view on line 4-4 of Fig. 2.

The illustrated embodiment of the invention comprises a turbine 4 connected to operate the mechanical draft fan 6 as by shaft 7. The turbine has six independent sets of nozzles indicated at 8, 1O, 12, 14, 16 and 18. Admission of steam to the several nozzles is controlled by a set of cam actuated valves, one of which is indicated generally at 20. The valves are enclosed in a valve chest 22 which receives steam from the main 24 and selectively delivers it to the nozzles through the pipes 26.

Each valve comprises a sliding piston 27 fitting in the cylinder 28 and mounted on a stem 30. The stem also carries a mushroom valve 32 adapted to seat on the end of the cylinder. The valve has a triangular port 34 which is adapted to be opened to varying degrees by movement of the stem. The valves are actuated by cams 36 which are mounted on a cam shaft 38 and are rotated by the control mechanism.

The quantity of steam admitted to the nozzles is controlled in accordance with the demand placed upon the plant whereby the speed or" the turbine and the volume of air handled by the fan may be varied. Accordingly, the usual constant speed governing devices cannot be employed. In,

its broadest aspects, the invention may comprehend any means of speed control which is dependent upon the load placed on the plant,- but it is preferred to employ the illustrated control mechanism which is actuated by changes in the steam pressure. A spring loaded diaphragm 40 is subjected to the pressure of the steam in the main 24 and controls the pilot regulator 42.

The regulator comprises a casing or cylinder 44 having an hydraulic admission tube 45, the venting port 46 and upper and lower outlet ports 4'7 and 48 which are controlled by'the sliding piston 49 connected to the diaphragm. The ports are in connection with flexible pipes 50 and 51 which serve to apply hydraulic pressure to the under 6 or upper side, respectively, of the actuating piston 52 of the control cylinder 54. This piston 52 is connected by a rod 56 with the casing 44 of the pilot valve.

As the load on the plant increases, the boiler pressure falls, thereby permitting collapse of the diaphragm and admitting pressure to the tube 51 and depressing the piston 52. The casing 44 is thereupon given a follow-up movement to close the regulator ports. The piston therefore takes at any time a position which is directly related to the steam pressuraand hence indirectly related to the load on the plant.

The rod 56 carries a rack 58 which engages with a gear 60 on the cam shaft 38. As the piston 52 is moved, the cams are rotated to open or close the steam valves. Therefore, for each value of steam pressure, there is a definite position of the cams and valves.

It is desirable that the volume of air handled by the fan be indicated directly by the position of the piston 52. To this end, a stationary indicator scale 62 is provided adjacent to the rod 56. The rod carries a pointer 64 which moves over the scale. According to the present invention, the nozzles are so constructed that the graduations on the scale shall not vary to such an extent as to interfere with their accurate reading for any portion of the scale. Preferably, these graduations are uniform, the nozzles being so proportioned that movements of the control rod 56 produce proportionate changes in the air handled by the fan 6. Inasmuch as the power necessary todrive the fan varies theoretically as the cube of the volume, it will be seen that for the preferred embodiment, the nozzles must be so designed as to introduce steam at a rapidly increasing rate for increasing movements of the control apparatus. The cams 36 are so arranged that the separate nozzles come successively into action as the demand for draft increases. The cams are ofthe form shown in the development of Fig. 3, wherein the'lifting portions of the cams areindicated at 36 36*, etc.

'110 Each actmg cam completely opens V its corresponding valve in a period occupying onesixth of the complete displacement of the control rod.

Starting with minimum draft, the first cam opens the valve which feeds steam to nozzle 8. As the draft requirement increases, the second valve starts to open and so on, until all of the nozzles receive the full supply of steam. As shown in Fig. 1, the first three valves are wide open, thus admitting steam directly to the

nozzles

8, 10 and 12, the fourth valve is partially open and the fifth and sixth valves are closed. Further rotation of the cams will continue to open the fourth valve, and then cut in the fifth and sixth valves successively.

In order to illustrate the construction of the nozzles, it will be assumed that nozzle No. 1 is designed to operate the turbine at such a speed as to deliver a certain volume of air, say 10,000 cubic feet per minute; that nozzles 1 and 2 together will deliver twice as much air; nozzles 1, 2 and 3 together three times as much; and so on, that is to say, that for each additional nozzle out in, the volume of air handled by the draft apparatus increases progressively. The total quantity of steam delivered to the turbine, assuming the efficiency to be constant, will vary as the horse power, which in turn, will vary as the cube of the volume of air delivered. Therefore on the assumption of constant efiiciency, the areas of the several nozzles will be in the following relation to the area of the first nozzle;

Thus, the sum of nozzle areas for any number of nozzles cut into operation will vary as the cube of the volume of air handled. For example, with the first five nozzles in service, the total quantity of steam delivered to the turbine is represented by 5 or 125, corresponding to a volume of 5 10,000 or 50,000 cubic feet of air per minute handled by the fan.

The values given above are theoretical or effective areas only and require adjustment to compensate for variable efiiciencies and water rates at the different speeds. Thus, as the speed increases, the efiiciency of the turbine usually increases and the larger nozzles will not require to be increased in the proportion indicated in the above table. The correction to be applied to convert the effective area into actual area will depend, of course, upon the efliciency and water rate at such speed, which quantities may be readily determined by those skilled in the art. It will be noted that the total effective area in service progresses in accordance with the cubes of successive integers, these integers being the numerators of fractions having the same denominator which represents the equal divisions of the total range of speed. Thus, with six nozzle sets, as in the above example, the speed range from zero to full speed is divided into six equal divisions, and the successive integers are 1, 2-, 3, 4, 5 and 6.. These integers also represent the numbers of nozzle sets in service for a particular selected speed.

, By this construction, the amount of displacement of the rod will be proportional to the speed and hence to the volume of air handled by the mechanical draft apparatus. Therefore, the draft conditions may be readily determined by inspection of the indicator.

The valves 34 are so constructed that at intermediate positions of any valve, the quantity of steam admitted to the nozzle increases in such a manner as to follow approximately the cube law. The combination of a mushroom or tappet valve with a piston valve having a triangular port has been found to produce the proper variation in steam quantity to effect the proportional variations in volume of air delivered by the fan.

The steam main 24 includes a governor valve 66 which is adapted to be operated by a high speed safety governor of any usual or preferred form.

It will be understood that the usual constant speed governor cannot be employed because the turbine necessarily operates at Variable speeds. A governor, if employed in the present invention, must be set to operate at a speed higher than any speed which would be normally met in practice, and is useful only for protecting against abnormal or excessive speeds, such as might occur if the load were suddenly removed.

Having described the invention, what is claimed is:

1. The combination with apparatus required to be driven at variable speed and having a characteristic such that the power varies substantially as the cube of the speed, of an elastic fluid turbine having a plurality of nozzle sets of graded areas, and means for successively placing in service additional nozzle sets to increase the speed, the effective area of each nozzle set being such that the total effective area of the nozzle sets in service for one speed is to the total effective area of the nozzle sets in service for another speed as the ratio of the cubes of the numbers of nozzle sets in service for the respective speeds.

' 2. The combination with apparatus required to be driven at variable speed and having a characteristic such that the power varies substantially as the cube of the speed, of an elastic fluid turbine having a plurality of nozzle sets of graded areas, a supply valve connected with each nozzle set, and means for successively opening the valves to place additional nozzle sets successively in service, the nozzle sets being of progressively increasing effective areas such that the total effective area in service progresses in accordance with the cubes of successive integers, whereby the speed may be varied in increments of the total range of speed representing the numbers of nozzle sets successively brought into service.

3. The combination with apparatus required to be driven at variable speed and having a characteristic such that the power varies substantially as the cube of the speed, of an elastic fluid turbine having a plurality of nozzle sets of graded areas, a supply valve connected with each nozzle set, and means for successively opening the valves to place additional nozzle sets successively in service, the nozzle sets being of progressively increasing effective areas such that the total effective area in service progresses in accordance with the' cubes of successive integers which are the numerators of fractions having the same denominator representing equal divisions of the total range of speed, whereby the speed may be varied in 1 15 equal increments through the total range.

OLIVER D. H. BENTLEY.