US2530638A - Liquid heater control - Google Patents

Description

Nov. 2l, 1950 J. c. WHITE LIQUID HEATER CONTROL Filed March l1, 1947 n. NN w1 lll WW WN NN IN VEN TOR.

Patented Nov. 21, 1950 UNITED STATESv PATENT OFFICE LIQUID HATR CONTROL .lohn C. White, Madison, Wis.v

Application March 1'1, 1947, Serial No. 733,973

v2 claims. (ci. zel- 62) The invention relates to the control of liquid heaters by which acids and other liquids are heated by the injection of steam into a stream of the liquid. This application is a continuation in part of my copending application Serial Number 547,455, led July 31, 1944, now aban doned.

Liquid heaters of the type mentioned are used in various commercial operations including the heating of acid and pulp mixtures in digesters and cookers in the paper industry. A heater for a pulp digester has been chosen for exemplifies.- tion herein in aid of effecting disclosure of the invention.

In a sulphite process the sulphuric acid which may have a gravity of about 1.03, is the circulating medium which must be heated and, for optimum conditions, must be caused to absorb enough heat during each cyclethrough a heater as to raise the temperature of the digester or cooker contents from 22 to 23 F. so that after repeated cycling a final temperature of 325 F. will be reached, within a digester of the usual size, in a period of about seven hours. The problem is complicated by the fact that at the time of the start of a cook the acid temperature will be in the neighborhood of 150' to 160 F. with a vapor tension (pressure) about 3.8 lbs. per square inch, absolute, while at the end of a cook` the acid temperature may be 325 F. with a pressure of 96.16 lbs. absolute.

The rate of rise of temperatureV and pressure` in part will depend, of course, on the rate of circulation and the size of the digester as well as some other factors but, as above stated, with optimum conditions and the usual size of digester, the desired temperature and pressure will be reached in about seven hours. Normally the acid is held at this temperature and pressure for about half an hour or more, circulation through the heater being continued for this purpose, and after the cook has been completed the digester is blown down. The heater thus works throughl a temperature range of from, say, 150 F. to 325 F. and a corresponding range of pres-V sures of from 3.8 lbs. to 96.16 lbs. absolute.

The preferred types of heater used forl this work are those designed on the principle ofY the Giffard injector wherein the liquid enters the steam and liquid combining tube atY a high velocity around the voutside of a jet of steam issuing from a conical nozzle High Velocity forthe liquid is necessary to furnish a suicient contact area of acid to absorb the required heat from the steam. As an example, with an acid pressure on the system of 8O lbs., the acid should enter the combining tube at a velocityv of not less than feet per second. Unless the proper relationship of acid contact area to steam pressure is attained and maintained, vibration and hammering develop or the heater efliciency drops. In heaters of the type mentioned the velocity of the cireulating acid (under pump pressure) at the inlet to the injector is proportioned by adjusting the combining tube to vary the inlet oriiice area until the point of most quiet and vibration free operation is attained with a relatively constant pressure steam supply. However, after a rela-V tively short period of operation the combiningr tube may freeze in position because of baking of lime and ber in its bearing in the heater whereupon no further adjustment can be effect,- ed. Thevelocity of the acid, set up by choking its flow at the inlet, isV partially converted to pressure head later on, and, With the small in crement due to the steam action, may be entirely recovered. On a rise of no more than, say, 23 F. per cycle, the steam `can impart almost no circulating energy to the liquid for which reason the liquid circulation must be eiected by pumping although a rise of 40 F. is ordinarily suicient to establish` circulation in a hot Water heating system for buildings.

Steam flow, that is, the volume thereof, from the steam inlet nozzle intoV the combining tube or chamber, is controlled by a valve which, iny turn, is either controlled or adjusted by hand or by relatively automatic means such as a thermostatically operated mechanism responsive, say, to temperature of the acid in the digester. Automatic control is preferred to hand control, of course, but in most cases provision is made for both as a safety measure since the hand control may be operated should the automatic control become inoperative for any reason. One type of automatic operating mechanism includes an air actuated diaphragm connected through a connecting rod and a bell-crank lever with the stem of the steam control valve so that a movement of the diaphragm in one direction will tend to open the steam valve and a movement in the opposite direction will tend to close the steam valve. This type of control will be illustrated herein.

In a typical installation using a steam valve and control such as above mentioned, the conical valve head shouldy be set with the controller so that a minimum volume of steam enters the combining chamber at the start of the cook, the controller thereafter effecting continued opening of the steam inlet orifice as the process proceeds until, toward the last oi the cook the valve may be Wide open to admit full volume inlet of steam. Since, at the start of a cook, the acid temperature is W, say, lc" F., and has a velocity oi pei'- haps, llii feet per second Vat the liquid inlet orifice, condensation of the steam creates a low pressure area oi substantial degree adjacent to the downstream end of the valve thereby exerting a strong force on the valve head tending to close the valve. rfhis iorce therefore is supplementary to and operates in the saine direction as the steam pressure, and the two forces so created i'orm a heavy working load on the controller at the start but as the cook progresses and the digester temperature approaches the heating steam temperature (at which time the valve may be i'ully open) the load on the controller decreases.

The controller, in its efforts to hold the temperature rise within its predetermined or set limits, and under the iniluence of the heavy load imposed on it, opens and closes the valve so rapidly that it results in a relatively continuous clatter of the valve head against its seat. This produces undesirable noise and vibration, increases wear and tear on the valve head and seat and other parts and interferes with the accuracy of control by the controller.

The primary purpose of my invention, therefore, is partially to counterbalance the forces tending to close the steam inlet valve thereby to eliminate the objectionable conditions mentioned. To this end a counterbalancing chamber is provided about the stem of the steam inlet valve and arranged to have communication with the low pressure area in the combining tube adjacent to the downstream end of the valve head so that the pressure effective at the latter place is also eiective in the counterbalancing chamber. In this chamber a portion of the valve stem serves as a differential piston operative under a pressure drop in the chamber to draw or tending to draw the valve head from its seat, but since the eiective area of the differential piston is less than the eifective area of the steam nozzle inlet orifice, there will always be an overbalancing force tending to close the Valve although such force will be substantially less than otherwise would be the case and the hunting of the valve and the overload thereon and on the controller is practically eliminated, while the valve and controller operations become more sensitive and accurate. This differential effect persists proportionately throughout the entire range of opening movements of the Valve.

In order to avoid stoppage of the passageway (and the entry of acid thereinto) by which communication between the counterbalancing chamber and the low pressure area within the combining tube is established, a very small passage- Way is provided through the wall of the counterbalancing chamber to the steam supply so that a slight leakage of steam into the counterbalancing chamber may occur. Also this small passageway or orice permits condensate to drain from the counterbalancing chamber. It should be observed, however, that the size of this passageway or orifice should not be such as materially to aiect (increase) the pressure in the counterba-lance chamber. This, accordingly, constitutes another object of the invention.

Many other important features as well as other advantages and the several uses of the invention will become apparent and understood after reading the following description and claims in connection with the accompanying drawing in which:

Fig. l is a longitudinal sectional view through an apparatus embodying my invention;

Fig. 2 is a transverse sectional View on the line 2 2 of Fig. 1;

Fig. 3 is a similar View on the line 3-3 of Fig. 1; and l Fig. 4 is a plan view of the structure shown in Fig. 3.

On the drawings, reference character 5 indicates the body of the liquid heater within which is mounted the combining tube 6 adapted for longitudinal adjustment Within the body. VThe tube may be adjusted longitudinally or" the body, for purposes which will be later explained, by means of a hand operated adjusting lever I xed upon the end of a vertical shaft Il provided at its lower end with an arm 9 having a stud or pin II engaged with the combining tube, so that actuation of the shaft 8 by the lever I will impart a longitudinal adjusting movement to the tube. The lever "I may be locked in adjusted position by means of a locknut I2 threaded upon a bolt I3 which passes through the lever 'I and through a slot in an underlying sector I4.

The body 5 is shaped to provide a chamber I5 surrounding and communicating with the inner or receiving end of the combining tube 6. The body is also shaped to provide a connection I6 communicating with said chamber and adapted to be connected with the outlet pipe of a cooker, digester or other piece of equipment for which the liquid is to be heated. The outer end of the body is anged, as indicated at I1, for connection with a pipe constituting the inlet pipe for the cooker or the like.

In operation the liquid to be heated is recirculated through the heater and cooker, entering the heater from the cooker through connection I6 and returning to the cooker from the heater through the pipe (not shown) connected to the flange II of the body and into which the delivery end of the combining tube 6 extends. A pump (not shown) in the line between the digester or other apparatus and connection I6, serves to effeet the liquid circulation.

The opposite end of the body is connected by bolts I8 with a flanged T I9 including a flanged connection ZI adapted to be connected with a pipe leading from a suitable source of steam under pressure. The body and connected end of the T are constructed to receive the valve guide 22 and the steam nozzle 23 which are clamped in position upon tightening of the bolts I8. A round tapered member 24 has a leak-tight nt with the hub 25 of the valve guide 22, and at its other end has a similar t with the hub 26 of an end piece 2'! which is bolted to and closes that end of the T member I9. A chamber 28 within the cylindrical member 24 is thereby formed, which will be referred to herein as the balancing chamber.

The hub 25 and the guide are hollow, as shown, providing a bore within which a piston 29 snugly but slidingly fits. At its outer end the piston carries the frusto-conical valve SI adapted to close against the seat 32 surrounding the discharge opening of the steam nozzle 23. The inner end of the piston 29 is threadedly connected with the valve stem :i3 extending longitudinally within the balancing chamber and outwardly through the stuing box 34 carried by the head 2l. The outer portion of the stem is threaded, as indicated at 35, for cooperation with a hand wheel 30,1: bymanipulati'onvr` of which longitudinal move'-- rent may b' imparted to theV stein 33. A link 31 connected to the extremity of the stem 33 connects the stem with an operating lever 3S, which in' turn isY adapted to be actuated by a controller 39, thermostatically or pressure operated in a manner well known in the art, for the purpose of adjusting the position of the valve 3| to regulate the volume supply of steam delivered from the nozzle so as to produce the predetermined temperature rise in the fluid being heated.

As shown on the drawing, the steam valve 3| is hollow and provided with a passage 4| opening at the small end of the valve into the combining tube. The piston 29 guided in the hub 25 of the guide 22is also hollow, providing a passage communicating with the passage in valve 3| and with a passage 43 in the end portion of the stem threaded into the piston. Communication between this passage 43 and the balancing chamber 28 is afforded by a plurality of radial passages 44. It will be apparent, therefore, that through the passages 4|, 42, 43 and 44 communication is established between the balancing chamber 28 and the area adjacent the small end of the valve. The perimeter of the piston 29 and that portion of the stem 33 passing through the end plate 21 may be lubricated to render their movement easy and to protect against leakage. Lubricant passages 45 and 43 adapted to accommodate the connection of pressure grease guns are provided for that purpose.

It will be understood by those skilled in this art that the fluid to be heated, entering the body of the heater through the connection I6, is delivered under pressure into the combining tube 6 at the inner end thereof around the tapered steam nozzle 23. The liquid, therefore, enters the tube in a stream substantially conical in shape. The steam delivered by the steam nozzle, in an amount determined by the proximity of the perimeter of the tapered valve 3| to the surrounding seat 32, is also in a stream of substantially conical shape, but inside the conical stream of fluid with which it combines. In the early stages of a cook, the admission of the fluid to the combining tube at high velocity and condensation of steam therein produces a zone of low, or negative, pressure within the cone upon its entrance to the tube, and into this cone the entering steam is projected.

As the acid or other liquid being heated rises in temperature, the controller tends to open the steam inlet valve member 3| wider and wider since more and more steam must be admitted to effect each succeeding increment of temperature rise of the liquid. But, of course, as this takes place the degree or intensity of the low pressure area in the combining tube adjacent to the nozzle or valve member 3| will become less and less which, in turn, progressively lessens the effective closing force on the valve and the counterbalancing effect of chamber 28. Because there must always be a positive pressure tending to close the steam inlet valve, the counterbalancing piston should have an effective area of not more than about 65% to '70% of the area of the steam nozzle or inlet orifice; 65% is preferred.

This low pressure area, which may or may not be a minus atmospheric pressure, tends to pull the valve toward the right (Fig. 1) toward its seat 32, and this tendency to movement is augmented by the steam pressure on the back face of the valve. Under certain conditions, therefore, depending upon the temperature of the liquid being heated, upon the extent-y1 of tem-pera: ture rise to beA produced in the heater, upon relative' pressurerv responsive areas, and upon other factors the' pull exerted by the stern' 33 upon the controller 39 amounts to several hundred pounds. By applying this low pressure', however, to the inner' endy of piston 29, it counteracts the pull or partially counterbalances the valve so that the strain exerted upon the controller is very materially red-uced.l This renders the adjusting movement much easier and contributes towardaccuracy of control and uniformity of results produced.; The degree of counterbalancing action attained may be varied in different designs by increasing or diminishing the end area of the piston exposed in the" balancing chamber 28, other proportions remaining the same.

The counterbalancing chamber wall, that is, the conical wall 24 has a small aperture or perforation 41 at its low point which not only may serve to drain the chamber but also permits the entry of a small quantity of steam which may serve to scour the passageways 4|, 42, 43 and 44 and prevent acid and ber or other matter from entering and clogging such passageways. It may also be desirable to provide a second aperture or perforation 48 of about the same size of that at 41, for the admission of steam but if such aperture is located at a high point as shown in Fig. 1, it will not serve also as a drain.

It is believed my invention and its principle of operation will be understood from the foregoing Without further description, and it will be manifest that the structural details illustrated and described may be varied Within considerable limits without departing from the essence of the invention as defined in the following claims.

I claim:

1. In a liquid heating apparatus having a combining tube, means for delivering a stream of liquid in the form of a hollow cone into said tube, a relatively fixed nozzle providing a valve seat adjacent to its outlet end and adapted to discharge into said hollow stream, a tapered valve projecting from within said nozzle into the tube and movable toward and from said seat for controlling the discharge from said nozzle, means for supplying steam to be discharged from said nozzle under control of said valve, the tip of said valve normally being disposed within the hollow conical portion of said liquid stream, means operatively associated with said valve for moving the same positively from said seat, and means for counterbalancing a portion of the forces tending to close said valve, said means comprising a balancing chamber, a piston upon which the valve is mounted presenting a pressure area to the interior of the chamber, and a passage through the valve and piston establishing communication between the area at the tip of said valve and said chamber.

2. In a liquid heating apparatus having a liquid-steam contact chamber, means providing a liquid inlet of annular form for liquid entering the chamber, and means providing a single steam outlet orifice disposed concentrically within the liquid inlet, said steam outlet means including an orice defined by a valve seat, a valve mechanism for controlling the emission of steam from said orifice into said chamber comprising, a valve stem guide, a valve stem mounted in said guide for movements in the direction of the stem axis, a conical valve head carried by said stem and cooperative with said valve seat, the base of the cone being disposed on the upstream side of said orice and the small end of the cone normally being disposed on the downstream side of said orice and within said contact chamber, means providing a walled Valve balancing chamber, a passageway communicating between said balancing chamber and the interior of said contact chamber adjacent to said small end of said valve head, means for moving said stem to move said head toward and from said seat, a valve balancing piston in said balancing chamber and connected with said stem, said piston being constructed and arranged to oi-set a substantial portion of the eiect of reduced pressure in said contact chamber adjacent to the small end of said valve head tending to close said valve head against said Seat whereby to reduce the effect of forces acting on said stem moving means in a direction tending to move said valve toward the closed position, and an aperture of small area connecting said counterbalancing chamber with a place of drainage for said chamber, said aperture area being of such small size as to have a relatively immaterial effect on the pressure within said chamber.

JOHN C. WHITE.

REFERENCES CITED The foliowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 615,914 Schutte Dec. 13, 1898 1,243,999 Snediker Oct. 23, 1917 2,372,533 Torbett Mar. 27, 1945

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