US2296426A - Steam generating system - Google Patents

Description

Sept. 22, 1942. J. G. COUTANT 2,296,426

STEAM GENERATING SYSTEM Filed Nov. 7, 1938 2 Sheets-Sheet l NVENTOR;

. K'bww dj ATi'oRNEYs.

Pt- 1942- J. G. COUTANT 2,296,426

STEAM GENERATING SYSTEM Filed Nov. 7, 1938 2 sheets sheet 2 W I T1 INVENTOR QM W wowoifkmzd -Wll.

ATToRNEYs.

Patented Sept. 22, 1942 UNITED STATES PATENT OFFICE STEAM GENERATING SYSTEM Jay Gould Coutant, New York, N. Y.

Application November 7, 1938, Serial No. 239,305 In France November 12, 1937 8 Claims.

This invention relates to steam generating systems, such for example as are used for industrial, central station and motive power purposes. This system while particularly adapted for the generation of vapors for the production of light, heat and power, may be employed to supply steam for refining or cracking, chemical and other procsystems are the means for obtaining high rates of heat liberation, together with great density of heat radiating particles per unit of furnace volume, and simultaneously therewith, high rates of heat absorption per. unit area per hour for generator, economizerand air heater surfaces.

Another valuable factor lies in causing a very just itself to fluctuating demands for vapors with rapid response. This invention incidentally pro- I vides an excellent opportunity for saving of space and building structure and weight, resulting in low investment cost of apparatus or generator, and maximum overall economy in operating cost.

An important object and advantage of this invention is the burning of fuel at high rates of combustion at flame temperatures higher than the theoretical temperatures calculated from the constituents of the combustion, thereby providing the maximum intensity of radiantheat passing from the incandescent particles suspended in the gaseous products of combustion to the generator tubes. With this invention the generator or circulation tubes are of relatively small diameter, and the thickness of the tubes is reduced to a minimum so as not to retard or diminish unduly the amount of radiant heat utilized, thus reducing resistance to the conduction of the heat through the tube to the convecting or heat-conand a temperature greater than the pressure and temperature existing in the generator drum, as will be further described. This prevents pockets or voids in the fluid, due either to eddy currents in circulation, or due to bubbles and spheroidal state in evaporation. Thus the tubes can not become overheated by reason of the inside surfaces not being wetted and cooled. Also there is prevented evaporation within the tubes and consequently there will be no incrustation or scale formation. The heat at the tube surface is communicated to the circulating fluid, superheating it say 38 C. to 75 C. superheat. Further, being maintained, as stated, under pressure greater than that in the generator drum wherein the vapor from the fluid is liberated, this develops additional temperature, 16 C. more or less, to the temperature of the circulating medium. The excess heat thus contained in the circulation medium, on reaching the drum space, flashes a part of the liquid into vapor.

Another object or feature of the invention, co-

operating for more rapid steam liberation and heat exchange, by the increase of velocity of combustion and of intensity and density of surfaces emitting radiant heat, per unit of furnace volume, is the use of preheated air at more than 278 0., which use increases the flame temperature beyond the theoretical temperature based on the normal constituents of the burning fuel. Therefore, the combustion is caused to take place, by this invention, in a positive atmosphere where the pressure is greater than atmospheric pressure by at least 1 kg, per sq. cm. above zero, and may be as high as 5 kgs; such a pressure in the furnace compresses the number of radiant particles into a smaller space, with closer distribution, consequently increasing the amount of emitting surface per unit of furnace volume, with a resulting slight increase in temperature, which is enhanced because of reduction in time of fuel burning. By these features the amount of heat received by direct furnace and generator heating surface is much increased.

Further, the distance between suspended par ticles being reduced, the flame has less distance to travel, and the velocity of combustion is greatly increased. The heat'transfer from flame to tubes is at a maximum. To utilize these conditions, it is the purpose of this invention to provide a heat-conveying fluid circulation system for properly carrying away the intense heat and cooling the tubes. At first glance this purpose may seem unnecessary because one naturally.

thinks of ordinary pulverized fuel furnaces with flame temperatures below the fusion point of the 1 pulverized fuel, and 5%- follows.

duce furnace temperatures 120 0. higher than fuel oil alone; while with preheated air, the furnace may attain in the neighborhood of 1,900 0., corresponding to a, radiant heat absorption of 460,000 calories per square meter per hour. The weight of metal per square meter of generator.

' heating surface and the amount of water in the ,tubes need then be but a fraction of the usual case, for example, in the neighborhood of onetwelfth; consequently the heat storage capacity of the unit in that case would be reduced proportionally, and meet fluctuating demands twelve times quicker.

Another featurev of the invention is the use of relatively small steam drums, made possible because large water storage is not necessary to supply the aforesaid small diameter furnace and generator tubes. Large drum volume for steam liberation is not necessary, since this invention 1 circulates and delivers the superheated, circulating water as a liquid, under pressure, audit is released to flash into steam in the drum space, with means relatively to increase the vapor liberating, surfaces.

A particular object hereof is the delivery of the superheated liquid to the drum at substantially constant and uniform velocity above the water line, into the steam space, and preferably in an atomized condition. A supplemental obvapor from the full length of the drum space, thereby to eliminate the longitudinal racing therein of vapor and consequently to eliminate entrained moisture, in the outgoing steam.

Another object is to dry further the vapor as The feed water; or infed fluid may be delivered over a series of chains through which the rising steam passes, thus serving as a washing apparatus for removing moisturefrom the vapor, while the chains being free to swing, are

self cleaning. 1

Another useful feature and object of the invention is in the use of a blow-off collector pipe placed low within the steam-and-water drum,

this being possible .since the water is in a calm or orifice for delivering from the tube system ject is the substantially uniform collectionof state, which allows for the precipitation of sedimen's which may be removed from'time to time through this blow-off collector pipe.

An object is to improve operation by the recirculation of water from and back to the .drum at a very high rate, preferably at least or more than ten times greater than the steam output by weight, this recirculation being through small tubes, as already stated; The high velocity'and large quantity of liquid circulated, without allowing evaporation in the small tubes, permits the use of untreated or raw water if necessary, while in emergency operation even salt water may be used.

-An object of the low heat storage generator units described is to eliminate substantial time and heat losses in the generator operation whenever starting and'stopping; further to allow quick cooling in case of need of repairs, a large unit being cooled in about an hour sumciently to allow workmen to go inside; also that the generator may be put into service from cold condition to full steaming capacity, in a few-minutes, comparable to the fact that low heat storage capacity steam turbines may be put into full service within two to five minutes from cold condition.

The features and objects of this invention, in actual service, can reduce the relative heating as compared with usual or natural circulation boilers operating at pressures up to kg. per

sq; cm.; and the weight of a generator unit complete, and its space in a building, may be as low as 10 to 12 per cent of that of a modem power plant boiler and 15 to 20 per cent of a marine unit.

These various described objects and features will be better understood by referring to the ac-- com'panying drawings, of which Fig. 1 which is a vertical cross-section view of a large generator or unitsuitablefor instance for supplying more than 50 tons of steam 'per hour.

Fig. 1, on a relatively enlarged scale, is an interior elevation view of a part of the wall of the overhead drum showing two of the nozzles or orifices delivering from the generator tubes into the drum with release of pressure; and Figs.

3 and 4 are similar views of other forms of delivery restriction means or nozzles.

Fig. 5 is a vertical section view, on the same scale as Fig. 1, taken on the section line 5-5 of Fig. 1, showing substantially all of the interior elements within the drum.

- Fig. 6 shows in section a portion of the length of one of the water tubes, provided with an interior device or whirling means which may be variously located along the length of the tubes.

Fig. 7 in similar section view shows a water whirling device ormeans adapted to constitute a restriction at the discharge of the tube and to impose a whirling motion on the delivered water.

tance between them being only 20 per cent more or less of normal. It is obvious the flame propagation, velocity of combustion, rate of fuel burning, completeness of' combustion will be very greatly increased. This reduces the time factor, and consequently the losses from slow combustion will. be reduced. This in turn results in higher temperatures and greater intensity of the radiant heat emission from the fiame. The generator is preferably built with gas-tight casing,- and the combustion air along with the fuel is injected into the furnace under such pressure as to cause the same conditions within the generator setting, which is to be considered as covered by this invention.

Referring first to the mainelements of the.

steam generator hereof, it comprises the combustion chamber, which may be sectional, comprising in the illustrated case three furnace Bythis chambers 4, 4 and 4 separated by division walls 3 and all delivering into a general space or furnace chamber 4 above the sectional chambers. All of these chambers are enclosed within an exterior metal casing which has a refractory floor l and refractory linings or firebrick walls 2 around the sides of the furnace. All of the combustion spaces deliver eventually to fines 2 extending upwardly and out at the top of the generator, and eventually to a stack.

An overhead drum 9 is shown, representative of one or more high drums, into which the generator tubes deliver. The drum may be described as a steam-and-water drum, having a steam space 6 above the water space 6, with a water line 26 between, to be maintained substantially steady. For this purpose the water infeed pipes 1, supplying water to offset the consumption of steam, are assumed to be controlled by any usual boiler feed regulator, not shown, adapted to maintain the water level lower than the orifice outlets I6 but higher than the water outlet pipe ID to be referred to. At the top the drum has-the usual steam outlet 29 extending to the place of consumption. The drum 9 'is shut efi or shielded from the direct heat of the combustion by a refractory housing wall 9 extending under the drum and upwardly to the walls of the fiues 2.

While the drum 9 has been described as an overhead drum it is not intended to restrict it to a drum of high location in relation to the tubes, the important thing being that the drum should be substantially higher than the pump. The tubes, receiving from the pump, might even trend downwardly through the chamber to a low drum, so long as the pump is still lower than the drum. The drum is relatively small, and may be from 25 to 5 0 per cent less in volume than ordinary drums as used for similar outputs of steam of the same degree of dryness.

By this invention rapid recirculation of the generator water is maintained, and the circulation system may be described as follows. The water collector pipe l0 within the drum has perforation ll] so as to receive water from the full length of the drum. From one end of the water collector extends, at a downward slant, toward the left, a downtake pipe H which extends first to the intake of a force pump I2 driven by a motor [2 and is continued downwardly at l3 to the low point of the circulation system at which drum, the tubes separately entering the drum so as to deliver transversely into the steam space thereof, above the water line 26. I

As already stated the flow in the tubes may be reversed, if the drum is at a low point,,- .The tubes are preferably of quite small size compared to standard boiler tubes, for example inch in diameter more or less, the tube wall beingof steel of a thickness of 1% inch more or less depending on the pressures used.

It is an essential characteristic of this invention that the several water tubes, delivering into the steamand-water drum throughout its length are provided with restriction means, of any suitable kind adapted to impede the flow, such as the restriction orifices l6 shown separately in several forms in Figs. 2, 3 and 4. On delivery of the heater water thus into the drum, the impact thereof is preferably taken by a series of bafile strips 21, causing unevaporated water to descend into the water space, a substantial fraction of the water however being converted or flashed into steam and passing into the steam space of the drum. The liquid water therefore passes through the closed circuit consisting of the drum, the water collector pipe, the downtakes leading to the low headers, the force pumps associated with said downtakes, and the uptakes or generator tubes exposed to the combustion heat and delivering back, through the restricted orifices 3 into the drum. The result of the described combination is that, beyond the force pump, and throughout the length of the generator tubes, up to their delivery orifices, the hot circulation water remains in liquid condition and under a temperature and pressure substantially higher than those existing within the drum. The tubes therefore carry only liquid medium or water,

is a. series of headers 14 interconnected by pipes.

I3 The motor IZ may be energized through a conventional motor controller l2 from line wires 12. From the other end of the water collector, extending at a downward slant, is a right-hand downtake 23 leading to a force pump 22, in this case turbine-driven, and delivering to a down- .take extension l3 which at that side delivers into water or generator tubes 5, taking off from the low headers l4, and extending upwardly through the combustion chambers 4, preferably along the walls 2 and 3 and eventually delivering into the drum after passing through a tortuous configuraand there is no steam formation within them, the water only evaporating upon passing through the restriction devices into the lower pressure prevailing within the drum.

Taking a specific example, the drum pressure may be about 400 lbs. per sq. in. absolute while that beyond the pump up to the tube delivery orifices'may be boosted by the pump to about 420 lbs., these pressures corresponding to steam temperatures of about 445 and 449 F. respectively. The higher pressure water is progressively heated in each of the-tubes nearly to the orifice, but does not break into steam until passing the'orihigh pressure developed by the pump with the aid of the restriction, these elements being detion in the chamber 4 as shown by the bent 7 tube portions l5, occupying the upper combus-- signed and operated for the conditions prevailing in the system. On entering the drum, part of the superheated water breaks into steam with the drop in pressure, taking heat from the balance of the water for this result, the unevapo- I than the orifices 16 of tubes 5, allowing a greater weight of water to pass per second, and thus avoiding the formation of steam ahead of the This differential showing of the' two orifices in Fig. 1 is considerably exaggerated, in

forder to show the principle, and the actual differences in orifice diameters will not usually be as great as indicated in this figure. In any case the orifices are calculated to deliver a predetershown. The water preferably sprayed mined rate of liquid at the existing predetermined pressure.

This being the general plan and operation of the present invention the various elements and details will now be further described.

The generator setting preferably has an air tight casing i, insulated from the fire by insulating refractories, or low-heat storage capacity or cellular firebrick 2. Similar refractories form the shatterproof division walls 3 between the multidrum by convection. The liquid or water is supplied to the drum by regulated feed pumps, not into the drum by the feed pipes 1, and is showered upon a free swinging series of small baffle chains 8, from which it drops into the relatively calm water pool in the drum. The heat conveying medium or water flows thence under steam generator I I pressure-and temperature into the collector pipe 1 i0, perforated to collect water uniformly from along the whole length of the drum 9. The water flows by gravity through the downtake pipes i l and 23 to the'driven pumps l2 and 22 which discharge at a pressure, for example, 1.3 kgs. per sq. cm. greater than the generator pressure. This pressure is maintained in the circulating water in pipes l3 and the headers M that supply the radiant heat absorbing tubes 5 which are in series circuit with the convection heat absorbing tube banks l5 leading to the orifices which discharge into the drum.

Fig. 2 shows a special construction of restriction orifice IS, the tube being inserted and expanded in a perforation of the drum 9 in usual manner but extending beyond the inside face,

and this. interior end being swedged, rolled or contracted to form the orifice IS. A preferred orifice construction is shown in Fig. 3, in which the tube 5 has its end extending inside, in which an annular metal block or ring" is fixed, this having a threaded hole to receive a removable orifice piece l8, which therefore is interchangeable as to size of orifice. An orifice or restriction device of convenient construction is that shown in Fig. 4 wherein the orifice piece I6 is a simple apertured disk. In this construction a short pipe length or nipple II is fitted permanently to the drum wall, this and the tube end 5 having welded flanges 11 between which the orifice piece is clamped by means of exterior bolts I8 Instead of a simple apertured orifice-the throttling or restriction of flow. from each tube into the drum may be effected otherwise, as by means of a multitude of small perforations constituting a spray nozzle, or a porous body through whiehthe liquid must pass into the steam space, or amovable device or vane obstructing free discharge. In any case the outflow from the tube is preferably throttled to afford a uniform desettling operation. 'From one or both ends of the 'bers 4.

- weight of water-per hour, the restriction at the same time cooperating and maintaining the desired elevated pressure within the tubes 5 and their bent portions [5.

Fuel oil, colloidal fuel, or other fluid fuel is supplied to a series of burners IQ, for example, in the furnace front wall, for delivery into the combustion chamber sections 4, 4, 4. The fuel is ignited with the combustion supporting air, preferably under elevated pressure, in the cham- The combustion may be at moderate temperatures at first; following which the hot gases in the usual manner may pass through an air preheater (not shown) and excessively'heat the air, the air being delivered to the burners H), which gradually increases the temperature and pressure in chamber 4.

In the meanwhile steam has been generated by evaporation in drum 9, creating high pressure, and part of the steam flows by a pipe 20 to a steam throttle valve 2l, which, when opened,

supplies steam to the pressure-controlled turbinedriven pump 22. The drum water flows through pipe 23 and through its check valve 24 into the pump 22, which discharges by pipe l3 to headers M. The pressure-controlled steam turbine and pump maintains a uniform water pressure in the circulation system, at say 3 kgs. per sq. cm. greater than that in the steam drum. I

The pressure-combustion supporting air entering the furnace at high temperature and pressure with the fuel, causes temperatures and radiant heat intensities to be developed superior to present practise. This intense heat is transferred by radiation, conduction and convection to the cooling and heat conveying liquid or water which is under pressure in the tubes 5. Thewater, being superheated, flows through the tubes 5, tube banks l5 and discharges through the orifices l6, located either inside or outside of drum, and at points above the water line in drum in such manner that the main body of the water remains relatively calm. From each orifice'lli the water is atomized by impact against bafiies 21, whereupon the small particles of water escaping from thehigher pressure and superheated temperature give up their excess pressure and superheat by being partly converted to saturated vapor, or steam. The water due to the sudden drop of pressure causes a rain which actually washes the vapor. The vapor rises toward the self cleaning chains 8, where it is again washed by the incoming feed water from pipe 1; and is then collected uniformly, transversely of the drum by the steam collector ordry pipe 28, that delivers to steam outlet 29.

drum, above the blow-off pipe, to protect the pipe 30 is a sludge downtake pipe containing a blow-off cock 30 k livery from each of the tubes, or a predetermined As the liquid in circulation in the tubes, for

absorption and entrainment-of heat, is maintained under pressure considerably higher than the pressure in the generator drum, this resultsin an increased capacity for entrainment of heat per kilogram of liquid in circulation, which retubes and of the generator drum itself; and this allows the metal to receive and transmit more heat because of the elimination of the known phenomenon which obstruct the transmission of heat by convection to the liquid in circulation, as occurring with natural circulation of the liquid.

As the tubes 5, in which ci'rculates the liquid for absorption and for entrainment of heat under pressure and at high temperatures, pass into the generator drum above the water level, a part of the liquid is vaporized by the excess heat Without effecting the calm state and temperature of the main body of liquid stored in the drum, so that-the level does not tend to rise and fall with the increase and decrease rate of fuel burning or steam output, and this allows the use of relatively small generator drums.

The tubes 5 for the absorption and for entrainment of heat are preferably exteriorly accessible at or near their ends, for permitting quick repairs, in the case where a tube explodes or develops leaks, without putting the generator out of service. This is shown in Fig. 1, where at the left side each tube 5 may be reached near its bottom end at the header l4, also at its upper end near the drum. For example apowerful implement may pinch and seal the defective tube at these two points, without interrupting operations.

The following further considerations apply to the disclosed embodiment of the invention. As stated, the generator or water tubes are as thinwalled as is consistent with safety. There are indeed no thick metal parts at any point which are exposed to excessive fluctuations of temperature. Within the tube system described, substantially uniform temperatures of circulating fluid are maintained at each specific location. Because of this, temperature variations in metal parts are minimized, .which substantially eliminates caustic embrittlement and fatigue of metal,

especially under corrosion.

An advantage of the described invention is that when the generator is out of service, for

, example one generator among many in a station,

it is practicable to have the generator stand by, ready for resumption of service, without possibility of damage even in cold weather; it being only necessary to stop the operation of the recirculation pump, maintaining a pilot fire for low heat and allowing the water to circulate in the system by natural or unforced fiow.

Referring further to structure, the bent tube system I5 is shown suspended by means of depending hangers |5 from which extend horizontal cross members 32, preferably hollow for cir-.

culation of cooling fluid; the pipes |5 passing around the members 32 in two or more tiers, as shown, separated by spacers I5. The reinforcement bars 3| in the partition walls 3 may also be hollow, constituting pipes for fluid circulation, for their protection and that of the wall.

Referring further to the force pump, this is to be controlled from the inlet and delivery sides of the pump, by any suitable type of governor or control device, so as to maintain a predetermined pump pressure at the orifices. This has reference to a predetermined pressure difference, the pump'elevating the pressure by a predetermined amount, as in pounds per square inch, and the pressure dropping by the same amount on traversing the orifices. The orifices are calculated so as to deliver a predetermined rate of liquid at such predetermined pressures.

A com antional means to maintain the desired elevated pressure beyond the force pumps l2 and 22 and up to the orifices l6 is'indicated at the righthand side of Fig. 1 and in Fig. l Since both pumps deliver recirculated water intothe same system of exposed tubes 5, the desired control may be at both sides or either side to maintain a predetermined recirculation pressure,

above the pressure existing in the drum 9. Such a control is shown at the righthand side of Fig. 1 where there is indicated a steam turbine 22 which drives the centrifugal pump 22 that applies forced pressure to the recirculated water. The turbine is fed by steam, received from the drum through the tube 20, containing a hand throttle or cut-off valve 2|. For automatic recirculation pressure control there is shown, also, interposed in the pipe 20, a special control valve 40 adapted to open or throttle more or less the steam passing to and operating the turbine, under the control of the elevated water pressure in the downtake I3 beyond the pump.

The valve 40 is shown in a conventional form in Fig. 1*. Its movable member or gate 4| is carried on a stem 42, these sliding through the valve for the adjustment of steam fiow from the upper to the lower part of the steam pipe 20. The valve gate 4| is adjustable slidingly through a guideway 43, so that its tapered end may approach more or less the valve seat 44, through which the steam flows from the first to the second part of the pipe 2|]. The parts 43 and 44 are fixed or. integral with the valve casing 45, to one side of which is attached an arched cover or cap 46, the casing and cap forming a control chamber. As a typical pressure responsive means, between the valve casing and cap'is clamped a diaphragm 4'1, to which the valve stem 42 is attached, so that diaphragm movements shift the valve. In a conventional way, the diaphragm and stem movements may be controlled or biased by a resilient means or helical spring 48, shown applied to the stem, as at one end, and adjustably confined by a threaded hand wheel or nut 49 f xed on the threaded end of the stem by a lock nut 49 The spring 48 is confined between the adjusted wheel 49 and an outer fixed thrust bracket 48*; and the adjustment should be such that, through the compression of the spring, tending to open the valve, the valve operates in accordance with the existing conditions and requirements, taking into account the head of water between drum and pump, and other factors, to afford the desired control. 1

The diaphragm 41 divides the valve chamber into a low pressure compartment 50 and a high pressure compartment 5|. The drum pressure is communicated to the chamber 50 by a passage 52 in an interior wall of the valve, this pressure therefore being substantially the same as the pressure of the water passing from the drum to the pump through pipe 23, Fig. 1. The high pressure of the water beyond the pump is communicated back to the chamber 5| by a pilot passage or tube 53, tapped into the downtake |3 and extended upwardly and through the wall of the arched cap of the valve.

By this described arrangement, when the delivered water pressure in the downtakes I3 and |3 and the exposed tubes 5 tends to drop to a relative pressure where vaporization might occur, the lowered pressure is communicated through the pilot tube 53 to the valve chamber 5|, causing the diaphragm and the valve gate to recede under the counterpressure of the chamber 50,

- the wider opening of'the valve thus admitting more steam to the turbine, so that the greater force and speed of the turbine and pump autoy matically correct and restore the predetermined delivered pressure. When the delivery pressure has risen to the predetermined relative pressure, above the boiler and drum pressure, the

ing the valve and compressing the spring, until the adjustment is such that the turbine will tend of exposed water tubes of the generator. If both pumps are desired to be automatically controlled in the manner described, the delivered water pressure need merelybe utilized also to adjust the electrical controller I2 at the left analogously to the adjustment of the steam valve 40 at the right. By the use of three orother plural number of combustion chamber sections 4, 4 and 4 the operation of the generator is made flexible, since any one or more of these sections may be put into or out of service, and each has its pounding walls lined with water tubes.

v The water whirling device shown in- Fig. 6 is illustrated as a twisted strip or helical vane 35, for the purposes to be described, and it may be located at any one or more places along the length of each tube or selected tubes. This de- I vice is in the nature of a steep-pitched screw,

developed for example from a sheet metal strip,

.and its immediate effect is to impose a rapid rotation upon the advancing stream of water. The effect of this rotation is to create a powerful centrifugal force, and the operation of this force. is to classify the advancing flow. The

portions of the water which are colder, and

therefore denser or heavier, are constantly thrown toward the periphery, into what may ,be considered as an outer zone X which is directly in contact with the-metal wall of the tube 5. The classification may tend to produce an intermediate zone Y, while the central zone or core 2 of advancing water is of the lowest the central zone Z, while the coldest water, the

most receptive to heat absorption, takes its proper place in contact with thetube wall. It is believed that there will be a constant interflow between the zones X, Y and Z as the relatact of the advancing water with the wall of the diaphragm will have moved inward, further clostube, and as well the velocity-of-flow' contact is greater, to the enhancement of general efiiciency.

Referring to the modification shown in Fig. '7, it has already been stated that the restriction near the delivery of each tube may be by means other than an orifice, and Fig. 7 shows a restriction 36 in the form of a twisted vane analogous to that shown in Fig. 6, but preferably of much lower pitch. This device 35 impedes greatly the passage of water from the tube into the drum 9, because the fast advancing flow of the water is converted, by this fixed helix, into a very high state of rotation, the absorption of energy for this purpose affording the desired restricting effect.

An advantage of the form of restriction shown in Fig. 7 is that in delivering the hot water into the drum, the rapid whirling throws the water violently into a spray, even pulverizing it into a fine mist. The result of this is that the release of steam from the water is promoted to a maximum degree.

What is claimed is:

1. The method of operating a steam generator of the kind comprising a steam-and-water drum having a feedwater inlet and steam and water outlets and a bank of water tubes exposed to the combustion heat and connected for delivery into the steam space in the drum" and a water pump arranged to force hot water recirculation ,from the drum water outlet back to and through the tubes; said method comprising substantially restricting the water flow by predetermined throttling in the several tubes at a. restriction point between the tube-heating zone and the delivery into the drum, while cooperatively operating the pump with control from its pressure side and in coordination with the flow restricting action to maintain in the tubes a water pressure predeterminedly elevated above the drum pressure sufliciently to preclude vaporizative temperatures and densities therein are al- 4 of the operation of the whirling devic 35,"'it renders substantially greater the mass-flow contion and flow acceleration in the tubes beyond the pump and up to the restriction point and-to cause recirculation at a rate at least several times by weight of the steam consumption rate;

whereby the recirculated water within the heating zone is maintained as a solid water column flowing at low velocity and therefore with optimum contact and capacity for high rate of heat absorption thus to become superheated in its liquid form at the elevated pumped pressure until upon release and delivery into the drum with substantial pressure drop the solid water flashes partly into outgoing steam and partly settles as water for forced recirculation; and

whereby the fuel combustion in the generator may be maintained at'a super rate accompanied by high intensity of heat generation affording high rate of heat transmission to the tubes and liquid water flowing therethrough and thereby aflording super rate of steam generation.

2. The method of operating a steam generator of the kind having a steam-and-water drum and a feed-water inlet, the drum having-water outlet and steam outlet, with a bank of water tubes exposed to the combustion heat and connected for delivery into the steam space above the water in the drum, and a force pump arranged to promote hot water recirculation from the drum water outlet back to the tubes; said method comprising restricting the tube water flow at a restriction point between the heatab sorbing zone and thgdelivery into the drum tion in the heating zone and so becomes superheated at the elevated pumped pressure and upon release and delivery into the drum flashes partly into steam for consumption and partly settles as water for forced recirculation; controlling the water force pump from its pressure side in a manner to maintain substantially a predetermined elevated pressure in the tubes up to the restriction point, with recirculation rate of not less than about ten times by weight of the steam consumption rate; and effecting the water -flow restrictions through calibrated throttlings to afiord a predetermined substantially constant recirculation rate at the elevated pumped pressure.

3. A steam generator comprising a steamand-water drum having a steam outlet from the upper part drum steam space, consisting of a steam collector extending lengthwise of the drum with inlets along its length to receive steam transversely from the drum, a bank of water tubes arranged for absorption of combustion heat and for delivery into the steam space of the drum, a water recirculation passage extending from the drum water space back to the tubes, and a force pump operable in such passage to promote recirculation of water through the tubes and back to the drum; the same characterized in that saidwater tubes are provided with circulation restriction means located beyond the heat-absorption zone between such zone and the place of delivery into the drum above the water space therein, and that the deliveries thereof are in distributed arrange ment along the length of the drum, and that said pump and restriction means are cooperative to maintain the circulating water in the tubes at'a pressure substantially higher than that in the drum and thereby in the condition of solid water throughout the heat absorbing zone; whereby such water is caused to flow through said tubes without appreciable vaporization up to such restriction means while becoming superheated substantially above the temperature of the water in the drum, and thereupon beyond the heat-absorption zone to flash partly into steam within the steam space above the water in the drum; and thereby preventing bubbling of the steam through the water, minimizing water agitation, minimizing vapor flow lengthwise of the drum, and promoting steadiness of the water in the drum.

4. A steam generator comprising asteam-andposes, and a longitudinal wall immersed above and shielding the setting of sludge; and the said generator being further characterized in that said water tubes are provided with water flow restricting means located beyond such heating zone between such zone and the delivery into the drum, and that said pump and r'ectricting means are cooperative to maintain the recirculating hot water in the tubes at a water pressure substantially higher than that in the drum sufficient to maintain it liquid throughout the heating zone; whereby such water is caused to flow through said tubes so solid water without vaporization up to such restricting means at the higher pressure while becoming superheated in the tubes substantially above the temperature of the wa ter in the drum, and thereupon beyond the heating zone discharging into the lower pressure of the drum partially as steam and partially as water passing into the steam and Water spaces re-. spectively of the drum.

5.' A steam generator comprising a steam-andwater drum having water infeed means and a steam outlet from the drum steam space, a bank of water tubes arranged for absorption of combustion heat and for delivery into the drum, a water recirculation passage extending from the drum water space back to the tubes, and a force pump operable in such passage to promote recirculation of water through the tubes and back to the drum; the same characterized in that said water tubes are provided with circulation restriction means located beyond the heat-absorption zone between such zone and the place of delivery into the drum, and that said pump and restriction means are cooperative to maintain the circulating water in the tubes at a pressure substantially higher than that in the drum and thereby in the condition of solid water throughout the heat absorption zone; whereby such water is caused to flow through said tubes without appreciable vaporization up to such restriction means while becoming superheated substantially water drum having a low water outlet and a high characterized in that at the lowest part of the drum is a longitudinal sludge collector with means for discharging it for sludge blow-off purabove the temperature of the water in the drum, and thereupon beyond the heat-absorption zone to flash partly into steam within the drum; and characterized further in that at the lowest part of the drum is a sludge collector with means for discharging it for sludge blow-ofipurposes, and above said sludge collector a shield adapted to protect the settling of sludge, and thereabove a water collector extended longitudinally and delivering to the recirculation passage.

6. A steam generator comprising a steam-andwater drum having a low water outlet and a high steam outlet, a bank of water tubes exposed within the zone of radiant and convection heating in such generator and connected for delivery into the drum, a header connected for distributing water to said tube, a water recirculation passage extending from the drum water outlet back to the header and tubes, and a water pump arranged and operable in such passage to force recirculation of water from the drum through such passage, the header and the tubes and back to the drum; said generator being characterized in combustion heat and to become superheated as liquid before release and partial vaporization beyond the heat-absorption zone; and the said generator being further characterized in that said water tubes are provided with water flow tially higher than that in the drum suflicient to maintain it liquid throughout the heating zone; whereby such water is caused to flow through said tubes as solid water without vaporization up to such restricting means at the higher pressure while becoming superheated in the tubes substantially above the temperature of the water in the drum, and thereupon beyond the heating zone discharging into the lower pressure of the drum partially as steam and partially as water passing into the steam and water spaces respectively of the drum.

7. A steam generator comprising a steam-andwater drum having a low water outlet and a high steam outlet, a bank of water tubes exposed within the zone of radiant and convection heating in such generator and connected for delivery into the drum, a header connected for distributing water to said tubes, a water recirculation passageextending from the drum water outlet back to the header and tubes, and a water pump arranged and operable in such passage totion passage leading to the pump, and in that the combustion chamber is divided into subchambers each extending parallel with the drum and each having circulation tubes,'with means to put part or all of the subchambers into or out a of service to adjust operation to varying output and the said generator being requirements further characterized in that said Water tubes are provided with water flow restricting means located beyond such heating zone between such zone and the delivery into the drum, and that said pump and restricting means are cooperative to maintain the recirculating hot water in the tubes at a water pressure substantially higher than that in the drum suificient to maintain it liquid throughout the heating zone; whereby such'water is caused to flow through said tubesas solid water without vaporization up to such restricting means at the higher pressure while becoming superheated in the tubes substantially above the temperature of the water in the drum,

and thereupon beyond the heating zone discharging into the lower pressure of the drum partially as steam and partially as water passing into the steam and water spaces respectively of the drum.

8. A steam generator comprising a steam-andwater drum having water infeed means and a steam outlet from the drum steam space, a bank of water tubes arranged, for absorption of combustion heat and for delivery into the drum, a water recirculation passage extending from the drum water space back to the tubes, and a force pump operable in such passage to promote recirculation of water through the tubes and back to the drum; the same characterized in that said water tubes are providedwith circulation restriction means located beyond the heat-absorption zone between such zone and the place of delivery into the drum, and that said pump and restriction means are cooperative to maintain the circulating water in the tubes at a pressure substantially higher than that in the drum and thereby in. the condition of solid water throughout the heat absorption zone; whereby such water is caused to flow through said tubes without appreciable vaporization up to such restriction means while becoming superheated substantially above the temperature of the water in the drum, and thereupon beyond the heat-absorption zone to flash partly into steam within the drum; and

characterized further in that its combustion chamber is partitioned into a plural number of subchambers, with burners ineach, and with-the walls of each lined with circulation tubes; where'- by one or more or all of said subchambers may be put into or out of service to adjust the generator operation to the vapor output requirements.

JAY GOULD COUTANT.

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