US3320934A - Vapor generator - Google Patents

Description

y 1957 P. M. DOELL ETAL 3,320,934

VA POR GENERATOR Filed April 5, 1965 FIG! mVENToRs Dayld E. James BY Ph|||p M. Doell ATTORNEY United States Patent 3,320,934 VAPOR GENERATOR Philip M. Doell, Wadsworth, and David E. James, Barberton, Ohio, assiguors to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Filed Apr. 5, 1965, Ser. No. 445,658 6 Claims. (Cl. 122-406) The present invention relates in general to the construction and operation of a forced flow fluid heating unit and more particularly to improvements in the construction and arrangement of fluid heating circuits especially adapted for use in a forced circulation once-through vapor generating and superheating unit.

The general object of the present invention is the provision of a fluid heating unit of the character described so constructed and arranged as to assure an optimum distribution of fluid to all fluid flow paths and to assure an optimum relationship of fluid velocity within the tubes to heat input into the tube walls to effect adequate cooling of the tube walls to a safe temperature without imposing an excessive pressure drop in the fluid flow path.

A further and more specific object of the invention is improvement in the construction and arrangement of fluid heating circuits of a forced flow vapor generator of the type described in US. Patent No. 3,081,748, issued to Paul H. Koch, wherein the vapor generator is fired by a plurality of cyclone furnaces. Specifically, the invention is directed to the provision of fluid flow circuitry in a unit of the character described permitting by-passing of a portion of the fluid around the fluid heating circuitry of the cyclone furnaces during operation in the upper part of the load range without overheating the tubes of the cyclone furnaces, thus realizing an appreciable decrease in pressure drop in the fluid flow path and a corresponding reduction in the feed pump cost and power requirements.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described a preferred embodiment of the invention.

FIG. 1 is a sectional elevation of a once-through forced flow steam generator embodying the invention;

FIG. 2 is a partial sectional view taken along the line .2-2 of FIG. 1.

In the drawings the invention has been illustrated as embodied in a forced flow once-through steam generator intended for central station use. The particular unit illustrated is designed to produce a maximum continuous steam output of 3,840,000 lbs/hour at a pressure of 3600 p.s.i.g. and a total temperature of 1000 F. at the superr heater outlet, based on feedwater being supplied at a temperature of 548 F., with provisions for reheating the steam.

The main portions of the unit illustrated include an upright furnace chamber 10 of substantially rectangular horizontal cross section defined by front wall 11, rear wall 13, side walls 14, a roof 16 and a floor 17 and having a gas outlet 18 at its upper end opening to a horizontally extending gas pass 19 of rectangular vertical cross section formed by a floor 21 and extensions of the furnace roof 16 and side Walls 14. Gas pass 19 communicates at its rear end with the upper end of an upright gas passage 22 of rectangular horizontal cross section formed by a front wall 23, a rear wall 24, side walls 26 and an extension of the roof of the gas pass 19.

The fuel firing section comprises independently operable horizontally extending cyclone type furnaces 27 of relatively small volume and boundary wall area disposed on opposite walls 11 and 13 at the lower portion of the furnace chamber 10. Each cyclone furnace is arranged to burn solid fuel at high rates of heat release and separately discharge high temperature gaseous products of combustion and separated ash residue as a molten slag into the lower portion of the chamber 10. Floor 17 is formed with suit able openings, not shown, for the discharge of molten slag to a slag tank, not shown.

Gas pass 19 is occupied by a secondary superheater 28, a high pressure reheater section 29 and a low pressure reheater 31 arranged in series with respect to gas flow; while gas pass 22 is occupied in the direction of gas flow by a high pressure reheater section 32, a primary superheater 33 and an econ-omizer 34.

In the normal operation of the fluid heating unit, combustion air and a relatively coarse crushed fuel is supplied to the cyclone furnaces from independently controllable sources and the fuel is burned in the cyclone furnaces at high rates of heat release suflicient to maintain a normal mean temperature therein above the fuel-ash fusion temperature. Ash separates as a molten slag which flows into the lower portion of the chamber 10 and is discharged to the slag tank, while gases with a relatively small amount of slag particles in suspension discharge into the lower portion of the chamber 10. The heating gases then flow upwardly through chamber 10 to the outlet 18 of gas pass 19, thenpass successively over and between the tubes of secondary superheater 28, reheater 29, and reheater 31 in gas pass 19 and over and between the tubes of reheater 32, primary superheater 33 and economizer 34 in gas pass 22, and then discharge to another heat trap, not shown, before flowing to the stack. It will be understood that in accord ance with well-known practice, each of the superheater and reheater sections extends across the full width of its corresponding gas pass and is formed for serial flow by multiple looped tubes.

Feedwater at high pressure is supplied by feed pump, not shown, to economizer inlet header 25, then passes through economizer 34 to outlet header 30 from which it flows through a downcomer 35 to the cyclone furnace fluid heating circuits. Each cyclone furnace has its boundary walls lined or formed by tube panels constructed and arranged in a manner similar to that described in the aforesaid US. Patent No. 3,081,748. The high pressure fluid from the downcorner 35 flows in parallel to cyclone furnace supply headers iii by way of supply tubes 45, each one of the parallel flow streams passing through the circumferential wall tubes of the corresponding cyclone furnace to a discharge header S0. Streams of fluid discharging from headers 50 are collected in a conduit 36 for flow to the fluid heating circuitry of furnace chamber 10.

Each of the upright boundary walls of furnace 10 is lined by upwardly extending parallel tubes so arranged as to provide three passes of fluid. Thus front wall 11 comprises initial upflow tubes 37A, second upflow tubes 37B disposed in the spaces between and contiguous to initial upflow tubes 37A, and third upflow tubes 37C. Rear wall 13 includes initial upflow tubes 38A, second upflow tubes 38B situated in the spaces between and contiguous to tubes 358A, and third upflow tubes 38C forming a screen extending through gas pass 19. Each side wall 14 has initial upflow tubes 39A, second upflow tubes 3913 located in the spaces between and contiguous to tubes 39A, and third upflow tubes 39C. Rear wall tubes 38A, 383 have their upper portions bent inwardly and upwardly and then rearwardly and upwardly to form a nose arch 41. Floor 17 is lined by a row of tubes 42 ex tending between an inlet header 43 and an outlet header 44, with header 43 being arranged for supply of fluid from conduit 36 and header 44 being connected by a conduit as for discharge of fluid to a ring shaped header a high pressure turbine, not shown.

3 47 extending about and outside of the lower end of furnace and adapted to supply fluid to initial upflow tubes 37A, 38A and 39A of furnace 10.

The initial upflow tubes of the front, rear and side walls of furnace 10 have their outlet ends connected to a ring shaped header 49 extending about and outside of furnace 10 at about the level of nose arch 41. Fluid passing through initial upflow tubes 37A, 38A and 39A is collected in header 49 and then passed through a conduit 51 to a ring shaped header 52 disposed about and outside of furnace 10 at around the level of floor 17 and arranged to supply fluid to second upflow tubes 37B, 38B and 39B. The second upflow tubes of the front, rear and side Walls of furnace 10 extend from the floor 17 to about the level of nose arch 41 and have their upper ends connected to headers 53, 54 and 56, respectively.

Third pass upflow tubes 37C, 38C and 39C extend from the level of nose arch 41 to the top of the furnace, tubes 37C extending between inlet and outlet headers 57 and 58, tubes 38C between inlet and outlet headers 59 and 61, and tubes 39C between inlet and outlet headers 62 and 63, with headers 57, 59 and 62 being respectively connected for supply of fluid from headers 53, 54 and 56. Outlet headers 58, 61 and 63 are connected for flow of fluid to a header 66 which is arranged to distribute the fluid to tubes 67 forming the roof of furnace 10 and gas passes 19 and 22 and having their discharge ends connected to a header 68. From header 68 the fluid flows through a conduit 69 for distribution to boundary wall tubes of gas passes 19 and 22.

Each of the upright boundary walls of gas passes 19 and 22 includes upright parallel tubes, front wall 23 having tubes 71 extending between inlet and outlet headers 72 and 73, rear wall 24 having tubes 74 extending between inlet and outlet headers 76 and 77, each side wall 26 having tubes 78 extending between inlet and outlet headers 79 and 81,- and each side wall of gas pass 19 having tubes 82 extending between inlet and outlet headers 83 and 84. Floor 21 is lined by a row of tubes 86 having their inlet ends connected to headers S7 and their outlet ends to headers 73, with headers '73 being connected for flow of fluid to headers 88 by a row of screen tubes 89. Headers 72, 76, 79, 83 and .87 are connected for parallel supply of fluid from conduit 69, while headers 77, $1, 84 and 98 are arranged for discharge to a common collection header 91 from which fluid passes to the primary superheater 3 3 by way of a conduit 92.

Thus in operation up to a predetermined partial load the high pressure fluid supplied by the feed pump passes through economizer 34; then flows in parallel through the fluid heating circuits of cyclone furnaces 27 then passes through floor tubes 42; then flows upwardly in parallel through the radiant heat absorbing initial upflow tubes of the front rear and side walls of the furnace to collecting header 49; then passes in parallel upflow through the second upflow tubes 37B, 38B and 39B of the furnace; then in parallel through third upflow tubes 37C, 38C and 39C; then through tubes 6'7 forming the roof of furnace 10 and gas passes 19 and 22; then in parallel upflow through convection heat absorbing tubes of the upright boundary walls of gas pass 22 and the side and floor boundaries of gas pass 19; then successively passes through primary superheater 33 and secondary superheater 28 to Partially expanded steam from the turbine successively passes through reheater sections 32 and 29 to and through an intermediate pressure turbine, not shown, then flows through reheater 31 to a low pressure turbine, not shown, wherein final expansion takes place.

In accordance with the invention, during operation throughout the upper part of the load range of the vapor generator a portion of the fluid flowing through the downcomer is by-passed around the flow circuitry of the cyclone furnaces 27 and around floor tubes 42 by means of a conduit 94 connecting downcomer 35 and header 44, with conduit 94 being provided with a fluid flow control valve 96. Valve 96' always remains closed at low loads and during start-ups. When a predetermined partial load is reached valve 96 may be opened manually, or may be opened automatically with the controlling impulse coming from an indicator of the load on the vapor generator, such as by an impulse generator or controller 95 which automatically and continuously measures the rate of fluid flow in conduit 35 and translates any deviation from some preset minimum value of rate of fluid flow into an impulse force change which is transmitted to valve 96 by way of line 95A to actuate the valve. By-pass valve 96 may be operated in a number of ways. It may be operated to maintain the pressure drop of the fluid due to flow through the circuitry of cyclone furnaces 2'7 and floor tubes 42 substantially constant from the predetermined partial load to full load. It may be operated in response to variations in load in such a manner as to have a given opening at a given load. It may also be completely opened at the predetermined partial load and maintained in this position to full load, in which case the pressure drop across the cyclone furnace flow circuitry and floor tubes 42 immediately sharply decreases at a predetermined partial load and then gradually increases as the load increases. By any of these modes of valve operation, the pressure drop across the cyclone furnace fluid heating circuitry and floor tubes 42 will be considerably less throughout the operative load range of valve 96- than the pressure drop that would exist without by-passing fluid around such circuitry, thereby providing a corresponding reduction in the feed pump cost and power requirements.

A cyclone furnace is characterized by a nearly constant heat absorption rate (B.t.u./hr./ft. over its operative load range. In the present embodiment the cyclone furnace tube metals are designed for a predetermined partial load, about one-third of a full load. Since the cyclone furnaces have a substantially constant heat absorption rate over their operative load range and since the cyclone metals are set by one third load conditions, it is possible to by-pass fluid around the cyclone fluid heating circuitry throughout the upper part of the load range without overheating tubes of that circuitry, thus affording a marked reduction in pressure drop through such circuitry in the upper part of the load range. Similarly, the tube metals of floor 17 are designed for a predetermined partial load and have a substantially constant heat absorption rate over the load range because they are protected by a slag covering. So it is possible also to by-pass fluid around floor tubes 42 in the upper part of the load range without overheating such tubes, thereby providing a further reduction in fluid pressure drop.

By way of example, and not of limitation, in a commercial embodiment of the invention, valve 96 is designed to by-pass a portion of the fluid flowing through downcomer 35 around the flow circuitry of cyclone furnaces 27 and floor tubes 42 at loads above 55 percent of full load. As the load increases, the flow through conduit 35 increases causing impulse generator 95 to automatically transmit an impulse by way of line 95A to actuate valve 96 such that flow in excess of 55 percent of full load up to percent of full load is by-passed through conduit 94, while flow rate through the cyclone furnace fluid heating circuitry and tubes 42 is maintained substantially constant. Valve 96 is at its maximum open position at 85 percent full load, so that flow through the cyclone furnace fluid heating circuitary and tubes 42 gradually increases as the load increases beyond 85 percent full load. Immediately before valve 96 opens on increasing load beyond 55 percent full load, the pressure drop across the cyclone furnace fluid heating circuitry and tubes 42 is about 45 p.s.i. When the valve 96 opens the pressure drop remains substantially constant up to 85 percent load and then gradually incresases to a full load value of 50 psi, which is about one-quarter of the pressure drop which would exist at full load without by-passing fluid around such circuitry.

What is claimed is:

1. In a forced circulation fluid heating unit, walls including fluid heating tubes forming a furnace chamber having a gas outlet, walls including fluid heating tubes forming a combustion chamber of circular cross'section having a gas outlet opening to said furnace chamber,

means for burning fuel at high rates of heat release in said combustion chamber, means for supplying a vaporizable fluid to said combustion chamber wall tubes, means connecting said combustion chamber wall tubes for serial flow of fluid to said furnace chamber wall tubes, and means for maintaining the pressure drop of the fluid due to flow through said combustion chamber Wall tubes substantially constant from full load to a predetermined partial load, said last named means including means for by-passing a portion of the fluid inflow to said combustion chamber wall tubes to said furnace wall tubes, and means responsive to variations in total rate of fluid flow to said combustion chamber wall tubes for increasing the rate of flow of fluid by-passing said combustion chamber wall tubes as the load increases beyond said predetermined partial load.

2. In a forced flow vapor generating and superheating unit having walls forming a gas flow path, a combustion chamber of circular cross-section supplying heating gases to said gas flow path, a once-through fluid flow path arranged to receive a vaporizable fluid at one end and discharge superheated vapor at its opposite end and including a first fluid heating section lining the walls of said combustion chamber and a second fluid heating section in said gas flow path connected for series flow of fluid from said first fluid heating section, and a valve-controlled conduit around said first fluid heating section, the method of operating said unit which comprises passing all of the fluid entering said fluid flow path successively through said first and second fluid heating sections in the lower part of the load range, and regulating the resistance of fluid flow through said first fluid heating section in the upper part of the load range by by-passing a portion of the fluid inflow to the first section through said conduit to a position downstream of the fluid outflow side of said first section.

3. A once-through forced circulation vapor generator comprising walls including radiant heat absorbing fluid heating tubes defining an upright furnace chamber having a heating gas outlet, means including convection heat absorbing fluid heating tubes forming a gas pass serially connected to said gas outlet, at bank of vapor superheating tubes positioned in said gas pass in the path of gas flow, walls including fluid heating tubes forming a combustion chamber of circular cross-section having a gas outlet opening to said furnace chamber, means for burning fuel at high rates of heat release in said combustion chamber, means for supplying a vaporizable fluid to said combustion chamber wall tubes, and means for interconnecting said fluid heating tubes and vapor super-heating tubes to provide a serial flow of fluid successively through the combustion chamber wall t-ubes, some of the radiant heat absorbing fluid heating tubes of each of said furnace chamber walls, the remaining radiant heat absorbing fluid heating tubes of said furnace chamber walls, the convection heat absorbing fluid heating tubes, and the bank of vapor superheating tubes.

4. A once-through forced circulation generator comprising walls including radiant heat absorbing fluid heating tubes defining an upright furnace chamber having a heating gas outlet, means including convection heat absorbing fluid heating tubes forming a gas pass serially connected to said gas outlet, at bank of vapor superheating tubes positioned in said gas pass in the path of gas flow, Walls including fluid heating tubes forming a combustion chamber of circular cross-section having a gas outlet opening to said furnace chamber, means for burning fuel at high rates of heat release in said combustion chamber, means for supplying a vaporizable fluid to said combustion chamber wall tubes and means for interconnecting said fluid heating tubes and vapor super heating tubes to provide a serial flow of fluid successively through the combustion chamber wall tubes, alternate radiant heat absorbing fluid heating tubes of each of said furnace chamber Walls, the remaining radiant heat absorbing fluid heating tubes of said furnace chamber walls, the convection heat absorbing fluid heating tubes, and the bank of vapor superheating tubes.

5. In a forced circulation fluid heating unit, walls including fluid heating tubes forming a furnace chamber having a gas outlet, walls including fluid heating tubes forming a combustion chamber of circular crosssection having a gas outlet opening to said furnace chamber, means for burning fuel at high rates of heat release in said combustion, chamber, means for supplying a vaporizable fluid to said combustion chamber Wall tubes, means connecting said combustion chamber Wall tubes for serial flow of fluid to said furnace chamber Wall tubes, and means for regulating the pressure drop of the fluid due to flow through said combustion chamber wall tubes from full load to a predetermined partial load, said last named means including means for bypassing a portion of the fluid inflow to said combustion chamber Wall tubes to said furnace Wall tubes, and means responsive to variations in total rate of fluid flow to said combustion chamber wall tubes for varying the rate of flow of fluid by-passing said combustion chamber 'Wall tubes as the load increases beyond said predetermined partial load.

6. In a forced circulation fluid heating unit, walls including fluid heating tubes forming a furnace chamber having a gas outlet, walls including fluid heating tubes forming a combustion chamber of circular crosssection having a gas outlet opening to said furnace chamber, means for burning fuel at high rates of heat release in said combustion chamber, means for supplying a vaporizable fluid to said combustion chamber wall tubes, said combustion chamber having a nearly constant heat absorption rate over its operative load range, means connecting said combustion chamber wall tubes for serial flow of fluid to said furnace chamber wall tubes, and means for regulating the pressure drop of the fluid due to flow through said combustion chamber wall tubes from full load to a predetermined partial load, said last named means including means for bypassing a portion of the fluid inflow to said combustion chamber wall tubes to said furnace wall tubes, and means responsive to variations in total rate of fluid flow to said combustion chamber wall tubes for varying the rate of flow of fluid by-passing said combustion chamber Wall tubes as the load increases beyond said predetermined partial load.

References Cited by the Examiner UNITED STATES PATENTS 3,033,177 5/ 1962 Koch et a1. 122-235 3,081,748 3/1963 Koch 122-406 3,135,251 6/ 1964 Kane 122406 FOREIGN PATENTS 912,029 12/ 1962 Great Britain.

CHARLES J. MYHRE, Primary Examiner.

Claims (1)

1. IN A FORCED CIRCULATION FLUID HEATING UNIT, WALLS INCLUDING FLUID HEATING TUBES FORMING A FURNACE CHAMBER HAVING A GAS OUTLET, WALLS INCLUDING FLUID HEATING TUBES FORMING A COMBUSTION CHAMBER OF CIRCULAR CROSS-SECTION HAVING A GAS OUTLET OPENING TO SAID FURNACE CHAMBER, MEANS FOR BURNING FUEL AT HIGH RATES OF HEAT RELEASE IN SAID COMBUSTION CHAMBER, MEANS FOR SUPPLYING A VAPORIZABLE FLUID TO SAID COMBUSTION CHAMBER WALL TUBES, MEANS CONNECTING SAID COMBUSTION CHAMBER WALL TUBES FOR SERIAL FLOW OF FLUID TO SAID FURNACE CHAMBER WALL TUBES, AND MEANS FOR MAINTAINING THE PRESSURE DROP OF THE FLUID DUE TO FLOW THROUGH SAID COMBUSTION CHAMBER WALL TUBES SUBSTANTIALLY CONSTANT FROM FULL LOAD TO A PREDETERMINED PARTIAL LOAD, SAID LAST NAMED MEANS INCLUDING MEANS FOR BY-PASSING A PORTION OF THE FLUID INFLOW TO SAID COMBUSTION CHAMBER WALL TUBES TO SAID FURNACE WALL TUBES, AND MEANS RESPONSIVE TO VARIATIONS IN TOTAL RATE OF FLUID FLOW TO SAID COMBUSTION CHAMBER WALL TUBES FOR INCREAS-

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