US3370572A

US3370572A - Vapor generating and superheating system

Info

Publication number: US3370572A
Application number: US583038A
Authority: US
Inventors: Paul E Kurrle
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1966-09-29
Filing date: 1966-09-29
Publication date: 1968-02-27
Anticipated expiration: 1985-02-27
Also published as: GB1163072A; NL6713239A; ES345858A1

Description

F3127, 1968 P, E. KURRL E 3,370,572.

VAPOR GENERATING AND SUPERHEATING SYSTEM Filed Sept. '29, 1966 s Sheets-Sheet 1 1 M M wt INVENTOR.

Paul E. Kur rle Feb. 27, 1968 KURRLE 3,370,572

VAPOR GENERATING AND SUPERHEATING SYSTEM Filed Sept. '29, 1966 v 3 Sheets-Sheet 2 I i l 53 f v 91 I 5 4 r 55 w '1 3 71 7/0 3 l I 9 as Feb. 27, 1968 P. E. KLAJFERLE 3,370, 7

VAPOR GENERATING AND SUPERHEATING SYSTEM Filed Sept. 29, 1966 3 Sheets-Sheet 3 PEAK STEAM FLOW 3o (I I E 3 o J V LL -ACCUMULATOR DISCHARGE W 7 7 "7 7 J 9 1o '20 3o 40 5o FBLOWING o TAP AND CHARGE NExT 18 MINUTES 30 MINUTES CYCLE United States Patent tion of New Jersey Filed Sept. 29, 1966, Ser. No. 583,038 9 Claims. (Cl. 122-7) The present invention relates to vapor generating and superheating apparatus, and more particularly to apparatus wherein steam produced in the course of a cyclic exothermic process is combined with steam from a separately fired power boiler to provide a steam power source of substantially constant flow rate at uniform temperature and pressure.

The production of steel in a basic oxygen furnace is an example of such a process. Here the hot gases emitted from the furnace are passed through a water cooled conduit or hood wherein and whereby the gases are cooled, the water cooled conduit walls absorb heat from the gases and thereby generate steam. The operation of the oxygen furnace is cyclic in nature since the introduction of the oxygen to initiate the refining operation is but of relatively short duration with respect to the total elapsed time for one cycle. Moreover the rate of steam generation closely follows the heat release pattern of the furnace cycle, with maximum generation occurring during the period of oxygen flowing. The steam produced in the hood has sometimes been condensed by heat exchange with other fluids and recycled to the walls of the hood without any attempt to benefically recover the heat absorbed from the hot furnace gases. Some installations have attempted to use the steam produced in the hoods by passing the cyclically produced steam to accumulators and then flashing it to some lower pressure so that a generally uniform flow of saturated steam, from the accumulator, will result. The steam so discharged may be utilized for various steel plant purposes but it is highly desirable to increase the usefulness of such steam by superheating.

In the present invention a separately fired power boiler served by high heat value fuel is utilized to generate saturated steam, or even slightly superheated steam, and the steam so produced is mixed with saturated steam from an accumulator and then passed through a superheater disposed in a gas pass receiving gases from the power boiler, where the mixture may be superheated to the desired degree. The final superheat temperature of the steam may be controlled by the firing rate of the power boiler and by fiow regulation of the power boiler gases passing over the superheater serving the steam mixture. With this arrangement it has been found possible to adequately control both the quantity and the superheat temperature of the combined steam flows produced in the installation to provide a substantially uniform steam superheat temperature leaving the superheater.

Of the drawings:

FIG. 1 is a diagrammatic flow sheet showing the equipment arrangement of the present invention;

FIG. 2 is an enlarged elevation, in section, of a portion of the apparatus shown in FIG. 1;

FIG. 3 is a plan View, in section, taken on the line 3-3 of FIG. 2; and

FIG. 4 is a diagram illustrative of steam production and accumulator discharge rates from an oxygen furnace hood.

In the embodiment of the invention illustrated in the drawings, steam produced by the hot gases cyclically discharged from a basic oxygen furnace is discharged at a relatively high pressure to an accumulator so that a uniform quantity of relatively low pressure saturated steam will be available for external use. The steam from 3,370,572 Patented Feb. 27, 1968 the accumulator is mixed with steam produced in a power boiler, where the mixture of accumulator steam and power boiler steam is passed through a super-heater provided with heat from the gases of combustion produced in the power boiler. As hereinafter described, the operations of the power boiler are regulated to permit a substantially uniform temperature and pressure in the mixed superheated steam discharged from the superheater.

Referring particularly to FIG. 1, two

oxygen furnaces

10 and 11 are illustrated, where in general only one furnace is operated at a time. In the usual operation of a plant of this type one furnace is operated while the other furnace is being repaired although under some conditions both furnaces may be simultaneously operated for a short period of time. It will be further understood that more than two furnaces may be connected into the system without changing the basic arrangement of apparatus or its mode of operation.

With one of the furnaces in operation (for example, furnace 10) the hot gases discharged from the furnace during the oxygen refining period are discharged through a fluid cooled hood 12 of the general type disclosed, for example, in U.S. Patent 3,168,073. In hoods of this type a continuous stream of high pressure water is discharged by a pump 13 to inlet headers 14 adjacent the lower end of the hood to flow in parallel through tubular elements lining the walls of the hood and discharge as a steam and water mixture to outlet headers 15 from which the mixture is discharged to a steam and water drum 16.

The drum 16 is provided with the usual blow down connections, vents and safety valves (not shown) and with makeup water supplied through a valved inlet pipe 17 which receives water from a feed water pump 18. The drum 16 is provided with a water level control of conventional type. In the drum the steam and water discharged from the riser tubes 20 is separated, with the water combined with makeup water being discharged through a downcomer 21 to the pump 13. The separated steam discharges from the drum 16 through a valved conduit 22 which joins a corresponding conduit 23 from a corresponding vapor generating unit 24 associated with the basic oxygen furnace 11. The steam from either or both of the steam generating units of the

furnaces

10 and 11 is discharged through a line 25 to an accumulator tank 26.

The accumulator tank 26 is sized to receive the steam produced in either or both of the steam generating units of the basic oxygen furnaces. Suitable quantities of makeup water are supplied to and excess water removed from the accumulator tank through pipe 27 so that the steam discharged thereto through valved pipe 28 is condensed and stored for a continuous, substantially uniform discharge of lower pressure steam through the valved pipe 30 opening to the upper side of the accumulator tank. Suitable pressure reducing and flow control valves are provided for regulation of the high pressure water which is flashed to steam in leaving the accumulator. As shown, the high pressure steam inlet pipe 28 to and the relatively low pressure outlet pipe 30 from the accumulator are interconnected by a conduit 31 which is provided with a check valve 32 for pressure regulation between the inlet and outlet pipes. The low pressure saturated steam discharged from the accumulator is passed through pipe 30 and a suitable cut off valve 33 for delivery to a mixing T 34.

The mixing T receives saturated steam from the accumulator and in addition also receives steam from a power boiler 35. It will be understood the steam from the power boiler may be saturated or superheated depending upon the overall heat requirements of the system. The steam from the accumulator 26 and from the power boiler will be at substantially the same pressure, are mixed in the mixing T and delivered through a pipe 37 to the inlet header 36 of a superheater 38 associated with the .power boiler. The steam is superheated for discharge through an outlet header 40 and through a pipe 41 which is connected to the steam main (not shown) of the plant in which the basic oxygen furnaces are installed. The power boiler 35 is provided with a feed water pump 42 for delivery of feed Water to the power boiler to com- 'pensate for the steam discharged therefrom. In the usual installation, a common hot well will supply makeup water to the oxygen furnace hoods and the power boiler.

The operation of a basic oxygen furnace for the refining of steel is well known and while the exact cycle of operation will vary from plant to plant a typical cycle is illustrated in FIG. 4. As shown in this figure, the blowing time during which oxygen is injected into the furnace will average about 18 minutes while the tap and charge period will approximate 30 minutes. Thus each cycle will be completed in a period of approximately 48 minutes. During the blowing period the steam discharged from the hood such as shown in FIG. 1 will reach a peak in a'matter of minutes and then decline to a substantially zero steam production at the end of the blowing :period. During the steam production period, in the illustrated example, approximately 300,000 pounds of steam .per hour will be supplied for a period of time measured in one or two minutes.

As also indicated on FIG. 4 the accumulator 26 of FIG. 1 Will be sized and controlled to discharge a substantially uniform fiow of steam therefrom. In the illustrated example of FIG. 4 the steam discharge will be of the order of 50,000 pounds of steam per hour. It will be understood that in the ordinary operation of a basic oxygen furnace 'the amount of steam produced in each cycle of iron refining will vary and thus the the total amountof steam available in the accumulator will also vary and fora uniform availability of steam to a steam main -it is desirable to arrange the power boiler so it can compensate for "relatively limited variations in theavailability of steam from the accumulator. As hereinafter described, the power boiler is constructed and arranged to permit a limited change in its vapor generating rate and also to permit a controllable variation in both the temperatureand weight of gases'passed through the superheater. With this arrangement the combination of steam from the accumulator and from the power boiler can be regulated to produce a substantially uniform quantity of superheated steam discharged from the superheater outlet header where the steam may also be controlled for a substantially uniform superheated temperature and pressure.

The power boiler 34 and superheater 38 of FIG. 1 are shown in detail in FIGS. 2 and 3. The boiler includes an upper steam and water drum 51 and a lower water drum 52 interconnected by a bank 53 of vapor generating tubes. A furnace chamber 54 is positoned on one side of the tube bank 53, with the walls of the furnace lined by vapor generating tubes '55 opening to the drums 51 and 52. The furnace is provided with a conventional "high heat valuefuel burner 56 in a-port 57 in one wall'58 for the supply of fuel to the furnace to produce hot gases of combustion. The gases of combustion move through the furnace 54 between a side wall 60 and a bafile wall '61 toward the rear wall 62 to discharge through a gas outlet 63 formed between the rear wall and the end of the bafile wall 61. As shown, the convection tube bank 53 ends adjacent the end of the baflle wall '61, and a gas outlet 64 is formed in the side wall 65 leading directly into the superheater 38. A second gas outlet 66 is formed inthe opposite end'of the wall 65, so that the flow of gases leaving the furnace 54 can pass to both 'of the gas outlets 6 4 and 66, or either, as regulated by dampers hereinafter described. With this construction the proportions of gas flow through the superheater and through the vapor generating bank 53 can be controlled for superheat temperature regulation.

The boiler may be provided with a bank of superheater tubes 67 between the

gas outlets

63 and 64 and between the rear row 68 of tubes in the bank 53 and the wall 62. (See FIG. 3.) Under these circumstances the steam from the drum 51 will pass through the superheater to the mixing T 34. When the superheater '67 is omitted the flow of steam from the drum 51 will pass directly through pipe 70 to the mixing T 34, as shown in FIG. 2.

The superheater 38 is formed with ceramic refractory Walls, with the roof 67, rear wall 68 and floor 70' cooled by a row of tubes 71 connecting the superheater inlet header 36 with a steam distributing header 72. The superheater housing is provided with a longitudinal bafile 73 which extends the full height of the superheater housing and projects from a position adjoining the gas outlet 64 to an end position 74 spaced from the rear wall 68 of the superheater housing. With this arrangement, heating gas flow entering the superheater housing from the outlet 64 passes lengthwise along one side of the superheater and reverses its flow direction around the end position 74 to flow through an outlet 75 formed in a side wall 76 of the superheater housing. A duct 77 connects the outlet 75 with a second duct 78 which interconnects the convection gas pass outlet 66 with an induced draft fan 80. The power boiler may be pressurized, omitting the fan 80, with the combined gases from duct 78 discharged directly to a stack. The

gas ducts

77 and 78 are provided with dampers S1 and 82, respectively, so that the flow from the vapor generator 35 (FIG. 1) can be regulated with controllable proportioning through the superheater and through the vapor generating section of the boiler.

A shown particularly. in FIG. 2, the steam passing from the accumulator shown in FIG. 1 flows through its discharge duct 30 to the mixing T 34 where the accumulator steam is combined with a flow of steam originating the upper steam and water drum 51 of the power boiler. The mixture of steam discharging through the pipe opens to the inlet header 36 of the superheater. Thereafter the steam passes through the row of tubes 71 to the header 72, as hereinbefore described, for discharge through tubes 83 to the steam inlet end portion 84 of the steam outlet header 40. Each of the headers ,gas flow through the gas pass 91 defined by wall 76 and bafiie 73. The steam entering the header 88 passes through the interconnecting tubes in succession through the

headers

87, 86 and 85 for discharge into the dis-' charge header 40.

It will be noted in the diagram of FIG. 4, the accumulator discharge of saturated steam represents a flow of approximately 49,000 pounds of steam per hour. Under these conditions the power boiler may be operated to produce approximately 12,000 pounds of steam per hour. It is of course understood that the accumulator 26 will be regulated by known valve controls to discharge steam at a generally uniform rate therefrom at a pressure which is maintained substantially uniform. The pressure from the accumulator is selected so that the pressure of the steam entering the mixing T 34 from the accumulator will be substantially equal to the steam pressure entering'the mixing T 34 from the power :boiler. It is known in the use of an accumulator that under the conditions described in connection with FIG. 21, the hood will be operated at a pressure of the order of 600 pounds per square inch absolute (p.s.i.a. so that the stored'steam'in the accumulator may be discharged therefrom at a pressure, for example of 200 p.s.i.a. With this construction the supply of steam will be continuous at'the-pressure selected, :and'if for'any reasonthe steam added to the accumulator during the blowing cycle of the oxygen furnace is not adequate to provide for a uniform discharge of 49,000 pounds of steam per hour from the accumulator, the difference between the accumulator discharge and the desired flow rate of the steam mixtrue can be compensated for by increasing the steam generation of the power boiler. This can be a complished without adverse afiect upon the total superheat temperature of the mixture discharged from the header 40 by increasing the firing rate to the power boiler. Such an increase will permit an increase in the flow of gases over the vapor generating portion of the power boiler while still maintaining adequate gas flow rates and gas temperature through the superheater to maintain superheat temperatures in the mixture discharged.

In controlling the apparatus shown in FIGS. 2 and 3 the basic control will be a proportioning control device indicated at 93 positioning the dampers 81 and 82 in response to the temperature of the steam discharged from the header 40, as determined by a temperature sensor 94. The supply of fuel to the burner 56 may also be regulated in known manner in accordance with the steam flow and temperature conditions prevailing in the steam outlet 40.

What is claimed is:

1. A steam generating and superheating system'ineluding a power boiler, said power boiler comprising a furnance, means for burning high heat value fuel in said furnace, a convection gas-pass divided into a pair of parallel gas flow sections communicating with said furnace, a bank of steam generating tubes positioned in one of said sections, a bank of steam superheating tubes in the other of said sections, means for proportioning gas flow from said furnace to said parallel gas flow sections, a steam accumulator, mixer means for combining a flow of saturated steam from said accumulator and steam from said steam generator for delivery of the mixture to said superheater tubes, and means responsive to the temperature of the mixed superheated steam leaving said superheater tubes to proportion gas flow through said parallel gas flow sections.

2. A steam generating and superheating system according to claim 1 wherein means provide a substantially uniform flow of saturated steam at a substantially uniform pressure from said accumulator.

3. A steam generating and superheating system according to claim 1 wherein steam generating means supply said accumulator with saturated steam at a cyclic rate of flow.

4. A steam generating and superheating system according to claim 3 wherein said accumulator steam supply means includes a water cooled hood served by a cyclic flow of high temperature heating gases therethrough.

5. A steam generating and superheating system according to claim 4 wherein an oxygen steel making furnace discharges hot gases into said hood during a minor portion of a steel refining cycle.

6. A steam generating and superheating system according to claim 2 wherein the steam produced by said power boiler is superheated, and said superheated steam is combined with saturated steam from said accumulator for further heating in said superheating tubes.

7. A steam generating and superheating system according to claim 2 wherein the rate of high heat value fuel burned in said furnace is regulated in accordance with a desired steam production in said power boiler in cooperation with proportional gas flow through said parallel gas fiow sections.

8. A steam generating and superheating system according to claim 1 wherein wall means define an elongated superheater housing to enclose said bank of steam superheating tubes, battle means in "said housing direct a reversed series fiow of heating gases over said bank of steam superheating tubes, and the flow of mixed steam through said tubes is countercurrent with respect to said heating gas flow.

9. A steam generating and superheating system according to claim 8 wherein a row of tubes are extended along the roof and rear wall and through the floor of said superheater housing to receive steam from said mixer means and to supply steam to said bank of superheater tubes.

References Cited UNITED STATES PATENTS 3,118,429 1/1964 Hochmuth l227 3,217,695 11/1965 Durham 122-7 3,303,827 2/1967 Kemmetmuller et al. 1227 KENNETH W. SPRAGUE, Primary Examiner.

Claims

1. A STEAM GENERATING AND SUPERHEATING SYSTEM INCLUDING A POWER BOILER, SAID POWER BOILER COMPRISING A FURNANCE, MEANS FOR BURNING HIGH HEAT VALUE FUEL IN SAID FURNACE, A CONVECTION GAS-PASS DIVIDED INTO A PAIR OF PARALLEL GAS FLOW SECTIONS COMMUNICATING WITH SAID FURNACE, A BANK OF STREAM GENERATING TUBES POSITIONED IN ONE OF SAID SECTIONS, A BANK OF STEAM SUPERHEATING TUBES IN THE OTHER OF SAID SECTIONS, MEANS FOR PROPORTIONING GAS FLOW FROM SAID FURNACE TO SAID PARALLEL GAS FLOW SECTIONS, A STEAM ACCUMULATOR, MIXER MEANS FOR COMBINING A FLOW OF SATURATED STEAM FROM SAID ACCUMULATOR AND STEAM FROM SAID STEAM GENERATOR FOR DELIVERY OF THE MIXTURE TO SAID SUPERHEATER TUBES, AND MEANS RESPONSIVE TO THE TEMPERATURE OF THE MIXED SUPERHEATED STEAM LEAVING SAID SUPERHEATER TUBES TO PROPORTION GAS FLOW THROUGH SAID PARALLEL GAS FLOW SECTIONS.