US2707458A

US2707458A - Vapor generators and superheaters

Info

Publication number: US2707458A
Application number: US217809A
Authority: US
Inventors: Hayden Robert Leslie James
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1951-03-27
Filing date: 1951-03-27
Publication date: 1955-05-03
Anticipated expiration: 1972-05-03

Description

May 3, 1955 R. L. J. HAYDEN VAPOR GENERATORS AND SUPERHEATERS Filed March 27, 1951 nventors Clttorneg United States Patent O VAPOR GENERATRS AND SUPERHEATERS Application March 27, 1951, Serial No. 217,809 4 Claims. (Cl. 1221) This invention relates to steam generators. ciiically, it is concerned with controlling the temperature in a steam generator.

In its most usual form, a vapor generator comprises a furnace red by burners and in which are arranged the steam generating tubes which connect the water drum to the steam drum. The saturated steam from the steam drum passes to a superheater which is heated by furnace gases which have already served for heating the steam generating tubes. Those gases then proceed through a waste heat recovery system including an economizer and an air heater. The thus preheated air is used as combustion air in the furnace.

In order to control the degree of superheat, i. e. the final steam temperature, means may be provided for bypassing a certain proportion of the furnace gases round the superheater. This is not very satisfactory, however, in installations in which, at times, the degree of superheat is to be very low because, at those times, the residual heat in the furnace gases is greater than can be conveniently dealt with by the heat recovery system.

An alternative manner of reducing the superheat is to provide a two-stage superheater, i. e. a superheater having two sections connected in series, and to cool or desuperheat the steam coming from the first section before feeding it to the second section. Generally, the desuperheating medium is water which is thus preheated and serves as boiler feed water. It has, however, also been proposed to use air as a desuperheating medium and to use Vthe thus heated air as combustion air. Although air More spenal steam desuperheating has attractions, it has the disadvantage that where very low final steam temperatures are required, the air temperature becomes too high for the air to be used in the furnace burners.

The present invention is concerned with the problem of enabling a water tube boiler to provide a wide range of superheat with a very low minimum, otherwise than at the expense of the thermal economy of the boiler.`

According to the present invention, a water tube boiler is provided with a multi-stage superheater arranged to be heated by furnace gases which have served for the generation of steam, with a heat exchanger in which steam from an early superheating stageis cooled by indirect heat exchange with air before being passed to a later superheating stage and with means for by-passing the furnace gases, when desired, round the said later superheating stage and with means for by-passing the air round the heat exchanger when desired.

ln the preferred form of boiler in accordance with the invention, a controller is provided which is under the inuence of the inal steam temperature and which automatically controls dampers regulating the ow of the furnace gases through the superheater and also the flow of air through and round the heat exchanger.

The invention will be understood from the following description when considered in connection with the accompanying drawing forming a part thereof, and in which 'ice the single figure is a diagrammatic transverse vertical section of the apparatus of the present invention.

Referring to the drawing, the apparatus of the present invention is disclosed as embodied in a vapor generator comprising a setting 10 having vapor generating surface therein with an upper steam and water drum 11 associated therewith together with a lower water drum 12 in the lower part of the setting in substantial vertical alignment with said upper drum. Drums 11 `and 12 are connected by a substantially vertical bank of steam generating tubes 13.

At one side of the bank of tubes 13 is a furnace or combustion chamber 14 fired, as shown, by a plurality of burners 15. The roof, side wall and iioor of chamber 14 are lined by

water tubes

16, 17 and 18.

At the side of the tube bank opposite to that on which the chamber 14 is located is a substantially vertical extending gas passage 19 having an outer side wall 20 and an inner side Wall Ztl. Passage 19 has a4 lower gas inlet 21 at the bottom thereof and an intermediate gas inlet 22 in spaced relationship with said lower gas inlet. Lower gas inlet 21 receives gases through a furnace gas outlet 23 controlled by a damper 24, while intermediate gas inlet 22 of passage 19 receives gases through a furnace gas outlet 25 controlled by a damper 26. As shown, damper 24 is in its open position so that gases passing over the tube bank 13 will flow into gas inlet 21 of gas passage 19, while damper 26 is illustrated as closed preventing the flow of gases into intermediate gas inlet 22.

A superheater having an upper or one section 27 with a saturated steam inlet 2S and a steam `outlet 29 is disposed in passage 19 above intermediate gas inlet 22. Upper section 27 receives steam from drum 11 through saturated steam conduit 30 which communicates at the inlet end thereof with drum 11 and at the outlet end with saturated steam inlet 28 of the upper superheater section. The superheater also has a lower or other section 31 having a desuperheated steam inlet 32 and 4a steam outlet 33. Lower section 31 is disposed below intermediate gas inlet passage 22 and above gas inlet 2l.

As shown, gas passage 19 has economizer sections 34 and 3S positioned above the superheater and also has an air heater 36 disposed therein above the economizer sections. The air heater comprises a plurality of vertical tubular members 37 through which gases of combustion pass, said air heater being divided into an upper pass 38 and a lower pass 39 by a battle 40. An air conduit 41 is disposed at the furnace chamber side of setting 10 and has a by-pass damper 42 therein which is disposed adjacent bafe 40. When damper 42 is closed, as illustrated, air is caused to iiow through upper pass 38 of the air heater, through lower pass 39 and thence back into duct 41. When the damper 42 is open, air flows directly through duct 41 by-passing the air heater. Duct t1 communicates with a further duct 43 which has an enlarged portion 44 at the upper part thereof and cornmunicates with burners 15 through an enlarged portion 45 at the bottom thereof.

The enlarged portion 44 of air duct 43 is divided into a vertically extending by-pass passage 46 and a main passage 47 by a vertically extending baffle 4d. By-pass passage 46 is controlled by a by-pass damper 49, while main passage 47 is controlled by a plurality of dampers Si?. As shown, by-pass damper 49 and dampers Sil are actuated by an actuator 51 through a lever S2, the dampers being so connected to lever 52 that as by-pass damper 49 is actuated into a closed position, dampers Stb are actuated into an opened position and as damper 49 is actuated into an opened position, dampers Si) are actuated into a closed position. A tubular coil 53 forming a flow path for steam is positioned in main passage 47 below dampers 50, said coil having an inlet 54 and an outlet 55. The

inlet 54 is in communication with steam outlet 29 of the upper superheater section 27 through steam conduit 56, while outlet 55 is in communication with desuperheated steam inlet 32 through a conduit 57.

By-pass damper 4Z controlling the flow of air through air heater 36 is operated by an actuator 53, while dampers 24 and 26 controlling the flow of gases into passage 19 through gas inlet passage 21 and intermediate gas inlet passage 22 respectively are operated by an actuator 59.

Actuators

51, 53 and 59 are operated by a damper controller 60 which is responsive through thermostatic connection 61 to the outlet temperature of steam flowing from lower section 31 of the superheater through steam outlet 33.

When the vapor generator of the present invention is operating under normal working conditions and a predetermined degree of superheat is required, damper controller 60 is set to the final temperature required.

Dampers

24 and 26 are partially open so that gases flowing over tube bank 13 pass through furnace gas outlets 23 and 25 into passage 19 through gas inlets 21 and 22 respectively, when said gases pass over the superheater sections thereafter to ow over

economizer sections

34 and 35 thence through tubular members 37 of air heater 36. By-pass damper 49 and dampers Sti in air duct 43 are set as shown in the drawing, that is, these dampers are partially open so that a portion of the air passes over the tubular coil 53 and another portion flows through by-pass passage 46. Air heater by-pass damper 42 is in a partially closed position so that a portion of the air will flow from duct 41 through upper pass 38 of the air heater and thence through lower pass 39, while another portion of the air by-passes the air heater thereafter both portions of the air flow into conduit 41 prior to passing into air duct 43.

Should a higher final steam temperature be required, controller 60 is set to a higher temperature with the result that actuator 58 moves damper 4 toward its closed position so that more air will ow through air heater 36, while actuator 51 will move by-pass damper 49 in conduit 43 toward a more open position and at the same time moves dampers toward a more closed position so that less air flows over tubular coil 53.

Should a lower final temperature be required, controller is set to a lower temperature thereby actuating actuator 58 so that damper 42 in air duct 41 is moved towards a more open position and a greater quantity of air by-passes air heater 36 and actuates actuator 51 so that by-pass damper 49 is moved toward a closed position and dampers 50 are moved toward an open position so that more air ows over tubular coil 53. Controller 60 will also control actuator 59 so that by-pass damper 24 controlling the ow of gases over superheater section 31 is moved toward a closed position, while damper 26 controlling intermediate gas passage 22 is moved toward an open position.

When the plant is idling and, therefore the degree of superheat is at a minimum, controller 60 is set at a minimum temperature with the result that damper 24 is entirely closed by actuator 59 and damper 26 is entirely open so that gases entirely by-pass superheater section 31. Damper 42 in air conduit 41 is completely open by actuator 58 so that air by-passes air heater 36, while actuator 51 moves by-pass damper 49 in airconduit 43 to a closed position and dampers 50 to a wide open position so that all the air flows over coil 53 to the burners` v heating in the waste heat recovery system. f

Inasmuch as changes may be made in the form, loca-f. tion and relative arrangement of the several parts of the y apparatus disclosed Without departing from the essential characteristics of the invention, it will be understood that the invention is not to be limited excepting by the scope of the appended claims.

What is claimed is:

1. In vapor generating apparatus comprising a vapor generator having a setting and means forming a saturated vapor space, a furnace in the setting, said furnace having a gas outlet, means for firing the furnace, an air duct in communication with said furnace so as to conduct air to support combustion thereto, baffle means disposed in said duct so as to divide the duct longitudinally thereof into an air duct passage and an air duct by-pass passage laterally adjacent one another, air duct passage damper means associated with said air duct passage, air duct by-pass passage damper means associated with said bypass passage, actuating means operatively associated with the damper means and the by-pass damper means so as to act simultaneously thereon to move said damper means and the by-pass damper means in directions opposite to one another, tubular means arranged to form a fluid path of ow and disposed in the air duct passage in heat exchange relationship with air flowing therethrough, gas passage forming means having a passage gas inlet and a gas outlet, the inlet being in communication with the furnace so as to receive gases of combustion therefrom, a superheater disposed in said gas passage forming means beyond the passage gas inlet in the direction of ow of the gases from the furnace and in heat exchange relationship with said gases, the superheater having a plurality of sections, one section being positioned beyond and in spaced relationship with another section in respect to the flow of said gases through the passage, the portion of the gas passage forming means between the superheater sections being in communication with the furnace through an intermediate gas inlet, the inlet of one of said superheater sections being in communication with the saturated vapor space to receive vapor therefrom and the outlet of said one superheater section being in communication with the vapor inlet of the tubular path of flow, the vapor inlet of said other superheater section being in communication with the vapor outlet of the tubular path of ow, a furnace gas damper disposed to control the ow of gases from the furnace into said passage through the intermediate gas inlet, another furnace gas damper disposed to control the flow of gases from the furnace to said passage through said passage gas inlet, other actuating means operatively associated with the furnace gas damper and the other furnace gas damper so as to act simultaneously on said furnace gas damper and said other furnace gas damper to move said furnace gas damper toward a closed position when said other furnace gas damper is moved toward an opened position and vice versa, and control means acting simultaneously on said actuating means and said other actuating means and responsive to the temperature of superheated vapor flowing from said other superheater section, said control means being adapted to so operate the actuating means and other actuating means when the temperature of the superheated vapor exceeds a predetermined degree as to cause the actuating means to move the air duct by-pass passage damper means toward a closed position wherein -ilow of air through the air duct by-pass passage is prevented and as to move theair duct passage damper means toward an opened position wherein the flow of air through the air duct passage is permitted, and as to cause the other actuating means to move the furnace gas damper toward an opened position to permit flow of furnace gases through theintermediate gas passage inlet and as to move the other furnace gas damper towardV a closed position to prevent the flow of furnace gasesthrough the gas passage inlet.

2. The apparatus of claim l wherein when the superlheated vapor temperature falls below a predetermined degree said control means simultaneously acts on said actuating means and said other actuating means respectively to move the air duct by-pass damper means toward an opened position and the air duct damper means toward a closed position, and to move the furnace gas damper toward a closed position and the other furnace gas damper toward an opened position.

3. In vapor generating apparatus comprising a vapor generator having a setting and means forming a saturated Vapor space, a furnace in the setting, said furnace having a gas outlet, means for firing the furnace, an air duct in communication with said furnace so as to conduct air to support combustion thereto, baffle means disposed in said duct so as to divide the duct longitudinally thereof into an air duct passage and an air duct by-pass passage laterally adjacent one another, air duct passage damper means associated with said air duct passage, air duct by-pass passage damper means associated with said by-pass passage, actuating means operatively associated with the damper means and the bypass damper means so as to act simultaneously thereon to move said damper means and the by-pass damper means in directions opposite to one another, tubular means arranged to form a fluid path of flow and disposed in the air duct passage in heat exchange relationship with air flowing therethrough, gas passage forming means having a passage gas inlet and a gas outlet, the inlet being in communication with the furnace so as to receive gases of combustion therefrom, a superheater disposed in said gas passage forming means beyond the passage gas inlet in the direction of flow of the gases from the furnace and in heat exchange relationship with said gases, the superheater having a plurality of sections, one section being positioned beyond and in spaced relationship with another section in respect to the flow of said gases through the passage, the portion of the gas passage forming means between the superheater sections being in communication with the furnace through an intermediate gas inlet, the inlet of one of said superheater sections being in communication with the saturated vapor space to receive vapor therefrom and the outlet of said one superheater section being in communication with the vapor inlet of the tubular path of ow, the vapor inlet of said other superheater section being in communication with the vapor outlet of the tubular path of flow, a furnace gas damper disposed to control the ow of gases from the furnace into said passage through the intermediate gas inlet, another furnace gas damper disposed to control the flow of gases from the furnace to said passage through said passage gas inlet, other actuating means operatively associated with the furnace gas damper and the other furnace gas damper so as to act simultaneously on said furnace gas damper and said other furnace gas damper f to move said furnace gas damper toward a closed position when said other furnace gas damper is moved toward an opened position and vice versa, an air heater comprising heat exchange means wherein air and gases of combustion ow in indirect heat exchange relationship with one another, said heat exchange means communieating with said gas passage beyond said one superheater section in the direction of flow of gases through the passage to receive gases therefrom, the heat exchange means being in communication with the air duct prior to said air duct passage and said air duct by-pass damper means in the direction of ow of air in said duct, the air heater having an air flow by-pass passage therein arranged to by-pass air around said heat exchange means, air flow by-pass damper means disposed to control the flow of air through said air ow by-pass passage, further actuating means operatively associated with the air ow by-pass damper means to actuate said air flow by-pass damper means, and control means acting on said actuating means, said other actuating means and said further actuating means, said control means being responsive to the ternperature of superheated vapor flowing from said other superheater section, said control means being adapted to so operate the actuating means, other actuating means, and further actuating means when the temperature of the superheated vapor exceeds a predetermined degree as to cause the actuating means to move the air duct byapass passage damper means toward a closed position wherein How of air through the air duct by-pass passage is prevented and as to move the air duct passage damper means toward an opened position wherein ow of air through the air duct passage is permitted, and as to cause the other actuating means to move the furnace gas damper toward an opened position to permit ow of furnace gases through the intermediate gas passage inlet and as to move the other furnace gas damper toward a closed position to prevent the flow of furnace gases through the gas passage inlet, and as to cause the air flow bypass damper means to move toward an opened position wherein flow of air through the air flow by-pass passage is permitted.

4. The apparatus of claim 3 wherein when the superheated vapor temperature falls below a predetermined degree said control means simultaneously acts on said actuating means, the other actuating means and said further actuating means respectively to move the air duct by-pass damper means toward an opened position and the air duct damper means toward a closed position, to move the furnace gas damper toward a closed position and the other furnace gas damper toward an opened position, and to move said air flow by-pass damper means toward its closed position.

References Cited in the file of this patent UNITED STATES PATENTS 1,785,334 Black Dec. 16, 1930 1,983,624 Lundgren Dec. 1l, 1934 FOREIGN PATENTS 575,509 Great Britain Feb. 21, 1946

Claims

1. IN VAPOR GENERATING APPARATUS COMPRISING A VAPOR GENERATOR HAVING A SETTING AND MEANS FORMING A SATURATED VAPOR SPACE, A FURNACE IN THE SETTING, SAID FURNACE HAVING A GAS OUTLET, MEANS FOR FIRING THE FURNACE, AN AIR DUCT IN COMMUNICATION WITH SAID FURNACE SO AS TO CONDUCT AIR TO SUPPORT COMBUSTION THERETO, BAFFLE MEANS DISPOSED IN SAID DUCT SO AS TO DIVIDE THE DUCT LONGITUDINALLY THEREOF INTO AN AIR DUCT PASSAGE AND AN AIR DUCT BY-PASS PASSAGE LATERALLY ADJACENT ONE ANOTHER, AIR DUCT PASSAGE DAMPER MEANS ASSOCIATED WITH SAID AIR DUCT PASSAGE, AIR DUCT BY-PASS PASSAGE DAMPER MEANS ASSOCIATED WITH SAID BYPASS PASSAGE, ACTUATING MEANS OPERATIVELY ASSOCIATED WITH THE DAMPER MEANS AND THE BY-PASS DAMPER MEANS SO AS TO ACT SIMULTANEOUSLY THEREON TO MOVE SAID DAMPER MEANS AND THE BY-PASS DAMPER MEANS IN DIRECTIONS OPPOSITE TO ONE ANOTHER, TUBULAR MEANS ARRANGED TO FORM A FLUID PATH OF FLOW AND DISPOSED IN THE AIR DUCT PASSAGE IN HEAT EXCHANGE RELATIONSHIP WITH AIR FLOWING THERETHROUGH, GAS PASSAGE FORMING MEANS HAVING A PASSAGE GAS INLET AND A GAS OUTLET, THE INLET BEING IN COMMUNICATION WITH THE FURNACE SO AS TO RECEIVE GASES OF COMBUSTION THEREFROM, A SUPERHEATER DISPOSED IN SAID GAS PASSAGE FORMING MEANS BEYOND THE PASSAGE GAS INLET IN THE DIRECTION FLOW OF THE GASES FROM THE FURNACE AND IN HEAT EXCHANGE RELATIONSHIP WITH SAID GASES, THE SUPERHEATER HAVING A PLURALITY OF SECTIONS, ONE SECTION BEING POSITIONED BEYOND AND IN SPACED RELATIONSHIP WITH ANOTHER SECTION IN RESPECT TO THE FLOW OF SAID GASES THROUGH THE PASSAGE, THE PORTION OF THE GAS PASSAGE FORMING MEANS BETWEEN THE SUPERHEATER SECTIONS BEING IN COMMUNICATION WITH THE FURNACE THROUGH AN INTERMEDIATE GAS INLET, THE INLET OF ONE OF SAID SUPERHEATER SECTIONS BEING IN COMMUNICATION WITH THE SATURATED VAPOR SPACE TO RECEIVE VAPOR THEREFROM AND THE OUTLET OF SAID ONE SUPERHEATER SECTION BEING IN COMMUNICATION WITH THE VAPOR INLET OF THE TUBULAR PATH OF FLOW, THE VAPOR INLET OF SAID OTHER SUPERHEATER SECTION BEING IN COMMUNICATION WITH THE VAPOR OUTLET OF THE TUBULAR PATH OF FLOW, A FURNACE GAS DAMPER DISPOSED TO CONTROL THE FLOW OF GASES FROM THE FURNACE INTO SAID PASSAGE THROUGH THE INTERMEDIATE GAS INLET, ANOTHER FURNACE GAS DAMPER DISPOSED TO CONTROL THE FLOW OF GASES FROM THE FURNACE TO SAID PASSAGE THROUGH SAID PASSAGE GAS INLET, OTHER ACTUATING MEANS OPERATIVELY ASSOCIATED WITH THE FURNACE GAS DAMPER AND THE OTHER FURNACE GAS DAMPER SO AS TO ACT SIMULTANEOUSLY ON SAID FURNACE GAS DAMPER AND SAID OTHER FURNACE GAS DAMPER TO MOVE SAID FURNACE GAS DAMPER TOWARD A CLOSED POSITION WHEN SAID OTHER FURNACE GAS DAMPER IS MOVED TOWARD AN OPENED POSITION AND VICE VERSA, AND CONTROL MEANS ACTING SIMULTANEOUSLY ON SAID ACTUATING MEANS AND SAID OTHER ACTUATING MEANS AND RESPONSIVE TO THE TEMPERATURE OF SUPERHEATED VAPOR FLOWING FROM SAID OTHER SUPERHEATER SECTION, SAID CONTROL MEANS BEING ADAPTED TO SO OPERATE THE ACTUATING MEANS AND OTHER ACTUATING MEANS WHEN THE TEMPERATURE OF THE SUPERHEATED VAPOR EXCEEDS A PREDETER MINED DEGREE AS TO CAUSE THE ACTUATING MEANS TO MOVE THE AIR DUCT BY-PASS PASSAGE DAMPER MEANS TOWARD A CLOSED POSITION WHEREIN FLOW OF AIR THROUGH THE AIR DUCT BY-PASS PASSAGE IS PREVENTED AND AS TO MOVE THE AIR DUCT PASSAGE DAMPER MEANS TOWARD AN OPENED POSITION WHEREIN THE FLOW OF AIR THROUGH THE AIR DUCT PASSAGE IS PERMITTED, AND AS TO CAUSE THE OTHER ACTUATING MEANS TO MOVE THE FURNACE GAS DAMPER TOWARD AN OPENED POSITION TO PERMIT FLOW OF FURNACE GASES THROUGH THE INTERMEDIATE GAS PAS SAGE INLET AND AS TO MOVE THE OTHER FURNACE GAS DAMPER TOWARD A CLOSED POSITION TO PREVENT THE FLOW OF FURNACE GASES THROUGH THE GAS PASSAGE INLET.