US3139068A

US3139068A - High temperature high pressure steam generator

Info

Publication number: US3139068A
Application number: US70607A
Authority: US
Inventors: Henry J Blaskowski
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1960-11-21
Filing date: 1960-11-21
Publication date: 1964-06-30
Anticipated expiration: 1981-06-30
Also published as: GB948410A

Description

June 30, 1964 H. J. BLASKOWSKI HIGH TEMPERATURE HIGH PRESSURE STEAM GENERATOR Filed Nov. 21, 1960 INVENTOR.

Henry J. Bloskowskfi A TTORNE Y United States Patent 3,139,068 HIGH TEMPERATURE HIGH PRESSURE STEAM GENERATOR Henry J. Blaskowski, Simsbury, Conn., assignor to Combustion Engineering, Inc., Windsor, C0nn., a corporation of Delaware Filed Nov. 21, 1960, Ser. No. 70,607 4 Claims. (Cl. 12231) This invention relates generally to the steam generating art and has particular relation to an improved steam generating system and method for generating high pressure superheated steam.

The present invention is contrasted with the conventional steam generating system wherein water is vaporized by being conveyed in indirect contact withthe burning fuel or the combustion gases generated from the burning of a fuel in that the invention effects an evaporation of the feedwater by introducing the feedwater into direct contact with superheated steam with the heat from the steam causing the feedwater to be vaporized or flashed into steam. The superheated steam is produced by a steam circulating system in which system steam is continuously circulated with this system including a heat exchanger portion where heat is imparted to the steam with the steam thus becoming superheated in this portion of the circulating system. The broad arrangement for producing steam by contacting feedwater with superheated steamis not new in the art although this system has not received a wide acceptance and is not at all applicable to present day steam cycles. Such a system was proposed some time ago in what is known as the Loet'der boiler. The system employed by the Loefiler boiler has a number of serious disadvantages which make its present day commercial adoption impracticable. In the Loeiiier arrangement the portion of the steam circulating system wherein heat is imparted to the steam, i.e., the portion in the furnace and gas pass of the boiler, has passing through i it not only the steam which is circulated continuously but also the steam produced by vaporization of the feedwater introduced into the steam. Furthermore this entire steam volume, i.e., the circulated steam and the steam produced by vaporization of the feedwater, passes through the superheater of the unit and is raised to the desired high superheated value that output steam of the generator is to have. Moreover, in the Loeffier design, the evaporation takes place in a drum wherein the steam is introduced into the feedwater by a distributor arrangement with the drum containing feedwater to a predetermined level. These various features render the system costly from a manufacture point of view and from an operation point of view with there being a substantial pressure drop because of the amount of steam passing through the heat exchange portion of the boiler and with there being a relatively large amount of high temperature piping because of the large amount of steam that is superheated to the final steam temperature.

It is the purpose of the present invention to employ the basic arrangement wherein steam is continuously circulated through a circuit which includes a heat exchange portion for superheating the steam with evaporation of the feedwater taking place by introducing the same into direct contact with the steam but with the present invention obviating the undesirable features of the previously known Loefiier boiler organization.

In accordance with the present invention the evaporation of the feedwater takes place by spraying the same into a number of parallel circuits which contain superheated steam that is circulated through the circulating system. The location and amount of feedwater introduced into the circulating steam is such that the circulated steam is reduced to a temperature slightly above saturation after 3,139,068 Patented June 30, 1964 it has traversed the heat exchange portion of the circulating system. It is at this location that steam is separated from the circulating system and conveyed to a superheater with the amount of steam so separated being generally equal to the amount produced by evaporation of 'the feedwater. This steam in passing through the superheater is superheated to its desired temperature and conveyed to a point of use such as a turbine or the like. Only the amount of steam that is continuously circulated passes through a substantial portion of the heat exchange portion of a circulating system with the arrangement being such that the pressure drop through the circulating system is thereby maintained at an acceptable value. Furthermore at least a portion of the feedwater is introduced into the superheated steam of the circulating system after it has passed through the heat exchange portion of this system so that the steam produced by the evaporation of this portion of the feedwater is not conveyed through the heat exchanger and accordingly does not produce a high or increased pressure drop as would otherwise be the case.

Accordingly it is an object of this invention to provide an improved steam generator organization and method which has a circulating system wherein steam is continuously circulated through a circuit with the steam being superheated in one portion of the circuit and with feedwater being introduced into the superheated steam and accordingly evaporated by contact with the steam and with this steam produced by evaporation of the feedwater being separated from the circulating circuit, superheated to a desired value and conveyed to a point of use with the arrangement providing for an economic operation and construction.

Other and further objects of the invention will become apparent to those skilied in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawing wherein:

FIG. 1 is a diagrammatic representation of a steam generator organized in accordance with the present invention and;

FIG. 2 is a longitudinal sectional view of a spray device that forms part of the system of the invention.

Referring now to the drawing, wherein like reference characters are used throughout to designate like elements, the illustrative and preferred embodiment of the invention depicted therein includes a housing 10 which may be horizontally elongated as shown or which may be in the arrangement of a conventional high pressure high temperature steam generator employing an upright furnace connected at its upper end with a horizontal gas passage from which there extends downwardly an additional gas pass in parallel space relation with the furnace. It will be understood that the housing arrangement disclosed is merely a diagrammatic illustration of a housing within which fuel may be burned and heat exchange surface disposed either on the walls thereof or in the enclosed area of the housing. As illustratively disclosed fuel and air are introduced into housing 10 by burner 12 with the fuel being burned in the housing and the combustion gases thus produced passing longitudinally therethrough and out the far end as indicated by arrow 14.

Steam is continuously circulated through a circuit which is designated generally 16 and which includes compressor 18 and the heat exchange portion or bundle 20 with the compressor 18 having its outlet connected with the inlet of heat exchange portion 20 through conduit 22 and its inlet connected with the outlet of this heat exchange portion through conduit 24 so that steam circulates through this circuit in the manner indicated by arrows 26. The

.heat exchange portion 20 is comprised of a number of parallel circuits in the form of sinuously bent tubes 28 with there being four such separate parallel circuits or tubes illustrated in the drawing although it will be understood that the number employed will vary with the particular design and with there generally being a large number of such parallel tube circuits.

In the operation of the circulating system 16 steam is continuously circulated through the system and upon its traversal of the heat exchange portion 20 the steam is heated, accordingly raising the temperature thereof. This heat exchange portion 20 is disposed within the housing and accordingly receives heat from the burning of the fuel and the combustion gases produced thereby and this heat exchange portion may take any desired form and configuration with the tubes either lining the walls of the housing 10 or being disposed in groups and/or panels within the interior of the housing.

Steam is produced by introducing feedwater into the steam circulated through the circulating system 16 and, as illustratively disclosed, this feedwater is introduced by spraying the same into the steam passing through the parallel connected tubes 28 at two locations along the length of the tubes. This feedwater is conveyed from feedwater heater 30, wherein it is heated substantially to saturation temperature, through conduit 32 to the

spray devices

34 and 36 located in each of the tubes 28. These spray devices may be generally of the design employed in spray type desuperheaters used to control the superheat and reheat temperature in steam generators. FIG. 2 illustrates one type of spray device which may be employed with the invention and in this figure the steam enters through the inlet opening 37 and is conveyed as indicated by the arrows through the length of the device being discharged through the discharge opening 39 which of course is connected with the tube 28 as is the inlet. The device is of a tubular nature and includes outer member 41. A liner sleeve 43 is disposed within this outer member 41 and is retained in space relation with the inner surface thereof. Feedwater is sprayed into the steam passing through this sleeve 43 by means of the spray nozzle member 45 which extends radially through the wall of member 41 and the sleeve 43 as illustratively disclosed. Sleeve 43 prevents the spray water from directly contacting the wall of member 41 and accordingly prevents the development of large stress concentrations in this wall.

The sprays in the circulating system are located so that the tubes on the furnace walls are relatively cool with no large amount of superheating of the steam in tubes 28 being permitted. Intermediate sprays such as those identified as 34 are employed when the runs of tubes 28 are relatively long. As disclosed, the spray de vices 34 are disposed so that after the steam passing through the tubes has been superheated to a desired degree it is reduced by the spray. Sufiicient feedwater is sprayed into the steam being circulated so that the temperature of the steam is substantially reduced but the arrangement is such that all of the feedwater is evaporated to steam and the circulating steam temperature is lowered to a value somewhat above saturation.

A like action takes place at the location of spray device 36 with this spray device being positioned at the outlet of the heat exchange portion 20. Accordingly the steam leaving the heat exchange portion through the several parallel tubes 28 (downstream of device 36) and which is a combination of the steam that is circulated and the steam produced by the evaporation of the feed- .water is preferably at a temperature somewhat above ature of the steam be somewhat above saturation. A slight amount of water, however, can be tolerated if absolutely necessary although, as is well recognized, water in the steam passing through the compressor will have a tendency to erode the blades of the compressor.

At the outlet of the heat exchange portion 20, in that location identified on the drawing as 38, there is separated from the circulating system a portion of the steam issuing from the heat exchange portion 20 with the amount of steam separated being generally equal to that produced by evaporation of the feedwater sprayed into the circulating steam at the

locations

34 and 36. From this location 38 this separated steam is passed in heat exchange relation with the combustion gases passing through housing 10 so as to raise the temperature of this steam from that close to saturation to a desired degree of superheat and with this steam progressively passing through low temperature portion 40, intermediate portion 42 and high temperature portion 44 of the superheater of the unit. Upon emerging from high temperature portion 44 the steam is at its desired high temperature and is conveyed through conduit 46 to the high pressure turbine 48. The temperature of the steam delivered to turbine 48 through conduit 46 is maintained generally constant by means of the spray type desuperheater 50 with this desuperheater eing automatically controlled, as is known in the art, to maintain the temperature delivered to the turbine 48 constant. The exhaust from turbine 48 is reheated by being passed through the reheater 52 and this steam after having its temperature increased to a desired value is conveyed to the low pressure turbine 54 from reheater 32 through conduit 56. The temperature of the steam enten'ng low pressure turbine 54 through conduit 56 is maintained generally constant by the spray type desuperheater 58 With the control of this steam also being automatically regulated as is conventional. As illustratively disclosed compressor 18 is driven from the

turbine

48 and 54 although it may be independently driven from a separate steam or electric motor if desired.

From the location 38 in the circulating system 16 the steam which is not separated and conveyed through the superheater is returned to compressor 18 through conduit 24. As previously mentioned this steam is at a temperature slightly above saturation and upon passing through the compressor 18 the pressure of the steam is increased so that at the outlet of the compressor the steam is close to the saturation temperature. This steam is again conveyed through the circulating system with the cycle being continuously repeated.

While the feedwater has been illustratively shown as mtroduced at two locations in each of the parallelly disposed tubes 28 the number of locations that are employed may be varied as desired with more than two or with only one location being perhaps preferable in certain environments. The number of spray locations in each of the tubes will, as previously mentioned, depend upon the length of the tube run. Intermediate sprays are required for long tube runs in order to insure that large degrees of superheat are not produced within the tubes of heat exchanger 20. It should be mentioned that each of the spray devices will serve more than one of the tubes 28 and in a typical arrangement there might be a grouping of ten tubes which are connected with each of the spray devices that are employed. When only a single spray location is employed this location will preferably be that of the illustrated spray device 36, i.e., at the outlet of the heat exchange portion 20, since it is at this location that it is desired to decrease the temperature of the circulating steam to slightly above that of saturation.

It will be appreciated that with the arrangement of the present invention a relatively inexpensive construction is employed for contacting the feedwater with the steam with the spray devices hereinbefore referred to having been developed over a period of years so that their technology and construction has been well established.

In the operation of the organization of the invention the steam that is circulated through the circulating system is superheated to a relatively minor extent in passing through heat exchange portion 20 so that excessive tube metal temperatures are not encountered. In fact, with the invention, the circulation of the steam is such that a simple furnace construction may be employed because the tube metal wall temperatures are very near uniform and these wall temperatures may be maintained at a value so as to provide for economic construction with it being unnecessary to employ high temperature metals in these regions. Furthermore with the present invention the steam generator may operate at either subcritical or supercritical pressures and may operate over the full load range, i.e., from zero to 100 percent of the rated load of the unit. Since the steam that is developed by evaporation of the feedwater in contact with the circulating steam, at best, passes only through a portion of the heat exchange portion 20, with some of this developed steam passing through none of this heat exchange portion the pressure drop in the circulating system is maintained relatively low. Moreover, since the steam is not superheated in the circulating system to a high degree and particularly not to the final high outlet temperature of the unit the problems with regard to high temperatures are not encountered in the steam circulating portion of the unit.

The temperature of the steam downstream of each of the

spray devices

34 and 36 is preferably maintained at a value somewhat above that of saturation and there is illustrated in the diagrammatic arrangement of the drawing a control organization for insuring this result with this organization including temperature responsive member 58 which responds to the temperature of the steam leaving the spray device with this member controlling the motor control valve 60 to regulate the amount of feedwater sprayed into the particular device to maintain this temperature at its desired value.

After passing through the low pressure turbine 54 the steam is conveyed in conventional manner to condenser 62 and from this condenser the condensate passes successively through feedwater heater 64, the feedwater pump 66 and economizer 30.

The system of the present invention oifers the advantage that a balancing of the evaporating and superheating may be eifected by varying the temperature of the steam at the location 38. It is extremely difficult and as a practical matter impossible to precisely calculate the exact amount of steam generating, superheating and reheating surface in one of these units to produce the correct amount of steam and the correct superheat and reheat steam temperatures. It is often necessary after a unit has been erected and put into operation to make very costly corrections with regard to the heat exchange surface in the unit. For example, it is sometimes necessary to install additional or remove some of the superheat or reheat surface because the superheat and/or reheat steam temperatures are too low or too high respectively. This unbalancing may be corrected with the organization of this invention by varying the temperature of the steam leaving the steam generating portion and entering the superheater, i.e., the temperature of the steam at the location 38. A or 20 degree change in this temperature will have a very substantial effect with regard to the necessary heat input to the steam passing through the superheater. This change can be effected by varying the amount of feedwater sprayed into the circulating steam at

locations

34 and 36 with relation to the amount of fuel fired.

Furthermore, with the organization of this invention the pressure at which the steam generator operates may be easily varied with it being possible to vary the pressure with the load in any manner desired and with it being possible to operate the steam generator at virtually any pressure desired. The pressure of the unit may be changed by merely varying the amount of the evaporation relative to the amount of steam that is withdrawn from the circulating system.

Illustrative of the organization and operation of the present invention, a unit having a single spray location for each of the parallel tubes 28, and corresponding with the location 36 in the drawing, may operate as follows:

The steam that is circulated may be 3,090,000 lbs. per hr. With the pressure entering the compressor being 2,580 lbs. per sq. in. and the pressure leaving the compressor being 2,640 lbs. per. sq. in. The temperature of the steam entering the compressor may be 675 F. and that leaving the compressor may be 680 F. Upon passing through the heat exchange portion '20 this circulated steam may be raised in temperature 45 so that it has approximately 50 of superheat and with the temperature and pressure of the steam immediately upstream of the spray device 36 being 725 F. and 2,610 lbs. per sq. in. respectively. At the locations 36 there may be sprayed into this superheated steam 1,000,000 ibs. per hr. of feed- Water with this feedwater being at a tempertaure of 595 F. and 2,670 lbs. per sq. in. pressure. Upon being sprayed into the superheated steam this million lbs. per hr. of feedwater is evaporated to steam and the steam issuing from these spray devices and accordingly from the outlet of heat exchanger 20 is at the temperature and pressure, previously mentioned, of that entering the compressor, i.e., 2,580 lbs. per sq. in. and 675 F. At location 38 the 1,000,000 lbs. per hr. of steam is separated from the circulating system and is conveyed through the various stages of the superheater with the steam issuing from the superheater being at a temperature of 1,050 F. and 2,450 lbs. per sq. in. Upon leaving the high pressure turbine 48 this steam is reduced to 650 F. and 660 lbs. per sq. in. It is conveyed through the reheater and upon leaving the reheater is at a temperature of 1,000 F. and 600 lbs. per sq. in. pressure. Accordingly 1,000,000 lbs. per hr. of steam is generated while 3,090,000 lbs. per hr. of steam is continuously circulated through the circulating system. The temperatures in the circulating system are relatively low with there only being approximately 50 of superheat so that high temperature problems are not encountered.

With the present invention a steam generator organization is provided which is relatively simple and economic in construction yet which has the universal use and relatively large range of a once through boiler as well as the simplicity and advantages of a control circulation boiler with the unit being capable of operating either at subcritical or supercritical pressures and of producing high temperature high pressure steam in large quantities as is required in present day practice.

While I have illustrated and described a preferred embodiment of my invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein Without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

What I claim is:

1. A steam generating system for producing high pressure steam with a predetermined amount of superheat comprising a chamber into which fuel is introduced and burned at a predetermined zone and through which the combustion gases pass, a steam circulating system a portion of which is disposed in said chamber in surrounding relation with said zone to absorb heat produced by the burning fuel with said portion being comprised of a plurality of parallel circuits, compressor means forming part of the circulating system and receiving steam from the outlet of said portion and delivering the same to the inlet thereof for passage therethrough whereby a continuous circulation of the steam is had with the compressor develop'ing only suflicient head to circulate the steam through the circulating system, means operative to spray feedwater into each of the parallel circuits at a number of locations along the length of each circuit with one such location being adjacent the outer end thereof with the amount of water so introduced being such that the water is evaporated by the heat of the steam into which it is introduced and the steam finally issuing from the circuits is slightly above saturation temperature, a superheater in said chamber and connected with the circulating system downstream relative to steam flow of all of said cations and between the outlet of said portion and the inlet of the compressor to receive from the system the steam produced by the evaporation of the feedwater to superheat the same to a desired high temperature, means for conveying this superheated steam to a point of use, condense the same and return it as feedwater.

2. The method of producing steam of a predetermined degree of superheat comprising burning fuel at a predetermined zone, providing a continuous circulation of a stream of steam at a predetermined high pressure, forming a plurality of sub-streams of said stream at one region and disposed about said zone with the sub-streams being in parallel flow relation and with said, sub-streams having heat imparted thereto from the burning fuel to raise the temperature thereof, spraying feedwater into the substreams at a plurality of locations along the length thereof including the downstream region thereof; with the spray being regulated so that the water is converted to steam and the temperature of the sub-streams is not less than saturation, withdrawing from the circulating path and downstream of said one region an amount of steam generally equal to that produced by spraying said feedwater into the sub-streams, raising the temperature of this withdrawn steam to said predetermined degree by imparting heat thereto, after thus withdrawing said steam conveying the remaining steam in the circulating system to a given location, raising the pressure of this steam at this location and redirecting this steam through said one region.

3. A steam generating system for producing high pressure steam with a predetermined amount of superheat comprising a furnace into which fuel is introduced and burned and through which the combustion gases thus produced pass, a steam circulating system a portion of which is disposed in said furnace to absorb heat produced by the burning fuel and with said portion being comprised of tubes disposed on the furnace walls, compressor means forming part of the circulating system and receiving steam from the outlet of said furnace wall tubes and delivering the same to the inlet thereof for passage therethrough whereby a continuous circulation of steam is had, a plurality of spray devices for spraying feedwater into the circulating steam each of which communicates with a plurality of said furnace wall tubes, means for introducing feedwater into said spray devices, said spray devices being connected into the circulating system at a number of locations along the length thereof with one such location being adjacent the outlet of said furnace wall tubes and with the amount of water so introduced being such that the water is evaporated by the heat of the steam into which it is introduced and the temperature of the resulting steam is slightly above saturation, a superheater disposed to receive heat evolved by the burning of fuel in the furnace and connected with the circulating system downstream relative to steam flow of all of said locations and between the outlet'of said furnace Wall tubes and the inlet of the compressor to receive from the system the steam produced by the evaporation of feedwater to superheat the same to a desired temperature, means for conveying this superheated steam to a point of use, con dense the same and return it as feedwater.

4. The method of producing steam of a predetermined degree of superheat comprising burning fuel at a predetermined zone, providing a continuous circulation of a stream of steam at a predetermined high pressure, forming a plurality of sub-streams of said steam at one region and disposed about said zone with the sub-streams being in parallel flow relation and with said sub-streams having heat imparted thereto from the burning fuel to raise the temperature thereof, combining a plurality of the substreams at a plurality of locations along the length thereof including the downstream region thereof and spraying feedwater into the thus combined sub-streams at said 10- cations with the spray being regulated so that the water is converted to steam and the temperature of the resulting steam is not less than saturation, withdrawing from the circulating path and downstream of said one region an amount of steam generally equal to that produced by spraying said feedwater into the sub-streams, raising the temperature of this withdrawn steam to said predetermined degree by imparting heat thereto, after thus withdrawingsaid steam conveying the remaining steam in the circulating system to a given location, raising the pressure of this steam at this location and redirecting this steam through said one region.

" References Cited in the file of this patent Young et al. July 31, 1962

Claims

1. A STEAM GENERATING SYSTEM FOR PRODUCING HIGH PRESSURE STEAM WITH A PREDETERMINED AMOUNT OF SUPERHEAT COMPRISING A CHAMBER INTO WHICH FUEL IS INTRODUCED AND BURNED AT A PREDETERMINED ZONE AND THROUGH WHICH THE COMBUSTION GASES PASS, A STEAM CIRCULATING SYSTEM A PORTION OF WHICH IS DISPOSED IN SAID CHAMBER IN SURROUNDING RELATION WITH SAID ZONE TO ABSORB HEAT PRODUCED BY THE BURNING FUEL WITH SAID PORTION BEING COMPRISED OF A PLURALITY OF PARALLEL CIRCUITS, COMPRESSOR MEANS FORMING PART OF THE CIRCULATING SYSTEM AND RECEIVING STEAM FROM THE OUTLET OF SAID PORTION AND DELIVERING THE SAME TO THE INLET THEREOF FOR PASSAGE THERETHROUGH WHEREBY A CONTINUOUS CIRCULATION OF THE STEAM IS HAD WITH THE COMPRESSOR DEVELOPING ONLY SUFFICIENT HEAD TO CIRCULATE THE STEAM THROUGH THE CIRCULATING SYSTEM, MEANS OPERATIVE TO SPRAY FEEDWATER INTO EACH OF THE PARALLEL CIRCUITS AT A NUMBER OF LOCATIONS ALONG THE LENGTH OF EACH CIRCUIT WITH ONE SUCH LOCATION BEING ADJACENT THE OUTER END THEREOF WITH THE AMOUNT OF WATER SO INTRODUCED BEING SUCH THAT THE WATER IS EVAPORATED BY THE HEAT OF THE STEAM INTO WHICH IT IS INTRODUCED AND THE STEAM FINALLY ISSUING FROM THE CIRCUITS IS SLIGHTLY ABOVE SATURATION TEMPERATURE, A SUPERHEATER IN SAID CHAMBER AND CONNECTED WITH THE CIRCULATING SYSTEM DOWNSTREAM RELATIVE TO STEAM FLOW OF ALL OF SAID LOCATIONS AND BETWEEN THE OUTLET OF SAID PORTION AND THE INLET OF THE COMPRESSOR TO RECEIVE FROM THE SYSTEM THE STEAM PRODUCED BY THE EVAPORATION OF THE FEEDWATER TO SUPERHEAT THE SAME TO A DESIRED HIGH TEMPERATURE, MEANS FOR CONVEYING THIS SUPERHEATED STEAM TO A POINT OF USE, CONDENSE THE SAME AND RETURN IT AS FEEDWATER.