US2822784A

US2822784A - Apparatus for and method of generating and superheating vapor

Info

Publication number: US2822784A
Application number: US506999A
Authority: US
Inventors: Lewis W Heller; Township Lower Makefield
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1955-05-09
Filing date: 1955-05-09
Publication date: 1958-02-11
Anticipated expiration: 1975-02-11
Also published as: GB818159A

Description

1958 L. w. HELLER 2,822,784

APPARATUS FOR AND METHOD OF GENERATING AND SUPERHEATING VAPOR- Filed May 9, 1955 ECONO IZER CONTACT commss HEAT EXCH. 5 wALLTuaEs YCONVEGTIOIII 3 mamas mass PRIM.$H.

\ Lens FLOW VAPOR PUMP sec. sn. 9

VAPOR OUTLET RADIANT m, V .FuRNAcE TUBE$ INVENTOR.

LEWIS W HELLER ATTORNEY United tats APPARATUS FOR AND METHOD OF' GENERAT- ING SUPERHEATING VAPOR Lewis." W. Heller, Lower ,Makeiield Township, Bucks ".County, Pa'., assignor to The Babcock & Wilcox Company, New York; N. Y., a-corporation of NewJersey Application May 9, 1955,- Serial No. 506,999

3 Claims. (Cl. 122-'31) This invention relates to apparatus and method for. the

generation and superheating of vapor in a once-through type vapor generator.

'More specifically, the invention relates to improve- .ments in superheated vapor generatorslof. the type in which the working fluid is forced into one end .of. an elongatedflow path, wherein the fluid stream receives,..thermal energy from a source thereof as it flows therethrough and issues from the end of the flow path as highly heated vapor.

Vapor generators of the, once-through type havefrequently suffered from tube failures in the zone where the fluid completes achange of state from liquid to avapor. This zone is generally. referred to as the transition or. terminal evaporation zone. .The transition zone usuallyconsistsof an externally heatedtube or conduit and the tube l failureshave been-thedirect result of internal corrosion .and/or non-vola-tilelsolid deposition. The usual impuri- -ties in boiler water, for instance, are conduciveto cor- .rosionqof. the flow channel metal Walls and the deposition 'of such solids on the walls also creates additional rehave been made to solve thisproblemran adequate solu- .tion hasnot been found.

I One'of the most frequent devicesfor reducing the effects'of solid depositions in once-through type vapor generators has been to separate the liquid from the generated vapor while sending the vapor on to the superheater and ejecting the high solid concentration liquid from the vapor generator to thus avoid the deposition of such solids in the unit. This type of arrangement is dependent upon the possibility of adequately separating the liquid from the vapor and thus is restricted to vapor generators which operate with a fluid pressure below the critical. Therefore, such a method is not effective in vapor generators which are devoted to generating and superheating vapor at a pressure above the critical pressure of the fluid. The conversion process does not involve ebullition or boiling nor does the fluid to be vaporized have a heat of vaporization such that it requires the addition of considerable amounts of thermal energy to effect vaporization and during which heating the fluid is at constant temperature, termed boiling temperature. Above the critical pressure when a fluid is heated, every minute addition of heat causes a rise in temperature which is inversely proportional to its specific heat. This continues until the fluid is heated to the point where the molecular thermal excitation is so great that the individual molecules overcome the natural energy of attraction between molecules and the individual molecules become free, thus they are in a gaseous form. This transition takes place without a heat of vaporization and is considered to cover only a few degrees of fluid temperature rise. It is also significant to note that because the transition takes place with relatively small additions of heat, that the molecules of vapor and liquid contain about "atent-O r :2 approximately thesamexenergy resulting in practicjallyno difference in density betweenthe twostates.

The present invention eliminates Solid -depositi0n,,-in the transition zone bycausing.completelvaporization to occur in a contact heat. exchanger which allows, the ,thermal energy required, for the. completion ,of ,vaporization to be transferred homogeneously throughout the fluid and results in the complete suspension of thecliquid. carrying solids in the vapor, ,The vaporizable.fluid when it has received a major portion of thermalenergy required, vfor complete vaporization is admixed with a ,sufficient quantity of superheated, vapor. from ansuperheater. zonelto effeet complete, vaporization of the highly heated fluid.

The various features of noveltywhich,characterize the invention are pointedgout ,With .particularityin the ,claims annexed to and forming a-partofthe specification. For a better understandingfofthe invention-,its operating ,advantages and, specific objects attained ,byrits use, reference should be had to, the accompanyingdrawing and descriptive mattervin which is,;illustrated,andldescribed a preferred embodimentfofthe invention.

In the drawingthere is schemati,cally,.shown avapor generator havingseries connected heatabsorbingsurfaces which are arranged inn-accordance with the invention. The heating surface, issopQsi-tionedthat thevcombustion gases first transmit .heat to; the -furnace tubes .1 and then pass over the second-arvsuperheater 2,.and thence-into a convection ,pass ,boundedbythe wallttubes 3 as it passes -,in succession overithe. primarylsuperheater 4,,,c,onvection heating section 5 and economizer 6.

The path, of,thevaporizableliquid, as indicated, ,shows the liquid entering theeconofmizer 6 v.underthe impulseof the' feed pump" 7. After heating, the liquid leaves} the .econornizer; via transfenline l8. and ,enters the radiant furnace tubes LjfThence' theflpfluid flows via line 9 to the convection passcooling walls.,, Itthenfiowsto arconvec- ,tion heated section 5 which brings1,-thef fluid to alpqint where it, has received a major pQrtionjQf theheat required to efliect complete-vaporizationfi The ,fluid then enters a contact oi'jdirect typeheatlexchanger 10 where it is mixed with heatedvapor tofieffect theHfinalichange-iof, state to vaporJTThe resulting yaponthen enters the, primary superheater 4 and as it passes through its cross-connection 11 to the secondary superheater 2, some of the vapor is removed by the pump 12. The superheated vapor which is removed by the pump is then delivered to the cont-act heat exchanger in sufficient quantity and at a temperature so as to furnish the energy for the complete vaporization of the highly heated liquid to vapor. The vapor which has not been drawn out by the pump 12 goes through the convection secondary superheater 2 where it is heated to its final desired temperature and delivered to the outlet 13.

The direct heat exchanger 10 may be located at a position out of contact with the thermal energy source so that as the highly heated liquid is brought in contact with the superheated vapor, the heat transfer takes place homogeneously throughout the bulk of the fluid and thus there are created conditions which will result in the liquid carried solids being suspended in the vapor and carried through the vapor generator. As the heat exchanger receives no external heat, there is little possibility of a pressure part failure due to solid deposition 'as is in the prior art. In the present case the change of state of a fluid t0 vapor occurs rapidly without any of the dangers attendant with combustion heated transition zones of oncethrough type vapor generators.

The superheated vapor which is recirculated must be at a temperature and in suflicient quantity to completely effect vaporization of the highly heated fluid and to pro duce a limited degree of superheat so as to avoid introducing liquid particles into the primary superheater. v

In the embodiment shown the process may be carried out where the vaporizable fluid is water and is equally applicable in the cases where such water is maintained at a pressure above and where the pressure is belowthe criti' cal pressure (3206.2 p. s. i. -a.). For example, in case of a once-through boiler operating at 2500 p. s. i. a., the fluid would be heated until about 85 percent of the liquid has been converted to vapor and then superheated steam at a temperature of at least 750 F. would be admixed in a contact heat exchanger to produce 100 percent vapor leaving the exchanger with a slight degree of superheat, say 5 or 672 F.

In a supercritical pressure vapor generator the fluid constantly completely changes from a liquid to a steam over a few degrees of temperature and with a small addition of heat. In the case of the present invention applied to a steam generator at critical pressure (3206 p. s. i. a.), the water would be heated to within about 10 of the critical (705.4 R). Then superheated steam at a temperature of at least 75 F. would be admixed in a contact heat exchanger so that the steam issuing from the exchanger is at least superheated or 711 F.

Although I have described a partial embodiment with respect to a combustion heated vapor generator, it is considered that the invention will cover any type of vapor generator which may be heated by liquids, solids, as well as gases, and is not meant to be restricted to use a water tube or fire tube type vapor generator.

While in accordance with the provisions of the statutes I have illustrated and described herein a specific form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of: other features.

I claim:

1. In the art of generating and superheating vapor un der pressure in a once-through type vapor generator wherein a vaporizable liquid is converted to superheated vapor by the transfer of thermal energy thereto, the method which comprises transmitting thermal energy from an appropriate source to said vaporizable fluid to an extent not less than 80 percent of the thermal energy required to effect the complete vaporization of the fluid, introducing said fluid into a contact heat exchange zone wherein it is vaporized, superheating the vapor in a subsequent superheating zone, withdrawing superheated vapor from said vapor superheating zone, and introducing said withdrawn superheated vapor and the highly heated fluid into said contact heat exchange zone in intimate heat transfer relationship to each other whereby superheated vapor completely vaporizes said highly heated fluid.

2. In a once-through type vapor generator including a heat source, a conduit presenting heating surfaces wherein a vaporizable fluid receives from said heat source not less than percent of the thermal energy required to complete vaporization, a contact heat exchanger receiving the highly heated fluid, a vapor superheater in communication with and arranged to superheat the vapor issuing from said heat exchanger, means for circulating a sufl'icient quantity of superheated vapor from said superheater to said heat exchanger to etfect complete vaporization of said highly heated fluid, and said contact heat exchanger being arranged to intimately mix the highly heated fluid and superheated vapor in direct thermal contact to eifect complete vaporization therein.

3. In a once-through type vapor generator including a heating source, a conduit presenting heating surfaces wherein a vaporizable fluid receives from said heat source not less than 80 percent of the thermal energy required to complete vaporization, a contact heat exchanger receiving the highly heated fluid, a vapor superheater in communication with and arranged to superheat the vapor issuing from said heat exchanger and having primary and secondary heating sections, means for withdrawing a sufficient quantity of superheated vapor from said superheater intermediate said primary and secondary sections and circulating said vapor to said heat exchanger to efiect complete vaporization of said highly heated fluid, and said contact heat exchanger being arranged to intimately mix the highly heated fluid and superheated vapor in direct thermal contact to effect complete vaporization therein.

References Cited in the file of this patent UNITED STATES PATENTS 1,784,426 Gleichmann Dec. 9, 1930 2,107,101 Bredtschneider Feb. 1,1938 2,202,507 Sweitochowski May 28, 1940