US1701171A - Power plant - Google Patents

Description

Feb. 5, 1929.

a. N. awonac;v

POWER PLANT zuhrn 1 E sans v; E. l.

Filed Deo. 3, 1925 km, Sh

INVNToR. runnin u. noma,

Patented Feb. 5, 1929.

UNITED STATES PATENT OFFICE.

BENJAMIN `N. BROIDO, OF NEW YORK, N. Y., ASSIGNOB T THE SUPERB:EAIIEI` COM- PANY, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE.

POWER PLANT.

Application led December 3, 1925. Serial No. 73,014.

lVith the notable tendency, in the development of modern power plants, towards high steam pressures, even the highest superheat, namely, 750-8500, that is advisable with the present commercially, available material, is not suiiicient to keep the steam dry during the entire period of expansion. For pressures above 400 pounds, it is desirable, therefore, to resort to reheating, i. e., taking the steam from the turbine after its pressure and teniperature have been reduced considerably by expansion in the first stages of the turbine, and reheating it to a high temperature so that it will remain dry while passing through the lower stages of the turbine. As the super-heating of live steam is usually accomplished in the setting of the main boiler by the boiler gases, it` was generally thought that this would also be the best method of relieating the steam. The usual method of reheating is, therefore, to take the steam` from the turbine, convey it back to the boiler setting, reheat it, and bring it back to the turbine. This arrangement, however, has many disadvantages, because as the pressure of the steam to be reheated is comparatively low, and the volume large, pipes of large diameter are required to carry the low pressure steamto and from the turbine. This not only involves considera-ble installation cost, and

also complicates the already crowded arrangement of a present-day large power plant, but in addition, because of the great distance to the main boiler from the turbine', considerable heat is lost by radiation from the large surface area resulting from the use of the long, large diameter' pipes. Furthermore, reheating steam in a boiler involves the following difiiculties: The final temperature of the steam in the live steam superheater may vary, dependinf1r upon the load, the temperature drop of tic steam in the turbine also usually varies according to the load, and if the steam is then sent back to a reheater installed in the boiler setting, we have a third considerable variation, sothat the total fluctuations of the temperature of the reheated steam may become very serious.

In order to obtain the greatest possible economy in the operation of a turbo-power plant, it has been recognized as desirable, in addition to reheating as described above, to employ the regenerative cycle in the operation of the plant, i. e., stage heatingfor heating the feed water, the basis of which is the utilization of separate quantities` of steam at diiierent pressures and temperatures `for `heating the water in successive stages, a`

portion of the heat contained in the `steam being used, preferably for developing power, before the steam is utilized for the heating of the feed water. Regenerative feed water heating, as it is called, uses steam tapped off successive sta-ges n of the turbine. In this process the steam taken from various stages of the turbine, has, in'developing power in the turbine, been expanded down to the pressure and temperature at which it is required to heat the feed water. Since a certain amount of heat is required in any event, for feed water heating, the work performed by the tapped-ott' steam in heating the water represents merely the expenditure of `an amount of heat equal to the Work done, or in other words, 100% eihciency. Moreover, the utilization of some of theheat of the steam to heat the feed water reduces the amount of"u heat lost by condensation in the condenser. l y

It has heretofore been proposed totake the steam required for regenerative feed water heating from the different stages ofthe main turbine. In a sensitive apparatus, such as a large steam turbine, the relation between the` turbine stages should be maintained as constant as possible.` IVhen, however, steam is taken from the main turbine for regenerative heating 1t 1s practlcally lmpossible to maintain the desired constant relationship, because the amount of water fed to a boiler usually varies. Therefore, the amount of steam required for heating such water will vary accordingly. In addition, the variation of pressure in the turbine will involve still further variations of the steam amount. It will thus be seen that regenerative heating as heretofore proposed is also subject to objection. 1 p i Although it has been recognized as desirable to employ bothlreheating and regenerative feed water pre-heating in orderto increase the eiiciency of the plant, the use of these principles involves many diiiiculties because of the objections noted above.

A further objection to using both reheating and regenerative pre-heating in connection with the main steam turbine, is that a great number of inlet and outlet nozzles are required which complicates the turbine cas'- ing.` Furthermore, it is a well known fact thata turbinecasing should be lept free from vibration. If both reheating and regenerative preheating are used in connection with the main turbine, itis very diiiicult, if not inipossible, to prevent the many steam connections from transmitting serious vibration of the main turbine, due to the many `changes in temperatures and pressures in the pipe connections.

The principal object of this invention is to provide a new and improved turbo-power plant designed for using both reheating and regenerative feed water pre-heating in such a manner that "the efficiency of the plant will be greatly increased and the difficulties and 'objections above set forth will be eliminated.

A further object is to provide a turbo-plant, of the character set forth, which will be of marked simplicity of design, installation and operation.

In accordance with the principles of the invention *to be hereinafter more fully set fort-h, other objects of the invention are to provide; first, an arrangen'ient in which the lregenerative cycle for preheating the feed water nmay `be utilized without taking steam from the main turbine; second, the most efficient method of reheating, independently of the application of the regenerative cycle; thirdfthe use of electrically7 driven auxiliaries and a separately fired superheater having a water screen for preheating the feed water; and fourth, the application of a house turbine for driving the auxiliaries electrically, the stages ofthe `house turbine being tapped for regenerative feed water heaters. Although the highest possible efficiency will be obtained inv a plant designed to carry into effect the four objects last enumerated, all mutually contributing to secure such eliiciency, it will be understood that various combinations and subicon'ibinat-ions of the principles of construction and arrangement enumerated may be resorted to without departing from the spirit or object `of this invention.

In most power plants, auxiliaries are driven by steain operated prime movers, the exhaust steam of which is used for heating the water. In accordancewith this 'invention the auxiliaries are driven electrically7 preferably from a so-called house `turbine which generates the `power or current required inside of the plant. The steam required for the regenerative feed water heating is taken from the house turbine. In this ivay, the full benefit of thereheating or regenerative cycle is obtained without unnecessarily complicating the arrangement and operation of the power plant or disturbing the operation of the main turbines. A

In order that the principles of reheating the steam may be successfully employed, a

separately fired superheater is utilized for this purpose. lThe present invention makes vit possible to employ the separately i'ired su- `perheater and attaina much greater eficiency not only of the superheater unit itself, but of the whole plant. It has been generally accepted heretofore that the separately fired superheater was inefficient because of the fact that no high temperature could be obtained in the super-heater furnace without burning out the superheater units; also because the steam not being as good a heat absorber as water, requires a higher temperature difference between it and the heating gases, so that the exit gas temperature of a separately fired superheater is usually higher than that of a boiler. Both of these features are responsible for the low el'liciency of the separately fired superheater as heretofore constructed.

In accordance with this invention as the auxiliaries are electrically driven, a separately fired superheater in provided for reheating the steam between the stages of the main turbine, and the super-heater includes water heating elements for pre-heatingl the feed water, which elements are placed bctween the superheater furnace and the units, as disclosed in my co-pending application for United States Patent Serial tl-718,695, filed J une 9` 1924, which has matured into Patent dumber l,G7-l,4t2t, granted June 19, 1928. The `steam from the main boiler is delivered to the main turbine where it eX- pands by passing through a number of stages. After its pressure and temperature is materially reduced, the steam is taken from between the lower stages of the turbine and passed through the units of the separately fired super-heater where its temperature is increased preferably to the original temperature of the live steam. It is then returned to the turbine where expansion is continued downto the condenser pressure and temperature. The separately red superheater can be located directly under or near the turbine, so that no long piping is required. The temperature of the reheated steam can be regulated perfectly by the amount of fuel burned. This is particularly true if oil or gas is used as fuel, in which case the temperature may be regulated automatically by means of a thermostat for controlling the amdunt of fuel supplied to the burner. If the regenerative feed water heating is also employed, the successivestages for such heating can be connected either before, or after, the feed water has passed through the heating elements of the separately fired superheater. In some cases it may be preferable to have one or two stages of heating before the separately fired superheater, and the balance after.

In order that the principles of my invention may be more readily understood, I have shown in the accompanying drawing, a diagrammatic illust-ration of a power plant, in which the numeral l0 indicates a battery of main boilers connected to the main steam line 11. Branches 12 connected to the main steam line lead the steam to the main turbines 13, two of which are shown. Steam is takenfrom between the lower stages of the main turbines by the pipes 14 and 13 led thereby tothe separately iii-ed superheaters 15 and after being re-heated therein is returned to the turbines by the pipes 16. Each of the separately fired superheaters include means for preheating the 'feed water which may, for example, consist of a water screen 15L such as shown in my said co-pending application for patent Serial gti-718,695, filed June 9, 19211, to which water is supplied from the hot well 17 by means of the electrically driven pump 18, the suction side of which has connected with it the pipe 19 leading to the hot well and the pressure side being connected by the pipes 20 and 21 to the water screens of the super-heaters 15.

`The water from the water screens ot' the superheater is conducted by the pipes 22 to the first element Q3 of the regenerative feed water heater, which element is heated by steam bled Jtrom fthe last stage of the house turbine 24 by the pipeQ, the house turbine being connected to, and receiving its` actuating steam from, the main steam line 11 by the pipe 26. The feed water then passes to the second and third stages, 27, 28 of the regenerative heater which are heated respectively by steam conducted by the pipes 29, 30 from the second and first stages of the house turbine. After the final heating in element 28 the water is returned to the boilers through the pipes 31 and 32.

Each of the main turbines has connected therewith a condenser 33 for condensing the exhaust steam from the last turbine stage, the water of condensation being pumped from the condensers 33 by the pumps 34 to the hot well 17 through the pipes 35 and 36. The exhaust steam from the house turbine is also led to the eondensers through the pipes 37.

The separately iiredsuperheater may also include an economizer as shown in my copending application above referred to, or may be used for heating the combustion air supplied to the main boiler; in the latter case a pipe 3S (indicated in dotted lines) for such air leads t'rom the sulvierheater to the main boiler.

The operation of the `plant willA be readily ululerstood; steam from the main boilers 10 being supplied through the supply lines l1 and to the main turbines 13 and through the supply lines 11 and Q6 to the house turbine 24. The steam used in the main turbine is reheated in the separately fired snperheaters 15 which are also employed for pre-heating the feed water. The regenerative heating of the feed Water is effected in the elements Q3, 27 and 28 by steam from the house turbine. It will be noted that there is a complete closed circuit for the steam from the main boiler and its water of condensation in both `the main and house turbines,the steam to the main turbines passing through the first turbine stages, thence tothe reheating super heaters, back to the turbines, to the condensers and then to the hot well, while a portion of the steam to the house turbines fioWs through the turbine stages, and finally to the condensers 33 thence to the hot well aswater of condensation. Simultaneously other portions of the steam supplied to the house turbine is used for the regenerative heating in the elements 23, 27, and 28, to which the water `from the hot well is pumped by way ot' the water screen or other feed water pre-heating means in the superheaters 15.

It will be understood that while I have shown asa preferred arrangement the combination of a separately tired superheater for reheating the steam for the main turbine, auxiliaries driven electricallv from a house tubine, the steam from which is used for regenerative heating, and waterf heating means also combined with a superheater, it

will be understood that various combinations of the principles ot' my invention may be resorted to without departing from the spirit of the invention, for example, regenerative heating from the house turbine without reheating ot' the main turbine steam, or with reheating of the main turbine steam in any desired way without a separately iired superheater, `as for example by live steam as disclosed in my copending application Serial No. 41,119; or the reheating by a separately tired superheater with electrically driven auxiliaries without employing either-a house turbine, or a regenerative heating cycle; the above examples forming sub-combinations of the preferred most efficient plan, each of `said combinations having its particular advantages. i

It will be understood that the expression regenerative feed Water heating as usedin the claims hereunto appended is meant to refer to that type of feed water heating in which the feed water is heated in successive stages by steam bled from between successive stages of a prime mover, as hereinbefore ex plained.

I claim:

1. In a power plant including a boiler, the cimibination with house and main turbines, ot' regenerative. boiler ieed water heating elements, connections from the house turbine to said elements for supplying heating steam thereto, and a separately fired reheat-ing superheater connected with the main turbine, said superheater including means for preheating the feed water, and connections for leading the water from said means to said heating elements.

2. In a power plant including a boiler, main and house turbines, a plurality of e1ecaeV Csi

trically driven auxiliaries operated by current generated by said house turbine7 a separately fired superheater connected with said inain turbine for reheating the steam between successive turbine stages, ineans for preheating the boiler feed water combined with said super-heater, a plurality of boiler feed water heating elements, connections betw-een said feed water prehcatinI ineens and said elements, and connections between said elements andthe stages of said house turbine for the regenerative heating of said feed water` 3. In a `power plant, a. niain boiler,1nain and house turbines, connected with said boiler to be actuated by steam therefrom, condensers to which the exhaust steain from said turbines is led, a separately tired unit ineluding a feed water heater and a superheater for reheating the steam between the stages of said main turbine, a plurality of regenerative feed water heatingv elements and steam connections thereto from the house turbine, and

electrically driven auxiliaries for circulat-l heating elements connected with and supe plied with steam from said house turbine; a feed water heater combined with said superheater, a condenser connnon to said inain and auxiliary steam lines, and ineans for cireu loting the water of condensation from said condenser through said feed water heater and heating` elements to said boiler.

6. In a Vpower plantya inain boiler, a closed inain power stica-1n line including a inain turbine and a separately tired reheating superheater; an auxiliary stcani line including1 a house turbine, and a plurality of feed water heating elements connected with and supplied with steain from said house turbine; a

feed water `heater combined with said superheater, a condenser connnon to said inain and auxiliary steam lines and auxilaries driven electrically froin saidhouse turbine for circulating' the water of condensation from said condenser through Said feed water heater and heating elements to said boiler.

Intestirnony whereof I have hereunto set iny hand.

BENJAMIN N. BROIDO.

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