US3238729A

US3238729A - Steam turbine power plants

Info

Publication number: US3238729A
Application number: US295035A
Authority: US
Inventors: Frankel Adolf; Brazier Peter Harding
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1962-07-23
Filing date: 1963-07-15
Publication date: 1966-03-08
Anticipated expiration: 1983-03-08
Also published as: SE305221B; GB971195A; CH418361A

Description

United States Patent 3,238,729 STEAM TURBINE POWER PLANTS Adolf Frankel, Altrincham, Cheshire, and Peter Harding Brazier, Sale, Cheshire, England, assignors to Associated Electrical Industries Limited, London, England, a British company Filed July 15, 1963, Ser. No. 295,035 Claims priority, application Great Britain, July 23, 1962, 28,277/62 Claims. (CI. 60-67) This invention relates to improvements in steam turbine power plants, and more particularly to steam turbine power plants in which feed water is heated by steam bled from the steam turbine.

It is usual in large power plants to use a number of feed water heaters heated respectively by steam flows from dilferent stages in the turbine and acting in turn upon the feed water, the hotter steam being used to heat the hotter feed water, since this increases the thermal efficiency of the steam turbine power plant.

Such a feed Water heater may contain desuperheating, condensing and drain cooling sections. In a condensing section, steam tapped from a suitable stage in the turbine is condensed, so heating the feed water up to a temperature below the saturation temperature of the steam by the temperature difference required to effect the required transfer of heat from the steam to the feed Water. The saturation temperature in the heater depends upon the steam pressure in the heater, and this is equal to the steam pressure at the turbine stage from which the steam is tapped less the pressure drop between the turbine stage and the condensing section of the feed water heater. Some pressure drop will be necessary to overcome the resistance to flow of steam through the associated steam pipes or mains. If the tapped steam has a high degree of superheat, the feed water may be heated further after the condensing section by the transfer of the sensible heat, providing the superheat, to the feed water in a desuperheating section, the desuperheated steam passing on to the condensing section of the feed water heater. The pressure drop of the tapped steam in the desuperheater has the effect of further depressing the saturation temperature of the heating steam in the condensing section, so that the temperature of the feed water leaving the condensing section is lowered by the use of a desuperheating section.

An object of the present invention is the provision of a steam turbine power plant having an improved feed water heating system.

According to the present invention, in a steam'turbine power plant including a steam turbine and feed Water heating means arranged to heat feed Water passing to a steam generating unit supplying the steam turbine, a feed water heater of the feed water heating means comprises a first condensing section arranged to heat feed water and a second condensing section arranged further to heat water discharged from the first section, the two sections being supplied with heating steam by parallel connections from the same bleed point on the steam turbine or from equivalent bleed points on cylinders operating in parallel, and the pressure of the steam entering the second section being greater than the pressure of the steam entering the first section, whereby the saturation temperature of the steam in the second section is greater than the saturation temperature of the steam in the first section.

Since both sections of the feed heater obtain steam from the same bleed point on the steam turbine, an additional pressure drop is available in the steam supply system to the first section of the feed heater, and in accordance with the invention this additional pressure drop is available for "ice an economically useful application, for instance, for increasing the velocity and reducing the size of steam supply pipes, for increasing the pressure drop across a desuperheating section, and thereby decreasing its size, for passing the steam through an ejector entraining additional steam quantities from a lower pressure level, or for any other economically or thermodynamically practicable application.

Preferably the second section is arranged to impart to the feed water only some 15 to 25% of the total temperature rise imparted to the feed water in both sections.

By way of example, one of the two connections may convey superheated steam first to a third desuperheating section arranged to receive heated feed Water from the second section, the desuperheated steam flowing on to the first section, while the second connection conveys superheated steam with little pressure drop to the second section.

The invention will now be described, by way of example with reference to the accompanying drawings, in which:

FIGURE 1 is a schematic diagram of a steam turbine power plant to which the invention is applied; and

FIGURE 2 is a sectional side elevation of a tubulous desuperheating feed Water heater.

The steam turbine power plant includes a steam generating and superheating unit 1, a steam turbine having a high pressure cylinder 3H and two parallel connected low pressure cylinders 3L, and a steam condenser 5.

The steam generating and superheating unit 1 is shown diagrammatically as consisting of upper and lower drums 7 and 9 respectively, connected together by a bank of tubes 11, and a superheater 13 arranged to receive saturated steam from the upper drum 7 and to pass superheated steam through a steam main 15 to the inlet of the turbine high pressure stage 3H. The exhaust of the stage 3H is connected by a steam main 17 to the common inlet of the two lower pressure stages 3L, and the exhausts of the two stages are connected separately to the condenser 5. Cooling water passes through the condenser in a bank of cooling tubes indicated diagrammatically at 19. The detailed constructions of all of the foregoing items are well known in the power plant art.

Condensate collecting in the condenser 5 is removed by a condensate pump 21 and from the pump outlet pipe 22 passes through

feed water heaters

23, 25, 27, 29' and 31 in turn. All these feed water heaters are of the indirectheat-transfer type, in which the feed Water passes through a bank of tubes contained in a cylindrical shell, and heating steam is caused to flow through the shell over the outsides of the tubes. In the case of

heaters

27 and 29, they are combined in the form of a single bank of tubes passing through a single shell formed with a partition 28 which serves to separate the steam flow in heater 27 from that in heater 29.

Heaters

23 and 25 are similarly combined.

The high pressure turbine stage 3H is provided with a higher pressure bleed 35 which bifurcates into a low velocity steam conduit 35S and a high velocity steam conduit 35F. The low pressure stage 3L is provided with a lower pressure bleed 37 which bifurcates into a low velocity steam conduit 37S and a high velocity steam conduit 37F.

Conduits

35F, 35S, 37S and 37F are connected to the steam inlets of the

feed water heaters

31, 29, 25 and 23 respectively. Feed water heater 31, a desuperheater, is provided with a steam outlet which is connected to the steam inlet of heater 27. The condensate outlets from the

heaters

29 and 25 are connected respectively by

condensate pipes

41 and 42 to the water spaces of

heaters

27 and 23 respectively, and heater 23 is arranged to discharge condensate into the condenser 5.

During operation of the power plant, condensate from the condenser 5 is fed by the pump 21 through the feed water heaters to the water space of the drum 7. Steam separated in the drum 7 passes through the superheater 13 to the turbine high pressure stage 3H, in which most of the steam is expanded and passes on through steam main 17 to the two low pressure stages 3L. Steam exhausted from these stages SL is condensed in the condenser 5.

Suitable amounts of steam are bled from the turbine stages 3H and 3L through the

bleeds

35 and 37, and pass through conduits 35F, 355, 37-5 and 37F to the

feed water heaters

31, 29, 25 and 23. The steam entering the

heaters

29, 27, 25 and 23 is condensed, but the superheated steam entering heater 31 is for the most part only fully or partly desuperheated and then passes on to the heater 27, in which it is condensed.

The dimensions of the conduits 37F and 37S and of the associated

feed water heaters

23 and 25 are such that the mass flow rate of steam through the conduit 37F is considerably larger than that in conduit 37S and amounts to some 75 to 85% of the steam bled through the bleed 37. At the same time, the cross-sectional area of conduit 378 is so selected that the velocity of the steam flowing through it is much smaller, for example one third, than the velocity of the steam flowing in the conduit 37F.

Such an arrangement results in the use of a total crosssectional area of conduit which is of the order of 50 to 80% of the cross-sectional area of conduit which would be used in a conventional installation, in which the conduit conveying the steam from bleed 37 would need to be of such cross-sectional area that the pressure drop along the conduit was not excessive.

The dimensions of the conduits 35F and 355 are similarly chosen so that the steam mass flow rate in conduit 35F amounts to some 75 to 85% of the steam bled through the bleed 35.

The pressure drop produced in the conduit 37F is much larger than that produced in the conduit 375, while the pressure drop produced in the conduit 35F and the desuperheater 31 is much larger than that produced in the conduit 355. In the case of each bleed 35 and 37, the steam bled from the steam turbine to a given feed water heater as shown is split into two flows, one of which carries considerably more than half of the total steam flow. This larger steam flow is subjected to a pressure drop and is then supplied to the feed heater means. Because of the pressure drop mentioned above, the saturation pressure and the saturation temperature of that portion of the steam will be lower than those obtainable if the steam was supplied to the feed water heater means in a more direct way with a minimum of pressure drop. Therefore, the final temperature to which it will be possible to heat the feed water in the portion of the feed water heater means to which this steam is supplied will be correspondingly reduced. In accordance with the invention, the second and smaller part of the steam flow is supplied to a second condensing part of the feed water heater means, arranged in series with the first condensing part, in such a way as to involve the minimum practicable pressure drop. As a result the feed water is heated in the second part of the feed water heater means to the highest possible temperature obtainable with the given saturation temperature of the steam, so that the provided pressure drop to the second section of the feed water heater is no greater than the pressure drop which isv normally economically acceptable between the turbine and the feed water heater of a conventional arrangement, the invention does not involve any additional thermodynamic loss compared with the conventional arrangement. If the temperature rise in the second section of the feed water heater is arranged, by suitable proportioning of the pressure drops to each section, to be a small proportion of the total temperature rise in both sections, say 15 to 25%, then the steam flow to this section is small and a steam velocity and hence the pressure drop between the turbine and the heater which are less than those in a conventional arrangement can be economically justified. This would result in a thermodynamic improvement compared with the conventional arrangement.

As shown above the pressure drop involved by the processes to which the steam to the first section of the feed water heater is subjected, does not involve any additional thermodynamic loss, and hence may be used for a number of purposes with advantage, for example in the case described above with rerference to

heaters

23 and 25 where only 15 to 25% of the heating is carried out in the second section of the feed water heater, to of the heating must be carried out in the first section of the feed water heater requiring 75 to 85% of the total steam to the feed water heater. Since the pressure drop required to cause the steam to flow from the turbine to the first section of the feed water heater does not involve any additional thermodynamic loss, it may be transferred as a much higher velocity than would be justified economically with the conventional arrangement, so permitting a considerable reduction in the size of pipe through which this steam fiows.

Alternatively, if the tapped steam to the feed water heater is superheated, then the process to which the steam to the first section of the feed water heater is involved, can include a feed water heater where the steam is desuperheated, as described above in connection with

heaters

31, 29 and 27, before passing to the first section of the feed water heater where it is condensed. Since the pressure drop to the first section of the feed water heater does not involve any additional thermodynamic loss, the pressure drop required to pass the steam through the desuperheater may be much greater than would be economically justified in a conventional feed water heating arrangement, and as a result the heat transfer coefficients will be greater and the size and cost less than with the conventional arrangement. If the feed Water to the desuperheater is taken from after the second section of the feed water heater, the inlet feed water temperature to the desuperheater, which is the outlet feed water temperature from the second section of the feed water heater, is unaffected by the pressure drop of the steam passing through the desuperheater. The invention thus overcomes the compromise which has to be made in the conventional feed water heating arrangement when the steam velocities in the desuperheater are very low so as to prevent excessive depression of the outlet feed water temperature of the condensing section due to the pressure drop through the desuperheater, and as a result requires a very large desuperheater. The feed water temperature out of the second section of the feed water heater is not depressed at all by the desuperheater, so that the arrangement should show a thermodynamic gain compared with the conventional arrangement, as well as a cheaper desuperheater due to the reasons given above.

The conduit 35S can also include an ejector 38 through the nozzle of which the steam flowing in the conduit fiows and the suction chamber of which is arranged to entrain additional steam from the steam bleed 37 which operates at a steam pressure lower than that of the steam bleed 35.

It would also, of course, be quite practicable, and in accordance with the teaching of the invention, to run only one pipe line from the tapping point on the turbine to the vicinity of the

heaters

27, 29, 31, with the pipe branching out to supply heater 29 and desuperheater 31 as near to these heaters as convenient. Because of the pressure drop across desuperheater 31, even if the pressure drop through the short branch lines to

heaters

29 and 31 was equal (in any case it is likely to be negligible) the steam supply pressure to heater 27 will be lower than the steam supply pressure to heater 29, which is the essence of the invention.

The invention is applicable to feed water heaters using heat transfer surfaces, which are usually of the type which feed water flows inside heat transfer tubes with the heating steam condensing on the outsides of the tubes, and to direct contact heaters in which the feed water flows, or is sprayed, in a chamber to which the heating steam is supplied. In the case of indirect heat transfer feed water heater means, the two parts of the heater which are arranged in series either can be arranged in separate vessels or a suitable bafile can be provided inside one common vessel, separating the two parts which operate at different pressure and temperature levels. As the diiference in pressure and temperature involved is not very large, even appreciable leakage of heating steam from the high temperature final part of the feed water heater means to the main part of the feed water heater means is thermodynamically insignificant. There is little additional thermodynamic loss in such a leakage. Under the circumstances a simple bathe in one common casing is mechanically practical.

FIGURE 2 illustrates a single feed water heater which includes sections corresponding to feed

water heaters

31, 29 and 27 in FIGURE 1. A group of nested U-tubes 51 are mounted on a tube plate 53 so that their inlet ends lie opposite an inlet chamber 55 and their outlet ends lie opposite an outlet chamber 57 provided in a body 59 to which the tube plate is secured. An inlet pipe 61 communicates with the chamber 55 and would be con nected to the feed water oulet from heater 25, while an outlet pipe 63 communicates with the chamber 57 and would be connected to the drum 7. The tubes 51 are enclosed by a shell 65, and

bafile plates

71, 72, 73 and 74 fitted to the tubes 51 before assembly and battle plate 75 secured to the tube plate 53 define, together with the shell, three separate chambers. 74 define a sinuous steam flow passage leading from a steam inlet 77 and extending about the outlet ends of the tubes 51 through a passage in the bafile plate 75 into the main part of the shell. Bafiles 71 and 72 define a closed chamber having a steam inlet 79 and a condensate escape hole equivalent to and given the same reference as condensate pipe 41. The remainder of the space inside the shell forms the third chamber and is provided with a condensate drain equivalent to the condensate pipe 42.

When the invention is applied to direct contact feed water heater means, the two parts of the heater can be arranged in separate vessels, or they can both be accommodated in one common vessel with an internal partition wall separating the two parts. For the reasons referred to above, the partition wall separating the two parts need not be very strong structurally. Also, if the final part of the feed Water heater means is arranged below its first part, arrangements can easily be made for the mixture of the feed water and the condensed heating steam from the first part to flow by gravity, through suitable loop pipes, into the second part. As a result of such an arrangement, the total volume of the direct contact feed water heater will be smaller than the volume of the conventionally arranged feed water heater, because a smaller volume for the required heat turnover can be provided in the first part of the feed water heater than would otherwise be considered prudent. The only effect of such a reduction of volume will be a modest increase in terminal temperature dilference between the feed water leaving this portion of the feed water heater and the saturation temperature of the steam at this point. As explained above this does not involve a thermodynamic loss as long as the second portion of the heater means, handling a much smaller steam flow, is suitably dimensioned and designed.

The volume to be provided in the first part of the direct contact feed water heater means, arranged in the way described above, can be further reduced by arrang- Thus baflles 72, 73 and ing in the partition wall between the two halves suitable perforations and/or stubs projecting into the bottom of the first part. Steam from this final part of the heater means will then be injected into the first part of the heater means, and in the process, if the stub pipes are suitably arranged, it will entrain large quantities of the feed water lying at the bottom of the first part of the heater means, and project that water into the open space above the general water level. As explained above, such a leak of steam from one part to the other does not involve a direct thermodynamic loss. The effect ofthe disturbance created by the process described above will be to expose a much larger surface of the water to the heating steam supplied to the first part of the heater means, i.e. to produce the same elfect as that produced by sprays and drip trays in direct contact heat exchanges. Due to that effect the heat exchange required for condensation of the steam in the first part of the feed water heater can be carried out in a very much smaller volume than would otherwise be necessary. As the bulk of the heat exchange in the feed water heater means is in the first part, this can result in a considerable reduction in the volume of the heater means.

In some instances it may prove advantageous to split the total flow of steam to the heater means into three or even more sections, each of which is subject to a diiferent degree of pressure drop by flowing to the heater means through pipes at different velocities. They would be supplied to successive parts of the heater means, the steam flow submitted to the largest pressure drop passing to the feed water heater at the entry to the heating means and the steam flow subjected to the minimum pressure drop passing to the feed water heater at the outlet from the heating means.

For example, in machines using three low pressure cylinders or stages, it may be particularly advantageous to split each of the feed water heaters into three sections, so that steam bleeds from the three equivalent bleed points on the parallel connected low pressure stages flow respectively to the three sections.

What we claim is:

1. A steam turbine power plant including:

(a) a steam turbine;

(b) feed water heating means arranged to heat feed water passing to a steam generating unit supplying the steam turbine;

(c) a first condensing section of the feed water heating means arranged to heat the feed water;

((1) a second condensing section of the feed water heating means arranged further to heat water discharged from the first section;

(e) a bleed point on the steam turbine; and

(f) first and second bleed conduits connected to said bleed point to furnish bleed steam to the first and second condensing sections respectively, means for proportioning the pressure in said first and second bleed conduits so that the pressure of the steam entering the second condensing section is greater than that entering the first condensing section where.

by the saturation temperature of the steam in the second condensing section is greater than the saturation temperature of the steam in the first condensing section.

2. A power plant according to claim 1, in which the first bleed conduit which furnishes bleed steam to the first condensing section is arranged to operate with a higher steam velocity through it than is the second bleed conduit which furnishes bleed steam to the second condensing section.

3. A power plant according to claim 1, in which the first bleed conduit which furnishes bleed steam to the first condensing sections includes a desuperheating feed water heater of the feed water heating means arranged further to heat feed water from the second condensing section.

4. A power plant according to claim 1, in which the first bleed conduit which furnishes bleed steam to the first condensing section includes an ejector through the nozzle of which the steam flowing in the first bleed conduit flows and the suction chamber of which is arranged to entrain additional steam from a steam bleed operating at a steam pressure lower that that of the steam supplied to the first and second bleed conduits.

5. A power plant according to claim 1, in which the second section is arranged to impart to the feed water only some 15 to 25 percent of the total temperature rise imparted to the feed water in both sections.

6. A power plant according to claim 1, in which a third bleed conduit is arranged to supply heating steam to a third condensing section from the same bleed point on the turbine, the pressure of the steam entering the third section being intermediate the pressure of the steam entering the first and second sections and the third section being arranged to heat water flowing from the first section to the third section.

7. A power plant according to claim 1, in which the feed water sections are indirect heat exchangers including tubes through the walls of which heat is transferred from the steam to the feed water.

8. A feed water heater suitable for use in a power plant according to claim 7, and including a bank of 'U-shaped tubes arranged inside a shell and connected at their ends respectively to inlet and outlet chambers for the feed water, the space inside the shell outside the tubes being divided into a first compartment through which the parts of the tubes adjacent the outlet chamber extend, a second compartment through which the parts of the tubes adjacent the inlet chamber extend, and a third compartment through which the intermediate parts of the tubes extend, a steam inlet for a first flow of heating steam into the first compartment, a steam inlet for a second and separate flow of heating steam into the third compartment, and passage means by which cooled fluid from the first compartment and condensate from the third compartment can flow into the second compartment, and a drain for condensate from the second compartment.

9. A steam turbine power plant including:

(a) a steam turbine;

(d) a second condensing section of the feed water heating means arranged further to heat water discharged from the first section;

(e) equivalent bleed points on cylinders of the turbine which are arranged to operate in parallel; and

(f) first and second bleed conduits connected to said bleed point to furnish bleed steam to the first and second condensing sections and respectively, means for proportioning the pressure in said first and second bleed conduits so that the pressure of the steam entering the second condensing section is greater than that entering the first condensing section whereby the saturation temperature of the steam in the second condensing section is greater than the saturation temperature of the steam in the first condensing section.

10. A power plant according to claim 9, in which the first bleed conduit which furnishes bleed steam to the first condensing section is arranged to operate with a higher steam velocity through it than is the second bleed conduit which furnishes bleed steam to the second condensing section.

11. A power plant according to claim 9, in which the first bleed conduit which furnishes bleed steam to the first condensing sections includes a desuperheating feed water heater of the feed water heating means arranged further to heat feed water from the second condensing section.

12. A power plant according to claim 9, in which the first bleed conduit which furnishes bleed steam to the first condensing section includes an ejector through the nozzle of which the steam flowing in the first bleed conduit flows and the suction chamber of which is arranged to entrain additional steam from a steam bleed operating at a steam pressure lower than that of the steam supplied to the first and second bleed conduits.

13. A power plant according to claim 9, in which the second section is arranged to impart to the feed water only some 15 to 25 percent of the total temperature rise imparted to the feed water in both sections.

14. A power plant according to claim 9, in which a third bleed conduit is arranged to supply heating steam to a third condensing section from an equivalent bleed point on a cylinder operating in parallel to the said cylinders, the pressure of the steam entering the third section being intermediate the pressures of the steam entering the first and second sections and the third section being arranged to heat water flowing from the first section to the third section.

15. A power plant according to claim 9, in which the feed water sections are indirect heat exchangers including tubes through the walls of which heat is transferred from the steam to the feed water.

16. A feed water heater suitable for use in a power plant according to claim 15, including a bank of U-shaped tubes arranged inside a shell and connected at their ends respectively to inlet and outlet chambers for the feed water, the space inside the shell outside the tubes being divided into a first compartment through which the parts of the tubes adjacent the outlet chamber extend, a second compartment through which the parts of the tubes adjacent the inlet chamber extend, and a third compartment through which the intermediate parts of the tubes extend, a steam inlet for a first flow of heating steam into the first compartment, a steam inlet for a second and separate flow of heating steam into the third compartment, and passage means by which cooled fluid from the first compartment and condensate from the third compartment can flow into the second compartment, and a drain for condensate from the second compartment.

17. Method of operating a power plant including a steam turbine and feed water heating means arranged to heat feed water passing to a steam generating unit supplying the steam turbine, comprising bleeding steam from the turbine through first and second bleed conduits connected to the same bleed point on the turbine, supplying steam to a first condensing section of the feed water heating means from the first bleed conduit and supplying steam to a second condensing section of the feed water heating means from the second bleed conduit proportioning the pressure of the steam in the first and second conduits so that the pressure of the steam entering the second section is greater than the pressure of the steam entering the first section, and heating feed water in the first condensing section and then heating this water further in the second condensing section.

18. The method according to claim 17, in which the steam flowing through the first bleed conduit towards the first section is caused to flow through a desuperheating feed water heater of the feed water heating means and the feed water leaving the second condensing section is further heated in the desuperheating feed water heater.

19. Method of operating a power plant including a steam turbine and feed water heating means arranged to heat feed water passing to a steam generating unit supplying the steam turbine, comprising bleeding steam from the turbine through first and second bleed conduits connected to equivalent bleed points on cylinders operating in parallel, supplying steam to a first condensing section of the feed water heating means from the first bleed conduit and supplying steam to a second condensing section of the feed water heating means from the second bleed conduit,

proportioning the pressure of the steam in the first and second conduits so that the pressure of the steam entering the second section is greater than the pressure of the steam entering the first section, and heating feed water in the first condensing section and then heating this water further in the second condensing section.

20. The method according to claim 19, in which the steam flowing through the first bleed conduit towards the first section is caused to flow through a desuperheating feed water heater of the feed water heating means and the feed water leaving the second condensing section is further heated in the desuperheating feed water heater.

References Cited by the Examiner UNITED STATES PATENTS 1,750,035 3/1930 Brown 60- 67 X 5 1,781,368 11/1930 Davidson 60-107X 1,846,047 2/1932 Brown 6067 OTHER REFERENCES German printed application No. 1,007,779, May 1957.

10 SAMUEL LEVINE, Primary Examiner.

ROBERT R. BUNEVICH, Examiner.

Claims

1. A STEM TURBINE POWER PLATE INCLUDING: (A) A STEAM TURBINE; (B) FEED WATER HEATING MEANS ARRANGED TO HEAT FEED WATER PASSING TO A STEAM GENERATING UNIT SUPPLYING THE STEAM TURBINE; (C) A FIRST CONDENSING SECTION OF THE FEED WATER HEATING MEANS ARRANGED TO HEAT THE FEED WATER: (D) A SECOND CONDENSING SECTION OF THE FEED WATER HEATING MEANS ARRANGED FURTHER TO HEAT WATER DISCHARGED FROM THE FIRST SECTION; (E) A BLEED POINT ON THE STEAM TO THE FIRST AND (F) FIRST AND SECOND BLEED CONDUITS CONNECTED TO SAID BLEED POINT TO FURNISH BLEED STEAM TO THE FIRST AND SECOND CONDENSING SECTIONS RESPECTIVELY, MEANS FOR PROPORTIONING THE PRESSURE IN SAID FIRST AND SECOND BLEED CONDUIT SO THAT THE PRESSURE OF THE STEAM ENTERING THE SECOND CONDENSING SECTION IS GREATER THAN THE ENTERING THE FIRST CONDENSING SECTION IS GREATER BY THE SATURATION TEMPERATURE OF THE STEAM IN THE SECOND CONDENSING SECTION IS GREATER THAN THE SATURATION TEMPERATURE OF THE STEAM IN THE FIRST CONDENSING SECTION.