US3744459A

US3744459A - Condensate drain subcooler for moisture separator and reheater

Info

Publication number: US3744459A
Application number: US00188090A
Authority: US
Inventors: W Reed
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1971-10-12
Filing date: 1971-10-12
Publication date: 1973-07-10
Anticipated expiration: 1990-07-10

Abstract

A moisture separator and reheater for separating moisture from wet steam and heating it using condensing-type tube bundles operating under saturated conditions incorporates a special heat exchanger in the condensate drain line to subcool the condensate and prevent instability or cavitation in the drain. The subcooling heat exchanger boils liquid taken from the moisture separator and reheater cycle to perform the condensate cooling.

Description

United States Patent 1191 Reed 1451 July 10, 1973 CONDENSATE DRAIN SUBCOOLER FOR MOISTURE SEPARATOR AND REHEATER [75] Inventor: William G. Reed, Cumberland Foreside, Maine [73] Assignee: .General Electric Company,

Schenectady, N.Y.

22 Filed: Oct. 12,1971

211 App1.No.: 188,090

[52] US. Cl 122/483, 60/73, 165/113 51 1111.0. F22g 1/04 58 Field of Search 122/483; 60/73;'

[561' 1 References Cited UNITED STATES PATENTS 7/1970 Viscovich et a1. 6(1/73 4/1970 Durrer 122/483 4/1971 Rabas 122/483 Primary Examiner Albert W. Davis, Jr. Att0meyWi1liam C. Crutch'er et a1.

57 ABSTRACT A moisture separator and reheater for separating moisture from wet steam and heating it using condensingtype tube bundles operating under saturated conditions incorporates a special heat exchanger in the condensate drain line to subcool the condensate and prevent instability or cavitation in the drain. The subcooling heat exchanger boils liquid taken from 'the moisture separator and reh'eater cycle to perform the condensate cooling. 5

2 Claims, 1 Drawing Figure DRY REHEATED STEAM OUTLET I 1 SATURATED STEAM INLET VENT SAT. STEAM INLET CONDENSATE OUTLET WET STEAM INLET CONDENSATE DRAIN SUBCOOLER FOR MOISTURE SEPARATOR AND REHEATER BACKGROUND OF THE INVENTION This invention relates generally to moisture separator and reheater apparatus used in steam turbine power plants, and more particularly relates to improvements for the condensate drain lines from condensing-type tube bundles.

Moisture separator and reheater devices, hereafter referred to as MSRs, are well-known in turbinegenerator power plants and serve to separate moisture from wet steam leaving a turbine section and then to reheat the steam to a superheated condition before it enters the next turbine section. The moisture separating and the reheating functions of MSRs have either been performed in separate pressure vessels or more recently the two functions have been combined into a single pressure vessel or shell.

In order to perform the heating function, cycle steam is often taken from the powerplant cycle at a higher energy level, usually near a saturated condition, and is then condensed in tube bundles inside the MSR..Since the condensatedrains from a header in a substantially saturated state, any transient pressure or temperature differences in the drain line can cause flashing into steam with resulting instability problems or blocking of the drain lines.

Accordingly, one object of the present invention is to provide an improved construction for an MSR condensate drain system. I 7

Another object of the invention is to provide an improved construction for drain lines from condensingtype heat exchangers. I

SUMMARY OF THE INVENTION Briefly stated, the invention comprises improvements in an MSR of the type using condensing-type reheater sections, by means of incorporating a subcooling heat exchanger in the condensate drain line from the reheater. The heat exchanger draws separated liquid from the MSR cycle by means of the natural pressure difference through the MSR. The liquid boils in the heat exchanger, thereby subcooling the condensate an reducing its tendency to flash into steam.

DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, the MSR includes a horizontal cylindrical shell 1 with end pieces 2, 3 welded in place to form a pressure vessel. Wet steam from a turbine section enters at an inlet such as 4 from the bottom and dry reheated steam exists at an outlet such as 5 on the top. A portion of the length of shell 1 is omitted in order to enlarge the scale of the drawing,

but in practive there are a number of such inlets and outlets 4, 5 and the MSR shell 1 may be on the order of 50 to 80 feet long and 12 feet in diameter.

Although the details of the particular MSR construction are immaterial to the present invention, there being many different types known in the art, a brief descriptionfollows of the type of MSR to which the, pres-' ent invention is applied, more complete details being set forth in acopending application, Ser. No. 190,538 filed Oct. 19, 1971 filed in the names of T. Carnavos, W. Hubble and K. Woods and assigned to the present assignee. 7

Dual banks of corrugated moistureseparatorelements, one bank being shown at 6, serve to remove moisture from steam entering inlet 4. The moisture flows to the bottom of the shell and is removed through suitable conduits 5a. A first stage reheating tube bundle 7 and a second stage bundle 8 are disposed on top of one another. The steam flows over tube bundles 7, 8 to be reheated before it exits at the top of the vessel through outlet 5.

As more fully described in the aforementioned pending application, first and second stage reheaters 7, 8 are of the type having transversely extending internal headers 9, 10, respectively, with a vertical partition, such as '1 l, separating the inlet and outlet sides. The individual tubes of the bundles extend the length of the pressure vessel, make a horizontal bend at the end as indicated at 12, and then return to the header of the opposite side of partition 11. Both of the headers'9, 10 are similar in construction and completely contained within the MSR. Header 9 is shown in cross section to indicate the internal features, whileheader 10 is shown in full'to illustrate that there is a manway 13 on either end thereof to permit access for tube maintenance and inspection.

Entry into the pressure vessel for the reheater piping is through the end wall 2, and the internal piping generally includes pipe sections of substantial length running transversely across the pressure vessel, as indicated at 14, in order to allow for thermal transients without overstressing the pipes and headers. The piping for the first stage reheater 7 comprises a steam inlet line 15, a condensate drain outlet line 16, and a vent line 17. Similarly, piping for the second stage reheater includes steam inlet line 18, condensate outlet line 19, and vent line 20. The steam inlet lines 15, 18 are connected to one end of the respective headers 9, 10 while the

condensate outlet lines

16, 19 and

vent lines

17, 20 are connected to vtheopposite sides of their respective headers on the other side of the vertical dividing partitions 11.

Steam for the reheaters at a substantially saturated condition is bled from the turbine power plant cycle and introduced to first stage inlet 15. Similarly, steam at a higher temperature and pressure, but also substantially saturated, is introduced to inlet line 18. By way of example, but no limitation, steam entering 18 may be saturated'and on the order of 1,000 psi (545F) while steam entering inlet 15 may be" on the order of v 500 psi. (467 F).'The wet cycle steam being treated by conventional type, well known to those skilled in the art, and can be of extended surface applied to the drain lines within an enclosure, or can be shell-in-tube with either the condensate drain fluid or the cooling fluid running through the tubes. The construction shown, for purposes of illustration, in the cross section of heat exchanger 21 comprises a transverse shell 23 running beneath header 9 and connected thereto by a pipe section 24. A transversely extending tube bundle 25 is supported within shell 23 and has headers on opposite ends for connecting to a water inlet line 26 and a steam out- OPERATION OF THE INVENTION In operation, wet cycle steam has liquid separated from it by separator banks 6, and the steam is reheated by passing over first and second stage reheaters 7, 8. Steam bled at substantially saturated condition from higher pressure and temperature energy levels in the cycle flows into the headers 9, 10, passes through the reheater tubes and returns to headers 9, 10,- condensing along the way. Substantially saturated conditions exist inthe outlet headers.

The normal pressure drop encountered by the main cycle steam flowing through the MSR over the separators and reheater tubes may be on the order of psi. Thus, the pressure difference between that of the water in well 30 and that of heat exchanger steam outlet 31 is sufficient to pump water through the heat exchangers. Since this water is substantially in saturated condition at these lower pressures, it boils inside tube bundles 25 which are surrounded by the higher temperature liquid condensate draining from headers 9, 10. This serves to subcool the condensate below its saturation'temperature. The steam from the tube bundles 25 exits to rejoin the cycle steam at outlet pipe 31.

Although the invention has been illustrated with respect to an MSR with internal headers, it is equally applicable to units with external headers where headers such as 9, are disposed on the outside of the pressure shell. In this case,

heat exchangers

21, 22 are also external, as is the connecting piping. I

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended. to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a shell containing a separator and reheater of the type having means separating a first liquid portion from a first lower pressure, lower temperature vapor and also having means for reheating said first vapor, said reheating means comprising a condensing heat exchanger adapted to condense a second higher pressure, higher temperature vapor flowing therethrough into a second condensate portion, the improvement comprismg:

boiling heat exchanger means connected to pass said first separated liquid portion in heat exchange relationship with said second condensate portion within said shell so as to cause said first liquid portion to boil, thereby subcooling said second condensate portion.

2. In a moisture separator and reheater of the type having means separating a first water portion from a first lower pressure, lower temperature wet steam flow, and having at least one condensing tube bundle adapted to reheat said first steam flow by condensing a second higher pressure, higher temperature saturated steam flow passing throughsaid tubes into a second condensate portion, said first steam flow undergoing a pressure drop through the moisture separator, the improvement comprising:

a condensate drain conduit for removing said second condensate portion from the reheater tubes,

a boiling heat exchanger disposed in heat exchange relationship with said condensate drain conduit and having an inlet and an outlet,

first conduit means connected between said heat exchanger inlet and said first separated water portion, and

second conduit means connected between said heat exchanger outlet and a lower pressure region downstream of said reheater, whereby the pressure difference across said moisture separator reheater causes the first separated water portion to flow through the boiling heat exchanger to subcool the second condensate portion.

* I8 I! i

Claims

1. In a shell containing a separator and reheater of the type having means separating a first liquid portion from a first lower pressure, lower temperature vapor and also having means for reheating said first vapor, said reheating means comprising a condensing heat exchanger adapted to condense a second higher pressure, higher temperature vapor flowing therethrough into a second condensate portion, the improvement comprising: boiling heat exchanger means connected to pass said first separated liquid portion in heat exchange relationship with said second condensate portion within said shell so as to cause said first liquid portion to boil, thereby subcooling said second condensate portion.

2. In a moisture separator and reheater of the type having means separating a first water portion from a first lower pressure, lower temperature wet steam flow, and having at least one condensing tube bundle adapted to reheat said first steam flow by condensing a second higher pressure, higher temperature saturated steam flow passing through said tubes into a second condensate portion, said first steam flow undergoing a pressure drop through the moisture separator, the improvement comprising: a condensate drain conduit for removing said second condensate portion from the reheater tubes, a boiling heat exchanger disposed in heat exchange relationship with said condensate drain conduit and having an inlet and an outlet, first conduit means connected between said heat exchAnger inlet and said first separated water portion, and second conduit means connected between said heat exchanger outlet and a lower pressure region downstream of said reheater, whereby the pressure difference across said moisture separator reheater causes the first separated water portion to flow through the boiling heat exchanger to subcool the second condensate portion.