US 3590912 A
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United States Patent  Inventors Frederick T. Elder  Field of Search 165/39, Mountain Lakes; 142, ll1l l4, l58-l63, l75-176 Renato R. Noe, Union City, both of, NJ. [21 Appl. No. 792,953 References Clted  Filed Jan. 22, 1969 UNITED STATES PATENTS  Patented July 6. I9 2,665,556 1/1954 Otten 165/142 1 1 Asslgnec Worthington Corporalwn 2,946,570 7/1960 West 165/161 3,390,722 7/1968 Kotelewsky 165/112 Primary Examiner-Charles Sukalo Attorney-Daniel H. Bobis  STAGGERED SURFACE FEEDWATER ABSTRACT: A mu1tipass vertical heat exchanger constructed 9 cl 4 D n to provide ditferent lengths of heat exchange tubing for carrywing ing liquid on different passes through the heat exchanger. The  US. Cl 165/39, construction avoids unnecessary flooding of heat exchange 165/1 1 1, 165/175 tube surface with steam condensate in the higher passes of the  lnt.Cl 86% 1/00 heat exchan etubin throu h the heat exchan er.
I 70 1o i 1 .6 o o o u 1? 20 l ,1 I Z 11 7LT 52 E 1 m T a l: 54- 5 1 x L k 33 3O 26 72 78 VERTICAL STAGGERED SURFACE FEEDWATER HEATER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to heat exchange apparatus having structure within a flow path maintaining a stream of fluid of one density in communication with a fluid ofa second density. The chamber in which the two fluids communicate has separate discharge ports for separate withdrawal of each of the fluids and further, within the chamber there is a means for changing the temperature and pressure of one of the fluids through the use ofa relatively cooled surface forming a part of the apparatus.
2. Description of the Prior Art In multipass vertical feedwater heaters, and many other multipass vertical heat exchangers, the lower portion of the heat exchange chamber is flooded with steam condensate so that the unheated liquid entering the heat exchange tubes, which are located in the heat exchange chamber, will subcool the condensate below saturation temperature. However, the subcooled condensate which floods the lower portion of the heat exchange chamber also covers portions of the heat exchange tubes which are carrying heated liquid on a second or higher pass through the heat exchange chamber.
All of the second or higher pass tube surface which is submerged beneath the level of steam condensate in the heat exchange chamber is usually wasted and of no effect to the functioning of the feedwater heater because the temperature of the heated liquid in the higher pass heat exchange tubes is higher than the temperature of the condensate which is supposed to be subcooled by these very same tubes. The cost of material for heat exchange tubing makes this waste of tube surface expensive in relation to the overall cost of the feed water heater.
Attempts have been made in the past to eliminate this waste of tube surface by preventing the steam condensate in the lower portion of multipass vertical heat exchangers from flooding any portion of the higher pass heat exchange tubes. U.S. Pat. No. 2,756,028 issued July 1956 to W. M. Byerley illustrates a method of building an inclosure within the lower portion of the heat exchange chamber and introducing the steam directly into this lower inclosure. The higher pressure of the steam and the baffling means about the inclosure prevent the steam condensate in the subcooling zone of the heat exchange chamber from flooding those portions of the heat exchange tubes carrying second pass liquid.
Other devices, as for example the vertical feedwater heater shown in U.S. Pat. No. 3,390,722 issued July 2, 1968 to G. P. Kotelewsky, attempt to establish two different levels for the steam condensate in the heat exchange chamber.
SUMMARY OF THE INVENTION To overcome the difficulties in the prior art relating to the loss of effective tube surface area in vertical feedwater heaters and other vertical heat exchangers, the present invention sets forth a construction in which heat exchange tubes carry liquid to be heated through the heat exchange chamber in a plurality of passes of unequal length. The heat exchange tubes carrying liquid on the higher passes need not extend into the subcooling zone and, therefore, there is rep loss of effective tube length due to unnecessary flooding. Separate tube sheets are used for connecting the inlet end of the heat exchange tubing to the liquid inlet distribution chamber and the outlet end of the heat exchange tubing to the liquid outlet collection chamber.
Accordingly it is an object of the present invention to provide a multipass, vertical heat exchanger in which the heat exchange tubes are of different lengths in at least two passes.
Another object of the present invention is to provide a multipass vertical heat exchanger in which effective heat exchange tube area in higher tube passes is not lost due to flooding by steam condensate.
Yet, another object of the present invention is to provide a multipass vertical heat exchanger having increased heat transfer efficiency.
Still, another object of the present invention is to provide a multipass vertical heat exchanger which is of simplified and relatively inexpensive construction.
Still, a further object of the present invention is to provide a multipass vertical heat exchanger constructed with staggered tube sheets to allow different lengths of heat exchange tubes in separate passes.
Various other objects and advantages will be apparent from the following description of several embodiments of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows a side elevation in section ofa multipass vertical feedwater heater built in accordance with the teachings of the present invention.
FIG. 2 is a sectional long line 2-2 of FIG. 1.
FIG. 3 is a side elevation in section of another embodiment of a multipass vertical feedwater heater built in accordance with the teachings of the presentinvention.
FIG. 4 is a view taken along lines 44 of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. I, a multipass vertical feedwater heater generally indicated at 10 consists of an outer shell 12 which encloses a heat exchange chamber I3 having a condensing zone I4 and a subcooling zone 16. Steam enters through steam inlet 18 where it heats feedwater flowing through heat exchange tubes 20 and in the heat exchange process condenses and falls to the subcooling zone 16 and leaves through condensate outlet 22.
The feedwater to be heated enters feedwater distribution chamber 24 through inlet 25. Distribution chamber 24 is formed by the thicker lower wall 26 of shell 12, the bottom plate 28 for the shell and a lower tube sheet 30. A plurality of heat exchange tubes 20 are connected at their lower end 36 to the lower tube sheet 30 to carry the feedwater in long section 38 of the heat exchange tubes on a long first pass from the distribution chamber through the subcooling zone 16 and the condensing zone 14. The heat exchange tubes 20 then bend around and carry the feedwater in short section 39 of the heat exchange tubes in a short second pass through the condensing zone to the feedwater collection chamber 40. The ends 42 of the heat exchange tubes are connected to an upper tube sheet 44 which forms the top of collection chamber 40. The feedwater collection chamber 40 is formed from a portion of the sidewall 46, upper tube sheet 44, an annular upper cover plate 48 and a skirt 50 extending from the wider portion of the shell 12. The heated feedwater leaves the feedwater collection chamber 40 through outlet 52.
Because the pressure of the feedwater in the feedwater distribution chamber 24 and feedwater collection chamber 40 is much higher than the pressure in either condensing zone 14 or subcooling zone 16 of the heat exchange chamber 13, both the upper and lower tube sheets are relatively thick in comparison to the thickness of the upper wall sections of shell 12. Similarly, the skirt 50, and the lower wall section 26 and the upper and lower plates 48 and 28 respectively are also made of relatively heavy material. However, this is not the case for the sidewall portion 46 of the shell which forms the feedwater collection chamber 40, and therefore, reinforcing struts 54 are placed within the feedwater collection chamber 40 to strengthen that section of the wall.
The annular upper plate 48 is connected to the feedwater heater by bolts 56, which extend through the plate and secure to inner and outer bolting rings 58 and 60, respectively. A drain fitting 62 for feedwater collection chamber 40 is also provided in the bottom of upper plate 48. Similarly, the bottom plate 28 is connected to the shell to form the feedwater distribution chamber by a plurality of bolts 64 which extend through bolting flange 66 into the bottom plate 28.
A plurality of baffles 68 extend from the wall of shell 12 in the subcooling zone 16 in order to induce circulation of the steam condensate in the subcooling zone as the condensate travels towards the steam condensate in the subcooling zone as the condensate travels towards the steam condensate outlet 22. Flange 70 on the steam inlet 18, flange 72 on the steam condensate outlet 22, flange 74 on the feedwater inlet 25, and flange 76 on the feedwater outlet 52 are used for connecting these structures to associated conduits in the system.
The level of the steam condensate in subcooling zone 16 is maintained just slightly above the level of the upper tube sheet 44 by means of valve 78 installed downstream of the steam condensate outlet. Valve 78 is controlled by liquid level sensing means 80 which is connected to actuating mechanism 82 which positions valve 78 automatically to maintain the desired level of condensate in the device.
ANOTHER EMBODlMENT OF THE lNVENTlON FIG. 3 and 4 show a second embodiment of a feedwater heater built in accordance with the teachings of the present invention. A vertical feedwater heater indicated generally as 90, consists of an upper shell portion 92 having a condensing zone 94 and subcooling zone 96. A steam inlet 98 to provide a steam for the condensing zone 94 is disposed in the side of the shell and a steam condensate outlet 100 is disposed at the bottommost portion of the upper shell portion 92 to provide a means for removing the condensate from the feedwater heater. The bottom section of the shell 102 is divided by lower partition member 104 into a feedwater distribution chamber 106 referred to as the inlet channel with a feedwater inlet 108, and a feedwater collection chamber 110 referred to as the outlet channel with a feedwater outlet 112. The bottom section 102 of the shell has thicker walls 103 in order to withstand the higher pressures of the feedwater relative to the pressure in either the condensing zone 94 or the subcooling zone 96 of the heater.
A lower plate 114 extends across the entire length of the feedwater heater at the upper end of the bottom section 102 of the shell. Lower plate 114 forms the top of the feedwater collection chamber 110 and forms the lower tube sheet 116 which in turn forms the top of feedwater distribution chamber 106. An upper tube sheet 118 extends horizontally from the wall of upper shell 92. An upper partition member 119 connects the upper tube sheet to the lower plate 114, and the walls of the shell to form an upper watertight cell 120. A highpressure conduit 122 communicates the upper tube sheet with the feedwater collection chamber 110.
Feedwater in distribution chamber 106 enters ends 124 of heat exchange tubes 126 to travel in the longer first pass leg 128 of the heat exchange tubes through subcooling zone 96 and condensing zone 94. The heat exchange tubes then bend around into the shorter second pass leg 130 which carries the feedwater through the condensing zone. The end 132 of heat exchange tubes 126 is connected to upper tube sheet 118 and delivers the now heated feedwater into the enlarged section 134 of high pressure conduit 122. The heated feedwater passes from high pressure conduit 122 into the feedwater collection chamber 110.
The upper watertight cell 120 which surrounds high-pressure conduit 122 is completely dry. A manway or manhole cover 136 allows for access into the upper watertight cell 120 for servicing of the upper tube sheet 118 or the lower plate 114. By carrying all of the heated feedwater in high-pressure conduit 122 instead allowing it to flood upper watertight cell 120, a space is maintained which acts to insulate the subcooling zone from the heated feedwater passing through the highpressure conduit. Additionally, by keeping all of the relatively high'pressure heated feedwater within the high-pressure conduit 122, the pressure differential across upper partition 119 is kept low enough so that the partition need not by constructed in the same manner as a tube sheet.
A manway or manhole cover 138 is also located in the bot tom section 102 of the shell to allow for access to that portion of the feedwater heater. Baffles 140 extend horizontally from the wall of the shell in the subcooling zone to provide for proper circulation of the steam condensate as it passes towards the condensate outlet 100. The steam condensate level 142 is maintained slightly above the upper tube sheet 118 in the same manner as shown in previous embodiment of the invention, but not shown in this figure, by suitable apparatus connected to the condensate outlet.
lt should be noted that although the embodiments of the invention described above are for two pass feedwater heaters, the principal of the invention could apply with equal merit to vertical feedwater heaters or other vertical heat exchangers with four passes or more. In one example of such a case, the feedwater collection chamber could be subdivided to provide for the multiple higher passes. The higher pass tubes would pass from the upper tube sheet back to the upper tube sheet, so that a minimum of tube surface in the higher passes would be flooded by steam condensate. Other arrangements are also possible where flooding of the tube surface would occur only in the odd number passes.
It will be understood that various changes in the details materials, and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention, as expressed in the appended claims.
What we claim is:
l. A vertical heat exchange device comprising: an upright shell forming a heat exchange chamber having steam inlet means and steam condensate outlet means therein; said heat exchange chamber having a condensing zone in communication with said steam inlet means and a subcooling zone in communication with said steam condensate outlet means;
a first chamber means in said shell disposed near the bottom of said shell for holding liquid to be heated and including inlet means to provide feed water thereto;
a second chamber means in said shell for holding liquid which has been heated, including outlet means for removing the heated liquid therefrom;
a plurality of heat exchange tubes in said heat exchange chamber communicating said first chamber means with said second chamber means; each of said head exchange tube means having at least first pass portion which passes through said subcooling zone and condensing zone and a second portion which passes primarily through said condensing zone only; an inlet end of said first pass portion of each of said heat exchange tubes connected to said first chamber means and an outlet end of said second pass portion of each of said exchange tubes connected to said second chamber means.
2. The combination claimed in claim It wherein: said first chamber means include a tube sheet forming the upper wall thereof;
said second chamber means include a tube sheet forming the upper wall thereof; and
said inlet end of said first pass portion connected to the tube sheet of said first chamber means and said outlet end of said second pass portions connected to the tube sheet of said second chamber means.
3. The combination claimed in claim 2 wherein: said steam inlet means in said shell are disposed above the tube sheet of said second chamber means; said condensate outlet means in said shell are disposed near the level of the tube sheet of said first chamber means;
and further comprising:
means connected to the condensate outlet means to cause condensate to accumulate in said subcooling zone, whereby the accumulated condensate will be subcooled by the liquid flowing through said heat exchange tubes.
4. The combination claimed in claim 3 wherein said means to cause the condensate to accumulate in said subcooling zone includes means to control the level of said condensate in said shell to maintain said condensate level slightly above the tube sheet of said second chamber means.
5. The combination claimed in claim 3 further comprising horizontal baffle means disposed in said subcooling zone of said shell to effect circulation of the condensate therein as the condensate flows to said condensate outlet means.
6. The combination claimed in claim 3 wherein:
said first chamber means is cylindrical in form and is disposed at the bottom of said shell; and
said second chamber means is annular in form.
7. The combination claimed in claim 3 wherein said second chamber means comprise:
an upper tube sheet extending horizontally from the wall of said shell;
a lower plate extending horizontally from the wall of said shell below said upper tube sheet;
upper partition means substantially vertically disposed and connected to said upper tube sheet, said lower plate, and the wall ofsaid shell forming a fluid tight cell;
lower partition means connected to said lower plate, the
wall of said shell and the bottom of said shell to form an outlet channel; said outlet means for removing liquid from said second chamber means communicating with said outlet channel; and high-pressure conduit means connected to said upper tube sheet and extending the length of said fluidtight cell to collect heated liquid from the outlet end of said heat exchange tubes and carry said liquid to said outlet channel. 8. The combination claimed in claim 7 wherein: said lower plate fully extends across the inside of said shell;
and said tube sheet for said first chamber means is formed from the portion of said lower plate extending beyond said fluidtight cell. 9. The combination claimed in claim I wherein said outlet end of said second pass portions are disposed above said inlet ends of said first pass portions.