CA2199209C

CA2199209C - Steam condensing apparatus

Info

Publication number: CA2199209C
Application number: CA002199209A
Authority: CA
Inventors: Crispin Lawrence Debellis; Robert Joseph Giammaruti; Thomas Wayne Strock; Harold Walter Wahle
Original assignee: Hudson Products Corp
Current assignee: Hudson Products Corp
Priority date: 1996-03-06
Filing date: 1997-03-05
Publication date: 2000-05-16
Anticipated expiration: 2017-03-05
Also published as: KR100250863B1; MX9701495A; AU690048B2; AU1509397A; TW360769B; BR9701200A; CA2199209A1; KR970066264A; EP0794401A2; JPH102683A; ID16111A; JP2807992B2; SG54463A1; EP0794401A3

Abstract

An air-cooled steam condenser that also uses heat pipe technology so as to provide steam tubes that are freeze proof under any ambient conditions and offer a simple approach to the management of noncondensable gases. Steam flows through the main condenser with concurrent steam and condensate flow downward.
The heat transfer surface area and fan air flow are designed such that all of the steam does not completely condense and steam vapor continuously exits each tube row. This continuous flow of steam vapor purges these rows of noncondensable gases. The excess steam flows into the lower header to a secondary condenser section that utilizes heat pipes. In the secondary condenser section, the excess steam condenses on the evaporator side external surface of the heat pipes. The noncondensable gases that remain in the lower header are vented with an air removal system similar to conventional condensers. Condensate in the lower header is collected for reuse in the power generation cycle.

Description

21 9920n.

STEAM CONDENSING APPARATUS

BACKGROUND OF THE INVENTION
1. Field of the Invention The invention is generally related to steam condensers and more particularly to steam condensers that combine the use of air-cooled vacuum dry steam condensing technology with heat pipe technology.

2. General Background Air-cooled steam condensers used in the steam power-generation cycle are typically arranged in an A-frame construction with a fan at the base and inclined condenser tube bundles on each side. Air flows through the fan and across several sections of the steam condenser. The steam inlet is at the top of each bundle and the vapor and condensate flow concurrently downward. Typically, there are four rows of tubes in each condenser bundle. As air flows through the four rows, the air temperature increases and the temperature difference between the condensing steam and air deceases. The lower temperature difference for each successive tube row results in less condensation. Since the condensate and steam flows are lower for each successive tube row, the two-phase flow pressure drop is also lo~er for each tube row. If the tube rows discharge into a common rear header, the differences in tube row exit pressures are resolved by steam and noncondensable gases in the rear header entering the ends of the tube rows that have a lower pressure. Since the lower tube rows have lower exit pressures, they have steam entering both ends and over time noncondensable 219g209 gases collect in the tubes. These pockets of noncondensable gases block local steam flow, allowing condensate to freeze during cold weather, which can result in tube rupture.
Noncondensable gases are normally vented from the rear header with vacuum pumps or air ejectors. To overcome this problem, the classical solution has been to design for excess steam flow through each tube row. The excess steam prevents the accumulation of noncondensable gases and maintains condensate temperatures above freezing. This excess steam, typically twenty to thirty-three percent of the total steam flow, is condensed in a secondary or vent condenser. The typical vent condenser is a dephlegmator (reflux condenser) which has steam flow up an inclined tube, condensation on the tube walls, and drainage of the condensate downward. The noncondensable gases flow upward out of the tube and are removed by vacuum pumps or air ejectors.
Steam condenser freezing problems have also been overcome in the past through the use of heat pipes. Heat pipes were used to condense steam. The steam was passed over the evaporator side of the heat pipes and condensed while ambient air was forced over the condenser side of the heat pipes. The condensate was collected at the bottom of the steam duct and returned to the boiler for reuse. These approaches are subject to some limitations and do not necessarily offer a simple approach to the management of noncondensable gases.
SUMMARY OF THE INVENTION
The invention addresses the limitations of the prior art.
What is provided is an air-cooled steam condenser that also uses heat pipe technology so as to be freeze proof under any ambient conditions and offer a simple approach to the management of noncondensable gases. Steam flows through the main condenser with concurrent steam and condensate flow downward. The heat transfer surface area and fan air flow are designed such that, over the range of operating conditions, all of the steam does not completely condense and vapor continuously exits each tube row. This continuous flow of steam vapor purges these rows of noncondensable gases. The excess steam flows into the lower header to a secondary condenser section that utilizes heat pipes. In the secondary condenser section, the excess steam condenses on the evaporator side external surface of the heat pipes.
The noncondensable gases that remain in the lower header are vented with an air removal system similar to conventional condensers. Condensate in the lower header drains to a condensate tank for reuse in the power generation cycle.
In a first aspect, the present invention provides steam condensing apparatus comprising: (a) an upper steam header;
(b) a main condenser in fluid communication with the upper steam header, the main condenser being designed such that only a predetermined portion of the steam flow therethrough is condensed therein; (c) a lower steam header in fluid communication with the main condenser; (d) a secondary condenser in fluid communication with the lower steam header; and (e) a plurality of heat pipes received in the secondary condenser that cause condensation of steam not condensed in the main condenser.
In a second aspect, the present invention provides a steam condensing apparatus comprising: (a) an upper steam header; (b) a main condenser in fluid communication with the upper steam header, the main condenser being designed such to condense approximately twenty to eighty percent of the steam flow therethrough; (c) a lower steam header in fluid communication with the main condenser; (d) a second condenser in fluid communication with the lower steam header in position in line with the main condenser; and (e) a plurality of heat pipes received in the secondary condenser that cause condensation of steam not condensed in the main condenser.
In a third aspect, the present invention provides a steam condensing apparatus comprising: (a) an upper steam header; (b) a lower steam header; (c) a condenser adjacent positioned between the upper and lower steam headers; (d) a plurality of steam tubes positioned in the condenser and in fluid communication with the upper steam header and the lower steam header; and (e) a plurality of heat pipes positioned in the condenser such that the evaporator section of the heat pipes extend into the lower steam header.
BRIEF DESCRIPTION OF THE DRAWINGS
For a further understanding of the nature and objects of the present invention reference should be had to the following description, taken in conjunction with the accompanying drawing in which like parts are given like reference numerals, and wherein:
Fig. 1 illustrates a prior art air cooled steam condenser.
Fig. 2 illustrates a prior art air cooled steam condenser.
Fig. 3 illustrates a prior art air cooled steam condenser.
Fig. 4 illustrates the invention.
Fig. 5 illustrates an alternate embodiment of the invention.

219g209 Fig. 6 illustrates a second alternate embodiment of the invention.
Fig. 7 is a sectional view that illustrates one of the heat pipes used in the invention.
Fig. 8 is a sectional view of an alternate embodiment of a heat pipe that may be used with the invention.
Fig. 9 is a sectional view that illustrates an alternate embodiment of the lower steam header of the invention.
Fig. 10 is a view taken along lines 10-10 in Fig. 9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As seen in the prior art illustrations of Fig. 1, air-cooled steam condensers are typically arranged in an A-Frame construction with a fan 10 at the base and inclined condenser tube bundles 12 on each side. Air flows through the fan across several sections of the steam condenser. Steam from steam turbine 14 is directed to an upper steam header 16 which provides a steam inlet at the top of each bundle 12. The vapor and condensate flow concurrently downward in the bundle to a lower or rear header 18. An air ejector or vacuum pump 20 is used to vent noncondensable gases from the rear header 18. The condensate is collected in tank 22 and directed to condensate pumps not shown for reuse.
Fig. 2 illustrates a prior art solution to prevent freezing of condensate. The condenser tube bundle 12 is designed to cause excess steam flow through each tube row. The excess steam prevents the accumulation of noncondensable gases and maintains condensate temperatures above freezing. This excess steam is ~ CASE 5727 condensed in a secondary or vent condenser 24. The typical vent condenser 24 is a dephlegmator (reflux condenser) which has steam flow up an inclined tube, condensation on the tube walls, and drainage of the condensate downward. The noncondensable gases flow upward out of the tube and are removed by vacuum pumps or air ejectors.
Fig. 3 also illustrates a prior art solution to prevent freezing of condensate. Heat pipes 26 are set up in a Y
configuration. The evaporator side of the heat pipes is enclosed in a steam header 28. The steam is condensed as it passes across the evaporator side of the heat pipes 26. The condensate is collected at the bottom of the header 28 and returned to the boiler for reuse. Fan 10 causes induced air flow across the condenser sides of the heat pipes to cause cooling and recondensation of the working fluid contained in the heat pipes.
The present invention is generally indicated by numeral 30 in Fig. 4. Steam condensing apparatus 30 is generally comprised of main condenser 32, lower header 34, and secondary condenser 36.
Main condenser 32 is formed from upper steam header 38 and one or more tube bundles 40. Upper steam header 38 receives steam from steam turbine 42 via line 44 and then directs the steam into tube bundles 40. Each tube bundle 40 is similar to tube bundles generally known and used in the industry in that several rows of tubes, usually four, are provided for receiving and condensing steam. The main difference in the tube bundles of the present invention from the prior art is that they are not designed to condense as much of the steam as possible. Instead, the heat transfer surface area and fan air flow from fans 46 are designed such that over the range of operating conditions, all of the steam does not completely condense and steam vapor continuously exits the bottom of each tube row into lower header 34. In the preferred embodiment, sixty-seven to eighty percent of the available surface area is used in the tube bundles 40.
This surface area, combined with fan air flow, results in approximately twenty to eighty percent of the steam being condensed in main condenser 32. The continuous flow of steam vapor purges the tube rows in main condenser 32 of noncondensable gases. The excess uncondensed steam and noncondensable gases flow into flow into lower header 34 and then to a secondary condenser 36.
Secondary condenser 36 is in fluid communication with lower header 34 and positioned in line with main condenser 32. Heat pipes 48 are positioned in secondary condenser 36 such that the evaporator side of each heat pipe is at the lower end of secondary condenser 36 and extends into lower header 34. The condenser side of each heat pipe is positioned toward the upper end of secondary condenser 36. In this manner, the uncondensed steam from main condenser 32 condenses on the evaporator side of heat pipes 48 and flows out of lower header 34 through condensate drain 50. Noncondensable gases are vented off to an ejector as indicated by numeral 52.
Fig. 5 illustrates an alternate embodiment of the invention wherein main condenser 32 and secondary condenser 36 are oriented ~ CASE 5727 in a W-shape configuration instead of an in-line configuration.
As above, the invention condenses the excess steam in secondary condenser 36. Noncondensable gases are vented off via lines 54.
Fig. 6 illustrates another alternate embodiment of the 5invention wherein the main and secondary condensers described above are consolidated into a single condenser 56. Single condenser 56 includes conventional finned tubes 58 that direct steam flow from top to bottom and heat pipes 26. As before, the heat transfer surface area and fan air flow are designed such 10that over the range of operating conditions, all of the steam is not condensed in tubes 58. The continuous flow of steam purges tubes 58 of noncondensable gases. The remaining steam that exits the bottom of tubes 58 is condensed by heat pipes 26 which have their evaporator side extending below the exit end of tubes 58 15in lower header 34. Condensate drains from condensate drain 50 to be collected for reuse. Noncondensable gases are removed via vent lines 54. Fig. 6 illustrates four rows of pipes, with heat pipes 26 being the lower or first row. It should be understood that heat pipes 26 may be positioned in any row of the tube bundle.
Fig. 7 is a detailed sectional view of a heat pipe 26 and lower header 34 as used in the invention. Heat pipes 26 may be fabricated out of straight round, elliptical, or flat oval tubes that may or may not contain an internal wick. Heat pipes 26 are 25sealed at both ends and contain a predetermined quantity of heat transfer fluid 60 at a predetermined vapor pressure. The fluid used will depend upon the application and conditions. Examples 2lss2as of heat transfer fluid used in different heat pipe applications are, but not limited to, methanol, ammonia, and freon. Heat transfer fluid 60 normally resides in evaporator section 62 of heat pipe 26. When heat flows into evaporator section 62, heat transfer fluid 60 vaporizes, removing heat from the steam and causing condensation thereof, and travels upward into condenser section 64 where the fluid is cooled and condensed, releasing the fluid heat to the air flow. The heat transfer fluid condensate returns to evaporator section 62 by gravity flow. Condenser section 64 may be provided with fins 66 to provide a large heat rejection surface area. Fins 66 may be extruded, embedded, or wrapped aluminum or steel and can be solid or serrated depending upon the pressure drop and heat transfer requirements. Heat pipes 26 may be placed in inline or triangular tube pitches depending upon the pressure drop and heat transfer requirements of the system.
For improved heat transfer performance and corrosion resistance, Fig. 8 illustrates a heat pipe 26 that has the outer diameter of the evaporator section sleeved with a low friction coating 68 such as polytetrafluoroethylene. The low friction coating promotes drop wise condensation which improves the condensing heat transfer rate by about one order of magnitude.
In addition, the coating provides a corrosion proof boundary that allows the use of inexpensive carbon steel based tubes for heat pipes 26.
Fig. 9 and 10 illustrate an embodiment of a lower header 34 that is provided with a plurality of thermowells or sleeves 70 that are welded directly to lower header 34 to form a leak-proof seal. Each sleeve 70 is sized to provide a small slip-fit clearance between the inner diameter of sleeve 70 and the outer diameter of the evaporator section of a heat pipe 26 to reduce thermal resistance. If required to improve heat transport, a thermally conductive substance such as grease or liquid may be used to fill the annulus. Heat pipes 26 are held in place by gravity and the tube supports commonly found in the condenser bundle frame. This provides another means of eliminating corrosive contact of heat pipes 26 with the steam. As referred to above, the exterior of sleeves 70 may be coated with a low friction coating to promote drop wise condensation, thus improving the condensing heat transfer rate.
In operation, steam received in upper header 38 flows into the tubes in tube bundles 40 where some of the steam is condensed and flows into lower header 34. The remaining steam flowing out of the tubes into lower header 34 purges the tubes of noncondensable gases. The remaining steam is condensed on the evaporator section 62 of heat pipes 26. Noncondensable gases are removed via vent lines and/or vacuum pumps. The arrangement of tubes and heat pipes causes a constant steam flow through the tubes in the tube bundles to provide for freeze-proof tubes in the tube bundles. The only freezing possible in the design of the invention is on the outside of the heat pipe section located in the lower header. Since this occurs on the exterior of the heat pipes, it will not damage the heat pipes. The lower header embodiment of Fig. 9 provides the advantage of being able to ' 2~99209 ~ CASE 5727 remove and install heat pipes in the field without the need to cut and reweld the difficult seal weld between the heat pipe 26 and lower header 34.
Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.

Claims

1. A steam condensing apparatus, comprising:
a. an upper steam header;
b. a main condenser in fluid communication with said upper steam header, with said main condenser condensing only a predetermined portion of the steam flow therethrough;
c. a lower steam header in fluid communication with said main condenser;
d. a secondary condenser in fluid communication with said lower steam header; and e. a plurality of heat pipes received in said secondary condenser that cause condensation of steam not condensed in said main condenser;
wherein said heat pipes are provided with a low friction coating on the evaporator section thereof and said lower steam header is provided with a plurality of sleeves that extend into said lower steam header and are each sized to receive the evaporator section of one of said heat pipes.

2. The steam condensing apparatus of claim 1, wherein said main condenser condenses twenty to eighty percent of the steam flow therethrough.

3. The steam condensing apparatus of claim 1, wherein said main condenser and secondary condenser are arranged in an inline configuration.

4. The steam condensing apparatus of claim 1, wherein said main condenser and secondary condenser are arranged in a W-shaped configuration.

5. A steam condensing apparatus, comprising:
a. an upper steam header;
b. a main condenser in fluid communication with said upper steam header, said main condenser condensing twenty to eighty percent of the steam flow therethrough;

c. a lower steam header in fluid communication with said main condenser;
d. a secondary condenser in fluid communication with said lower steam header and positioned in line with said main condenser;
e. a plurality of heat pipes received in said secondary condenser that cause condensation of steam not condensed in said main condenser;
wherein said heat pipes are provided with a low friction coating on the evaporator section thereof, and said lower steam header is provided with a plurality of sleeves that extend into said lower steam header and are each sized to received the evaporator section of one of said heat pipes.

6. A steam condensing apparatus, comprising:
a. an upper steam header;
b. a lower steam header;
c. a condenser positioned lower between said upper and steam headers;

d. a plurality of steam tubes positioned in said condenser and in fluid communication with said upper steam header and said lower steam header; and e. a plurality of heat pipes positioned in said condenser such that the evaporator section of said heat pipes extend into said lower steam header wherein the evaporator section of each of said heat pipes is provided with a low friction coating, and said lower steam header is provided with a plurality of sleeves that extend into said lower steam header and are each sized to receive the evaporator section of one of said heat pipes.