US3287001A

US3287001A - Steam desuperheater

Info

Publication number: US3287001A
Application number: US242880A
Authority: US
Inventors: Le Roy S Harris
Original assignee: Schutte and Koerting Co
Current assignee: Schutte and Koerting Co
Priority date: 1962-12-06
Filing date: 1962-12-06
Publication date: 1966-11-22
Anticipated expiration: 1983-11-22

Description

Nov. 22, 1966 LE ROY s. HARRIS 3,287,001

STEAM DESUPERHEA'IER 2 Sheets-Sheet 1 Filed Dec. 6, 1962 INVENTORZ LeROY S. HARRIS ATTY S.

Nov. 22, 1966 Filed Dec. 6, 1962 LE ROY S. HARRIS STEAM DESUPERHEATER 2 Sheets-Sheet 2 mvzu'ron LeROY 5. HARRIS WW ATTYS.

United States Patent 3,287,001 STEAM DESUPERHEATER Le Roy S. Harris, Huntingdon Valley, Pa., assignor to Schutte and Koerting Company, Cornwells Heights, Pa., a corporation of Pennsylvania Filed Dec. 6, 1962, Ser. No. 242,880 7 Claims. (Cl. 261-78) This invention relates to a steam desuperheater and has for an object the provision of improvements in this art.

One of the particular objects of the invention is to provide a desuperheater which has high efficiency over a very high turndown ratio in the range of about 50 to 1, that is, a steam flow of from 100% rated capacity down to about 2% with controlled desuperheating down to F. above saturation in the lowest capacity range without the use of water or steam pressures higher than that of the main flow of steam entering the desuperheater.

A common form of desuperheater is the venturi type in which the superheated steam passes through a central venturi nozzle provided with Water inlets around the periphery. This works well at high steam velocity but at low steam velocity the action is not very efiicient because the steam =area exposed to water contact is relatively very small. A turn down ratio of about 10 to 1, that is from 100% to about 10%, is the best effect that can be obtained.

According to the present invention an arrangement is provided which spreads the injected water over a very wide area so as to provide a very great surface area of contact with the steam; also which brings the spread-out water into contact with most of the total steam flow in a short space along the length of flow; which keeps the injected water in contact with a large part of the total steam flow for a considerable length to provide thorough mixing, distribution and break-up of the injected water particles within the confines of the desuperheater, which will permit complete evaporation to occur by the time the stream reaches the temperature sensing well, which is usually located to feet beyond (downstream from) the desuperheater; and which does not permit the accumulation of unvaporized water in the system.

These results are accomplished by passing the steam through an annular orifice which has an outer diameter almost or substantially as large as that of the main inflow and outflow sections of the steam pipe and a cross sectional area in the range of about one-half to one-fourth of the steam pipe area, a minimum length of approximately three feet in the smaller sizes and approaching a length of three (3) to six (6) times the entering pipe diameter in the larger units. The length of the orifice varies somewhat with the ratio of the minimum flow area to the pipe line area. The lower the minimum flow area with respect to the pipe line area, the higher the velocity through the orifice and the shorter the orifice length. Water supply inlet ports are provided around the annular steam orifice on the outside, and if necessary also on the inside of the annular cross section.

When the annular sectional area of the passing body of steam is thin, due to this arrangement, it is much easier for the water to penetrate through the steam section from one side to the other. Considering the fluid flow as concentric cylinders with assigned velocity, the situation for full mixing of steam and water is far more favorable when the diameter is large and the cross section is thin.

Another feature of the present invention is that the thin annular section is relatively long both ahead or upstream of the water inlet ports and beyond or downstream of the water inlet ports.

3,287,001 Patented Nov. 22, 1966 ice Preferably the thin annular venturi section is arranged vertically and with the steam flow directed upwardly so that any non-vaporized droplets of liquid will fall back into the body of fastest flowing steam.

Complete homogeneous mixing of the water with the steam in a relatively short distance from the point of water injection is not only desirable in itself but it provides additional benefits in controlling desuperheating operations. A desuperheater is controlled, at least in part, by a temperature sensing device which is located at a considerable distance (.say 25 or 30 feet) downstream from the point of water injection and if the evaporation has not been completed at the sensing device this can cause an incorrect indication and the injection of an incorrect amount of water.

Another important feature of the present invention is that the desuperheater device is rigid and has no moving parts.

In order to provide a better undestanding of the invention, certain illustrative embodiments will be described reference being made to the accompanying drawings wherein:

FIG. 1 is a side elevation of a steam pipe line and desuperheater unit;

FIG. 2 is an axial section through the form of annular desuperheater venturi mixing unit shown in FIG. 1;

FIG. 3 is a transverse section taken on the line 3-3 of FIG. 2;

FIG. 4 is a transverse section taken on the line 4-4 of FIG. 2;

FIG. 5 is a view like FIG. 2 showing a modified unit; and

FIG. 6 is a transverse section taken on the line 6-6 of FIG. 5.

As shown in FIGS. 1 to 4, a steam inlet pipe 10 and a steam outlet pipe 11 have secured between them, as by flanges 12 and bolts 13, a desuperheater venturi unit 14. The desuperheater unit 14 includes an outer pipe section 15 with flared ends 16 and a long straight portion 17 which is almost as large in diameter as the normal pipe portions 10 and 11.

A core 20 is secured inside the pipe section 15, as by spiders 21 at the ends of the tapered end elements 22. A tubular section '23 is secured between the end elements 22. The pipe section 15 and the tubular section 23 form between them a thin annular venturi space 24 of considerable length which has a net cross-sectional area considerably less than that of the normal pipe section, 10 or 11, in the range of about /2 to 4, so as to impart high velocity to the steam passing through. Here the space 24 is of uniform size throughout its length except where it expands at its ends.

At about the mid-length of the annular space 24 there is provided an external water manifold 27 supplied by an inlet pipe 28 and having an annular group of water injection holes 29 with ports on the inner surface of the pipe section 15. If desired, a second water manifold 30 with injection holes 31 may be provided on the tubular section 23.

As an idea of the relative sizes of parts of one installation for a 3" steam pipe line, the pipe section 15 is a 2" pipe 4' long and the tubular section 23 has an CD. of 1.050". There are 30 holes 29 around the circumference, each of diameter. The cross sectional area of the 3" pipe is 7.40 sq. in. and the area of the annular venturi space is 2.50 sq. in. or approximately one-third of the pipe area.

The form shown in FIGS. 5 and 6 is similar to that of FIGS. 1-4 except that the pipe section 15' is the same size as the main pipe parts 10' and 11' and the upper end of the tubular core section 23' is tapered, as at 23a from connections.

internal dimensions of the pipe line.

a point somewhat above the middle where the outer water manifold 27' is located.

The parts are separable at the middle at flanges 35 secured by bolts 36 with the water manifold 27 clamped .between them.

The present forms of desuperheater can be used in any orientation but for best results at lower steam velocities they are preferably arranged vertically so that any unvaporized water particles which cannot be supported by aerodynamic forces of the upflowing steam, say in the ficient amounts of water to attain controllable desuperheating down to 10 F. above saturation with at least 400 F. superheat inlet steam at pipe line flow velocities down to 5 ft./sec. The high' velocity section or throat area of the annular venturi desuperheater is in the range of A to k the area of the inlet and outlet pipe line The internal dimensions of these connections are generally the same or almost the same as the In practice, the radial flow clearance between inner and outer concentric walls is kept above A" to avoid the laminar range of flow. As an idea of useful dimensions, the radial flow clearance for a 3" diameter pipe unit may be 0.507 and for a 20" diameter pipe may be 1.34". As

can be .seen, although there is a change in diameter of about seven (7) to one (1) and a change in flow area of about forty-four (44) to one (1), the change in radial clearance is held to about 2.7 to 1. By using water injection ports on both the inner and outer surfaces on the larger pipes, for example the 20" pipe, the mean radial distance of Water particle travel reduces to one-half of 1.34, or 0.67", which is only 1.34 times that of a 3 unit (with waterinjection ports on the outer'surface only), even though there is a change in flow area of 44 to 1 It has been found by experimental tests on a 3" annular venturi unit that satisfactory desuperheating can be obtained down to 10 F. above saturation of steam at desuperheater throat velocities as low as ft./ sec. In a conventional 3" desuperheater with an inside venturi orifice, throat velocities of 75 ft./s ec. were required to produce the same performance. With 501 flow range, the throat velocities in the annular venturiwould vary from 15 ft./ sec. to approximately 750 ft./ sec. With a pipe line to throat area ratio of 3 to 1, the corresponding pipe line velocities would be 5 ft./sec. to approximate ly 250 ft./sec. The 250 ft./sec. pipe line velocity is a normal velocity rating for conventional steam piping.

If the same approach is applied to the conventional inside orifice desuperheater, there would be a throat velocity of 50 times the 75 ft./sec. minimum valuewhich would be a thermodynamically impossible value of 3750 ft./sec.

In flowing through a restricting orifice, the velocity of steam cannot exceed the velocity of sound, which for steam is approximately 1800 ft./sec., the value varying with the temperature of the steam. Such velocities through the throat would cause very high, critical pressure drop through the unit; and even with this high pressure'drop (approximately 50% of upstream pipe line pressure), the maximum range obtainable would be 24 to 1, as compared to 50 to 1 with an annular venturi unit. I Because of the achievement ofthe wide range operation with much lower throat velocities, the pressure drop or loss in the annular orifice desuperheater is a maximum of 10% of the upstream pressure. The conventional inside orifioe desuperheater has pressure drops or losses in excess of 50% of the upstream pressure. 1 The latter is due to the thermodynamic phenomena of flow through an orifice at critical velocity.

As an idea of practical sizes, the length will be a minimum of about 3 feet in smaller sizes down to about 3" diameter and a maximum of about 10 feet in the larger sizes up to about 20" diameter, which comes within the range of 3 to 6 times the diameter for larger pipes mentioned above.

It is seen that the invention provides a rigid type desuperheater unit which has a very great water wetted area to the thickness of the body of passing steam and produces complete vaporization of all the water within a short length of travel and complete intermixing and temperature stabilization even at very low steam flow rates. By this arrangement a very great range of turndown ratios of 50 to 1 can be realized to 10 above satura-v tion' even Witha high initial superheat and at low velocity.

While certain embodiments of the invention have been described for purposes of illustration, it is to be under stood that there may be various embodiments and modiconnected between the supply and discharge pipes, said de-. superheater unit including an outer tubular section approximately the diameter of the supply and discharge pipes and a core wit-bin said tubular section and spaced radially inwardly therefrom to define an annular venturi passage for the flow of steam, means to supply Water into said annular venturi passage at approximately the midpoint thereof, said annular passage having a length of between three feet in smaller sizes of about. three inch diameter up to about three to six times the pipe diameter in larger sizes up to about twenty inches, and said annular venturi. passage having a cross sectional area of between one-quarter to one-half of the supply and discharge pipes.

2. A desuperheater as set forth in claim 1, in which said discharge pipe is arranged above said supply pipe to cause unvaporized water particles to fall back down into the annular passage to be vaporized by the high speed ascending body of steam.

3. A desuperheater as set forth in claim 1, in which said annular passage is of approximately constant radial width throughout its length.

4. A desuperheater as set forth in claim 1, in which said annular passage is of approximately constant radial width from said inlet pipe to an intermediate point slightly beyond the water inlet openings and is of increasing radial width from said intermediate point to the discharge pipe.

5. A desuperheater as claimed in claim 1 including an of circumferentially spaced openings in said core communicating with said manifold whereby water is delivered to said annular venturi passage around the entire circumference thereof. v

7. A desuperheater as claimed in claim 1 including a first annular manifold ex-teriorly of said outer tubular sec- 1 tion communicating with said water supply means and a plurality of, circumferentially spaced openings in said outer tubular section communicating with said manifold and a second annular manifold interiorly of said core and communicating with said water supply means and a plurality of circumferentially spaced openings in said core communicating with said manifold whereby waterisde- 5 6 livered to said annular venturi passage around the entire 3,085,793 4/1963 Pike et a1 26111-8 circumference thereof. 3,139,331 6/1964 Boudreau 261118 References Cited by the Examiner FOREIGN PATENTS 446 061 6/1926 Germany. 5 UNITED STATES PATENTS 15,598 2/1 889 Great Britain.

1,832,652 11/1931 Peebles 122479 1,841,362 1/ 1932 Cabell 239--4 4 HARRY B. THORNTON, Primary Examiner.

2,252,955 8/1941 Woods 26176 2,276,055 3/1942 Mastenbrook 236124 RONALD WEAVER 2,568,875 9/ 1951 Wethly et a1 261-118 10 T. R. MILES, D. M. RIESS, Assistant Examiners.

2,604,185 7/1952 Johnstone et a1 261-118 3,034,771 5/1962 Harris 122459 X

Claims

1. A DESUPERHEATER COMPRISING A RIGID ASSEMBLY INCLUDING A SUPPLY PIPE FOR SUPERHEATED STEAM, A DISCHARGE PIPE FOR DESUPERHEATED STEAM, AND A RIGID DESUPERHEATER UNIT CONNECTED BETWEEN THE SUPPLY AND DISCHARGE PIPES, SAID DESUPERHEATER UNIT INCLUDING AN OUTER TUBULAR SECTION APPROXIMATELY THE DIAMETER OF THE SUPPLY AND DISCHARGE PIPES AND A CORE WITHIN SAID TUBULAR SECTION AND SPACED RADIALLY INWARDLY THEREFROM TO DEFINE AN ANNULAR VENTURI PASSAGE FOR THE FLOW OF STEAM, MEANS TO SUPPLY WATER INTO SAID ANNULAR VENTURI PASSAGE AT APPROXIMATELY THE MIDPOINT THEREOF, SAID ANNULAR PASSAGE HAVING A LENGTH OF BETWEEN THREE FEET IN SMALLER SIZES OF ABOUT THREE INCH DIAMETER UP TO ABOUT THREE TO SIX TIMES THE PIPE DIAMETER IN LARGER SIZES UP TO ABOUT TWENTY INCHES, AND SAID ANNULAR VENTURI PASSAGE HAVING A CROSS SECTIONAL AREA OF BETWEEN ONE-QUARTER TO ONE-HALF OF THE SUPPLY AND DISCHARGE PIPES.