WO1992008534A1

WO1992008534A1 - Spray degasser

Info

Publication number: WO1992008534A1
Application number: PCT/NL1991/000227
Authority: WO
Inventors: Willem Wiemer
Original assignee: Stork Ketels BV
Current assignee: Stork Ketels BV
Priority date: 1990-11-19
Filing date: 1991-11-11
Publication date: 1992-05-29
Anticipated expiration: 1993-05-19
Also published as: JP3092852B2; US5549737A; JPH06502346A; ATE112695T1; DE69104622T2; DE69104622D1; EP0558577A1; EP0558577B1; DK0558577T3; FI103640B; FI103640B1; FI932008A7; ES2061276T3; NL9002521A; FI932008A0

Abstract

The invention relates to a spray degasser (8) for removing gas from a liquid, comprising: i) a boiler (9); ii) at least one radial sprayer (15) which is connected to a liquid feed (18) for spraying the liquid for degassing as a spray screen (17) in the boiler; iii) a vapour feed (11) for the vapour phase of the liquid; iv) an outlet (20) for gas removed from the liquid; and v) an outlet (19) for degassed liquid; characterized by separating means (24, 25) which separate off a compartment in the boiler above and adjoining the spray screen and onto which the gas outlet connects.

Description

Spray degasser

The present invention relates to a spray degasser for removing gas from a liquid, which comprises: i) a boiler; ii) at least one radial sprayer which is connected to a liquid feed for spraying the liquid for degassing as a spray screen in the boiler; iii) a vapour feed for the vapour phase of the liquid; iv) an outlet for gas removed from the liquid; and v) an outlet for the degassed liquid. The invention relates in particular to a spray degasser for removing oxygen from water. Oxygen is an important factor which can result in corrosion in steam boilers and turbines. The problem of corrosion occurs particularly when work is done at high temperatures and pressures. Using a degasser the oxygen content in the water must be reduced in general to less than 10 ppb, preferably to less than 5 ppb.

In a known spray degasser the gas is separated from liquid in two steps. A first step is the so-called "scrub" step, wherein steam and water are brought into contact at generally equilibrium temperature and pressure, wherein the steam has a very low oxygen partial pressure. The water is degassed with this steam. The second step is the "heating" step, wherein almost all the steam condenses into water which is sprayed as a spray screen, wherein the water is brought to the equilibrium temperature. A small portion of the steam is discharged via an outlet using the released gases which do not condense under these conditions (see "Deaerating boiler feed water - The theoretical background" by G.S. Solt and . iemer, and "The Stork spray type deaerator: design, development and experience" by W. Wiemer and G.S. Solt in Symposium on Degassing, 15 June 1978, pages 49-56 and 57-70 respectively) .

A spray degasser with a radial sprayer is described for instance in NL-A-72.03333. US-A-2.379.753 describes a water treatment and degassing apparatus having a series of annular cone sprayers in tangentially slanting arrangement for the purpose of generating a powerful water rotation in the underlying liquid. The cone-like spray screens are surrounded by a cylindrical partition. Steam can only pass laterally through the spray screens and via short-circuit openings between two adjoining cone spray screens and the partition into the space situated thereabove. It will be apparent that the level of the partial oxygen pressure in the space above the spray screen deter¬ mines the operation of the spray degasser. An improvement of the degassing action can be obtained by a further lowering of the partial oxygen pressure therein, which however requires an increase in the quantity of steam to be blown off, which is attended by greater heat losses.

Further research into a spray degasser has shown that the partial oxygen pressure of steam which passes through the spray screen is location-dependent. The temperature in the spray screen increases namely from the place where the spray screen is formed as a result of the condensation of steam passing therethrough. Steam which passes through the spray screen at a lower temperature will be richer in oxygen after passing through the screen than steam which passes through the spray screen at a higher temperature. By separately collecting the steam relatively enriched with oxygen and then blowing this off, the degassing action of the spray degasser can on the one hand be improved with the same quantity of blown off steam, thereby obtaining deeper degassing, while on the other hand, for the same degree of degassing, it can suffice to blow off a smaller quantity of steam, thereby reducing heat losses.

A spray degasser according to the invention is therefore also characterized by separating means which separate off a compartment above and adjoining the spray screen in the boiler and onto which the gas outlet connects. It is noted that steam which passes through the spray screen at a warmer location can also reach this compartment by again passing radially in counterflow through a spray screen that is becoming colder and as a result of further condensation reaches the compartment enriched with oxygen. According to a preferred embodiment the compartment surrounds the sprayer. In a practical embodiment the separating means comprise a compartment wall which extends from a boiler wall to the spray screen.

If in preference the compartment wall is provided at its free end facing towards the spray screen with a foot extending along the spray screen, the passage of steam is elongated radially in counterflow through the spray screen towards the compartment, which is associated with a further enrichment with oxygen. The foot preferably extends beyond the compartment. Since the spray screen has a lowest temperature immediately after leaving the sprayer, and steam which passes through the spray screen at this location is thereby maximally enriched with oxygen, it is recommended that the compartment is located at a short distance from the sprayer. If the spray screen has no splash plate or plates bounding its periphery, or if the steam passing radially through the spray screen must preferably be further enriched with oxygen, it can be advantageous if the degasser contains in addition to the first compartment another, second compartment which likewise adjoins the spray screen and adjoins the first compartment on the other side.

For constructional reasons it is recommended that the second compartment surrounds the first compartment.

Mentioned and other features of a spray degasser according to the invention will hereafter be better com¬ prehended from the following description of a number of non- limiting embodiments of spray degassers according to the invention which are only given by way of example and to which the invention is in no way limited. In respect of these embodiments reference is made to the drawings, in which figure 1 shows a flow diagram for an electricity power station incorporating a spray degasser according to the invention; figure 2 shows a perspective partially broken away view of a spray degasser according to the invention from figure 1; figure 3 is a section along the line Ill-Ill from figure 2; figures 4, 5 and 7 show sections corresponding with figure 3 of other embodiments; and figure 6 is a perspective view of a variant of detail VI from figure 2.

Figure 1 shows a flow diagram for an electricity power station which comprises a steam boiler 1, a turbine 2, a condenser 3, a low pressure heating unit 4 which is connected to the condenser 3 via a pump 5, and a high pressure heating unit 6 which is provided with degassed water via the pump 7.

The spray degasser 8 according to the invention is situated between the low pressure heating unit 4 and the pump 7.

The spray degasser 8 (see figure 2) comprises a boiler 9 partially filled with liquid 10, in this case water. Reaching into the water 10 are steam pipes 11 which are provided in the portion thereof protruding into the water with holes out of which steam enters the liquid. The steam pipes 11 are connected to a steam conduit 13 which is connected to a vapour feed 14, in this case a steam feed 14 , which is connected to the turbine 2. The boiler 9 is further provided with spray means 15 which comprise a per se known sprayer 16 with which is formed a number of spray screens 17 lying one above the other. The spray means 15 further comprise a feed 18 for liquid for degassing which is connected to the low pressure heating unit 4.

In addition the boiler 9 is provided with an outlet 19 for degassed liquid and, finally, with outlets 20 for discharging removed gas into the atmosphere. Finally, it is possible via the pipe 121 to carry condensate from the high pressure heating unit 6 back to the degasser 8.

The spray degasser 8 according to the invention will be discussed in more detail with reference to figure 3.

Using the sprayer 16 a number of spray screens 17 are generated which are bounded on their periphery by a splash screen 21 and concentric splash rings 22 and 23 arranged thereon, from which the water falls downward.

Using separating means 24 according to the invention, in this case using a compartment wall 25 which reaches to the top spray screen 26 without thereby substantially coming into contact therewith, a compartment 27 is separated from the space above the spray screens. The outlets 20 for gas removed from the liquid debouch into this compartment 27. Steam 24 which is injected via the steam pipes 11, can reach the compartment 27 directly after passing through the spray screens 17, 26. Steam 28 which has entered the remaining space 29 via the warmer spray screen portions, can reach the compartment 27 indirectly by going under the compartment wall 25 through the colder spray screens as according to the arrow 30. Steam thus enters the compartment 27 which is relatively rich in gas removed from the liquid, in this case oxygen.

Figure 4 shows a degasser 31 according to the invention. In this case the spray means 24 according to the invention comprise a compartment wall 32 which separates the compartment 27 around the sprayer 16, and is provided at its end 33 facing towards the spray screens 17, 26 with a foot 34 which extends along the spray screen 26 into and outside of the compartment 27, while the spray screen 26 is not substantially disturbed. Steam which enters the compart¬ ment 27 indirectly as according to the arrow 30 is thus constrained to opt for a longer path through colder spray jet portions.

Figure 5 shows a spray degasser 135 according to the invention in its most simple form. Omitted in this case are means for bounding the spray screens 17 and 26, in particular the splash screen 21 and the splash rings 22 and 23. The advantages according to the invention can nevertheless be obtained because the compartment 27 from which gas separated from the liquid is removed via the outlets 20 is separated off around the sprayer 16, using a compartment wall 35 at a short distance therearound.

Figure 6 shows another spray degasser 36 according to the invention with which a compartment 27 is separated off around the sprayer 16 using the compartment wall 25 comprised of the separating means 24. In this case the separating means 24 according to the invention comprise a second compartment wall 37 with which a second compartment 38 is separated around the first compartment 27. Further omitted is the splash screen 21 but splash rings 39, 40 and 41 are retained. Preferably only gas with a small quantity of steam is removed from the compartment 27. If desired, it is likewise possible to discharge gas-enriched steam out of the compartment 38 via the gas outlets 42 and 43.

Finally, figure 7 shows a spray degasser 44 according to the invention. The compartment 45 has the form of an annular container 46 open to the bottom, which surrounds the sprayer 16. The sprayer 16 extends through and beyond a central container opening 117. An outer peripheral edge 48 is provided at the free end 49 with a foot 50. The container is fixed to the outlets 20. The container 46 thus hangs free of the boiler 9 above the spray screen 26.

Although the spray degasser is only described for degassing water in combination with its vapour phase steam, it will be apparent that other liquids can also be degassed insofar as use can be made of their vapour phase. For example, lower alcohols can be degassed in the same manner of non-condensing gases, such as oxygen, nitrogen and the like.

Claims

1. Spray degasser for removing gas from a liquid, comprising: i) a boiler; ii) at least one radial sprayer which is connected to a liquid feed for spraying the liquid for degassing as a spray screen in the boiler; iii) a vapour feed for the vapour phase of the liquid; iv) an outlet for gas removed from the liquid; and v) an outlet for degassed liquid; characterized by separating means which separate off a compartment in the boiler above and adjoining the spray screen and onto which the gas outlet connects.

2. Degasser as claimed in claim 1, wherein the compartment surrounds the sprayer.

3. Degasser as claimed in claims 1-2, wherein the separating means comprise a compartment wall which extends from a boiler wall to the spray screen.

4. Degasser as claimed in claims 1-3, wherein the compartment wall is provided on its free end facing towards the spray screen with a foot which extends along the spray screen.

5. Degasser as claimed in claim 4, wherein the foot extends outside of the compartment.

6. Degasser as claimed in claims 1-5, wherein the compartment is situated at a short distance from the sprayer.

7. Degasser as claimed in claims 1-6, characterized by at least one other second compartment surrounded by the separating means.

8. Degasser as claimed in claims 2-7, wherein the second compartment surrounds the first compartment.

9. Degasser as claimed in any of the foregoing claims, wherein the compartment is arranged freely suspended in the boiler.