Gas separation: apparatus – Degasifying means for liquid – Liquid flow slinger – spreader – deflector – disperser – or...
Patent
1993-05-17
1996-08-27
Spitzer, Robert
Gas separation: apparatus
Degasifying means for liquid
Liquid flow slinger, spreader, deflector, disperser, or...
96206, 96207, 96215, 96220, B01D 1900
Patent
active
055497373
DESCRIPTION:
BRIEF SUMMARY
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 W. Wiemer, 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 FR-A-2 379 753.
U.S. Pat. No. 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 determines 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 characterized in that the sprayer compartment comprises a gas compartment above and adjoining the colder spray screen, delimited by a gas compartment wall extending from a boiler wall to the colder spray screen, onto which the outlet in the sprayer compartment 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 w
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Lacey, M. G., et al., Deaerator design considerations, Engineering and Boiler House Review 76(12):410-417, 1961.
Spitzer Robert
Stork Ketels B.V.
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