Liquid heaters and vaporizers – Circulation
Patent
1994-12-20
1996-12-31
Bennett, Henry A.
Liquid heaters and vaporizers
Circulation
122 33, 1224064, 122451R, F22D 700
Patent
active
055884008
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method of generating steam in a forced-through-flow boiler or steam generator, in particular a BENSON boiler where during operation of the boiler, water is conveyed at least through a preheater, an evaporator and, if needed, a superheater, and during the start-up phase, and if desired in low load states, a water-steam mixture is conveyed to a separation tank, from which steam is withdrawn and separated feed water is supplied to the preheater.
With forced-through-flow boilers that are direct fired with fossil fuels, the evaporator, in which the water path is disposed downstream of the feed water preheater, contains a relatively small quantity of water which at the beginning of the formation of steam can be easily withdrawn via the separation tank.
Where waste heat steam generators, especially those disposed after gas turbines, are embodied as forced-through-flow boilers, care must be taken that due to the relatively great quantities of flue gas, evaporator heat transfer surfaces having a large water content are provided. Thus, during start-up of such steam generators, one must count on a large water discharge.
It is therefore an object of the present invention to provide a method of the aforementioned general type that is suitable in a straightforward manner to generate steam in a forced-through-flow steam generator that operates with waste heat.
SUMMARY OF INVENTION
This object is realized in that for a forced-through-flow boiler that operates with waste heat, the evaporator is divided into at least two sections, one of which being supplied with water at the beginning of the start-up phase and being included in a water circulation, while the other, starting from a dry state, is gradually supplied with water in a controlled manner until, in an operating state, water successively flows through both of the evaporator sections.
The evaporator section that at the beginning of the start-up phase is "dry" ensures that at the beginning of evaporation in the evaporator section to which water is supplied only that quantity of water is discharged that can be reliably handled by the separation tank.
In a preferred manner, that section of the evaporator that at the beginning of the start-up phase is kept in the water circulation is that section through which the gas from which the waste heat is to be extracted flows first.
It is furthermore expedient to dispose in the connecting line between the feed water flow-through means (e.g. the preheater) and the evaporator a three-way valve, the branch line of which, as a bypass line, leads to the evaporator section to which water is to be supplied.
It also appears to be expedient to associate with the outlet of the evaporator section to which water is not to be initially supplied a check valve in such a way that a back filling of the evaporator section via the bypass line is precluded.
BRIEF DESCRIPTION OF THE DRAWING
The present invention is also directed to an apparatus for carrying out the method.
The inventive method and the inventive apparatus will now be described in detail with the aid of the accompanying drawing which shows one exemplary embodiment of the inventive apparatus for carrying out the inventive method.
DESCRIPTION OF PREFERRED EMBODIMENTS
The drawing shows that a flue gas G, from which heat is to be withdrawn, flows through a waste heat tank or exchanger 1. The gas initially flows through a superheater 2, and then enters an evaporator section 3; thereafter, the gas flows through an evaporator section 4 and a feed water preheater 5 that is disposed downstream therefrom. The preheater 5 for feed water is supplied with feed water that is conveyed by a feed water pump 6 over a line 6a. Disposed in the connecting line 7 between the feed water preheater 5 and the evaporator section 4 is a three-way valve 8. The branch line 9 is connected with the connecting line 10 between the two evaporator sections 4 and 3. Disposed between the point of connection 11 and the evaporator section 4 in the line 10 is a
REFERENCES:
patent: 3120839 (1964-02-01), Glahe
patent: 3464393 (1969-09-01), Chambert
patent: 3576178 (1971-04-01), Zmola
patent: 4072182 (1978-02-01), Cheng
patent: 5189988 (1993-03-01), Budin et al.
Cesnik Friedrich
Stefan Ion
Bennett Henry A.
L. & C. Steinmuller GmbH
Ohri Siddharth
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