Liquid heaters and vaporizers – Circulation
Patent
1994-12-28
1996-11-19
Bennett, Henry A.
Liquid heaters and vaporizers
Circulation
122488, 122489, 122491, 1224481, F22D 700
Patent
active
055752446
DESCRIPTION:
BRIEF SUMMARY
SUBJECT OF THE INVENTION
The invention relates to a heat recovery boiler in which the water circulation is ensured without resorting to a thermal siphon effect.
It also relates to a process for the optimum use of such a boiler, for example in an electrical power station.
TECHNOLOGICAL BACKGROUND
Heat recovery boilers necessarily comprise means for ensuring the circulation of fluids.
They find an industrial application in so-called combined-cycle electrical power stations and in so-called cogeneration plants for producing electricity and steam simultaneously.
They can be employed in other conventional applications.
Such boilers are used to recover the large quantity of heat contained in the exhaust gas stream of a gas turbine and to convert water into steam. The latter is then itself employed in a steam turbine which drives an alternator.
STATE OF THE ART
Boilers are fed with water by means of a feed pump. They comprise one or more steam generating circuits, each including an evaporator device and a water/steam separating flask. These are mutually connected by conduits in which water circulates at the beginning and then a water/steam mixture. A number of steam generating circuits can be installed in a boiler in order to supply steam at different pressures and thus to improve the overall efficiency of the plant.
Heat exchanges between the gases originating from the gas turbine and initially water and then subsequently the water/steam mixture circulating in the boiler take place at the evaporator device. The latter consists of circuits of finned pipes fitted, depending on the case, vertically or horizontally, and installed in a stream of hot gases originating, for example, from a gas turbine. Conventionally, when it is running, each evaporator device is fed with water from the corresponding water/steam separating flask via a so-called entry manifold, to which are welded the entries of the pipes constituting this evaporator device and a so-called exit manifold which collects the water/steam mixture obtained. This exit manifold is connected to the same separating flask, thus creating a closed circuit.
The number of pipe circuits mutually connecting the so-called entry and exit manifolds depends on the size and the operating conditions of the boiler.
The pressure drop in the water between the entry and exit manifolds of the evaporator device is particularly a function of the configuration of the conduits. According to different alternative forms, the pipes of the evaporator device can be arranged either vertically or horizontally.
Essentially two types of boilers are distinguished as a function of the type of water circulation in the circuits.
The circulation is said to be "natural" or by a thermal siphon effect, when the water circulates in the boiler by virtue of the density difference of the water when it changes from the liquid phase to the vapor phase. Natural-circulation boilers are described, for example, in patents U.S. Pat. No. 2,031,423 and U.S. Pat. No. 2,702,026.
U.S. Pat. No. 2,257,358 describes a steam generator device with circulation using thermal siphon in which a device referred to as an ejector, consisting of two coaxial conduits and not described otherwise is fitted at the exit of a water/steam separating flask to accelerate the thermal siphon effect.
The device described includes two independent circuits in which the water to be heated circulates in horizontal pipes from the bottom upwards while the combustion gases circulate from the top downwards, said separating flask being fitted above the boiler.
As indicated, a circulation using thermal siphon is produced under the combined effect of a "natural" and artificially accelerated circulation.
It should be noted that the device referred to as an ejector is relatively unrefined and not controllable. Moreover, it is fitted in the bringing (downward) line of one of the circuits originating from the separator flask.
Patent application EP-A-0357590 describes a boiler with horizontal pipes, operating on the basis of a natural water circulati
REFERENCES:
patent: 2031423 (1936-02-01), Keenan, Jr.
patent: 2257358 (1939-08-01), Wightman
patent: 2702026 (1955-02-01), Dalin
patent: 4151813 (1979-05-01), Gorzegno et al.
patent: 4531479 (1985-07-01), Gilbert
Bennett Henry A.
Cockerill Mechanical Industries S.A.
Ohri Siddmarth
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