Liquid heaters and vaporizers – Circulation – Once through
Patent
1994-03-11
1995-03-21
Yuen, Henry C.
Liquid heaters and vaporizers
Circulation
Once through
1224511, 1224797, F22D 700
Patent
active
053986440
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The technical field to which this invention relates is temperature measurement of the fluid at the outlet from the evaporator in a once-through boiler of so-called benson type. The invention comprises a method for such measurement and a device for carrying out the method.
BACKGROUND OF THE PRESENT INVENTION
A benson boiler comprises an economizer, an evaporator, a steam/water separator, a number of usually two, superheaters and an intermediate steam cooler as well as possibly one or more reheaters with associated steam coolers.
Benson boilers exist in a number of different designs. Most common in existing plants is that the evaporator consists of membrane walls which constitute the walls of a furnace. At the top of this furnace a flue gas channel starts which passes the flue gases to the chimney. At the very transition from furnace to flue gas channel, radiation superheaters are located, the main heat absorption of which consists of radiation from the flames in the furnace. Behind the radiation superheaters inside the flue gas channel, convection superheaters are located, which take up the main part of the heat via convection. Further towards the interior of the flue gas channel, where the flue gas temperature is lower, the economizer is placed. In this type of plants, the fuel is injected either in finely-divided form via special burners, whereby it is finally burnt freely floating in the furnace, or it is injected in larger lumps on a firing grate at the bottom of the furnace, whereby the volatile constituents escape and are burnt in the furnace whereas the solid constituents are burnt down on the firing grate.
Recently it has become increasingly more common to use so-called fluidized bed boilers where the main combustion of the fuel takes place in a bed consisting of absorbent and ashes. The bed is enclosed in a bed vessel built up of membrane walls in the same way as the furnace in a conventional boiler. The combustion air is supplied from below through a number of air nozzles, which causes the bed to become fluidized. At a moderate gas speed in the bed vessel, the particles will remain and a so-called bubbling bed is obtained. At higher gas speeds, the particles will accompany the gas and are separated in cyclones so that they can be returned to the bed vessel. The latter is called a circulating fluidized bed. The pressure in the bed may in some cases be considerably higher than the atmospheric pressure. One example of this are the so-called PFBC steam boilers in which a gas turbine uses a pressurized fluidized bed boiler as combustor. Common to the fluidized bed boilers is that the heat surfaces, that is, economizer, evaporator, superheaters and reheaters, are at least partly located in the bed itself. The PFBC boilers constitute an extreme case since the entire evaporator, superheater and reheater surfaces consist of one tube bundle placed in the bed whereas the bed vessel wall is almost to be compared to an economizer. Atmospheric fluidized bed boilers are more like a conventional boiler since the bed vessel wall constitutes part of the evaporator and the superheaters are at least partly located in the convection parts downstream of the bed vessel.
A benson boiler operates in the following way. Feedwater is supplied to the economizer where its temperature is raised. At the outlet from the economizer there should be a certain margin with respect to the boiling point. From the economizer the water is supplied to the evaporator where it is evaporated completely and superheated somewhat. The slightly superheated steam is passed via the steam/water separator to a first superheater where the temperature of the steam is raised. After the first superheater the steam passes through a first controllable steam cooler where the steam is cooled somewhat before it is raised to the desired final temperature in a second superheater. After that, the steam is passed to a high-pressure turbine after which it is returned to the reheater of the boiler via a second controllable steam cooler. I
REFERENCES:
patent: 2800887 (1957-07-01), Profos
patent: 3004529 (1961-10-01), Argersinger et al.
patent: 5037766 (1994-05-01), Pearce
Nilsson Karl-Johan
Schill Stefan
ABB Carbon AB
Yuen Henry C.
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