Liquid heaters and vaporizers – Supports
Patent
1992-12-15
1994-07-19
Favors, Edward G.
Liquid heaters and vaporizers
Supports
122 4D, F22B 3724
Patent
active
053298926
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to an energy plant with a bed vessel in which a fuel is burnt in a fluidized bed of particulate material, the bed material usually being a mixture of fuel and a sulphur absorbent. The combustion may take place at a pressure close to the atmospheric pressure or at a considerably higher pressure. In the latter case, the pressure may amount to 2 MPa or more. Combustion gases generated in the bed vessel are then utilized in one or more turbines for driving a compressor for supplying the bed vessel with combustion air and a generator which delivers current to an electricity supply network. An energy plant with combustion at elevated pressure is internationally generally referred to as a PFBC energy plant, the letters "PFBC" being the initials of the English expression "Pressurized Fluidized Bed Combustion". In such a plant the bed vessel and usually also a cleaning plant for combustion gases are enclosed within a pressure vessel.
BACKGROUND OF THE INVENTION
In energy plants of the above kind the walls of the bed vessel are subjected to heavy forces because of the pressure difference between the inside and the outside of the bed vessel. In a PFBC energy plant with the bed vessel enclosed in a pressure vessel and being surrounded by compressed combustion air, a pressure difference between the space in the pressure vessel outside the bed vessel and the space inside the bed vessel arises because of the pressure drop in inlet channels and nozzles for the supply of air for fludization of a bed material in the lower part of the bed vessel and a pressure drop in the fluidized bed. This pressure difference may amount to about 0.1 MPa. The side walls of the bed vessel may have the size 10.times.15 m, so the forces acting on the bed vessel walls will be very great. This, in addition to a high temperature, entails design problems which are difficult to deal with.
The walls of the bed vessel consist of panels of tubes which are connected to intermediate fins. These walls, often called panel walls, may be cooled by feedwater circulating in the tubes. The panel walls are incapable of absorbing the loads caused by the pressure difference between the two sides of the walls. The bed vessel is therefore surrounded by a force-absorbing frame structure. The bed vessel is connected to this frame structure by means of force-transmitting bars or links. In case of a cold plant, the frame structure and the bed vessel have the same temperature. In operation, the bed vessel wall assumes the temperature of the circulating coolant and the frame structure the temperature of the surrounding air. Depending on temperature differences between the bed vessel wall and the force-absorbing frame structure, the bed vessel may expand or contract in relation to the frame structure.
The connection between the frame structure and the bed vessel must be designed in such a way that the difference in expansion does not give rise to impermissible stresses in the bed vessel, the frame structure or the connecting members between these.
German Offenlegungsschrift 2 055 803 shows one way of carrying out the connection between a conventional boiler and a force-absorbing frame.
Another known design already occurs in the PFBC energy plants existing at the Varta plant in Stockholm and at Escatron in Spain. In these plants, a stiffening of the panel walls has been obtained by means of continuous support frames with stiff corners extending horizontally around the bed vessel. These frames have been made in the form of box girders welded-together at the corners and they have been given the ability to absorb thermal movements in the bed vessel, among other things by means of an arrangement with auxiliary beams in the corners of the bed vessel, as shown in European patent application 87117795.2.
The factors which must be taken into consideration when dimensioning beams in a frame construction of the kind mentioned are, among other things, horizontal bending stress caused by forces due to pressure difference along the beam from the
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ABB Carbon AB
Favors Edward G.
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