EP2706293A2

EP2706293A2 - Boiler for liquid metal heating in heating systems, especially chemical reactors

Info

Publication number: EP2706293A2
Application number: EP20120461541
Authority: EP
Inventors: Piotr Sarre
Original assignee: Biopal Spolka Z Oo
Current assignee: Biopal Spolka Z Oo
Priority date: 2012-08-01
Filing date: 2012-09-07
Publication date: 2014-03-12
Also published as: PL400215A1; PL222997B1

Abstract

Body of the boiler for heating of liquid metal in heating systems, especially of chemical reactors, is built from a bundle of pipe couples of "pipe in pipe" type 8 and 6, has at least two liquid metal chambers created between perforated bottoms 1 and 2 and also 3 and 4 connected with this bundle of pipe couples, whereas at least one of liquid metal or flue gas chambers is equipped with expansion compensator. Chambers are supported in such way, that they can freely and independently displace on beds 19 of supports 18, and the whole boiler can displace on rolls under feet of supports 20.

Description

The presently disclosed subject matter relates to the boiler included in heating system, especially designed for membrane heating of chemical reactors, in which liquid metal is used as a heat carrier between boiler and heater.
In scientific and patent literature liquid metal as heat carrier appears practically exclusively as a working medium intermediating in heat exchange process between nuclear fast reactor and generating electric power steam turbine system, and recently also in processor cooling systems. In power systems nuclear reactor plays a role of boiler and steam generator - a role of heat sink. Dozens descriptions of various structural solutions of such arrangements for heat transfer can be found in patent literature, as for example US 4515109 , US 6904754 , US 2865827 , US 3033538 , US 4324617 .
In heating systems of chemical reactors there is, however, technological need of their periodical tuning on and turning off, which is giving rise to completely different problems, associated with phase transition of a heat carrier from solid state to liquid and inversely. Technical problem connected with stress changes in fitting points of heat exchangers pipes in false bottoms is rather hardly recognized in case of chemical reactor heating pot. Only in few publications, as for example US 3336974 , this problem is mentioned in some scope.
Process of delivery of large amounts of heat at relatively small temperature gradient between working fluid and reaction mixture and at high process temperature, excluding using any organic fluids as heat carriers, requires using liquid salts or liquid metal, as for example in patent PL205686 . Eutectic alloys, characterized with possibly low melting temperature, are mostly useful for this goal, if boiler design ensures sufficient strength for bimetallic stresses and enables intensive heat transfer from flue gas to metallic heat carrier flowing through boiler in its whole volume. It is also important to carry out the heating process using possibly small amount of heat carrier in the circuit due to its high price.
On the basis of tests of heating system of chemical reactor for depolymerization process of plastic waste material carried out in industrial conditions the design of boiler for heating of liquid metal has been developed and realized. This design is a subject matter of presently disclosed invention.
Body of boiler for liquid metal heating in heating systems especially of chemical reactors, is built from a bundle of pipe couples of "pipe in pipe" type and possess at least two liquid metal chambers created between perforated bottoms connected with this bundle of pipe couples, where at least one of liquid metal chamber or flue gas chamber is equipped with elongation compensator and chambers are supported in such way, that they can freely and independently displace on supporting beds, and the whole boiler can displace on rolls mounted under support feet. Moreover, the boiler is characterized with it, that elongation compensator is built-in almost one liquid metal chamber, and if compensator is built-in one of flue gas chambers it works effectively for compression. The jacket of the boiler separating one of heating media from surroundings is built from many separate surfaces. The boiler has a stock chamber, connected freely with heating circuit of the boiler, with capacity greater than the capacity of heating circuit apart from the boiler. Liquid metal is transferred between chambers connected with bundle of pipes of "pipe in pipe" type in spaces between flue gas pipes and jacket pipes, where boiler design enables exchanging the route of those heating media.
The boiler has at least two chambers for liquid metal, connected with bundle of pipes of "pipe in pipe" type, where each outer pipe is a separate boiler jacket separating one of heating media from the surroundings, thus creating from the sum of external surfaces of pipes of that bundle a multi-surface boiler jacket. Those chambers are confined with even number of perforated bottoms and with surfaces perpendicular to them, with compensating components built-in some of them. External perforated bottoms of liquid metal chambers are connected with flue gas pipes passing favourably inside bundle pipes, where it is also possible to lead flue gas in the section between a couple of pipes from the bundle and leading the liquid metal in the internal pipe. Metal flows in favourable way between liquid metal chambers in areas of annular or close to annular shape between jacket pipes and flue gas pipes. Chambers are also provided with connector pipes for outflow and inflow of the metal to and from heating circuit. The whole boiler is supported loosely on support beds and supports are founded on rolls enabling rolling displacement of the structure. Boiler is also provided with storage chamber enabling accumulation of whole circulating metal in the boiler during turning off the installation, connecting pipe for protective atmosphere and overflow connection for short circulation during boiler start-up.
Boiler design according to the present invention provides very well conditions for heat transfer from flue gas to liquid metal and simultaneously eliminates all stresses which could destroy boiler structure, especially during start-up and turning off the boiler. These features are completed by very small capacity of heat exchanger part of the boiler, liquid metal is forced through, thus enabling increase of multiplicity of liquid metal circulation and increase of its linear velocity, providing also much greater heat flux delivered to heaters.
The presently disclosed subject matter is depicted in example of embodiment in following Figures, where longitudinal section of mostly typical solution of boiler design is depicted in Fig. 1 and its transverse section in Fig.2, whereas Fig. 3 presents the scheme of solution with exchanged flue gas and liquid metal circulations. Such a solution is possible, however due to worse conditions for uniform leading of flue gas and hotter medium at multi-surface jacket of the boiler, it is less advantageous.
Boiler according to the present invention is provided with four perforated bottoms 1, 2, 3 and 4, of which external ones 1 and 4 are connected by means of flue gas pipes 6 and internal perforated bottoms 2 and 3 are connected by means of pipes of greater diameter, constituting multi-surface jacket 8 of the boiler. Perforated bottoms are closed, in pairs with cylindrical surfaces 16; moreover between bottoms 1 and 2 a circular compensator 7 is built-in. A tube 15 equipped with a valve is welded into cylindrical surface connecting perforated bottoms 1 and 2, used for venting this liquid metal chamber during filling up of heating circuit with liquid metal. A support screen 5 preventing deformation of hot pipes in the course of long-term operation of the boiler is mounted in a half of the lengths of jacket pipes 8. Liquid metal chamber created between perforated bottoms 1 and 2 is equipped with connector pipe 10 leading liquid metal from heating circuit to the boiler, and chamber between perforated bottoms 3 and 4 is provided with connector pipe 9 to which liquid metal circulating pump is connected.
On the top of liquid metal chamber, between perforated bottoms 3 and 4 a storage chamber 11 is added of capacity required for storage of metal from the whole given heating circuit. This chamber is provided with overflow connection 12 for short circulation of liquid metal used during boiler start-up and connection pipe 14 for connecting protective atmosphere protecting liquid metal against oxidation. Chamber 11 has also a charging hole closed with cover 13. Mobile flange 17 connects the boiler with furnace chamber. Boiler rests freely on beds 19 of supports 18 and these supports have rolls facilitating displacement of the whole structure, mounted under their surfaces 20. Rolls facilitating displacement at beds 19 are also foreseen for greater weights of the boiler.
After turning the burner on with properly selected small power, flue gas is heating at first perforated bottoms 4, pipes 6 and perforated bottom 1. After obtaining at mentioned above boiler components temperature higher by 10 - 15 °C than melting temperature of used eutectic metal alloy, very thin layer of it is melted, eliminating bimetallic stresses caused by different linear expansion of eutectic alloy and structural material of the boiler. Up to this moment those stresses are taken over by compensator 7 and elastic deformations of thinner perforated bottoms 1 and 4. After melting the entire metal in the boiler burners' power is increased and temperature of liquid metal is being raised. Due to different length of pipes 6 and 8 they expand unequally, what is taken over by compensator 7. Expansion of pipes 6 and 8 causes that liquid metal chambers, included between perforated bottoms 1 and 2 and also 3 and 4, move away each other. To avoid stresses in boiler structure caused by this reason, both chambers have freedom of displacement on beds 19 of supports 18. Full independence of moves of the whole boiler is provided by rolls located under feet 20 of supports 18. The boiler is connected with flue gas pipe by means of standard longitudinal compensator working for compression. Each liquid metal chamber of the boiler has one connector pipe for connection to serviced heating installation. Lower connector pipe 9 is connected to liquid metal pump and other connector 10 works as an inlet of liquid metal returning from the heating system. On the top of one of liquid metal chambers a storage chamber 11 is added, capacity of which enables to store of liquid metal required for filling the whole heating circuit. In case of shutting off the installation it enables withdrawing almost whole liquid metal from heaters to the boiler, which radically facilitates another start-up. Depending on needs it is possible to install such stock chambers in the larger amount than one. It is also possible design of the boiler based on the same structural principles, but with circulation of heating media as shown in Fig.3.

Claims

Boiler for liquid metal heating in heating systems, especially chemical reactors, characterized in that the body of said boiler is built of a bundle of pipe couples "pipe in pipe" type 8 and 6, and comprises at least two liquid metal chambers created between perforated bottoms 1 and 2 as well as 3 and 4 connected with this bundle of pipe couples, where at least one of liquid metal chambers or fumes gas chamber is equipped with elongations compensator and chambers are supported in such a way, that they can freely and independently displace on beds 19 of supports 18, and the whole boiler can displace on rolls mounted under support feet 20.
Boiler according to claim 1, characterized in that a circular compensator 7 of thermal expansions working for tension is built-in at least in one liquid metal chamber.
Boiler according to claim 1, characterized in that jacket pipes 8 separating one of heating media from the surroundings is built of many separate surfaces.
Boiler according to claim 1, characterized in that it has a storage chamber 11. Freely connected to heating circuit of the boiler, capacity of which is greater than the capacity of heating circuit out of the boiler.
Boiler according to claim 1, characterized in that liquid metal is transferred between chambers connected with a bundle of pipe couples of "pipe in pipe" type in the space between flue gas pipes 6 and jacket pipes 8, whereas boiler design enables exchanging the route of those heating media according to the scheme shown in Fig. 3.