Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Fluidized bed
Patent
1997-03-14
1999-06-08
Zimmerman, John J.
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Fluidized bed
110263, 427455, F23M 508, F23C 1102, F27B 1504, B04C 5085
Patent
active
059102900
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arrangement in a wall in a fluidized bed reactor. By means of such an arrangement, a very reliable and abrasion-resistant wall is achieved.
The present invention also relates to a method of coating in a fluidized bed reactor a wall. By means of such a method, a long-lasting abrasion-resistant coating for the wall is achieved.
2. Description of the Related Art
The abrasion of various walls is a harmful phenomenon in many industrial applications. Various transport systems, such as pneumatic fuel conveyors and reactors in which various mixtures are treated, are often subjected to abrasion, even hard such abrasion during their operation. Especially gas suspensions containing solids can cause excessive abrasion. The pneumatic transport, for instance, of solid fuel, such as coal and peat, subjects the parts of the transport channels to hard abrasion. Many points of discontinuity, bends or elbows cause local abrasion points in the flow system.
Also, in fluidized bed reactors in which the fluidizing velocity is so high that the reactor functions as a so called circulating fluidized bed reactor, the abrading effect of the circulating material on the walls of the reactor, especially at certain points, has been found to be a serious problem.
Fluidized bed reactors are used in a variety of different combustion, heat transfer, chemical and metallurgical processes. Depending on the process, various bed materials are fluidized and/or circulated in the system. In combustion processes, the fluidized bed consists mainly of particulate fuels, such as coal, coke, lignite, wood, wood waste, coal waste or peat as well as other particulate matter, such as sand, ash, sulphur absorbent, catalysts or metal oxides.
A fluidized bed reactor generating heat comprises an upright reactor chamber having substantially vertical outer walls. The walls are made as waterwalls, i.e., tube walls in which vertical tubes are connected to each other by flat plate material or "fins". The walls in the lower part of the reactor are usually refractory lined so as to withstand heat and erosion. The violent turbulence and abrading effect of the particles and the relatively high density of solid material result in highly erosive conditions, particularly in the bottom part of the reactor.
In certain regions of the reactor, there are both downward and upward flows of bed material. The absolute mass flow varies in radial as well as in axial directions of the reactor chamber. The downward mass flow is at its biggest near the outer wall. As the density of particles increases in the downward direction in the rector chamber, the layer of particles flowing down along the outer walls also thickens. The downward flowing layer can have a thickness of up to 10-50 mm, or even greater. Any change in the flow direction of the downward flowing layer causes erosion.
The upper edge of the refractory lining in the waterwall construction forms a shoulder in the reactor chamber, which causes a vortex in the downward flowing layer of bed material. The direction of the layer flowing vertically downwards along the fins connecting the tubes is partly changed, whereby the layer begins to flow along the edge of the refractory lining. The vortex and the horizontal flow of particles along the edge cause heavy erosion of the waterwall tubes, especially in those parts that are close to the lining. The erosion is in particular problematic in boilers using solid fuel and in which the conditions are highly conducive to erosion.
The tubes in the waterwall have to be inspected from time to time and, if needed, be recoated with protective material or replaced by new tubes. Extensive shutdown time is required to cut off the damaged tubes and to install new ones or to renew the protecting surface. Both alternatives are difficult, expensive and time consuming processes.
While the problem with erosion of tubes in fluidized bed reactors is well known and various solutions have been suggested to minimize ero
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Foster Wheeler Energia OY
Zimmerman John J.
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