Liquid heaters and vaporizers – Miscellaneous
Reexamination Certificate
2001-05-18
2002-10-29
Wilson, Gregory (Department: 3749)
Liquid heaters and vaporizers
Miscellaneous
C165S104160, C165S104180
Reexamination Certificate
active
06470833
ABSTRACT:
The present invention relates to a method and an apparatus in a fluidized bed reactor.
The furnace of a conventional fluidized bed boiler comprises an inner section having a rectangular horizontal cross section and defined by four side walls, a bottom and a roof, in which inner section the bed material containing at least solid particulate fuel material is fluidized by means of fluidization gas introduced through the bottom, mostly by primary air required by exothermal chemical reactions in the boiler. The side walls of the furnace are typically also provided with conduits for the introduction of at least fuel and secondary air.
The walls of the furnace are usually made of panels formed of finned tubes, whereby the energy released from the chemical reactions of the fuel is used for vaporization of the water flowing in the tubes. Also, superheating surfaces are often arranged in the boiler to further increase the energy content of the steam.
When the aim is to manufacture a high-capacity boiler, a large reaction volume and a lot of vaporizing and superheating surfaces are required. The basal area of the boiler is directly proportional to the capacity of the boiler on the basis of the required volume and velocity of the fluidization area. As it is at least structurally disadvantageous to have a very long and narrow surface bottom, also the height of the boiler and the width of its bottom have to be increased in order to have a sufficiently large vaporizing surfaces on the side walls. To increase the height significantly can result in structural problems and increasing the width makes it more difficult to arrange a uniform supply of fuel and secondary air. In order to solve these problems, additional structures can be arranged inside the furnace to increase the vaporizing surfaces of the boiler.
The most conventional way to increase the vaporizing surfaces of the boiler is to arrange such on the partition walls extending from one side wall of the boiler to another. An arrangement of this kind is disclosed, e.g., in U.S. Pat. No. 3,736,908. Special openings have to be arranged in such partition walls in order to ensure the uniformity of the materials and processes in various parts of the boiler. Even if there were plenty of these openings, it is difficult, however, in the boilers having partition walls to reach the homogeneity required by the optimal efficiency and the minimization of environmental emissions. These problems are most apparent in the lower corners of the boiler being the most critical points in respect of the uniform performance of the boiler, and the number of these corners is unavoidably increased by the existence of partition walls extending from one side wall to another.
The water flow passing in two phases in the vaporizing pipes is a phenomenon difficult to control in complicated geometrical patterns. From this point of view, one problem associated with simple partition walls is that there, in contrast to the boiler's side walls, heat energy is transferred to the wall pipes from both sides. To get the vaporization and water circulation in the partition walls in balance with the vaporization in the side walls, the size of the partition wall pipes has to be larger or they have to be located more densely than in the side walls. To arrange partition walls, which can be relatively thin, considering their height, extending from the bottom of the furnace to the top thereof, can be difficult in a high boiler in view of achieving a sufficient rigidity for the walls.
It is known from the prior art also to provide the cooled partition walls with various kinds of elements necessary for the operation of the fluidized bed boiler. For example, U.S. Pat. No. 5,678,497 and International publication WO 98/25074 disclose arrangements where means for secondary air supply are attached to the cooled partition walls.
Instead of partition walls, it is also known to arrange other kinds of auxiliary structures inside the furnace used for producing steam and possibly for other operations as well. U.S. Pat. No. 5,070,822 discloses an arrangement, in which a cylindrical concentric particle separator, the outer casing of which is formed of a heat transfer surface, is arranged inside a cylindrical furnace. In the lower portion of the same structure, there are also elements for the introduction of fuel into the furnace. U.S. Pat. No. 4,817,563 discloses an arrangement, in which cooled upward tapering structures arranged in the lower portion of the furnace covering 40-75% of the furnace bottom are used for the supply of secondary air and fuel. U.S. Pat. No. 4,947,803 discloses a fluidized bed reactor where cooled cylindrical contact units are arranged. All these arrangements are, however, quite expensive and less applicable in a large scale fluidized bed boiler, and the auxiliary vaporizing surface provided by them is less significant.
It is an object of the present invention to provide a new and improved method and apparatus in a fluidized bed reactor.
It is thus an object to provide a new technical solution, by which fluidized bed boilers of various sizes can be provided with vaporizing surfaces and the above mentioned problems and defects of the prior art solved or minimized. An object is especially to provide a system to arrange vaporizing surfaces in large fluidized bed boilers.
It is a further object to provide a structurally simple and cost-effective apparatus eliminating or minimizing the above problems.
It is a further object to provide auxiliary vaporizing surfaces in a fluidized bed boiler so that as similar vaporization conditions as possible are created on all vaporizing surfaces.
It is still a further object to provide a fluidized bed reactor, in which a good mixing of materials and uniform process conditions in the furnace in spite of the auxiliary vaporizing surfaces and thus a good combustion efficiency and reduction of emissions are achieved.
In order to fulfill these objectives, the characteristics of the method and apparatus in a fluidized bed reactor in accordance with the present invention are set forth below in the claims.
The invention is especially applicable to a fluidized bed boiler. When applying the invention, vaporizing surfaces are arranged in the fluidized bed boiler so that mostly vertical chambers are arranged inside the furnace. In this specification of the invention and in the claims, the term ‘chamber’ refers to a structure surrounded by walls, inside which structure, a principally closed gas volume is formed. The walls are typically made of straight water tube panels formed of finned water tubes. The height of the chambers in a fluidized bed boiler is generally about the same as the height of the furnace, preferably at least 80% of the height of the furnace. The chambers extend preferably from the bottom of the furnace to the top thereof, whereby they can be used to reinforce the furnace.
When using an arrangement according to the present invention, a desirable amount of chambers can be arranged in the furnace of the fluidized bed boiler and, therefore, the size of the boiler is not restricted by the required vaporizing surfaces. In a small boiler, there can be preferably, e.g., one or two chambers according to the present invention. In a large boiler, there are preferably a plurality of, e.g., three, four, six, eight, even up to ten or more chambers. The chambers can be arranged one after the other, in two or several rows, or in another order considered best in each particular case. In a fluidized bed boiler, preferably about 20-70%, more preferably 40-60%, of the boiler's vaporizing surface is arranged in the chambers, according to the present invention.
The chambers arranged according to the present invention are typically two-dimensional in cross section, whereby two opposite walls thereof are spaced at a short distance from each other. Both sides of the opposite vaporizing surfaces are not substantially heated, but only one side thereof is. Therefore, the conditions for all vaporizing surfaces, i.e., for the vaporizing surfaces of the boil
Fitzpatrick ,Cella, Harper & Scinto
Foster Wheeler Energia Oy
Wilson Gregory
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