Furnaces – Process – Incinerating refuse
Reexamination Certificate
2002-04-02
2003-09-02
Lazarus, Ira S. (Department: 3749)
Furnaces
Process
Incinerating refuse
C110S190000, C110S243000, C122S040000, C208S080000, C165S104160
Reexamination Certificate
active
06612250
ABSTRACT:
This nonprovisional application claims priority under 35 U.S.C.§119(a) on Patent Application No. 20010676 filed in Finland on Apr. 2, 2001, which is herein incorporated by reference.
The invention relates to a method for defining the temperature at every point of a multiphase reactor within desired upper and lower limits.
In particular, the invention concerns a method of controlling the temperatures of an exothermic process carried out in a suspension of solids in a reactor system formed by a wind box, a vertical riser, which is essentially not cooled, a particle separator, at least one set of recycling channels, which are not cooled, and at least one set of recycling channels with a heat exchanger for controlling the temperatures of an exothermic process carried out in a suspension of solids in a multiphase reactor.
In this application, the “multiphase reactor” refers to a reactor, wherein, in addition to a continuous phase, which usually is a gas, at least one solid phase in particulate form is simultaneously present. Such a reactor system usually comprises a wind box with a gas feed nozzle, a vertical, essentially not cooled, riser tube connected with the wind box, generally having a vertical central axis and having a lower portion, which is equipped with a feed nozzle for solid matter, a particle separator fitted on the riser at the upper portion thereof for separating particles from the flow of the solids suspension in the riser, and an outlet pipe or opening or similar outlet means or channel for the separated particles for withdrawing the particles from the separator, and recycling channels connected with the particle separator, which channels can be used for recycling at least a part of the solid matter to the lower portion of the riser, whereby the recycling channels comprise at least one set of recycling channels, which are not cooled, and at least one cooled set of recycling channels.
In terms of fluid mechanics, the multiphase reactors can be divided into those with packed bed, fluidised-bed, and circulation states. In the packed state, the particles are in continuous contact with one another and gas flows between the particles. If the falling speed of a single particle is greater than the voids content velocity of the gas, the volume fraction of the particles can settle at such a value that any supporting reactions between the particles disappear, whereby the system sets in the fluidised state. In the circulation state, the falling rate of a single particle is lower than the voids content velocity of the gas.
The processes with a circulation state are further divided into those, where both gas and the particles travel once through a riser tube and into those, where the particles are returned back to the lower part of the riser tube. Regarding the latter systems with a circulation state, the Circulating Fluidised Bed (CFB) is the most well known. The necessary parts of the CFB are a vertical riser tube or riser, a particle separator, and a return pass. Furthermore, its essential parts comprise a gas distribution plate and often a generally pneumatic device that controls the solids flow of the return tube. Invariably, the particle separator is a cyclone, the shape and structure of which are defined, among others, in accordance with manufacture technology compromises. The purpose of the return tube is to return the solids separated in the cyclone back to the lower part of the riser.
As the effect of the temperature on the final result of the process is crucially important irrespective of the type of reactor, efforts should be made to maintain the temperatures in all parts of the reactor and in all conditions within a required temperature window.
Regarding the known reactor types, the CFB reactors offer prerequisites which have the best starting points for solving any problems related to the control of temperatures. Cooling surfaces are fitted in the riser chamber, by means of which, when operating on a nominal power and fuels, the temperature level of the reactor settles approximately at the desired level. In the CFB reactors, heat transfer can be influenced to a limited extent by the amount of particles in the riser tube. An example of an invention based on this is the FI Patent Application No. 851296, which makes it possible to maintain the temperature of a certain part of the riser chamber within the desired range of operation, if operation is carried out near the design values. The PCT Application No. PCT/SE83/00089 discloses an invention, wherein by adjusting the solids flow going through the cooled riser tube, efforts are made to keep the temperature of the fluidised bed within the permitted limits.
The 1-point temperature control of both inventions mentioned above is defective and results in the desired result only when many conditions are fulfilled. Both the above-mentioned inventions are also characterized in that heat transfer in them mainly takes place in the riser tube.
It is also known in the art to place two or more recycle channels in parallel and to provide at least one of them with a heat exchanger, to which a part of the solids separated in a cyclone is directed based on the temperature of a specific point of the riser. Examples of embodiments of this type are disclosed in FI Patent Application No. 842098 and U.S. Pat. No. 4,552,203.
FI Patent Application No. 842098 discloses an apparatus having at least one cooled and at least one not cooled recycle channel fitted between the cyclone separator and the reaction chamber, the flows of which are being adjusted with the aid of regulators at the upper and lower ends of the set of channels. It can be seen from the description of the patent application that the invention concerns “regulation of the combustion temperature to value in the range of 800 to 900° C”, i.e. 1-point regulation.
U.S. Pat. No. 4,552,203 concerns an embodiment, which essentially is the same as the one of FI Patent Application 842098 and which differs therefrom mainly with respect to the field of application and the technical layout of the apparatus. Because the technical solution of U.S. Pat. No. 4,552,203 primarily concerns carburators (substoichiometric oxidation), it does not deal with any cooling of the reaction chamber. In carburators, cooling is generally to be avoided, whereby the need for cooling is either small or nonexistent. The regulation of the temperature level of carburators is usually based on an adjustment of the stoichiometry of the oxidation process. The method according to U.S. Pat. No. 4,552,203 is characterized in that even if several separate control signals are transmitted from the regulating means to the regulators of the solids flow, the incoming control signal of the regulating means only comprises one temperature signal. This means that the separate control signals transmitted from the regulating means are determined by various correlations derived by control engineering and the embodiment is actually based on 1-point temperature regulation. Thus, not even the invention disclosed in US Patent Specification 4,552,203 solves the problem relating to a control of the temperature difference over the reaction chamber.
The fludized bed heat exchanger arranged in the second recycle channel of the apparatus of U.S. Pat. No. 4,552,203 is in practice problematic as far as erosion is concerned. As regards heat transfer, it is also disadvantageous since the heat-releasing solids are almost in isothermic state because of efficient mixing, which minimizes the average temperature difference.
The cooler for the recycle channel disclosed in FI Patent Application No. 842098 is thermally disadvantageous and prone to erosion because the velocity of the free-falling solids becomes very high and the flow is turbulent. Since the total amount of recycled solids is not known, it is possible to end up in a situation, in which either the lower part of the riser channel is cooled too much by the cooled solids recycled from the fluidized bed cooler, or not enough energy is transferred to the heat exchanger of the recycle channel.
It is
Ruottu Lauri Tapio
Ruottu Seppo Kalervo
Einco Oy
Lazarus Ira S.
Rinehart K. B.
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