Combustion – Process of combustion or burner operation – In a porous body or bed – e.g. – surface combustion – etc.
Reexamination Certificate
1999-05-17
2001-09-25
Price, Carl D. (Department: 3743)
Combustion
Process of combustion or burner operation
In a porous body or bed, e.g., surface combustion, etc.
C431S170000, C110S204000, C110S205000, C110S343000, C110S348000
Reexamination Certificate
active
06293781
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of and an apparatus for decreasing attack of detrimental components of solid particle suspensions on heat transfer surfaces particularly in heat transfer chambers in fluidized bed reactors.
The present invention is particularly applicable for recovering heat from solid particles in circulating fluidized bed reactors, but can also be applied to other fluidized bed reactors. Such circulating fluidized bed reactors comprise a reactor or processing chamber, such as a combustion chamber, having a fluidized bed of solid particles therein, and a heat transfer chamber (HTC), being in solid particle communication with the processing chamber and having heat transfer surfaces disposed therein. The heat transfer chamber may be connected in various ways and various locations to the processing chamber so that there is solid particle exchange between the chambers. The heat transfer chamber may in some special case even be formed within the processing chamber itself.
BACKGROUND OF THE INVENTION
Fluidized bed reactors, such as circulating fluidized bed reactors, are used in a variety of different combustion, heat transfer, chemical and metallurgical processes. Typically heat, originating from combustion or other exothermic processes, is recovered from the solid particles of the fluidized bed by using heat transfer surfaces. Heat transfer surfaces conduct the recovered heat to a medium, such as water or steam, which transfers the heat from the reactor.
The heat transfer surfaces are typically located in the processing chamber or within a convection section arranged in the gas pass after the processing chamber or, in circulating fluidized bed reactors, within a particle separator. Additional heat transfer surfaces are often arranged in a separate heat transfer chamber (HTC), which may be a part of the processing chamber, a separate chamber adjacent to the processing chamber or, in circulating fluidized bed reactors, part of the solid particles recycling system.
An HTC is typically a bubbling fluidized bed, which comprises inlet means for introducing a continuous flow of hot solid particles from the processing chamber into the HTC, heat transfer surfaces, and outlet means for continuously recycling solid particles discharged from the HTC into the processing chamber.
Corrosion is a factor which must always be taken into account when designing heat transfer surfaces. It is especially important when the heat transfer surfaces are in a fluidized bed reactor utilized in processes which use or produce corrosive materials. An example of such is burning difficult fuels, such as straw or RDF, which contain highly corrosive impurities, e.g., chlorides. Corrosive impurities are then also present in the fluidized bed material, and thus come into contact with the heat transfer surfaces in an HTC, leading to rapid corrosion of said surfaces. For example, chlorine in the bed material may cause chloride corrosion on the heat transfer surfaces.
Corrosion problems are especially severe when the temperature in an HTC is high, e.g., due to afterburning, which may easily take place when the HTC is directly connected to the furnace. Afterburning or other chemical processes in an HTC can also lead to a reducing atmosphere, where Co-corrosion easily takes place. Reducing conditions together with chloride deposits are especially susceptible to increased corrosion attack.
Corrosion and erosion based wastage of metals is an essential problem in all bubbling fluidized beds, and many efforts have been made to minimize it. Normal remedies against corrosion are changes in the metal surfaces and their temperatures. Surface treatments, such as chromising, nitriding, or coating with tungsten carbide are in some cases effective. Because all corrosion mechanisms are temperature dependent, corrosion of the heat transfer surfaces can to some extent be avoided by locating the surfaces at appropriate positions in the system.
However, surface treatments are not always feasible, as conditions and temperatures may vary at different locations and stages of the processes. Also, when choosing operating temperatures, the corrosive impurities present in each specific system have to be taken into account. These impurities may vary when using different parameters, such as different fuels, in the process. Therefore, procedures to minimize the risk of corrosion by reducing the concentrations of the actual corrosive impurities are highly wanted.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a method and an apparatus for heat transfer in fluidized bed reactors in which the above mentioned drawbacks due to attack of detrimental components of solid particle suspensions on heat transfer surfaces in external heat transfer chambers have been minimized.
It is particularly an object of the present invention to provide a method and an apparatus for recovering heat from fluidized bed reactors in which the risk of impurities-based corrosion has been minimized.
SUMMARY OF THE INVENTION
The present invention provides an improved method of and apparatus for decreasing attack of detrimental components of solid particle suspensions on heat transfer surfaces of heat transfer chambers in fluidized bed reactors. The invention is particularly applicable in fluidized bed reactors comprising:
a reactor chamber, such as a processing chamber or a combustion chamber, having a bed of solid particles therein, means for fluidizing said bed of solid particles, a reactor chamber outlet and a reactor chamber inlet, and
a heat transfer chamber having a bed of solid particles therein, means for fluidizing said bed of particles, heat transfer surfaces at least partly in contact with said bed of solid particles, a heat transfer chamber inlet connected to said reactor chamber outlet and a heat transfer chamber outlet for solid particles connected to the reactor chamber inlet.
According to a preferred embodiment of the invention, the new method comprises the steps of:
discharging solid particles from said reactor chamber through said reactor chamber outlet;
introducing said discharged solid particles into a dilution chamber, having a bed of solid particles therein;
inactivating in and/or separating from the bed of solid particles in said dilution chamber, impurities detrimental to heat transfer surfaces;
discharging solid particles from said dilution chamber through a dilution chamber outlet therein;
introducing solid particles discharged from said dilution chamber into said heat transfer chamber through said heat transfer chamber inlet;
discharging said solid particles from said heat transfer chamber through said heat transfer chamber outlet and
recycling solid particles discharged from said heat transfer chamber to said reactor chamber through said reactor chamber inlet.
Thereby detrimental components, such as corrosion-inducing components, are separated from the solid particle suspension being forwarded through the dilution chamber and/or are inactivated while flowing therethrough. Detrimental gaseous or fine solid particle components may easily be separated by flushing off with a flushing gas, which flushing gas may simultaneously be used to fluidize the bed of solid particles in the dilution chamber. The flushing gas may be an inert gas or a gas inducing a chemical reaction in the bed of solid particles. Thus, air or other oxygen-containing gas may be used to induce oxidizing reactions. The delay time needed for flushing of f or chemical reactions in the dilution chamber may be controlled for optimal results. The delay time may be regulated by, e.g., controlling the bed density, solid particle flow velocity or the bed volume in the dilution chamber.
According to another aspect of the present invention, there is provided in the fluidized bed reactor, having a reactor chamber and a heat transfer chamber, additionally a dilution chamber, having
a bed of solid particles therein,
means for inactivating impurities, detrimental to heat transfer surfaces, in said bed of solid particles in the
Fitzpatrick ,Cella, Harper & Scinto
Foster Wheeler Energia OY
Price Carl D.
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