Claims
- 1. A system for the recovery of chemical constituents or heat energy from a fluidized bed combustion process comprising:
- a fluidized bed combustor section having a generally vertically-oriented chamber within which fluidized bed combustion takes places and wherein small and large particles of unburned constituents are formed by and provide the bed medium for the combustion process, said chamber having a passageway adjacent its lower end through which larger particles of the bed medium can be extracted for recovery purposes;
- a heat exchange section including a shell positioned about said combustor section chamber so that the lower end of said chamber is disposed beneath said shell and the upper end of said chamber extends upwardly into the shell cavity for discharging gaseous products of the combustion process and small particles entrained by the combustion gases into the shell cavity and so that the shell is spaced from and encompasses the portion of the combustor section chamber adjacent the upper end thereof, said shell including a lower portion for collecting small particles which separate from the combustion gases so that the collected small particles accumulate in a bed in the shell lower portion and an upper portion having an opening therein through which the substantially particle-free combustion gases exit the shell cavity;
- heat exchange means associated with the shell cavity for extracting heat from the bed of small particles which accumulate in the lower portion of the shell; and
- means associated with the lower portion of the shell and the combustor section for routing an amount of the small particles which accumulate in the shell cavity to the combustor section.
- 2. A system as defined in claim 1 wherein said combustor section includes a head section associated with the upper end of the combustor section chamber for directing combustion gases and the small particles entrained therein out of the combustor section and into the shell cavity along a substantially downwardly-directed path, said head section is positioned within the upper portion of said shell and the cavity provided by said shell upper portion is relatively large in cross section in comparison to the cross section of the head section so that combustion gases which enter the shell cavity from the head section decelerate relatively rapidly.
- 3. A system as defined in claim 2 wherein said head section includes a plurality of conduits joined in flow communication with said combustion section chamber and arranged so that each conduit opens generally downwardly toward the lower section of said shell cavity.
- 4. A system as defined in claim 2 wherein said head section includes at least one conduit connected in flow communication with said combustion section chamber and said conduit opens into said shell cavity in a generally downward direction so that combustion gases which enter the shell cavity from the conduit decelerate while moving downwardly to facilitate gravitational separation of entrained particles from the combustion gases.
- 5. A system as defined in claim 4 further comprising cyclone separator means positioned within the shell of the heat exchange section and associated with the opening of the shell upper portion so that the gaseous products of the combustion process exiting the combustion section, having previously entered the shell cavity from the head section so that a substantial portion of the entrained particles gravitationally separate from the combustion gases upon entering the shell cavity, along with the remaining entrained particles are directed through the cyclone separator means before passing out of the shell through the opening, said cyclone separator means adapted to separate the remaining entrained particles from the gaseous products entering the cyclone separator means for delivery of the separated particles to the bed of collected small particles.
- 6. A system as defined in claim 5 wherein the cyclone separator means includes a dip leg through which particles which are separated from the gaseous products by the cyclone separator means are directed to the bed of collected small particles, said dip leg including a lower portion which extends downwardly into the bed of collected small particles so as to, be embedded beneath the upper level of the collected particle bed.
- 7. A system as defined in claim 1 wherein said heat exchange means includes a plurality of heat exchange tubes through which a heat exchange medium is directed for the purpose of extracting heat from the bed of particles collected within the shell and said heat exchange tubes are totally submerged within the bed of collected particles.
- 8. A system for recovering process salts and heat energy from the burning of spent pulping liquor associated with a lignocellulosic pulping process comprising:
- a fluidized bed combustor section having a vertically-oriented chamber within which fluidized bed combustion of spent pulping liquor takes place and wherein the combustion bed medium includes small and large particles of process salts, said chamber including a passageway adjacent its lower end through which the large salt particles are extracted for recovery purposes;
- a heat exchange section including a shell positioned about said combustion section chamber so that the lower end of said chamber is disposed beneath said shell and the upper end of said chamber extends upwardly into the shell cavity for discharging gaseous products of the combustion process and small salt particles entrained by the combustion gases into the shell cavity and so that the shell is spaced from and encompasses the portion of the combustion section chamber adjacent the upper end thereof, said shell including a lower portion for collecting small salt particles which separate from the combustion gases so that the collected small salt particles accumulate in a bed in the shell lower portion, said shell including an upper portion having an opening therein through which substantially salt-free combustion gases exit the shell cavity;
- heat exchange means associated with the shell cavity for extracting heat from the bed of small salt particles which accumulate in the lower portion of the shell and to thereby recover heat energy from the fluidized bed combustion process; and
- means associated with the lower portion of the shell and the combustor section for recirculating a portion of the small salt particles which accumulate in the shell cavity to the combustor section.
- 9. A system as defined in claim 8 wherein said combustor section includes a head section associated with the upper end of the combustor section chamber for directing combustion gases and the small particles entrained therein out of the combustor section and into the shell cavity along a substantially downwardly-directed path, said head section is positioned within the upper portion of said shell and the cavity provided by said shell upper portion is relatively large in cross section in comparison to the cross section of the head section so that combustion gases which enter the shell cavity from the head section decelerate relatively rapidly to facilitate gravitational separation of entrained particles from the combustion gases, and the system further comprises cyclone separator means positioned within the shell of the heat exchange section and associated with the opening of the shell upper portion so that the gaseous products of the combustion process exiting the combustion section, having previously entered the shell cavity from the head section so that a substantial portion of the entrained particles gravitationally separate from the combustion gases upon entering the shell cavity, along with the remaining entrained particles are directed through the cyclone separator means before passing through the opening, said cyclone separator means adapted to separate the remaining entrained particles from the gaseous products for delivery of the separated particles to the bed of collected small particles.
Parent Case Info
This is a division of application Ser. No. 461,695 filed Jan. 8, 1990 now U.S. Pat. No. 4,979,448.
This invention relates generally to apparatus and methods for recovering chemical constituents and/or heat energy from a fluidized bed combustion process and relates more particularly to such apparatus and methods for recovering chemical constituents and/or heat energy from feed material delivered to a fluidized bed combustion process.
The type of fluidized bed combustion processes with which this invention is concerned includes such processes involved in the chemical pulping of lignocellulosic material, the fluidized bed combustion of high and/or low sulfur fuels, fluidized bed catalytic processing, fluidized bed gasification of fuels, and the generation of exothermic or endothermic reactions in which heat is desired to be extracted from or added to the reaction zone.
In processes involving the chemical pulping of lignocellulosic material, it is known that reusable sodium constituents in the form of process salts can be recovered from the burning of spent, or black, pulping liquor. One prior art system for recovering such process salts involves three separate equipment elements: a fluidized bed combustor; a cyclone separator; and an external heat exchanger. During operation of the conventional system, black liquor is supplied to the combustor and burned in a multi-solids fluidized bed environment comprised of process salts derived from the combusting of black liquor. The process salts include small particles which become entrained within the combustion gases from the combustor and larger particles, or prills, which remain within the combustor bed medium. Prills are removed from the bottom of the combustor for reuse during a pulping process and for controlling the accumulation or inventory of prills in the combustor.
The combustion gases and entrained salts are conducted from the combustor and enter the cyclone separator where the salts are separated from the gases. The combustion vapors then exit the separator as salt-free off gas, and the separated salts are directed from the separator and into the external heat exchanger. The separated salts accumulate in a bed within the heat exchanger, and heat exchange tubes positioned within the bed transfer heat from the bed to water directed through the tubes for the purpose of generating steam and to cool the accumulated salts. A portion of the cooled salts are returned to the combustor for controlling its operating temperature.
A disadvantage associated with the discussed above prior art system, relates to its separate combustor and heat exchange vessels. The separate vessels contribute to relatively large heat losses due to the relatively large amount of vessel surface area which is normally exposed to surroundings of lower temperature. Moreover, the separateness of the vessels contributes to the complexity and cost of the conventional system. In addition, the cyclone separator of the type used in the aforedescribed system is limited in that its operation is sensitive to the pressure drop across the separator, and the more desirable separator efficiencies are reached only at higher operating rates. Thus, the system does not operate efficiently at turndown conditions.
Accordingly, it is an object of the present invention to provide a new and improved system and method for recovering chemical constituents from a fluidized bed combustion process, such as one involving the burning of spent pulping liquid, and/or for recovering heat energy from the combustion process.
Another object of the present invention is to provide such a system and method which circumvents the need for a cyclone separator and wherein entrained particles are separated from the combustion gases with less sensitivity to pressure drop and with improved separating efficiency.
A further object of the present invention is to provide such a system and method which results in lower heat losses and is less costly and less complicated in construction than that of the aforedescribed prior art system which utilizes separate combustor and heat exchange vessels.
US Referenced Citations (22)
Divisions (1)
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461695 |
Jan 1990 |
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Patent Grant
5012750
