Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Fluidized bed
Reexamination Certificate
2001-09-28
2003-08-05
Rotman, Alan L. (Department: 1625)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Fluidized bed
C422S145000, C422S143000, C208S159000, C502S041000, C502S051000, C549S315000, C558S308000, C558S330000, C558S435000, C560S232000, C560S241100, C560S242000, C560S261000, C562S521000, C562S548000, C562S549000, C562S607000
Reexamination Certificate
active
06602476
ABSTRACT:
The present invention relates in general to apparatus and process for heat exchange with fluidised beds of material.
BACKGROUND OF THE INVENTION
Fluid bed reactors and their use in processes involving heterogeneous gas-phase reaction which are exothermic are known, for example from EP-A-0546677, EP-A-0685449 and EP-A-0847982.
EP-A-0546677 discloses a process for oxidising ethane to acetic acid in a fluidized bed reaction zone. In the example illustrated in EP-A-0546677, ethane is joined with a recycle stream containing water, CO, CO
2
, O
2
, ethylene and ethane and the combined stream is fed to the fluid bed reactor. A molecular oxygen-containing stream and steam are introduced separately into the fluid bed reactor. The hot oxidation products exit the top of the reactor and flow through a steam generator heat-exchanger, coolers and an air cooler. The fluidised bed reactor is also said to contain cooling coils (not shown) in the bed into which water is introduced and from which steam exits.
EP-A-0685449 discloses a process for manufacturing vinyl acetate in a fluid bed reactor comprising feeding ethylene and acetic acid into the fluid bed reactor through one or more inlets, feeding an oxygen-containing gas into the fluid bed reactor through at least one further inlet, co-joining the oxygen-containing gas, ethylene and acetic acid in the fluid bed reactor while in contact with a fluid bed catalyst material to enable the ethylene, acetic acid and oxygen to react to produce vinyl acetate and recovering the vinyl acetate from the fluid bed reactor. EP-A-0685449 describes the use of a fluid bed reactor containing a fluidisable microspheroidal catalyst which is equipped with cooling coils which provide for heat transfer from the reactor.
EP-A-0847982 discloses a process for the production of vinyl acetate by reacting at elevated temperature in a fluid bed reactor ethylene, acetic acid and an oxygen-containing gas in the presence of a fluid bed catalyst material characterised in that a liquid is introduced into the fluidised reactor for the purpose of removing heat therefrom by evaporation of the liquid.
Heat-exchange tubes in a fluid bed reactor may be used to remove heat of an exothermic reaction. They may also be used for heating the bed of fluidisable catalyst or even drying the catalyst, for example following a shutdown.
According to EP-A-0847982, it is desirable to use some cooling tubes/coils to provide “fine tuning” of the heat removal. According to EP-A-0847982, typically, about 70% of the heat removal may be provided by liquid addition to the reactor. It is further stated that any appropriate percentage between 100 and greater than 0% of the heat removal may be by means of liquid additions to the reactor without exceeding the safety margins of the equipment operated.
EP-A-0776692 describes the use of heat exchange elements in a fluid bed reactor, in which means for supporting one or more essentially horizontal support beams is achieved by replacing a continuous ledge with a discontinuous support structure.
EP-A-1034837 relates to the use of a fluid bed reactor containing cooling tubes for oxychlorination of ethylene to produce vinyl chloride monomer. The cooling tubes are spaced equidistant relative to each other and may be arranged in a square (90°) and/or triangular (60°) configuration.
A problem with the use of heat-exchange tubes in fluid beds is that they may interfere with the fluidisation characteristics of the fluid bed. This problem is particularly significant in very exothermic fluid bed reactions, requiring a large number of heat-exchange tubes. The problem to be solved therefore is to provide an apparatus for use with fluid beds in which the impact of the heat-exchange tubes on the fluidisation characteristics of the fluid bed is reduced whilst retaining heat exchange capacity. It has been found that this can be achieved by using a defined arrangement of heat-exchange tubes.
SUMMARY OF THE INVENTION
Thus, according to one embodiment of the present invention there is provided apparatus comprising a vessel having:
(1) means for fluidising a bed of fluidisable material within a fluidisation zone in the vessel; and
(2) heat-exchange tubes located in the fluidisation zone for removing heat from the fluidisation zone and/or for providing heat to the fluidisation zone,
characterised in that the heat-exchange tubes are located longitudinally with respect to the axis of the fluidisation zone with a rectangular pitch, one side of which having a length at least one and a half times the length of the other side and/or with a triangular pitch, having two sides each at least one and a half times the length of the shortest side.
According to another aspect of the present invention there is provided a process for removing heat from a fluidised bed of material and/or supplying heat to a fluidised bed of material which process comprises
(i) fluidising a bed of fluidisable material within a fluidisation zone in a vessel having means for supporting the fluidised bed of material; and
(ii) removing heat from the fluidised bed of material and/or providing heat to the fluidised bed of material, by heat-exchange tubes located in the fluidisation zone longitudinally with respect to the axis of the fluidisation zone with a rectangular pitch, one side of which having a length at least one and a half times the length of the other side and/or with a triangular pitch, having two sides each at least one and a half times the length of the shortest side.
The present invention solves the technical problem defined above by using heat-exchange tubes located in a rectangular pitch, one side of which having a length at least one and a half times the length of the other side and/or in a triangular pitch, having two sides each at least one and a half times the length of the shortest side.
It has been found that this arrangement allows for a large number of heat-exchange tubes to be located in the fluidisation zone without significantly interfering with the fluidisation characteristics of the fluid bed of material.
The rectangular pitch of the heat-exchange tubes has sides of length x and y in which x is at least one and a half times y, preferably at least 2.5 times y. The triangular pitch arrangement has two sides each of which is at least one and a half times the length of the shortest side, preferably 2.5 times the length of the shortest side.
It is important that the heat-exchange tubes are not too close together—that is, for the rectangular pitch the value of y should not be too small and for the triangular pitch the shortest side should not be too small to be ineffective. For example, for tubes of 50 mm diameter a minimum distance between tubes of 25 mm corresponding to a minimum distance of 75 mm centre to centre, is appropriate.
Other parameters may also have an impact on the fluidisation characteristics of the bed of fluidised material. For example, the heat-exchange tube diameter, the proportion of cross-sectional area of the vessel occupied by the heat-exchange tubes and the degree of compactness of the heat exchange tubes (&PHgr;) which is the tube cross sectional area divided by the pitch area.
It has now been found that for heat removal from a fluidisation zone using heat exchange tubes, the heat exchange tubes should be operated at a temperature of not less than the dew point of the fluid in the fluidisation zone and preferably at a temperature of at least 10° C. above the dew point of the fluid in the fluidisation zone.
Thus, according to another aspect of the present invention there is provide a method for heat removal from a fluidisation zone by using heat exchange tubes in which the heat exchange tubes are operated at a temperature of not less than the dew point of the fluid in the fluidisation zone and preferably at a temperature of at least 10° C. above the dew point of the fluid in the fluidisation zone.
For removing heat from the fluidised bed of material in the fluidisation zone, the heat-exchange tubes are supplied with a cooling fluid such as water. The present invention is pa
Becker Stanley John
Bristow Timothy Crispin
Fiorentino Michele
Newton David
Williams Bruce Leo
BP Chemicals Limited
Covington Raymond
Nixon & Vanderhye
Rotman Alan L.
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