Patent GB-695338-A (GB)
Title: Improvements in or relating to the control of temperature in beds of fluidized solids
IPC: B01J8/18
Filed: 1951-09-18
Abstract: <PICT:0695338/IV (b)/1> In a plant for the hydroforming of naphtha fractions, the temperature of a bed 75 of fluidized particles in a regenerator 70 is controlled (see Group XIII) by varying the level 76 of the bed and thereby the area of heat-exchange tubes or coils 112 in contact with the bed.  The catalyst is alumina-molybdenum oxide or may be other Group VI oxides supported on alumina or zinc spinel as a carrier, between 200 and 400 mesh in size and having particle sizes between 0 and 200 microns in diameter.  Synthetic, virgin or cracked naphtha, boiling between 175 DEG  and 450 DEG  F., is heated to 800-1000 DEG  F. and passed through line 18 and nozzles into a reactor 10 above a grid 20 which distributes the gases and particles in a fluidized bed 12.  The reaction zone is maintained between 850 DEG  and 925 DEG  F.  Gas, e.g. made in the process, containing 50-70 per cent hydrogen and heated to 1150-1200 DEG  F., picks up hot regenerated catalyst in a line 24 to form a suspension which is introduced below the grid 20.  The pressure in the reaction zone is 100-500 lbs./square inch.  The space velocity is 1.5-0.15 lbs. of feed/hour/lb. of catalyst.  The catalyst to oil ratio by weight is 0.5-3.  The superficial velocity of the gasiform material is 0.2 to 0.9 feet/second. Coke-contaminated catalyst is withdrawn from the bed 12 through one of several openings 26 in a conduit 28 which comprises a stripping section.  The external portion of the conduit 28, which may be reduced in diameter, forms a stand-pipe 30, for building up pressure, with a control valve 32; gas may be added to this portion to maintain fluidization.  Steam, nitrogen or flue gas is passed through a line 34 into the bottom of the conduit 28 for stripping the particles.  The reaction products pass out at the top through cyclone separators to remove the catalyst and are cooled to 550-700 DEG  F. in a cooler 42 by feed or recycle gas. High-boiling polymer is condensed in a drum 44 by cooling to 275-400 DEG  F.  A pump 44a circulates a slurry of catalyst particles in condensed oil from and to the drum through a cooler 45.  Vapour passes through line 48 to be cooled to 100 DEG  F. in a condenser 49 and a drum 52 separates petrol from the process gas which is recycled through a heater 58 to the reactor 10.  The catalyst drawn off through the valve 32 for regeneration is picked up by a carrier gas and led through a line 64 into the regenerator 70 below a grid 72.  Oxygen-containing gas such as air may enter the vessel entirely through a line 74, in which case inert gas such as flue gas or nitrogen is used as the carrier gas in line 64 or some of the air is introduced with the particles as the carrier gas. The pressure in the regenerator is 100-500 lbs./square inch as in the reactor, the temperature 1050-1200 DEG  F., and the superficial velocity of the air 0.3-1.5 feet/second.  1000-4000 cubic feet of hydrogen-containing gas per barrel of feed is recycled to the reactor 10 by way of line 24.  As with conduit 28, a gas, such as flue gas, hydrogen or hydrocarbons, from a pipe 84, serves to strip the catalyst in a conduit 82 which has a standpipe portion 83 provided with a valve 85 to control the rate of withdrawal of regenerated catalyst.  The temperature of regeneration is controlled by cooling coils 112 (see Group XIII) in the regenerator, the steam produced being collected in a drum 92.  The level 76 of the fluidized bed 75 is controlled by the outlet valve 85 which is operated manually or by a device responsive to the temperature of the bed.  In a modification, Fig. 3 (not shown), the catalyst is cooled in an auxiliary vessel containing cooling coils, the particles circulating between this vessel and the regenerator.  Valves at the inlet and outlet to the auxiliary vessel control the level of the fluidized bed therein.  In this case, also, the distribution grid in the reactor is mounted in a conical inlet and is surmounted by a cylindrical wall, the particles for regeneration being withdrawn through the annular passage between this inlet structure and the reactor wall.ALSO:<PICT:0695338/III/1> The temperature of a dense bed 75 of fluidized solid particles, e.g. catalyst particles for use in the synthesis of hydrocarbons by the Fischer-Tropsch process, in the conversion of hydrocarbons (see Group IV(b)) or in the catalytic cracking of oils, is controlled by varying the level 76 of the bed and thereby the area of a heat exchanger, e.g. tubes or coils 112, 114, in contact with the bed.  A dilute phase 77 exists above the dense bed 75 of the fluidized material in a vessel 70 and consists of a dilute suspension of particles entrained in the upflowing gases. At least one of the lowermost, closely-spaced coils 112 is permanently in the dense bed and the widerspaced, upper coils 114 are normally in the dilute phase 77.  By varying the rate of supply of solid to the containing vessel and/or the rate of removal of solids from the vessel, the bed level 76 is varied to be above or below any of the upper coils 114 and also the residence time of the solids in the heat exchange region may be varied.  The temperature may be controlled further by varying the circulation rate and/or temperature of the liquid flowing in the heat exchanger of which the coils may be of flat, spiral form, the upper coils being inclined.  In the vessel 70, catalyst particles of metallic oxide are regenerated by the burning off of carbon particles deposited thereon, by the introduction of oxygen-containing gas such as air.  This gas may enter entirely through a line 74, in which case an inert gas such as flue gas or nitrogen is used as a carrier for conveying the catalyst particles from a reactor vessel 10 through a line 64 to the regenerator 70; otherwise, some of the air is introduced with the particles as a carrier gas.  A grid 72 distributes the gas and particles.  Details of the gas velocity, pressure and temperature and densities of the phases in the regenerator, together with dimensions of the vessel, are given.  Water is used to cool the regenerator and is directed, e.g. by a pump 106, from a drum 92 to the coils 112, 114 which are in parallel between headers.  Devices in inlet lines 110 distribute the water evenly to the coils. Steam passes back to the drum 92 for the separation of water and is taken off at 2000 lbs./sq. in. pressure.  Regenerated catalyst particles for return to the reactor 10 are withdrawn through ports 78 in a conduit 82 wherein they are stripped by gas, such as flue gas, hydrogen or a hydro-carbon, from a line 84.  A valve 85, in a stand pipe 83 to which gas for aeration may be introduced, controls the outflow of catalyst and is regulated by a temperature-responsive device Fig. 2 (not shown) to determine the level 76 of the fluidized bed 75.  For the hydroforming of naphtha fractions (see Group IV(b)), naphtha is passed through line 18 into the reactor 10 above a grid 20 which distributes the gases and particles in a fluidized bed 12. Hydrogen-containing gas, e.g. recycled from a train of coolers 42, 45, 49, for the separation of reaction products and entrained catalyst particles, picks up regenerated catalyst from the valve 85 to form a suspension which is introduced below the grid 20. Coke-contaminated catalyst for regeneration is withdrawn through one of several openings 26 in a conduit 28 which comprises a stripping section.  The external portion of the conduit 28, which may bereduced in diameter, forms a standpipe 30, with a control valve 32; gas may be added to this portion to maintain fluidization.  In modifications, solid particles are circulated between a reaction vessel, such as a regenerator, Fig. 3 (not shown), or a reactor Fig. 4 (not shown), and an auxiliary vessel containing a coil, or coils, or straight tubes, for controlling the temperature in the reaction vessel.  A valve controls the rate of supply of particles to the auxiliary vessel which also has taps to maintain fluidization as well as a valve at its outlet for the particles.  An exothermic reaction such as the Fischer-Tropsch reaction may be conducted in the reactor, or, in any of the heat control methods described, heat may be supplied to support an endothermic reaction.