Low residence time solid-gas separation process

#1. Field of the Invention

#This invention relates generally to a separation system and process to obtain a primary separation of particulate solids from a mixed phase gas-solid stream in a Thermal Regenerative Cracking (TRC) apparatus and process described in U.S. Pat. No. 4,061,562 to McKinney et al and U.S. Pat. No. 4,097,363 to McKinney et al.

#2. Description of the Prior Art

#FIG. 1 is a schematic diagram of a TRC system and process according to the prior art.

#FIG. 2 is a schematic flow diagram of the separation system of the present invention as appended to a typical tubular reactor.

#FIG. 3 is a cross sectional elevational view of the preferred embodiment of the separator.

#FIG. 2 is a schematic flow diagram showing the installation of the separator system of the present invention in a typical TRC tubular reactor system handling dilute phase solid-gas mixtures. The prior art TRC system is illustrated in FIG. 1 and provides that thermal cracker feed oil or residual oil, with or without blended distillate heavy gas, enters the system through line 10 and hydrogen enters the system through line 12. Together the feed oil and hydrogen pass through hydrodesulfurized zone 14. Hydrodesulfurization effluent passes through line 16 and enters flash chamber 18 from which hydrogen and contaminating gases including hydrogen sulfide and ammonia are removed overhead through line 20, while flash liquid is removed through line 22. The flash liquid passes through preheater 24, is admixed with dilution steam entering through line 26 and then flows to the bottom of thermal cracking reactor 28 through line 30.

#A stream of hot regenerated solids is charged through line 32 and admixed with steam or other fluidizing gas entering through line 34 prior to entering the bottom of riser 28. The oil, steam and hot solids pass in entrained flow upwardly through riser 28 and are discharged through a curved segment 36 at the top of the riser to induce centrifugal separation of solids from the effluent stream. A stream containing most of the solids passes through riser discharge segment 38 and can be mixed, if desired, with make-up solids entering through line 40 before or after entering solids separator-stripper 42. Another stream containing most of the cracked product is discharged axially through conduit 44 and can be cooled by means of a quench stream entering through line 46 in advance of solids separator-stripper 48.

#Stripper steam is charged to solids separators 42 and 48 through lines 50 and 52, respectively. Product streams are removed from solids separators 42 and 48 through lines 54 and 56, respectively, and then combined in line 58 for passage to a secondary quench and product recovery train, not shown. Coke-laden solids are removed from solids separators 42 and 48 through lines 60 and 62, respectively, and combined in line 64 for passage to coke burner 66. If required, torch oil can be added to burner 66 through line 68 while stripping steam may be added through line 70 to strip combustion gases from the heated solids. Air is charged to the burner through line 69. Combustion gases are removed from the burner through line 72 for passage to heat and energy recovery systems, not shown, while regenerated hot solids which are relatively free of coke are removed from the burner through line 32 for recycle to riser 28. In order to produce a cracked product containing ethylene and molecular hydrogen, petroleum residual oil is passed through the catalytic hydrodesulfurization zone in the presence of hydrogen at a temperature between 650.degree. F. and 900.degree. F., with the hydrogen being chemically combined with the oil during the hydrocycling step. The hydrodesulfurization residual oil passes through the thermal cracking zone together with the entrained inert hot solids functioning as the heat source and a diluent gas at a temperature between about 1300.degree. F. and 2500.degree. F. for a residence time between about 0.05 to 2 seconds to produce the cracked product, such as ethylene and hydrogen. For the production of ethylene by thermally cracking a hydrogen feed at least 90 volume percent of which comprises a light gas oil fraction of a crude oil boiling between 400.degree. F. and 650.degree. F., the hydrocarbon feed, along with diluent gas and entrained inert hot gases are passed through the cracking zone at a temperature between 1300.degree. F. and 2500.degree. F. for a residence time of 0.05 to 2 seconds. The weight ratio of gas oil to fuel oil is at least 0.3, while the cracking severity corresponds to a methane yield of at least 12 weight percent based on said feed oil. Quench cooling of the product immediately upon leaving the cracked zone to a temperature below 1300.degree. F. ensures that the ethylene yield is greater than the methane yield on a weight basis.