Patent GB-766506-A (GB)
Title: Improvements in or relating to a control valve applicable to petroleum catalytic cracking units
IPC: F16K1/38
Filed: 1955-02-01
Abstract: 766,506. Valves. KELLOGG CO., M. W. Feb. 1, 1955 [Feb. 8, 1954], No. 2948/55. Class 135. In apparatus of the kind in which powdered catalyst collecting in the well 16, Fig. 1, of the regeneration chamber 14 of a petroleum cracking plant is continuously conveyed during operation of the plant into a superposed reaction chamber through a vertical conduit 12 by an entraining stream of hydrocarbon vapour passing through the hollow stem 38, Fig. 2, of a valve head 32 coacting with a seat 18 at the lower free end of the conduit, springs arranged coaxially with the valve stem are provided to permit downward expansion of the conduit, in the event of the head being closed against the conduit while the plant is being brought up to operating temperature, and mechanical means are provided for maintaining the head in the closed position during contraction of the conduit while the plant is cooling down after operation. A similar valve, but with a solid head 33, may be used to control the flow by gravity of spent catalyst through a conduit 13 from the reaction chamber to the regenerating chamber. The valve stem slides in a guide sleeve 45 extending through the wall of the chamber 14 and separated by heat insulation 52 from a casing 51 carried by the cover 36 of a nozzle 35 secured to the chamber wall. The admission of particles of catalyst to the space 48 between the stem and the sleeve is prevented by steam supplied through a passage 49 in the insulation and issuing into the chamber through the clearance space between the upper end of the sleeve and the stem. The hollow valve stem is connected to a spindle 39 which extends through a bonnet 37 secured to the cover 36 and having an inlet 43 for hydrocarbon vapour, and to which is attached a yoke member 71 having side apertures 58, 59 and formed with guides 120, Fig. 5, for a member 121 secured to the spindle 39 which is thus prevented from rotating. The valve spindle is moved axially by a nut 123 rotated through a driving sleeve 131 splined on the nut and driven through a clutch collar 130 splined on the sleeve and rotated through worm and spur gearing from a motor 128. Alternatively, the collar may be rotated by engagement with the pinion 139 on a shaft rotated by a handwheel 129. The nut is prevented from moving axially by springs 124 which are loaded by an adjustable cover 126, and which are compressed when the conduit 12 expands. The position of the valve is indicated on a scale 157 on the yoke by a pointer 156 carried by the member 121 and communicated to the tape 159 of a conventional positioner mechanism 155 by a clamp 158 also carried by the member 121. During operation of the plant, the motor 128 is regulated by the positioner mechanism which is controlled by means sensitive to the operating conditions of the plant. Owing to the large gear ratio of the motor drive it is possible to continue rotation of the nut 123 after the valve has closed so that the springs 124 are compressed beyond their usual limit and means are provided for both indicating and limiting such over-compression. Said means comprises a cam block 143, Figs. 7 and 8, adapted to be slid vertically on guides 144 through rollers 142 carried by the block and engaged by a collar 136 at the upper extremity of the nut. The cam block engages a lever 145 coacting with a push button 147 which controls the motor 128 and having an adjustable extension formed with a rack 146 engaging a pinion 149 controlling a signal flag 160. Compression of the springs by downward movement of the nut after closure of the valve results in inward movement of the press button and the opening of the electrical circuit to the motor and at the same time causes the signal flag to drop. A warning may also be given on a whistle. The motor may be controlled by pneumaticallyoperated means. Specification 737,956 is referred to.