Patent GB-1157144-A (GB)
Title: Supervisory Control System for a Simulated Moving Bed Separation process
Inventor: BOYD DAVID MILTON
IPC: B01J8/08
Filed: 1966-07-08
Abstract: 1,157,144. Separating hydrocarbons. UNIVERSAL OIL PRODUCTS CO. 8 July, 1966, No. 30709/66. Headings B1J and B1L. {Also in Divisions C5 and G3] In a continuous fluid-solid contacting process in which the fluid is circulated through an elongated zone containing solid contacting material, the points of connection to the zone of a number of fluid supply and extraction conduits are moved cyclically in a downstream direction and the composition in the zone between a specific pair of conduits is maintained constant, despite the movement of the points of connection, by automatically controlling (the rate, of flow in one of the conduits in dependence on said composition. In Fig. 1, a mixture of iso and n-hexanes to be separated is supplied through a conduit 131 to a column 101 containing a bed of molecular sieve sorbent, e.g. dehydrated calcium aluminosilicate through which the mixture is circulated by a pump 103 associated with a conduit 104. The n-hexanes are retained by the sorbent so that the iso-hexanes can be drawn off through a conduit 134. A desorbent such as n-butane is supplied through a conduit 133 to displace the n-hexanes from the sorbent, and these, together with desorbent, are taken off through a conduit 132. Desorbent is removed from the two output streams by fractionation. An automatically operated multi-port rotary distributing valve 106 connects the four conduits 131-4 to column 101 through a selected group of four of the conduits 107-130 and the group selected .is moved downstream, step by step, in a cyclic manner to simulate a moving bed of sorbent. After each step, the connecting conduit previously used to supply the mixture (e.g. 124) is flushed out mainly by desorbent circulated through conduits 135, 136 from the conduit next due to carry desorbent (e.g. 114) Control systems. The control systems provided may utilize electrical, pneumatic or hydraulic signals in analogue and/or digital form. The flows of feed mixture and desorbent. which are preheated, are maintained constant by flow controllers 170, 172 respectively adjusting valves 171, 173. Pressure within the column is maintained constant, at such a valve as to prevent sporadic vapourization, by a pressure controller 174 adjusting a valve 175 in iso-hexane output conduit 134. A solidstate digital computer 180 comprises flip-flop circuits and counters is outlined in block diagram form (not shown) and is in two sections. One section of computer 180 automatically maintains a constant fluid composition in a given zone by obtaining signals from a dielectric constant detector 161, which measures iso/normal hexane ratio each time a cam operated switch 157 associated with valve 106 indicates that the zone has reached circulating conduit 104, and controlling the datum of a flow controller 167 associated with the n-hexane output conduit 132. Composition measurement by differential refractometer or chromatograph, control of composition by control of iso-hexane output flow, and measurement of composition at more than one point are referred to. The other computer section sampled flow rate signals from turbine-type flowmeters 147, 149, 151, 153 associated with the conduit as shown and position signals from a switch 155 cam operated' by rotary valve 106. Using a different equation for each position of rotary valve 106, this section of the computer derives control signals which when applied to a flow controller 163, adjusts the rate of flow of fluid circulated by pump 103 so that the rate of flow of fluid in given zone within column 101 is automatically maintaining constant despite the fact that the zone is a shifting one. There are also references to (a) separation of heavy naphthas, diesel oils, benzines, toluenes, xylenes, polycyclic aromatics and cyclo-paraffins (b) purification of water by ion-exchange resins (c) othercontacting materials such as urea and thiourea adducts, desoxyoholic acid, and nickel cyanide-ammonia for hydrocarbon separation and hydroquinone for purification of argon.