GB924896A - An improved method and apparatus for detecting interfaces between two liquids flowing consecutively in a pipeline - Google Patents

Abstract

924,896. Controlling distribution of liquids. SANDALL PRECISION CO. Ltd. Feb. 18, 1960 [Feb. 27, 1959], No. 6832/59. Class 135. A method of detecting an interface between two liquids having a different detectable property and flowing consecutively in a pipeline, comprises continually withdrawing a sample of the liquid flowing through a region of the pipe-line, forming from the withdrawn sample two streams of liqud flowing respectively through two parallel-flow sampling circuits, causing a flow delay in one of the circuits intermediate its ends to delay the passage of liquid through the remaining portion of said circuit as compared with the passage of liquid withdrawn at the same time from the pipeline through the corresponding portion of the other circuit, and then comparing the detectable property of the liquid in one sample stream as received from the flow delayed source with that of the liquid in the corresponding portion of the other sample stream. The detectable property may be viscosity, temperature, density, colour, refractive index, electrical or thermal conductivity, dielectric constant, magnetic permeability, or pH. In a modified method the first of the two parallel-flow streams is passed, in turn, through a first viscosity sensitive restriction, a delay circuit and a second viscosity sensitive restriction, the second stream is passed, in turnthrough two viscosity sensitive restrictions, and, the pressure of said first stream at the end of the first restriction or beginning of the second restriction is compared with the pressure of the second stream between the two restrictions in the second stream. The detection of the arrival of an interface at the delivery end of a pipe-line serves as an indication that the second liquid is arriving and should be diverted to a separate destination. In Fig. 1 the pipe-line is indicated at 1 and liquid is drawn off at 2 by a pump 3, the liquid passing to a manifold 5 dividing the liquid sample between a pair of sampling circuits 6, 7 that are identical but for the inclusion in circuit 6 of a time-delay vessel 8. Liquid from the downstream ends of the circuits 6 and 7 passes back through a manifold 9 and conduit 10 to the pipe-line 1, preferably at a point downstream of the branch 2. The circuits 6 and 7 are each in two parts, namely 6a, 6b and 7a, 7b, respectively, these parts being used in bridge fashion with a manometer 11 connected across the balancing points 6c, 7c and with the delay vessel 8 in the arm 6b. When an interface passes the branch 2 the new liquid being carried by the pipe-line 1 is fed rapidly into the parts 6a, 7a and 7b but, due to the delay vessel 8, a period of time, for example five minutes, elapses before the new liquid fills the part 6b. During this period of time a pressure difference exists across the balance points 6c, 7c and this pressure difference is indicated by the manometer. The manometer 11 may be a differential pressure gauge and may operate a remote indicator such as a flashing light or an audible signal. One or both of the circuit parts 6b, 7b includes a balance-adjusting device, such as a needle valve, whereby the flow through the two circuits 6 and 7 can be adjusted to give a " zero " reading on the manometer 11 when liquid of the same constant viscosity is flowing through the circuits. The apparatus of Fig. 1 may include an electrical resistance bridge circuit, two arms of which are constituted by resistances that vary in value with changes in temperature of the liquid near the downstream ends of the sampling circuits, the bridge circuit being balanced in the absence of a temperature differential between the liquids in the sampling circuits. With such an additional bridge circuit a pressure difference indicated by the manometer 11 and due to a temperature gradient in the pipeline can be distinguished from a pressure difference due to the passage of an interface. The delay vessel 8 is a body having internal tubes dividing it into a number of parallel and longitudinally extending flow-passages producing lamina flow. The vessel 8 has a tangential inlet for imparting a swirl to the incoming liquid to distribute it uniformly amongst the flow passages.