Patent GB-765437-A (GB)
Title: Improvements in or relating to a method and apparatus for blending two or more miscible liquids of different vapour pressures
Inventor: SUMNER FRED
IPC: B01F3/08
Filed: 1955-03-17
Abstract: 765,437. Mixing fluids in flow. SHELL RESEARCH, Ltd. March 17, 1955, No. 7814/55. Class 86 In a method of blending two or more miscible liquids of different vapour pressure to a mixture having a specific vapour pressure characteristic, the liquids are fed to a buffer reservoir vessel so that they are mixed before or as they enter the vessel and the vapour pressure of the liquid mixture in the vessel is compared with the vapour pressure of the reference fluid maintained at the same temperature as that of the liquid mixture in the vessel, the supply of one of these liquids being automatically controlled in dependence upon this infusion so as to reduce any difference between the two vapour pressures. Preferably the reference fluid is a sample of a standard blend of the liquids being blended. In the apparatus shown, which is used for the blending of liquid petroleum gas, a reservoir 1 is supplied with liquid butane or a mixture of C 4  hydrocarbons through a valve 5 from a pair of centrifugal pumps 4 and with liquid propane or a mixture of C 3  hydrocarbons through a valve 7 from a second pair of centrifugal pumps 6, both blend components passing through a mixing valve 3. The blended liquid is withdrawn through line 12 by a pair of centrifugal pumps 13 and discharged either through the valve 14 to storage or through the valve 15 to the mixing valve 3. A bulb 21 containing the reference fluid projects into the line 12 adjacent its connection with the vessel 1, the bulb being connected to a differential pressure cell 22 so that the vapour pressure of the reference fluid is applied to one side of a diaphragm 23a. The other side of the diaphragm is exposed to the pressure of the vapour in the space above the liquid in the vessel 1. The cell 22 is associated with a differential pressure recorder and controller 23 which is actuated by the resultant pressure on the diaphragm 22a and operates the valve 7 controlling the supply of propane to the vessel 1 to supply propane only when the pressure in the vessel 1 is less than the pressure in the bulb 21. The valve 7 is normally closed when the pressures are equal although the controller 23 can be adjusted so that the vapour pressure in the vessel 1 is maintained at a predetermined difference from that of the reference fluid in the bulb 21. The valve 7 is operated by a compressed air motor, the air pressure being controlled by the recorder and controller 23. This device records automatically the pressure difference in the cell 22. There is also a recorder 24 which records the pressure at the top of the vessel 1 and the temperature of the blend in the line 12 near the vessel 1. A pressure recorder and controller 25 is provided which opens the valve 15 to an extent depending on the pressure at the inlet side of the valve 14. The pumps 13 normally pump at a rate greater than the maximum demand warrants, the excess output being circulated back through to valves 15 and 3 to the vessel 1. The valves 5, 14 are controlled by a liquid level controller 20 within the vessel 1. The controller includes a pair of valves; the first of which is operated when the liquid in the vessel 1 rises above a predetermined level and the second of which is operated if the liquid in the vessel 1 falls below a predetermined level. The first valve causes the valve 5 to be closed when the level of liquid is excessive, and the second valve causes the valve 14 to be closed if the liquid in the second falls below the predetermined level.