Method and apparatus for online switching between supply vessels

An apparatus for switching supply from a first vessel containing a first batch of a liquid composition to a second vessel containing a second batch of the liquid composition, both supplying the liquid composition to a downstream process, comprising:

• (a) a first vessel isolation valve;
• (b) a second vessel isolation valve;
• (c) a vessel selection valve including a first switch valve and a second switch valve;
• (d) a first outlet conduit from the first vessel isolation valve to the first switch valve;
• (e) a second outlet conduit from the second vessel isolation valve to the second switch valve;
• (f) a first conductivity sensor located in the first outlet conduit at a first known distance from the first switch valve for measuring electrical conductivity of the composition in the first outlet conduit;
• (g) a second conductivity sensor located in the second outlet conduit at a second known distance from the second switch valve for measuring electrical conductivity of the composition in the second outlet conduit;
• (h) a delivery conduit connected to the vessel selection valve for transmitting fluid therethrough downstream of the vessel selection valve;
• (i) a process control computer receiving input from the first and second conductivity sensors and controlling actuation of the first and second switch valves in response thereto, the computer opening the second switch valve and closing the first switch valve when the conductivity of the liquid in the first outlet conduit is outside a predetermined range, the computer determining a period of delay for closing the first switch valve that will allow the liquid in the first outlet conduit below the first conductivity sensor to reach the first switch valve before closing the first switch valve.

A method for switching supply from a first vessel containing a first batch of a liquid composition to a second vessel containing a second batch of the liquid composition, both supplying the liquid composition to a downstream process, comprising the steps of:

• (a) flowing the liquid composition from the first vessel through a first outlet conduit from the first vessel and through a vessel selection valve to a downstream process, the vessel selection valve including a first switch valve and a second switch valve;
• (b) sensing a conductivity level of the liquid composition at a point in the outlet conduit from the first vessel before the vessel selection valve, the computer means comparing the conductivity level to a predetermined range;
• (c) the computer signaling a vessel isolation valve in a second outlet conduit from the second vessel to open, thereby displacing air in the second outlet conduit and filling the second outlet conduit with the liquid composition from the second vessel to the vessel selection valve;
• (d) the computer determining a first period of delay for closing the first switch valve that will allow the liquid in the first outlet conduit below the first conductivity sensor to reach the first switch valve before closing the first switch valve;
• (e) the computer closing the first switch valve and opening the second switch valve after a first time period that is not greater than the first period of delay;
• and
• (f) flowing the liquid composition from the second vessel through the second outlet conduit and through the vessel selection valve to the downstream process.