Producing or Dispensing Liquid Products

Abstract

A liquid product is dispensed via a membrane contactor. The contactor employs a plurality of gas-permeable hollow fibres. The contactor has a gas port communicating with the interior of the fibres and input and output ports for liquid communicating with space within the contactor surrounding the fibres. A gas comprising carbon dioxide or nitrous oxide is dissolved in the liquid in the contactor. The gas at a controlled pressure is supplied to the gas port. The liquid is supplied at a higher pressure than the gas to the input port for liquid from a supply of such liquid via a first valve having a first valve inlet port communicating with the supply of liquid and a first valve outlet port communicating with the inlet port for liquid. Liquid with the gas dissolved therein is dispensed from the outlet port for liquid via a dispense tap to ambient. The dispensing liquid step includes a start dispense step in which dispensing commences and a stop dispense step in which dispensing is stopped. The first valve is opened with the dispensing tap in the start dispense step, and is closed in the stop dispense step. Pressure build-up is relieved in liquid in communication with the space within the contactor surrounding the fibres after closure of the first valve and while maintaining the first valve closed. The balance between gas pressure and liquid pressure during the systems' standby periods protects the membranes from flooding.

1 . A method for producing or dispensing liquid products in which a membrane contactor employing a plurality of gas-permeable hollow fibres, the contactor having a gas port communicating with the interior of the fibres and input and output ports for liquid communicating with space within the contactor surrounding the fibres, is employed to dissolve a gas comprising carbon dioxide or nitrous oxide in a liquid, the method comprising the steps of:
 supplying the said gas at a controlled pressure to the gas port;   supplying a liquid at a higher pressure than the gas to the input port for liquid from a supply of such liquid via a first valve having a first valve inlet port communicating with the supply of liquid and a first valve outlet port communicating with the inlet port for liquid; and   dispensing liquid with said gas dissolved therein from the output port for liquid via a dispense tap to ambient, the dispensing liquid step including a start dispense step in which dispensing commences and a stop dispense step in which dispensing is stopped, the first valve being opened with said dispensing tap in said start dispense step, and being closed in said stop dispense step; and   relieving pressure build-up in liquid in communication with the said space after closure of the first valve and while maintaining the first valve closed.   
     
     
         2 . A method according to  claim 1 , wherein the step of relieving pressure build-up comprises withdrawing at least a predetermined volume of liquid from an otherwise closed volume of liquid in communication with the said space. 
     
     
         3 . A method according to  claim 2 , wherein said predetermined volume comprises a characteristic volume corresponding to the expansion of liquid that would otherwise occur in said space absent said withdrawing step due to continuing dissolving of the gas in liquid in said space after stopping dispense. 
     
     
         4 . A method according to  claim 3 , wherein the characteristic volume is determined by the formula (1) below:
   Δ v=K·V   c   ·C ·(1−0.5η)  (1)
   
       where
 K=a constant specific to the particular gas, 7.2×10 −4  when the gas is carbon dioxide 
 Δv=characteristic volume, in millilitres 
 V c =liquid volume of contactor, in millilitres 
 C=saturation level of the gas in the liquid, in grams per litre 
 η=efficiency of contactor at continuous flow condition. 
 
       A method according to  claim 1 , wherein the step of relieving pressure build-up comprises allowing a closed volume of liquid in communication with the said space to expand by at least a characteristic volume in an expansion step. 
     
     
         5 . A method according to  claim 1 , wherein the step of relieving pressure build-up comprises allowing a closed volume of liquid in communication with the said space to expand by at least a characteristic volume in an expansion step. 
     
     
         6 . A method according to  claim 5 , wherein the characteristic volume is determined by the formula (1) below:
   Δ v=K·V   c   ·C ·(1−0.5η)  (1)
   
       where
 K=a constant specific to the particular gas, 7.2×10 −4  when the gas is carbon dioxide 
 Δv=characteristic volume, in millilitres 
 V c =liquid volume of contactor, in millilitres 
 C=saturation level of the gas in the liquid, in grams per litre 
 η=efficiency of contactor at continuous flow condition. 
 
     
     
         7 . A method according  claim 1 , wherein the withdrawing step is performed by closing the dispense tap at least a pre-determined interval corresponding to said predetermined volume after closure of the first valve. 
     
     
         8 . A method according to  claim 1 , wherein a second valve having a second valve input port and a second valve output port, and coupled to receive liquid from said space at said second valve input port, is opened in the interval from and including one of opening of the first valve and closure of the first valve and closed a pre-determined interval corresponding to said predetermined volume after closure of the first valve to pass liquid from said second valve output port to a position permanently at a pressure below that of said space. 
     
     
         9 . A method according to  claim 8 , wherein the start dispense step comprises opening the first and second valves and the dispense tap at the same time. 
     
     
         10 . A method according to  claim 8 , wherein the second valve is opened when the first valve closes. 
     
     
         11 . A method according to  claim 8 , wherein the second valve outlet port communicates with the outlet of the dispense tap. 
     
     
         12 . A method according to  claim 8 , wherein the step of supplying a liquid at a higher pressure than the gas comprises delivering liquid from a supply thereof at a pressure lower than said higher pressure by a pump having a suction side and a delivery side, the suction side being coupled to said supply and the delivery side being coupled to the inlet port for liquid; and wherein the second valve outlet port communicates with one of said suction side and said supply. 
     
     
         13 . A method according to  claim 5 , wherein said expansion step comprises coupling a diaphragm chamber having respective compartments on either side of a flexible diaphragm between liquid in communication with the said space and gas at the gas port. 
     
     
         14 . A method according to  claim 1 , wherein the liquid comprises a beverage supplied substantially at ambient pressure in a bag-in-box container, the step of supplying a liquid at a higher pressure than the gas comprising delivering liquid from the said container by a pump having a suction side and a delivery side, the suction side being coupled to said container and the delivery side being coupled to the inlet port for liquid.