Bubble size monitoring and control

A system comprising:

• a first conduit for flowing a multiphase fluid;
• a flotation gas source;
• a mixing system having a first inlet in fluid communication with a downstream end of the first conduit, a second inlet in fluid communication with the flotation gas source, an outlet, and a variable orifice plate valve positioned proximate to the outlet, the mixing system configured to mix the multiphase fluid flowing from the downstream end of the first conduit with flotation gas from the flotation gas source so as to produce at the outlet an enhanced multiphase fluid having bubbles of the flotation gas therein;
• a second conduit having an upstream end in fluid communication with the outlet of the mixing system;
• a separator comprising:
• a tank in communication with the second conduit,
• a sludge outlet positioned proximate to a lower end of the tank,
• an inner cylinder forming a flotation and degassing zone between the inner cylinder and the tank,
• an inlet guide vane positioned between the tank and the inner cylinder,
• a circular plate proximate to the lower end of the tank,
• a first open space positioned between the inner cylinder and the inlet guide vane, and
• a second open space between the circular plate and the tank;
• and
• a bubble control system associated with the second conduit and configured to:
• calculate a pressure drop across the mixing system via a first pressure sensor positioned upstream of the first inlet and a second pressure sensor positioned downstream of the outlet, and
• control the mixing system in response to the-calculated pressure drop so as to influence the size of the bubbles of the flotation gas to be above a threshold value.