Single Tank Tangential Return Concept

Vessel, Line or Vessel and Line CIP

As Electrol Specialties continued the revision of a family of Single Tank CIP Skids to meet the needs of the Biopharm industry, it became obvious that a single tank concept capable of disengaging return flow air bubbles would find some application opportunities.  Since the major advantage of a small single tank unit was the ability to achieve high volume recirculation with minimal water in the circuit, which in turn required the control of the size of the puddle in both vessels in the circuit, a hold-back valve (HBV) was added to the CIPR path.  The flow control (throttling) type valve was placed under control of the diaphragm type level sensor (LS) already in the system for On-Off control of the Water Valve. The conical bottom water tank with an 18″ leg (6″ in diameter) containing only 2.2 gallons, could support continued recirculation at up to 60-80 Gpm return flow with only 10-12 gallons total in the Water/Solution tank.  This added water was required only for the chemical (alkaline and acid) solutions and represented a miniscule increase in the total water required for a complete program. The hold back valve could control the size of both puddles, by controlling only the Water/Solution Tank level, eliminating the normal level balancing problems encountered with two tanks and two pumps in the conventional manner.  The early systems actually used a tangential inlet on the upper side of the tank for maximum air disengagement.  This was replaced with a spray, for continuous tank surface washdown, designed to return perhaps 40% of the CIPR flow through the spray and the remaining flow through a nozzle on the bottom of the ball directed at the sidewall for maximum air disengagement.  The major difference between this system and the STBP skid described on these pages is that all Single Tank Tangential Return CIP skids provide for the solution washes to be recirculated through the Water/Solution tank, when cleaning both vessel and line circuits.

ClronWSlide14STTR

COMPONENTS: The required components of the Single Tank Tangential Return CIP Skid for vessel cleaning, and their function, include:

Water/Solution Tank – This tank serves the dual purpose of isolating the facility high purity water loop from the chemical solutions required for cleaning, and providing a reservoir for solution recirculation.  The specifications are otherwise the same as the Water Tank for the STBP Skid described previously with respect to construction, nozzles for the required water supplies, sight glass, and a vent with or without a filter. 

Tank Outlet Valve – A single valve of diaphragm type, rising stem, or mixproof design will control flow from the water tank to the pump inlet header.

CIP Supply Pump– A centrifugal pump is required, with flow rate and discharge head capabilities to meet the delivery requirement of the largest vessels to be cleaned, fitted with a casing drain valve.  The positioning of the tank and pump should permit drainage of all of the skid components at the end of each cleaning program or cycle through the casing drain valve.

Heat Exchanger -This component, generally of shell and tube construction, should be capable of heating the recirculated wash solution approximately 5 – 7C per pass, to raise the temperature of the equipment in the circuit from the normal ambient temperature to the wash set-point of 60C to 80C.  A steam control valve(s) is required, and also condensate handling components.

Instrumentation Sensors – CIPS side instrumentation will generally include, downstream of the HXR:

  • CIPS RTD – To sense HXR outlet temperature for control of the steam valve.
  • CONDUCTIVITY SENSOR – To verify addition of the required chemicals for control and recording purposes.
  • PRESSURE SENSOR – To produce a record of supply side pressure and provide pressure based interlocks for other contol purposes. 
  • FLOW ELEMENT- Vortex shedding meters are most commonly used.  Meters with moving parts should be avoided as the lubricity of rinse water is very minimal and wear will be great, perhaps accompanied by particulate generation.  The metering system should provide both flow rate, rate control for sprays, and line circuit velocity records, and will often monitor gallons passed data to control program step advance, rather than time.
  • CIPS Flow Control Valve – Or, alternatively a blocking valve to permit CIPS Air-Blow forward to the circuit.  The Flow Element signal may control flow via the valve, or by use of a VFD (variable frequency drive) on the CIPS Supply Pump.
  • CIPS Air Blow – A control valve to introduce Clean Air into the CIPS piping to drive all of the flush, wash and rinse water to the end of the circuit whenever changing the nature of the solution in the circuit; i.e., after the Alkaline Solution Wash, Acid Wash or Rinse, and before the Final Rinse to Resitivity.

CIPR side instrumentation will generally include, just before the Drain valve:

  • RESISTIVITY PROBE – To monitor progress of final once-through to drain rinse, to verify removal of all product soil and chemicals from total circuit.
  • RETURN PROBE – Discrete probe to confirm passage of water to drain within a fixed time after the program starts to verify integrity of circuit and operation of all components in path.
  • CIPR RTD – To sense and record temperature of all flush, wash and rinse solutions leaving the circuit, from start to finish.
  • CIPR Hold Back Valve – A throttling type valve controlled an analog signal from the Water/Solution tank level sensor.
  • SAMPLE DEVICE– The system may or should include some method for easily collecting a sample representative of the solution passing through the circuit at any desired time.  An automatic sampler may be used. 
  • CIPR Tank Recycle Valve – A normally closed shut-off valve to permit return flow to the Water/Solution Tank when energized open.
  • CIPR Drain Valve – A normally open shut-off valve to block return flow to the Drain when energized closed.

The flow paths of flush, wash and rinse solutions through the above components, and the connected circuit, include:

RINSE TO DRAIN – Typical for all pre-intermediate, post and final rinse steps, as shown in the smaller inset image on the schematics.

SYSTEM FILL– This step proceeds every recirculation step. The Tank Recycle valve will open, the Drain valve will close, and the return pump will be on. Water is added to the circuit through the flow element, in sufficient pre-determined quantity to create an adequate puddle in the vessel to maintain reliable recycle with the Tank LS controlling the Tank Recycle valve.  The volume of both puddles is thus fixed.   For Line circuits, with the Drain valve closed and the Tank Recycle valve open, water is added to the circuit through the flow element, in sufficient quantity to fill the circuit and the Solution tank to the desired operating level. In either case, subsequent chemical addition is based on the fill volume required.

WASH RECYCLE – This is the larger of the two circuits shown on the schematic.  When cleaning tanks, the volume of the puddle in the circuit (in the vessel being cleaned) is controlled by fixing the SYSTEM FILL volume to be equal to the circuit puddle requirement (not more than 2-3 gallons), plus the content of the CIPS/R piping, plus the Water/Solution Tank puddle, defined above as 10-12 gallons.  Return side air disengagment from the recirculated solution is to the Water/Solution tank. Gravity alone, or more commonly in combination with a low speed CIP Return pump will move the solution from the vessel to the skid, and the Hold Back valve will control level in both vessels.   The solution volume required for recycle is that necessary to fill the skid piping, the CIPS/R pipng, and create a minimal puddle in the tank.  Heating and chemical addition and mixing occur in this mode.   The flow path is identical for line circuits, and the control loop on the Hold back valve should be inoperative.

These program phases will be described step by step on the following Operating Details page.