Single Tank By-Pass Concept
Electrol Specialties pioneered the application of the STBP (Single-Tank By-Pass) concept in the 1960-1976 period, when more than 700 nearly identical CIP units were supplied to the dairy, brewing, wine processing, and food processing industries. The original system combined a 60 gallon rectangular tank for water supply and solution recirculation (line circuits only), three 2 inch air operated valves, a steam injection mixer and ball valve on the suction side of a 7-1/2HP industrial pump, fabricated to 3-A standards, to provide CIPS flow of 80 to 105 Gpm at 75-78 Psi discharge pressure. Return flow was by gravity or 2 HP 1750 Rpm industrial return pumps. These systems were applied to clean 42 foot plus transport tankers, vessels from 100 gallons to 60,000 gallons in capacity, and line circuits including up to 2500 feet of 2″ and 3″ tubing and 100 plus air-operated valves. They were supported by facility water (wells or municipal mains) supplied at a flow rate greater than required for 5 Fps velocity in the largest diameter line, and discharged to drains capable of handling that flow also.
During the past 25 years this concept has been continuously modified to meet the more stringent and ever changing needs of the biopharmaceutical user, Though the size and/or capacity of the components may be varied the operating concept remains fixed. The Bypass Skid can be supplied in two versions including (a) for vessels only, and (b) vessels or line circuits also, via recirculation through the Water Tank, used also as the solution tank.
The system for spray CIP of vessels will be described first, followed by the combination system for vessels and lines, both of current vintage for biopharmaceutical applications.
COMPONENTS: The required components of the Single Tank Bypass Skid for vessel cleaning, and their function, include:
Water Tank – This tank serves the single purpose of isolating the facility high purity water loop from the chemical solutions required for cleaning. It may be for atmospheric or pressure/vacuum operation. A dished head with a small access handhole or manway must also include nozzles for the required water supplies, generally one or two, perhaps a sight glass, and a nozzle for a vent with or without a filter. Water is introduced through a spray designed to provide full coverage of the dish head, nozzles and sidewall, using the facilities pure water pressure and flow rate. The bottom may be conical, or dished, but for best hydraulic performance at minimum water volume, should incorporate a vertical leg 6″ in diameter and 12-18″ in height to assure adequate NPHS to the pump until the tank is nearly empty. A diaphragm type level transmitter near the bottom of the leg is required for control of the water valve.
Water Valve– AWFI, HWFI or an alternative water(s) is supplied by a diaphragm valve, controlled by the tank Level Sensor (LS).
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.
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 start 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.
- 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 Return Valve – A normally closed shut-off valve to permit return flow to the CIPS Pump when energized open.
- CIPR Drain Valve – A normally open shut-off valve to block return flow to the drain when energized closed.
The required components of the Single Tank By-Pass Skid for vessel and line circuit cleaning, and their function, include all of the above, plus:
CIPR Tank Recycle Valve – A single valve of diaphragm type or rising stem will control flow from the CIPR line to the Water/Solution tank during the recycle portions of the program. The recyled flow will be introduced to the tank through a spray device designed to assure continuous wash-dowm of all upper surfaces of the tank.
The skid mounted tank thus serves the dual purposes of (a) serving as a break tank between the facility pure water supply and the circuit being cleaned, and (b) serving as the solution tank and providing for disengagement of air from return flow during recycle.
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. For vessel spray circuits, with the Drain valve closed, and any return pump off, water is added to the circuit through the flow element, in sufficient metered quantity to achieve and maintain reliable recycle. The Tank Outlet valve will then close and the Return valve will open as the return pump starts. For Line circuits, with the Drain valve closed and the Tank Recycle valve open, water is added to the circuit through ihe flow element, in sufficient quantity to fill the circuit. 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 each schematic. When cleaning tanks, the only puddle in the circuit is in the vessel being cleaned and all air disengagment from the recirculated solution is to that vessel. Gravity alone, or in combination with a low speed CIP Return pump will move the solution from the vessel to the skid, and enter the CIPR Manifold at approximately 2-5 Psi maximum. 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. When a return pump is used, the two pumps operate in series, and this nearly eliminates all tendencies for air-binding of the supply pump, even when operating at very low levels (desirable) in the vessel being cleaned. Heating and chemical addition and mixing occur in this mode.
When cleaning line circuits (second schematic) return flow from the piping is via the Tank Recycle valve to the combination Water Supply/Recirculation Tank. Whereas vessels could be sprayed in this same configuration, the presence of two uncontrolled puddles would cause flow balancing problems and probably require 3 to five times the combined puddle volume, increasing fill and drain times and water/chemical consumption.
These program phases will be described step by step on the following Operating Details page.