Spray Ball Design
Fixed Ball Spray Devices
As spray CIP technology was applied in the pharmaceutical industry (circa 1977 and later) nearly all vessels were found to be of a vertical cylindrical design, with an ASME dish tank head and bottom. Field studies by Seiberling and Douglas in dairy-type silo tanks in the early 1960s confirmed that uniform distribution of 2.0 Gpm/Ft of tank circumference to an ASME shaped tank head would assure a vertical downwards flow that would cover all surfaces in vessels up to 65-70 feet in height. The dairy silo-type tanks used for these studies had no nozzles, agitator collars nor manways in the tank head or upper sidewall areas, and was therefore generally fitted with a simple dish or disc distribution device to “flow” water onto the ASME head.
The flow rate criteria developed for dairy silo-type tanks was found applicable only for adequate coverage of the pharmaceutical tank head, sidewall shell and dish bottom. The general presence of agitator collars, manways, and nozzles of various diameters in the tank head, plus a variety of agitator designs, sometimes accompanied by baffles, made it necessary to consider use of multiple spray heads to avoid “shadowing” of sidewalls by the agitator shaft, assure coverage of both sides of deep manway and agitator collars, and contact both sides of sidewall mounted baffles. If a tank was fitted with one or two baffles, two spray heads were required. Subsequent experience confirmed the need for the number of sprays to be equal to the number of baffles present. The most common ESC spray device selected (see photo at right) was the 2-1/2″ ball fitted to a 1-1/2″ supply tube with a slip joint, welded through a 3″ TC cap, with three holes drilled directly beneath the cap to clean the installation nozzle.
The first spray CIP of pharmaceutical tanks by ESC was accomplished with multiple sprays of “standard” design; i.e., 20, 30, or 40 Gpm, selected and located to distribute 2.5 – 3.0 Gpm/Ft circumference on the top head only, thus enjoying the run-down or “sheeting” action of all of the solutions on the sidewalls and bottom. As the first large biotech processes went on lune it was found impossible to accomplish CIP cleaning with “standard” sprays. The piping design process generally favored nozzle locations in the top head and spray nozzles were relegated to the remaining space. An intermit concept of a “standard tear-drop” shaped pattern sprays was found inadequate to handle rapidly increasing tank head complexity in the mid-90s and custom-designed directionally drilled fixed spray devices were recognized as the preferred solution.
Computer Assisted Drilling Pattern Design
The effective, validateable chemical cleaning by CIP, i.e., by the spray application of flush, wash, and rinse solutions to all soiled surfaces of the equipment, requires contacting all areas of the vessel and it’s installed components with a uniform distribution of these solutions. The tank head and side view drawings at the left and the photo at the right illustrate the methodology developed by ESC in the mid-90s to satisfy all early pharmaceutical process and later biotech and API equipment cleaning requirements. The drawing of the vessel and the photo of the CAD aided spray pattern design are both for a typical tank which included:
- Deep manway and agitator collars in the tank head, of which is treated as a tank with in a tank at the 2.0 Gpm/Ft of circumference manner.
- A top mounted agitator with two impellers.
- A fixed baffle welded to one area of the sidewall.
- Nine tank head nozzles of various diameters, fixed in location for process piping design purposes before any consideration of the spray CIP issue.
This design began with analysis of the CAD drawing of the tank head supplied by the tank vendor. Three sprays were required, one being a ball with a tube and bubble to apply the required 2.0 Gpm/Ft of circumference to the manway collar, and of course, the manway cover. Every nozzle in the tank received a spray stream from at least two different sprays, preferably separated by 90 -120 degrees. Several streams were directed downwards to the arc of the slowly rotating agitator impellers and to the tops of both sides of the baffle. This design methodology generally results in total spray flow rates for a vessel in the range of 2.5 to 3.0 Gpm/Ft of vessel circumference. Perhaps 10 years ago the fixed ball spray was modified via a horizontal tube from the bottom fitted with a 1-1/2″ “bubble” to accomplish a portion of tank head coverage and manway collar and cover coverage via a single 3″ TC nozzle. This variant of the single ball can be fitted to the same supply tube positioned to place the bubble under the manway, See drawing above.