"EXTREME" High Viscosity Filtration Technology
Viscous product gel removal increases yield & decreases disposal costs
High viscosity can be described by some as a fluid possessing 10 weight oil characteristics, and others as being a fluid similar to cool molasses with a difference between the two being several thousand centipoise. When discussing process filtration most would not consider the removal of gelatinous particles from a fluid having a viscosity of 125,000 cPs a viable exercise in process filtration engineering and media application.
Fortunately for a mid-west silicone sealant manufacturer an experienced and knowledgeable Fischer-Robertson, Inc., field application representative was available to provide a solution to this demanding process filtration challenge.
In the manufacturing of silicone sealant occasionally upset conditions present themselves resulting in gel formations within the finished bulk material. These "gel balls" will bridge the opening of the nozzle at the applicator tip resulting in an inconsistent bead of applied sealant or possible plugging at the nozzle resulting in waste and the downtime required for cleaning or premature change.
When presented with a process upset the manufacturer would simply store the drums of waste sealant and pay for disposal as previous methods of gel removal from the material to acceptable quality standards proved uneventful. Previous filtration efforts included disc type self-cleaning filters allegedly designed for gel removal and various screen type surface media, both failing miserably.When discussing viscous filtration identifying with the characteristics of the material and debris to be removed is critical to the media technology selection process. Knowing the sealant standing viscosity was 2M centipoise and thixotropic (shear thinning) in nature, it was acknowledged that once moving within the pump and piping it would shear thin to approximately 125,000 cPs. The gels, considered "soft" would extrude through surface type filtration media once differential pressures approached 22psi. Given the vastl gel size distribution a tight screen with little open area would be required. To initiate flow through realistic applied and sized surface filter media would required a clean differential pressure of 50psig, hence this media technology was not considered a viable alternative.
Fischer-Robertson introduced the manufacturer to the concept of depth filtration incorporating Parker Process Filtration Fulflo® ProBond phenolic resin bonded depth cartridge designed for gel removal and filtration under what would be considered abnormally high differential pressures. Pilot testing and subsequent data acquisition demonstrated the ProBond cartridge effectively removed the unwanted gels and the once filtered sealant was now within specification and meeting quality standards.
Several tests were conducted during the pilot phase to determine; extrusion, clean differential, and collapse pressures, as well as flow at pressure cartridge characteristics. Extrusion pressure was required to establish at what differential pressure the cartridge would need to be changed prior to contaminating the filtrate with passed "extruded" gels. Clean differential pressure was defined as the pressure required to induce flow at the standing viscosity of the sealant. Knowing the standing, opposed to shear thinned viscosity was much higher the pressure required to induce flow through the cartridge would be much higher at start-up. It was this pressure that was employed when determining feed pump pressure required. Collapse pressure was identified to establish a maximum allowable pressure differential and safe cartridge operating limit to avoid downstream contamination and to establish the added load factor required by the supply pump.
Test results illustrated the ProBond rigid fiber matrix cartridge did not deform or collapse under differential pressures well in excess of the 150psid @ 70oF published limitation. Fact being, established tested collapse pressure of the cartridge exceeded 375psid. The pressure required to induce standing flow through the cartridge was established at 100psid. To avoid oversizing the feed pump it was decided to "slow start" the filtration process until the material reached its shear thinned viscosity thus 100psi was assigned as the clean differential pressure.
Test flow was determined based on a single 10" long ProBond 150µm cartridge. At 125,000cPs a clean cartridge provided 0.9gpm filtrate at a differential pressure starting at 100psid and terminating at 375psid. At completion of pilot testing it was determined that extrusion pressure exceeded terminal change pressure, therefore gel extrusion was no longer considered to be an issue. While the cartridge did not collapse it was determined that at differential pressures exceeding 375psi cartridge end sealing issues did surface, however, given the volume of sealant filtered and the somewhat rapid rise from 225-375psi at a flow constant of 0.9gpm it was decided to assign 225psig as the recommended cartridge change pressure.
Paper engineering and pilot testing having proven successful scaling to permanent installation was the last step in providing the manufacturer with a total filtration solution. Time required to accomplish the recycling task was left at the pilot flow of 0.9gpm, however, to lessen operator involvement and the cleaning process between cartridge change, media life cycle now found a position on the priority pyramid.
During pilot testing of the 10"L cartridge it was noted the cartridge could filter between 1+ / 2+ drums of sealant depending on gel load. Based on this data it was estimated a 30"L cartridge could process the requested six drums between change target. The decision was made to install a a Parker Process MSN1T1TN high pressure single cartridge vessel which would employ one 30"L ProBond cartridge. This vessel and cartridge combination would provide six drums of recycled silicone sealant at an approximate rate of one drum /hour while meeting the six drum between change life cycle goal.
Since its installation the MSN vessel with the ProBond cartridge has averaged in excess of the six drum/cartridge change goal and the once unusable sealant is now finding its way onto the shelves of contractor supply and hardware stores throughout the United States.
As with many innovative process filtration users success breeds new application and investigations into reducing production costs. Presently, a silicone sealant vessel/cartridge combination tasked with polishing all sealant at the point of filling is underway. Success at this point in the process will relieve the manufacturer of double drumming, handling and storage of upset batch material.