Volume 43 Number 6
Control Valves: Chemical Batch Processing -- A Commercial/Industrial Case Study
Summary: For industrial water applications, chemical batch processing may be one of the most difficult processes to consolidate. Many factors such as calibration, fluid control and flow rate must be considered before initiating a system. One company has found a cost-effective measure that also promotes safety and saves time.
It's simple to explain how industrial cleaning products are made: Start with clean softened water, add solvents and mix the batch in a large tank.
This is how it works. To provide a continuous supply of softened water, dual resin beds are used. While one softener is online, the other softener is regenerated. This softener system regenerates after a certain volume of water has passed through each softener. The water's hardness is checked before each batch is made. The hardness must be removed from the water prior to mixing with the desired concentrated ingredients to achieve the desired chemical batch formulation without precipitation or undesirable specifications.
Additionally, before the next batch begins, the vessel is completely flushed and rinsed from the previous batch. This effluent rinse water is monitored using pH and/or conductivity to ensure the vessel is thoroughly flushed. This assures the previous batch is completely removed before the next batch is made.
In short, the above process is completely automated, improving formulation accuracy and reducing the batch overfill rate by almost 80 percent (from 5 percent to less than 1 percent), which helped in developing and implementing an ISO 9000 system.
The ISO 9000 standard states the organization must plan, define and implement inspection, testing/measurement and monitoring activities to assure conformity and achieve improvement. Processes are subject to the same inspection and test requirements as products and services. Any process that's deemed to have an impact on conformity is subject to verification. Moreover, not only do processes have to conform, they must improve.
To obtain its ISO 9000 Certification, State Chemical, a division of State Industrial Products, replaced its deteriorating batch control systems with cost-effective in-line flow transmitters with digital display directly linked to high-reliability, Y-pattern valves using "decentralized" local loops.
State Chemical now automatically controls all bulk and mixed chemical transfers by using the menu-driven programming capabilities of the batch controllers for automatic or manually entered batch volumes. This approach also saves material by reducing the plant's overfill rate, and reduces necessary human interaction with chemicals during the transfer process, offering a system payout in two months.
Impact of equipment
Depending on which of approximately 300 batch recipes are being made, the compounding process takes place in stainless steel compounding tanks of various sizes. First, softened water and then raw chemicals are dispensed in preset quantities and mixed. Following quality control approval, each batch is filled into finished products, which range from pint and gallon bottles to bulk pails and drums.
Until recently, the plant had been making do with outdated equipment and technology according to Tim Gale, State Chemical production engineer.
"We determined that new process control equipment would have a significant impact on our product quality. To become ISO 9000 certified, we must have equipment that can be calibrated. The positive displacement meters we had been using for 10 to15 years had become so inaccurate they could no longer be calibrated," Gale explained.
"That meant we had to manually measure the level of fluid in the tank to determine how much was actually dispensed. We were losing a lot of fluid so we were adding more than was necessary. The old valves leaked and didn't always stop, causing a lot of spilled product."
So with ISO 9000 certification as the goal, Gale contacted his distributor, HLT Inc., of Parma, Ohio. After several engineering meetings, he and Mike Coughlin, of HLT, agreed on a solution utilizing in-line batch controllers with high cycle Y-pattern valves, rated to 5-million cycles, for precise volume control. Four, wall-mounted transmitter/valve combinations and several remote batch controllers are used for solvent and process water dispensing. Another flow transmitter and valve are mounted on a portable transfer unit supplied by HLT for controlled filling of finished goods.
For each batch, the control process is the same. A programmable batch controller, consisting of an electronic module with brass fitting, meters the flow of softened process water in 2-inch lines into the mixing vessel. The quick, quarter-turn interface between the fitting and sensor facilitated the upgrade without additional cables or plugs.
Similarly, solvents are metered in precise amounts from 4,000-gallon underground storage tanks, using a controller with PVDF fittings. Each "smart" batch controller/transmitter is programmed to deliver a particular quantity of material directly controlling the ON/OFF valve in a local control loop.
Nuts and bolts
The controller has an open-cell, in-line rotor sensor built into the body with ceramic bearings, which affects negligible pressure drop with long-life reliability. When liquid flows through the line, the in-line rotor rotates, inducing a frequency in the transducer proportional to the flow, with accuracy to 0.5 percent of full scale.
Using standard relay output, the batch controllers are linked directly to the valves, creating individual ON/OFF control loops that automatically add the proper materials to the batch in the right amounts.
Selected for their flexibility, reliability and extended life cycle, the valves feature two sets of self-compensating Teflon-like seals to keep all process materials from the actuator mechanism. Positive valve sealing is assured through use of an articulated seat, also made of Teflon-like material. Like the flow transmitter, the valve is also easy to install. Its compact actuator allows valves to fit in tight spaces never possible with traditional ball valves. Installation is made simple because the valve's pneumatic inlet ports and pilot valve can be rotated 360 degrees around the valve stem.
Easy on the operator
"Depending on how quickly the operator closed the valve, and how badly the float gauges were beat up, we lost nearly 5 percent of our material by overfilling. Now, we lose less than 1 percent," claims Tim Gale. The valve offers high flow with excellent shut-off performance.
The new system also lets operators be more productive. "Formerly, the operator couldn't do anything but stand there and watch the drum fill, and then he had to go around and label the drums. Now, he can label the drum while it fills, paying no attention to the filler whatsoever," Gale explained.
Moreover, filling 5-gallon pails used to be stressful on the operators' backs, requiring them to remain bent over while the pail filled. Now, they just insert the hose and the system starts and stops automatically… and reliably.
"The system saves time and prevents injuries… and we were just hoping to save money," Gale said. He added that since the portable dispensing unit was installed in November 2000, followed in January 2001 by the last five solvent dispensing units, the system had "without a doubt" paid for itself within two months.
Following ISO 9000 Certification of both its Cleveland, Ohio, and Tulsa, Okla. plants, State Chemical is considering adding similar highly-reliable, Y-pattern steam valves for temperature control as discussed above. According to Gale, the greatest benefit would be the elimination of scrap and rework because the mixing tank has been overheated or the wrong material added to the chemical batch.
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