Replacing Weigh Scale In Reactant Addition Processes

In many manufacturing processes, chemicals are added to a process reactor to improve product quality or achieve a specific performance characteristic. Manufacturers of personal care products require chemical addition for a variety of purposes. One example involves adding a specialty agent during the compounding of toothpaste to promote adhesion of a gingivitis compound onto the tooth surface after brushing and rinsing. Other examples include denture adhesives, clarifying agents utilized in hairsprays and shampoos, and other personal care products.

In many cases, the manufacturer’s existing delivery system for these additives comprises a feedstock vessel on a weigh scale, a delivery pump followed by a chiller (due to the low vapor pressure of the chemistry), and a manually adjusted variable speed metering pump. In use, the operator would monitor weight loss hourly, calculate the mass flow rate, and adjust the metering pump speed to increase or decrease chemical addition.


THE CHALLENGE

Several obstacles are present in this arrangement:

• Controlling the delivery of reactants is a manual process. An automated delivery of reactants would improve control and repeatability.
• Process flow rate calculations are made hourly by manual weight/time calculation. It is preferable to control reactant addition in real-time, to avoid over- or under-addition and risking the possibility of a scrapped batch.
• The weigh scale is susceptible to environmental influences, such as an accidental bump by the operator during the process run. A more stable process reduces or even eliminates additional uncertainty due to environmental influences.

THE BROOKS SOLUTION

In a new automated installation, a Brooks QUANTIM® Coriolis mass flow controller becomes part of a totalizer solution that stops reactant addition when the desired mass of reactant has been added. The QUANTIM measures and controls instantaneous reactant flow rates with better than 1% of rate accuracy. Installation details comprise the following:

• Installation of QUANTIMs with 500 gram/hour and 1,000 gram/hour flow rates.
• Reactants delivered from a pressurized chamber using an inert push gas at 80 psig.
• Process area is Class 1, Division 2 so a protected, purged enclosure is required for the secondary electronics and totalizer. This was designed and produced by the local Brooks representative.
• The totalization function enables the QUANTIM to stop reactant delivery when a preset mass of reactant chemistry has been added to the reactor vessel.

With the manufacturer’s system fully automated, operators no longer depend upon manual weight/time calculations to determine if process flow is at the proper rate. Because QUANTIM’s Coriolis flow sensor technology is immune to environmental effects, chemistry addition is precise and repeatable. Over a period of time, the customer can continue to use the weigh scale to confirm the batching accuracy of the QUANTIM, and may still perform periodic weight/time computation, but this would only be optional for record-keeping purposes. With additional process experience, this activity could be eliminated. In addition, the feed pump, chiller, and variable speed metering pump have been completely eliminated.

The customer can now have a high level of confidence in the QUANTIM automated flow delivery and control installation, and can expect that his R&D process runs are easier, quicker, require less manpower, and provide more consistent product batches.

An unexpected benefit is the diagnostic value of QUANTIM. When the QUANTIM becomes ‘starved’ for reactant flow, or has difficulty controlling flow, the operator receives this feedback automatically, and knows that these indicate reactant contamination, inadequate cleaning, and/or incipient filter plugging. The prior system provided no such diagnostic information about purity of reactant feeds or the efficacy of the cleaning process.