Magazine Article | July 11, 2011

Seamlessly Upgrade Your Mixing Operation

Source: Life Science Leader
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By Christine Banaszek, Charles Ross & Son Company

Improving manufacturing process efficiencies is a continuous endeavor in the life sciences industry. In today’s fiercely competitive markets, it has become necessary to regularly evaluate cost position to increase profitability and customer satisfaction. This calls for a cross-disciplinary effort from research and development to manufacturing and sales.

Among the various parameters considered in total production cost analysis is the mixing operation. A relatively simple unit operation, mixing is often overlooked in terms of upgrades. Many managers and operators will tend to settle on a mixing process that may require several transfer steps, a long cycle time, or costly, labor-intensive maintenance all because … well, it works. “That’s how we’ve always done it.”

While “Don’t fix what isn’t broken” is probably a sound theory in certain situations, refusing to upgrade mixing operations can cause any company to miss out on significant cost savings. Lost value due to inefficient mixing includes wasted income as a result of low yield, prolonged mix times, corrections and reworks, unrevealed full functionality of mixture components, product contamination, and even worker safety issues. Fortunately, these issues are certainly avoidable and correctable. This article presents some strategies for implementing mixer upgrades seamlessly and cost-effectively.

Identify Your Opportunities For Improvement
Go through each mixing step and the operations surrounding it: loading of raw materials, powder wet-out, dispersion or dissolution, emulsification, reaction, heating/cooling, deaeration, let-down, drying, discharge/transfer, product changeover, cleanup, maintenance, etc. Are any of these procedures a process bottleneck? If different stages of mixing are performed in multiple vessels, what can be combined in order to eliminate transfer steps and reduce cleanup? If rework is done frequently, what is the typical cause? Can batch-to-batch inconsistencies be reduced or operator safety improved? Once you’ve made a list of “opportunities,” it becomes easier for you and your mixer supplier to decide which mixing system can accomplish most, if not all, of the items on your list.

As an illustration, let’s explore the experience of one company specializing in synthetic bone graft technologies. The company’s laboratory used to make small batches of a putty-like bone graft substitute through a two-step process: The base gel was prepared in a chilled glass reactor equipped with a stirrer and later transferred to a single planetary mixer in order to add the granular active material. This procedure took a total of 7 hours.

Looking for a better way to make the putty, the company evaluated a double planetary mixer and discovered that the almost day-long two-step process can be completed in a single mixer and in just 30 minutes. The tremendous improvement in cycle time was accompanied by lower contamination risk and improved mixture quality.

In another example, the plant manager of an ophthalmic solutions manufacturing facility was looking to make its working environment safer and more efficient. In particular, one part of the process was tricky for the operators: They were preweighing salt powders and climbing up a mezzanine to dump the solids into any of six 500-gallon tanks.

After researching his options, the plant manager decided on an inline rotor/stator mixer with powder induction system and had this installed by the weighing station and piped to all six tanks for recirculation. Simple valves are used to divert finished product downstream or switch instantly from one source vessel to another. Now, an operator simply weighs the salt powders right in the mixer’s feed hopper and opens the powder induction valve to introduce solids into any of the large tanks. The solids meet the incoming liquid stream right in the high shear zone of the mix chamber and are dispersed instantaneously. The upgraded mixing process is not just more convenient and operator-friendly but also faster.

Some opportunities are less obvious than others. For instance, a mixer upgrade may not only improve cycle time but also allow you to conserve certain raw materials, due to enhanced mixing. When a more stable emulsion is produced in a mixer with increased shear input, it is possible to use less surfactant. Or perhaps a more efficient means of powder dispersion could benefit a process where solids are intentionally overdosed to compensate for agglomerates that remain in the batch and which are subsequently filtered downstream. Explore as many opportunities in your process as possible.

Get Empirical
Calculations on throughput, energy savings, or return of investment will almost always rely on several assumptions, but as much as possible, these assumptions must be based on solid information, not guesses. Performing mixing trials is the best way to evaluate potential solutions while providing solid justification for your mixer upgrade. Testing will give you an apples-to-apples comparison between a new mixer design and an existing one that may need replacement.

One approach is to perform mixer tests at the equipment manufacturer’s facility. Most well-equipped testing facilities will have many types of mixers available for demonstration. The flexibility to shift from one mixer design to another during process simulation is very advantageous. The mixing engineer helping you with the test can impart a new understanding of your own application and share processing techniques gained from years of experience. It could be as simple as modifying the order of ingredient addition, applying vacuum at a certain stage of mixing, or utilizing an entirely different mixer configuration that you may not be familiar with. To obtain reliable data for scale-up, a good rule of thumb is to test on a mixer no smaller than 10% of the capacity you are looking to eventually install.

Another method of getting empirical data is to test rental equipment right in your own plant. Producing a batch out of your own raw materials on the mixing system which you are geared at purchasing will gain you important information such as power loads, expected cycle times, flow rates, or ease of cleanup and changeover. Immediately after mixing you also would be able to analyze the finished product according to your quality check procedures, something which simulation testing at a manufacturer’s facility may not allow you to do readily.

For example, a manufacturer of transdermal drug delivery systems assessed a multishaft mixer in its facility. The company was able to prove that this mixer configuration delivers the key parameters required in their manufacture of biocompatible pressure-sensitive adhesives and drug-adhesive solutions: homogeneity (samples taken from the top, middle, and bottom of the mixing vessel were taken to establish batch homogeneity), predictable viscosity (the well-mixed batches yielded consistent viscosity readings at defined temperatures), accurate drug content, and variable agitator speeds (variable frequency drives enabled the operator to independently control the speed of each agitator to fine-tune flow patterns and optimize the vortex during ingredient charging). After repeated simulations, the company proceeded to upgrade its entire mixing operation using data obtained from the in-house trials.

When Practical, Consider Reconditioned Equipment
Limitations in capital spending do not necessarily have to result in a development freeze. For mixing upgrades that need to happen right away and on a tight budget, purchasing reconditioned equipment is one of the practical solutions worth considering.

Reconditioned mixers have been inspected and rebuilt back into perfect working order. Beware of buying equipment simply labeled as “used” as these could cost extra in repairs and parts replacement even before they can actually be used. It is highly recommended to purchase reconditioned equipment from the original equipment manufacturer (OEM) to ensure the machine is serviced completely and spare parts will be readily available when you need them in the future. Just as importantly, an OEM will offer reconditioned mixers with the same warranty as their new equipment. It’s one creative option that will help you handle surges in production or serve a new product line while getting you to the profitable stage sooner.

Get A Head Start On Operator Training
Normally, it takes months to build full-scale equipment. While waiting for a new unit to be delivered and installed, research or production can still continue using rental equipment. This period can thus be utilized for operator training and establishing processing routines.

Many rental programs credit a considerable portion of rental fees against the mixer purchase price, so that in the end, renting does not have to cost you much. In most cases, the gains reaped from several weeks’ worth of training or production more than compensate for rental charges.

A careful evaluation of R&D mixing equipment at the early stages of any project is ideal. Even though lab-scale batches may be easy to prepare in simple, kitchen-type mixers, it’s often a good idea to invest in truly scalable equipment right from the beginning. This kind of foresight and long-term planning will prevent a great deal of future scale-up headaches and delays. In fact, taking the time to map out strategies and discuss them with your equipment manufacturer ahead of time, rather than strictly working on a project-to-project basis, ultimately pays off. More than just taking your orders, a dependable and competent supplier can help engineer your success in the mixing room and beyond.


About The Author
Christine Banaszek is an application engineer at Charles Ross & Son Company, manufacturer of specialty mixing and blending equipment. She received her B.S.Ch.E. from the University of the Philippines – Diliman, where she also subsequently served as instructor of chemical and environmental engineering.