A US based biotech manufacturing facility needed to increase their production with larger vessels for buffer hold. The challenge was to fit the larger vessels in the existing production facility with limited floorspace as well as limited headspace. The answer was to go from round to square tanks and replace the top mounted mixer with a bottom mounted magnetic mixer. The close cooperation and know-how from the integrator Acuity Process and the Metenova, was the key to the successful solution.
Problem
A biotech manufacturing facility needed to expand the buffer capacity to meet increasing demand. The request was to increase the existing 500 liter and 1000 liter buffer mix/hold tanks capacity to 3000 liter and 4500 liters respectively. A buffer capacity upgrade of this volume was a significant challenge based on the available space in the existing suites, low ceiling heights, and existing doors and hallway dimensions. These existing dimensional constraints immediately ruled out the ability to use a conventional cylindrical mix tank design. The low ceiling heights and the site’s desire to stick with conventional top mounted mixers presented dimensional and structural support challenges. The low ceiling heights also squatted the tanks down to a less than optimal height to diameter mixing ratio. Lastly, the process required 10-30 doses of 12 Kgs of salt minerals to be manually dosed into the tank through a top mounted port.
The minimum space above the tank to complete the manual dosing needed to be at least 24”.
Design Considerations
The first step was to model the suite and review the proposed locations for all 3 tanks. It was clear that cylindrical tanks would not be optimal for mixing. Given the batch size, the low ceiling heights would force the tank height to diameter ratios out of optimal mixing ratios. The integrator designing the project, Acuity Process, decided to explore non-traditional square mix tanks as an option.
The original design concept with a top mount mixer was replaced by a Metenova Zero-g 8 plastic bottom mount magnetic drive mixer. The mixer removed the need for structural support of a large mixer, motor, and gearbox above a non-metallic tank. It also removed the difficulties of installing a large shaft without removing the tank cover. And it removed the safety concerns for maintenance personnel to work on top of the tanks. Bottom Mount mixing technology for buffers had been well proven in cylindrical tanks and was in wide use across the Life Science industry.
Given that the salt minerals were heavier than water, the low liquid level mixing capability of the Metenova Zero-g Plastic magnetic mixer would conceivably shorten batch mix times. The corners of a square tank act as half baffles aiding in the ability to mix efficiently. To counteract the baffle effect of a rectangular tank the mixer size and power was increased accordingly. The outward sweeping of the Metenova mixer would also help avoid salt particles settling. The tank was designed with welded fillers in each corner to minimize dead zones in the corners. Metenova made recommendations for the mixer to be located as close to the tank bottom valve located in the center of the tank. The tank floor was sloped in a pyramid style to the tank bottom valve to enhance drain and mix ability.
The biggest advantage of the bottom mount mag mixer is the ability to mix small to large batch sizes ranging from 0-4500 Liters.
From a safety standpoint, the bottom mount mixer motor and gearbox were easily accessible. Use of Metenova’s Lowering Device allows the external drive magnet to be lowered, decoupling it from the Mix Head without the need to fully remove the motor and gear reducer. This feature was vital in simplifying routine PM activities, especially given the limited space underneath the vessels.
Big Problem, Simplified
In summary, the manufacturing facility managed to scale up their business by introducing a square tank design that delivered approximately 33% more buffer hold capacity in the same usable footprint. The square tank design delivered fast, repeatable, homogeneous mixing. The Polypropylene bottom mount Metenova Zero-g 8 Plastic magnetic mixer delivers flexibility from small to large batch sizes across the full range of the tank. The Acuity Process Design team also incorporated custom sight glasses for visual verification of liquid level, impeller speed, vortex formation, and homogeneity. In addition, design considerations were included to limit dead zones in the corners and ensure full drain and CIP ability. Moving the mixer from the top to the bottom of the tank improved the site’s safety objects and made life a bit easier for preventative maintenance technicians.
The key for the successful solution was the close cooperation and share of knowledge between Metenova, Acuity Process Solution and the end-user.