Purpose: Flow Sciences was approached to design and build an enclosure that could house the Buchi B-290 Mini-Spray Dryer during process. Particle sizes would range from 1 to 25 µm, requiring the enclosure to offer containment down to less than one microgram per cubic meter. The client planned to weigh API and dissolve weighed sample into various solvents which would then be introduced into the Buchi B-290.

Process: 50 grams of powder would be dissolved in 725ml methanol outside of the enclosure. Liquid will then be brought into the enclosure in a sealed container and fed into the peristaltic pump of the B290. The maximum amount of powder dissolved in liquid of API at one time is 50g. Upon connecting to the B-290, the client would be spray-drying at a rate of 15mL/min. Upon completion of the cycle, the client planned to remove the collection vessel, seal it with a cap, and remove the vessel from the enclosure via a pass through on right side. The client would then disassemble the glassware and spray down with a misting wand to get as much powder off as possible and then bag out through a continuous liner what glassware was to be sterilized in the cleaning room. All glassware was to be misted, wiped, and then double bagged. Once complete, the client would transfer the product to another room, disassemble all glassware, replace the HEPA filter, and take everything to a cleaning room.

Equipment: Due to its strength and chemical resistance, polypropylene was chosen for the superstructure and a removable sash door designed with 10” oval glove ports. In order for visual clearance around the entire enclosure, acrylic viewing panels were incorporated into all four sides, with glove ports on both ends to help facilitate cleaning and process assistance. Due to the equipment inside the enclosure, the size of the enclosure was quite large—90” exterior width and approximated 50” deep. BIBO Dual HEPA fan filter units were placed on the top of the enclosure, requiring 968 CFM at the thimble connections connected to house exhaust to maintain 100 LFPM at the face opening, and 842 CFM if recirculating.

Given the weight of the Buchi, as well as the other equipment that would be placed inside the enclosure, FSI designers made a table with a cutout for a cart that would lock into place inside the enclosure. Using this method, the Buchi would be rolled in and out of the enclosure on the table for ease of cleaning and service between cycles.

The client also wanted the base to be a drillable material so the air pump could be brought outside of containment and moved below for easier cleaning. Engineers designed a solution that would move the pump outside of the enclosure by adding more iris ports, connections, and hoses. Also, a sink was designed for the glassware allowed easier access while cleaning.

A one-to-one ratio mock-up made of MDF and acrylic was created and sent to the client who wanted some design changes. The client wanted the pass thru to be bigger so it could fit a 1 liter bottle that is 9.25″ tall out through it. Also, the client wanted a glove port in the upper door so that the customer could reach the top of the B-290 for removing and cleaning parts. They wanted the glove port on right side lowered by 2″ for better ergonomics and wanted the rear plenum split into four pieces for easier cleaning.

In lieu of adding a glove in the door, a fifth glove was added to the draft shield in the center. The entire enclosure’s height was reduced by two inches due to facility constraints. An N2 fitting for the pump was also added.

Evaluation & Testing: Between July 12th and July 18th, 2019, factory acceptance testing was performed on the enclosure in the presence of the client to measure equipment compatibility with the process and to determine the containment effectiveness during simulated operations. Overall performance indicated that the enclosure met the specifications determined. During surrogate powder testing, no individual sample exhibited a TWA exposure of more than 0.316 ng/m3., far better than 1 µg/m3 requested.

Findings: These exposures, well below the CPT, indicate that with good laboratory practices, this enclosure is highly effective at providing containment for compounds with Occupational Exposure Limits (OEL)s < 1000 ng/m3.

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  • What is being done inside of the enclosure? What type of material (powder, liquid, gas, nuisance odor) is being worked with? How does the material enter and exit the enclosure system? etc...
  • What type of filtration is required? Single HEPA, Dual HEPA, Carbon, House Exhaust, etc... What is the required OEL (Occupational Exposure Limit) for the process, or any other details about containment goals? What is the quantity of powder or liquid, task duration, composition of powder, etc...?
  • What equipment is being worked with? What is the equipment model, size, scope, function, and any other information that will affect the design of the enclosure, including movement, heat output, etc...? *State the specific equipment make and model if available*
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  • Are there any additional notes or information that should be considered? Are there any special design requirements?