Powders in their place
Contained drum filling and continuous liner technology

In the pharmaceutical, fine chemical and toxic chemical industries, containing the discharge of potent active powders into lined drums is required to protect operators as well as products. Plants must be kept up to standard, either by installing new contained filling systems or by improving containment on existing equipment.

As new pharmaceutical active ingredients become more potent, requirements to protect operators and prevent product contamination become stricter. At the same time, however, manufacturers increasingly need to keep their production systems flexible. Powder filling, for example, may be required to work with different container types, such as IBCs as well as drums, different drum sizes and different product weights in a given drum size. All this presents considerable challenges to drum filling containment systems (see Table).

The traditional solution for drum filling is for each drum to have its own liner, with an inflatable seal or equivalent system to prevent leakage, and perhaps local exhaust ventilation. The problem with this arrangement is that after every fill the seal needs to be deflated so that the liner can be detached. This releases dust into the atmosphere from the liner and the upstream process chute, and can allow product contamination as well as exposing the operator to the product. Stopping this powder from spreading often requires complex and expensive systems, including separation of rooms, enhanced cleaning regimes, advanced ventilation systems with different pressure regimes, airlocks, and the need for staff to shower or change their clothing when moving between rooms.
A better solution
There is a better solution. The double
O-ring continuous liner system (Figure 1), in which a complete batch is filled without breaking the seal between the liner and the filling chute, is inherently simple, yet offers excellent protection for both operators and products, without the need for complex bolt-on equipment and procedures. It eliminates the need for complex and expensive inflatable seals, and can achieve an OEL of 100 µg/m3 based on 1-hour operation over an 8-hour time-weighted average (TWA).
The system consists of a stainless steel chute surrounded by a cartridge in which a continuous tube of liner material is stored. The liner is fixed to the chute by O-rings at the top and bottom, and the bottom of the liner tube is closed using a bag tie.
To start filling, the sealed end of the
liner tube is placed into a drum and product is discharged (Figure 2). When the drum is full, the liner is gathered, twisted together and tied using two closely-spaced bag ties. The liner is then cut between the ties, so that the bottom tie seals the liner of the drum that has just been filled. The top tie, meanwhile, secures the base of the liner that will be used for the next filling operation. Before filling, the liner is opened by inflating it with air or nitrogen. After filling, the liner is deflated again to create a “neck” that can be easily tied off by the operator. The entire filling cycle is controlled by a series of safety interlocks.
Liners can be changed without exposing the chute to the atmosphere: the remaining part of the old liner is simply placed inside the new liner, tied off and cut. One O-ring is lost at each liner change, but because they are outside the powder flow, the O-rings can be made of inexpensive materials. For loading, the liner cartridge is positioned on a special table, the liner is placed inside, and the cartridge is attached to the chute using a simple bayonet coupling. The system allows any thickness of liner to be used—an important factor if product/liner stability data has already been established and compliance bodies prevent changes.
Adding versatility
The continuous liner system can be enhanced in various ways. To prevent dust explosions, for instance, a nitrogen purge can be added to the filling chute, reducing the oxygen concentration to 5 percent or less. A balanced nitrogen and exhaust system provides a sweep of nitrogen through the chute.
For cleaning, a wash tundish can be connected to the chute outlet via a Tri-Clamp connection, without the need for an inflatable seal. The wide range of solvents used in pharmaceutical plants can attack the silicone rubber typically used for inflatable seals. The double O-ring continuous liner system allows for product contact surfaces to be uniquely metallic, giving considerable extra flexibility for solvent usage.
A full range of weighing systems can be used with continuous liner filling, ranging from a simple scale with local indication to full autofill systems with setpoint control. Special low-profile weighing systems can also be developed for retrofitting to existing equipment.
Analysis of material properties such as bulk density and cohesion allows metering systems such as rotary valves or screw feeders to be designed to suit the products being filled. The continuous liner cannot be opened to allow product samples to be taken, since this would invalidate the point of the system. An alternative is to use an in-flight screw auger to collect samples from the product chute. The outlet of the auger can be connected to the sample container via a split butterfly valve: one half of the valve remains fixed to the auger, while the other is attached to the sample container. To achieve containment of 10–50 µg/m3 for 1-hour operation over an 8-hour TWA, the basic continuous liner system needs to be upgraded by surrounding it with a horizontal crossflow booth.
Key design features include and inward air velocity of greater than 1 m/s, an extraction plenum for uniform airflow, and a sloping base for drainage after cleaning. The extract air filters can be integrated into the cabinet or housed separately. Doors on the cabinet, with roller conveyors inside and outside, allow drums to be positioned and removed easily.
Even higher containment standards can be achieved by surrounding the continuous liner system with a glovebox. Previously, containment down to 1 µg/m3 would have required a double glovebox, but the PSL DrumBox (Figure 3) achieves this standard using a single-glovebox design. Extract air is introduced at low level via a slot whose height can be varied, and extracted via HEPA filters at the back of the top of the glovebox. The top section of the cabinet is fitted with a simple lift-off window.
Flexibility is a key issue in many modern plants, and a big advantage of the PSL DrumBox is that it can operate in three modes to provide containment in the range 1–50 µg/m3. This ensures that when handling powders with different OELs, operators always have the easiest working conditions consistent with the OEL requirements for the powder being handled at the time.
The three operating modes of the PSL DrumBox are:
Level 1 (50 µg/m3): top window open;
Level 2 (10 µg/m3): top window sealed, but open gloveports (no gloves); and
Level 3 (1 µg/m3): top window sealed, and gloveports fitted with gloves.
The very highest containment—less than 1 µg/m3 for 1-hour operation over an 8-hour TWA—requires a double-chamber glovebox around the continuous-liner filling system. The PSL FlowBox (Figures 4) provides this containment for drums of up to 220 litres in volume.
Extract air flows into the front of the lower glovebox chamber and out at the back of the upper chamber. The top and bottom chambers are separated by a shelf, in which is a hole for the drum. The hole is slightly larger than the drum diameter, creating an engineered gap that provides a high upward air velocity at this point. Any dust particles released when the liner is tied and cut are thus forced to remain in the upper chamber because they cannot make their way through the gap against the upward airflow.
Optional features of the PSL FlowBox include a system to ensure accurate drum alignment, a hinged plate to seal off the chute and residual liner after each filling operation, and an interlock that requires the gloves to be turned inside out and pulled out of the chamber before the door is opened. The latter arrangement reduced the risk of dust on the gloves becoming airborne when the door is opened.