To choose the appropriate conveying system, a pharmaceutical manufacturer needs a thorough knowledge of the benefits and limitations of each conveyor type. A company must also understand the physical characteristics of the production line and the material to be conveyed. Flexible-screw, aero-mechanical, and vacuum conveyors are common in the pharmaceutical industry. The following provides an overview of each type of system. 

 Flexible-screw conveyors are often the simplest solution (see Figure 1). They incorporate a heat-treated and tempered carbon or stainless steel spiral that rotates within an ultrahigh molecular-weight polyethylene tube. The term 

 means that these conveyors can be curved to some degree: The user can direct them around obstacles between the inlet and outlet. These machines carry powdered, granular, and flaky materials with bulk densities as great as 150 lb/ft

. They operate at rates as fast as 40 tons/h across distances as great as 65 ft. Systems can be linked together to move materials across greater distances. 

The flexible-screw conveyor’s simple design results in low initial cost, quick installation, and low maintenance. Pharmaceutical models can be quickly dismantled for cleaning. The system’s parts can easily be replaced. Abrasive products cause wear on these systems, but models with abrasion-resistant rubber tubes are available. 

Flexible-screw conveyors should always operate while full of product. It is used to deliver product from storage or a bag-tip station to a weigh hopper or a vessel with a high level switch. The system maintains a constant head of material in hoppers by gently filling to the high level control. The in-flight product is constant, and flexible-screw conveyors yield accurate, repeatable batches.

The aero-mechanical conveyor (AMC) is ideal for transferring products along 10–85-ft distances at rates as fast as 120 tons/h (see Figure 2). The AMC consists of several evenly spaced polyurethane disks, which are attached to a wire rope and travel within parallel steel tubes. The disks’ high speed produces an air stream that entrains the product in airflow until it is ejected. This method of conveying facilitates capacities as great as 120 tons/h with low energy requirements and virtually no separation of mixtures. 

The AMC’s major benefit is that its airflow shields materials from degradation. The material is separated from the air that carries it, and the unloaded air current is directed into the return section of the tube, where it is retained in the tube circuit. Because the air is recycled, the AMC eliminates environmental concerns. 

One disadvantage of an AMC is that it requires a lot of maintenance. Rope tension must be adjusted regularly during start-up and checked periodically. AMCs with automatic rope-tension monitoring and adjustment are available. Rope life depends on the length of the conveyor, the number of starts and stops, solids loading, and routine inspection and tensioning. Properly maintained rope-and-disk assemblies can last as long as 14 years.

Vacuum conveyors carry products over long distances and tortuous routes (see Figure 3). Vacuum conveying is usually restricted to throughputs of about 10 tons/h and distances as great as 330 ft.

A vacuum conveyor uses air to move materials through an enclosed pipeline. It is easy to route, has few moving parts, is dust-tight in operation, and leaves minimal residue when emptying a product. Because air is sucked into the unit, a vacuum conveyor is the preferred choice for toxic or hazardous materials. Accidental damage to the conveying tubes will not cause product to escape to the atmosphere. 

The motive force comes from an exhauster or a side channel, high-efficiency fan at the receiving end of the system. Air-powered venturi systems are a good choice for low-capacity conveying. Venturi systems impose little capital cost and are inexpensive to operate.

Vacuum systems are normally the only conveying choice for customers who want to suck material out of bags or open containers such as kegs and drums. These systems are also suitable for applications with multiple inlets.

Reverse jet self-cleaning filters clean the conveying air and return it to the atmosphere after use. These filters reduce maintenance and minimize product loss.

Flexible-screw, aero-mechanical, and vacuum conveyors are the most common devices for transferring pharmaceutical materials. Each has different operating speeds, distance limitations, maintenance requirements, and load tolerances. Understanding each system’s characteristics is essential to choosing the right system for a conveying application. 

Keith Simpson is a marketing manager at Spiroflow Systems.

Articles

In the Mixer

To choose the appropriate conveying system, a pharmaceutical manufacturer needs a thorough knowledge of the benefits and limitations of each conveyor type. The following overview compares several types of systems.

Selecting the Best Conveyor for Your Application

Esco Technologies
 Transfer hatches are easy to clean


 The new line of stainless steel transfer hatches from Esco Technologies (Hatboro, PA) are constructed entirely of stainless steel and feature internal coved corners. The hatches incorporate frameless, tempered-glass doors and single-piece, molded gaskets without joints. X.Q. Lin, president of Esco USA, says these features make the transfer hatches easier to clean than traditional pass boxes.

Lin adds that the transfer hatches include reliable mechanical interlocks designed without parts that could fail.

The hatches maintain a physical barrier between a cleanroom and the external environment. The devices permit material transfer without requiring personnel to enter a cleanroom, thus protecting the external environment from contamination. The units are suitable for pharmaceutical cleanrooms as well as biological safety laboratories.

Hawk Measurement
 Versatile level switch offers high sensitivity


 The "Vibration Smart Switch" is the newest addition to Hawk Measurement's (Middleton, MA) series of point-level switches. Jack Evans, president of Hawk, says the highly sensitive device detects the level of pharmaceutical water, powders, solids, and finished products within a process tank. 

A piezoelectric crystal vibrates two tines of the switch's sensing element at their resonant frequency. When material touches the tines, it dampens the signal and activates a relay. The relay can be used to turn a filling cycle off or on. 

Evans says the unit can be installed easily at the top or bottom of a process tank or silo. Operators can rotate the switch's head without affecting its conduit connection. An integral version of the switch contains the electronics and probe in one unit. Users can choose to install the unit's display in another location.

PharmTech's monthly newsletter, Equipment & Processing Report, reviews the Editor's Picks for the June 2008 edition: Esco Technologies and Hawk Measurement

June 2008 Editor's Picks: Esco Technologies and Hawk Measurement

The pharmaceutical industry has been using disposable containment technology for more than 10 years, and many applications have emerged during that time. Beginning with bulk bags and super sacks, options have multiplied to include flexible glove bags, flexible isolators, and flexible soft-wall cleanrooms. The technology’s containment capability has steadily improved to the point where it is comparable with traditional rigid systems. As a result, manufacturers have stopped seeing disposable containment as an 

 solution, and the technology increasingly incorporates thoughtful design and engineering. The future promises to bring more changes and new applications for disposable containment technology.

Huw Thomas, a principal pharmaceutical engineer at Foster Wheeler (Clinton, NJ), says multilayer flexible systems such as the one offered by ILC Dover (Frederica, DE) could point the way to further innovations. The company wrapped a small glove bag around the disconnection point of a continuous liner, and an operator double-ties or crimps and cuts the liner at the disconnection point inside the glove bag. “It’s the same principle as using a flexible liner inside a rigid glove box, which is a standard way of achieving nanogram-level containment,” Thomas explains. Multilayer flexible systems such as this can provide containment well below 1 µg/m

. “We’ve used this approach to ramp up containment on discharge systems,” says Thomas.

Connecting containers with heat sealing or crimping could be abandoned in favor of a zip-tight connection between two bags, Thomas remarks. This low-cost strategy has the benefit of simplicity and provides many potential applications. This technique “can convert a standard Tri-clamp into a well-contained, make-or-break connection,” he adds. 

More and more, companies are manufacturing drugs in multipurpose facilities. Many new products are cytotoxic and hazardous. “These materials create such a high demand for cleaning between products that flexible disposable technology is the best solution,” according to Richard Denk, director of the pharmaceutical department at Hecht Technology (Pfaffenhofen, Germany). He predicts that pilot plants and contract manufacturers that must produce different products with the same equipment within one facility will increasingly use disposable containment. 

Increasing production of high-potency products will make flexible containment kits more popular, says Thomas. Operators can attach these kits to standard equipment to improve containment whenever necessary. Several companies already use this approach. Rather than developing new high-containment equipment, Thomas says, equipment manufacturers could collaborate with containment vendors to provide low-cost containment kits to retrofit to existing equipment such as tablet presses and granulators.

Introducing a low-cost barrier system to a sterile manufacturing suite is another idea with great potential, according to Thomas. “A simple barrier between the aseptic zone and the operator would greatly add to the sterility assurance of that operation,” he explains.

Gene Fuchs, field marketing manager for aseptic transfer and drug delivery at Sartorius Stedim (Aubagne, France), says that disposable devices could be combined to change or eliminate traditional technology. For example, using rapid-transfer ports with disposable fluid paths eliminates the need for mouse-holes as a transfer system between classified spaces. In addition, disposable nozzle systems are replacing traditional spare filling nozzles for fillers. “Perhaps the most cost-effective change is the ability to reduce Class A space by using a fully disposable path from the holding vessel to the filling nozzle,” Fuchs says.

Technological advances now enable the industry to shift from an application-based to a systems-based approach to disposable containment, according to Fuchs. Disposables can be designed into the manufacturing process so that drug substance can be placed in a disposable bag, filtered, transferred into a cleanroom or isolator, and put into capsules using a disposable nozzle system.

Disposable containment also allows manufacturers to change the manner in which they design new facilities. For example, storing materials in disposable bags rather than in permanent vessels eliminates the need to include space to store vessels or wide hallways to transport them. This strategy also reduces the amount of cleaning required. Combined with isolators, disposable containment “is changing the entire fill-suite configuration,” Fuchs says.

Denk agrees. “Within the next 10 years, the design of process equipment, product-transfer systems, and facilities will be completely different from what we know today,” he says.

Production Lines

Manufacturers have stopped seeing disposable containment as an ad hoc solution, and the technology increasingly incorporates thoughtful design and engineering. The future promises to bring more changes and new applications for disposable containment technology.

Equipment and Processing Report-06-18-2008

Selecting the Best Conveyor for Your Application

June 2008 Editor's Picks: Esco Technologies and Hawk Measurement

The Future of Disposable Containment