Flexible screw conveyors can start and stop under full loads, making them ideal for batching. They readily handle compressible and irregularly shaped materials such as grain. They are fully enclosed, dust-free, easy to clean thoroughly, and can be configured on a caster-mounted frame for in-plant mobility. Care should be taken to specify the proper geometry of the spiral to achieve maximum efficiency. At the conclusion of a conveying cycle, flexible screw conveyors will not completely evacuate material, so they are not well-suited to conveying small amounts of material that must be fully introduced to a batch, such as a pre-weighed flavoring ingredient.
Tubular cable or chain conveyors consist of a convey line circuit, usually either a steel cable or a chain, with polymer discs attached at evenly-spaced intervals. The circuit is enclosed inside a steel tube, thus operating dust- and contamination-free. Two "wheels" are used, one to drive the circuit, and the other to maintain the cable or chain's tension. The material rides at relatively slow linear speeds inside the pockets created by the space between the discs. These conveyors are noted for their gentle handling of the material, a key factor when considering the handling of hops in particular. The convey lines can be routed in multiple directions, and feature a built-in, easy clean-in-place process, which reduces downtime. They can have one inlet and discharge point, or several. From a cost point of view, a tubular cable or chain conveyor will generally fall between the screw conveyor and the pneumatic conveyor. Monitoring disc wear and maintaining proper cable or chain tension are at the top of the list for this class of conveyor.
Bucket elevators are also well-suited for conveying highly fragile products since they essentially carry individual buckets of material, as implied by the name, without imparting any energy or shear directly to the material. They can also move large volumes of material very quickly over short distances and are well-suited for transporting material vertically. However, if control of dust is critical, a fully enclosed design must be specified. Bucket elevators can handle a very wide range of products, including wet or moist materials that may cause problems with the previously mentioned technologies. These advantages do come at a cost however, with bucket elevators using a large number of moving components, which increases cleaning difficulty and maintenance. Individual buckets, drive belts and chains all must be monitored for wear and replacement. Cost can vary widely depending upon the features required, but generally this type of conveyor will exceed the cost of screw and belt conveyors.
Belt conveyors provide a low-operating-cost method of moving material over long or short distances. They can handle a wide range of bulk materials from powders to lumps and can be loaded at almost any point that the belt is accessible. The smooth action causes virtually no product degradation. Side walls on the convey line prevent material waste and the open design allows for visual inspection. Belt conveyors can operate on the horizontal or at an incline, although material slippage may arise if the convey line exceeds a 15° incline. Higher friction belt material and/or some combination with bucket elevators is needed for steep inclines. The open design of these systems makes them less suitable for handling of contamination-sensitive materials or for meeting some regulations for food and beverage processing. Dust is not contained and cleaning the belt can be difficult if conveying moist or sticky materials. Further, sticky materials may cling to the belt on the return side, fouling the pulleys and rollers and ultimately impacting the belt tracking. Belt conveyors provide limited routing options and require careful planning for reliable operation.
Because of the characteristics of many of the materials used in brewing, these frames should be equipped with additional accessories to completely empty the bag contents. This includes features such as spring-loaded frames that will stretch the bags as they empty and lighten, to minimize residual material in the bag. Coarse grain particles can potentially interlock, impeding their flow into downstream processing equipment. Bag-activating devices are usually effective in agitating the material, dislodging pockets of material and promoting flow.
The dust generated during barley, grain, malt, spice, and sugar processing has been identified as a fine material that, in concentrated amounts, has the ability to cause an explosion when mixed with air in an enclosed space and exposed to an ignition source. Repeated exposure to these fine particles over time can potentially cause respiratory problems for workers. This makes dust containment methods a crucial feature to consider when handling these materials.
Most methods of discharging material from a bulk bag include an intermediate receiving hopper that feeds a conveyor. After the bag has been connected to the receiving hopper and the material begins to flow, the air inside the hopper is displaced. Unless this air passes through a filter, airborne dust particles can escape into the surrounding atmosphere. A dust collector mounted on the discharger frame will contain dust inside the sealed system. In some cases, the dust trapped in the filter media can be returned to the receiving hopper by a pneumatic pulse through the filter. This reduces waste and the time necessary to perform the routine cleaning and sanitation typically required in most beverage processing environments.
