Bulk Solid Handling & Pneumatic Conveying Systems - Assignment Example

 Introduction In many industrial applications there is a need for the conveyance of bulk solids through the various stages of operations and manufacturing. There are many ways of doing this – mechanical, hydraulic, and pneumatic handling systems. Materials conveyance through the mechanical systems is effected through the use of chains, buckets and screws, some of them to be shown in the next few pages. On the other hand, pneumatic conveying is defined by Woodcock and Mason (1987) as the transportation of dry bulk particulate or granular materials through a pipeline by a stream of gas. Normally, air is used, although where there are risks of fire or explosion nitrogen is the preferred gas. The main purpose of a pneumatic conveyor is to move solid particles from one location to another. For instance, particulate material is to be transported from the bulk transport vehicle to a storage hopper, and from there to a bagging machine. Requisites are a source of compressed air or gas, a feed into the pipeline, and a receiving hopper equipped with a means to separate the product from the gas. The systems available are quite flexible, sometimes transporting materials from several sources to a single receiving hopper, or from a single source into several receiving hoppers. Systems also provide for a means to monitor and control the material flow rate, and allows for design for fully automatic operation. Brief history of pneumatic conveyance technology One of the earliest applications to which pneumatic conveying was applied is the capsule transport lines designed and built during the early 1800s. In 1886, B.F. Sturtevant showed that solid particles can be conveyed in a stream of air in a controlled fashion. The first practical system used fan-driven vacuum systems used mostly for sawdust and grain. By the 1900s, positive pressure systems were the preferred technology, wherein the conveying velocities of air were high and the particles were carried in suspension at low concentration (the “dilute phase” of transport). Today, the principle of pneumatic conveyance has many practical applications across several industries. It is used to convey PVC resins, asbestos powder, coffee beans, moulding sand, grass seeds, gold ore, talcum powder, and an infinite number of similar particulate materials. Considerations for selection of pneumatic conveyance systems Three major problem areas to be considered in the selection of bulk solids handling systems, particularly pneumatic conveyance methods: 1. Erosion of the plant by the conveyed product 2. Effect of the plant on the product in terms of particle degradation 3. Explosion risk with certain products. For instance, product must be conveyed at low velocity, to minimize plant erosion by abrasive products and in order that excessive degradation of friable products may be avoided. Where the product is potentially explosive when suspended in air as a dust cloud, there is a chance that ignition may be initiated by static electricity or friction sparks. The risk of explosion can be minimized/eliminated entirely as it is observed that pneumatic conveyors reduce fire and explosion hazards, in comparison with mechanical handling systems. Combustible materials include starch, flour, cellulose acetate, wood flour, gunpowder pellets. According to TSM Houston (2009), there are generally four main options for pneumatic conveyor systems. These are: • Dilute phase pressure operation • Dilute phase vacuum operation • Dilute phase pressure-vacuum operation • Dense phase pressure operation Below: Dense phase pneumatic conveyor Source: TSM Houston When choosing between dilute phase and dense phase pneumatic conveyor systems, consider how abrasive or easily degraded the properties being conveyed are. Dense phase pneumatic conveyor systems are ideal in situations where abrasiveness and degradation of the material are not concerns. Dilute phase pressure pneumatic conveyor systems typically convey bulk material from a single input to one or multiple destinations. Pressure systems can convey material in larger capacities and over longer distances than vacuum systems. Dilute phase vacuum pneumatic conveyor systems are used to move material from multiple sources to one or multiple destinations. Because vacuum systems are better at picking up materials than dilute phase pressure pneumatic systems are, they are useful for transporting material from places like storage containers and rail cars. With dilute phase vacuum pneumatic conveyor systems it is possible to use wands for material pick-up. Dilute phase pressure-vacuum operation pneumatic conveyor systems are a combination of the pressure and vacuum systems that are best suited for applications like unloading a rail car where the material can be pulled through the air to a filter and then pushed toward the final receiver with a blower. C.K. Airtech India Private, Ltd. Pneumatic conveying system Testing and Commissioning Pneumatic Conveying Test Facilities : From Handbook (Mills, et al., 2004) p. 651 1. Conveying Requirements It is suggested that any system should be capable of both dilute and dense phase conveying, at a reasonably high material flow rate, and over a reasonably long conveying distance. The conveying system should have a wide range of controls, and be suitable for test, development and research work, and conveying trial demonstrations to potential clients. 2. Preliminary Decisions A number of initial decisions need to be made which will affect the scope of the work that will be possible to undertake, and the capital investment on the test facility. In some cases a definite recommendation will be made, where it is felt that the given parameter should be adopted for an initial facility. In other cases a range of values will be given so that the cost implications can be considered. System Type. If a single pneumatic conveying system is to be installed initially, it would be recommended that this should be a positive pressure conveying system. This is probably the most useful and versatile of all conveying systems for test work. At a later date a vacuum conveying system could be considered. Material Capability If there is no previous experience with pneumatic conveying it would be suggested that testing should initially be limited to non-explosive materials. At a later stage, a suppressant system could be fitted, or provision could be made for explosion venting or making the system into a closed loop and employing nitrogen. The conveying system should be capable of handling most powders and granular materials. Commissioning Problems : From Handbook (Mills, et al. 2004) pp. 537, 539-540 The inability to convey a material, pipeline blockages, and systems not capable of meeting the required duty are, unfortunately, not uncommon problems to be experience with pneumatic conveying systems, and particularly so at the time of commissioning a system. The cause of a particular problem, however, is not always obvious and it may required some “detective” work to identify the cause of the problem. It might related to the type of system, the system components, or to the material being conveyed. Problems often occur if a change is made to a system, the most common being a change of conveyed material and distance transported. Pipeline blockages are a major problem, and when they are encountered during commissioning trials it may mean anything from a simple adjustment needed in the plant, or a serious design fault with the system. Incorrect Air Mover Specification If it is due to a design fault, the most likely reason is that the air mover is incorrectly sized for the duty. If the volumetric flow rate of air available for conveying the material in the pipeline is insufficient, it is unlikely that it will be possible to convey the material. A minimum value of conveying air velocity must be maintained at the material pick-up point at the start of the conveying line. The value depends upon the material being conveyed and, for materials that are capable of being conveyed in dense phase, in moving bed type flow, varies with the solids loading ratio at which the material is conveyed. Since air is compressible it is extremely important that the pressure of the air at the material pick-up point, is taken into account in evaluating the free air requirements for the air mover specification. Conveying Air Velocity. Because air is compressible, with respect to both temperature and pressure, the starting point in the determination of any relationship for the determination of conveying air velocity is the Ideal Gas Law. The appropriate model for checking conveying air velocity is: 576 po Vo T1 C1 = -------------------------- π d2 p1 To where C1 = conveying line inlet air velocity - ft/min p1 = conveying inlet air pressure - lbf/in2 abs T1 = conveying inlet air pressure - R d = pipeline bore - in Vo = volumetric flow rate at free air conditions - ft3/min po = free air pressure = 14.7 lbf/in2 and To = free air pressure = 519 R Pipeline Bore Influence Pipeline bore quoted are ‘nominal’ sizes only since it is generally the outer diameter that is standardized because of the needs of flanging and threading. The diameter of a 4 inch nominal bore pipeline, therefore, is rarely 4 inches. If a conveying air velocity is based on a diameter of 4 inches, for example, and it is a schedule 10 pipeline, the actual bore will be 4.176 in and not 4.000 in. This difference will mean that the conveying air velocity will be about 9% lower. If 3,000 ft/min is the velocity in a 4 inch bore pipeline, it will only be 2,750 ft/min in a 4.176 in bore line and the pipeline is likely to block if the minimum conveying air velocity for the material is 3,000 ft/min. Pneumatic conveying system for bulk products FLEXICON Flexicon's PNEUMATI-CON(R) dilute phase pneumatic conveying systems range from single-point "up-and-in" installations to cross-plant systems with multiple pick-up and discharge points and automated controls, satisfying an exceptionally wide range of bulk conveying applications. All are custom-engineered and fully integrated with other Flexicon equipment and systems, and your new or existing process. The following material show the component equipments of a bulk material handling system. It is sourced from Flexicon Corporation’s published information concerning its bulk material handling system (2009). Bulk Material Handling Equipment Granulated and dry bulk materials such as grain, powdered chemicals, sugar, flour and dry cereal require specialized conveying, mixing and processing systems. These bulk material handling and powder bulk handling systems are designed for the integrated industrial mixing, conveying, measuring and packaging of delicate, friable, sticky or free-flowing solids. Unlike parts, equipment and other products which are conveyed through fabrication, assembly and packaging by belt and chain conveyors, bulk solids and powdered solids require a closed screw conveyor, flexible screw conveyor or pneumatic conveyor system which prevents caking, packing, liquefying, contamination and agglomeration. Industrial mixers, dryers, pulverizers and vibratory feeders are integrated into bulk material handling systems for complete processing. Bulk Material Handling System Diagram: Equipment Used in Bulk & Powder Bulk Solid Handling: Pneumatic Conveyors Pneumatic conveyors are hollow, tubular structures which transport bulk solids and powdered solids from one processing station to another. Bulk materials are pushed through these conveyors by an airstream generated at the base of the tube by a blower or vacuum. Images provided by Flexicon® Corporation Screw Conveyors Screw conveyors use single rotating screws encased within a hollow, tubular structure which transport friable bulk materials from one process to another. Also known as auger conveyors, screw conveyors are often fabricated as flexible screw conveyors in order to reach across areas and building stories more easily. Without the restriction of rigidity, flexible screw conveyors can bend and conform to virtually any configuration. Images provided by Flexicon® Corporation Vibratory Feeders Vibratory feeders are conveying ramps or feeding tubes which assist in transferring bulk and powder solids to and from conveyors, processes and hoppers. By vibrating the discharge end of a hopper or conveyor, powdered material caked on the sides and within is loosened until it falls freely. Bulk handling sometimes uses vibratory feeding ramps to convey over short distances, and most bulk bag filling, bag dumping and hoppers are equipped with vibrating feeders. Images provided by Eriez Manufacturing Company Pulverizers Pulverizers de-agglomerate clumps or blocks of bulk solid materials into friable or free-flowing materials with uniform consistency. This is necessary for pneumatic or screw conveying as well as for uniform processing. (Images provided by Stedman) Industrial Dryers Industrial dryers are often integrated into the final processing stages of a variety of bulk materials for the final removal of contaminating moisture. Products such as dry cereal or flour are rotated through an air dryer, rotary dryer or flash dryer to ensure the bulk solid or powdered material has the proper uniform consistency and will not grow bacteria due to moisture. Images provided by Carrier Vibrating Equipment, Inc. Industrial Blowers Industrial blowers provide air and gas movement in ventilation, circulation and drying applications. Pneumatic conveying systems depend on blowers and vacuums to convey bulk materials, and drying and dust collecting stations within a bulk material handling system use blowers at multiple stages as well. Images provided by AMETEK Technical & Industrial Products Industrial Mixers Industrial mixers in a variety of configurations are used to blend multiple bulk or powdered materials together as part of a bulk material processing system. Mixers used in powder & bulk applications are typically paddle mixers or ribbon blenders; sometimes powdered or dry materials are mixed with wet materials to form products such as bread dough or slurries. Images provided by IKA® Works, Inc. Bulk Bags Bulk bags are used as large volume portable containers in multiple stages of bulk and powder material processing systems. Materials are loaded into bags through conveyors by bulk bag fillers, a frame designed specifically to hold a bag during filling; bag fillers often serve dually as bulk bag conditioners by weighing the materials within the bag and shaping the filled bag into a manageable shape. Bag dump stations, or bulk bag dischargers, turn filled bags upside-down over a pneumatic conveyor, screw conveyor, hopper or vibratory feeder for the powdered or bulk material inside to be distributed to other processes. Image provided by Flexicon Corporation     |    Image Provided by IKA® Works, Inc. Types of Materials Handled in Bulk & Powder Bulk Solid Handling: Abrasive Materials Materials which Fluidize or Liquefy Hazardous Materials Large Particles Contamination-Sensitive Products Products which Pack, Cake, Smear or Plug Non-Free Flowing Materials Free-Flowing Materials Moist, Sticky Materials   Heterogeneous Mixtures Friable Materials   All Materials Images Provided by Flexicon® Corporation Pneumatic conveyance systems in application: References Autonomous Dust-Exposure Measurement During handling, processing, identifies emission sources. Foundry Management & Technology, Nov2009, Vol. 137 Issue 11, p10-10 Explosion-proof drum discharging system with surge hopper. Processing (08968659), Feb2009, Vol. 22 Issue 2, p38-38 Flexicon Corporation, 2009. Accessed 5 December 2009 from http://www.iqsdirectory.com /industry/bulk_material_handling/images/bulk_material_handling.jpg High-speed above ground bulk intake system receives up to 500 tons per hour Processing (08968659), Feb2009, Vol. 22 Issue 2, p37-37 Iinoya, K; Masuda, H; & Watanabe, K 1988 Powder and Bulk Solids Handling Processes Instrumentation and Control. CRC Press Mills, D; Jones, M G; Agarwal, V K. 2004 Handbook of Pneumatic Conveying Engineering. CRC Press. Sturdy Bins from Sturdy Products. Checkout, Jan2009, Vol. 35 Issue 1, p65-65 Tamhankar, V D 2009 Materials handling systems. Popular Plastics & Packaging, May2009, Vol. 54 Issue 5, p57-58 TSM Houston 2008 Accessed 6 December 2009 from http://www.tsmhouston.com/pneumatic-conveyor-systems.html Woodcock, C R & Mason, J S 1987 Bulk Solids Handling: An Introduction to the Practice and Technology/ Blackie Academic & Professional, Chapman & Hall, Glasgow Read More