In the field of powder conveying, the three main “workhorses” used to be chain conveyors, pneumatic conveying chutes, and belt conveyors. Why have these once-reliable “workhorses” lost their luster in the face of today’s pneumatic chain conveyors? Let me break it down for you one by one:
Product 1: Chain Conveyor
The chain conveyor, model FU, is primarily designed to replace the original screw conveyor. Screw conveyors suffer from difficulties in sealing the intermediate suspension bearings (bushing), which are prone to wear and result in a high equipment failure rate. Furthermore, for longer conveyors, strict requirements for the concentricity of the screw shaft must be met; installation errors or wear on the intermediate suspension shaft can lead to excessive drive torque, resulting in high energy consumption and significant equipment wear. If failed suspension bearings are not replaced promptly, the screw blades can easily wear through the bottom of the housing, affecting normal operation. The FU chain conveyor completely overcomes the shortcomings of screw conveyors. It utilizes a trough with a high aspect ratio, where a continuous chain drives the material forward through friction between the particles. Its conveying principle is more advanced than that of screw conveyors, and its structure is more rational and reliable. It has quickly become the preferred choice in the field of powder conveying, replacing many existing screw conveyors in numerous applications.
Since the start of the new century, with the widespread adoption of large-scale new dry-process cement production, new demands have emerged for larger-scale powder conveying equipment. On the one hand, conveying capacity has increased from tens or hundreds of metric tons per hour to hundreds or even thousands of metric tons per hour; on the other hand, conveying distances have extended from 20 to 30 meters to 60 to 70 meters, or even over 100 meters. Under these circumstances, FU-type chain conveyors struggle to meet production requirements. First, as conveying capacity increases, the equipment must be built on a much larger scale; more critically, once the conveying distance exceeds 30–40 meters, the equipment’s power consumption and component wear become excessive. Consequently, FU-type chain conveyors are no longer capable of meeting the demands for larger-scale production. At this point, with no ideal alternative currently available, the only option is to use belt conveyors, which have certain drawbacks (discussed in detail below).
Product 2: Air-Conveying Inclined Chute
Air-conveying inclined chutes can be said to have entered the domestic market alongside rotary kiln technology; they were rarely used during the era of vertical kiln cement production. Around the year 2000, the author was dedicated to promoting the widespread adoption of air-conveying inclined chutes in the cement industry, particularly in vertical kiln cement production lines. This effort helped secure the first major profit for the company’s development. The principle behind the air-conveying inclined chute’s transport of powdered materials is straightforward: air is forced into the material within a shell inclined at a certain angle by a high-pressure blower, passing through a permeable layer to aerate the material. Once aerated, the internal friction of the material within the chute decreases, which manifests macroscopically as a reduction in the material’s natural angle of repose. When the chute’s installation angle exceeds the critical angle for the flow of aerated material, the material flows naturally. During continuous feeding, the material naturally forms a continuous flow.
The structure of an air-conveying inclined chute consists of an upper chute body, a lower chute body, an air-permeable layer, a high-pressure centrifugal blower, air ducts, a discharge device, elbows, and side discharge valves. The primary material is 3–4 mm thick Q235 steel plate, making this an extremely cost-effective powder conveying system. During operation, the material is conveyed from a higher to a lower elevation through the aeration effect generated by a high-pressure centrifugal blower, resulting in extremely low energy and material consumption. This makes the air-conveying inclined chute a highly cost-effective conveying solution in the field of powder handling. Consequently, it has become the equipment of choice and is widely adopted during equipment selection.
The installation of an air-conveying inclined chute requires a specific angle. When the conveying distance is long, this can present challenges in process layout, as a certain elevation difference is required between the inlet and outlet to meet operational conditions; otherwise, the system will not function properly. Of course, there are also requirements for the material being conveyed; for example, moisture content must not be too high (generally less than 2%), and particle size distribution should generally be less than 20%. The presence of granular material (slag) can also affect conveying efficiency. Therefore, when these conditions arise, the air-conveyed inclined chute proves inadequate, and as a last resort, one must resort to the less-than-ideal belt conveyor.
Product 3: Belt Conveyors
Belt conveyors are ideal for handling blocky and granular materials. Since the contact between the conveyor belt and the idlers involves rolling friction, operational resistance is minimal. As a result, belt conveyors consume relatively little power, have low equipment maintenance costs, and can meet process requirements for high throughput, long distances, and curved routes, making them widely applicable.
However, when it comes to powdery and granular materials, the selection of belt conveyors is approached with caution due to challenges such as difficulty in achieving proper sealing, severe material adhesion to the belt, harsh on-site conditions, and the high labor intensity involved in operators clearing accumulated material. Belt conveyors are typically chosen only when the previously mentioned FU-type chain conveyors and pneumatic inclined chutes are not viable options. Today, in the field of powder conveying, belt conveyors are widely used for applications involving high throughput, long distances, minimal elevation differences, high moisture content, or the presence of a certain amount of granular material in the powder. Examples include discharge points beneath silos in cement plants and ship loading/unloading areas at docks. While their conveying capacity is entirely adequate and operation is relatively economical, environmental pollution caused by leakage and material spillage remains a significant headache for many companies.
It’s fair to say that pneumatic inclined chutes, chain conveyors, and belt conveyors are the three cornerstones of powder handling. Pneumatic inclined chutes are the equipment of choice due to their low capital costs and minimal operating expenses. However, given their specific requirements regarding process elevation differences, material moisture content, and particle size, these conditions must be carefully considered during selection; otherwise, optimal performance cannot be achieved. When process elevation differences are not a constraint, the conveying capacity is not very high (below 300 t/h), and the conveying distance is short (less than 40 m), FU chain conveyors can handle the task, though they have higher energy consumption and equipment wear. When the conveying capacity is high (over 300 t/h) and the conveying distance is long (over 40 meters), belt conveyors are the only viable option. However, issues such as difficulty in sealing the equipment, severe spillage, environmental pollution, and the need for intensive cleaning associated with belt conveyors are problems that everyone has simply had to put up with.
How to achieve long-distance, high-capacity, low-consumption, and clean conveying of powdered materials is a research focus for our company. Recently, building on the successive launch of pneumatic equipment such as the pneumatic sedimentation slag remover and the combined pneumatic-mechanical mixer, we have discovered that integrating pneumatic systems with traditional mechanical equipment offers significant potential for reducing energy consumption and mechanical wear while increasing conveying capacity. Therefore, we undertook a bold experiment by integrating a gasification system into a chain conveyor—essentially combining two traditional conveying systems, the chain conveyor and the pneumatic inclined chute, into a single unit. Through research, refinement, and optimization, we successfully launched the pneumatic chain conveyor, which was granted a national patent (ZL 2013 2011 68890) and has received unanimous praise from users in the field of long-distance powder conveying.
Contact us for professional powder material handling solutions.
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