COMPRESSED AIR
PNEUMATIC RIGHT-SIZED, EVERY TIME P
neumatic conveying is a tried and trusted means of transferring powders, granules and dry bulk around manufacturing and process environments. Subsequently, it is used in an incredibly diverse range of industrial applications. Whether flour in bakeries, grain in breweries or chemical compounds in pharmaceutical plants, pneumatic conveying represents a flexible and cost-effective solution for transporting materials to their required destination.
But selecting the right pneumatic conveying equipment can be challenging, with many considerations coming into play. For example, what type of substance is being handled? The size, weight and type of material can significantly affect the flow and pressure required. Also, are the goods being conveyed for human consumption or as a constituent part of a pharmaceutical product? If so, rigorous quality standards will define the purity of the compressed air that can be used. Meanwhile, other factors such as energy and safety are also critical considerations that must be fully understood.
THE PRINCIPLES OF PNEUMATIC CONVEYING
Before evaluating the selection criteria in greater detail, it is worth looking at the basic principles of pneumatic conveying and how materials can be moved. Pneumatic conveying uses compressed air to transport materials through enclosed pipelines in places like manufacturing and industrial plants using different air pressures. This process can be achieved in two distinct ways.
Pressure conveying, or positive conveying as it is also known, deploys the compressed air from a
Choosing the most suitable systems and components for conveying can have a significant impact on operational performance – guaranteeing product quality, avoiding blockages and reducing costs
compressor or blower at the start-point to ‘push’ the material through the pipeline. This method provides a particularly efficient way of covering larger distances. Meanwhile, vacuum or negative conveying uses compressed air to ‘suck’ the bulk material through the pipeline, with the compressor or blower positioned at the endpoint. One benefit is that there is no contact between the compressed air and the material being transported – and hence no contamination – and the product is not exposed to the heat generated in the air compression process. However, the distance that can be covered by vacuum conveying is more limited than by pressure conveying.
Within these two fundamental approaches, there are three phases of pneumatic conveying – dilute, dense, and transient. These phases relate to how different materials move through the pipelines.
Firstly, there is the dilute phase, where a blower or low-pressure compressor is used to send the material through the pipeline as though it is floating without any of it accumulating at the bottom of that pipeline. The dilute phase allows the material to be moved with an air pressure of up to 2.5 bar and at high speed and is a great way to transport a large volume of material quickly. Secondly, in the dense phase, the material is pushed (or sucked in the case of negative conveying) through the pipeline. That means it moves more slowly and requires higher pressure, usually above 2.5 bar. The dense phase is, therefore, more complex, expensive, and requires more energy. Finally, the transient phase is between the dilute and dense phases. Some material is ‘flying’ through the pipeline, and some are moved along the sides - again, impacting pressure requirements.
These phases are critical because powders, granules and dry bulk come in various forms with varying compositions. By fully understanding the make-up of the specific material – whether flour, sand, sugar, grain, plastic, cement, or fly ash - it is possible to select the correct technical specification for the pneumatic conveying system, ensuring it is rightsized for the task at hand. Getting the selection right can guarantee product quality, avoid blockages, minimise the risk of combustion, and reduce operating costs.
CHOOSING THE RIGHT EQUIPMENT
Once the primary material for transportation is identified and its composition fully understood, it is time to select the required compressed air components for the pneumatic conveying
16 JUNE 2023 | FACTORY&HANDLINGSOLUTIONS
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