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Pneumatic conveying systems: improving flow

21 May 2017

Tony Brennan explains how to improve flow control in pneumatic conveying applications. 

Modern industrial processes are under increasing pressure to reduce costs and improve reliability and productivity. Where these processes involve pneumatic conveying there are opportunities to improve the design and flexibility of both existing and new installations.

The most significant advantages of pneumatic or vacuum conveying over mechanical conveying include:

• Reduced maintenance due to the lack of moving parts.
• Improved operational environment with no dust due to the fully enclosed design.
• High flexibility of the transfer route.
• The possibility to carry out physical or chemical processes during the conveying process.

Optimising the flow
The process of transporting materials often requires the ability for the  destination point to change. For example, when a storage container is full and the product is diverted to another container. The volume of air in the transport system is crucial to maintaining the product in suspension and making changes to the required volume must be matched by a suitable adjustment to the airflow in order to keep the product in suspension and avoid unnecessary wear to the pipework or degradation of the conveyed material. 

The same applies to making a change to the product itself - which will require an adjustment to the airflow to ensure that the correct air velocity and product quality are maintained. However, the way that the air is introduced to the conveying system can have a significant effect on the system design and the power requirements to operate it.

More traditional ‘blow pot’ solutions are giving way to systems that use multiple air injection points to provide a uniform airflow throughout the system. Increased levels of computer control and monitoring allows new installations to be delivered with much lower power requirements, which form a significant proportion of the operating costs. 

Improving productivity
The key to managing these power requirements, and the subsequent costs, is to implement a control system that can react to changes in the internal volume of the transport system, to help maintain optimum airflow. This approach has resulted in a shift from steady state systems towards non-steady state systems. The ability to operate a plant with product quality variation without stopping the process due to plugged pipes can greatly improve the productivity of the plant.

To implement such a system requires an airflow controller that can continually assess the demands of the system and provide feedback signals for the compressors. Integrating such a solution into a pneumatic conveying system that has had little or no control in the past, can be challenging.

However, recent developments in data networking, connectivity and microprocessor control has resulted in an increase in the amount of technology available to measure and control such processes.

When applied to pneumatic conveying it enables the continuous measurement of material mass flow rates and the adjustment of airflow rates using computer algorithms to both within an optimum range. This data can also be collected and analysed centrally to ensure that the plant continues to help operate at the best efficiency.

Maximising efficiency
One possible solution for delivering improved efficiency is a closed loop controller that features a flow sensor, a process controller and a control element, all in one unit. Such a compact and flexible design would enable the flow controller to be easily installed and would provide accurate management of the compressors.

Creating flow control systems can be a complex issue. The standards that need to be met when designing and constructing processing infrastructure for the food sector, in particular, can be very stringent. Bürkert has been designing and installing flow control systems for the food industry for 70 years so has developed an in-depth knowledge of the requirements for success.

Tony Brennan is field segment manager, Gas and Micro at Bürkert.

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