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Milk powder plant addresses volatile safety concerns

01 June 2010

Netherlands-based Hobré Instruments serves many industries with a variety of solutions centred round the design, manufacture and maintenance of on-line analysers, sample systems and complete turnkey analyser systems.

Milk powder plant addresses volatile safety concerns
Milk powder plant addresses volatile safety concerns

Its engineering and service division designs and constructs analysers, pre-conditioning systems, sample-conditioning systems, sample-recovery systems and complete analyser system packages for a broad range of gas and liquid applications. The company is able to offer corrective and preventive maintenance, start ups, commissioning, site surveys, training and factory and site acceptance testing for both on- and off-shore analyzer applications.

In manufacturing processes where fine powder is involved, there can exist a substantial risk of explosion if the powder-laden air should ignite. In many instances, this can be instigated without a naked flame; all it needs is a local ignition source to get hot enough to reach a trigger temperature.

Rockwell Automation was asked to provide a solution for a spray drying installation – the product being processed being seemingly innocuous milk powder. However, no matter how harmless milk powder may appear, if the right air/product ratio is reached and subsequently ignited it can turn into a major safety issue very quickly.

For this very reason, significant steps are taken by processing companies to mitigate these risks. In most cases advanced monitoring solutions are placed at key points within the plant to monitor a number of different variables; variables that can all point to potential safety issues if levels go above certain thresholds.

The whole concept of spray drying means that the presence of powder-laden air is non-negotiable. In this instance, the process engineers keep an eye out for the sources of ignition. As well as static, a common source of ignition is clumping of the product in localised masses. These can heat up incredibly quickly – up to 800°C in some cases – and if they break open an ignition source is exposed. The good news is, as they clump and smoulder they cannot get enough oxygen resulting in unfinished oxidisation, so their primary by-product is carbon monoxide (CO) – which is relatively easy to detect. In fact, CO smouldering detection is the only preventive protection system available.

Dirk-Jan Ruijter, product manager at Hobré Instruments, explained: "Our Nicosys system, with an Allen-Bradley CompactLogix unit at its heart, is a stand-alone, early-warning analyser used to detect varying levels of CO. The unit helps detect any level changes and offers the plant managers a variety of alarms (low, medium and high) depending on the measured CO level."

Hobré Instruments' customer in this instance – a very famous multi-national food company – already standardised on Rockwell Automation equipment. Ruijter continued: "Hobré Instruments has been using Allen-Bradley hardware for a number of years, so the incorporation of a CompactLogix unit as the 'brains' of the system was no problem at all for our engineers. In the mid 90s we switched to Allen-Bradley SLC units and about three years ago we made the switch to CompactLogix.

"The Nicosys system monitors the outgoing and the incoming CO concentration, to prevent false alarms due to high CO concentration peaks in the environment, such as those caused by truck exhaust pipes. The trends of the ambient and exhaust CO concentrations can also be stored so that they are available for evaluation at any time."

Crucial to the system is the conditioning of the sample. Inside the sampling cabinet a blowback filter and dryer are installed. Drying is done without condensation of water if hygienic risk needs to be avoided, for example (and especially pertinent in this case) in the dairy industry.

"The system works very well and we are very happy with it," explained Ruijter. "Field engineers from Rockwell Automation completed all the programming for us on the SLC units; then, using a functional description supplied our engineers, they created new programmes for the CompactLogix. They were also on hand during commissioning, tweaking the software to get the best possible performance out of the analysers."

Rockwell Automation's Field Engineers created programs for three types of analysers (2000, 4000 and 6000). All the analysers work in different ways – using different valves, circuits, hardware and operation sequences – and there are also several options that can be used, depending on the system and its application. The programs were built in such a way that they contain the logic for all the systems and their options and engineers at Hobré Instruments are able to choose the operating software and options that match the customer's installation.

In most instances, the CompactLogix unit is accompanied by a PanelView HMI and a variety of other Allen-Bradley components such as contactors, circuit breakers, switches and buttons.
The Nicosys system also has a self-diagnostic capability controlled by the ControlLogix unit, which interrogates flow switches, flow alarms, temperature alarms and other components within the system and generates a major alarm should any of them be out of tolerance.

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