Safety in sugar milling systems

Whether for biscuit doughs or cream fillings, powdered sugar is an essential ingredient in the biscuit industry.

Due to its tendency to form lumps and its high hygroscopicity, and in order to avoid cumbersome handling and the generation of packaging material waste, it is common practice to mill sugar in the factory rather than buying it in bags.

Is sugar dangerous?

There are significant safety risks associated with the milling of sugar. Sugar, especially in powder form, is prone to explosions, originating either from an electric arc inside the hoppers or from the presence of a metal particle causing a spark in the mill. Any ignition event is amplified by the ease with which powedered sugar is suspended in the air, leading to chain explosions.

The explosion at the Imperial Sugar refinery in Georgia in 2008 is a sad but stark example of the gravity of an explosion in a sugar processing plant.

A dust cloud of any combustible material will explode when:

• The concentration of dust in the air is conducive to an explosion.
• There is an ignition source with the necessary energy.

In order to minimise the risk of explosion, three fundamental points must be considered:

1. Understanding and identifying the hazards associated with combustible dusts.
2. Proper design and maintenance of equipment.
3. Minimising the presence and accumulation of combustible dusts in milling areas.

Safety elements of a sugar milling plant

For the reasons given above, it is important not only that the milling system produces powdered sugar of optimum quantity and quality, but also that it has adequate safety features.

These components are:

1. Explosion exhaust. This is a duct which, in the event of an explosion in the crystal sugar hopper, conducts the flames to the outside of the building. It has a thin metal membrane inside with a sensor that gives an alarm signal in case of rupture.
2. Magnet to retain metal particles and protect the mill.
3. Rotary valve for metering the sugar inside the mill. It also acts as a firewall in the event of an explosion inside the mill-buffer assembly.
4. Non-return valve. During normal operation, the air flow into the mill keeps it open; when the flow stops, it closes automatically. In the event of an explosion in the mill, it closes to act as a firewall.
5. Ventex-type valve. At normal pressure it allows air out of the mill. In the event of an explosion in the mill-buffer unit, the valve shuts and acts as a firewall.
6. Explosion vent. This is a duct which, in the event of an explosion in the mill-buffer assembly, conducts the flames to the outside of the building. It has a thin metal membrane inside with a sensor that gives an alarm signal in case of rupture.
7. Rotary valve to discharge the sugar from the buffer. It also acts as a firewall in the event of an explosion inside the mill-buffer assembly.

In addition to these components, the environment in which the system operates must meet certain safety requirements, such as

• Non-sparking lights and switches.
• An equipment design and working method that minimises the amount of sugar released into the environment when opening the system for maintenance, and makes it easy to clean.
• Electrical panel in a separate room.
• Ideally, the mill should be located in a room that is physically separated from the staff work and circulation areas.

It is also important that the system is thoroughly maintained and monitored to ensure that no sugar is lost to the environment and that all functional and safety aspects are working properly and have not been bypassed.

How to ensure the safety of a grinding system?

The ATEX standard is a comprehensive standard for assessing and minimising risk and should be the benchmark to follow.

For existing systems, it is advisable to have a safety specialist carry out an audit to identify risks and areas for improvement.

For the design and purchase of new equipment, it is advisable to work with first class companies who can guarantee the supply of systems that are ATEX certified.

Safety should not be considered an obligation, but a fundamental value for companies and individuals.

This article is part of a training module on sugar milling technology for the bakery industry.