Dryers are among the biggest energy guzzlers in the process industry. They are also responsible for substantial emissions. It is therefore important to improve the efficiency of existing dryers, but without sacrificing product quality and quantity. SiccaDania has various solutions for this. 

An important part of the portfolio of SiccaDania, supplier of process equipment, consists of drying installations for the food industry. These are complex systems, not only because of the large number of components, but also because of their control. Variations in the composition of the ‘wet’ ingredients also play a role, in addition to fluctuations in utilities such as steam, gas, water and compressed air. In short, enough variables that influence the functioning of the drying system.

Existing drying systems

Existing drying systems are often decades old and usually lack facilities to gain sufficient insight into their functioning. It often appears that information about the design of the drying system has been lost over the years. It is then a challenge to determine how a dryer performs on themes such as:

• Product quality and quantity
• Stability
• Emissions
• Energy consumption

In addition, these quantities influence each other. For example, an unstable system or slow control can be detrimental to product quality or lead to an increase in energy consumption and emission values.

Product quality and quantity

The most important design parameters of a dryer are product quality and quantity. There are optimal process conditions for each product that guarantee market- based quality. These conditions must be taken into account if an optimization is necessary because a dryer does not reach its designed capacity (quantity). 

Increasing the inlet temperature to produce more can lead to reduced product quality. In addition, increasing the inlet temperature can cause other negative effects, such as increased energy consumption and an increased risk of fire and dust explosion.

Stability

Both product quality and quantity depend largely on the stability of the dryer. This can be compromised by, for example, irregular dosing of the wet food, differences in the moisture content of the food or a slow operating control system. Sometimes dirty product filters or suction filters are the cause of a decreasing air volume and therefore a decreasing product quantity.

Stability also affects the accuracy of the dryer control. When stability is reduced, a ‘certain’ control setting is often chosen. But this makes the end product too dry and energy consumption increases. Furthermore, the stability influences the availability of the dryer on an annual basis. An unstable dryer can lead to unplanned downtime due to contamination or blockages and requires more maintenance.

Emissions

Existing dryers were often built in a period when the requirements for CO2, NOx and dust emissions were less strict than they are today. For example, 30 years ago, a limit value of 150 mg/Nm³ still applied for dust emissions. Nowadays, the emission standard for existing installations in the food industry is < 10 mg/Nm³, and for new installations < 5 mg/Nm³, with higher values sometimes being tolerated temporarily.

Optimizing dryers to reduce emissions is often not easy because the existing separators for product recovery are often large cyclone batteries and the air volumes are also quite large. However, in many cases SiccaDania can reduce emissions below the required level in a fairly simple and inexpensive manner using VTK cyclone technology alone. In addition, product is recovered that would otherwise have been lost.

     
Fig. 2 The modification of the drying tube of a flash dryer.

Energy consumption

The efficiency of a dryer mainly depends on energy consumption. This concerns the power required to achieve the required evaporation. An efficient dryer has the highest possible allowable inlet temperature and the lowest possible outlet temperature. A number of things influence this, such as the desired product quality, variations in the wet feed as well as the response time and accuracy of the control. Poor thermal insulation or air leaks will increase energy consumption.

Heat recovery

SiccaDania has systems to recover heat from waste gases and thus reduce energy consumption by approximately 20%. With the use of heat pumps, a reduction of 30% to 50% can even be achieved. The investment in this technology has a very short ROI (Return On Investment) with current energy prices and CO2 tax.

Dryer optimization in four phases
SiccaDania normally optimizes existing dryers in four phases. The phased approach ensures a thorough solution and prevents high initial expenses as well as surprises at a later stage.

Phase 1 Evaluation of the current situation and an assessment of the available information.

Phase 2 Collecting data, performing process measurements and determining the mechanical quality of the drying system. The findings and opportunities for optimization are recorded in a report.

Phase 3 Elaboration of a concept for optimization.

Phase 4 Implementation of the optimization concept in the existing drying system.

This means that all aspects of the dryer are examined, both process-wise and mechanically. SiccaDania has all the knowledge and experience to successfully optimize existing dryers.

Another option for energy savings is the OptiPC monitoring system from SiccaDania. This advanced software package determines the optimal process conditions of a dryer based on various parameters. This can result in savings of up to 15%, without major investments. OptiPC also ensures a more stable operation of the dryer. The system is an add on to the customer’s existing control system and provides the operator with input for the optimal dryer settings.

     
Fig. 3 The optimization of a drum dryer led to a significant emission reduction.

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