Geelen counterflow dryers and coolers

Friday, 07 January, 2011 | Supplied by: Furnace Engineering Pty Ltd

Geelen counterflow dryers and coolers exclusively use the counterflow principle which is claimed to be the most efficient method to exchange energy between any two flows of gases, liquids or solids. By applying this principle in the dryers, users can minimise the amount of drying air needed and maximise the amount of energy that can be transferred. This results in a lower air exhaust volume and a lower exhaust air temperature.

In Geelen counterflow dryer-coolers, users can recover the product heat which is injected by hammermills, conditioners and extruders. That energy is recovered from the cooler in the form of warm air. All of that warm air can be re-used as make-up air for the dryer. However, it is important to properly design the coater, cooler and air system to make sure that the warm air is sufficiently clean when entering the dryer.

In addition, each counterflow dryer has internal air recirculation systems, which ensures that only air with a very high relative humidity passes the exhaust fan. For a typical pet food dryer this means that only 25-30% of total drying air is ever exhausted.

Even the most efficient dryer can waste energy if not controlled properly. The key is to ensure that all of the relevant process variables can be accurately measured and controlled in real time. Product flow rate, moisture percentage, air volume, air temperature and drying time must all be measured and controlled. Variables such as air volume and air temperature must even be controlled in each individual stage of the drying process (which typically consists of between two and eight stages, depending on evaporation load). To be able to measure and control air volume accurately at every drying stage, it is critical that the dryer is completely sealed from the ambient environment.

Calculating the mass and energy balance of the dryer in real time allows the operator to see how many kJ are being used for every kg of water evaporation

Behind the technology is an advanced control system that measures one variable (speed) and influences another (fuel). The control system knows exactly how much to correct under each set of circumstances. Operators want their dryers to always deliver the exact same moisture content for that particular product, independent of variations in raw material or weather. In counterflow dryers Geelen employs an accurate planar microwave sensor in the dryer hopper, which performs online measurement of moisture, product temperature and bulk density. The moisture signal is used to finetune the temperature of drying air, such that the dryer reacts automatically to any deviation from setpoint.

In counterflow dryers we show operators the way to their target moisture. The control screen shows the operators the actual moisture, temperature and air volume in each drying stage. When a new product recipe is selected, a preferred drying curve is loaded into the control system that leads the operator to the desired target.

All of the above technologies combine to achieve an energy-efficient dryer.

For example, drying of extruded pet food of 2500 kJ per kg of evaporated water, which is at least 20% better than any available alternative and up to 50% better than a 10- to 15-year-old horizontal dryer. A 10 tph conveyor dryer that is 10-15 years old, running 6000 hours per year, will use $450,000 to $750,000 worth of gas. With a modern counterflow dryer that number can be reduced by $150,000 to $400,000 per year. Add to that the fact that gravity flow enables very high mechanical reliability and a much lower cleaning frequency and the payback calculation is straightforward.

Phone: 03 9544 2922
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