Drying application benefits from the addition of VFDs

26 June 2020

Tea manufacturers in Sri Lanka have benefitted from both energy reductions and increased product quality since the adoption of variable frequency drives into the leaf drying process.

Traditionally, almost 50% of energy consumption in Sri Lanka’s tea manufacturing process comes from the withering process – the method used for drying tea leaves. 

Tea withering uses fans to remove moisture from the black tea leaves, drying them up to 50% during a 12 to 18-hour period.

The costs of this process have been almost halved in many cases, along with the industry’s impact on the environment, thanks to the use of variable frequency drive (VFD) technology.
In 2018 hundreds of Invertek’s Optidrive Eco drives were installed and commissioned in many tea plantations throughout the country as part of NAMA, a project led by the Sri Lanka Sustainable Energy Authority, under the direction of the Ministry of Power and Renewable Energy, and the United Nations Development Programme, to reduce greenhouse gas emissions through greater efficiencies.
Traditionally, the withering process would require fans to run at a constant speed blowing air through dampers to dry the leaves. The dampers would be manually controlled to adjust the airflow. The introduction of drives into the system meant that the airflow could be controlled more accurately and efficiently by varying the fan speed rather than adjusting the dampers. This had the effect of considerably reducing energy usage.
Working with Invertek’s sales partner in Sri Lanka, Hayleys Aventura Pvt. Ltd, the existing starters were replaced with the Optidrive Eco drives.
“Quality of the produced tea will mainly depend on the withering process. Withering troughs use DOL or Star/Delta Starters to start its fan and use dampers to control the air flow to obtain the withering of tea leaf in the existing system,” said Anushka Chandrasoma, assistant manager, Hayleys Aventura Pvt. Ltd. “While replacing the traditional starter with VFDs, operators can control the airflow by reducing the fan speed through a VFD, which enables savings of up to 25% of the energy used in the withering process. We used Optidrive Eco VFD’s with IP66 enclosures, which have the maximum protection against the dust and the water.”
VFDs are also being introduced to other parts of the tea manufacturing process, including controlling furnaces and the amount of energy they produce.
Explaining why the Optidrive Eco range was so well suited for the tea project because of its ability to control motors efficiently. Dylan Davies, product manager at Invertek, said: “The Optidrive Eco’s advanced onboard features also mean there is no need for peripheral equipment, reducing costs and the need for additional space. It also provides intelligent maintenance interval timing that allows maintenance reminders, reducing the need for costly downtime in production. 
“With its motor current monitoring function, it also means that any faults in the motors are identified early, again reducing any potential downtime that could affect the aeration of the tea leaves.”
A built-in keypad and OLED text display helped speed up commissioning times and also makes ongoing operation more easy to manage and Bluetooth access is also possible.

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