Variable speed drives cut fan consumption in half

A waste incineration facility in London has reduced the electricity consumption of its boiler fans by over 50% since installing ABB drives. London Waste's plant at Edmonton, in North London, receives domestic waste from a number of North London local authorities, as well as commercial and clinical waste, and uses this as fuel to generate electricity. 'The fans that bring air into the boilers to assist combustion were driven by 735rev/min slip ring motors running at full speed, with the airflow controlled by pneumatically actuated dampers', explains Richard Hobson, Electrical Engineering Manager at the plant.

'However, the type and age of the equipment made the airflow difficult to control, leading to large increments between damper positions'.

As part of the company's programme to improve environmental performance, Hobson approached ABB Drives Alliance partner Mid Kent Electrical (MKE), as one of a number of companies to look at improving the process by installing variable speed drives.

Following an energy audit of the application, MKE proposed controlling the motor with a 55kW variable speed drive from ABB.

This form of control would remove the air damper in favour of variable speed of the fan motor.

To reduce costs, Hobson asked MKE to use the new drive with the existing motor with its slip rings linked out, rather than replacing the motor.

An energy audit was carried out to compare the new control equipment with the old one.

The result of the audit showed that energy consumption had been cut by more than 50%, giving an expected payback of less than two years based on current consumption, as well as reduced CO2 emissions.

MKE supplied a turnkey package with all components, installation and modification to the existing switchgear and motor.

In addition, MKE supplied training at its Sittingbourne works for London Waste employees, to familiarise them with the new ABB drive.

Since the first installation, two further drives have since been installed, providing better control and greater savings.

Under the new variable speed control, the new ABB motor needs to draw only 22A compared with the 53A drawn by the old motor, figures confirmed by Hobson's own tests.