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Automation

Sewage Treatment Works

The first of a new type of sewage treatment plant is being kept running 24/7 with the assistance of ABB Drives Alliance member Quantum Controls Ltd.

The company has supplied £100,000 of motor control equipment as part of the plant, which is the only one of its kind in the UK. Built and operated by sewage recycling specialist Agrivert on behalf of Northumbrian Water, the plant operates as a single processing line without the benefit of a backup line, so reliability is the key requirement.

Based at the Howdon Sewage Treatment Works on Tyneside, the Agrivert plant relies on the company's new processing technology to dewater and lime treat sewage sludge to produce a sterile, low-odour cake that can be used as agricultural fertiliser. While other sewage recycling plants typically operate with an entire processing line on standby in case of breakdowns, Agrivert and Northumbrian Water needed to keep the Howdon plant as compact and economical as possible, so a single-line approach was adopted.

With sewage entering the plant constantly, it's crucial to keep the process working 24 hours a day, seven days a week. "The plant has now been running problem free for around 19 months and has already processed over a million cubic metres of sewage sludge," says Alexander Maddan, managing director of Agrivert. "We chose this control equipment because reliability is paramount and we get that from ABB and Quantum Controls Ltd."

The equipment includes 32 ABB motor starters, 8 ABB variable speed drives and associated control gear, all assembled into a custom-built motor control centre panel by Newcastle-based Quantum Controls Ltd. The equipment controls the motors that move sludge around the site and run the centrifuge dewaterer.

Quantum Controls also holds the maintenance contract for the motor control centre, complete with 24-hour call out and a four-hour response time. "If something goes wrong it's urgent for us to get a rapid reaction. We need a supplier that can provide the right backup and we've been very pleased with Quantum Controls and ABB," says Maddan.

Cooling tower drives save chip maker £30,000 in energy

A semiconductor manufacturer in Plymouth, UK is saving over £30,000 a year in energy costs, since installing six, 37 kW ABB HVAC drives on its three cooling towers. The £15,000 installation is set to give a payback in only six months. The drives were installed by the local ABB HVAC partner.

X-FAB UK Ltd is one of the largest semiconductor makers in the UK. A clean, vibration-free environment is a top priority in semiconductor manufacturing and the company uses large quantities of air and water to maintain cleanliness. The three cooling towers produce chilled water for the manufacturing process.

The ABB drives are used to control six, 37 kW fan motors in the cooling towers.

Originally, the fans were star/delta connected, arranged in cascade style so that they would come in, or disconnect, one by one as demand varied. This meant the final fan would constantly be switching on and off, sometimes as often as every 10 minutes. With a large 37 kW motor, this would draw significant start-up current. Additionally, whenever an odd number of fans were connected, air from the last fan would blow out through one of the other fans.

With the ABB drives, two fans start on the first towers at 20 Hz when the building management system indicates that cooling is needed. If more cooling is required, the next two fans start at 20 Hz and then the remaining two start if there is demand for still more cooling.

For further cooling, all six fans run together between 20 Hz and 50 Hz. At an installed cost of £15,000, an annual saving of £31,400 is achieved.

Maintenance costs have also been reduced, as drive belts would break at least once a month with the old system.

We worked out the cost at fixed speed, measuring power consumption and power factor and then estimated the savings at variable speed. Erring on the side of caution, we predicted 18 months payback but in the event, X-FAB actually got the money back in six months.

I hadn't used drives much before our ABB partner came along to give me a demonstration, " says Ted Judge, senior facilities engineer at X-FAB UK Ltd.

However, I now see that using variable speed drives is the most effective way for us to save energy. I have a 10-year plan for how to reduce energy use at this site and it will mainly be achieved with drives; 70% of electricity here at the plant is used by motors so there is vast potential for using drives.

Further energy saving projects with drives have since been carried out, enabling Judge to reduce electricity use by about 5% across the site so far.

Not many people in my profession are interested in drives, but with electricity prices increasing at the rate they are now, you start to develop an interest, " says Chris Bailey, financial director at X-FAB UK Ltd in Plymouth. "In the past, payback for energy saving projects was often many years, but with electricity prices having tripled in the past three years, the long payback has become short.

There is a strong case for saving energy, " says Judge. "The days of cheap energy are gone. The causes of climate change may be under debate, but what you can't get away from is that in general, energy is used very inefficiently. For me, it's simply about using what we buy more efficiently. There's no use buying energy and then sending it up the chimney.