Cutting electrical energy use in motor-driven applications through the use of variable- speed drives (VSDs) is a well-proven method, but not everyone is getting the message. ABB takes a systematic approach to energy sustainability that provides proof of just how much can be saved
A major part of sustainable manufacturing is using energy wisely. As energy prices continue to rise, it is becoming increasingly important to make the most efficient use of energy, both as responsible companies that care about the impact on the environment and for the future profitability of the company.
Yet, many companies do not know where their biggest energy use is and have misguided ideas about how best to cut it. A survey of UK manufacturing managers revealed the most common method of reducing the electricity bill was to switch suppliers, yet as all suppliers are increasing their prices, this can only provide a minimal saving. Other managers cited increased compressor efficiency or improved factory heating. The real answer lies in looking objectively at where electricity is used most and assessing how it can be reduced cost- effectively.
The elephant in the room is electric motors when you consider 65% of the total electricity at industrial sites is consumed by electric motors driving pumps, fans and compressors to name but a few.
A drive and electric motor combination, when used to control the speed of applications such as pumps and fans, can reduce the energy bill by up to 70% and give paybacks in less than 12 months. Yet, only about 5% of all the installed motors within these applications use a VSD to regulate the speed according to demand. Therefore the potential for motor-driven applications to save energy is enormous.
Get the facts
Saving electricity needs to be based on facts. ABB helps companies achieve this through its energy appraisals, a systematic way of identifying which motors are most suitable for VSDs. To perform energy appraisals, ABB has set up a large team of over 50 electrical energy specialists, comprising of ABB engineers and selected technical partners, all of whom have extensive practical experience of carrying out electrical energy appraisals over the past 20 years. Within half-day they will look at an organisation’s installed motor base, identifying applications that can benefit from the installation of VSDs.
The results, based on measured data from the application, will help a user target their investment so that it produces the highest possible savings and gives the best return.
Following an initial meeting to assess the inventory of the plant’s motors, the data collection phase involves an on-site appraisal with selected motor-driven applications, to determine operating parameters such as voltage, current and power factor and the energy being used.
The findings will be analysed and potential savings identified using dedicated software. A detailed action plan will then be prepared, usually comprising an Executive Summary and a detailed engineer’s report, highlighting applications that can save the most. The figures will normally be translated into monthly savings, and there will be detailed recommendations for fitting particular VSDs or motors.
Once new equipment is fitted it is normal to track the actual savings against the predictions shown in the report. Expected benefits of the appraisal will include:
s Clearly identified energy savings and CO2 emissions reduction
s Complete appraisal results and energy saving calculations
s History of other appraisals and associated energy savings
s Estimated payback times
s Degree of customer training given as part of the process
It was just such an energy appraisal that produced spectacular benefits for steel maker Corus Colors at Deeside, cutting 70% of the energy used on a hydraulic system.
Typically, hydraulic systems waste much of their energy because a constant amount of fluid circulates at all times, although the work is only carried out in short bursts. Corus Colors achieved significant energy savings by retrofitting the existing system with a VSD. The pump speed was greatly reduced both when the system was in neutral and during actuation of the cylinders.
When in neutral, power consumption was initially around 9 kW. Under drive control, power consumption was reduced to 2 kW, a reduction of 77%. With the system under load, power consumption was reduced from 22 kW to 12 kW, a saving of 48%.
With a 16% duty on-load time for the system, the average energy saving over time was 70%.. The reduced energy consumption will allow a payback time of just 18 months and reduce the company’s carbon footprint by 33 tonnes of CO2 annually.
Cutting £25,000 off energy costs
Similar large savings are being made by Express Asphalt, which produces 40,000 tonnes of asphalt a year. The asphalt production process involves a burner supplying heat to an aggregate dryer in the form of a rotating drum. The dryer creates steam and dust, which are extracted by an exhaust fan.
Because the 90 kW fan was run at full speed with its output damped, it was wasting a lot of electrical energy. To solve this, a 110 kW ABB standard drive was fitted to the fan. The fan had its damper placed in the fully open position and the dryer pressure was then controlled via a pressure transmitter feeding a signal back to the ABB drive. A 30 kW ABB drive was also fitted to the dryer. The burner uses kerosene and it was found that running the drive at 55 Hz gives the optimum drum rotation speed for drying. The company used half a litre per tonne less of kerosene than before, saving £8,000 per annum in burner fuel costs.
Altogether, this cut energy costs by around £2,100 a month, or £25,200 a year. The payback time was less than 12 months.
Taking the guesswork out of saving energy paid off for these two companies, who are now enjoying large cuts in energy costs and an enhanced reputation as sustainable energy users.