Control Engineering Online Update for August 11, 2006

In the past, energy consumption was rarely a priority for an engineering team. In industries such as cement, chemical, pulp and paper, metal, and oil and gas, the focus was primarily on technology and the ability of automation systems to increase productivity. Now, industrial companies and utilities are faced with a growing list of concerns, including increasing customer demands on efficiency and quality, the environment, increased competition, and the maintenance of quality standards. It is becoming increasingly difficult for a company to meet demands and at the same time, cut production costs.

One of the answers lies in reducing energy consumption and in particular, the energy consumed by electric motors. This can be reduced in two main ways: efficient control of the speed at which the motors
operate using variable speed drives, and making the motors themselves more efficient.

Savings potential
In an electrical grid system, there must be a balance between the supply (power plants) and demand (end-users) at all times. Because the total efficiency of the energy chain from a power plant fuel depot to a process pump is very low (due to various losses along the way), a conscientious consumer is not the only one responsible for overall energy savings

Manufacturers that use high-efficiency motors and variable-speed ac drives create the potential for huge energy savings and less negative environmental impact. A recent study by the European copper institute showed that, per year, an electricity savings potential of some 200 TWh (billion kWh) exists. This translates into a reduction of about 110 million tons of CO2 emissions from industries in the European Union.

Around the world, 15,500 TWh of electricity is generated each year. Industry is responsible for 41.7%, or 6,500 TWh, of the total. It is assumed that 65% of the 6,500 TWh powers industrial motor drive systems,
and a small portion of ac motors (perhaps 5%) is already speed-controlled. It is estimated that an additional 25% of this energy is used by motors that would most likely benefit from speed control. If
the average energy saving was 50%, the total energy savings potential is approximately 500 TWh or 3.2% of the world’s electricity generation.

Depending on the baseline methodology and the CO2 emission factor used, this saving potential translates into 250-420 million tons of avoided CO2 emissions. This analysis, which is only a rough estimate, demonstrates the large amount of CO2 emissions that can be reduced if ac drives are used in all viable motor applications.

Case UK: Boliden MKM
Central Electrical, one of ABB’s channel partners in the UK, did an energy audit on filtration plants belonging to Boliden MKM (a leading manufacturer of brass and copper products) by measuring energy used in a typical production week. The audit mainly covered the fume extraction filter plant for the brass casting process, which consists of two Luhrfilter filtration plants, one with a 250 kW fan and the other with three 132 kW fans. Airflow from the fans was controlled using dampers as restrictors.

The results pointed to potential energy savings with ABB drives of at least $44,650 a year for the 250 kW fan and $26,800 a year for each of three smaller fans – a savings of $125,000 a year and a payback of just 9 months. In any case, the total savings achieved from the installation proved to be higher. Boliden’s energy measurement system verified $232,200 in savings.

In addition to direct energy savings, ac drives can be used to upgrade existing production machinery. Cantex is a leading U.S. producer of PVC (polyvinyl chloride) pipes. At one of its plants in Reno, NV, Cantex upgraded two of 18 extrusion lines with ABB’s ACS 800 adjustable speed direct torque control drives. This extruder retrofit increased
production by at least 30%.

ABB and the EU’s Motor Challenge Program
In 2003, the European Commission introduced a voluntary program known as The Motor Challenge Program (MCP) in which industrial companies are given help to improve the energy efficiency of their motor driven systems. The MCP is one of a series of energy-saving initiatives under the European climate change program. MCP officials estimate that the replacement of all inefficient EFF3 classed motors then used across Europe with standard efficiency EFF2 versions would yield energy savings
of 6 TWh or 300 million Euros, while the EFF1 would produce even more savings. The greatest saving potential of all comes if more variable speed ac drives were used to control these motors.

Control methods for a pumping system
In pump and fan applications, using variable-speed drives can cut energy consumption by as much as two-thirds. A pump or fan running at half speed consumes only one-eighth of the energy compared to one running at full speed. The traditional way of controlling the flow through a pump is by using a throttling valve, which is similar to a water tap in the home.

The operating point of a pump is a balance between the resistance in the pipes and the work done by the pump. Therefore an increase in resistance forces the pump to generate more pressure, as system fluid flow decreases. But energy efficiency becomes the casualty in this scenario.

Another method of flow control is by means of an ac drive which regulates the frequency fed to the motor driving the pump, thereby altering pump speed.

Motor and ac drive efficiency compensation must be accounted for. Because the same motor can be used in both cases, its effect in total power consumption is equal. Even with losses of 2-3% at nominal power, the energy efficiency obtained using variable speed drives is by far superior. A small reduction in speed can make a big difference in the energy consumption, and as many pump systems often run at less than full capacity, a variable speed drive can produce huge savings.

Most plants—whether factories or utilities—have ample opportunities for saving energy and increasing productivity. It is just a matter of finding the applications, quantifying potential, and starting to save.
In many cases, an investment in a variable speed drive will enable payback in less than a year.

For more information visit the Control Engineering Resource Center at resource.controleng.com .

Visit the pages below for more information about energy savings and variable speed drives.

Specifying adjustable frequency drives for Electromagnetic Compatibility (EMC) in Industrial Applications by ABB

Achieve quick payback on your HVAC energy savings via these four (4) easy steps by ABB

www.abb.com