Designing an energy efficient factory
Manufacturers across a range of sectors are reaping the rewards of addressing energy efficiency.
Energy efficiency has been on the agenda for a number of engineering operations for at least a decade now. The message that reducing CO2 emissions means using less energy, and thus utility bills will fall, has come across loud and clear, bolstered by government incentives to assist with the inevitable investment needed to bring in new equipment and to ensure that existing machinery is up to scratch.
The classic first stop for energy-efficient factories is to look at the electric motors used in the production equipment. Often accounting for up to two-thirds of the electricity used in industrial processes, motors especially those that power pumps to circulate air or liquids were traditionally set to run full tilt, with the flow rate of the fluids controlled by valves.
This is, however, a very inefficient use of energy, and the advent of variable-speed drives or inverters, which control the flow of power into the motor, provides the opportunity to use power more effectively. Running the motors at the speed required to provide the flow rates needed can cut energy use so dramatically that, according to electrical equipment company ABB, a variable-speed drive can pay for itself in as little as six weeks.
In addition, variable-speed drives can extend the lifetime of electric motors by allowing them to be started up slowly, rather than jolted into action with a surge of power up to full speed. This soft-start function is easier on the mechanical components and the electrics and electronics of the motor. The digital operation of the drives allows operational data to be captured more easily by condition-monitoring equipment and software, allowing maintenance to be scheduled and providing an early warning of potential breakdowns by highlighting the unusual behaviour of equipment.
Variable-speed drives can extend the lifetime of electric motors by allowing them to be started up slowly
This is becoming increasingly well known in industry as a quick hit to make cuts in energy usage. But once this has been done or if this course of action isn’t suitable factory managers have to be a little more inventive about how to operate their production operations more efficiently.
Reducing the energy profile of production touches on many aspects of the process, not all of which are actually within the walls of the factory. Brian Davy, purchasing director for materials, facilities and services at Jaguar Land Rover (JLR) and who, in his own words, is ’responsible for everything that isn’t actually screwed to the car’, said logistics and component sourcing can also play a big role.
JLR has a challenging set of environmental targets for its production processes; based on 1990 figures, it aims to reduce CO2 from operations and waste to landfill by 25 per cent and cut water use by 10 per cent. It has found that the biggest opportunities for emission reduction were in materials processing.
One example of this, said Davy, was a decision to change the sourcing for the 12 cast aluminium components that form part of the body structure of the Jaguar XK, which is assembled at JLR’s Castle Bromwich plant in the UK. Previously, these had been made in Germany, but a UK supplier proposed supplying the components using a different alloy, which would allow them to be made with a lower energy annealing process than the one employed by the German supplier.
Davy initiated a study looking at the energy used in both options, starting from the production of an aluminium ingot and ending with the parts ready on the production floor in Castle Bromwich.
From the German supplier, this process consisted of alloy production, casting, heat treatment and pre-treatment at the supplier’s factory near Munich, then transporting the parts 834 miles (1,342km) to Castle Bromwich. The alternative required the aluminium ingot to be made in Rheinfelden, near Basel, then transported 730 miles in that form to the supplier’s casting facility near Worcester, then heat-treated and pre-treated in West Bromwich before being taken on to JLR Castle Bromwich. In all, the aluminium would have to travel 979 miles.
’It’s a longer distance, but most of that is travelling as the ingot, and that makes a difference,’ said Davy. ’Using the UK supplier actually turned out to represent a 32 per cent reduction in emitted carbon and therefore in spending on energy. The change entailed a £1.6m investment in retooling, but that was paid back over one year. What this shows is that a green outcome and a business outcome are often compatible with each other. Sustainability is a source of competitive advantage, not just a sop to tree huggers.’
This conclusion is echoed by a report from DEFRA showing that the efficient use of energy and water could save British businesses a total of £23bn per year. Most of the potential savings come from the more efficient use of raw materials and reducing waste generation, but energy efficiency on its own could lead to £4bn in annual savings.
One way to save energy has been developed by compressed-air specialist Atlas Copco, which has installed heat exchangers on its compressors to recover the electrical energy used in compressing air as heat specifically as hot water. Initially embodied in a series of large oil-free compressors, the technology is now available as a retrofit kit that can be used with smaller, oil-lubricated rotary screw compressors. The kit consists of a stainless steel oil/water heat exchanger with pre-mounted mechanical parts, designed as a simple plug-and-play system.
Heat recovery works by transferring the heat from the cooling fluid of the compressor’s motor to another water circuit. Previous units, which worked on water-cooled compressors, could heat water to 60°C. But Atlas Copco’s Anthony Cornes said temperatures up to 90°C can be achieved, recovering 72-94 per cent of the energy used to power the compressor.
“Sustainability is a source of competitive advantage, not just a sop to tree huggers”
BRIAN DAVY, JAGUAR LAND ROVER
The hot water produced has a variety of uses, added Cornes. ’More than 45 per cent of industrial applications use hot water in their process operations,’ he said. The particular application would depend on the temperature of the water. For example, water at 60-90°C can be used for the return circuit of a heating boiler or for heating buildings; at 40-60°C, it can be used to supply hot taps; and at 30-40°C, it is suitable for pre-heating tap water, process water or supply air or for maintaining background heating. ’There may well be other very specific roles within a particular process application,’ he added.
Heating, ventilation, air conditioning and lighting are often fruitful sources of energy savings in factories. Dedicated systems for controlling this type of energy usage have been available for some time, but according to Cedric Rodrigues, managing director of clean technology group Ener-G, many such systems have two flaws that can restrict their ability to deliver energy savings. The first of these is inconsistent programming, rather than a programme based on a recognised standard for control strategies; the second is the tendency for users to adjust the settings of the system, eroding its ability to save energy.
Ener-G’s solution to these problems is to lock down the system, pre-configuring the operating parameters before installation and then making it tamper proof. Its E-magine building energy management system features a front-end energy management tool to analyse the energy performance of a building and devise a strategy to cut energy usage while complying with legislation and standards. But once these optimal settings have been determined, they are locked into the system. Rodrigues said this could reduce energy usage by up to 25 per cent, while also cutting capital purchase costs, commissioning and maintenance.