Sheetfed offset printing is an energy-intensive process. So it is all the more important to develop energy-efficient assemblies and to utilise waste heat wherever possible. Koenig & Bauer (KBA) has long been pursuing this train of thought in the interests of its customers and the environment, and has come up with some useful ideas.

With a sheetfed offset press, the amount of energy consumed depends to a large extent on the type of job being printed. Alongside general efforts to optimise energy efficiency, from which any printer would benefit, there are some additional options for reducing the primary energy input where the financial outlay would only be worthwhile for specific print applications. Given the diversity of the production parameters involved, determining the potential benefits of recovering and reutilising waste heat off the press in the most effective way required a series of precise measurements taken over a prolonged period of time.

Drawing on a solid foundation of captured data, KBA has developed an array of standard and optional features for enhancing the energy efficiency of Rapida presses from the feeder to the delivery. The most effective examples are given below.

Efficiency-enhancing four-quadrant drives
Rapidas are fitted with four-quadrant drives which enhance overall press efficiency by feeding braking energy back into the grid. This has proven particularly effective at reducing power consumption during makeready processes. KBA favours direct belt drive onto the first impression cylinder.

Shaftless DriveTronic feeder
KBA's DriveTronic feeder has no mechanical gears, longitudinal shafts or other energy-guzzling consumable parts. In their place are direct drives which are much more efficient. Proportional valves, in conjunction with a self-regulating air-compression cabinet, ensure that only the volume of blower and suction air actually required at the sheet separator is provided. This means a lower energy input for the air supply. Individual, distributed blowers at the suction belt ensure an energy-efficient sheet transport.

DriveTronic SIS sidelay-free infeed
Unlike mechanical or pneumatic systems, KBA's sidelay-free DriveTronic SIS infeed, which is now available as an option in every format class, requires no air suction and therefore also reduces the amount of energy consumed by the air-supply system.

Energy-saving roller-bearing technology
Smooth-running roller bearings with reduced backlash allow the impression cylinders and transfer drums to be rotated with very little effort using a hand crank. This bearing technology, which has been incorporated in KBA presses for many years now, is a major factor in cutting the Rapidas' energy consumption. The venturi effect is exploited to reduce the volume of blown air applied at the sheet guides. Spoilers at the transfer drums are effective in preventing undercurrents.

Fewer rollers in the printing unit
The number of rollers in the inking unit has been reduced to promote a quicker response. At the same time the single-ribbon ink train has been optimised to minimise abrasion and energy losses. The same applies to the triple-roller dampening unit. The ability to disengage inking units not required for the production run is a further energy-saving option. This on its own can deliver a total energy saving of around 3kW per inking unit. It is also good for the environment and the budget, since it eliminates the need for costly roller paste and the time spent applying it and washing it off.

AirTronic delivery requires smaller volume of blown air
The KBA AirTronic delivery has fewer blower pipes and thus consumes less air. Energy-efficient venturi nozzles help to stabilise the air-cushioned sheet travel. Aerodynamic spoilers at the gripper carriages maximise energy efficiency by optimising air currents. Less air resistance and improved sheet guidance automatically reduce air consumption.

Energy-saving VariDry dryer
The new generation of KBA drying systems dramatically enhances the efficiency of the coating systems as well. For example, the VariDry^BLUE infrared/hot-air dryers with heat recovery cut energy input by as much as 50 per cent compared to conventional systems. The new VariDry UV dryers have also been made much more energy efficient by optimising reflector geometry and heat management at the radiation units, thus substantially increasing the level of radiation efficiency. The use of electronic ballasts delivers further savings by reducing energy consumption in stand-by mode.

Free cooling of temperature control circuit
Another energy-saving option KBA offers is free cooling of the temperature-control circuit. With this system, where the outside temperature is low enough the return circuit is coupled directly to the temperature-control circuit. The level of utilisation depends on plant location and the volume of waste heat generated. Test measurements revealed that free cooling was effective for more than 1,000 hours, the equivalent of 11.5 per cent of the annual total.

Assuming 220 working days, each with two shifts, as the operating time for the dual-purpose cooling system, and an average power rating of 6kW for the temperature-control circuit, this represents a total input of 20.9MWh from the cooling circuit. If all other parameters remain unchanged, 1,000 hours of free cooling per year would cut power consumption to 6.45MWh. In the best-case scenario free cooling would be available for 3,000 operating hours, resulting in a potential cost saving of up to €850 per year.

Energy-efficient air supply
An energy-efficient air-compression cabinet should always be water-cooled. By modifying the deployment of different types of compressor energy input for the air supply can be cut by up to 24MWh per year compared to rival cabinets. This is equivalent to a saving of 28 per cent in electricity consumption.

Utilising waste heat in the return cooling circuit
The waste heat emitted by the press and the water-cooled ancillary devices, and recovered via the return circuit, is potentially a major source of energy, eg for heating purposes. However, it is advisable to consider a number of factors prior to utilising this energy. If the plant is heated via an economical high-temperature system, there is a problem.

The average temperature in the cooling-circuit feed flow is 40°C. The feed flow of a high-temperature heating system is generally around 70°C to 80°C and the return flow 50°C to 60°C. It is therefore inadvisable to re-utilise directly the heat in the return cooling circuit, since it would cool the heating circuit. One way of circumventing this would be to install a heat pump, which would raise the temperature from 40°C to the level required for heating.

A feasibility study for such an installation would have to factor in the cost of substituting gas for the heating, the different levels of usage (heating only in the winter months, press not continuously in operation) and the energy consumed by the heat pump. In the most favourable scenario the return on investment would be around 15 years, which would make the installation uneconomical. If, however, the printing plant is a new build with a low-temperature heating system, waste heat from the return circuit can be used to reduce energy consumption for heating. Waste heat could also be used relatively easily to heat the paper stores or similar.

Reutilising exhaust air from the IR dryer
Some of the energy contained in dryer exhaust air can be re-utilised directly via a heat exchanger to pre-warm the air entering the dryer, thus reducing energy input. Much bigger savings can be achieved by cooling the exhaust air and warming the inflowing air via an exhaust heat pump. Depending on the press type, this can deliver energy savings of up to 50MWh per year.