Energy Optimization

Due to the raising energy cost and environmental requirements, Nebb is currently working on a program for reduction of the energy consumption for production of press and dryer felts. The program is divided into two sub-programs, where the first sub-program is related to improvements on the current machine design and the second is working on the development of alternative methods for energy supply to the finishing process.

The timeframe for the two programs is “next delivery” for the first one and "a couple of" years for the second program.

The energy saving targets for the two sub-programs are very different, realising that the current hot roll/air box design limit the energy saving potential. However, modelling programs have indicated that an energy consumption reduction up to approximately 15 % should be possible without major redesign. 

The energy saving target for “the alternative system” is 50 % or more reduction. In addition shall the program obtain a reduction in sequence time, preliminary aimed at 35 – 40 %. The indicated targets are based on detailed pseudo-static and dynamic simulations of the various process stages involved in finishing of a typical press felt. The concept is currently subject to patent application preparation and more information about the system will be available as soon as patent protection is secured.

The current Nebb hot roll machine design will be prepared for later installation of the new energy supply and ancillary systems with minimum modification of the existing mechanical equipment.

Current Machine Design

Suction Box Efficiency

The efficiency of the suction box process is very important for the drying energy consumption. The main parameters for control of the moisture are water temperature, suction pressure (vacuum) and the suction “face” design. An optimisation of these parameters may result in 3-4 % reduction in energy consumption (equal to approximately 10 % of the drying energy).

End Moisture Control

The drying end moisture content is extremely important for the drying energy consumption. Terminating the drying process at equilibrium content at fabric storage conditions instead of keeping the fabric under “machine conditions for some time” may under certain circumstances save up to 15 % in dryer energy. A reliable control of end moisture is however necessary. A system for this will be included in the Nebb Process Pilot, utilising the unique technique developed for the NebbPerm permeability control system.

Roll Weight Reduction

The largest single consumer of energy is the hot roll, i.e. the sequential heating and cooling of the steel materials. Hence a reduction in steel weight will result in a corresponding reduction in energy consumption. This may com from an optimisation of the material utilisation with respect to roll stiffness and stability during heating and cooling. Preliminary evaluation indicates that 2-3 % energy saving may be within reach. This optimisation shall not lead to stronger restrictions for temperature change rates.

Shorter Hot Oil Pipe runs

The oil amount in the hot roll and the distribution line between the roll and the crossover valves must be both heated and cooled. Typical line diameter is 100 mm. Installation of the crossover valves close to the roll may lead to a considerable reduction of heating energy consumption. E.g. will 50 m distance reduction mean approximately 1.5 % reduction in energy consumption.

Sequence time

The total sequence time for on typical press felt is dominated by the following operations:

• Installation and removal of felt
• Roll heating (Restricted)
• Felt drying
• Roll (and felt) cooling

All operations involving heating or cooling will influence on the sequence duration. The duration of the drying process may be reduced from both the suction box improvement and the end moisture control. E.g. will the combined effect of these improvements reduce the dryer sequence duration 5 to 6 minutes.