There are several environmental issues concerning air quality around and in the immediate vicinity of a paper machine. Environmental concerns related to the air include noise and the formation of dust, moisture, mist and droplets. Noise can cause serious health problems and therefore the official requirements in different countries, together with EU directives, have all led to increased demands for noise prevention.

With effective wet end ventilation the airflow can carry about 0.5 percentage weight of water in the form of droplets, in addition to the vapor in the saturated exhaust air. Taking into account the air amounts required, this means that during one month over 1000 m3 of water may be collected from a large paper machine.

Metso Paper has a patented solution for plume reduction. A reduction in the amount of discharged moisture and avoidance or reduction of plume formation can bring several benefits. These solutions reduce the possibility of ice forming on the mill roof or in the vicinity of the mill, and reduce or completely remove visible mist. By removing mist and droplets heat can be recovered more effectively, and damage and discoloration of buildings can be reduced. The operator can also reduce water consumption by re-circulating condensate water from the exhaust air back into the process.

The external noise level requirements in the paper industry have steadily increased since the 1980's. The average distance from the imagined paper mill center to the immission point limit level (an equivalent sound pressure level of 45 dB (A)) has decreased considerably. Metso Paper manufactures noise abatement absorptive silencers, resonators and sound insulation hoods. External noise sources are attenuated according to the customers' requirements: in an LWC-line, for example, there are about 80 external noise sources. These are normally attenuated to an A-weighted sound pressure level of 65-75 dB (A) vicinity of the paper machine.

A compact pipe resonator and absorptive silencers in series for vacuum pump exhaust air attenuation.