Noise protection & noise refurbishment Less noise from the paper mill
Splitter silencers ensure noise protection compliant with the TÜV (German Technical Inspectorate)
From 120 to 90 dB(A) – or in other words: from a rock concert to chamber music. That was the challenge for BerlinerLuft. Technik GmbH in the noise refurbishment of a paper mill. The supply and exhaust air systems on the factory roof, through which the sound escapes to the outside, were refurbished. And it was precisely here, on the roof, that the 90 dB(A) had to be achieved. Five splitter silencers from the ventilation and air conditioning specialists now ensure a minimised noise level – and that residents can sleep peacefully at night again.
The paper mill is located in a so-called mixed area in Thuringia, Germany. In mixed neighbourhoods, residential and commercial areas meet and it could hardly be more drastic than in this case: A neighbour lives directly next to the factory premises. Behind it is the production site for paper manufacturing: Rolls for paper tissues, facial tissues and toilet paper. Production is noisy – not only because of the production machines but also because of the heating and ventilation systems. The resident complained about the noise to the environmental authority in Thuringia and the TÜV confirmed this: At night, his bedroom window reached more than the permitted 45 dB(A). The paper mill had to take action and reduce its emission values.
As experts in the field of industrial sound, this is a typical case for us: A lot of acoustic power in a small space. Good planning and preparatory work were required.
explains Achim Rockel from Sales and Product Management Sound Insulation Systems at BerlinerLuft.
Following an on-site visit to the paper mill and based on the TÜV measurements, the ventilation and air conditioning technology specialists developed a concept for noise refurbishment and noise reduction. They were faced with a particular challenge: "We had to fit a lot of acoustic power into a very small space. Good planning and preparatory work was required", emphasized Rockel.
From 120 to 90 dB(A)
Noise refurbishment work was carried out on the roof of the paper mill at a height of around ten metres. This is because the ventilation and extraction systems used in paper production were identified as the source of the noise: The TÜV measured 120 dB(A) on the roof. "We had to reduce the sound power to 90 dB(A) so that only 45 dB(A) would reach the resident's bedroom window thanks to the distance attenuation," explains Rockel. To give you an idea: 120 dB(A) corresponds to an air plane taking off or a loud rock concert. 90 dB(A) is the noise level for an orchestra or chamber music, for example.
Four sound sources
The TÜV identified a total of four noise sources on the roof, which the specialists from BerlinerLuft addressed: a system for vacuum exhaust air, a system for mist extraction, a supply air system for the burner room and a supply air system for the Machine Control Centre (MCC) for the paper machine. The main causes of the noise are the many fans installed in these systems to cool the hot air generated during paper production. But the heating and burner systems downstairs in the production hall also make noise, which escapes to the outside via the ventilation systems.
In order to reduce the noise on the factory roof to the 90 dB(A) required by the TÜV, splitter silencers were installed on each ventilation system, as are primarily used in ventilation and air conditioning systems (HVAC systems).
Noise reduction for vacuum exhaust air
The most extensive noise refurbishment was carried out on the vacuum exhaust air system. Here, the ventilation professionals reduced the noise level of the vacuum pumps by 50 dB(A). Another challenge: As moist air containing cellulose fibres is extracted and the extracted water vapour is up to 150 °C hot, BerlinerLuft. Technik manufactured the splitter silencer entirely from stainless steel. The built-in silencer measures 1,300 x 1,400 x 2,800 mm (W x H x L) and creates a volume flow of 35,145 m3/h.
In addition to the stainless steel design, the splitter silencer should also be accessible for cleaning and inspection. "We have installed a special inspection opening. The baffles can be removed via a maintenance door in the silencer housing," explains Rockel. The special construction of BerlinerLuft. Technik has two advantages for the paper mill: Firstly, the silencer does not have to be completely replaced when it has built up a layer of dust but is cleaned instead. Secondly, the retractable baffles minimise the downtime of the system during an inspection. "With trained personnel, the inspection takes two to three hours. This is usually done by the paper mill when it changes the paper grade and the plant is therefore at a standstill anyway," explains Rockel.
Less noise with mist extraction
Humid, hot, dusty air is also a challenge in the mist extraction system. Here too, the specialists opted for a stainless steel design and accessible baffles for cleaning and maintenance. The system is also equipped with a removable rain cover and a trickle guard.
The 1,600 x 1,200 x 2,000 mm (W x H x L) splitter silencer operates with a volume flow of 28,190 m3/h. Thanks to a resonator section tuned to 125 Hz; the system also achieves the required guideline value of 80 dB(A) in the low frequencies. Overall, BerlinerLuft. Technik reduced the level at the mist extraction system by 32 dB(A).
11 dB(A) less for supply air
The two supply air systems, one for the burner room and one for the Machine Control Centre (MCC) for the paper machine, each achieved a level reduction of 11 dB(A) after the noise refurbishment. For the supply air system for the burner room, a completely new silencer including housing was constructed over the existing fan. The splitter silencer is square (1,250 x 1,250 x 1,250 mm) and creates a volume flow of 30,000 m3/h.
The new design is equipped with a mounting frame for the axial fan, an integrated splitter silencer and a customised intake bonnet made of galvanised sheet steel. "The construction height was a challenge here: All in all, we were only allowed a maximum of 2.20 metres above the parapet," emphasises Rockel.
The second supply air system, the one for MCC room ventilation, was extended by two additional splitter silencers made of galvanised sheet steel and the existing filter unit continued to be used. The silencers each measure 1,250 x 1,250 x 1,000 mm (W x H x L) and operate with a volume flow rate of 32,500 m3/h.
Challenging flexibility during assembly
The noise refurbishment project at the paper mill in Thuringia took place in two stages: BerlinerLuft. first worked on the two supply air systems. This was followed by the order for the two large and more complex retrofits to the two exhaust air systems (vacuum and mist extraction). In total, the project was spread over three construction phases and the assembly work had to be completed quickly.
"We planned the renovation work from one plant shutdown to the next," explains Rockel. "Our installation work was linked to the overhaul work in the paper factory. We therefore always had to be able to react very flexibly within six to eight weeks and have everything ready on site in a short amount of time."
The closely coordinated planning, the special solutions and the flexibility have paid off. The final measurement by the TÜV has shown: All requirements are met and the permissible final levels are complied with.
