An efficient combination: DuoDry CC and EvoDry steel cylinder
To prevent the curl effect, Chinese paper manufacturer Sun Paper is using Voith's DuoDry CC concept for its new PM 37. This technology reduces curl during the production of corrugated base paper, allows high production speeds and lowers energy consumption of a plant. In case of PM 37 the energy consumption is additionally reduced due to EvoDry steel cylinders.
As the first paper machine in China Voith is equipping the PM 37 from Chinese paper manufacturer Sun Paper with the DuoDry CC drying concept. The abbreviation stands for Curl Control and describes one of the key features of the concept: the reduction of paper curl in single-tier dryer sections.
No additional energy input necessary
Curl , which impedes the converting process of paper, can be avoided, for example, by using a double tier dryer section. However, at the production speeds that are standard practice today, the risk of web breaks leading to costly machine downtime does increase when using this conventional technology. In addition, the removal of paper broke is often difficult and dangerous for operators. Single-tier dryer groups, on the other hand, allow higher production speeds and have therefore long since become established as state-of-the-art for modern paper machines. The downside is that the paper tends to curl in these systems. In conventional systems, the curl can be counteracted by spraying water on paper bottom side. However, the problem with this is that it requires additional energy input, as the water added then has to be evaporated in the dryer section. This is where the DuoDry CC concept comes into its own, as it utilizes the thermal energy that is needed in any case to dry the paper by introducing it as steam into the last vertically inverted dryer group from the other side and preventing the curl effect. The steam and condensate system is identical to that of other dryer groups. An additional heating medium is not necessary. DuoDry CC therefore reduces the energy input during production and lowers the operating costs of the paper machine. Another advantage is that the steam pressure in the last dryer group is highly variable, allowing the operator precise control of the curl and as a result optimization of paper quality. Despite the vertical arrangement the system is not higher than the press section, so special civil construction measures are not necessary.
Reliable production at high speeds
And the DuoDry CC concept does not just increase cost efficiency. Particularly in case of low basis weights down to around 60 g/m2, this drying principle protects against costly web breaks at high production speeds (the PM 37 is designed for speeds of up to 1200 m/min) and improves machine availability. Moreover, the developers of DuoDry CC paid particular attention to operator safety during broke removal. In conventional machines this process is difficult and involves risks for the personnel. This is why Voith designed the DuoDry CC in such a way that paper broke drops easily into the pulper.
EvoDry drying cylinders reduce electricity consumption
The two cylinders of the DuoDry CC will be located immediately adjacent to the end of the dryer section of the PM 37. Voith installed the same EvoDry steel cylinders that are used in the rest of the entire after-dryer section. Compared with conventional cast iron cylinders, the EvoDry steel cylinders have a 7 to 10 percent better heat transfer and despite their lower shell thickness offer higher material strength. The lower weight of the steel cylinders already enables much faster heating and cooling rates and therefore higher productivity – an EvoDry cylinder weighs about 30 percent less than its casted counterpart. This means that less electricity is needed to operate the dryer section. The higher thermal conductivity of steel at drying cylinders also offers saving potential: at an electricity price of EUR 0.06 per kilowatt hour, the use of EvoDry steel reduces the annual electricity cost of a plant by around EUR 80,000. In addition, the even temperature distribution over the entire width of the cylinder improves the quality of the paper. All of this forms the basis for much more efficient paper manufacturing. The slightly higher price of an EvoDry steel compared to a conventional cast iron cylinder therefore pays for itself after just a short time.
The order from Sun Paper for the construction of the new XcelLine production lines PM 36 and PM 37 at the location Zoucheng came in January 2017. The machines are based on the PM 31 and 32 that Voith realized in 2016. The order or the two new lines are the result of Sun Paper's high satisfaction with these machines. At PM 37, Sun Paper plans to produce 300,000 tons of corrugated paperboard per year.