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Drastic Savings in the Press Section with Consequences for the Dryers

O. Kääpä (Dipl.-Ing.) Vice President Sales, Heimbach GmbH & Co. KG,

After the cost of raw materials the energy costs constitute the next highest component, depending on the paper grade to 20-30 % of total manufacturing costs. By this reason the motivation to save costs by optimising the processes has never been so strong.

Overcoming the major cost factor
The major cost factor is the drive to the vacuum pumps. By optimising their adjustment the costs of the other "consumers" can be reduced to a minimum as well. The essential requirement for this is bringing about a nip dewatering. Additionally, on fast machines the laws of physics conflict with Uhle box dewatering: there is just not enough dwell time available. In addition the water has to be pulled from the horizontally running felt at an angle of 90o vertically into the slot.

Depending on the paper grade 10-20 % of the power consumption is required for the production of vacuum for the various dewatering elements, around 25 % of this vacuum capacity is usually required for the Uhle boxes. So the optimisation of the Uhle box vacuum alone can save more than 1 million Euro per year – subject to the "correct" dewatering techniques being applied. Figure 2 shows with a high speed newsprint machine that the felts can be run throughout their whole life at a significantly lower vacuum level (20-40 kPa) than was previously the case (45-75 kPa), without any problems. In many cases, at least one of the water-ring pumps can be shut down shortly after the start for the rest of the felt life, subject to the use of "appropriate felts for the correct style of dewatering".

Advantages for the cost balance
Permanent saving of between 100 and 300 kW per felt from the reduction in vacuum energy – + saving of approx.100 kW from the drive to the press rolls as a result of reduced braking of the felts – + saving of drive energy, lubricating and sealing water from the elimination of a water-ring pump. Total savings/yr: around 1,000,000 EUR

Nip Dewatering – the optimal clothing
A felt specially designed for nip dewatering is the non-woven layered felt ATROCROSS from Heimbach Main features: no yarn system in Z-direction, high openness combined with low free volume, life-long minimal base compressibility, specially active water removal from the sheet and fast barrier-free water flow through the felt. Special feature of the base: the cross directional alignment of the upper layer. This causes its yarns to function as "micro-foils", which "shovel" the water very fast from the sheet into the felt. This also leads at low specific pressure to a high level of saturation and reduces the risk of further water take-up (oversaturation, crushing, rewetting). For all of these reasons the non-woven felt from Heimbach has proved in practice to be an extremely fast starter, a pronounced nip dewaterer and an active "energy saver".

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