Redesigning 7 bar compressed air network at Sioen spinning part of Energy plan

The modification of the 7 bar compressed air network at our Spinning mill, directly provides an answer to the appeal of the UN set in goals 7, 12 and 9.

7 bar compressed air network

Two compressed air networks serve the spinning unit. One at 7 bar, the other at 13 bar. This case is about the 7 bar network used both in the spinning application and in the transportation of pellets (raw material for the yarns we produce at the spinning mill). The redesign in 2017 has a direct environmental and financial impact.

Problem definition: faulty design

This 7 bar network is not optimally designed. It does not work in a loop and the diameter of the pipes is unnecessarily undersized.

Although 7 bar is sufficient for the spinning application, the supply is still between 7.5 and 8.5 bar, in order to ensure a 7 bar pressure for the application. Our investigations show that with an optimal distribution network, cascade operation of the compressors and optimised control management, a supply pressure of 6.5 bar should be considered.

The compressed air network at 7 bar also supplies the raw material (PET pellets) transport system, whereas this transport system only requires a pressure of 3.5 to 4 bar. According to the operators of the spinning unit, point pressures of 5 bar seem to be necessary. The relevance of these point pressures at 5 bars could be the subject of a subsequent pre-feasibility study. Therefore, it is clear that a 7 bar feed is not efficient for this transport of PET pellets.

It should also be noted that the transport of crystallised pellets must be carried out with highly dehumidified air. Absorption dryers lower the dew point to -80 °C.

Pellet transport system

The solution to the problem was rethinking and redesigning flows. The tracks for the pellet transport system were:

  • Establishment of a new and independent compressed air distribution network for pellet transport;
  • Acquisition of single stage compressed air compressor;
  • Integration or coupling of dryers with heat recovery;
  • Mains connection 7 bar so that the pressure can be boosted at certain points. This is to limit the investment of low pressure compressors;
  • Placement of the compressors of the new distribution network close to the crystallisers and above the existing dryers. The connection of this new network delivering dried compressed air is of course to be provided downstream of the existing absorption dryers.

Spinning application

Impact on the network at 7 bars for the spinning application:

  • Decrease in flow rates (total, average and peak) and decrease in distribution network losses;
  • Possibility of reducing the set pressure;
  • Possibility of installing a global management control for compressed air. Pressure sensors are to be provided on the buffer tank close to the application and not on the compressors.


A feasibility study was carried out in order to evaluate the environmental and financial impact of the allocation of the current compressors on the low pressure compressed air network. In this case, the maximum savings will be reduced as well as the investment.


Electricity 580 000 kWh energy savings
Emissions 291 276 kgCO₂ reduction
Investments 50 518 EUR