Membranes Flow Control
Membranes are made of hollow fibres. The fibre is a flexible tube with a porous wall and its diameter is < 0,1 micron, which is smaller than a human hair. The fibres are stretched in a pipe and assembled at in and outlet.
The process is a reversed osmosis, which efficiency depends on stable in and outlet pressures. One can compare it with blowing up a balloon. By oscillating pressure, the balloon extends and shrinks constantly. Consequently purity changes, which will be corrected by the control system, but causes non desired aging and decrease in lifetime of the membranes.
Experience in nitrogen and air compressor packages business has taught us, that air demand is overestimated and nitrogen requirements are under estimated. An easy solution is available by placing one or two membranes extra. Air compressor capacity is available, moreover the air demand decreases with aging, consequently more air is available.
To overcome these problems in practice, we equip our oil free screw compressor package with a blow off valve, which is more cost efficient than an early replacement of membranes. Below we explain by a typical example.
Standard compressor has an inlet valve, which closes at 10 bar(g) unloading and opens at 9 bar(g) fully loading.
Compressor capacity: 1000 Nm3/h
Power absorbed loaded at 10 bar(g) : 111 kW
Power absorbed unloaded: 85 kW
At 30% lower air consumption compressor is running 70% loaded and 30% unloaded.
Power consumption per hour: 0,7 x 111 = 78 kWh
0,3 x 85 = 25,5 kWh
103,5 kWh
Special membrane capacity control of the compressor discharge flow control. Power absorbed at 9 bar(g) with 105 kW.
Energy loss: 105 – 103,5 = 1,5 kW membrane replacement is much more expensive.
Some contractors are mistaken by stating having enough buffer capacity, which means the load-unload cycle is longer. In fact application of this device does not require any buffering.