[Global] A 10% higher algae output in a glass PBR due to thinner walled glass tubing? This is an impressive increase in productivity. How can this be explained? And what properties must such glass tubing have so that it can achieve such results in daily operation over many years?
Various PBR field tests have shown that the thickness of glass walls has influence on the PBR‘s productivity. In recent years, improved glass manufacturing processes have made it possible to further reduce the wall thickness.
The logic of thinner walled glass tubing
For a long time, common wall thicknesses lay between 2.5 – 3.3 mm for a 5.5 meter long tube to ensure mechanical stability of the glass tube. Depending on the supplier‘s ability to produce tubes with tight wall thickness tolerances, glass tubes used in PBRs can have thinner wall thickness. It seams logical that for typically used tube dimensions tubes with equal outer diameters but smaller wall thickness are more productive – because the larger inner diameter would offer more overall volume and a larger illuminated culture cross section.
Field test in Israel
SCHOTT Tubing and a partner in Israel tested the output of a 16 kilometer long tubular PBR with a reduced wall thickness of 1.8 mm for one year and compared these results with a PBR tubing with 2.5 mm wall thickness. The result: tubing with the same outer diameter and the reduced wall thickness of 1.8 mm led to 10% more output (Heamatococcus Pluvialis was cultivated during the test).
How to explain the increase in productivity
A certain share of the productivity increase can be attributed to the larger cross sectional area of the algae culture within the tubing. This larger area leads to increased light absorption. Simultaneously, the temperature fluctuates less in such tubing which also promotes productivity.
Of course, thin walled tubing raises the question if it is more susceptible to breakage. The test in Israel showed: Not a single case of breakage was recorded during transport, installation, start-up and full operation of the reactor. The prerequisite for this was glass with tight wall thickness tolerances and high quality end forming.
This text is an excerpt from our e-book “Why is a photobioreactor made from high end glass far more efficient”. There you can learn more about the five main reasons why you should focus your attention on selecting the right glass components.
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