Membrane stress analysis of collapsible tanks and bioreactors

• The paper aims at membrane stress calculation for large scale collapsible tanks.
• A method was developed for calculating stress in collapsible tanks and bioreactors.
• Equations for calculating tension and the shape of the vessels were developed.
• Tension per length in 100–1000 m3 of these vessels was between 300–20000 N/m.
• How cost and safety can be optimized when designing these vessels was explored.

Collapsible tanks, vessels or bioreactors are finding increasing usage in small/medium scale processes because they offer flexibility and lower cost. However, if they are to be used at large scale, they need to be shown capable of handling the physical stress exerted on them. Because of their nonconventional shape and non-uniform pressure distribution, thin shell analysis cannot be used in calculating their stress. Defining curvature in terms of pressure addressed these challenges. Using curvature and numerical analysis, the membrane stress in collapsible tanks designed as bioreactors of volumes between 100 to 1000 m3 were calculated. When the liquid/gas height and static pressure are known, an equation for calculating tension per length was developed. An equation that could calculate the liquid height from the bioreactor’s volume, dimensions and working capacity was generated. The equation gave values of liquid height with a maximum deviation of 3% from that calculated by curvature analysis. The stress values from the liquid height and tension equations had a maximum deviation of 6% from those calculated by curvature analysis. The calculated tensile stress in a 1000 m3 collapsible tank was 14.2 MPa. From these calculations, materials that optimize both cost and safety can be selected when designing collapsible tanks.

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