The theoretical determination of regeneration volume flow can be carried out with accuracy, the design and, the construction of the regeneration orifice, can cause a multiplicity of practical problems. The air velocity inside the regeneration orifice, and the volume of regeneration air flowing out, depends on the construction and surface characteristics of the orifice. For an orifice with straight cylindrical form with apered form, the volume of funnelled and emerging regeneration air depends on the smallest cross-section. If the pressure behind the orifice is lower than the critical pressure, the pressure within the orifice cannot drop below the critical pressure but will only expand to atmospheric pressure downstream from the orifice and without increase in velocity. The regeneration volume flowing through an orifice at above critical pressure conditions, is calculated in accordance with Formula 7.2.4.1.
Formula 7.2.4.1
The effectiveness of the orifice is below 1, causing the volume of the outlet regeneration flow Vrfo to be smaller than the theoretically calculated regeneration volume flow Vrf. In practice, a degree of effectiveness is additionally obtained from the ratio between adsorption period length tA to desorption time tD , which is taken into account when calculating the orifice by :
Formula 7.2.4.2
After simplification and conversion of Formula 7.2.4.1, the orifice diameter do is calculated, depending on regeneration volume flow Vrf at the inlet pressure pi and outlet pressure po , establishing first the orifice cross-sectional area AO, taking into account the overall degree of effectiveness from Formula 7.2.4.2. Thus the following applies to air :
Formula 7.2.4.3
The theoretically determined orifice diameter is rounded up to appropriate practical manufacturing possibilities. An alternative solution consists of using diagrams or tables in order to determine the orifice diameter and to adapt it to changed operating conditions.
Diagram 7.2.4.1 - Air flow through orifice to atmosphere (as a function of initial pressure)
Further diagrams of regeneration air orifices for different performances are listed in the Appendix Part 12.
