a) Total energy heater
The total energy requirement Qtot is calculated with Formula 7.3.4.6 and used for obtaining the heating power Pe, taking into account the efficiency of the heating system.
Formula 7.3.7.1
b) Heater power
The heater power arises from the total energy of the heater Ph and the heating time th. The theoretically obtained figure is rounded off to form a standard value. If required, an addition to be on the safe side can be included. The difference between the theoretically obtained value and that after rounding up to a standard figure incorporates a heating capacity reserve. There must, however, be some harmony between the safety factor and the reserve, so that costly over dimensioning of the heating capacity is avoided.
Formula 7.3.7.2
c) Blower power
The most commonly used method for determining the blower power Pb consists of extracting the appropriate data from the performance curves of the blower (Diagram 7.3.7.1). As an alternative, there is the following Formula for calculating blower power, which takes into account the efficiency with a mean value of about 0.3 - 0.4:
Formula 7.3.7.3
For adsorption dryers with external heat regeneration, the blower draws ambient air and heats this by means of the heater to reach regeneration temperature, so that it can subsequently be passed through the dryer system.
Diagram 7.3.7.1
If a high differential pressure (see Section 7.3.1) rise or the blower is designed on the low power side, there is a danger of insufficient regeneration. This can be compensated for only by a longer heating period. The situation then becomes critical if a long heating period prevents sufficient cooling.
d) Mean power requirement, heating
The mean power requirement for the heating device Phm is of importance to the operating costs as these determine the economic viability of an adsorption dryer.
Formula 7.3.7.4
e) Mean power requirement, blower
Whereas for the mean power requirement of the heating arrangements, only the desorption period is of significance, assessment of the mean power requirement of the blower Pbm must, in addition, consider the cooling period.
Formula 7.3.7.5
f) Mean total power requirement
The mean total power requirement Pm provides a specific value which can, pro-rata, be used for calculating the operating costs of adsorption dryers.
Formula 7.3.7.6
g) Flushing air quantity
In order to prevent a pressure dewpoint peak (see Section 5.5.3) it may, under certain circumstances, be necessary to flush the adsorber with a fraction of already dried compressed air after the cooling phase. As a guideline quantity, one calculates a requirement of 3 - 6% for the duration of about 1 hour determines the difference between the theoretical and the effective blower volume flow.
Formula 7.3.7.7
h) Remarks
When considering the design layout of adsorption dryers with heat regeneration, it becomes clear in the heat allowance that an under sized dryer does not have favourable overall power requirement. Savings in the initial investment can easily be confused with the apparent saving of energy used in its operation. Additionally, if the ageing of the desiccant due to the higher thermal loading is taken into account, any reduction in capital costs are lost through higher service costs over a relatively short period.
