In line with the installations described, the following applies to differing load situations according to Fig. 10.4.5.1: One compressor (item 1) is available for the duty output, the second compressor (item 1.1) as standby. Both compressors remain in standby, with the variants: Two-compressor operation 100 % dryer load One-compressor operation 50 % dryer load Compressor standby 0 % dryer load The varying running periods of the compressors call for an adaptation of the adsorption dryer (item 4), to maintain economic performance. In order to match the regeneration performance with the load, the loading fro 0 - 50 - 100% must be coped with. This is achieved in practice by means of a modified Dewpoint Dependent control of the dryer system. Deviating load ranges are always part loads. A load governed control system caters for this part load and adapts the dryer running= periods in an effective manner. Full load operation can follow immediately after a part load use. For this reason, the length of the regeneration period has to be set in such a way that continuous drying is possible when changing over from part load to full load operation without a dewpoint peak (dewpoint collapse) during continuous operation. Regeneration time and regeneration air quantity remain constant. In the partial load range, the loading time will be inversely proportional to the load, i.e. with 50 % load, the loading time will be made longer by the factor 2. Regeneration air requirement is likewise inversely proportional to the loading. The ratio of regeneration time to loading time determines the regeneration air requirement and economic utilisation of the adsorption dryer.
Figure 10.4.5.1
Using a load governed control system, the power supply to the dryer must be ensured at zero loading, i.e. the dryer remains open allowing the pressure monitor in the compressor to trigger the pre-selected lower switch-on and upper switch-off point as limiting values for operation. As an alternative to load depending control, it is possible to link the compressors directly to the dryer. Dryer/compressor simultaneous running have been discussed in section 10.4.2. As varying load situations are unpredictable, the following assumption applies: Compressor 1 supplies points of use for brief periods only, remaining off-load for long periods, compressor 1.1 is required as a standby. These conditions, long periods of standby and short periods of operation have a detrimental effect upon the pressure dewpoint. Long standby periods call for additional regeneration phases. With connection of the dryer/compressor, automatic regeneration can be simply achieved. Two additional time relays are included in the control system. Relay 1 has the maximum period of availability and relay 2 the time of regeneration. Setting these relays is based on the acceptance of a pressure dewpoint peak. The return feed for regeneration air from the receiver has to be provided with this installation scheme also.
