Specific enthalpy condensation process

If air infiltration is avoided (or minimized to an acceptable level), it is possible to recover all of the latent heat supplied in the SSD from the exhaust by condensing the exhaust stream or by mechanical- or thermocompression to elevate its specific enthalpy for reuse in the dryer. As SSD will necessarily produce steam equal in amount to the water evaporated in the dryer, it is necessary to have a useful application for this excess steam in the process plant. If this steam is used elsewhere, the latent heat recovered is not charged to the SSD, leading to a net energy consumption figure of... 

The mean specific molar heat capacity of the dry gas mix Cpm.ilT l, can be easily calculated or extracted as a stream property from a process simulator, for example, Aspen Plus [2]. The moisture exergy ei,H,tni,H20 must include the complete condensation of any water vapor. Although the specific enthalpy ho = 1890.3 kJ/ kmol and entropy So = 6.616 kJ/(lcmol K) of the reference water are fixed, the enthalpy hi in kj/kmol and entropy s, in kJ/(kmol-K) are computed applying the IAPWS-IF97 formulation for the gas temperature and partial H2O pressure. 

The process will be subject to multiple disturbances. If fed firom an upstream unit the feed rate, feed composition and feed enthalpy can all vary. Disturbances may enter through the reboiler - particularly if the duty is provided through heat integration with another part of the process. Disturbances can enter through the condenser—particularly from air-fin types that are subj ect to sudden changes in ambient temperature or rainfall. We may deliberately vary pressure to optimise the column and we may occasionally change product specifications. 

Many of the factors discussed above pertain to considerations in choosing the technique and specific instrumentation. Others are concerned with the nature of the particular material or process under investigation (enthalpy, reversibility, potential condensation, etc.) and an awareness of the potenti caveats associated therewith. Finally, there is the selection of the specific experimental conditions (sample size, temperature program, atmosphere and its flow rate, data analysis, etc.). 

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