Efficient waste heat recovery in a cryogenic distillation air separation plant using heat pumps
The separation of the air in its components by cryogenic distillation has a high electric consumption due to the required air compression process. This work analyses the energy recovery of the heat dissipated at the intercooling stages of the main compressor by the integration of two types of heat pumps: an Absorption Heat Transformer (AHT) and a Vapour Compression Heat Pump (VCHP). The upgraded heat from the compressor is used in the regeneration of a Molecular Sieve used to eliminate some undesirable components before the distillation process. Real operation data from an air separation plant in Tarragona (Spain) is used to compare the two configurations using both types of heat pumps. The results show that the present consumption of thermal energy for the regeneration of the Molecular Sieve could be reduced up to 50%, when an AHT is coupled in series with the existing heating system and using first the waste heat at the desorber of the AHT and later at the evaporator of the AHT system with a Tcon=20°C. For the second configuration, the basic VCHP with a Teva=55°C and Tcon=120°C could reduce the thermal energy consumption almost up to 72% with a reduction of about 14% in the heat rejected to the ambient with respect to the current situation but with an additional expense in mechanical work for the heat pump of about 4%.
Single-Stage Vacuum Pressure Swing Adsorption for Producing High-Purity Oxygen from Air
The maximum oxygen concentration obtained using a conventional single-stage pressure swing adsorption unit is ca. 95% balanced mostly with argon. However, there are several applications requiring simple and compact units for producing high-purity oxygen (≥99%), such as medical, military, or aerospace. This article studies a single-stage vacuum pressure swing adsorption (VPSA) unit, loaded with silver-based zeolite AgLiLSX, for producing ca. 1 LSTP·min–1 of high-purity oxygen. The unit was designed on the basis of the experimental and simulation results obtained with a lab-scale unit. For a product concentration of 99.0%, the recovery obtained was ca. 8.0% with a productivity of 9.0 m3·h–1·ton–1.
Single stage and double absorption heat transformers used to recover energy in a distillation column of butane and pentane
This paper presents the theoretical analysis of the use of single stage and double absorption heat transformers operating with the water–lithium bromide mixture coupled to a butane and pentane distillation column in a Mexican refinery. A mathematical model of the heat transformers was developed in FORTRAN and integrated as a user model to the Aspen Plus simulation code. Both components coupled to the column were modelled on steady‐state conditions. The results show that it is theoretically possible to reduce the energy consumed in the reboiler between 26 and 43% by the use of single stage heat transformer at specific conditions, and between 28 and 33% with double absorption heat transformers for a wide range of operating conditions. Copyright © 2003 John Wiley & Sons, Ltd.