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%.
Industrial Gas Handbook: Gas Separation and Purification
“The molecular chemistry of gases is well known and it seems nlikely that any new discoveries will cause Lavoisier, the father of odern chemistry, to turn in his grave. On the other hand, there are lways new applications to discover, or to develop some of which ill require phenomenal quantities of well known industrial gases.” o ends this book, written by a mechanical engineer based on his ifetime experience of 60 years—and I might add, well written. The book has 14 chapters covering virtually every aspect of the opic offering “. . . detailed discussions and up-to-date approaches o process cycles for cryogenic separation of air, adsorption proesses for front-end air purification, and related process control nstrumentation.” In addition, the book “. . . covers topics such as hronological development, industrial applications, air separation echnologies, noble gases, front end purification systems, insulaion, non-cryogenic separation, safety, cleaning for oxygen systems, conomics, and product liquefaction, storage and transportation.” One feature I appreciated was a historical review (at approriate points) of discoveries and developments of gases and their ses. This historical review starts with a discussion of the Eigheenth Century work of French physicist Guillaume Amontons in hermometry and mathematics which led to the supposition of bsolute zero. This discussion of the historical background of the opic being reviewed provides the reader with some understanding f the development of the field. The book has the following 14 chapters:
Contamination of Zeolites Used in Oxygen Production by PSA: Effects of Water and Carbon Dioxide
Pressure swing adsorption (PSA) is one of the technologies used for producing oxygen from air. Besides the cycles employed, the adsorbent used plays an important role. Many adsorbents are nowadays available showing different adsorption properties. The adsorbent contamination that may occur in a working PSA unit has a great impact on the performance of the separation; it is then important to know the behavior of the selected adsorbent toward major contaminants such as water vapor and carbon dioxide. From the study conducted it was possible to conclude that some adsorbents are contaminated in a large extent even after being regenerated at 70 °C for 2 h. In this paper, the adsorption equilibrium data for several adsorbents used for oxygen production from air are presented. Oxysiv MDX and Oxysiv 7 from UOP as well as AgLiLSX from Air Products and Chemicals are shown to have very good selectivities for the separation of oxygen from air. The contamination study in a working laboratorial PSA unit packed with MS ...