The refrigeration section of the condensation recovery device determines how low the exhaust temperature can be pressed, and also determines the recovery ratio of low boiling point components. How to match the refrigeration system, the common choice is between two-stage compression and cascade refrigeration: both can reach the cryogenic temperature level, but the initial investment and operating characteristics are obviously different. The selection puts out the working conditions, and the answer is clear: how deep the temperature is, how stable the load is, and how big the site is. once the three conditions are put, the route will naturally float out.
Two-stage compression uses one (or two) compressors to pressure the refrigerant to the condensing pressure in two stages, with intermediate cooling, simple system, low initial investment and few maintenance points. Common refrigerant systems have good economy in the medium and low temperature range. Cascade refrigeration uses two sets of high-temperature stage and low-temperature stage to couple through heat exchangers. The low-temperature stage uses low-temperature refrigerant, which can press the evaporation temperature deeper and has good operation efficiency in the deep cooling range, however, the complexity of the system, initial investment and maintenance requirements have reached a higher level.
In a word: two-stage win in simple and reliable, cascade win in cryogenic efficiency, watershed in the required temperature level.
The required evaporation temperature is the watershed for selection: the two-stage compression in the medium and low temperature range is sufficient, and the system is simple and reliable; In the cryogenic range below the freezing point, the efficiency of two-stage compression drops obviously, and the advantages of cascade refrigeration appear. Solvent dew point accounting is done in this step: the intake air concentration and component composition determine the dew point, and the dew point plus heat exchange temperature difference is the required evaporation temperature level-many device configuration disputes, the root cause is that the dew point is not calculated, the temperature level is set at the wrong level, and both investment and energy consumption suffer losses. During the calculation, the two working conditions in winter and summer are all passed through. The difference between the dew point of intake air in low temperature season and normal temperature season is not small, and it is set according to the unfavorable first gear.
The fluctuation characteristics of the load affect the configuration: the batch production volume fluctuates greatly, the energy adjustment range of the refrigerator is wider, and the model with multiple heads connected in parallel or with economizer has better adaptability; Cooling water conditions determine the design of the condensation side, and the heat exchange surface in areas with hard water quality is cleaned frequently. Maintenance accessibility is included in the selection. Defrosting methods (hot gas defrosting, electric defrosting) and recovery of defrosting heat in low temperature section, also included in the configuration list, the defrosting energy consumption of cryogenic devices cannot be ignored. The installation site also affects the choice: the two sets of units of the cascade system occupy a larger area and maintenance space, and the project with a compact site needs to put out the layout plan in the scheme stage.
| Considerations | two-stage compression | cascade refrigeration |
|---|---|---|
| Temperature range | medium-low temperature interval | Below deep freezing point |
| Initial investment | low | high |
| system complexity | Simple maintenance points less | High maintenance requirements for two cycles |
| cryogenic efficiency | Decline is obvious | Perform well |
| energy regulation | Multi-head parallel flexible | Adjust by level |
| Applicable occasions | Medium and low temperature condensation recovery | low boiling point component deep cooling |
When the temperature level demand does not reach the cryogenic range, the initial investment and maintenance complexity of the overlap are paid for nothing. According to the actual calculation of dew point, the route is determined. If the temperature level really needs to be explored in the future, the modification interface is reserved in the plan, which is more pragmatic than one-step implementation.
The refrigeration section in the condensation device usually accounts for the majority, with 60% common. The efficiency of the refrigeration section also has a great influence on the operating cost. When selecting the model, the energy consumption of the whole life is compared with the initial investment, not only the purchase price.
Refrigerant policy has an evolving trend, the selection of priority mainstream, long-term supply of refrigerant system, the plan indicates the refrigerant model and alternative path, to avoid falling into passive in the future.
This article by LuoyangWohong PetrochemicalEquipment Co., Ltd. arranges that the company provides design, manufacturing and operation and maintenance services for condensation recovery, membrane separation recovery and complete solvent recovery devices for chemical and pharmaceutical enterprises. If you need process evaluation or scheme configuration, please contact and exchange.
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