Auto refrigeration

Absorption of heat (auto-refrigeration) and eonsequent temperature reduetion on flashing may have a serious effeet on assoeiated heat transfer media, upon the strength of materials of eonstruetion, and result in frosting at the point of leakage. Exposure of personnel eandes a risk of frostbite. 

In the auto-refrigerated reactor shown below, an exothermic reaction A —> B is carried out using a low boiling solvent C. The heat of reaction is removed from the reactor by vapourising the solvent, condensing the vapour in the reflux condenser and returning the condensate as saturated liquid to the reactor. The total holdup of liquid in the reactor is maintained constant, but the temperature of the reactor is controlled by regulating the mass flow of vapour to the condenser. The example is taken from the paper of Luyben (1960). 

Auto-refrigerated reactor 357 Automatic control 94 Axial concentration profiles 563 Axial dispersion 560, 578... 

Because of its large reactor volume, the auto-refrigerated process can operate at very low alkene space velocities of about 0.1 h-1 LHSV (WHSV ca. 0.03 h 1). This design helps in increasing the octane number of the product and lowering acid consumption. The reaction temperature is maintained at about 278 K to minimize side reactions. Spent acid is withdrawn as 90-92 wt% acid. The isobutane concentration in the hydrocarbon phase is kept between 50 and 70 vol%. 

Fig. 12. ExxonMobil auto-refrigerated alkylation process. Adapted from Ref. (227).

REFRIC1 and REFRIC2 - Auto-Refrigerated Reactor System... 

Continuous Multicomponent Distillation Column 501 Gas Separation by Membrane Permeation 475 Transport of Heavy Metals in Water and Sediment 565 Residence Time Distribution Studies 381 Nitrification in a Fluidised Bed Reactor 547 Conversion of Nitrobenzene to Aniline 329 Non-Ideal Stirred-Tank Reactor 374 Oscillating Tank Reactor Behaviour 290 Oxidation Reaction in an Aerated Tank 250 Classic Streeter-Phelps Oxygen Sag Curves 569 Auto-Refrigerated Reactor 295 Batch Reactor of Luyben 253 Reversible Reaction with Temperature Effects 305 Reversible Reaction with Variable Heat Capacities 299 Reaction with Integrated Extraction of Inhibitory Product 280... 

An auto-refrigeration effect may be produced in a pressure vessel, which provides cooling of liquid contained in the vessel. 

During a several-day outage of the refrigeration unit outage, the ethylene tank absorbed ambient heat and the internal pressure increased. The backup plan to cool by auto refrigeration as vapor escaped via the open relief valve was underway. As planned, a flow of steam was routed to the stack in hopes of safely dispersing the cold gases. 

The alkylate released from the acid phase, will be absorbed by the Isobutane liquid and removed from the crystallizer. Without this removal of alkylate, crystal size growth control is difficult. A portion of the alkylation reactor auto-refrigerant recycle from the bottom of the depropanizer tower is used for this purpose. 

The extent of flashing depends upon the fluid being pumped, but flashing has two basic effects. First, it creates a vapor-lock situation where vapor generation prevents head buildup and causes cavitation, and the pump cannot be started up. Second, in the case of light liquefied products (both hydrocarbon and nonhydrocarbon), flashing within the pump can create very low temperatures and cause auto-refrigeration. 

Missimer, D. J., (1994) Auto-Refrigerating Caseade (ARC) Systems - an Overview, Tenth Intersociety Cryogenic Symposium, (AIChE Spring National Meeting, March. 

Many alkylation units use auto refrigeration to cool their reactors. Effluent refrigeration commonly used on Stratco units also falls within this classification. To maximize isobutane purity in the refrigerant recycle stream, circulating refrigerant is depropanized. 

Absence of chilling plant due to auto refrigeration by evaporation of liquid SO2... 

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