Serial absorption refrigeration process

A serial absorption refrigeration process comprising the steps of:

• (a) fractionating in a first absorption refrigeration cycle a water-ethylene glycol mixture, to provide a first-cycle overhead refrigerant component, comprising about 98 mole % water and about 2 mol. % ethylene glycol, and a first-cycle bottoms absorbent component, comprising about 85 mol. % ethylene glycol and about 15 mol. % water, at a reflux pressure of about 50 mm. mercury absolute and a reboiler temperature of about 85.degree. C., in indirect heat exchange with an external source of low grade steam;
• (b) fractionating in a second absorption refrigeration cycle a water-ammonia mixture, to provide a second-cycle overhead refrigerant component, comprising substantially anhydrous ammonia, and a second-cycle bottoms absorbent component, comprising about 38 mole % ammonia and about 62 mole % water, at a reflux pressure of about 75 p.s.i.a. and a reboiler temperature of about 60.degree. C.;
• (c) cooling the first-cycle overhead refrigerant component with an external cooling water source and transferring the cooled component to a first-cycle evaporation zone;
• (d) transferring the first-cycle bottoms absorbent component to a first-cycle absorption zone;
• (e) evaporating a substantial portion of the refrigerant component in the first-cycle evaporation zone, at a pressure of about 5 mm. mercury absolute to provide a temperature level in the residual portion thereof of about 5.degree. C.;
• (f) absorbing the evaporated portion of the refrigerant component in the absorbent component in the first-cycle absorption zone, at a pressure of about 5 mm. mercury absolute and at a temperature maintained at about 35.degree. C. by indirect heat exchange of the enriched absorbent component with an external cooling water source;
• (g) returning the water-ethylene glycol product of the absorption step (f) to the fractionating step (a);
• (h) cooling the second-cycle ammonia overhead refrigerant to a temperature of about 5.degree. C. in indirect heat exchange with the residual refrigerant component from step (e);
• (i) transferring the second-cycle water-ammonia bottoms absorbent component to a second-cycle absorption zone;
• (j) evaporating a substantial portion of the ammonia in the second-cycle evaporation zone, at a pressure of about 760 mm. mercury absolute to provide a second-cycle refrigeration temperature in the residual portion thereof of about -33.degree. C.;
• (k) absorbing the evaporated ammonia in the second-cycle absorbent component in the second-cycle absorption zone at a pressure of about 760 mm. mercury absolute and at a temperature maintained at about 5.degree. C. by indirect heat exchange of the enriched absorbent component with the residual refrigerant component from step (e);
• (1) returning the ammonia-water product of the absorption step (k) to the fractionating step (b);
• and
• (m) withdrawing a portion of the residual refrigerant component from the first-cycle evaporation zone and injecting said portion as reflux into the first-cycle fractionating step (a).

In a refrigeration system, comprising a first cyclic absorption refrigeration system, having as refrigerant substantially anhydrous ammonia, and as absorbent aqueous ammonia, containing from about 30 to about 60 wt. % ammonia and from about 40 to about 70 wt. % water, the improvement comprising the removal of heat therefrom to a second cyclic absorption refrigeration system employed serially with the first ammonia-aqueous ammonia system, whereby heat is withdrawn from the first system at substantially the refrigerant cooling temperature of the second system, said second cyclic absorption refrigeration system employing mutually soluble, normally liquid compounds in each of absorbent and refrigerant components, and comprising:

• (a) an evaporation zone, operating at a first, low atmospheric pressure;
• (b) an absorption zone, operating at the first low sub-atmospheric pressure;
• and
• (c) a fractionation zone, operating at a second, higher sub-atmospheric pressure, having a separation efficiency equivalent to at least about two theoretical plates;
• wherein the liquid compounds have normal boiling points differing by at least about 50.degree. C.;
• the absorbent component comprises from about 65 to about 95 mol. % of the higher-boiling compound;
• and the refrigerant component comprises from about 93 to about 99 mol. % of the lower-boiling compound.