All evaporation is accomplished in a single pass. In once-through evaporation, the feed liquor passes through the calandria tubes only once and releases vapor, and leaves the unit as thick liquor. Once through evaporator vs circulation evaporator Steam ejectors or mechanical vacuum pumps are often used to create a vacuum. Unless thermal losses are significant, they will all have the same capacity as well.Įvaporators are typically operated under a vacuum to reduce the temperature of boiling. Normally, all effects in an evaporator will be physically the same in terms of size, construction, and heat transfer area. This continues through the train: pressure drops through the sequence so that the hot vapor will travel from one effect to the next. Vapor from Effect I will be used to heat Effect II, which consequently will operate at lower pressure. Effects are thus numbered beginning with the one heated by steam. In a multiple-effect arrangement, the latent heat of the vapor product of of an effect is used to heat the following effect. Evaporating a portion of the solvent concentrates the solute into a more viscous liquid product The purpose of evaporation is to concentrate a solution of a non-volatile solute (i.e., solids) and a solvent (i.e., liquid), which is typically water. General: Evaporation is a unit operation that separates a liquid from solids by means of heat transfer via vaporization or boiling. The post covers General discussion of evaporators Key controls Heat and mass balance concept Performance of evaporators and steam economy Boiling point elevation and Duhring graph and Problem solution Calculate Steam consumption Heat transfer area, heat transfer coefficient U = 400 and, Steam economy Condensate may be assumed to leave at steam temperature and losses by radiation are neglected. The evaporator is supplied with saturated steam at 5 psig and operates with vapor space at a vacuum of 26 in. This is to be concentrated to 50% solution. Solve - A given evaporator is to be fed with 10,000 lb/hr of a 20% solution of sodium hydroxide at 100 deg F. RHS graph stands for the Enthalpy concentration chart for caustic soda.