Study On Concentrating Aqueous Urea Solution Efficiently By Using Multi-effect Membrane Distillation

Nowadays the method of deep hydrolysis and adsorptions technology has beenapplied widely in fertilizer plants to treat wastewater containing urea. In this paper,multi-effect membrane distillation (MEMD) with higher heat recovery was exploredto separate urea from feed solution following energy-saving policy. And the researchwas conducted with low urea concentration solution as media, hollow fiber membranemodule supplied by chembrane Research&Engineering Incorporation as main part.External low energy level heat supply and energy from pump were relied on. Hollowdense-wall fibers were selected as the main material for heat exchangers. Underatmosphere pressure, urea solution was concentrated at low temperature feed usingdevices above to provide experimental date and theoretical guidance for industry.The experiment was carried out to evaluate MEMD performance throughperformance ration (PR), distillate permeate (J), urea removal rate (Ru), by usingModule1and Module2. And four factors including membrane inlet temperature (T3),feed flow rate (F), tube inlet temperature (T1), urea concentration in solution (Wf)were respectively considered to explore their effects on MEMD performance. Underlong time operation, enrichment and stability experiments were accomplished. Ureawould hydrolysis at higher T3, therefore pH of permeates was measured andcontrolled to show amine concentration in hydrolysis product in order to get higherurea recovery. Finally, urea solution from industry with deep hydrolysis andadsorptions technology was simulated by using Aspen Plus, and the energyconsumption in the form of steam consumption was obtained.Results show that: J, PR and heat utilization will increase with the increasing ofT3; with the increasing of F, J will increase but PR decrease; with the increasing of T1,J will decrease but PR increase; with the increasing of Wf, J and PR will slightlydecrease, its effect on the process is weak. Rucan be to99.99%at all of studies, lowurea concentration solution can be concentrated to40%within continuous25hours,and module stability is good. The influence on urea hydrolysis at high T3is very low.The maximum PR and J are16and6.8L/(h m2) respectively. In comparisonexperiments, the porosity in Module1is higher than that in Module2, which leads tohigher PR and J in Module1at various T3and F. Additionally, energy consumption of MEMD is far less than that of deep hydrolysis and adsorptions technology.