Research On The Hydrodynamic Reciprocating-spiral Cleaning Technology In Natural Circulation Evaporators

Evaporator is a high energy consumption equipment for many industries such as food,medicine, metallurgy, petrochemical. In the solution concentration process,it exist aprevalence of severe crystallization fouling problems, which greatly reduces the efficiency ofproduction equipment. While energy consumption also greatly increased with the use of thecirculating pump for forced circulation evaporator. Based on the natural circulation evaporator,a hydrodynamic reciprocating-spiral cleaning technology that can be also used for forcedcirculation evaporator was demonstrated. The cleaning mechanism consists of a reciprocatingspring of small elasticity coefficient and a fouling removal spiral inserted in each heating tube.Relying on the pulsation of the vapor-liquid two-phase flow, the fouling removal spiralrealized reciprocating vibration for the uniform descaling purposes. To this end, this papercarried out the following research:(1) Reciprocating spiral dynamics feasibility and reciprocating institutions parameteroptimization experiments: single-U-tube cold model experiments were conducted to researchthe correlation among the reciprocating stroke of fouling removal spiral, the circulation flowvelocity, air flow rate, in which water and air are flowing through heat transfer tube. Itdemonstrated that the hydrodynamic reciprocating-spiral cleaning technology is feasible.Then based on the feasible cleaning technology, The preliminary optimization parameters ofthe reciprocating spring elasticity coefficient K, the working spiral pitch P and the outerdiameter of the working spiral D are obtained under the conditions of atmosphericevaporation with the heating tube38×2×2000mm. The experiment results show that theoptimum parameters of the reciprocating spring elasticity coefficient K is in7.6～8.2N/m,the working helical pitch P is in10～11mm, outer diameter D is in25～27mm.(2) Feasibility research on the hydrodynamic reciprocating-spiral cleaning technology inactual evaporators: theoretical analysis was given from equivalent impetus and kinetictemperature two aspects, then correspondence between the hot and cold model test underdifferent operating conditions was established,which used to judge the feasibility of technicalsolutions in actual evaporators. Finally, the thermal model test data verified the theoreticalfeasibility analysis,and the results show that the theoretical analysis and experimental resultswas consistent.(3) Research on the dimensionless function calculation of the circulation flow rate: usingdimensional analysis method, five dimensionless numbers used to describe the process of thenatural cycle were obtained. Atmospheric pressure natural circulation evaporator test rig withsingle-tube was designed. And on the basis of experimental data, the specific dimensionless function20.95910.16830.04340.04350.392was deduced.(4) Numerical simulation of natural circulation flow rate: starting from the movement ofthe reciprocating mechanism required flow conditions, the circulation velocity of the systemthat can be achieved under the hot and cold model test was simulated. On the base of test data,the relative error of the simulation and the experimental values are not higher than20%,which can be effective as a test design basis.(5) Reciprocating spiral dynamics medium-scale experiments: atmospheric evaporation testrig that contains6heating tubes was designed, in which water and steam are flowing throughheating tube. Validation and further optimization of the cold model test results wereconducted, then the optimization parameters of the spring and spiral and the correlation chartsthat between the reciprocating stroke of fouling removal spiral, circulation velocity and theheat transfer temperature are obtained.The experiment results show that when the elasticitycoefficient of the reciprocating spring is in7.0～8.0N/m, and the ratio that between the pithof the fouling removal spiral and the inner diameter of the tube is in0.676～0.764,and theheat transfer temperature is greater than18℃under the conditions of atmosphericevaporation with the heating tube38×2×2000mm,the circulation velocity is not lowerthan0.57m/s, and the reciprocating stroke of the fouling removal spiral is greater than a pith,which meets the needs of uniform scale removal.