Study On The Inhibition Of CaCO₃ Fouling By Sodium Alginate

The surface of heat exchange equipment is easy to deposit dirt,these dirt will increase the heat resistance of the dirt on the surface of the heat exchange equipment,affect the heat exchange efficiency of the equipment,and cause a lot of economic losses.In this thesis,CaCO₃ fouling is selected as the representative of fouling in the pipeline.CaCO₃ is the most common fouling in crystallization fouling,and at the same time,crystallization fouling is also the most representative type of fouling.In order to reduce the harm caused by CaCO₃ fouling deposited on the heat exchange surface and improve the heat exchange efficiency,the commonly used method is to add scale inhibitor into the circulating working medium.Sodium Alginate has good properties of inhibiting CaCO₃ fouling,and has no toxicity,degradability and no pollution to the ecological environment,which meets the requirements of current scale inhibitor.In this thesis,two methods of experiment and molecular dynamics simulation are adopted to study the anti-scaling properties of sodium alginate on CaCO₃ fouling.In static experiments,p H shift method and electrochemical method were used to verify that sodium alginate has good scale inhibition performance.Then dynamic experimental method was used to explore the growth characteristics of sodium alginate in inhibiting CaCO₃ fouling.Through the flow experiment,in the concentration range of 0-10mg/L,the scale inhibition efficiency of sodium alginate increases with the increase of the concentration.When the concentration is 10mg/L,the anti-scaling effect is the best.When the concentration is constant,in the range of 30°C to 50°C,increasing the temperature of the experimental fluid will reduce the thermal resistance of fouling on the heat exchange surface,thereby enhancing the effect of scale inhibition.In the mass flow range of 60kg/h to 100 kg/h,increasing the mass flow rate of the flowing working fluid,as the fluid flow rate increases,the dirt thermal resistance on the heat exchange surface decreases.The three methods have proved that it can effectively inhibit the growth of CaCO₃ fouling.In order to explore the scale inhibition mechanism of sodium alginate at the molecular level,and the experiment cannot clearly explain the scale inhibition mechanism,this paper uses the molecular dynamics simulation method to explore the interaction between the microscopic level of sodium alginate and different calcite crystal planes（110,104,1-10）.Firstly,the interaction between the different crystal faces of sodium alginate and calcite under anhydrous conditions is simulated,and the adsorption configuration and mutual binding energy are analyzed.After comparing the binding energies of the three growing crystal faces,there are obvious differences among the crystal faces:the combination of sodium alginate and calcite（110）growth crystal face is the strongest,followed by calcite（1-10）crystal face,and the weakest is calcite（104）crystal face.For exploring the functional groups with anti-scaling properties of sodium alginate,the radial distribution functions of oxygen atoms and calcium atoms of calcite of different functional groups on sodium alginate were analyzed.Through simulation,it is concluded that the sodium alginate molecule is mainly adsorbed by the formation of a chemical bond between the hydroxyl group on the molecular chain and the crystal face of calcite.Secondly,in order to simulate the real situation in the flowing working fluid,the next step is to simulate the influence of temperature and degree of polymerization on the scale inhibition characteristics under water conditions.By analyzing the mutual binding energy,radial distribution function and the deformation energy of sodium alginate,the influence law is revealed.When the temperature increases,the binding energy has no obvious change trend.When the degree of polymerization changes,the binding energy also increases as the degree of polymerization increases.In terms of radial distribution function,it is observed that all three crystal faces have obvious peaks at 2.2?,and the peaks appear close to each other.On the three growth crystal faces of calcite,the peak value of the function does not change proportionally with the temperature.At the same thermodynamic temperature,the probability of sodium alginate appearing on the three crystal faces of calcite decreases as the degree of polymerization increases.Finally,the influence of concentration on the scale inhibition characteristics of sodium alginate under water conditions is simulated.The binding energy of sodium alginate molecules on the three calcite crystal faces increases with the increase of the concentration of sodium alginate.As the number of sodium alginate molecules in the system increases,the diameters of the three crystal faces of calcite increase.The peak value of the distribution function gradually becomes smaller.At different concentrations,the first obvious peak appears between the crystal faces of sodium alginate and calcite at around 2.2?,and the second peak appears at 2.6?.It shows that sodium alginate and calcite crystal are bonded together by chemical bond,forming a strong interaction.