The Integrated Optimization Of The Water Systems In Coal Chemical Industries And The Softening Technology For Circulating Water

In this dissertation, the integrated optimization of the water system in coal chemical industries were performed based on the theory of system engineering. For the whole plant water network, the "genetic algorithm" available for the water network optimization was developed, while for the circulating water system, the optimization of the water network and the basic theory and technology on softening were studied in detail.According to the essence of the math problem during the water network optimization process, a "niche annealing genetic algorithm" was developed. The simplification of the solution space was firstly carried out in the optimization of the water network. The super-structure models of the water-consuming network and the circulating cooling water network were simplified using the constraints of concentration, flow and quality, as well as pinch technology, thus improving the convergence, accuracy and stability of the algorithm. Then a new self-adaptive fitness function was constructed for the complex constraints during the optimization of the water network. This fitness function could well balance the constraint functions and the objective function, thus ensured that the solving process of the algorithm kept accurate "genetic behavior". It has been validated by examples, that this algorithm was applicable in many situations, such as single impurity, multiple impurities, pipeline constraints, recycled water network optimization and so on.Based on the independent algorithm, a new software for water network optimization was developed. This software had a separate window interface, which reduced the difficulty of optimization operation for users. It had also been set up automatic constraint generation modules, thus solved the problems that the users could not generate constraints independently and improved the usability of the algorithm. Furthermore, a flow chart output module was constructed in this software for users to understand the optimization results easily. The application of the software in some coal chemical enterprise showed that the water was saved about21%, the demineralized water was saved about29%and the waste water was reduced66%.For the high turbidity and fines in softened water, nucleation mechanism, softening rate and the particle size distribution were studied in this dissertation. According to the model of calcium carbonate "aggregation model", and assuming that the breakup process was "binary random" process, the model of "aggregation-breakup model" was established. Based on the above model, the induction time for nucleation and the distribution of particle sizes under different saturations were studied using multiple Monte Carlo algorithm. The results showed that the simulation error of the "aggregation-breakup model"(9.8%) was much lower than that of the "aggregation model"(24.3%). Thus the simulated results might be closer to the actual nucleation process. The simulation results showed that the degree of supersaturation had significant effect on the generation of fine particles.The softening rates and the size distributions of product particles under different conditions (temperature, supersaturation, ionic strength, and pH) were investigated using the fixed component experimental apparatus, which was established by transforming the titrator Metrohm907. The results showed that, with the increase of these operation parameters, the softening rates increased at some degree, while the proportion of fine particles in the softening products gradually increased as well. Because the high proportion of fine particles would have a negative effect on the subsequent precipitation and separation, some measures such as adding seeds to suppress the occurrence of nucleation should be taken, when the parameters such as temperature in the softening process increased.Considering the poor softening efficiencies of discharge from circulating water system and the groundwater, studies were carried out on water quality analysis, coagulant screening and the addition of seeds. The existence of natural organics or scale inhibitors in the water samples, which were proved from the results of water quality analysis, resulted in different supersaturation degrees of calcite, dolomite, aragonite, etc. Thus they were difficult to be crystallized. The experimental results showed that organics of40%or scale inhibitors of more than90%could be removed by adding a coagulant, and the extent of softening could be enhanced by20%to30%by adding coagulants and seeds.A strategy of "enhanced softening" was proposed through the combination of the above research results, that is, adding coagulation agents and seeds in the traditional processes, and controlling the supersaturation at near the dosing points, which could effectively enhance the softening efficiency and improve the sedimentation. When the above strategy was applied to the design of the softening plan for make-up water of the circulating water in this enterprise, it is estimated that the water supply and the water drainage would be expected to be reduced for900and900tons, respectively, thus the investment would be recovered after20months.