Study On Process Integration For Waste Minimization

With the development of chemical and processing industry, pollution problem has attracted increasing concern in the global scope for its impact on the environment and human health. Waste minimization program is of great importance for sustainable development in the future. By avoiding or reducing the production of waste, or to recover and reuse the wastes if their creation cannot be avoided, waste minimization is an effective approach to solve the pollution problem in chemical industry. Except for improving the process efficiency and at the same time reducing waste generation, waste minimization can also bring the dual benefit of lower effluent treatment costs and lower raw materials costs.To address the pollution prevention problem of chemical industry, the current research status of cleaner production and the development of process integration technique for waste minimization is first introduced in this paper, then some research work is performed on process integration for the purpose of waste minimization. The practical application study of waste minimization method is also carried out in this paper. The main contents of this paper are as follows:1. Waste minimization depends on the overall process design that is intrinsically environment-friendly. Process integration can provide that approach as it has the primary goal of maximizing the efficiency of design by minimizing the consumption of materials and energy. The overall strategy of waste minimization is discussed in this paper. Environmental friendly process design should view the whole process as a integrated system including reaction, recycle and separation system, mass and heat exchange network and utility system, the interaction between different design levels should be considered to perform consistent design of the whole process. Mass and heat integration should also be considered to make reasonable distribution and utilization of mass and energy within the whole process, and then improve the overall performance of the process design.The general methodology of waste minimization is proposed in this paper, process integration supported by multi-objective optimization provides a framework for process design or process retrofit by simultaneously optimizing on the aspects of environment and economics.2. Environment concern should integrated in the process design in the context of waste minimization. Environmental impact assessment is to evaluate the environmental performance of a manufacturing process or different process alternatives to determine the environment friendly process rout or select the best option of a process, it can provide the guidance for process improvement, also can it be used as a preliminary evaluation methodand gives the initial solution to process optimization. The environment impact of chemical process is performed based on the environment impact index method of chemical species by applying the fuzzy set theory on the base of the relative membership degree. The process graph method is developed base on the pollutant balance theory, and it can be used as the process assessment and analysis tools to select the best flowsheet structure.3. Process design in the purpose of waste minimization need to trade-off between multiple objectives such as environmental, economic and others, to get simultaneously optimization of the process performance. Multi-objective genetic algorithm (MOGA) is used as a powerful solution approach for the multi-objective optimization problem. Multi-objective genetic-simulated annealing algorithm is developed on the base of non-dominated sorting genetic algorithm in this paper. In this algorithm simulated annealing algorithm is introduced to the multi-objective genetic algorithm by replacing the normal mutation operation. The improved mutation operation enhanced the algorithm the ability to escape local optimum. This algorithm is proved to be effective in solving of some test problems and the practical application in the waste minimization problem.4. The production system of ammonia synthe...