Design of a water allocation and energy network for multi-contaminant problems using multi-objective optimization

In this paper, a solution strategy based on an optimization formulation is proposed for the design of Water Allocation and Heat Exchange Networks (WAHEN) in the process industries. Such typical large problems involve many processes, regeneration units and multi-contaminants. For this purpose, a two-stage methodology is proposed. The first step is the Water Allocation Network (WAN) design by multi-objective optimization, based on the minimization of the number of network connections and of the global equivalent cost (which includes three criteria, i.e., freshwater, regenerated water and wastewater). The ɛ-constraint method is used to deal with the multi-criteria problem. In a second step, the Heat Exchange Network (HEN) is solved by two approaches, Pinch analysis and mathematical programming (MP). In both cases the HEN structure is found when the minimal energy requirement and the total annual cost are minimized for Pinch and MP, respectively. These results are compared and the best HEN network is then coupled to the WAN to verify the feasibility of the network. A case study including a change of phase among the streams is solved. The results show that this two-step methodology can be useful for the treatment of large problems

Monitoring of particle motions in gas-solid fluidized beds by electrostatic sensors

Gas-solid fluidized beds are widely applied in numerous industrial processes. Particle motions significantly affect the performance of fluidized bed reactors and the characterization of particle movements is therefore important for fluidization quality monitoring and scale-up of reactors. Electrostatic charge signals in the fluidized bed contain much dynamic information on particle motions, which are poorly understood and explored. In this work, correlation velocities of Geldart B and D particles were measured, analyzed and compared by induced electrostatic sensors combined with cross-correlation method in the fluidized bed. The results indicated that the average correlation velocity of particle clouds increased and the normalized probability density distributions of correlation velocities broadened when the superficial gas velocity increased in the dense-phase region. Both upward and downward correlation velocities could be acquired in the dynamic bed level region. Under the same excess gas velocity, the average correlation velocity of Geldart D particles was significantly smaller than that of Geldart B particles, which was caused by the smaller bubble sizes caused by the dominant bubble split over coalescence and less volume of gas forming bubbles for Geldart D particles. The experimental results verified the reliability and repeatability of particle correlation velocity measurement by induced electrostatic sensors in the gas-solid fluidized bed, which provides definite potential in monitoring of particle motions

Automatic Design of Multi-Impurity Refinery Hydrogen Networks Using Mixing Potential Concept

The hydrogen supply in many refineries is becoming a critical issue because of a trend of heavier crude oils and increasingly rigorous environmental legislation. One of the significant problems is that the concentration fluctuation of hydrogen affects product quality of refineries and causes economic losses. In this article, we investigate the disturbance resistance ability of the hydrogen network with multiple impurities. The previously defined mixing potential of a single impurity is extended to the multiple impurity case. Then, the disturbance resistance ability is optimized under minimum hydrogen utility consumption by the mathematical programming method. Later, such disturbance resistance ability of the obtained network structure is verified by Monte Carlo simulation. Several literature examples are investigated to illustrate the effectiveness of the method. Monte Carlo simulation results show that the disturbance resistance ability of the hydrogen network obtained by the proposed method is better than the literature performance in five cases, while one case stays the same

Energy and Water Management for Industrial Large-Scale Water Networks: A Systematic Simultaneous Optimization Approach

Water and energy management issues in process industries are generally related to the synthesis of heat integrated water networks (HIWN), because water and energy are inextricably intertwined in process water networks. The aim of this study is to present a novel mathematical programming model for HIWN synthesis problems and develop an efficient solution strategy. This research is an extension of our previous work, where the targeting of heat integrated water-using networks (HIWUN) has been addressed. In this model, wastewater treatment units and multiple contaminants are embedded, and the total annual cost (TAC) is optimized rather than targeting a simplified TAC. What is more, a three-step solution strategy is proposed to guarantee obtaining promising solutions. The freshwater consumption, the relaxed TAC (rTAC), and the TAC are optimized successively. Good initial points for the rigorous HIWN model in the last step can be generated by the minimizing the rTAC. Four examples including two large-scale examples are illustrated to demonstrate the applicability of the proposed model and the efficiency of the solution strategy. The results indicate that the proposed model is suitable for the synthesis of HIWN, and more significantly, better results for large-scale problems are achieved

New Insights into <i>T</i>–<i>H</i>/<i>H</i>–<i>F</i> Diagrams for Synthesis of Heat Exchanger Networks inside Heat Integrated Water Allocation Networks

Energy and resources saving is of significance to sustainable development. In the past decades, heat integrated water allocation networks (HIWANs) have been applied to generate effective strategies for water and energy management in chemical process industries, where large amounts of water and energy are consumed. In this paper, a graphical approach for the synthesis of heat exchanger networks (HENs) in HIWANs has been proposed to reveal the new insights into <i>T</i>–<i>H</i>/<i>H</i>–<i>F</i> diagrams and fully exploit the HEN structure possibilities. Current conceptual design methods for HENs in HIWANs by the original separate systems (<i>T</i>–<i>H</i> diagram) and the matching composite curve (<i>H</i>–<i>F</i> diagram) only generate two special kinds of HEN structures: series and parallel structures. A transformation method is proposed to generate HENs with different structures based on these two tools. Both simplex series or parallel structures and hybrid structures can be obtained via the transformation procedures. Two examples are illustrated to demonstrate the operability of the proposed procedures

Effects of agglomerates on electrostatic behaviors in gas–solid fluidized beds

This work for the first time shows that both falling polyethylene sheets and small agglomerates significantly affect the electrostatic behaviors in a fluidized bed. By cold model experiments, this work found that V-shaped fluctuations of induced electrostatic potentials were observed as a sheet fell to a certain position, and polarity reversals of induced electrostatic potentials were discovered as some small agglomerates were added and fluidized in the lower part of the bed. Further analysis found that the falling sheet could affect the particle concentration distribution in the bed as well as the surface charges of particles, and these two factors always had opposing effect on the induced electrostatic potential and thus caused V-shaped fluctuations to appear. The reason for the reversal of polarity as small agglomerates were added was the appearance of the positively charged agglomerates in the measuring sensitivity zone. This work opens up new possibilities for agglomerates detection