Integration Of Heat Exchanger Network Research Articles

Study on the influence of coal on coal-to-ethylene glycol process considering the integration of reactor, distillation column, and heat exchanger network

The ethylene glycol (EG) process has low energy efficiency and high emissions. The raw coals purchased from different mines have different compositions and affect the reactor/column parameters and the integration of the heat exchanger network (HEN). An integrated reactor-distillation column-HEN model is built for optimizing the coal-to-ethylene glycol (CTEG) process considering the variation of raw coal. The particle swarm optimization (PSO) algorithm is used to solve this model and target the optimal raw coal for the CTEG process based on the interaction of MATLAB and Aspen Plus software. The influence of raw coal is obtained based on the sensitivity analysis performed for key reactor parameters and energy consumption. For the identified optimal raw coal, the mass fraction of carbon, hydrogen, oxygen, and ash are 84.02%, 6.80%, 1.00%, and 5.00%, respectively; the water added in the coal-water slurry is 62.15 t·h−1, and the water-gas ratio is 0.32, the corresponding energy consumption and the CO2 emission per unit product are 0.093 kgce⋅kmol−1 and 0.247 kgCO2⋅kmol−1, both decreased by 32.61%. The proposed method can be used to optimize the design and operation of the CTEG process and extended to optimize the other coal-based processes to achieve cleaner production.

Industrial park heat integration considering centralized and distributed waste heat recovery cycle systems

The waste heat recovery cycle, such as Organic Rankine cycle and absorption refrigeration cycle, can convert waste heat to other forms of energy (heat, cooling and electricity) efficiently. Meanwhile, besides the traditional intra-plant energy utilization, the cluster of enterprises in an industrial park brings extra opportunities and benefits for the total site energy recovery and conversion. Therefore, in order to improve the energy utilization efficiency and reduce the overall cost, an optimization-based framework that enables the simultaneous integration of heat exchanger network, utility and waste heat recovery cycle systems of industrial parks is proposed in this study. Three heat integration technologies are simultaneously considered to achieve the design purpose, including the direct heat integration inside plants, the indirect heat integration across different plants, and the integration of heat exchanger network with waste heat recovery cycle systems. Two waste heat recovery cycle systems configuration modes, centralized and distributed, are proposed to achieve the flexible utilization of waste heat in industrial parks. A mathematical model in mixed integer nonlinear programming is formulated to optimize the design scheme subjecting to the objective of minimum total annualized cost. The effectiveness of the proposed method is demonstrated by two cases studies, and the applicable scenarios for the two waste heat recovery cycle modes are revealed by comparing and analyzing the economic performance of the total site systems. It is concluded that the two waste heat recovery cycle configuration modes do have specific conditions of applicability, that is, the distributed mode is the better choice if the utility cost plus transportation cost of the entire system dominates the total cost, conversely, the centralized mode is recommended. The results also indicate that the inter-plant distance is an important factor affecting decision making, so sensitivity analysis is subsequently conducted and indicates that the distributed mode is preferable only if a specific threshold of inter-plant distance is exceeded.

Energy recovery enhancement of heat exchanger network by mixing and azeotrope formation

Mixing two streams with different components and/or compositions could enhance heat recovery if they contain azeotrope-forming components. This study investigates the integration of Heat Exchanger Network (HEN) considering mixing and azeotrope formation. Two cold streams are mixed to form a minimum azeotropic mixture and vaporised. Variations in heat capacity flowrate, net heat flow, and Grand Composite Curve are analysed, and their quantitative relations and utility consumption are deduced. Principles behind mixing and azeotrope formation are clarified to enhance energy recovery. A styrene production process is studied using the proposed method. With steam condensate mixed with ethylbenzene and vaporised at the azeotropic composition, the minimum heating and cooling utility consumption can be reduced by 22.87% and 13.88%.

Recycle optimization of an ethylene oxide production process based on the integration of heat exchanger network and reactor

Ethylene oxide is an essential product with increasing demand and its production consumes a large amount of energy. For a practical ethylene oxide production process, the recycle of the reaction block is studied as it influences the reactor, the Heat Exchanger Network (HEN) and the profit of the process, and could be adjusted easily and efficiently. The recycle optimization of a practical EO production process is studied based on the integration of HEN and reactor. On the basis of the kinetic and thermodynamic equilibrium, relations among the recycle ratio, outlet temperature and the removed heat of the reactor are deduced. With both HEN and the reactor considered, the integration model is built, and an economic analysis diagram is developed to illustrate the variation of revenue and cost along the recycle ratio; the optimal recycle ratio is identified to be 1.7, the maximum annual profit is 8.4% more than the current value, the recovered energy increases by 29.8% and no other equipment or process changes required.

Heat exchanger network integration of a hydrogenation process of benzene to cyclohexene considering the reactor conversion

In chemical industrial processes, reactor is the core of the whole system and influences other units and the utility consumption. To reduce the energy consumption, it is necessary to consider the reactor design and heat exchanger network (HEN) simultaneously, and optimize the reactor parameters based on the HEN integration. A graphical method is proposed to optimise a selective hydrogenation process of benzene to cyclohexene. Since the selectivity of benzene to cyclohexene is affected by the reaction rate of the main reaction and the side reaction in CSTR, the relationship among reaction temperature, the conversion and selectivity of benzene is deduced based on the kinetic equations. Based on this, the HEN's Composite Curve diagram is extended with the conversion-temperature-energy curve accommodated, and the relation between the reactor and the HEN is analysed. In the analysis process, the temperature variation of the source is accommodated by shifting the corresponding inflection point of the composite curve. By this method, optimal reaction temperature, conversion, and the minimum energy consumption of the process are identified simultaneously.

Integration of heat exchanger network considering the pressure variation of distillation column

The pressure variation of distillation column causes the temperature variation of some sinks or sources of the Heat Exchanger Network (HEN). A graphical method is proposed to analyze this problem, with the inflection point of composite curve shifted. Rules are proposed for identifying the minimum heating and cooling utility without plotting the composite curves, as well as the variation of the pinch. The proposed method can be applied to design and retrofit industrial processes.

Heat exchanger network synthesis/retrofit using MINLP stage-wise superstructure with non-isothermal mixing

One of the major impacts on energy conservation in industrial processes is the integration of heat exchanger network (HEN). Thus, the design of an optimal-cost HEN is a challenging research topic in recently decade. A mixed-integer nonlinear programming (MINLP) stage-wise model by commercial optimization software; GAMS, is developed and allow any split stream flow through multiple exchangers in series as well as bypass stage before mixing non-isothermally for simultaneous synthesis. In the MINLP model where multiple local optima may present, the initialization strategy is therefore developed to systematically find feasible starting point resulting in better HEN design compared to published results in the literatures. In addition, the retrofit of HENs is obtained by adding retrofit constraints to HENS model.

Heat Exchanger Network Integration Considering Flow Exergy Loss

AbstractThis work describes a systematic procedure to integrate a heat exchanger network (HEN) considering heat and flow exergy consumptions. The flow exergy consumption by the HEN is calculated by means of pressure drop correlation and stepwise optimization. Case studies reveal that the flow exergy loss changes the two‐way trade‐off between the operating cost and the capital cost in the traditional method. The introduction of heat exergy loss adds the weight of energy cost by considering both the external utility consumption and internal heat exergy loss in the HEN, which benefits heat recovery and energy conservation at the cost of more area and investment. In contrast, the flow exergy loss shifts the balance to the capital cost by adding the cost relating to area in terms of flow frictional dissipation.

Heat Exchanger Network Integration Using Diverse Pinch Point and Mathematical Programming

AbstractA design approach based on diverse pinch point and mathematical programming for optimal integration of heat exchanger networks (HENs) is described. The effect of the dissimilar film heat transfer coefficients on the area target is considered by different pinch and composite curves. The approach combines insightful pinch analysis and rigorous mathematical programming, which enable systematic and automatic designs. A software platform is developed for the design of HENs. An example illustrates the application of the proposed approach.