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Fixed‐tube‐sheet shell‐and‐tube heat exchangers (FTHEs) are widely used in process plants to enhance energy efficiency and to control temperature levels of unit operations. Even moderate temperature differences between shell and tube bundle of FTHEs can lead to failure mechanisms induced by thermal stress. To avoid equipment failure, design codes require an analysis of the transient response of an FTHE during special operating conditions. This work presents a modular‐hierarchical approach for the dynamic simulation of FTHEs, which is applied to special operating scenarios such as a loss of tube‐side flow, a shell‐side steaming‐out (cleaning procedure to remove hydrocarbon residues with steam) and a reactor trip (sudden stop of exothermic reaction). [ABSTRACT FROM AUTHOR]

A large cryogenic test rig was built to investigate dynamic operation of plate‐fin heat exchangers, which is needed for flexible operation of air separation units. This paper presents results from distributed temperature and strain measurements that were conducted during a dynamic test scenario. Results show that strong temperature gradients appear in all spatial directions of the heat exchangers, resulting in locally varying strains. It is shown that spatially dissolved, dynamic strain measurements are possible using optical fibers. Results from the test rig will help to properly instrument heat exchangers in research and in the field and provide important information for design and operation of plate‐fin heat exchangers in dynamic processes. [ABSTRACT FROM AUTHOR]

The design of a multi-stream plate-fin heat exchanger is a highly integrated task with multiple opposing objectives and many degrees of freedom. This work shows how it can be fully or partially automated by the combination of a detailed three-dimensional simulation model and an optimization routine. The desired task is formulated as the target of a multi-objective optimization and solved using a genetic algorithm. The workflow is presented using a cryogenic plate-fin heat exchanger with four process streams. The design is optimized towards high efficiency, low pressure drop, and low unit weight by adjusting the outer geometry, the inlet and outlet distributor configuration, and the detailed stream geometry. A detailed analysis of the Pareto-set gives a good overview of possible solutions, and the optimization routine can automatically find a feasible design with a reasonable tradeoff between the objectives. All elements of the framework are implemented in open source software. A highlight of this research is that a very comprehensive and detailed simulation model is employed in the optimization framework. Thus, the presented method can be easily adjusted to fit the needs of other engineering tasks. [ABSTRACT FROM AUTHOR]

Flexible operation of air separation units may lead to enhanced thermal stress on the main heat exchanger, typically an aluminum plate‐fin heat exchanger. Hence, a large, cryogenic test rig has been built to investigate fatigue effects of dynamic operation. Nitrogen streams at –175 °C and 50 °C are applied to induce a highly repetitive series of temperature changes in two plate‐fin heat exchangers, which are extensively equipped with measurement technology to collect 3D temperature and strain data and to detect the provoked fatigue damages. Results of the measurements will be used to improve computational lifetime estimation tools. [ABSTRACT FROM AUTHOR]

As part of the Energiewende, the current research on energy‐optimized, flexible operation of air separation units is described. A realistic, pressure‐driven approach for dynamic simulation is presented, which is used to provide a detailed, transient simulation model, a digital twin, of an air separation unit. Extreme operation scenarios, such as start‐up and shutdown of the main heat exchanger, the distillation columns or the entire air separation unit, are described. Since the main heat exchanger experiences repeated temperature changes, its lifetime is investigated in a test rig. The gathered data is used to derive and validate detailed, three‐dimensional simulation models. [ABSTRACT FROM AUTHOR]

A major challenge for hydrogen liquefaction is the required catalytic ortho‐para hydrogen conversion. Efficient liquefaction plants use catalyst‐filled plate‐fin heat exchangers for the conversion. Kinetics of the allotropic reaction are determined using raw literature data on common first‐order and a Langmuir‐Hinshelwood kinetics, including temperature and molar concentration dependencies. Evaluation and comparison of the obtained kinetics results in the first‐order approach as the most stable model. A one‐dimensional continuum reactor model of the counterflow‐cooled, catalyst‐filled plate‐fin heat exchanger is developed and tested combining correlations for heat, mass, and momentum transfer as well as a state‐of‐the‐art equation‐of‐state. Catalytic ortho‐para hydrogen conversion is a key challenge for hydrogen liquefaction. Several kinetic models for such conversion over hydrous ferric oxide are evaluated. Experiments from literature are combined to include pressure and temperature effects. The superior first‐order kinetic model is successfully applied on a counterflow‐cooled, catalyst‐filled plate‐fin heat exchanger model. [ABSTRACT FROM AUTHOR]

Rotary heat exchangers have been widely used in paint shops, combustion power plants, and in heating, ventilation, and air conditioning systems in buildings. For these processes, many types of heat exchangers are available in the market: Tube-shell heat exchangers, plate heat exchangers, and rotary heat exchangers, among others. For the rotary heat exchangers, the problem is that there is no net present value method and lifecycle assessment method-based optimization found in the literature. In this work, we address this issue: An optimization is carried out with help of an empirically validated simulation model, a life-cycle assessment model, an economical assessment, and an optimization algorithm. The objective function of the optimization simultaneously considers economic and environmental aspects by using different CO2 pricing. Different CO2 pricing scenarios lead to different optimization results. The ambient air empty tube velocity v a ,   2.1 optimum was found at 1.2 m/s, which corresponds to a specific mass flow m s p of 5.4 kg/(m2·h). For the wave angle β , the optimum was found in the range between 58° and 60°. For the wave height h * the optimum values were found to be between 2.64 mm and 2.77 mm. Finally, for the rotary heat exchanger length l , the optimum was found to be between 220 mm and 236 mm. The optimization results show that there is still potential for technical improvements in the design and operation of rotary heat exchangers. In general terms, we recommend that the optimized rotary heat exchanger should cause less pressure drop while resulting in similar heat recovery efficiency. This is because the life cycle assessment shows that the use phase for rotary heat exchangers has the biggest impact on greenhouse gases, specifically by saving on Scope 2 emissions. [ABSTRACT FROM AUTHOR]

In the last 50 years, the technology of rotary heat exchangers has not changed considerably. A reliable simulation can help improve the design of this technology. In this work, a simulation for rotary heat exchangers was developed and validated with multiple experimental data. This simulation takes an innovative approach based on locally calculated heat transfer coefficients and considers the entry region effect. This approach proved to be accurate since the average difference between the experimental results and the proposed model with a constant heat boundary condition is 0.1% and the maximum absolute deviation 1%. Experimental, as well as simulation results, indicate that lower empty tube gas velocity (1 m/s) and higher rotational speed (12 rpm) improve thermal efficiency compared to commonly used operating conditions. Additionally, a new model for predicting the local internal Nusselt number for sine ducts in the rotor channels is proposed, which considers the entry region effect. [ABSTRACT FROM AUTHOR]

Power-to-Ammonia is widely discussed as a way to store and transport renewable energy. Conventional design methods in which only one operating point is considered can be inadequate to design such plants. This work carries out an optimization over two plant models at maximum and minimum load, respectively, for an integrated assessment of the optimum design and operating strategy. We obtain Pareto fronts for several sets of degrees of freedom representing the trade-off between load flexibility and plant cost. At the same time, the optimization provides suitable operating points for both load cases for each design. We found that the minimum achievable load can be reduced from 22 to 10% with an additional reactor cost of only 3 to 7% caused mainly by an increase in the heat exchanger area of the integrated feed-effluent heat exchanger. Increasing the ammonia fraction in the reactor feed is favorable if loads below 13% are targeted. The Pareto front was improved significantly by adding a split option to the reactor and additionally allowing the solver to increase the ammonia fraction in the reactor feed. [Display omitted] • Load-flexible NH 3 reactors enable smaller H 2 buffer tanks for green NH 3 production. • A design procedure for a load-flexible ammonia reactor is presented. • Simultaneous optimization of design, full- and part-load operation was conducted. • High load flexibility (10% part load) can be achieved at less than 7% cost increase. • Heat recovery in the reactor system is decisive for part-load capability. [ABSTRACT FROM AUTHOR]

• Flexible operation of air separation units causes wear on equipment. • Material fatigue can cause damage in plate-fin heat exchangers. • Large test rig is designed for proper validation of presented models. • Model results hint possible strategies for lifetime enhancement. Within the Kopernikus project "SynErgie", the sub-project "FlexASU" investigates an enhancement of the load flexibility of air separation units with the goal of synchronizing their power consumption with the availability of renewable energy sources. The main heat exchanger of these plants was identified as a key component for a dynamic plant operation, because startup, shutdown and load-change procedures can lead to thermal stress and an increased lifetime consumption of the apparatus. Aluminum-brazed plate-fin heat exchangers (PFHE) are used in these plants because of their high process integration, low production cost and compact design. The main focus of this work, which is an extended version of Haider et al. (2018a) , is the transient behavior of PFHE. The temperature profiles within a PFHE can be calculated, and a FEM-based model is available for investigation of the thermal stress induced by dynamic temperature changes in the apparatus. Hence, the reduction in lifetime due to certain dynamic plant operating scenarios can be estimated, and critical operating modes can be identified. For the further development of the model, a PFHE test rig is designed which is representative of extreme operating conditions in air separation units. A test scenario matching the conditions of plant startup after extended downtime in a cold state has been designed. The scenario leads to thermal stress that is expected to damage the PFHE within a few weeks of testing. The location of maximum stress in the FEM-model matches typical cracks observed in PFHE which have been exposed to severe thermal stress. [ABSTRACT FROM AUTHOR]

• Motivation for the simulation of heat exchanger dynamics in design accuracy. • Modular-hierarchical framework to represent different heat exchanger types. • Dynamic first principle heat exchanger model based on design correlations. • Pressure-driven simulation approach covering forward, zero and reverse flow. • Transient analysis of multiple heat exchangers of an air separation unit. As digitalization proceeds in the process industry, detailed pressure-driven plant models are developed to represent plant operation (Kender et al., 2021). Heat exchangers are applied in process plants to promote thermal integration and to enhance energy efficiency. Hence, dynamic pressure-driven heat exchanger models using design correlations for heat transfer and pressure drop are a crucial part of a plant model. This work presents a modular-hierarchical framework for the pressure-driven dynamic simulation of plate-fin, coil-wound and shell-and-tube heat exchangers. Model development is based on the method of lines and a finite volume discretization. Using selected heat exchangers of an air separation unit as industrially relevant examples, important modeling assumptions as well as numerical features such as different discretization schemes and grid resolutions are discussed based on steady-state results. In addition, the transient scenario of a sudden plant shutdown followed by a subsequent cold restart is analyzed, emphasizing the potential of pressure-driven simulation. [ABSTRACT FROM AUTHOR]