Process simulation of natural gas steam reforming: Fuel distribution optimisation in the furnace

This paper describes a two-step method to simulate the natural gas steam reforming for hydrogen production. The first step is to calculate reforming tube length and fuel distribution with equilibrium approach associated with heat transfer. The second step is to calculate and validate reforming performance with kinetic model. A short-cut simulation of hydrogen plant has also been performed to calculate inputs for the reformer model, such as total flow rate and composition of mixed fuel burning in the furnace chamber. Heat transfer, especially radiative heat transfer, is the key role in the steam reforming technology, due to the high heat fluxes involved. For this reason, energy modelling of the furnace chamber has been performed. The simulation evaluates the most important design variables, as tubes height, maximum tube-wall temperature, and tube pressure drop. The heat flux profile can be selected to have suitable metal temperatures to lengthen the reformer tube life. The model calculates the design parameters for reforming tube and fuel distribution among burners.     

考虑肋片与内外管壁辐射换热时肋片温度与散热量计算

建立了肋片与内外管壁的辐射换热方程及肋片的温度分布计算方程 ,分析了它们之间的辐射换热对肋片温度、散热量和外壁温度的影响     

Operation of an industrial steam reformer under severe condition: A simulation study

A rigorous two‐dimensional model is developed for simulating the operation of a less‐investigated type steam reformer having a considerably lower operating Reynolds number, higher tube diameter, and non‐availability of extra steam in the feed compared with conventional steam reformers. Simulation results show that reasonable predictions can only be achieved when certain correlations for wall to fluid heat transfer equations are applied. In all cases, strong radial temperature gradients inside the reformer tubes have been found. Furthermore, the results show how a certain catalyst loading profile will affect the operation of the reformer.     

Thermal model validation of plate heat exchangers with generalized configurations

Thermal models of plate heat exchangers rely on correlations for the evaluation of the convective heat transfer coefficients inside the channels. It is usual to configure the exchanger with one countercurrent single-pass arrangement for acquiring heat transfer experimental data. This type of configuration approaches the ideal case of pure countercurrent flow conditions, and therefore a simplified mathematical model can be used for parameter estimation. However, it is known that the results of parameter estimation depend on the selected exchanger configuration because the effects of flow maldistribution inside its channels are incorporated into the heat transfer coefficients. This work presents a parameter estimation procedure for plate heat exchangers that handles experimental data from multiple configurations. The procedure is tested with an Armfield FT-43 heat exchanger with flat plates and the parameter estimation results are compared to those obtained from the usual method of single-pass arrangements. It can be observed that the heat transfer correlations obtained for plate heat exchangers are intimately associated with the configuration(s) experimentally tested and the corresponding flow distribution pattern(s).     

Heat Exchanger Network synthesis with Detailed Heat Exchanger Design

Pressure drop and fouling are important issues in heat exchanger network synthesis, which are usually neglected. Heat exchangers were designed in detail during the heat exchanger network synthesis, and pressure drop and fouling effects were taken into account. Pinch analysis combined with exergoeconomic analysis was used for determining optimal minimum approach temperature (ΔT_min) for heat exchanger network synthesis. Exergy consumption of heat transfer in HENs was calculated using a subsection integral on balanced composite curves. The heat transfer coefficients of all heat exchangers in the network were calculated iteratively to meet the requirements of optimal area and allowable pressure drops. The proposed method was applied to an industrial case. Numerical results indicate the importance of the detailed design of heat exchangers in HENs synthesis.     

Dynamics of a solar thermochemical reactor for steam-reforming of methane

A nonlinear dynamic model is developed for a steam/methane-reforming reactor that uses concentrated solar radiation as the source of high-temperature process heat. The model incorporates a set of lumped-parameter reservoirs for mass and energy. For each reservoir, the unsteady mass and energy conservation equations are formulated, which couple conduction, convection, and radiation heat transfer with the temperature dependent chemical conversion. Radiative exchange, the dominant heat transfer mode at above 800 K, is solved by a band-approximation Monte Carlo technique. The dynamic model is applied to predict the transient behavior of a 400 kW prototype solar reformer in operational modes of purging, thermal testing, startup, chemical reaction, shutdown, and cyclical operation. Time constants vary between 2 s for species transport and for thermal energy transport through ceramic insulation. Validation is accomplished by comparing modeled and experimentally measured outlet gas temperatures obtained from reactor tests in a solar tower facility.     

可拆式板式换热器在换热站的应用

传统的管壳式换热器传热系数低、占地面积大、且维修不便;钎焊式板式换热器和激光全焊接式板式换热器设备购置成本高,且不可拆检;而可拆式板式换热器适用温度又有限,介绍了在可拆式板式换热器前加减温装置的方案在加热载体为高温蒸汽的换热站的成功应用.     

管壳式换热器温度控制方式的优化与应用

管壳式换热器是化工行业中应用最广泛的换热设备结构形式。论文对比了管壳式换热器一般温度控制方案的优缺点,并结合实际情况对温度控制方式进行优化和应用。结果表明,优化后的温度控制方案能克服大波动对系统稳定性的影响,非常适用于大型精馏塔蒸汽换热器的温度控制,对其他工业过程的温度控制具有借鉴意义。     

Stady‐state and Dynamical Simulation of an Autothermal Gasoline Reformer

Detailed numerical simulation is an important tool for the analysis, development and optimization of new reactor systems. In this contribution results of steady‐state and dynamic simulations of a hydrogen production system for mobile applications based on gasoline are presented. The system consists of an autothermal reformer, a high temperature shift reactor and a countercurrent heat exchanger for heat integration. The simulations are based on 1‐D, multiphase, dynamic models, which are solved with the simulation tool PDEX‐Pack. Firstly steady‐state and dynamic simulations of the autothermal reformer alone are presented. Concentration and temperature profiles in the reformer under different operation conditions are discussed and possibilities to improve the performance are assessed. Dynamic simulations of load change and cold start show the fast dynamic response of the reformer due to its low thermal mass. Simulations of the coupled system underline the impact of the heat exchanger design for the system performance, especially under dynamic conditions. Finally dynamic simulations of a possible cold start strategy for the system are discussed.     

旋流式蒸汽混合撬的研发与应用

旋流式蒸汽混合撬是直接将蒸汽平稳地掺入需加热介质的设备,在掺入蒸汽的过程中有效避免了水击、需加热介质中杂质较快堵塞管道的问题,不考虑壳程损耗的情况下蒸汽利用率可达100%。本文主要展示了由于工业生产中原油加热脱水时遇到的问题,传统原油脱水加热方法采用物理换热法,即通过金属的热传导作用将温度较高热源介质的热量传递给温度较低的需加热介质,使温度较低的需加热介质达到升温的目的,此种方法设备综合热利用效率普遍低于80%,如果再考虑介质流速、导热材料结垢、介质纯净度等因素,综合热效率不足60%;作者等通过对这些问题的分析设计并制造出旋流式蒸汽混合撬;在设计的过程中首先考虑了水击问题和需加热介质易堵塞通道的问题,颠覆了传统的换热理念,通过对该设备的完善和优化,达到了较理想的效果,同时理论上模拟了不同加热温度的节能指标,以及在现场投入使用后的应用效果评价,认为该设备适用于目前的生产工况,可产生较高的经济效益。     

Heat transfer characteristics of high temperature molten salt for storage of thermal energy

The heat transfer characteristics of molten salt for the storage of thermal energy were investigated. The temperature profiles and heat transfer coefficients during the storage and discharge stages were obtained with steam as the heat transfer fluid. Two kinds of inorganic salt were employed as the storage medium and two types of heat exchanger were tested in order to find the effect of heat exchanger configuration on the heat storage. The effects of the steam flow rates, the flow direction of steam in the storage tank, the temperature of the heat transfer fluid and the initial temperature of the discharge tank on the heat transfer were obtained and analyzed.     

热管蒸汽发生器在热法磷酸余热回收中的应用

新型热法磷酸生产技术中的特种燃磷塔以辐射换热方式回收了高温五氧化二磷气体的余热,副产工业蒸汽,获得了明显的节能效益。但对中温五氧化二磷气体余热,应采用对流换热方式加以回收。介绍了热管蒸汽发生器回收中温五氧化二磷烟气余热工作原理和运行特点,探讨了它在回收中温五氧化二磷气体余热上应注意的一些问题;最后分析了实施余热回收技术后的节能效果。     

Retrofitting of the Heat Exchanger Network with Steam Generation in a Crude Oil Distillation Unit

Steam generation through hot streams has an important impact on the utility consumption of a crude oil distillation unit. Retrofitting of the heat exchanger network with steam generation in a crude oil distillation unit is studied with regard to efficient energy usage. The grand composite curve is employed to provide insights into the steam generation problem, and a mixed‐integer linear programming model, presented previously for heat integration through hot discharges/feeds and steam generation, is used to obtain the optimal parameters for steam generation. Three heuristic rules are then proposed to determine suitable hot streams for steam generation. Finally, the heat exchanger network is modified based on pinch technology. After the retrofit, the hot and cold utility decrease.     

THERMAL PERFORMANCE AND EVALUATION OF SIPERHEATED STEM DRYING SYSTEM USING SOLAR-ASSISTED ABSORPTION HEAT TRANSFORMER

ABSTRACT

This paper summarizes the main results of our study carried out under the priority-area research “Energy Conversion and Utilization with High Efficiency” supported by the grant-in-aid of scientific research from the Ministry of Education, Science and Culture of Japan. In the research we focused on applications of solar energy utilization for industrial drying systems. In this paper a new concept of a closed drying system with superheated steam provided from a temperature boosting type heat pump (absorption type heat transformer) was proposed. The heat transformer is driven directly by heat from a solar collector. The performance for different three drying periods and a number of factors affecting it were predicted by a computer simulation. Furthermore the heat and mass transfer characteristics of water evaporation into superheated steam stream by radiative and convective heating were indicated experimentally. It was concluded that the system would be useful for industries where high temperature (over 100°C) drying is required.     

Modeling of a Methane Reformer Combined with a Recuperative Heat Exchanger

Mathematical modeling of catalytic steam reforming of methane in a reformer—an apparatus combining a heat exchanger and a reactor—is performed. On the basis of experimental data obtained on an operating reformer, the model is corrected and recommendations for redesigning the reformer are made.     

布朗工艺增产蒸汽能力的探讨

根据布朗工艺特点，从热力学角度对通过增加二段炉空气及提高一段炉负荷增产蒸汽的方法进行了分析，推导了二段炉增加空气、提高一段炉锅炉给水温度与增产蒸汽之间的量的关系，并分析了最大增产蒸汽能力。     

沉浸竖板式低温海水换热器的设计与应用分析

沉浸竖板式换热器适用于低温海水在换热过程中换热器表面结冰等工况。介绍了该换热器的结构和工作过程,给出了计算其海水侧、载冷剂侧传热膜系数及其结构尺寸的公式。针对一20 kW热负荷的实例进行了具体的设计计算,并分析了实际应用中需考虑的因素。     

Heat transfer of nanofluidics in hydrophilic pores: Insights from molecular dynamics simulations

Nanofluidics in hydrophilic nanopores is a common issue in many natural and industrial processes. Among all, the mass transport of nanofluidics is most concerned. Besides that, the heat transfer of a fluid flow in nano or micro channels is always considered with adding nanoparticles into the flow, so as to enhance the heat transfer by convection between the fluid and the surface. However, for some applications with around 1 nm channels such as nano filtration or erosion of rocks, there should be no nanoparticles included. Hence, it is necessary to figure out the heat transfer mechanismin the single phase nanofluidics. Via non-equilibrium molecular dynamics simulations, we revealed the heat transfer inside nanofluidics and the one between fluid and walls by setting simulation into extremely harsh condition. It was found that the heat was conducted by molecular motion without temperature gradient in the area of low viscous heat, while it was transferred to the walls by increasing the temperature of fluids. If the condition back to normal, it was found that the viscous heat of nanofluidics could be easily removed by the fluid-wall temperature drop of less than 1 K.     

多管式换热器的研究及工业应用分析

多管式换热器是一种较为新型的高效换热器，目前对于这种换热器的研究较少，其传热性能的研究也鲜见报道。对多管式换热器做了初步的研究，并以实际工业装置工况为例，采用管壳式、多管换热器和翅片管多管式作为换热器设计的三种方案，利用HTRI软件进行模拟，比较出三个方案在传热和经济方面的性能差异，分析多管式换热器在工业应用中优势，为研究和推广这种新型的换热器提供有价值的参考依据。