Increment of specific heat capacity of solar salt with SiO2 nanoparticles

Thermal energy storage (TES) is extremely important in concentrated solar power (CSP) plants since it represents the main difference and advantage of CSP plants with respect to other renewable energy sources such as wind, photovoltaic, etc. CSP represents a low-carbon emission renewable source of energy, and TES allows CSP plants to have energy availability and dispatchability using available industrial technologies. Molten salts are used in CSP plants as a TES material because of their high operational temperature and stability of up to 500°C. Their main drawbacks are their relative poor thermal properties and energy storage density. A simple cost-effective way to improve thermal properties of fluids is to dope them with nanoparticles, thus obtaining the so-called salt-based nanofluids. In this work, solar salt used in CSP plants (60% NaNO₃ + 40% KNO₃) was doped with silica nanoparticles at different solid mass concentrations (from 0.5% to 2%). Specific heat was measured by means of differential scanning calorimetry (DSC). A maximum increase of 25.03% was found at an optimal concentration of 1 wt.% of nanoparticles. The size distribution of nanoparticle clusters present in the salt at each concentration was evaluated by means of scanning electron microscopy (SEM) and image processing, as well as by means of dynamic light scattering (DLS). The cluster size and the specific surface available depended on the solid content, and a relationship between the specific heat increment and the available particle surface area was obtained. It was proved that the mechanism involved in the specific heat increment is based on a surface phenomenon. Stability of samples was tested for several thermal cycles and thermogravimetric analysis at high temperature was carried out, the samples being stable.

PACS

65.: Thermal properties of condensed matter; 65.20.-w: Thermal properties of liquids; 65.20.Jk: Studies of thermodynamic properties of specific liquids     

甲醇模块化生产中分时储热系统的优化设计

以“数量放大”为特征的模块化化工生产为克服原料供给和产品市场需求波动的生产流程优化操作提供新途径。为了提高生产系统的能量利用效率,需对生产系统中随时间变化的流股预热、冷却和反应热分时段进行储存和调度。针对可再生能源驱动的甲醇模块化生产系统,本文提出了分时储热策略,通过储罐设置及流股匹配、储罐储热温区确定和储罐容量配置及调度三步对甲醇模块化生产中分时储热系统进行优化设计,获得了分时储热系统的最优配置和优化调度方案。研究表明：在甲醇模块化生产系统中,分时储热系统可将前阶段的热量储存供后续阶段调用,以实现系统能量的最大化利用,而储热的适量废弃可降低储热系统的投资费用。本文所提出的储热系统优化方法可为波动生产过程中分时储热系统的优化设计提供分析工具。     

一种有效的潜热储能球床放热性能的数值分析方法

针对潜热储能床的数值计算,研究了现有多孔介质模型应用于该问题模拟时的不足, 提出利用等效显热容处理相变问题的方法,并将其应用于潜热储能床放能过程的数值模拟中,这样使模型得到极大简化,并且较其他模型能更全面地反映储能床中的相变换热与换热流体流动的信息。将数值计算的结果与实验数据进行了对比,两者吻合很好。同时,通过对储能床中的温度分布及换热流体的流场分析, 探讨了影响潜热储能床放热特性的因素。     

Integrated conceptual design of solar-assisted trigeneration systems

This work is aimed at the development of a systematic procedure for energy conservation through the integrated design of trigeneration systems (combined cooling, heating, and power - “CCHP”) while incorporating solar energy as a renewable form of energy with low GHG emissions. The focus is on developing preliminary screening and targets that guide the conceptual design of a trigeneration system. Absorption refrigeration is used to utilize excess process heat and external energy in the form of fossil and solar energy. To account for the seasonal fluctuation in collected solar energy, the decision-making horizon is discretized into multiple periods. An extended transshipment representation is developed to embed design configurations. Next, a nonlinear programming formulation is developed. The solution of the optimization formulation determines the optimal levels of power, external heating, external cooling, heat integration, mix of fossil/solar energy forms to be supplied to the process, and the scheduling of the system operation.     

Sustainability Index to Assess the Environmental Impact of Heat Supply Systems

A sustainable heat supply is studied by defining indicators to evaluate local heat supply systems based on renewable energies compared to fossil energy reference scenarios. Besides the energy production, the evaluation considers the heat distribution network and long‐term storage. The indicators include ecological, economic, and social aspects.     

A target‐oriented solid‐gas thermochemical sorption heat transformer for integrated energy storage and energy upgrade

An innovative target‐oriented solid‐gas thermochemical sorption heat transformer is developed for the integrated energy storage and energy upgrade of low‐grade thermal energy. The operating principle of the proposed energy storage system is based on the reversible solid‐gas chemical reaction whereby thermal energy is stored in form of chemical bonds with thermochemical sorption process. A novel thermochemical sorption cycle is proposed to upgrade the stored thermal energy by using a pressure‐reducing desorption method during energy storage process and a temperature‐lift adsorption technique during energy release process. Theoretical analysis showed that the proposed target‐oriented thermochemical sorption heat transformer is effective for the integrated energy storage and energy upgrade, and the low‐grade thermal energy can be upgraded from 87 to 171^°C using a group of sorption working pair MnCl₂‐CaCl₂‐NH₃. Moreover, it can give the flexibility of deciding the temperature magnitude of energy upgrade by choosing appropriate sorption working pairs. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1334–1347, 2013     

考虑中间换热器的能量集成精馏序列合成

针对考虑中间换热器（IHE）的精馏序列合成问题,提出基于随机优化策略的能量集成非清晰精馏序列（IHE-HIDSs）合成方法。通过对精馏序列分离任务合并处引入二元0/1变量表示是否存在IHE,以精馏序列的年总成本（TAC）为优化目标,建立了该合成问题的隐式混合整数非线性规划模型（MINLP）,通过模拟退火和粒子群优化（SA-PSO）混合随机优化算法进行求解。为验证在精馏序列合成中同时考虑IHE的必要性以及所提出合成方法的有效性,对五组分醇类混合物和五组分烷烃类混合物两个算例的精馏序列合成问题进行了研究。结果表明,相比同时考虑热耦合和能量集成的精馏序列,IHE-HIDS具有更低的TAC。此外,所提出的方法可以在合理的计算时间内以高概率获得多个分离序列方案。     

A novel hybrid adsorption heat pump water heater

A hybrid adsorption heat pump water heater has been studied for domestic use. It is a water heater with dual heat sources, and it combines the performances of adsorption heat pumps and conventional gas boilers. Moreover, functional adsorbent material‐zeolite (FAM‐Z02, Mitsubishi Chemicals) and water are a new adsorption pair for adsorption heat pumps. This article describes the operation, design, and performance analysis of one such water‐heating device. The experimental results showed that the hybrid water heater in the whole year has a stable COP even at low ambient temperature. The hybrid water heater can thus achieve high energy efficiency.     

基于全周期节能的有旁路换热网络裕量优化设计

换热网络全周期运行期间,由于设备老化等因素,换热性能逐步下降,能耗逐步提高。而当前工业换热网络的裕量设计并没有有效地解决此问题。因此提出了一种基于有旁路换热网络全周期节能优化的裕量优化设计方法,通过旁路调节,逐步释放有效面积裕量,达到全周期节能的目的。该优化方法以换热网络运行全周期内总累积费用为目标函数,同时考虑结垢热阻对换热器换热效果的影响以及旁路对换热网络的调节作用,在满足工艺条件的基础上求解换热网络的最优裕量,最终实现换热网络的持续节能。最后,以某炼油厂的常减压脱盐前换热网络为具体的研究对象,说明所提方法的有效性和使用前景。     

组合相变材料强化固液相变传热可视化实验

采用高清相机和红外热像技术，对组合相变材料融化-凝固循环过程与传热特性开展了可视化实验研究。以填充三种石蜡的相变蓄热腔体为研究对象，追踪了腔体内固液相界面的动态演化过程和温度分布的变化规律。在此基础上，考察了相变材料布置顺序对蓄热腔体热性能的影响，分析了组合相变材料蓄热腔体的相变行为及强化传热特性。结果表明，相变温度较高的相变材料应靠近加热壁面布置；组合相变材料蓄热腔体存在多个固液相界面现象，不同相变材料可同时融化/凝固；与单一相变材料相比，组合相变材料的应用改善了蓄热腔体各单元相变速率的均匀性，提高了平均相变速率；组合相变材料虽然降低了蓄热腔体的显热蓄热量，但减小了温度变化速率，增强了系统的稳定性，并显著增加了潜热蓄热量，有效提高了相变蓄热腔体的总蓄热量。     

有旁路换热网络全周期节能的动态优化控制实现方法

为了实现换热网络的全周期持续节能,在网络上设置旁路从而增加其控制自由度,同时设计一定的裕量来提供优化控制的操作空间。为了较好地利用旁路调节和裕量空间,提出一种基于换热网络动态模型的在线优化控制方法,巧妙地结合原有常规控制回路,不但扩大了优化控制的可行域,并且满足原常规控制回路的精度要求。该方法以换热网络一定周期内的累积费用最小为目标函数,同时考虑扰动对换热网络的影响,在满足工艺条件的基础上,求解最佳旁路开度,以实现换热网络的持续节能。由于采用闭环校正、迭代计算和滚动优化的实施方法,始终把优化建立在实际的基础上,尽管它每次不一定能得到全局最优解,然而使得实际控制结果达到最优。最后,以某炼油厂的常减压脱盐前换热网络为具体的研究对象,说明所提方法的有效性和使用前景。     

热化学复合吸附储热循环的理论及实验

对一种基于固-气可逆化学反应的热化学复合吸附储热循环的储热特性以及能量品位提升性能进行了理论分析,并以MnCl₂/SrCl₂/NH₃作为工质对进行了实验研究。理论分析表明,热化学复合吸附储热循环不仅可以降低外界驱动热源的温度并保证输出热能温度稳定,而且能大幅度地提升输出热能的温度品位。在MnCl₂和SrCl₂都参与放热的实验工况下,获得的储热效率为93.31%。MnCl₂复合吸附剂的总储热密度按单位质量反应盐MnCl₂和单位质量的固化吸附剂计量分别为4393.36和3734.36 kJ·kg^-1;SrCl₂复合吸附剂的总储热密度按单位质量反应盐SrCl₂和单位质量的固化吸附剂计量分别为1947.28和1655.19 kJ·kg^-1。结果表明,热化学储热是一种相当有潜力的储热方式,可为低品位热能的高效回收利用提供强有力的技术支持。     

热泵供暖系统动态操作节能优化

采用系统工程的方法优化热泵供暖系统操作, 实现节能运行具有重要意义。在建立热泵供暖系统基本动态方程的基础上, 给出了考虑室温控制精度和能耗节省的优化操控目标, 通过联立求解方法将原微分代数方程优化问题(DAOPs)转化为非线性规划问题, 然后对不同目标侧重下的动态操作优化问题进行了分析, 并提出了动态调整目标函数权重的优化策略。优化计算结果表明:在室温跟踪误差最大为0.85℃的情况下系统可实现16%以上的节能效果;环境温度和电价对系统操作优化具有重要影响, 根据两者的变化特征而动态调整目标函数权重可以进一步降低系统能耗4.7%左右。本研究对热泵供暖系统优化节能控制具有一定的现实意义。     

Linking renewables and fossil fuels with carbon capture via energy storage for a sustainable energy future

Renewable energy sources and low-carbon power generation systems with carbon capture and storage (CCS) are expected to be key contributors towards the decarbonisation of the energy sector and to ensure sustainable energy supply in the future. However, the variable nature of wind and solar power generation systems may affect the operation of the electricity system grid. Deployment of energy storage is expected to increase grid stability and renewable energy utilisation. The power sector of the future, therefore, needs to seek a synergy between renewable energy sources and low-carbon fossil fuel power generation. This can be achieved via wide deployment of CCS linked with energy storage. Interestingly, recent progress in both the CCS and energy storage fields reveals that technologies such as calcium looping are technically viable and promising options in both cases. Novel integrated systems can be achieved by integrating these applications into CCS with inherent energy storage capacity, as well as linking other CCS technologies with renewable energy sources via energy storage technologies, which will maximise the profit from electricity production, mitigate efficiency and economic penalties related to CCS, and improve renewable energy utilisation.     

Margin design,online optimization,and control approach of a heat exchanger network with bypasses

During the life cycle operation of a heat exchanger network (HEN), factors such as equipment aging, gradually decrease heat transfer performance and increase energy consumption. Industrial HEN design currently fails to effectively solve these problems. To resolve this problem, we present an online optimization and control approach method for an HEN with bypasses. The approach is based on the principles of sustainable energy conservation during the life cycle. The area margin of the heat exchanger is gradually released via bypass adjustment, thereby resulting in energy conservation. First, bypasses are set on the HEN to enhance HEN control and enable optimal manipulation of the equipment. Then, the total cumulative cost increment of the HEN, including the increment of utility costs and equipment investment costs, is regarded as the objective function. The effects of the heat transfer efficiency of the heat exchanger and the effects of bypass adjustment are also taken into account. We solve the optimal design margin of the HEN, thereby providing an operational space for optimal control. Finally, using the margin optimization design of the HEN with bypasses as basis, we treat the cumulative costs of the HEN in a certain cycle as the objective function to solve the optimal opening dynamically. While, we present an optimal control structure, which is combined with existing conventional control loops. The HEN of a given crude distillation unit in a refinery is chosen as the research object. And, results illustrate the effectiveness and application prospects of the proposed method.     

中温相变蓄热系统强化传热方法研究进展

中温相变蓄热系统在太阳能热利用、余热回收等领域有广泛的研究与应用前景,但相变材料较低的热导率严重削弱了相变蓄热系统的热响应速率和蓄放热效率。针对这一问题,本文从提高传热系数、拓展传热面积、增大平均温差3个方面对近年来中温相变蓄热系统强化传热方法进行了综述。通过分析可以看出,通过导热增强填料对相变材料进行改性时,应注意填料对导热和对流的共同作用,综合考虑填料对热导率、蓄放热时间等性能的影响;直接式相变蓄热系统重量轻,传热效率高,适合应用在移动式相变蓄热车中;梯级相变蓄热系统符合能量梯级利用理念,蓄放热效率高。在未来研究中,对导热增强填料的进一步改性、直接式相变蓄热系统、梯级相变蓄热系统及多种技术协同强化传热的作用机理和强化传热效果还有重要研究潜力与价值。     

Laser surface texturing and numerical simulation of heat flux on Cr2AlC MAX phase heat exchangers

The energetic worldwide emergency demands a significant drop in fossil energy to renewable energies as part of the sustainable solutions for global energy consumption. MAX phase materials, such as Cr₂AlC, are potential candidates for heat exchanger applications due to their excellent oxidation and corrosion resistance, good thermal shock response and relatively high thermal conductivity. This study uses laser surface texturing (LST) technology to design plate heat exchanger patterns on the Cr₂AlC MAX phase. Furthermore, performing numerical simulations on textured plate models under molten salt conduction and convection conditions, accessing temperature gradient and heat transfer behaviour were conducted on Cr₂AlC, as well as on 316 L stainless steel and alumina for comparison. As a result, combined microtextures with a corrugated surface and spaced V-shape channels were obtained using LST in a single step. The parametric study indicated that the optimal channels (groves) were found for 25 W in air and 20 s laser conditions, with approximately 145 µm width and 340 µm depth. Furthermore, the numerical simulation showed that ceramics materials present better heat transfer conditions than 316 L stainless steel, where Cr₂AlC and alumina only differ in 1.9% heat flux. In addition, the corrugated surface plate with 2.6% width of the total thickness increases heat transfer by 9.8%.     

General optimization model for the energy planning of industries including renewable energy: A case study on oil sands

A multi‐period optimization model is developed for the energy procurement planning of industries including renewable energy. The model is developed with the objective of identifying the optimal set of energy supply technologies to satisfy a set of demands (e.g., power, heat, hydrogen, etc.) and emission targets at minimum cost. Time dependent parameters are incorporated in the model formulation, including demands, fuel prices, emission targets, carbon tax, lead time, etc. The model is applied to a case study based on the oil sands operations over the planning period 2015–2050. Various production alternatives were incorporated, including renewable, nuclear, conventional and gasification of alternative fuels. The results obtained indicated that the energy optimization model is a practical tool that can be utilized for identifying the key parameters that affect the operations of energy‐intensive industrial operations, and can further assist in the planning and scheduling of the energy for these industries. © 2016 American Institute of Chemical Engineers AIChE J, 63: 610–638, 2017     

间歇化工过程热集成研究进展

间歇化工过程热集成问题的研究能够促进过程系统的可持续发展并且提高产业经济性和技术竞争力,顺应了化工发展大环境。本文介绍了以系统综合优化为目标的间歇化工过程热集成研究的发展现状,整理了早期研究的三大通用图解模型,并讨论和比较了在建模求解过程中常见算法。总结了当前研究的重点在换热网络设计优化、热储罐系统和考虑调度的热集成三个方面,并评述了与之相关的进展、瓶颈和研究意义。指出了热集成问题已成为当前间歇化工过程的研究热点,其中热集成和生产调度的协同优化十分必要,能够从系统全局的角度上给出优化方案。但由于间歇化工过程中存在较多的不确定性和约束条件,增加了热集成的研究难度,因此对间歇化工过程优化设计提出了更高的要求。     

具有相变的三介质换热器的分析

具有混合能源的暖通空调与制冷（heating, ventilation, air conditioning & refrigerating, HVAC&R）系统通常需要在3种或多种流体之间传递热量。三介质换热器能满足多流体换热需求,在该领域具有应用前景,其优化具有重要意义。对于具有相变的三介质换热器,现有的热阻定义不能很好地发挥作用,而最新提出的理论提供了另一种方法。本文采用分布参数法建立了翅片管三介质换热器的仿真模型,并用实验结果进行了验证。此外,还推导了三介质换热器中基于耗散的的热阻。根据传热量和理论,分析了不同结构和空气流量下的三介质换热器的换热性能。结果表明,采用基于耗散的热阻作为评价标准与采用传热量为评价标准相比,改变管路排布方式获得的优化结果不同,改变管径或风量获得的优化结果相同。以基于耗散的热阻为标准,考虑不同流体侧之间的传热和压降的匹配,以获得最佳的管路排布方式。本文的实验结果有利于制冷空调系统中三介质换热器的优化以及理论新应用领域的拓展。