储热罐改造对供热机组热电解耦及调峰能力的影响研究

采暖期供热机组的"以热定电"严重限制了其深度调峰能力,通过机组本体及辅助设备改造,实现供热机组的"热电解耦"是解决这一问题的重要途径。主要研究储热罐改造对供热机组热电解耦及调峰能力的影响,首先在深入分析储热罐供热原理的基础上,计算了原供热机组和配置储热罐供热机组的安全区;而后基于该安全区,进一步计算和对比分析了储热罐改造前后供热机组热电解耦及调峰能力的变化情况。结果显示:储热罐改造能够大幅提升供热机组的热电解耦能力,尤其在低负荷工况下,能够解决机组因"以热定电"供热能力不足的问题,但需要注意的是,储热罐改造无法进一步降低机组最低出力;同时储热罐改造也能够大幅提升供热机组的深度调峰能力,尤其当供热标准抽汽流量大于600t/h,配置储热罐的供热机组仍然具有一定的深度调峰能力。     

供热系统加储热后的调峰灵活性分析

国内供热机组通常"以热定电"的方式运行,这种运行方式为满足热用户的需求,限制了供热机组的调峰灵活性。给电厂配置储热罐实现"热电解耦"可以增大供热机组调峰灵活性。为此,建立了供热系统加储热后的几何模型和数学模型,提出了根据用户热量计算抽汽量的迭代方法,并分析了显式储热装置的最大储热量和最大放热量影响因素,最终将以上分析应用于某330MW供热机组的不同调峰情况进行定值计算。进行定值计算的意义是能够定量描述储热罐对机组低负荷运行的影响,为机组低负荷改造提供数据支撑。     

大型蓄热水罐流动传热模拟

为实现热电解耦,可通过在热电厂配置大型蓄热水罐,在供热负荷低时将多余热量储存在水罐中,在供热负荷高时将热量释放出来,从而提高火电供热机组深度调峰能力。为确保蓄热水罐在充放热过程中有较高的运行效率,必须保证罐内斜温层的稳定。本文对某大型蓄热水罐进行了流动传热模拟,验证了水罐结构及布水器设计的可行性,为蓄热水罐设计提供一定参考。     

辅助火电机组调峰系统的储热参数设计研究

  目的  为适应原有火电机组对新能源电力消纳的需求,提高其调峰能力是关键因素之一。  方法  储热系统作为燃煤热电机组“热电解耦”的重要方式,评价其参数匹配性具有工程参考价值。文章采用一种耦合储热装置来增加燃煤机组深度调峰能力的方法,并结合热负荷以及电负荷的功率曲线,对储热装置参数的影响规律展开了系统研究。  结果  结果表明:以区域负荷曲线为典型案例,随着储热罐的储热容量和充放热速率参数的提高,储热系统对机组的热负荷调节能力先逐渐提升并在分别在112.75 MW和129 37 MW·min时达到上限,此时深度调峰参数为77 MW左右;此外,储热容量与充放热速率具有一定的匹配关联,二者中瓶颈因素将直接制约系统的深度调峰性能。  结论  通过对储热和放热边界情景的积分,精确的展示了储热罐在辅助调峰过程的中作用,同时结合其运行策略的优化设计能够进一步分析储热辅助调峰系统的参数匹配关系,为后续火电机组耦合储热系统的参数设计提供参考。     

基于电锅炉的火电机组灵活性改造技术研究

为有效解决东北电力产能过剩,促进风电、核电等清洁能源消纳问题,提升燃煤供热机组的灵活性,针对东北地区某热电厂,通过对热电解耦时间、电锅炉型式以及不同电锅炉容量配置对机组实际发电负荷的影响等灵活性改造关键技术进行研究,确定了最佳电锅炉容量,提出了电锅炉装设方案,并对改造前后机组的调峰能力和性能指标进行对比分析。研究表明:随着电锅炉容量增长,抵减电锅炉用电后机组实际发电负荷率显著降低,提升火电机组灵活性改造后,电厂调峰能力显著提升,考虑以全厂172 MW发电负荷运行,电厂调峰能力在采暖初末期增加了368 MW,采暖中期增加了528 MW;全厂供热标煤耗由39.7 kg/GJ降低至34.3 kg/GJ,降低了5.4 kg/GJ;经济效益显著,扣除电锅炉用电成本后1个采暖季的调峰辅助服务补贴收益为1.47亿元;同时,电锅炉投运后可实现电厂的上网电量接近零,为清洁能源就地消纳做出贡献。     

利用热网及建筑物储热的热电联产机组深度调峰能力分析

利用热网及建筑物储热特性实施的"热电解耦"运行方式,是加深热电机组调峰深度的有效途径;考虑热网及建筑物储热后,研究热电机组在不同环境温度及供热面积下的深度调峰能力,对电网负荷调度及电厂运行具有重要意义。采用机组变工况模型、热网及建筑物换热模型,以某310 MW直接空冷热电联产机组为研究对象,分析了供热期内机组在不同环境温度及供热面积下的深度调峰能力。结果表明:利用热网及建筑物储热实施调峰,根据供热面积不同,其调峰能力可增加20～35 MW;相同供热面积下,机组深度调峰能力随室外温度变化相差较小。     

基于高温熔盐储热的火电机组灵活性改造技术及其应用前景分析

  目的  在分析常规火电机组灵活性改造方案存在问题的基础上,提出了一种新型的灵活性改造技术方案,即在传统的“锅炉-汽机”热力系统中嵌入大容量高温熔盐储热系统,削弱原本刚性联系的“炉机耦合”,实现火电机组深度调峰和灵活运行。  方法  根据汽、水和熔盐的不同热力特性,利用热力平衡原理,建立了“锅炉-高温储热-汽机”一体化热力系统。  结果  研究表明:火电机组进行高温熔盐储热改造,将极大地提高其深度调峰能力,且能解决常规改造方案存在的问题;同时,机组改造后对外提供高参数工业供汽的能力将得到大幅度提高,这将有效提高电厂经济效益,弥补调峰补偿机制的不足;高温熔盐储热技术也可以应用于火电机组延寿改造,不仅增加系统灵活调峰电源,还可以使老旧电厂企业资产继续发挥效益。  结论  在系统中选择一批火电机组进行大规模高温储热技术改造,可以在不增加煤炭总消费量的基础上,为系统提供大量灵活调峰电源,有效缓解新能源电力消纳问题;同时汽轮发电机组的容量被保留,可为电力系统提供备用容量和转动惯量,保障电力供应和系统安全稳定。该技术的推广,将有力促进火电厂转型升级,助力实现“碳达峰、碳中和”目标。     

热电联产机组储热罐最佳容量的确定方法

为解决“风热冲突”下储热罐的容量选择问题,以热电联产机组整个采暖期为研究对象,引入特征日概念,对配置储热罐后的热电机组建立了逐小时的运行模型。分别以机组深度调峰空间的增量、全年总收益和10年净现值为目标函数,寻找储热罐容量的最优值。结果表明,热负荷越高储热罐的最佳容量也越大,同时机组配置储热罐后所能获得的深度调峰空间也越大;不考虑初投资时,以全年总收益为目标的储热罐最优容量约为820 MW;在考虑初投资后,以10年净现值为目标的储热罐最优容量约为430 MW,容量几乎减半。     

基于高温熔盐储热系统的火电机组深度调峰方案对比及分析

为构建以新能源为主体的电力系统，亟须提高火电机组灵活性，火电机组与熔盐储热系统进行耦合能够强化调峰灵活性和调峰经济性。本文以某670MW电厂为依托，基于Ebsilon对该机组的4种熔盐—火电耦合系统改造方案进行仿真计算，并对比分析了各种方案的热力性能、调峰性能、环保性能及改造难度。结果表明：高温熔盐和低温熔盐储热组合方式有效克服了单种熔盐工作温度受限的问题，能够增强燃煤机组的调峰能力和循环效率；配置电加热器后熔盐能够以目标温度存储于热罐，热电转化效率得到提高，还额外平抑了部分可再生能源的不稳定性；通过低压缸零出力管道进行中压缸排汽蓄热和电加热提温的方案改造量最小、控制方式最为成熟灵活，能够兼顾调峰调频、节能环保和改造难度等方面的需求。     

我国火电机组灵活性现状与技术发展

电力发展"十三五"规划中明确要求充分挖掘现有系统调峰潜力,增强火电机组的灵活性,大幅度接纳新能源入网。文中阐述了我国火电机组缺乏灵活性的现状与潜在压力,主要从系统储热改造和调峰运行策略的角度介绍了国内外关于提升火电机组灵活性技术的发展状况,其中丹麦提升火电机组灵活性技术的实例有借鉴启示,并初步提出了我国火电机组灵活性改善的路径建议。     

Generalized charts of energy storage effectiveness for thermocline heat storage tank design and calibration

Solar thermal energy storage is important to the daily extended operation and cost reduction of a concentrated solar thermal power plant. To provide industrial engineers with an effective tool for sizing a thermocline heat storage tank, this paper used dimensionless heat transfer governing equations for fluid and solid filler material and studied all scenarios of energy charge and discharge processes. It has been found that what can be provided through the analysis is a series of well-configured general charts bearing curves of energy storage effectiveness against four dimensionless parameters grouped up from the storage tank dimensions, properties of the fluid and filler material, and operational conditions (such as mass flow rate of fluid and energy charge and discharge periods). As the curves in the charts are generalized, they are applicable to general thermocline heat storage systems. Engineers can conveniently look up the charts to design and calibrate the dimensions of thermocline solar thermal storage tanks and operational conditions, without doing complicated modeling and computations. It is of great significance that the generalized charts will serve as tools for thermal energy storage system design and calibration in energy industry.     

大直径高温熔盐储罐罐顶接管的强度及罐体稳定性分析

随着可再生能源技术的大力发展与应用,对太阳能热发电站中持久储热的钢制储罐的安全性能进行研究具有重要意义。以青海省某塔式太阳能热发电站中直径为25 m的高温熔盐储罐(储热罐)为例,利用ANSYS软件的平面实体轴对称单元建立了储罐有限元模型,着重对储罐顶部与熔盐管道接口处进行了强度和稳定性分析,通过对管道连接部位进行局部精细化建模,施加管口荷载,得到了储罐罐顶及罐体的等效位移、vonMises等效应力分布规律,以及该荷载对罐顶和罐体的屈曲临界荷载的影响。分析结果对今后大直径高温熔盐储罐的设计及施工具有一定的指导意义。     

Review of Molten-Salt Thermocline Tank Modeling for Solar Thermal Energy Storage

Molten-salt thermocline tanks are a low-cost option for thermal energy storage in concentrating solar power systems. A review of previous experimental and numerical thermocline tank studies is performed to identify key issues associated with tank design and performance. Published models have shown that tank discharge performance improves with both larger tank height and smaller internal filler diameter due to increased thermal stratification and sustained outflow of molten salt with high thermal quality. For well-insulated (adiabatic) tanks, low molten-salt flow rates reduce the axial extent of the heat-exchange region and increase discharge efficiency. Under nonadiabatic conditions, low flow rates become detrimental to stratification due to the development of fluid recirculation zones inside the tank. For such tanks, higher flow rates reduce molten-salt residence time inside the tank and improve discharge efficiency. Despite the economic advantages of a thermocline tank, thermal ratcheting of the tank wall remains a significant design concern. The potential for thermal ratcheting is reduced through the inclusion of an internal thermal insulation layer between the molten salt and tank wall to diminish temperature oscillations along the tank wall. Future research directions are also pointed out, including combined analyses that consider the solar receiver and power generation blocks as well as optimization between performance and economic considerations.     

Sensitivity analysis for thermocline thermal storage tank design

Concentrated solar power coupled with thermal energy storage is a promising approach for providing the world with clean, renewable, sustainable and cost-competitive power on a large scale. Thermocline thermal energy storage has been proposed as an efficient and cost-competitive alternative to the traditional two-tank design. The thermocline thickness is directly linked to the efficiency of the storage tank. Sensitivity analysis is thus applied to a model of the thermocline thickness to identify the parameters that influence it the most. Results indicate that the tank height along with the thermophysical properties of the solid filler material influence the tank efficiency the most, with fluid properties and having a secondary effect.     

Experimental investigation of a molten salt thermocline storage tank

Thermal energy storage is considered as an important subsystem for solar thermal power stations. Investigations into thermocline storage tanks have mainly focused on numerical simulations because conducting high-temperature experiments is difficult. In this paper, an experimental study of the heat transfer characteristics of a molten salt thermocline storage tank was conducted by using high-temperature molten salt as the heat transfer fluid and ceramic particle as the filler material. This experimental study can verify the effectiveness of numerical simulation results and provide reference for engineering design. Temperature distribution and thermal storage capacity during the charging process were obtained. A temperature gradient was observed during the charging process. The temperature change tendency showed that thermocline thickness increased continuously with charging time. The slope of the thermal storage capacity decreased gradually with the increase in time. The low-cost filler material can replace the expensive molten salt to achieve thermal storage purposes and help to maintain the ideal gravity flow or piston flow of molten salt fluid.     

Central solar heating plants with seasonal duct storage and short-term water storage: design guidelines obtained by dynamic system simulations

A central solar heating plant with seasonal ground storage is analysed by dynamic system simulations. A reference system, involving a collector area, water buffer storage and ground duct storage, is defined for typical Swiss conditions and simulated for several types of heat load. A methodology is established for the optimisation of the main system parameters. The thermal behaviour of such a system is highlighted. The short-term heat requirements are covered by the buffer unit, whereas the seasonal heat requirements are covered by the ground duct storage. As a consequence, a system such as this is intended to supply a large solar fraction (>50%). Optimal ratios between the main system parameters are sought for an annual solar fraction of 70%. An optimal buffer volume of 110 to 130 l per m² of collector area is obtained. The optimal duct storage volume and collector area vary respectively from 4 to 13 m³ per m² of collector area and from 2 to 4 m² per MWh (3.6 GJ) of annual heat demand. They depend mainly on the specific heat losses from the duct storage unit. A large annual heat demand (>3600 GJ or 1000 MWh) and/or low temperatures in the heat distribution are essential for satisfactory system thermal performance. The spacing of the boreholes which form the ground heat exchanger of the duct store is fairly constant and is found to be about 2.5 m for a ground thermal conductivity of 2.5 Wm⁻¹ K⁻¹. Some improvements of the system control are also investigated to assess the influence on the overall thermal performances of the system. They indicate that the system thermal performances are only slightly improved in contrast to the improvement brought by a simple but optimised system control.     

采用蓄热技术扩大供热机组调峰裕度的研究

本文介绍了国内外蓄热技术的利用情况,并且针对蓄热技术在热电厂供热方式转变中的应用进行了详细的研究。提出了增大供热机组冬季调峰能力的方法。通过该方法供热机组冬季能够大容量参与电网调峰,为更好地保证冬季稳定供电、节能降耗以及大量接纳风电提供了一种可行的措施。     

盘管式外融冰槽融冰过程试验研究（I）——取冷特性

作者在搭建的50RTH(1RTH=3517W·h)盘管式外融冰实验台上研究了外融冰取冷的动态过程,全面考察了取冷进出口模式、取冷流量、入口温度、初始蓄冰量、搭接等因素对冰槽取冷特性的影响。研究结果表明:1)取冷进出口模式严重影响冰槽取冷特性:不同进出口模式下取冷出口水温的变化过程有很大差异;在取冷的前4/5时间,下进模式取冷的出口温度比上进模式低2 5℃;2)取冷流量对于出口水温的影响小于1℃;3)恒定流量条件下,入口温度的变化会较大程度影响到取冷速率的变化,而对出口水温的影响小于0 5℃;4)初始蓄冰量对于取冷特性影响很小;5)冰柱搭接急剧提高取冷出口温度。