ABB Bailey公司主汽温度控制策略的应用研究

目前火电厂常用的汽温控制系统中,ABB Bailey公司的主汽温控制策略非常具有代表性。介绍了ABB Bailey公司主汽温控制策略的控制结构及特点,通过计算进入过热器的蒸汽应具有的焓值,来确定喷水减温阀出口温度的设定值。动态时系统输出与过热蒸汽温度相等,改善了过热蒸汽温度控制系统的动态品质。通过电厂实际投运试验,证明了此控制策略具有抗干扰能力强和适应负荷变化能力强的优点,使系统具有良好的控制品质。     

ABB Bailey公司的SMITH预估控制算法在超临界1000MW蒸汽温度控制中的应用研究

针对超临界在负荷的变化时模型参数变化大,导致过热蒸汽温度偏差大的缺陷,采用ABB Bailey自校正控制系统。该系统可以实现对象模型参数估计、转换、自适应参数修正和经过在线辨识进行预估控制的功能。通过运用到1 000 MW超临界二级过热蒸汽温度控制系统并进行试验研究。试验结果表明,负荷跟踪性能较强、过热器汽温偏差较小。     

槽式光热发电典型热工过程控制系统设计

针对槽式光热发电系统,结合火电厂控制系统设计经验,提出了包括机组负荷-供能控制系统、蒸汽发生器水位控制系统和过热蒸汽温度控制系统的槽式光热发电典型热工过程控制系统的设计方案。为了解决机组负荷和供能之间的耦合关系,提出了光热供能跟随汽轮机、汽轮机跟随光热供能、以光热供能跟随为基础的协调控制以及以汽轮机跟随为基础的协调控制等4种负荷-供能控制方案;为了降低蒸汽发生器水位系统中"虚假水位"现象对控制性能的影响,提出了蒸汽发生器三冲量串级汽包水位控制方案;为了补偿过热汽温大惯性、大时延的特性,提出了过热蒸汽温度内外环控制方案。该研究可以为槽式光热发电控制系统设计提供参考。     

100 MW级蒸汽轮机系统稳态变工况运行特性

  目的  为有效提高循环效率,整体煤气化联合循环（Integrated Gasification Combined Cycle, IGCC）发电系统因其自身所具备的热效率高、污染小、运行灵活等优势得到广泛关注。余热锅炉与蒸汽轮机共同构成了联合循环系统的底循环。  方法  文章主要采用能量平衡和热力学计算公式,运用MATLAB进行建模运算,研究了蒸汽流量、给水温度、过热蒸汽温度和再热蒸汽温度的变化对蒸汽轮机的输出功率、热效率和蒸汽总吸热负荷的影响,同时在稳态运行的条件下,对底循环的工作原理和传质传热流程进行分析。  结果  结果表明:增加高压蒸汽流量,减小低压蒸汽流量,可以在具有较高热效率前提下,使蒸汽轮机输出更高的功率。在优化运行参数下,吸热负荷比参考工况减小了45.7 kW,热效率由23.82%增至26.92%。  结论  高压过热蒸汽和再热蒸汽的温度升高,蒸汽轮机系统热效率越高,但吸热负荷和输出功率变化幅度很小,可适当提高高压过热蒸汽和再热蒸汽的温度,有利于提高蒸汽轮机的热效率。而给水温度升高时,输出功率不随给水温度发生变化,而蒸汽吸热负荷会随着给水温度的升高而降低。给水温度越高,蒸汽所需热负荷就越小,有利于减少热能的输入而提高蒸汽轮机的热效率。     

1025t/h锅炉高温过热器超温分析及改造

通过应用热偏差理论对国产1025t／h电站锅炉高温过热器超温问题进行分析研究发现；超温的根本原因是沿炉宽烟气侧热负荷分布与蒸汽流量分布不匹配。针对该炉型的特点提出改造方案，不仅降低了高温过热器外圈管出口汽温，同时减少了减温水量，提高了过热蒸汽出口温度。改造后测得的汽温值与计算值吻合得较好。图9参4     

1025t/h控制循环锅炉燃烧器摆动调温研究

1025t／b控制循环锅炉采用燃烧器喷嘴摆动调节过热蒸汽和再热蒸汽温度。锅炉投运后曾经发生燃烧器喷嘴摆动装置故障，不起调温作用，汽轮机高压缸排汽温度比设计值高10～20℃，被迫采取各用事故喷水调节再热蒸汽温度。锅炉再热器受热面偏大；使再热器减温水量比设计值多20-30tt/h，明显影响机组运行经济性。通过调查研究和实炉试验，对摆动机构采取改进措施。现在燃烧器喷嘴已能正常摆动，找到了减少再热器减温水量的途径。     

钠冷快堆直流蒸汽发生器建模与仿真研究

为了研究液态金属冷却快堆的运行模式和控制方案，需要对直流蒸汽发生器进行合理的建模仿真，以研究其动态特性。针对某大型钠冷快堆的直流式蒸汽发生器，采用Matlab/Simulink平台，基于三大守恒方程，建立了一种工艺仿真模型，包括稳态计算方法和瞬态计算模型。仿真结果表明，该模型的稳态精度较高，与设计参数的稳态误差在1%以内，且计算速度较快，能够满足控制系统设计的需求。基于该模型，对蒸汽发生器出口蒸汽参数的动态响应特性进行了仿真研究，得到了出口蒸汽和温度随入口钠、水参数阶跃变化的特性曲线，发现在其他条件不变时，直流蒸汽发生器出口蒸汽温度主要受入口钠温度影响，而出口蒸汽压力的主要影响因素为给水流量。在设计控制系统时，应当将钠入口温度作为蒸汽温度的主要调节参数，而将给水流量作为蒸汽压力的主要调节参数。     

135MW循环流化床机组过热汽温优化控制方案研究

大多数火力发电厂的过热汽温控制采用的是DCS自带的经典PID控制。这类控制系统对于滞后性较大的高阶被控对象、现场执行机构死区大和减温阀线性差等工况,其控制品质较差。如果将无辨识自适应控制器IFA、预估与大数据智能诊断等先进技术引入到锅炉过热汽温控制系统中来,优化DCS系统算法逻辑,这不仅能控制过热汽温在额定值允许范围这内,而且可以适当提高过热汽温,提高蒸汽品质。另一方面可以省去升级改造喷水减温装置即可投入自动,其经济效益是相当可观的。     

腔式太阳能水/蒸汽吸热器给水全称控制系统的设计

介绍了一种应用于塔式太阳能热发电系统中的腔式水/蒸汽吸热器给水全程控制系统。提出了系统运行对控制系统的控制要求,给出了吸热器的给水压力控制系统和给水泵转速控制系统的设计和研制方法。同时指出,为了避免两个系统之间的互相干扰,使各系统尽可能地协调动作,在给水压力控制系统中引入了水泵转速偏差前馈信号,在转速系统中引入压力偏差前馈信号,使系统的给水压力调节和给水泵转速控制互相联系起来,加快汽包水位的调节速度。     

1000 MW超超临界锅炉中间点温度和汽温控制

研究了国内2类不同型式的1000 MW超超临界锅炉的中间点温度控制、主蒸汽和再热蒸汽的汽温特性、各受热面的吸热比例和煤质变化对水煤比控制的影响等问题.结果表明:蒸汽参数基本相同的1000 MW超超临界锅炉,虽然采用了不同的水冷壁结构形式、不同的受热面布置以及不同的汽温调节方式,但反映运行特性的关键技术参数的控制值基本相同;过热汽温变化特性主要表现为辐射特性;再热汽温特性主要表现为对流特性;水冷壁吸热变化对中间点温度和汽温控制起主导作用;分隔屏对汽温特性起重要作用.     

Dynamic modeling and simulation of a solar direct steam‐generating system

A dynamic model of solar parabolic trough collectors has been developed and solved by explicit Euler's method to predigest partial differential equations to ordinary differentials in this paper. Different working conditions of the collector structure and thermal parameters have been considered in the model. The simulated results are validated using the selected real test data on typical summer and winter days, and the steam‐generating process from unsaturated water to superheated steam has been studied in the startup simulation. The disturbance analysis validates the model's dynamic responses and confirms the relations between output steam characters and solar radiation, inlet water temperature, flow rate and collectors' area. The results indicate the possible demarcation point of superheated steam generating in different working conditions. Therefore, the model can be used to analyze the performance of the solar direct steam‐generating system. Copyright © 2010 John Wiley & Sons, Ltd.     

Control concepts for direct steam generation in parabolic troughs

A new prototype parabolic-trough collector system was erected at the Plataforma Solar de Almería (PSA) (1996–1998) to investigate direct steam generation (DSG) in a solar thermal power plant under real solar conditions. The system has been under evaluation for efficiency, cost, control and other parameters since 1999. The main objective of the control system is to obtain steam at constant temperature and pressure at the solar field outlet, so that changes in inlet water conditions and/or in solar radiation affect the amount of steam, but not its quality or the nominal plant efficiency. This paper presents control schemes designed and tested for two operating modes, “Recirculation”, for which a proportional-integral-derivative (PI/PID) control functions scheme has been implemented, and “Once-through”, requiring more complex control strategies, for which the scheme is based on proportional-integral (PI), feedforward and cascade control. Experimental results of both operation modes are discussed.     

Transient performance of direct steam generation solar power plants

Parabolic trough power plants are currently the most commercial systems for electricity generation. In this study, a transient numerical simulation of a solar power plant was developed by using direct steam generation (DSG) technology. In this system, condensate water from a Rankine cycle is pumped directly to solar parabolic trough collectors. The pressurized water is heated and evaporated before being superheated inside the solar collectors and directed back to the steam turbines, where the Rankine cycle is a reheated‐regenerative cycle. The plant performance with saturated steam production is compared with the performance of a superheated plant. A mathematical model of each system component is presented, with the solar power cycle modeled by the TRNSYS‐17 simulation program. Annual transient performance, including plant power and efficiency, is presented for both plants. As expected, the power of the superheated plant outperforms the saturated plant by approximately 45%, whereas the efficiency decreases by approximately 10%. Furthermore, the power of such plants is considerably improved under the weather of Makkah, 22.4°N, and it is approximately 40 MW for both the spring and autumn seasons. The annual generated energy is approximately 8062 MWh. The levelized electricity cost (LEC) was estimated for both the DSG and the corresponding synthetic oil plants. The DSG plant has an approximately 3% higher LEC than a synthetic oil plant with heat storage and an approximately 11.2% lower LEC than an oil plant if the plant has no storage. Copyright © 2016 John Wiley & Sons, Ltd.     

Modeling analysis on solar steam generator employed in multi-effect distillation (MED) system

Recently the porous bilayer wood solar collectors have drawn increasing attention because of their potential application in solar desalination. In this paper, a thermodynamic model has been developed to analyze the performance of the wood solar collector. A modeling analysis has also been conducted to assess the performance and operating conditions of the multiple effect desalination (MED) system integrated with the porous wood solar collector. Specifically, the effects of operating parameters, such as the motive steam temperature, seawater flow rate, input solar energy and number of effects on the energy consumption for each ton of distilled water produced have been investigated in the MED desalination system combined with the bilayer wood solar steam generator. It is found that, under a given operating condition, there exists an optimum steam generation temperature of around 145°C in the wood solar collector, so that the specific power consumption in the MED system reaches a minimum value of 24.88 kWh/t. The average temperature difference is significantly affected by the solar heating capacity. With the solar capacity increasing from 50 kW to 230 kW, the average temperature difference increases from 1.88°C to 6.27°C. This parametric simulation study will help the design of efficient bilayer wood solar steam generator as well as the MED desalination system.     

Control scheme for direct steam generation in parabolic troughs under recirculation operation mode

Electricity production using solar thermal energy is one of the main research areas at present in the field of renewable energies, these systems being characterised by the need of reliable control systems aimed at maintaining desired operating conditions in the face of changes in solar radiation, which is the main source of energy. A new prototype of solar system with parabolic trough collectors was implemented at the Plataforma Solar de Almería (PSA, South-East Spain) to investigate the direct steam generation process under real solar conditions in the parabolic solar collector field of a thermal power plant prototype. This paper presents details and some results of the application of a control scheme designed and tested for the recirculation operation mode, for which the main objective is to obtain steam at constant temperature and pressure at the outlet of the solar field, so that changes produced in the inlet water conditions and/or solar radiation will only affect the amount of steam produced by the solar field. The steam quality and consequently the nominal efficiency of the plant are thus maintained.     

Dynamic behavior of superheated steam and ways of control

A simple way of calculating the dynamic behavior of a superheater is presented. A comparison of the measured data with the calculated result verifies the accuracy of this simple method. It is the first time that a phase compensation for real roots, i.e., the twin lead/lag loop which is facile for engineering applications, is used in superheated steam temperature control. Numerous simulation results show that both the response time lapse and maximal dynamic deviation are greatly reduced. Moreover, a formula to calculate the setting parameters is presented, together with a practical example of its engineering application in superheated steam temperature control with single-stage attemperation in a power plant boiler. This method can remarkably improve the control performance of superheated steam temperature and makes it possible for one stage attemperation to be sufficient for the superheater of power plant boilers, thus simplifying the superheater system and reducing investment. Because the control performance is remarkably raised, the set values of the steam temperature control system can be raised above rated values and also the operational economy, without impairing the operation safety. __________ Translated from Journal of Power Engineering, 2007, 27(2): 199–203 [译自: 动力工程]     

Simulation of an integrated steam generator for solar tower

Optical and thermal simulation of a new solar tower steam generator is presented. The steam generator, placed on top of a solar tower, has two integrated receivers, external for boiling the steam and a cavity for its superheating. These two parts of the solar steam generator are facing different sections in a surrounding heliostat field and therefore can be operated independently. The evaporation part is shaped as an external cylindrical receiver which creates a cavity with an aperture for the superheating part. This novel arrangement allows high optical and thermal efficiencies. This concept of the integrated solar steam receiver is illustrated through a modeling of a large-scale plant producing superheated steam at 550 °C and pressure of 150 bars.The decoupling of the steam superheating part from the evaporation makes the system more economical, easy and safe to operate.     

Superheated steam drying of sawdust in continuous feed spouted beds – A design perspective

Spouted bed drying technology shows promising results for the drying of unscreened sawdust in superheated steam. In this paper, the experiences from designing, running and evaluating two spouted bed continuous feed dryers are presented. Stable running conditions and drying results have been achieved. This has been particularly important for sawdust that will be compressed into pellets or briquettes. The spouted bed superheated steam dryer also shows high potential for energy efficient integration into sawmills. Our recommendation is thus, to use the outlet steam temperature as the control parameter for the outlet moisture content. A drying rate above and one below the fibre saturation level, can be identified. Visual observations through the viewing glass in the drying zone in both the dryers clearly showed that not all of the material participated in the spout at all times; there were, however, no indications of dead zones. A heat transfer analysis indicated that only about 70% of the surface area of the material was in thermal contact with the steam. This paper sums up the experiences regarding drying properties, control and system properties obtained when sawdust is dried using superheated steam as the drying medium. Further work on standardised dryers in series or in parallel is necessary to increase the capacity in the spouted bed dryer.     

An indoor experimental investigation of the thermal performance of a TPLT-based natural circulation steam generator as applied to PTC systems

An indoor experimental setup of a two-phase loop thermosyphon (TPLT)-based natural circulation steam generator, as applied to parabolic trough solar collector for medium temperature steam generation was proposed. Thermal performance of the TPLT steam generation system, especially the receiver, was investigated experimentally. Relatively low two–phase heat transfer coefficients, 263.03 and 265.03 W/m² K for two selected steam discharging pressures, were obtained in the receiver for such horizontally-arranged TPLT system. Two types of flow instability, i.e., backflow and bi-directional flow, were observed in the TPLT system. The effects of flow instability on thermal performance of the TPLT steam generation system were analyzed. The results showed that isothermality of the system could be improved due to the presence of both unstable flow conditions. The improved isothermality, however, finally resulted in a lower thermal efficiency. At the steam discharging pressure of 0.15 MPa, heat transfer coefficient was increased by 20.07% and was decreased by 0.40% for the bi-directional flow and backflow patterns, respectively.     

Finding the inversion temperature for water evaporation into an air–steam mixture

This paper deals with adiabatic evaporation of water into an air–steam mixture and pure superheated steam. The focus is made on the inversion temperature, which means that the rate of liquid evaporation into superheated steam becomes equal to the rate of evaporation into dry air. A simple analytical solution for the inversion temperature was derived. The analytical and numerical methods were applied for analysis of different factors (vapor quantity, flow rate, flow regime) on the value of inversion temperature.