Multivariable generalized predictive control of a boiler system

An application of a multiloop generalized predictive control (GPC) scheme to achieve self-tuning control of superheat pressure and steam temperatures in a 200 MW power station drum boiler are presented. Controllers have been designed and evaluated using a detailed nonlinear boiler model which is well established and validated. Results illustrating the performance of the plant with GPC are presented and compared with conventional PI control. The results show that substantial improvements in control can be achieved with the GPC. Steam pressure and temperature variations are greatly reduced, without offsets, and with less controller activity     

电站锅炉汽包壁温差的控制及预防

通过实践经验总结、分析了锅炉汽包壁温差产生的原因，指出了汽包壁温差大的危害，提出了电站锅炉汽包壁温差在运行中的控制及预防措施。     

垃圾焚烧炉汽包水位的模糊控制

针对循环流化床生活垃圾焚烧锅炉热负荷波动较大，给水调节阀调节特性差的状况，专门设计的锅炉汽包水位模糊三冲量串级自动控制系统，采用调节参数模糊智能自调整，主副回路采用异步控制方式，调节阀的调节特性进行线性化处理等策略。有效提高调节品质，将水位控制在较小的波动范围，满足垃圾发电机组运行的要求。     

A new method for optimum heating of steam boiler pressure components

A method for determining time‐optimum medium temperature changes is presented. The heating and cooling of the pressure elements will be conducted in such a way that the circumferential stresses caused by pressure and fluid temperature variations at the edge of the opening and point of stress concentration do not exceed the allowable values. However, the calculated optimum temperature changes are difficult to follow in practice during the initial stage of heating. Nevertheless, it is possible to increase the fluid temperature stepwise to the minimum value and then heat the pressure component according to the determined optimum temperature changes. Allowing stepwise fluid temperature increase at the beginning of heating ensures that the heating time of a thick‐walled component is shorter than the heating time resulting from the calculations according to EN 12952‐3 European Standard or TRD 301 (Technische Regeln für Dampfkessel) regulations. Copyright © 2010 John Wiley & Sons, Ltd.     

化工装置配套动力站锅炉主蒸汽压力等级选型研究

在化工项目中,尤其是配套动力站锅炉产汽主要为供应装置拖动透平所需蒸汽的化工项目中,锅炉主蒸汽压力的选择不仅需要考虑动力站锅炉的可靠性、安全性、经济性,还需要综合考虑动力站锅炉直供主蒸汽驱动的透平选型需求,以及该透平选型的成熟性、可靠性、经济性的要求,从而通过技术经济综合比较后确定最适合的锅炉主蒸汽压力等级。     

Hybrid model of steam boiler

In the case of big energy boilers energy efficiency is usually determined with the application of the indirect method. Flue gas losses and unburnt combustible losses have a significant influence on the boiler's efficiency. To estimate these losses the knowledge of the operating parameters influence on the flue gases temperature and the content of combustible particles in the solid combustion products is necessary. A hybrid model of a boiler developed with the application of both analytical modelling and artificial intelligence is described. The analytical part of the model includes the balance equations. The empirical models express the dependence of the flue gas temperature and the mass fraction of the unburnt combustibles in solid combustion products on the operating parameters of a boiler. The empirical models have been worked out by means of neural and regression modelling.     

大型电站锅炉的蒸汽温度特性及其调节方式

主要从六个方面分析影响大型电站锅炉的蒸汽温度高低的因素,并用实例加以说明.介绍了调节蒸汽温度的两种方式,即蒸汽侧调节和烟汽侧调节,以及这两种方式的优缺点.     

Analysis of thermal stress evolution in the steam drum during start-up of a heat recovery steam generator

A program to predict the transient characteristics of the heat recovery steam generator (HRSG) is constructed and the start-up behavior of the high-pressure part of an HRSG is analyzed with a special focus on the estimation of the thermal stress in the steam drum. Three HRSG start-up procedures (steady gas turbine without gas bypass, steady gas turbine with gas bypass, start-up gas turbine) are simulated. The gas bypass is conducted during the initial stage of the start-up. Estimation of the maximum thermal stress makes it possible to optimize the gas bypass mode. It is shown that bypassing part of the gas flow lowers the peak stress much in case of the steady gas turbine exhaust condition. Examples of the scheduling of the gas flow increase using the step and ramp modes are demonstrated. In case of the simultaneous start-up, the peak stress is considerably low due to the gradual increase of gas temperature and mass flow and bypassing just a small portion of gas flow is enough to keep it under the allowable limit.     

注汽锅炉烟气氧含量分析控制

介绍了注汽锅炉烟气氧含量分析仪的参数测定方法 ,排烟热损失的计算公式 ,以及分析仪的硬件和软件结构等。使用结果表明 ,利用烟气氧含量分析仪得出的氧含量和排烟热损失来控制过剩空气系数能提高锅炉热效率     

强制循环锅炉炉水循环泵启动对汽包水位的影响

300MW机组强制循环锅炉用炉水循环泵控制工质在汽水系统中循环，在不同的工质状态下．炉水循环泵启动对锅炉汽包水位有不同的影响，通过分析其原因，提出合理的炉水泵运行方法，以避免锅炉主燃料跳闸（MFT）事故的发生。     

The service life of steam boiler drums

The occurrence of cracks in steam boilers made in the Federal Republic of Germany, the Soviet Union and the German Democratic Republic led to a detailed investigation of the state of steam boiler drums in Czechoslovakia, and to an analysis of the computing methods used in operation. The properties of the material—particularly resistance to high-cycle fatigue, low-cycle fatigue and thermal fatigue—were studied on 15223 (cf ASTM A302) steel, a grade which is most frequently used in Czechoslovakia for the production of high-pressure steam boiler drums. This made it possible to plot a limit fatigue life for boiler drums made from this steel.     

超临界对冲燃烧锅炉主蒸汽温度两侧偏差分析

通过对某电厂超临界670 MW机组锅炉出现的两侧主蒸汽温度偏差较大现象进行分析,查找产生偏差的原因,并提出运行调整建议,减小主蒸汽温度两侧偏差。     

Mathematical modelling of a steam boiler room to research thermal efficiency

This paper introduces a mathematical model of a boiler room to research its thermal efficiency. The model is regarded as an open thermodynamic system exchanging mass, energy, and heat with the atmosphere. On those grounds, the energy and energy balance were calculated. Here I show several possibilities concerning how this model may be applied. Test results of the coefficient of thermal efficiency were compared to a real object, i.e. a steam boiler room of the Provincial Hospital in W?oc?awek (Poland). The tests were carried out for 18 months. The results obtained in the boiler room were used for verification of the mathematical model.     

Design and application of a novel coal-fired drum boiler using saline water in heavy oil recovery

In this paper, the design and operation of a novel coal-fired circulating fluidized bed (CFB) drum boiler that can generate superheated steam using saline water were introduced. The natural circulation water dynamics with a drum was adopted instead of the traditional once-through steam generator (OTSG) design, so that superheated steam can be generated for the better performance of the steam assisted gravity drainage (SAGD) technology in heavy oil recovery. The optimized staged evaporation method was proposed to further decrease the salinity of water in the clean water section of the boiler. The evaporating pipes of the salted water section were rearranged in the back pass of the boiler, where the heat load is low, to further improve the heat transfer safety. A CFB combustion technology was used for coal firing to achieve a uniform heat transfer condition with low heat flux. Pollutant control technologies were adopted to reduce pollutant emissions. Based on the field test, the recommended water standard for the coal-fired CFB drum boilers was determined. With the present technology, the treated recovery wastewater can be reused in steam-injection boilers to generate superheated steam. The engineering applications show that the boiler efficiency is higher than 90%, the blowdown rate is limited within 5.5%, and the superheat of steam can reach up to 30 K. Besides, the heavy oil recovery efficiency is significantly improved. Moreover, the pollutant emissions of SO₂, NO_x and dust are controlled within the ranges of 20–90 mg/(N·m³), 30–90 mg/(N·m³) and 2–10 mg/(N·m³) respectively.     

Transient numerical modeling and model predictive control of an industrial-scale steam methane reforming reactor

A steam methane reforming reactor is a key equipment in hydrogen production, and numerical analysis and process control can provide a critical insight into its reforming mechanisms and flexible operation in real engineering applications. The present paper firstly studies the transport phenomena in an industrial-scale steam methane reforming reactor by transient numerical simulations. Wall effect and local non thermal equilibrium is considered in the simulations. A temperature profile of the tube outer wall is given by user defined functions integrated into the ANSYS FLUENT software. Dynamic simulations show that the species distribution is closely related to the temperature distribution which makes the temperature of the reactor tube wall an important factor for the hydrogen production of the reformer and the thermal conductivity of the catalyst network is crucial in the heat transfer in the reactor. Besides, there exists a delay of the reformer's hydrogen production when the temperature profile of the tube wall changes. Among inlet temperature, inlet mass flow rate and inlet steam-to-carbon (S/C) ratio, the mass flow rate is the most influencing factor for the hydrogen production. The dynamic matrix control (DMC) scheme is subsequently designed to manipulate the mole fraction of hydrogen of the outlet to the target value by setting the temperature profile trajectory of the reforming tube with time. The proportional-integral control strategy is also studied for comparison. The closed-loop simulation results show that the proposed DMC control strategy can reduce the overshoot and have a small change of the input variable. In addition, the disturbances of feed disturbance can also be well rejected to assure the tracking performance, indicating the superiority of the DMC controller. All the results give insight to the theoretical analysis and controller design of a steam methane reformer and demonstrate the potential of the CFD modeling in study the transport mechanism and the idea of combining CFD modeling with controller design for the real application.     

Thermal–hydraulic analysis of a steam boiler with rifled evaporating tubes

Rifled evaporating tubes are applied in the steam boilers with the aim to increase the steam–water mixture turbulization and to prevent the burnout of tubes walls. The rifled evaporating tubes and the working fluid forced circulation are applied in the steam boiler at the Thermal Power Plant “Kolubara B” that is being built by the Electric Power Utility of Serbia. In order to investigate operating characteristics of the steam boiler of such an advanced design, a simulation and analysis of complex coupled thermal processes on the furnace gas side and thermal–hydraulics inside the evaporating tubes were performed for the whole range of plant operating loads. In this paper a methodology for hydraulic calculations of both forced and natural circulation loops is presented. The increased thermal safety margin of rifled tubes is predicted and compared with the safety margin of smooth tubes for uniform and variable heat loads among walls of the boiler furnace. The rifled tube provides an acceptable temperature of its wall even under a high void fraction of the coolant and prevents the occurrence of critical heat transfer conditions. The influence of the rifled tubes on an increase of the hydraulic resistance in the circulation loop is analyzed. Also, a range of operating conditions under which there is no need for the circulation pumps operation is determined.     

卷烟厂蒸汽锅炉的节能运行与改造

针对卷烟生产过程中蒸汽负荷波动范围大、运行操作困难、运行效率不高的情况,探索出了2台锅炉协调运行的节能运行模式;运用先进的节能技术去除了热力除氧器;对表面排污方式进行改造并对排污闪蒸汽、取样冷却器冷却水进行回收利用,取得了较大的经济效益和社会效益。     

The application of fracture mechanics to boiler drum/nozzle joints

Recent treatments of post yield fracture mechanics and fatigue crack growth laws are applied to a situation typical of a boiler drum/nozzle joint. Critical defect sizes are calculated for boiler plate material and the weld metals. It is shown that these defect sizes are less than those obtained using linear elastic fracture mechanics (LEFM), and that the amount of crack growth is larger than previously obtained.     

Thermal management of an independent steam reformer for a solid oxide fuel cell with constrained generalized predictive control

In this paper a systematic method for the development of a constrained generalized predictive control (CGPC) system for a steam reformer is presented. Firstly, a control-oriented dynamic model deriving from physical conservation laws is established and validated by experimental data. Based on the physical model, the control system adopts the Takagi-Sugeno (T-S) fuzzy model to rapidly and accurately predict the reforming temperature. This is identified on-line using the forgetting factor recursive least square (FFRLS) technique. In order to handle input amplitude constraints, the Lagrange Multiplier method is implemented in GPC while the optimal control sequence is obtained by minimizing a multistage objective function. The numerical test results demonstrate that the CGPC control system cannot only achieve rapid and smooth responses, but also possesses excellent disturbance rejection capability which allows it to maintain the reforming temperature during fuel flow rate fluctuations due to SOFC system load variation.     

Estimation of performance of steam turbines using a simple predictive tool

Mechanical drive steam turbines are major prime movers for compressor, blower, and pump applications. Steam turbines are available for a wide range of steam conditions, power ratings and speeds. In this work, a simple predictive tool, which is easier than existing approaches, less complicated with fewer computations, is presented for rapid prediction of steam rate, turbine efficiency, and the inlet and exhaust nozzle diameters to determine the actual steam rate (ASR) and total steam requirements for both multi-stage and single-stage turbines. The proposed method predicts the above mentioned parameters for inlet steam pressures up to 12,000 kPa, turbine ratings up to 10,000 kW as well as the exhaust air over inlet air ratios of up to 0.55. The predictions from the proposed predictive tool have been compared with reported data and found good agreement with average absolute deviation hovering around 1.4%.