Boiler Steam Drum Research Articles

Design of robust PI control systems based on sensitivity analysis and genetic algorithms

Sensitivity analysis and a genetic algorithm are used in the proportional–integral controller design. A systematic procedure is proposed to improve the results of the proportional–integral controller sensitivity analyses reported in the literature, and this procedure ensures a certain gain margin and phase margin in the proportional–integral control systems. The stability boundary of the proportional–integral control systems in a parameter space is obtained by the Tan method. The genetic algorithm is also used to meet the specifications of the integral absolute error, integral time-weighted absolute error, integral square error and integral time-weighted square error. Therefore, the genetic locus can be obtained in a parameter space. The method is also used to design a proportional–integral controller for Kharitonov plants and for process control, including time delay. Computer simulations show the effectiveness of the proposed method in this article. The proposed method is also applied in a robot function, an uncertain coefficient system of position control for a motor system and a boiler steam drum process control system.

Feedwater Level Control of Boiler Steam Drum using IMC and Lead-Lag IMC

Feedwater Level Control of Boiler Steam Drum using IMC and Lead-Lag IMC

Fault Diagnosis for Level Control System Based on SPC

In view of the appearance of instability and malfunction problem for level control system in the steam drum of boiler, a new method to use statistical process control (SPC) was proposed, which analyzed the level data by the SPC. It can extract the main features of the level variable, and set up the upper and lower monitoring limits for the level control system in the steam drum of boiler. The decision-making basis for the operator can be provided by monitoring control accuracy of the level control system. With this method, it can improve the control accuracy of the level variable and provide the information quickly and efficiently for the fault diagnosis of the level control system, prevent the malfunction occurs, ensure safety and stable operation for the boiler control system.

Design and Research for a Boiler Steam Drum Control System Based on PLC

] This paper introduces the composition of a boiler steam drum control system. It uses the application of a programmable PLC control unit for the boiler steam drum control system. By relying on MCGS configuration software, real-time automatic monitoring was accomplished.

대구경-후판 압력용기용 저 합금강(Mn-Mo)의 용접특성

Recently the low alloy steel plate made with manganese-molybdenum is used widely in steam drum and separator of the new coal-fired power plant boiler. This material is suitable for the vapor storage of high pressure and high temperature. The high temperature creep strength of Mn-Mo alloy is higher than the carbon plate(SA516) that used in the subcritical pressure boiler. It reduces the thickness of the pressure vessel and makes the lightweight possible. Recently in the power plant boiler operation and production process, the damage has happened frequently in the heat affected zone and base material according to the hydrogen crack and delayed crack. This paper describes the research result about the damage case experienced in the boiler steam drum production process and present the optimum manufacture method for the similar damage prevention of recurrence.

Fault Diagnosis for Level Control System Based on IDEF

In order to improve the dynamic stability of level control system in the steam drum of boiler, a fault diagnosis approach is proposed by using IDEF method, which can analyze the control system structure by the IDEF model. When the faults occur, the possible causes of fault can quickly be identified by using the model. The approach can provide a reliable basis of decision-making for the control and make a reasonable fault diagnosis in a timely and accurate manner. Using the method can effectively improve the speed of fault diagnosis, prevent the fault occurs, ensure safety and stable operation for the boiler control system.

Stress Problems at the Steam Drum Fatigue Checking Point of a Supercharged Boiler

On the basis of the proposed computing method for the low-cycle fatigue lifetime of a supercharged boiler steam drum, and the two computing principles, which super-pose the resultant stress of the internal pressure stress and the radial temperature difference heat stress at the boiler steam drum fatigue checking point, whose influences on the low-cycle fatigue lifetimes of one supercharged boiler steam drum were calculated, compared and analyzed, there out the computing principle of a supercharged boiler for superposing the resul-tant stress of the above-mentioned two stresses was opened out. The simplified computing method, which will be applied to calculating the alternating stress range in a stress cycle at the supercharged boiler steam drum fatigue checking point, was also derived from combining the design feature of a super-charged boiler steam drum with theory analysis, and com-paring with the Chinese Standard computing method, this computing method not only can reduce the calculational work-load, but also can simplify the calculational steps greatly. Thereby the proposed computing method for the low-cycle fatigue lifetime of a supercharged boiler steam drum was also further simplified.

Comparison of the Computing Method for the Radial Temperature Difference of a Supercharged Boiler Steam Drum Shell Based on the Approximate Solution and the Current Chinese Standard

The radial temperature difference calculation of a steam drum shell is an important step in the process of calcu-lating its heat stress, so the current Chinese Standard recommended a computing method which was derived from the further modification to the simplified solution for the radial temperature of a steam drum shell. In order to derive the feasibility for the application of the current Chinese Standard computing method to a supercharged boiler, the computing method for the temperature difference of a steam drum shell, which was based on the approximate solution for the radial temperature of a steam drum shell and highly approaches to its analytic solution, was exercised. By analysing the computed results of examples, the conclusions show as follows: The current Chinese Standard computing method for the radial temperature difference of a steam drum shell can’t meet the calculation requirements of all the running work conditions and their courses of a supercharged boiler, and as a universal computing method, it can’t serve as a computing method for the same problem of a supercharged boiler. Whereas the approximate solution can apply to calculating the same problem of a supercharged boiler and a peak shaving utility boiler. Thereby the basis is offered for the selection and usage of the computing method for the radial temperature difference of a supercharged boiler steam drum shell, the pioneering researches on its interrelated problems and prac-tical applications.

Feasibility for the Application of the Temperature Difference Computing Method Based on the Simplified Solution of the Radial Temperature for a Boiler Steam Drum Wall to a Supercharged Boiler

The radial temperature difference calculation of a steam drum wall is an important step in the process of calculating the low-cycle fatigue lifetime of a steam drum. So the German Standard TRD301 recommended a temperature difference computing method based on the simplified solution for the radial temperature of a steam drum wall. In order to validate the feasibility for the application of this computing method to solving the same problem of a supercharged boiler, on the basis of the reasonable simplifications to the unstable heat conduction problem across a steam drum wall, its heat-conduction equations and definite conditions were determined, then the analytical solution for the radial temperature of a steam drum wall, together with its approximate and simplified solutions, is derived. The running example of one super-charged boiler was calculated and analyzed by use of the radial temperature difference computing methods based on the approximate and simplified solutions respectively. The com-puted results show that the German Standard computing method of TRD301 has great limitations in the same problem calculation of a supercharged boiler, and it can’t apply to the researches on the same problem and its relevant problems of a supercharged boiler as a universal computing method.

Design of Fuzzy PID Controller for Water Level of Boiler Steam Drum Based on DSP

A control system for water level of boiler steam drum based on DSP microprocessor is designed in this paper. The technique of fuzzy control was applied to controlling the water level of the steam drum, the operational principle and application of the fuzzy-PID arithmetic are described. The water level controller with good control effect is developed. Firstly the hardware structure of system is introduced in the paper and then investigates the fuzzy-PID arithmetic carry out, and finally, the simplified program flowchart are given.

Hydrogen-Assisted Cracking in Boiler Steam Drums

A statutory inspection of a boiler steam drum that had seen 10 years of service revealed a few scattered cracks on the inner surface of the drum. The drum was used in the refinery and petrochemical industry. Remnant life assessment, including inspection of other drums, showed presence of several cracks in two out of seven boiler inspected. In situ microstructural analysis revealed a variation in the microstructure in the cracked regions compared to the microstructure in uncracked regions. Additionally, a wide variation in hardness was associated with the microstructural variation. Detailed study on a sample extracted from a cracked region demonstrated that the cracking occurred in a crescent zone similar in appearance to that of a heat affected zone (HAZ) generally associated with a spot weld or other sources of hot spots in the material. Subsequent examination of more samples confirmed that repair welding was carried out at several places on the inner surface of the drums before installation and commissioning and all the cracks were around the repair welds. The failure occurred by crack initiation in the HAZ of the repair welds and the cracks then propagated progressively across the inner surface of the drums. The failure mechanism was identified to be cold cracking and the failure analysis showed that all the factors required for cold cracking, namely, vulnerable microstructure, residual stresses and hydrogen atmosphere, during welding had been present in the drum material.

Investigation of probable cause of damage of steam drum of naphtha cracking furnace

This investigation was primarily aimed to examine the probable causes of damage in steam drum of heat recovery boiler in a naphtha cracking plant. Large number of cracks was detected of varying length on the inner surface of the drums. Preliminary visual examination, magnetic particle inspection, in situ metallographic examinations were carried out at the site. Detailed optical microscopic analysis along with scanning electron microscopic (SEM) and transmission electron microscopic (TEM) examinations on the scooped samples from different locations of the steam drum were carried out to understand the metallurgical reasons for damage. Stress analysis was carried out on the steam drum on the basis of strength for the internal pressure. Finally, it was concluded that metallurgical factors as well as operating conditions were responsible for the cause of damage in the steam drum.

Relay Feedback Autotuning Method for Integrating Processes with Inverse Response and Time Delay

Integrating processes with inverse response and time delay are frequently encountered in the level control of a boiler steam drum and are difficult to identify and control. In this paper, a systema...

Identification and Tuning of Integrating Processes with Deadtime and Inverse Response

The classical example of an integrating process with inverse response is level control of a boiler steam drum. The “boiler swell” problem can lead to a transfer function between the drum level and boiler feedwater flow rate that contains a pure integrator and a positive zero, in addition to some deadtime and lags. This paper presents a procedure for identifying the transfer-function parameters for this type of system from step response data. A proportional−integral controller tuning procedure is also presented. Because the process contains an integrator and the proportional−integral controller also contains an integrator, controller tuning is somewhat complex. The proposed method determines the smallest possible value for integral time. Then, using this value, the controller gain that gives a +2 dB maximum closed-loop log modulus is calculated. Simple Matlab programs are given for performing these calculations. The use of proportional−integral−derivative control is also briefly studied, but the typically ...

Crevice attack of a boiler steam drum

The mechanism of corrosive degradation of the interior of a boiler steam drum was investigated. This involved analysis of the feedwater and boilerwater, phase and elemental analysis of the corrosion products, and microstructural observation after preparing replicas of the attacked regions. The operation of crevice attack was identified as the most detrimental mode of corrosion in the present case. The accelerating influence of chlorine on such deterioration is discussed. The chronological deposition of the corrosion products are explained by the mechanism of attack. The presence of various transition compounds in the corrosion product are due to the sequence of chemical events during crevice attack.

蒸気ドラム内水面の盛り上がりと蒸気純度について

蒸気純度は, 蒸気ドラム内の気水分離器の性能および缶水の性状によって影響されるが, 水面の沸騰状態もとその高さによっても大きく左右される.また, ドラム内水位は降水管への流れや水面下のボイドによって, 水面計水位よりかなり高く盛り上がるため, 蒸気純度の検討にはその盛り上がりを定量的には握しておく必要がある.本研究は, 最近の舶用主ボイラと同じ形式の自然循環ボイラにおいて, ドラム内水面の沸騰状態とその盛り上がり高さおよび蒸気純度との関係を求めたものである.ドラム内水面の沸騰状態は, 蒸気ドラムに観察窓を設けてテレビカメラで観察した.その結果, ボイラの定常状態においては, 気水の境界は明りょうであり, その沸騰状態はドラムの中央部ではかなり激しい波立を呈しているが, ドラム端では降水管への流れが顕著である.また, ドラム圧力が低下すると蒸気室内に霧の発生が観察された.つぎにドラム内水位の測定は, 観察窓よりテレビカメラで求める方法とγ線透過法で求める方法の二方法で行なった.その結果, ドラム内水位の盛り上がり高さは, 蒸気速度が0.11m/sの場合110mmであり, 波立ち面はそれよりも高く160mmにもなる.つぎに, 蒸気純度は, 缶水および蒸気中の固形分を後放射化分析法により定量分析して蒸気乾き度として求めた.その結果, 蒸気速度が0.11m/s以内で蒸気室高さが300mmあれば, ドラム出口において99.9%の高乾き度の蒸気が得られる.

蒸気ドラム内水面の盛り上りについて

蒸気ドラム内ではドラム軸方向の水の流動および汽泡の混入などのために, ドラム中央部の実水面はドラム端に取付けられた水面計の指示点よりも場合によりはるかに高くなっていることがあり, ドラムにおける汽水分離性能を検討するにあたっては, このような水面の盛り上りを定量的に把握しておくことが必要となる.本研究は空気と水の混相流により, 実缶の1/2模型で実験を行ない, 水面盛り上りに対する気体量 (蒸発量または水面負荷) および水量 (循環量) の関係を定量的に明らかにするとともにドラム内部装置の影響を検討した.その結果, 実水面の盛り上りはドラム軸方向の流れによるものと, ドラム水内にボイドを含むことによるものの二つに分けてそれぞれ整理し, 近似的に両者の和として求めうることを示した.そのうち軸方向の水の流れによる盛り上りは, 循環水が仕切板の堰作用によって盛り上るものが最も大きく, これに対しては潜り堰の式が適用できる.一方ドラム水内ボイドは空気の上向き体積流速 (すなわち水面負荷) により主に支配され, 水流量も若干関係するが水面多孔板の影響はあまり大きくない.つぎに岐美らによる管内汽泡流の半理論式に筆者らのドラム水内ボイドの実験結果を適用し, ドラム水内ボイドに対する圧力の影響を調べた結果, 水面負荷が同じ場合にはボイドは圧力が高くなるほど大きくなり100atg以上ではその傾向は非常に顕著になる.さらに舶用補助ボイラで, 運転中のドラム内実水面をサンプリング法により実測した結果, 約360m3/m2hの水面負荷でドラム中央部の水面の盛り上りは200mm以上にもなることが確められた.この実測結果を本研究による計算値と比較するとかなりよく一致しており, 本計算方法が実用的に十分適用できることが確められた.