Drum Water Level Research Articles

A simulation study on the application of a fuzzy algorithm to a feedwater control system in a nuclear power plant

Abstract The feedwater control system is reponsible for maintaining the steam drum water level at the set point. The response of the feedwater system is so slow that it is difficult to maintain an optimal water level by using a traditional PI (Proportional-Integral) controller. The objectives of the present study are to apply the fuzzy control method, which can utilize the flexibility and the heuristic control strategy employed by humans, to the feedwater control system in a HWR (Heavy Water Reactor) type nuclear power plant, and to improve the starting performance on a steam drum eater level control. Numerical simulations on the step and ramp response for the water level set point and the reactor power, and on the response after manual closing of the feedwater control valve have been performed. The results of the study show that fuzzy control can reflect successfully the experience gained in skilled manual operation. It is expected that fuzzy control can contribute to the reduction of human errors and to the improvement of the reliability and safety of plant operation.

Nonlinearity of Dynamic Processes in a Drum Boiler Circulation Loop

The paper deals with mathematical modelling and numerical simulation of the dynamics of flow and heat processes inside the circulation loop of a power steam generator. The processes in the evaporator, drum and downcomers are modelled separately. The evaporator is treated ns n system with distributed parameters and is described by three nonlinear, partial differential equations for the mass flow, entropy and pressure. An eigenvalue analysis of evaporator system matrix A has been made. Linear and nonlinear models of circulation loop describe the phenomena of shrink and swell of drum water level. The comparative analysis of nonlinear model responses to the inputs of the same magnitude obtained at thre different load levels, clearly presents the nonlinearity of the circulation loop processes.

SENHOR-IV: A computer code for small pipe-break analysis of pressure-tube type reactors

A computer program SENHOR-IV was developed which describes blowdown phenomena associated with a small pipe-break accident in pressure-tube type reactors. Thermal-hydraulic transients of single-phase and two-phase flow in a primary cooling system, which is composed of the pressure tubes, a steam drum, downcomers, a lower header and pipings connecting these components, were calculated from the conservation equations of mass, momentum and energy by assuming pressure propagation and flow rate distribution to be quasi-steady and by applying the method of characteristics to enthalpy transport. The void propagation velocity in two-phase flow was given from Smith's equation for void-quality relationship to the program. Calculation of a flow transient, which has an exact solution, with use of this program showed small deviations from the exact solution. Predicted transients of pressure and water level in the steam drum indicated a good agreement with those observed in a full scale test facility at O-arai Engineering Center.

Senhor-II — A computer code for loss-of-coolant accidents of pressure tube type reactors

Abstract An ATR LOCA analysis code, SENHOR-II, was developed which evaluates the loss-of-coolant accident in a reactor primary loop composed of parallel pressure tubes and downcomers connecting a steam drum to a lower header. The reactor system is divided into reservoirs and channels. The reservoirs are assumed to be saturated and equilibrated. The channels are treated one-dimensionally and their flows are assumed quasi-steady. The reservoir effect of piping, the heating up of fuel rods, the thermal capacity of structures, and the effects of steam separators and water level in the steam drum are considered. Calculated results are compared with the experimental results of the blowdown test performed with the mock-up test loop in Ō-arai Engineering Center of PNC, and the adequacy of the calculation model and formulae is confirmed.

The Drum Waterlevel in the Multivariable Control System of a Steam Generator

The mutual effects on drum waterlevel and steam pressure due to sudden load changes of a boiler are to be studied by means of a suitable block diagram showing the steam pressure and waterlevel control loops and its mutual influence. Concerning normal load changes (?N 20 percent No)?for instance, heating changes in waste-heat boilers, load steps at industry boilers or at boiler-turbine units, operating on a separate electrical grid?the mutual effects of the variables of both control loops are to be taken into account, too. The effects of those load changes on the time behavior of changes of both the waterlevel and the boiler pressure are to be investigated. The drop in pressure following the operation of the safety valves?for instance, if the value of the exhausted steam flow is not measurable and thus cannot be used as a feed-forward signal for the feedwater controller?and in consequence the amendments of the control diagram are to be taken into consideration.

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.

Hydrastep: A ‘Fail Operative’ Gauge System to Replace Visual Boiler Water Level Gauges

Some major disadvantages of traditional drum water level gauges for high pressure boilers are considered, and features are presented of a new type of gauge—the ‘Hydrastep’—based on a series of independent electrical resistance measurements made concurrently to determine the presence of water or of steam at discrete levels in a side-arm vessel. The thermal considerations are described which result in a density error for Hydrastep systems of only one-sixth of the error of conventional visual gauges, and evidence is presented of the validity of resistance measurements for discrimination between water and steam at temperatures up to at least 360° C. Philosophies of redundancy, as well as of the use of parallel binary information collection and transmission, are incorporated in the basic gauge to give both ‘fail-safe’ and ‘fail-operative’ characteristics. The application of these philosophies is described to systems using a number of Hydrastep gauges on one boiler, whereby enhanced security of measurement may be achieved. Reference is made to the field trials to which a number of single Hydrastep gauges have been subjected on boilers operating at both 110 and 183 bar (1600 and 2650 lb. f/in2, 318 and 358° C respectively), and to the electronic reliability and electrode survival times achieved. Both indication and alarm facilities were provided, and the possibility is mentioned of extending the use of the equipment to provide signals for automatic control purposes, without endangering security of indication. A guide to the costs is included. Hydrastep has been approved by H.M. Chief Inspector of Factories as a legally acceptable alternative to the visual sight glass (Factories Act, 1961: Part II Section 32). The system is protected by U.K. and Foreign patents.

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.

Dynamic Analysis of a Boiler

Abstract Dynamic analysis of a boiler is accomplished by certain approximations which reduce the nonlinear partial differential equations to linear ordinary time-differential forms, and make it possible to obtain the time-dependent functions of large numbers of boiler variables. Linear equations thus obtained are solved by means of an electronic differential analyzer and open-loop response of drum pressure and water level for various input variables (feed-water rate, fuel-flow rate, and steam-flow rate) are shown as examples. A linearly controlled response of the same boiler is also given as an example of the flexibility of the method and the analog solution. It is shown that the potentiality of the method is not limited to this initial study, but can be extended for greater accuracy with the availability of machine computation. Analog simulation of the boiler also makes it possible to investigate the effects of the boiler physical dimensions, heat, or mass-transport constants and to verify some of the basic assumptions on the dynamic behavior of the over-all system.