The Study Of Control Method Of Dryness For Oilfield Steam-injection Boiler

Steam thermal drive oil is the method in which high pressure steam with suitable dryness fraction is injected into heavy oil stratum. Steam-injection boiler is the key equipment of thermal drive, and it is also the equipment whose energy consumption is the largest in the thermal drive process.As an important parameter for safe operation of steam-injection boiler, dryness is also an important target which affects the effect of heavy oil thermal drive. But at present dryness control basically is at the hand control stage, therefore the forecast and control of dryness for steam-injection boiler are affected by human factor observably, not only the safe operation of steam-injection boiler is threatened, but also the effect of heavy oil thermal drive is effected. Therefore, it is imperative to carry on the research of control method of dryness for oilfield steam-injection boiler.Since steam-injection boiler was introduced from America at 1980s, the manufacture of it has realized industrialization interiorly. But the control system of steam-injection boiler still stays at the quondam technologic level. Its control efficiency is not high, too. Along with the constant development of advanced control theory and computer technology, that applying the advanced control technologies such as fuzzy control, predictive control to the dryness control of steam-injection boiler and enhancing the control efficiency of control system has became an inevitable trend.Based on the systematic expatiation on technologic process of steam-injection boiler, this paper analyzes the control effects that the control system of steam-injection boiler must achieve and puts forth the difficulties that control system may encounter. Dryness fraction and steam pressure are the important parameters of steam-injection boiler. They are the bottlenecks that hamper the safe and economical operation of steam-injection boiler, too. So according to the characteristics of boiler system, this paper proposed the control scheme based on fuzzy predictive control to adjust the run parameters of boiler. In this scheme, a two dimension fuzzy controller is employed to steady steam pressure, and error and error change of steam pressure are used as the input variables of this fuzzy controller. A fuzzy predictive controller based on T-S fuzzy model is employed to obtain the control variable of fuel-dryness closed loop. And this control variable is multiplied by the feedforward control variable to form the feedforward-feedback control of dryness fraction.