The purpose of this thesis is to analyze the dynamic characteristics of industial natural circulation gas boiler which is economical and reliable with speedy and accurate control ability, and to make the analysis utilized for the design of control in industry. Our control system must be able to verify the following :
The dynamic characteristics of pressure control and water level control in drum are analyzed after a model for industrial natural circulation gas boiler. Here the complicated control system of the gas boiler and the multi-variable system that affects variables are simplified.
A linear differential equation for the control is derived from its physical variation process with time by Laplace-conversion. Then from the equation we get a transfer function for pressure and water level in drum. This means that a transfer function for the control system must be carried out from manipulated variables such as Ma, MFU, Mw and θFW to controlled variables such as pressure and water level in drum. Two kinds of methods are used to induce these processes.
Method- I , based on Profos' Theory, is used to derive tranfer function for water level in drum. The problem in Method- I is that it may have a big error with comparison of measurment, but the error out to be solved simply and easily. In addtion transfer function derived by Method- I is only view to the coefficient with function of the structure or design data.
The transfer function derived from Method-II is based on the variation with time within the vaporization system accompanied by thermodynamical variation of state of mixture of two-phase flow. An analysis of the dynamic characteristics of gas boiler by this method makes it possible to induce more accurate transfer function of pressure and water level control. In other words, it is verified that there is no di f ference between the measurement and reckoning in an analysis of the dynamic characteristics of water level and pressure by Method-II.
Acoording to the research on the influence Ms and MFU as major variable of control system of industrial natural-circulation gas boiler have on pressure and water level in drum, the following satisfactory result can be obtained; if Ms is cut down 15% by the hour, the difference between the measurement and reckoning of transfer function by Method-II is 12.4% in pressure variation and 21.7% in water level variation. This means that only trasfer function for the control system by Method-II is correct.