Some papers concerning boiler dynamics have been reported hitherto, but they are not so correct in high pressure ranges and accordingly they don't serve enough to analyze and synthesize the control systems.
Under such circumstances, the author deduced the following fundamental equations for dynamics and thermal capacity of evaporator:
_??_
WhereQ=Δq/q₀, θ_f=Δθ_f/θ_fo, G_f=Δg_f/g_fo, G₂=Δg₂/g₂₀, P₁=Δp₁/p₁₀, q (heat transmission rate), θ₁, θ_f (temperatures of saturated steam and feed water), g₂, g_f (flow rates of load steam and feed water), p₁ (pressure of saturated steam), i″, i′, i_f (enthalpies of saturated steam, saturated water and feed water), v″, v′ (specific volumes of saturated steam and saturated water), w_m, w′, w″ (weights of steel parts, water and steam contributing to thermal capacity of evaporator), b (volume of evaporator), c_m (specific heat of steel), A (thermal equivalent of work), suffix 0 (values at equilibrium conditions), Δ (small changes from equilibrium conditions), H_θ (effect of change of feed water temperature), H_w (effect of change of feed water flow rate), H_s (effect of change of load steam flow rate), T_B (time constant indicating thermal capacity of evaporator). T_B, H_θ, H_w and H_s are given in nomographs for convenience of calculation.
Optimum synthesis for two standard pressure control systems are discussed and a nomograph is given for optimum paprameter settings. Transient pressure changes induced by load change are also given in other nomographs.
The value of ∂i″/∂p₁ changes at p₁≈30kg/cm² abs., and it should be noticed that the control system changes its characteristics at this boundary pressure.