Controlling the Superheated Steam Temperature during Buffer Consumption of Gaseous Production Waste through Adjusting the Injection and Flame Position

Abstract

The article considers the possibility of achieving more efficient performance of a TP-13B industrial steam boiler fitted with a spray desuperheater and operating in the mode of buffer consumption of blast-furnace gas as applied to the superheated steam temperature automatic closed-loop control system. The main problem stems from the fact that the superheated steam temperature increases essentially due to large blast-furnace gas flowrates and displacement of the flame when shifting to operation with a large fraction of blast-furnace gas (with respect to the natural gas fraction). The usual injection adjustment range turns out to be insufficient for stabilizing the steam temperature downstream of the second-stage convection steam superheater (CSS2). In addition, the steam temperature downstream of the first-stage convection steam superheater (CSS1) increases significantly, because this section is not protected by injections. For solving the problem, it is proposed to use a combined system, which uses, in addition to the conventional steam temperature controller downstream of the CSS2, which adjusts the injection, a controller of steam temperature downstream of the CSS1, which adjusts the flame position by turning the air-control registers. With the steam temperature downstream of the CSS1 stabilized by adjusting the air-control registers, it becomes possible to pose less demanding requirements to the injections; in addition, with such stabilization, the CSS1 metal is protected from overheating. This is an advantage in comparison with the well-known arrangement in which such control is only performed when the injection valve position approaches the specified limit values. The functional and structural diagrams of the proposed control system are given. The parameters of the plant model channels’ transfer functions are determined proceeding from the known experimental data for the TP-13B boiler. The system has been studied by carrying out computations in the environment of the MathCad software system and the MatLab/Simulink modular simulation software package. The simulation model includes nonlinearities typical for the automation equipment used in thermal power engineering. The effectiveness of the proposed combined control system during operation with essential variations of the blast-furnace gas flowrate has been demonstrated. The information presented in the article can be used in fitting the industrial steam boilers operating with buffer consumption of gaseous production waste with means for automatic control of superheated steam temperature.