Air-Gas Path Modeling and Controls for Balanced Draft Boilers

摘要

At ENEL (Italian Electricity Board), a few steam generators which ran as pressurized units for many years are now being converted to a balanced draft operation. In a balanced draft boiler, the furnace pressure has to be automatically controlled and the most critical demands upon the control are met in emergency conditions (boiler trip, load rejection). The analysis of the possible control strategies and the main control parameters has been performed by using a reference model of the air-gas system. The model, based on physical principles and correlations, is described by algebric and ordinary differential equations. It has been developed not only to design and verify the air-gas control system, but also to be used in engineering real time simulation of a thermal power plant in which emergency situations have to be studied. A suitable implicit integration technique has been developed, which allows large time steps to be used while still maintaining good accuracy (large number of control volumes) and high stability margins. The validation of the model is also shown. First, a load rejection test has been performed on a unit equipped with a pressurized furnace. Then, a seriesof tests on a balanced unit are shown, and comparisons made. (ERA citation 14:004404)