INFLUENCE OF BURNER LOAD DISTRIBUTION ON FURNACE BEHAVIOR Željko Bogdan, Neven Duić and Daniel Rolph Schneider Faculty of Mechanical Engineering and Naval Architecture University of Zagreb, Croatia ABSTRACT Once-through boilers are very sensitive to the combustion process in the steam generator combustion chamber. Fuel to feed water flow ratio should be maintained in a very narrow range in order to ensure proper functioning. This is especially true when the combustion system is complex consisting of a great number of burners. In this paper influence of a 16 burner oil-fired combustion system of a real steam generator on the temperature, velocity and heat flux distributions inside the combustion chamber was investigated. Simulations of the combustion chamber performance for normal operation and for the anomalous operation without a burner were carried out and related to the actual situations. It was shown that poor functioning of a single burner can cause distortion of the main parameter distributions which may result in the damage of the steam generator vital parts. KEYWORDS Numerical simulation; mathematical modeling; combustion chamber operation INTRODUCTION The once-through boilers belong to the category of the greatest capacity boilers of today with highest steam parameters. They can satisfy very rigorous demands for load changes. Since there is no natural circulation of water and steam in such boilers, the positive circulation is realized by an external feedwater pump. The maintenance of fuel to feed water flow ratio in very narrow range for all operating regimes is obligatory in order to ensure proper functioning. It is achieved by sophisticated control system. During operation conditions for fuel and air injection in a burner change due to the fact that nozzles get soiled; and which nozzle would get choked first cannot be estimated. The change of total burner load due to poor operation or shutdown of a single burner can change combustion conditions in the combustion chamber dramatically. In this paper the three dimensional mathematical model of the steam generator combustion chamber was used for investigating the influence of burner load distribution on furnace behavior. Primarily attention was paid to the extent to which a single burner dropout can influence the operation of the combustion chamber as well as the steam generator itself. The furnace is a part of the tower type once-through 1000 t/h steam generator. The combustion chamber dimensions are 11.6x11.6x23 m. The superheated steam exit temperature is 540 °C at 175 bar. The oil-fired combustion system consists of sixteen burners placed in four levels on the front furnace wall. Each burner level may be controlled separately by choosing appropriate values of weight factors which ensure that overall load stays constant. During the operation the unbalance of the furnace thermal load is often encountered which results in different superheated steam temperatures on the outlet of evaporator tubes. For low load conditions the evaporator is furnished with Sulzer bottle which should be dry during higher loads. Appearance of the water level in the bottle during high load operation is undesirable and is caused by thermal unbalance of the furnace. By acting upon burner load distribution through the control system such situations may be avoided. The frontal burner position causes the domain of highest flue gas temperatures and velocities to drift toward the furnace rear wall. The evaporator tubes are placed spirally around the furnace in four distinct groups (shown in Fig. 1.) which should equalize heat flux distribution along tube groups.