Development and introduction of new designs for gas-dust flow mixing distribution systems at thermal power plants

Abstract

Translated from Élektricheskie Stantsii, No. 7, July 2008, pp. 10 -23.The successful introduction and setup of new designs for dust separators in Russian and foreign 200 -800 MW coal-fired power production units is described. Results from mathematical and physical modelling of these designs, as well as data on their operation in test stands, are presented. Recommendations are given for the most suitable equipment and configurations of new dust distribution systems in dust preparation systems.Keywords: dust-gas flow mixing distribution systems, introduction and setup, design models, test stand studies, mechanism for motion of stable dust layers, equipment recommendations.Operating experience and industrial research show that the operational efficiency and reliability of furnace systems, the explosion safety and operational reliability of dust preparation, the reliability and operating lifetime of heating surfaces, and the amount of nitrogen oxide emissions depend on the degree of uniformity of the distribution of fuel and air over the burners in a furnace. Failure to meet the required fuel-air ratio in the burners leads to a deterioration in ignition stability, reduced fuel burnup, and increased yield of toxic combustion products [1 -4]. Elevated concentrations of dust in the dust ducts can lead to dust deposits in the ducts or even to blockage of individual lines, which increases the explosion hazard for the system and reduces the productivity of the dust system [5 -7]. Nonuniform heating in different burners causes greater distortions in the temperature over the cross section and height and may make the flare stretch into the upper part of the furnace and cause a rise in the temperature at the furnace outlet; this sharply reduces the service lifetime of the heating surfaces and causes slag buildup on them [1,3,8,9].During operation of dust preparation systems this nonuniformity can be extensive (up to 100%) owing to different fuel dust feed rates at various outlets from the system: three-way distribution feeds, turns, separators, etc. Even with a uniform distribution over the outlets for the transport air, the dust can fall into one or several outlets as it is extruded toward the channel walls [9]. If the dust system includes dust ducts with greatly differing lengths and configurations, as is typical of most coal-fired thermal power plants with highpower energy production units, an additional nonuniformity is imposed on the distribution of air over the outlets.It should be noted that efforts to introduce new technologies and equipment for fuel burning may not yield the expected theoretical effect, if the specified distribution of fuel feed rate over the burners is not ensured. These problems are especially pressing in connection with the tasks now facing the national power generation system of enhancing the steam parameters (which requires the elimination of temperature distortions at steam superheater surfaces) and meeting modern ecological standards (through use of stepwise combustion and the strict need to ma...