INFLUENCE OF RADIATION PROPERTIES OF REFRACTORY LINING ON THERMAL CHARACTERISTICS OF RADIANT CHAMBERS OF TECHNOLOGICAL TUBULAR FURNACES

The article contains the results of numerical modeling of complex heat exchange in the radiant chamber of the BPK-6K tubular furnace for steam reforming of natural gas under indirectly directed heat transfer mode. The radiant chamber consists of two sections located symmetrically relative to a single-row tubular coil with vertical reaction tubes. The side walls of the chamber are lined with refractory material (chamotte SHA), the tubular screen is heated by fan burners GVN of a flat flame, located in two rows on the side walls of the radiant chamber. The fuel is natural gas. The research method is based on the numerical solution of a system of two-dimensional integro-differential equations of radiative gas dynamics, closed by the equations of the (k-ɛ)-turbulence model. Heat transfer by radiation is modeled within the framework of the S 4 -approximation of the discrete ordinate method. The radiation properties of the products of complete combustion of natural gas (water vapor H_2 O and carbon dioxide CO_2) are described by a broadband model taking into account the main spectral absorption bands: 1.5 μm; 2.7 μm; 4.3 μm; 6.3 μm; 10 μm and 15 μm. The gas-dynamic part of the problem is solved in natural (u-v)-variables on the so-called "chessboard" finite-difference grid (SIMPLE algorithm). The calculations are performed in the gray approximation and taking into account the selectivity of the refractory radiation properties. The spectral distributions of the area-averaged incident, absorbed and resulting heat fluxes to the tubular screen, as well as the velocity field of the combustion products are presented. It is shown that the calculation in the gray approximation for the radiation properties of the surfaces enclosing the furnace gives a distorted spectral distribution of heat fluxes, especially in the near infrared region. The influence of radiation selectivity on local heat exchange characteristics in combustion chambers is significant. This indicates the need for joint consideration of the radiation selectivity of the combustion environment and the enclosing surfaces involved in heat exchange.