THE FORMATION AND REDUCTION OF NO DURING THE COMBUSTION OF POWDERED PETROLEUM COKE—THE CASE OF CEMENT PLANT PRECALCINER CONDITIONS

ABSTRACT

In a cement plant precalciner, petroleum cokes are burned between 800 and 1100°C and NO present in the flue gas is mainly fuel NO. We have developed a thermochemical model that describes the combustion of powdered petroleum coke in laminar flow conditions. It takes into account the main thermal and chemical mechanisms which occur during combustion. The formation and reduction mechanisms for fuel, prompt, and thermal NO are modeled; as far as gas-phase reactions are concerned, detailed chemistry is treated. Specific experiments were conducted to characterize the species produced by each of the major reactions and to determine their reaction kinetics. These experiments were performed in an entrained-flow reactor at 900°C under conditions typical of those in a precalciner. A gas analysis device based on high-resolution Fourier transform infrared was specifically developed to quantify the main gases which participate in NO formation and destruction. Thanks to this work, the main mechanisms were distinguished, and their relative importance in NO formation was established. Gas-phase reactions form most of the NO in the flame zone but contribute only slightly to the final NO emission. The quantity of thermal NO is negligible. Fuel NO is formed principally during combustion of the carbon residue. In compensation, a significant quantity of NO is reduced by heterogeneous reaction with the carbon of the particles.

Keywords:

• petroleum coke
• combustion
• NO formation
• model