OCR Text |
Show Advanced Radiant Combustion System for High Temperature Petrochemical Process Heaters ABSTRACT Authors: J. D. Sullivan and R. L. Pam Alzeta Corporation, Santa Clara, CA The Advanced Radiant Combustion System (ARCS) is an integrated high temperature radiant burner and process control system designed to accurately regulate burner stoichiometry and to provide uniform and controlled heat flux to process tubes. The benefits provided by porous surface radiant burners have been demonstrated using Alzeta's Pyrocore ceramic fiber burner in industrial applications requiring process temperatures up to approximately 1000oP. These benefits include increased radiant section efficiency, uniform and controlled heat transfer to the process, lower system capital costs, and reduced NOx emissions. As part of the current program, the temperature capability of the ceramic fiber burner will be increased to allow use at process temperatures up to 1800oP. Controls are an integral part of the ARCS, and will serve two purposes. The first is to allow the user the ability to vary radiant flux along the length of process tubes in order to match process needs to energy requirements. In addition, the control system will allow more accurate control of burner fired duty and stoichiometry in order to provide high thermal efficiency and low emissions of NOx and CO. INTRODUCTION Radiant heating systems are used selectively in industries where high intensity uniform energy transfer is required. The fundamental distinction between radiant and conventional flame burner systems is that a large fraction of the combustion energy is transferred directly from the burner's surface to the process as infrared thermal radiation, instead of by convection or conduction. Since solid surface radiant output is proportional to T\ where T is the burner temperature, much higher fluxes are available to be transferred to the process load than by radiative or convective heat transfer from gases. Radiant burners are designed so that combustion reactions occur on or in close proximity to a surface. This surface is heated to incandescence and is itself the primary source of radiation. The heat transfer occurs at one temperature -- the temperature of the surface -- rather than with the temperature peaks and other nonuniformities characteristic of gas-phase energy transfer. Since up to 30 percent of the energy of combustion is radiated from the burner surface, peak gas temperatures are lower than in conventional flames. Radiant burners used in high temperature and high heat flux industrial processes can be classified into two groups: direct-fired impingement burners and porous surface burners. With the direct-fired burner, a premixed flame impinges on a solid refractory surface heating 1 |