OCR Text |
Show • Localized control of flux to the process m response to discrete process temperature measurements • Stoichiometry control of individual burners in a multiple burner system by remote sensing of radiant output With the current availability of advanced process sensors and programmable logic controllers (PLC's), more advanced process control techniques are now possible, either by responding more quickly to load variations or by optimizing the distribution of thermal flux to the load. Conventional combustion systems would be limited by the inability of the burner output to change quickly enough or to maintain adequate uniformity in response to these controls. The low thermal mass and distributed heat release of porous surface radiant burners make them an ideal energy source for an advanced control system. The ARCS concept applies existing advanced sensor and PLC technology, coupled with porous surface burners, to applications which require, or could benefit from, very precise heat flux and temperature control. In multiple burner systems as envisioned in this application, individual radiant burners or groups of burners will be controlled by an algorithm utilizing distributed sensor inputs, profiling the radiant flux according to the load requirements. As described above, an additional refinement to the concept involves stoichiometry control of individual burners or groups of burners to maintain high efficiency. One control system, already developed by UTRC (Reference 3), utilizes radiant flux measurements and a signal processing algorithm to tune the air/fuel ratio of individual burners in a multiple burner array. This type of control in conjunction with conventional stack O2 measurements will allow tighter control of burner fuel/air ratios resulting in reduced stack losses and increased thermal efficiency. The proposed high performance radiant system is applicable to a number of industries and processes where high uniform heat flux and precise temperature control are required. These applications include petrochemical processes, where either a fragile fluid (such as petroleum, heat transfer oils, glycol, etc.) or a reaction tube or vessel is to be heated, and metals processing, where loads are heated directly. Hydrogen steam reforming has been chosen as the initial application of this advanced system due to process benefits that will result from improved heat flux uniformity at temperatures of approximately 160QoF. Since this is a continuous, reacting process, optimization of heat flux to process tubes can significantly impact furnace efficiency and process throughput. In the steam reforming process, highly endothermic catalytic reactions occur inside process tubes, and heat flux requirements vary significantly over the length of a tube. Each tube in the proposed system would be divided into two or more zones. Discrete temperature measurements would be used to profile the heat flux provided by multiple radiant burners along the tube length. In a practical system, the control scheme to accomplish this profiling would use the process outlet temperatures to set baseline burner output, as is done in current systems; the optical sensing of process tube temperatures would be used to trim the radiant output above or below this baseline. 6 |