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Show Thermal management is extremely important in the overall operation of a hydrogen plant. Typically, the process streams are cooled with steam from steam generators, and the heat in the flue gas from the radiant box is recovered by preheating the process steam/hydrocarbon mixture, generating steam for the process and export, preheating boiler feed water, and preheating combustion air. Reaction tubes are mounted vertically to minimize mechanical support requirements and to simplify installation and replacement. Wall-mounted direct-fired burners, as well as roof and floor mounted flame burners are presently used. Burners are typically powered, and the entire system is usually provided with some form of modulated firing rate control. However, little control exists to vary heat flux to a process tube over its length. Minor variations of this design are in use for hydrogen plants ranging in size from 0.25 to 500 million standard cubic feet per day (scfd) of hydrogen. A well-designed furnace using heat recovery equipment with existing technology can achieve an overall thermal efficiency of 90-93 percent (LHV). Overall energy consumption for hydrogen production is roughly 400 Btu per standard cubic foot of hydrogen product, divided approximately equally between fuel and feedstock (Reference 4). Typical fired inputs for burner systems range from 2 MMBtu/hr to 4000 MMBtu/hr, requiring many burners in the larger reformers. Recent improvements in reformer design have been directed toward higher temperature alloy tubes, special casting techniques, improved tube suspension to avoid bowing and uneven heating, improved ceramic linings, better air preheaters, 10w-NOx burners, and improved catalysts. These are all incremental improvements intended primarily to increase thermal efficiency and plant reliability in an effort to reduce overall production costs (Reference 5). The goal of the ARCS is to improve the reformer furnace combustion system in a manner that dramatically increases radiant efficiency, reducing required fired duty and overall system size. A schematic of a reformer utilizing the advanced combustion system was shown as Figure 2. The design maintains the vertical orientation of the reaction tubes, but utilizes the advanced radiant burners to reduce burner to tube spacing, resulting in a smaller furnace volume and lower capital costs, or equivalently, higher capacity for the same capital cost. As described previously, the absence of an attached flame on the porous burner allows this close burner to tube spacing without sacrificing heating uniformity. Each burner segment constitutes a controllable heating zone used to profile the heat flux to a portion of the vertical length of the reformer tubes. Sensing of tube temperature at various elevations allows individual burner zones to be controlled independently. Because of the advanced system's improved performance, a number of benefits will be provided: • Reduced System Maintenance Costs -- Increased tube and catalyst life resulting from more uniform and controllable flux to the process tubes. • Reduced Fuel Usage -- Higher radiant section heat transfer rates will result in higher overall combustion system efficiency in applications with no export steam requirement. 7 |