Secondary reformer Burner

FameU, P.W., Investigation and Resolution of a Secondary Reformer Burner Failure, Prepared for Presentation at the 45 Aimual Safely In Ammonia Plants and Related Facilities Symposium - Tuscon, Arizona - Paper no. ID, September 11-14,2000. 

The secondary reformer vessel is a refractory-lined vessel that has an oxygen burner in its top neck and a fixed catalyst bed. Installation of a secondary reformer usually requires significant changes to the CO2 removal system Hydrogen purity can be increased up to 98%. The economics generally depend on a reliable source of low-cost oxygen172. 

In an ammonia plant (Figure 4.2), the synthesis gas from the reformer furnace is fed into a secondary reformer vessel, where air is added through a burner to create outlet vessel temperatures of -1,800° F (980° C). The outlet of the secondary reformer vessel is cooled in a quench steam generator and sent to a shift converter this is followed by a carbon dioxide removal system such as the one in a hydrogen plant. The purified nitrogen from the air added in the secondary reformer vessel and hydrogen synthesis gas is fed to a methanator to convert residual oxides of carbon back to methane (which is inert in the ammonia conversion) the gas is then compressed to -3,000 psia (2,070 kPa). The compressed synthesis gas is fed to an ammonia converter vessel. As the synthesis gas passes over catalyst beds, ammonia is formed. The ammonia product is then cooled and refrigerated to separate out impurities. 

The secondary reformer in an ammonia plant is a carbon steel vessel with a dual layer refractory lining. Internal temperatures reach -2,000°F (1,090°C) from burning as a result of air added through a burner at the top of the vessel to the feed gas (hydrogen, carbon monoxide, carbon dioxide, and steam). The burner is a refractory-lined device that is subject to failure if not carefully designed. Quench steam generators have refractory-lined inlet channels and tube sheets. Tubes are often made of carbon steel because the heat transfer from the steam on the outside of the tube is markedly better than that from the synthesis gas inside the tube. As a result, the metal temperature closely approaches the temperature of the steam. The inlet ends of the tubes are protected from the inlet gas by ferrules, usually made of type 310 (UNS S31000) SS with insulation between the ferrule and the tube. The tube material should be selected... 

Features, such as the inclusion of a prereformer, installation of a ring-type burner with nozzles for the secondary reformer and upgrading to an S-300 ammonia converter, are all features that can be applied for existing ammonia plants. These features will ease maintenance and improve plant efficiency. 

A typical secondary reformer is a cylindrical, refractory-lined, insulated vessel. The upper part is empty and serves as a combustion chamber in which the gas from the primary reformer is partially oxidized by preheated air. The lower part is filled with a catalyst similar to that in the primary reformer. The air should be free fronrdusT that might clog the catalyst bed arid from catalyst poisons (S, Cl, and As). The air is filtered, compressed to reformer pressure, and mixed with the gas in a burner at the top of the vessel. The combustion causes the temperature to rise to about 1200°C in the combustion chamber. As the hot gas descends through the catalyst bed, it is cooled by the endothermic reformir reactions and leaves the reformer at a temperature of about 950 -1000 C. The gas at this point contains, on a dry basis, about 56% Hg, 12% CO, 8% CO2, 23% Ng, plus argon, and usually less than 0.5% CH4. It also contains excess steam ranging from one-third to one-half of the total gas volume. 

An ATR is similar to an oxygen secondary reformer except that it does not receive feed from an SMR. Instead, it is fed directly with a natural gas/steam mixture, which is mixed directly with oxygen from a burner located near the top of the vessel (Figure 5). Again, partial oxidation reactions occur in a combustion zone just below the burner. The mixture then passes through a catalyst bed where reforming reactions occur. The gas exits at about 1900°F. 

Secondary reforming is carried out in an adiabatic, refractory-lined vessel. Gas from the primary reformer typically at about 800 °C and containing 8-12 vol% (dry) residual methane is mixed in a burner with preheated air. The partially reacted mixture passes through a bed of catalyst, where the reactions are completed. The gas leaves the reactor at about 1000 °C with a residual methane content of typically 0.3-1.0 vol% (dry). 

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