Quench steam generator

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... 

Heat recovery tor steam generation, pre-heating combustion air, and high efficiency burners Adjustable speed drives, heat recovery coke oven gases, and dry coke quenching Efficient hot blast stove operation, waste heat recovery for hot blast stove, top gas power recovery turbines, direct coal injection... 

The reaction generally takes place at a pressure of less than two bar with a very short residence time. The converter discharge gas is rapidly quenched to less than 400°C to avoid decomposition of HCN. The reaction gases are usually quenched in a steam-generating, waste-heat boiler that is directly below the catalyst129. The heat of reaction is recovered in the waste-heat boiler to generate about five (5) pounds of steam per pound of HCN produced. 

In the second alternative, i.e. with the quench, the task is to reduce an excessive steam/gas ratio. Method B shows one way of doing this. A waste heat boiler is located downstream of the quench. It operates in the saturation range of the gas. The excess water is removed by means of partial condensation of the water vapour, thus producing the desired S/G ratio. The heat of condensation obtained can be utilized for generating steam. The pressure of the steam generated in this way can, at the most, only correspond to the partial pressure of the steam within the gas. This method will therefore only be advisable when the total pressure is at an appropriately high level. 

The recycle of wood is thus evidently needed. Since the suspension leaving the riser is quenched in the external steam generating bed, further devolatilisation will be low. Since combustion of volatiles is a fast reaction, volatiles will be completely burned in the outlet duct after the cyclone. 

The flowsheet (Figure 17.9) contains a feed-effluent heat exchanger (FEHE), furnace, reactor, quench unit and steam generator. The following controllers can be considered ... 

The hot gas is quenched with process water to the inlet temperature of the shift conversion step (about 300°C), and most of the soot is removed in the water, which goes to a soot recovery unit. The soot is eventually recycled in the oil feedstock or used as fuel for steam generation, and the water from which the soot was recovered is recycled to the quench step. The quenching step also vaporizes some of the water into the gas stream, which supplies water vapor needed for the shift reaction. 

Cracking furnace 2 Quenching cooler 3 Steam generator 4 Primary fractionation ... 

The crude raw gas leaving the gasifier at 2,300-2,700°F contains a small quantify of unburned carbon and a significant portion of molten ash. Depending on the end use, this gas stream would either be directly quenched in water (to cool the gas and remove solidified ash particles) or would be cooled in radiant/convection boilers for sensible heat recovery (via high-pressure saturated steam generation) prior to water scrubbing. 

The hot gas fiom the incinerator is partially cooled to about 500°F by a heat recovery steam generator. The gas then flows through a de-superheater and a quench vessel. The quench vessel temperature is monitored to ensure that the gas entering the first absorber stage is cool enough to avoid damage to the fiber reinforced plastic absorption vessels. The gas then flows countercurrently through three absorbers where the SO2 is reacted with aqueous ammonia and converted to an aqueous solution of ammonium bisulfite and ammonium sulfite ... 

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