Plants with reduced primary reforming

ICI AMV Process. The ICI AMV process [1034], [1083], [1111] - [1122], also operates with reduced primary reforming (steam/carbon ratio 2.8) and a surplus of process air in the secondary reformer, which has a methane leakage of around 1 %. The nitrogen surplus is allowed to enter the synthesis loop, which operates at the very low pressure of 90 bar with an unusually large catalyst volume, the catalyst being a cobalt-enhanced version of the classical iron catalyst. The prototype was commissioned 1985 at Nitrogen Products (formerly CIL) in Canada, followed by additional plants in China. A flow sheet is shown in Figure 110. 

Application The ICIAMV process produces ammonia from hydrocarbon feedstocks. The AMV process concept offers excellent energy efficiency together with simplicity and reduced capital cost for plant capacities between 1,000 tpd and 1,750 tpd. Key features include reduced primary reformer duty, low-pressure synthesis loop and hydrogen recovery at synthesis loop pressure. 

Catalyst makers also succeeded in minimizing the activity reducing effect of the potassium in the alkalized catalysts [430], Pre-reduced primary reforming catalysts are now also marketed (ICI Katalco, Topsoe) [430], and splitloading of reformer tubes with more than one type of catalyst has now become very common. The benefitial effects concern pressure drop at increased plant load, carbon formation potential, catalyst activity, catalyst cost, and desired catalyst life. For example, a reformer tube may be loaded with 15 % alkali-free catalyst in pre-reduced form (top-section), 25 % unreduced alkali-promoted (middle section) and 60% alkali-free unreduced catalyst (bottom section). 

The profitability of this process is highly dependent on energy cost and capital investment. Energy and capital cost penalties associated with pollution control systems must therefore be minimized as far as practicable. The first step is to reduce the sulfur concentration in the ammonia plant feedstock to less than 0.1 ppmv to prevent poisoning the reformer catalyst. Once desulfurized, the feedstock is partially reacted with steam in a primary reformer to... 

The hydrogen-to-carbon monoxide mole ratio for the product gas is usually 4 to 9 however, it can be increased if additional steam is used in the reaction. This will reduce the demand in the carbon monoxide-shift converters, which follow the secondary reformer. Steam sometimes is introduced after the reformer before the gas is fed to the carbon monoxide-shift converters. In the single-train ammonia plants, the natural gas is reformed in two steps. In the first step, the reaction takes place in the primary reformer in tubes suspended in a refractory-lined furnace. The large amount of endothermic heat is supplied by burning natural gas with air in the furnace. The heat flux in the tubes can be as high as 35,000 Btu/hr sq ft. The methane leakage is about 10 percent in the effluent dry gas, or about 60 to 65 percent of the feed methane is converted to synthesis gas. 

From 1950, the demand for nitrogen fertilizers in North America led to the construction of many more ammonia plants all based on the steam reforming process. Modifications to the primary reforming catalysts by the incorporation of potash to reduce the level of caibon deposition have enabled operators in those parts of the World with no readily available supply of natural gas to use naphtha or refinery off-gases as feed for the primary reformer, and this has increased the versatility of the process even further. ... 

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