AMV process

In 2002 the Haber process was the most commercially attractive ammonia process even though it had high compression costs, and a large expenditure of energy was required to produce the feed hydrogen. Improvements such as the AMV process and the KAAP process may provide attractive cost reduction opportunities in ammonia production. 

Dual Pressure An ammonia synthesis process, based on the AMV process but providing more capacity by removing some of the product at an intermediate stage. Developed by Krupp Uhde in 2001-2002. 

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. 

Commercial plants Three plants have been built using the AMV process, one in Canada and two in China. 

The most notable development for the magnetite system was the introduction of cobalt as an additional component by ICI in 1984 [395], [396]. The cobalt-enhanced catalyst formula was first used in an ammonia plant in Canada using ICI Catalco s AMV process (later also in other AMV license plants) and is also successfully applied in ICl s LCA plants in Severnside. 

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. 

In units employing natural gas feedstock the expenditure was formerly about 37,10 fcj/t of ammonia produced (980 m1 of natural gas approximately). A number of optimizations helped to lower this consumption to 31. 10 kJ and even 27.10 kJ <61 (IG/AMV process), while allowing for lower capital investment. Table 1.20, which gives the average energy consumption of a unit producing 1000 t/day of ammonia, as a function of the raw material employed, shows that, from this standpoint, natural gas remains the most economically interesting hydrocarbon feedstock. "... 

Theoretically the optimum temperature and pressure are 200 °C and 600 atmospheres. However, in modern plant, since recycling is possible, such stringent conditions are not economically viable. In practice in conventional plant temperatures and pressures of 400 °C and 200 atmospheres are more realistic. In the AMV process similar conversions are achieved at much lower pressure (80 atmospheres). In neither case is the reaction allowed to reach equilibrium, and the resulting conversion is only about 14-15% by volume of ammonia, but this is compensated for by recycling. 

The factors affecting the choice of catalyst are cost and efficacy. In the Haber process the main catalyst used has been iron with potassium hydroxide as promoter. In the AMV process the iron catalyst has been improved with a new combination of promoters which gives longer life and higher activity. Many catalysts can easily be poisoned and iron is no exception. It is poisoned by H2O vapour, H2S, CO and CO2, and therefore these must be excluded from the process if long life is to be assured. 

The essential steps of the older, more common process and of the AMV process are described below. Initially the hydrocarbon feedstocks are desulphurized to avoid catalyst poisoning later on ... 

Synthesis of ammonia. The synthesis reaction is dependent on the conditions of equilibrium and the kinetics of the reaction. The latter is dictated by the efficacy of the catalyst, which in turn is chosen because of its cheapness and activity. Iron is the only realistic catalyst, but its activity can be greatly increased by the use of suitable promoters. It is prepared by melting iron oxide, refractory oxides such as potassium and aluminium oxides. A solid sheet forms on cooling, and is broken down into 5-10 mm lumps. The whole is then reduced in the ammonia synthesizer, where the oxide is converted to iron crystallites separated by the refractory oxides and covered in part by KOH as a promoter. The KOH can enhance the reactivity twofold. This catalyst must be used within the temperature range 400°-540 °C. Below this the catalyst becomes uneconomically inactive above, it sinters and loses surface area. An improved iron catalyst of higher activity and longer life is a feature of the AMV process. It is important to note that much of the reason for improved and continued activity is due to the careful removal of poisons such as CO, CO2, and H2S. 

ICI 74-1 catalyst which contains cobalt has been successfully developed, and applied in the low pressure ICI-AMV process by ICI. The catalyst used in this process is ICI 74-1. The diameter of the converter is 2.9m, with the height of 24m. The volume of the catalysts is 96 m (250 tons in weight) in total, which is separated into three catalyst beds. The operation conditions are Pressure of 10 MPa, temperature of 450°C, space velocity of 5,00h net value of ammonia (10%-11%) and pressure drop of 0.4 MPa. The content of inert gases such as methane is limited to about 7%. The reduction temperature at which water is produced is 370°C. The highest reduction temperature is about 480°C. In Hainan Fudao Fertilizer Plant of China, the volume of the catalyst of the converter is increased to 122.4 m in Ude-ICI-AMV process. 

The A2 series of catalyst has been used in ICI-LCA and ICI-AMV processes. The AMV is the process used in the Zhongyuan Fertilizer Plant. The ammonia... 

The ICI-AMV process was developed by the ICI Company for its 74-1 Fe-Co catalyst, where the process was designed by ICI and the engineering was designed by Uhde Company, Germany. The core of the synthesis loop at low-pressure is the radial-flow converter with three beds of catalysts using 74-1 catalyst of small-particle and indirect interchanger, and in series an inverted U-shaped waste heat boiler. " The process flow is shown in Fig. 9.5. The main technical parameters are shown in Table 9.2. 

As with the processes already discussed, the ICI AMV process is based on steam reforming of either natural gas or naphtha. It uses the same basic process steps as the Kellogg or Topsoe processes, but the operating conditions are significantly different. 

There has been an immense amount of research into variations of the original Haber catalyst first used commercially. Current catalysts have been improved so that commercial plants using the ICI AMV process operate at 70-80 atm pressure. The bed exit temperatures are still above 400 °C because of the equilibrium properties of nitrogen/hydrogen mixtures (see Appendix 5) and the reaction-rate requirements. The development of high-activity catalysts could lead to significant reductions in temperature and pressure, and consequent savings on capital and fuel costs. 

For example, Braun purifier process and AMV process (ICI) — bodi wifii increased duty of secondary reformer. 

The synthesis pressure has, as mentioned above, an important influence on the performance of the ammonia synthesis loop because of its influence on the reaction equilibrium, reaction kinetics, and gas/liquid equilibrium in the product separation. A wide range of operation pressures has been used in practice, from less than 100 bar (in the early Mont Cenis process and recently in the ICI AMV-process) to 1000 bar (in the early Claude and Casale processes). The trend in modern plants has been to select operating pressure in the low to medium pressure range typical operating parameters for modern synthesis loops at two different pressures are given in Table 6.1. 

ICI has been active in the design and operation of ammonia plants since before the Second World War. In recent years, they have commercialized two processes namely the AMV process, and the LCA process. 

As in the Braun process, the size of the primary reformer is reduced and the size of the air compressor increased in the AMV process compared to more conventional process schemes. This is due to the operation with excess process air and with high methane leakage. Power consumption in the synthetic gas compressor is low because of the low synthesis pressure and the low suction temperature (gas direct from the low temperature Selexol CO2 removal unit), but this is compensated by increased power consumption for the compression of excess nitrogen and high power consumption in the refrigeration section. 

The AMV process scheme may be considered as a variation of the classical scheme with some unique features. It has been used as described in the design of one plant and- with some modifications to accommodate integration with a urea plant-in another plant. Experience from operation of a plant using the process has been reported in [417]. The expected energy consumption has been given as less than 7.0Gcal/MT of ammonia (for a plant located in a cold climate), but actual data are not available. 

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