Feedstock for ammonia synthesis

The purified gas is fed into the Synthol and fixed-bed reactors. The products from the reactors are cooied and separated in a water phase, oil phase and tail gas. The + Ca olefinic products from the tail gas are separated in an oil absorption tower and oligomerized over an acidic catalyst to gasoline. Tite remaining tali gas can be treated in a cryogenic unit to provide methane and hydrogen, which is partly used as fuel gas or feedstock for ammonia synthesis. The remainder is steam-reformed over nickel catalysts to give CO/H3. 

Despite the apparently straightforward nature of these procedures to the feedstocks for ammonia synthesis and the free source of nitrogen from the air, this combination of approaches has become feasible only for relatively small ammonia plants of around 100 tonne/day, or for special process situations where abundant hydrogen is available. Today, ammonia plants of capacities of 900 tonne/day are common and a few as large as 1650 tonne/day are now operating worldwide. Thus it can be seen that the process sequence described above is not a major contributor to world ammonia production. 

In early days of Phase I, the predominant feedstock for ammonia synthesis was coke. Synthesis gas was either produced at atmospheric pressure in water-gas shift units or prepared by purification of coke oven gas. In these early plants, the process effluents from the ammonia converter were cooled without recovery of heat. Due to the lack of technology regarding the attainable size of the converter pressure shell, the physical dimensions of the converter were limiting factors for the achievable production capacity. Therefore, a particular emphasis was placed on maximization of the production capacity for a given volume [139]. During World War II, several plants were built in the United States, based on natural gas feedstock. Since then, natural... 

This excess hydrogen is normally carried forward to be compressed into the synthesis loop, from which it is ultimately purged as fuel. Addition of by-product CO2 where available may be advantageous in that it serves to adjust the reformed gas to a more stoichiometric composition gas for methanol production, which results in a decrease in natural gas consumption (8). Carbon-rich off-gases from other sources, such as acetylene units, can also be used to provide supplemental synthesis gas. Alternatively, the hydrogen-rich purge gas can be an attractive feedstock for ammonia production (9). 

Steam reforming was developed in Germany at the beginning of the 20th century, to produce hydrogen for ammonia synthesis, and was further introduced in the 1930s when natural gas and other hydrocarbon feedstocks such as naphtha became available on a large scale. 

Nitrogen fertilizers via ammonia synthesis account for more than 90 percent of the world s nitrogen fertilizers. Nitrogen supply for ammonia synthesis is truly inexhaustible since the atmosphere contains 3.8 quadrillion tons of the element. Various feedstocks can be used to obtain hydrogen, and during the last... 

This is a vital problem for liquefaction and has failed in the advanced German trials. In Japan, liquefaction has first to defeat incineration, the technique that has prevailed in most municipahties. The rate of incineration in municipalities has reached 80% or so and 40 million tons of garbage are incinerated every year. From this point of view, the reduction of collection and baling costs as described above is an easy way to achieve this. Second is the question of how to reduce the liquefaction cost compared with those for the other feedstock recycling methods, such as application in the iron and steel industry and gasification for ammonia synthesis. These methods have the merits discussed above. On the other hand, liquefaction has many weak points, it is small in scale, complicated with a mixed raw material for fine technology, and has a low degree of operation, 50% or so. 

In the former case, which is discussed in this study, only partial condensation is performed industrially. In the latter, scrubbing can piso be carried out with liquid methane or nitrogen (see Section 1.2). However, this means that the residual hydrogen gas is polluted by one or the other of these two compounds, and this could restrict its field of application or, on the contrary, facilitate its use. Hence the use of Hquid nitrogen offers an interesting solution for ammonia synthesis from an effluent produced by partial oxidation of organic feedstocks (see Section 1.3.1.1) in so far as, introduced with hydrogen at the rate of 2 to 8 per cent volume, this represents the use of one of the reactants for the production of ammonia, whereas methane, on the contrary, is a diluent... 

For the production of chemical commodities, chemical and industrial engineers choose reactions whose equilibrium constants favor products whenever possible. Often, this type of choice simply is not available. For example, equilibrium between H2, N2, and NH3 in the production of the ammonia feedstock for HCN synthesis does not favor the formation of ammonia. Nevertheless, the... 

Fig. 1.1 Schematic diagram for ammonia synthesis processes from different feedstock...

The concentrations of CO (10%-50%) are different in the synthesis gases produced from different feedstock. CO must be removed because it is a poison for ammonia synthesis catalysts. Generally, CO is converted via reaction with steam to form CO2 and H2 over a catalyst, and then CO2 is removed. The reaction between CO and steam over a catalyst is called CO shift reaction as shown in Eq. (1.16). 

It is possible to use Cu-based CO shift catalysts since sulfur content in synthesis gas can be reduced to below 0.1 ml m with the changes of industrial feedstock for ammonia s3mthesis and development of gas piu ification technology. Low-temperature shift process was first commercialized in the United States in 1963. The same process was also industrialized in China in 1965. 

The syn gas process is usually run for specific purposes. Examples include feedstock for ammonia production, feedstock for methanol production, feedstock for the Fischer-Tropsch synthesis, or for the energy output. Depending on the reason for running the reaction, a different ratio of H2 CO is needed. This ratio is influenced strongly by the material undergoing partial oxidation. Coal gives a 1 1 ratio of H2 CO petroleum about a 2 1 ratio and natural gas somewhat higher than a 2 1 ratio as will be evident from the discussion on methane oxidation. 

Natural gas with methane as the principal component is mainly utilized for heating, methanol and ammonia synthesis, or generation of electric power [7]. With the recent discovery of large reservoirs of shale gas, methane could soon increase its role as fuel and feedstock for the synthesis of chemicals [8], replacing oil. The conversion of methane via OCM into C2 hydrocarbons such as ethane (7.1) and ethene (7.2) [8] is an interesting technology for the direct conversion of natural gas into molecules which can find applications in the energy sector (ethane) or in the chemical and polymer industry (ethene) [9]. 

Figure 28.2 illustrates a process that starts with coal or oil as a raw material. The process includes coal handling, preparation, and pulverization and partial oxidation of coal or oil to synthesis gas, followed by carbon and ash removal, carbon monoxide conversion, carbon dioxide and H2S removal, low temperature scrubbing with liquid nitrogen, and compression for ammonia synthesis. Air separation and sulfur recovery are steps unique to coal or heavy oil feedstocks. 

Between 1930 and 1950, the primary emphasis of ammonia process development was ia the area of synthesis gas generation (3) (see Fuels, SYNTHETIC, GASEOUS FUELs). Extensive coal deposits ia Europe provided the feedstock for the ammonia iadustry. The North American ammonia iadustry was based primarily on abundant suppHes of low cost natural gas (see Gas, natural). 

Synthesis Gas Preparation Processes. Synthesis gas for ammonia production consists of hydrogen and nitrogen in about a three to one mole ratio, residual methane, argon introduced with the process air, and traces of carbon oxides. There are several processes available for synthesis gas generation and each is characterized by the specific feedstock used. A typical synthesis gas composition by volume is hydrogen, 73.65% nitrogen, 24.55% methane, <1 ppm-0.8% argon, 100 ppm—0.34% carbon oxides, 2—10 ppm and water vapor, 0.1 ppm. 

Steam-Reforming Natural Gas. Natural gas is the single most common raw material for the manufacture of ammonia. A typical flow sheet for a high capacity single-train ammonia plant is iadicated ia Figure 12. The important process steps are feedstock purification, primary and secondary reforming, shift conversion, carbon dioxide removal, synthesis gas purification, ammonia synthesis, and recovery. 

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