Energy consumption of ammonia production

It can be shown that the plant costs for a variety of processes correlate with the energy transfer (heat transfer, compression) within die process scheme [289]. As an example, the energy consumption of ammonia production has decreased over the last 50 years from about 40 GJ/t to 29 GJ/t corresponding to a thermal efficiency (LHV) of 65% or 73% of the theoretical minimum [169] [420]. 

However, in China the pressure of small to medium ammonia plants still exceed 30 MPa and the energy consumption of ammonia production is about 50% higher than the average international level. Such a situation is not consonant with the trend of development in the ammonia sjmthesis industry. Ironically, it is China that has already developed high activity catalysts that operate at low temperature and... 

Energy Consumption in Ammonia Production-Influence of External Conditions and Key Parameter, Undated Haldor Topsoe brochure. 

Natural gas is by far the most economical feedstock for ammonia production, achieving the lowest energy consumption and requiring the lowest investment [404], This can also be seen from Table 45, which gives an estimate of ammonia production costs in Northwest Europe for different feedstocks using state-of-the-art technological standards. The lump turn key price for the ammonia plant were assumed as 180 x 106 for steam reforming of natural gas, 270 x 106 for partial oxidation of vacuum residue and 400 x 106 for coal-based plants (Capacity 1800 mt/d). 

The presence of lithium salt in the wastewater is avoided. Also, the waste-air streams conform with legal requirements and are all used either in the process or for energy production. Increased recycling of ammonia and acetylene leads to reduction in the consumption of ammonia to 25 % of its former value acetylene consumption is reduced by 50 %. Thus, the stoichiometric excess of acetylene used in stage I of the reaction is reduced to ca. 12%. 

The thermodynamic energy requirement is 2 x lO" kJ/t NH3, which represents the theoretical minimum for all conceivable processes. Modern processes for the production of ammonia from natural gas have energy consumptions of around 3x10 kJ/t NH3, i.e., only 1.5 times the theoretical minimum energy consumption. Today much of the energy requirement can be covered by means of heat recovery. Modern ammonia plants produce up to 2000 t/d. 

Total reaction equation of producing ammonia process AH = AHv Theoretical energy consumption of process Theoretical energy consumption of product ... 

It can be seen from Table 9.13 that the designed energy consumption of synthetic ammonia production is changed with the difference in the raw materials, gasification pressure and plant scale. 

Energy system. The design of the energy supply and the recovery system is one of the main factors determining the energy consumption of production ammonia. For example, the modern ammonia plant has a lot of the characteristics favorable to increase the energy efficiency of whole plant. ... 

The economic benefit of synthesis ammonia production depends on energy consumption. Increase in productivity is influenced by many factors in which the reactor s volume plays an important role. The reactor s volume is limited by the possibility of mechanical manufacture. For example, high-pressure reactor is restricted by the allowed weight of forging. In addition, the size of the heat exchanger is limited by the number of tubes in the tube bundle. Usually the number of tube is not more than 10,000. The tube reactor, whose catalyst volume is more than 30 m, is rarely seen in the mechanical industry. Factors such as the size of reactors may pose difficulties in transporting from mechanical work to the construction site as well as the ability or the inability of the crane in capital construction and so on. 

At the same time, running in long periods, i.e. improvement of operating rate is also the efficient way of energy-saving of plant. The actual energy consumption in ammonia synthesis production can be calculated as following equation ... 

In the following section, energy balances in ammonia production will be discussed. The difficulties related to the comparison of energy consumption in different process schemes will be dealt with, and finally a description will be given of the main concepts in the integration of ammonia production units and steam and power systems. 

Ammonia Supply Temperature. A part of the energy consumption in ammonia plants is used to condense the product ammonia. If the ammonia could be supplied as a gas, this energy could be saved. On the other hand, extra energy must be used if the product must be supplied to an atmospheric storage as liquid at — 33 °C. The differences compared to supply of liquid ammonia at ambient temperature are ... 

As can be seen from this analysis, the natural gas feedstock and capital charges amount to over 93% of the total production cost before return on investment. Therefore, energy consumption and capital investment are the key factors in determining ammonia production profitabiUty. 

Ammonia synthesis is the second largest chemical process, after the production of sulfuric acid (see also Chapter 1). It accounts for about 1 % of the total human-related energy consumption. Roughly 80 % of the ammonia produced is used for fertilizers (either as liquid ammonia or as more easily handled salts such as ammonium nitrate, ammonium phosphate, etc.) and, as such, ammonia synthesis is indispensable for our society. Other applications of ammonia are nitrogen-containing... 

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