Energy consumption of ammonia

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... 

Table 9.13 Designed energy consumption of ammonia produced by various raw materials (in liquid ammonia per tons)...

Table 10.12 Comparison of investment and energy consumption of ammonia plemt using different raw materials...

Figure 8.19. The energy consumption of the ammonia synthesis has decreased steadily and is now comparable with the natural process. (Courtesy of HaldorTopsoe AS.)...

Figure 8. Energy consumption of Kellogg ammonia plant s steam reforming of...

Incorporating some or all of the above mentioned improvements will lead to a considerable reduction of energy consumption of an ammonia plant based on steam reforming of natural gas or naphtha. The actual plant design will depend on the project particulars and feed and utility price structure. 

Effluent vapors are cooled by ammonia refrigeration (13) and unreacted gases are recycled. Anhydrous liquid ammonia is condensed and separated (14) from the effluent. New energy-efficient and cost-effective designs are in operation with energy consumption of less than 25 MMBtu (LHV)/short-ton, with about 10% capital cost savings over the conventional process. 

Table 36. Development of ilie nei energy consumption of natural gas based steam reforming ammonia plants (rea plant data) in GJ/t NH ...

Haldor Topsoe Process. In addition to technology supply, Haldor Topsoe also produces the full catalyst range needed in ammonia plants. The energy consumption of a basically classic plant configuration has been reduced considerably by applying systematic analysis and process engineering. Descriptions and operational experience are given in [464], [623], [1028], [1071]-[1082]. 

Ube Industries commissioned a 1000 t/d ammonia plant in 1984 using Texaco s coal gasification process [1161], [1173]. An energy consumption of 44.3 GJ/t NH3 is stated, which is lower than the 48.5 GJ/t NH3 quoted for another Texaco coal gasification-based ammonia plant [544]. 

The unconverted ammonium carbamate and unreacted ammonia have to be removed from the reaction mixture which consists of an aqueous solution of urea, ammonium carbamate and ammonia. The numerous industrial processes particularly differ in the way in which this separation and the recycling of ammonia and carbon dioxide are carried out, the minimizing of the energy consumption of these large plants (up to 1700 t urea/d) being crucial. 

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. "... 

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. 

These examples indicate why only detailed case studies may show the real energy consumption of an ammonia plant... 

The sequence of the remainii steps of synthesis gas preparation is CO shift conversion, removal of H2S and CO2 by Rectisol wash (cold methanol), and liquid nitrogen wash. As in other partial oxidation processes, the H2S is converted to elemental sulfur. Ube Industries, Japan, commissioned a 1,500-tpd ammonia plant in 1984 using the Texaco coal gasification process. An energy consumption of 10.9 Gcal/tonne of ammonia is stated this is lower than the normal quoted f ure of 11.6 Gcal/ tonne of NH3 for coal-based processes 131]. Another 1,000 tpd coal-based ammonia plant is scheduled for startup at Wehei, China, in 1996. 

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

The introduction of high-pressure reforming meant that the energy consumption of the ammonia S5mthesis could be decreased significantly (refer to Section 2.5) As a result, a munber of natural gas-based ammonia plants were built in the US, primarily by M.W. Kellogg in the mid-1960s [224] [312],... 

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