AMMONIA PLANT DESIGN

Due to increased feedstock costs, some new ammonia plant designs use fuel more efficiently but their capital cost may be higher. The recovery of the hydrogen and ammonia from the synthesis purge gas by a cryogenic unit or a membrane system results in an ammonia capacity increase of about 5%57. 

Substantial improvements have been made in the energy efficiency of CO2 removal systems. The first large-scale ammonia plants in the 1960 s typically used monoethanolamine (MEA) as a solvent. Energy input was over 50,000 kcal/kg-mol of CO2 removed. In 2001 plants use improved solvents and designs that can reduce the energy input to about 10,000 kcal/kg-mol of CO2 removed57. 

A large ammonia plant in 2001 is more fuel-efficient than plants that were built in the 1970 s and 1980 s. A typical world-scale plant that was built in the 1970 s consumed about 42 billion BTU of natural gas per tonne of ammonia produced. Retrofitting such a plant to improve fuel efficiency can reduce gas consumption to about 36 million BTU per tonne. Ammonia plants that were built in the late 1990 s use only about 30 million BTU per tonne of ammonia, are easier to operate and have slightly lower conversion costs. Some new plants also recover more than one million BTU per tonne by generating electricity from waste heat57. 

Hpn 6JB. Block diagram of1,000 tonne/dayammontt plant. (Reproducedbypentusiion of Johns on Matthey Catalysts. Copyn xtJohnaonMattheyPLC.) 

Some of the ammonia process technologies that are available include KAAP/ /m.s , Haldor Topspe, LAC (or Linde Ammonia Concept), LCA (or Leading Concept Ammonia), Ammonia Casale, and Uhde. 

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The choice of a specific CO2 removal system depends on the overall ammonia plant design and process integration. Important considerations include CO2 sHp required, CO2 partial pressure in the synthesis gas, presence or lack of sulfur, process energy demands, investment cost, availabiUty of solvent, and CO2 recovery requirements. Carbon dioxide is normally recovered for use in the manufacture of urea, in the carbonated beverage industry, or for enhanced oil recovery by miscible flooding. 

Dehydration. Use of molecular sieve driers for final clean-up of the carbon oxides and water in the synthesis gas to less than 1 ppm levels has gained prominence in low energy ammonia plant designs. The sieves are usually located at the interstage of the synthesis gas compressor to reduce volume requirements. The purified make-up gas can then be combined with the recycle and routed direcdy to the converter. 

The example CO2 capture process, shown in Figure 8 as an Aspen Plus EO model representation, is part of an ammonia plant. Designed to scrub CO2 from ammonia synthesis gas, it includes an absorber and two solution regeneration columns, one stripping the rich, C02 laden solution leaving the absorber to semilean concentration of absorbed CO2, and the other cleaning the solution even further to lean solution... 

The Topsoe Low Energy Ammonia Process is flexible and can be adjusted to specific project requirements. Most operating ammonia plants designed by... 

Ammonia Converter Design - Today all low-energy designs use indirectly cooled converters. The design and layout offered by various ammonia plant designers differ considerably. Kellogg s Horizontal Converter and Topsoe s Series 200 Converter use two catalyst layers with an intermediate heat exchanger for... 

The KAAP ammonia plant design has the following technical features ... 

To examine how this has been achieved, the following aspects of ammonia plant design will be examined ... 

W. A. Zech, Centrifugal Compressors for Ammonia Plant Design and Operation Considerations, Proc. Meet. UNIDO-FAI Saf. Des. Oper. Ammonia Plants, Paper V (1976). 

In more leoent ammonia plant designs, in which the large steam reforming furnace has been leplaeed with -heated reformers or combined autothermal reformers, the HTS eatalyst ean be leplaeed by a temperature resistant copper catalyst that can operate at temperature as low as 260°-270°C. 

Dybkjaer, I. 1990. Advances in ammonia production technology. Lyngby Haldor Topsoe Dybkjaer, I. 1992. Large ammonia plants design and operating experience. Paper presented at the 1992 IFA-FADINAP Regional Conference for Asia and the Pacific, Bali, November 30-December 2, 1992. 

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