Thermodynamic ammonia plant

Cremer, H. Thermodynamic balance and analysis of syngas and ammonia plant. ACS Symposium Series, Vol. 122, ASME Washington, DC, 1980. 

In 2001 Hyprotech and Synetix announced an ammonia plant simulation that can be used for modeling, on-line monitoring and optimization of the plant. The simulation includes Synetix reactor models, customized thermodynamic data and information to simulate the performance of a range of catalysts. The reactor models in the simulation include Primary and Secondary Reformers, High Temperature Shift converter, Low Temperature Shift Converter, Methanator and Ammonia Synthesis Converter80. 

Cremer, H., "Thermodynamic Balance and Analysis of a Synthesis Gas and Ammonia Plant", Thermodynamics Second Law Analysis, A.C.S. Symposium Series, 122, 111-120, 1980. 

The energy consumption figures discussed so far represent a thermodynamic analysis based on the first law of thermodynamics. The combination of the first and second laws of thermodynamics leads to the concept of ideal work, also called exergy. This concept can also be used to evaluate the efficiency of ammonia plants. Excellent studies using this approach are presented in [1061], [1062], Table 39 [1061] compares the two methods. The analysis in Table 39 was based on pure methane, cooling water at 30 °C (both with required pressure at battery limits), steam/carbon ratio 2.5, synthesis at 140 bar in an indirectly cooled radial converter. 

Reaction R-4.7, the water-gas shift reaction, is an exothermic reaction. The water-gas shift reaction has influence on the CO/H2 ratio in the gasification product, which is very important when the gas is used for synthesis purpose. Therefore, the shift process can be found in almost all the ammonia plants and hydrogen generation process in gas plants. The shift reaction can generally be taken into account using thermodynamic chemical equilibrium, since gas-phase temperatures are high. 

Thermodynamic Balance and Analysis of a Synthesis Gas and Ammonia Plant... 

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. 

Design of energy efficient ammonia plants therefore requires an accurate knowledge of the following thermodynamic properties at the actual operating conditions ... 

The modem process for manufacturing nitric acid depends on the catalytic oxidation of NH3 over heated Pt to give NO in preference to other thermodynamically more favour products (p. 423). The reaction was first systematically studied in 1901 by W. Ostwald (Nobel Prize 1909) and by 1908 a commercial plant near Bochum. Germany, was producing 3 tonnes/day. However, significant expansion in production depended on the economical availability of synthetic ammonia by the Haber-Bosch process (p. 421). The reactions occurring, and the enthalpy changes per mole of N atoms at 25 C are ... 

The problems associated with new synthesis gas processes are far greater than problems associated with gas processing plants or refineries because of water, salt, sludge, ammonia, and cresols present in the process streams. This paper attempts to identify the magnitude of the problems and methods for solving these problems. The problem of predicting the thermodynamic properties of nonpolar-polar mixtures by means of equations of state is also identified as an area needing study. 

There are two principal approaches to build OTEC power plants. The first approach called the open OTEC cycle involves a flash boiler to obtain steam directly from the warm surface ocean water. The open OTEC cycle requires a very large turbine. The second approach is called the closed OTEC cycle, which involves heat exchangers and a secondary thermodynamic working fluid such as ammonia or freon to reduce the size of the plant. 

There are six vapor working fluids listed on the menu of CyclePad. The fluids are ammonia, methane, refrigerants 12, 22, and 134a, and water. Water has the characteristics of items 4, 5, 7, and 8 above and it remains a top choice for industrial central vapor power plants. Hence, steam power engineering remains the most important area of applied thermodynamics. 

Process simulation is used to determine the size of equipment in a chemical plant, the amount of energy needed, the overall yield, and the magnitude of the waste streams. Because the results of process simulation depend upon thermodynamics and transport processes, the mathematical models are complicated and would be time-consuming to solve without a computer. This chapter illustrates the use of a process simulator, Aspen Plus, to model a plant to make ammonia. 

In the mid 1980s, a new thermodynamic power cycle using a multicomponent working fluid as ammonia-water with a different composition in the boiler and condenser was proposed (known as the Kalina cycle). The use of a non-azeotropic mixture decreases the loss of availability in a heat recovery boiler when the heat source is a sensible heat source, and in a condenser when the temperature decreases with heat exchange. Most heat input to a plant s working fluid is from variable temperature heat sources. 

Industrial fertilizer synthesis starts from ammonia synthesis, and ammonia is then easily oxidized in a separate reactor to nitric oxide over PtRh wire gauze catalyst. Formation of nitric acid requires further oxidation of nitric oxide to nitrogen dioxide (NO2) and absorption of the nitrogen dioxide in water. Overall, three different chemical process plants are used for the synthesis of nitric acid. The ammonia synthesis reaction takes place in a high-tem-perature, high-pressure reactor that requires recycling of products due to the thermodynamic limitations of chanical conversion. The ammonia oxidation reaction is very fast and takes place over a very small reactor length. Finally, nitric acid synthesis takes place in absorption columns. 

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