Ammonia pressure drop

The possible remedial and preventive actions are hot soaks and drains during cooldown to help remove soluble deposited material, chemical cleaning to remove corrosion products and reduce the pressure drop (see Metal surface treatments), and reduced corrosion product transport into OTSG using amines other than ammonia in feedwater (14). 

Example 35.1 An ammonia compressor is rated at 312 kW with saturated suction at -15°C. It is installed with a very long suction line, causing a pressure drop of 0.4 bar, and picks up 6 K superheat from its evaporator condition. Estimate the capacity loss. 

In a synthetic ammonia plant the hydrogen is fed through a 50 mm steel pipe to the converters. The pressure drop over the 30 m length of pipe is 500 kN/m2, the pressure at the downstream end being 7.5 MN/m2. What power is required in order to overcome friction losses in the pipe Assume isothermal expansion of the gas at 298 K. What error is introduced by assuming the gas to be an incompressible fluid of density equal to that at the mean pressure in the pipe /r — 0.02 mN s/m2. 

The homogeneous mixture model is the simplest method for ealculating the frictional two-phase pressure drop, and has been found by Ungar and Cornwell (1992) to agree reasonably well with their experimental data representing the flow of two-phase ammonia in channels with d = 1.46—3.15 mm. 

Ungar EK, Cornwell JD (1992) Two-phase pressure drop of ammonia in small diameter horizontal tubes. In AIAA 17th Aerospace Ground Testing Conference, NashviUe, 6-8 July 1992 Wallis GB (1969) One dimensional two-phase flow. McGraw-Hfll, New York Yang CY, Shieh CC (2001) Flow pattern of air-water and two-phase R-134a in small circular tubes. Int J Multiphase Flow 27 1163-1177... 

In our calculation we assume that the gas mixture approaches equilibrium under conditions where the pressure is constant. This situation corresponds, for instance, to a volume of gas moving through a plug flow reactor with a negligible pressure drop. (Note that if the ammonia synthesis were carried out in a closed system, the pressure would decrease with increasing conversion.)... 

The dilution to threshold was before 3604 and after 232, reduction 94%. The ammonia was before 5 ppm and after 0, 3 ppm, reduction 94%, measured with Draeger tubes. The pressure drop over the biobed of the mixture of vibrous peat and heather was 5mm WK. In the tube between the breeding house and the biobed there is a sackfilter installed to remove sawdust, that otherwise should clog the under layer of the bed. 

Reaction (13.2) is highly undesired because SO, reacts with water present in the flue gas in large excess and with ammonia to form sulfuric acid and ammonium sulfate salts. The ammonium sulfate salts deposit and accumulate on the catalyst if the temperature is not high enough, leading to catalyst deactivation, and on the cold equipment downstream of the catalytic reactor, causing corrosion and pressure drop problems. The catalyst deactivation by deposition of ammonium sulfate salts can be reversed upon heating. 

The effectiveness is a measure of the utilization of the internal surface of the catalyst. It depends on the dimensions of the catalyst particle and its pores, on the diffusivity, specific rate, and heat of reaction. With a given kind of catalyst, the only control is particle size to which the effectiveness is proportional a compromise must be made between effectiveness and pressure drop. In simple cases t] can be related mathematically to its parameters, but in such important practical cases as ammonia synthesis its dependence on parameters is complex and strictly empirical. Section 17.5 deals with this topic. 

Nitrogen at 12 MN/m2 pressure is fed through a 25 mm diameter mild steel pipe to a synthetic ammonia plant at the rate of 1.25 kg/s. What will be the pressure drop over a 30 m length of pipe for isothermal flow of the gas at 298 K Absolute roughness of the pipe surface = 0.005 mm. Kilogram molecular volume = 22.4 m3. Viscosity of nitrogen = 0.02 mN s/m2. 

The steam requirements in an ammonia unit can be reduced by lowering the steam-to-carbon ratio to the primary reformer. However a number of drawbacks can exist downstream in the I I I S and LTS reactors. The drawbacks include By-product formation in the HTS, Pressure drop buildup in the HTS, Reversible poisoning of the LTS catalyst, and Higher CO equilibrium concentrations exiting the HTS and LTS reactors. 

The particle size and shape of commercial ammonia catalysts are determined mainly by two parameters a) the catalyst performance and b) the pressure drop. From the standpoint of space-time yield, it is desirable to use the finest possible particle, which is about 1-2 mm. However, with decreasing particle size, the pressure drop increases and the danger of destructive movement of the catalyst increases74. 

Two effects cause the low production capacity of large-grained catalyst. First, large grain size retards transport of the ammonia formed inside the catalyst into the bulk gas stream. This is because the ammonia transport proceeds by slow diffusion through the pore system. The second effect is a consequence of the fact that a single catalyst grain in the oxide state reduces from the outside to the interior of the particle. The water vapor produced inside the catalyst by reduction comes into contact with already reduced catalyst on its way to the outer surface of the catalyst. This induces a severe recrystallization. As an example, if the particle size increases from about 1 to 8 mm, the inner surface decreases from 11 to 16 m2/g to 3 to 8 m2/g74. Therefore the choice of catalyst requires the optimization of 1) catalyst size versus catalyst activity, 2) catalyst size versus pressure drop across the converter and 3) the impact of 1 and 2 on... 

The first application in 1992 used a two-bed, hot-wall KAAP reactor that featured a low pressure drop and radial flow. Because of the KAAP catalyst s high activity, thin beds are necessary to keep operating temperatures within the desired range203. In 2002 the KAAP reactor had evolved to a four-bed design. A magnetite catalyst is used in the first bed of the synthesis loop when the ammonia concentration is below 2% of the feed. Then the ruthenium catalyst is used in the next three beds to bring the ammonia level up to 18% or more215. 

Haldor Topspe s ammonia synthesis technology is based on the S-200 ammonia converter. This is a two-bed radial flow converter with indirect cooling between the beds. Features of the S-200 include efficient use of converter volume and low pressure drop (factors related to the use of small catalyst particles 1.5 to 3.0 mm), and high conversion per pass due to indirect cooling85. 

The choice of particle size and shape of commercial ammonia catalysts is determined mainly by the catalyst performance and the pressure drop. From the standpoint of space-... 

Selection of the laboratory reactor requires considerable attention. There is no such thing as a universal laboratory reactor. Nor should the laboratory reactor necessarily be a reduced replica of the envisioned industrial reactor. Figure 1 illustrates this point for ammonia synthesis. The industrial reactor (5) makes effective use of the heat of reaction, considering the non-isothermal behavior of the reaction. The reactor internals allow heat to exchange between reactants and products. The radial flow of reactants and products through the various catalyst beds minimizes the pressure drop. In the laboratory, intrinsic catalyst characterization is done with an isothermally operated plug flow microreactor (6). 

The ammonia synthesis loop uses two ammonia converters with three catalyst beds. Waste heat is used for steam generation downstream the second and third bed. Waste-heat steam generators with integrated boiler feedwater preheater are supplied with a special cooled tubesheet to minimize skin temperatures and material stresses. The converters themselves have radial catalyst beds with standard small grain iron catalyst. The radial flow concept minimizes pressure drop in the... 

Megammonia A process for making ammonia. It uses oxygen instead of steam, and novel axial-radial reactors that reduce pressure-drop and catalyst quantities. Developed by Lurgi Oel-Gas-Chemie and Ammonia Casale, for which they received the AstraZeneca Award for Green Chemistry in 2003. 

According to the ambiguous instructions written in the log for the operator, he should have pressured up the ammonia condenser to compressed air system pressure. Next, ho should block off the air supply and discharge ammonia fumes into the atmosphere. The operator pressurized the ammonia-laden condenser to full air system pressure, but unfortunately did not block it off. Therefore at the beginning of the day when the arriving maintenance mechanics and operators put a high demand on the air system, the condenser acted as a surge tank. As the system pressure dropped, undesirable ammonia fumes traveled to the sandblaster s hood. 

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