Ammonia conversion reactor

Fig. 3. compares the ammonia conversion for nanostructured vanadia/TiOa catalysts pretreated with O2 and 100 ppm O3/O2 gases. The reactions were conducted at 348 K for 3 h. No N2O and NO byproducts were detected in the reactor outlet. It is clear from the figure that higher vanadium content is beneficial to the reaction and ozone pretreatment yields a more active catalyst. Unlike the current catalysts, which require a reaction temperature of at least 473 K, the new catalyst is able to perform at much lower temperature. Also, unlike these catalysts, complete conversion to nitrogen was achieved with the new catalysts. Table 2 shows that the reaction rate of the new catalysts compared favorably with the established catalysts. 

Murase, A. H. L. Roberts and A. O. Converse. Optimal Thermal Design of an Autother-mal Ammonia Synthesis Reactor. Ind Eng Chem Process Des Dev 9 503-513 (1970). 

The reformer reactor performance as an ammonia cracker was evaluated. The experiments were conducted using a reformer feed composed of 6 seem ammonia. The reactor was heated with the electric heaters to determine the heater power required to achieve high conversion. In these experiments, approximately 97% of the ammonia feed was converted to hydrogen at 900 °C (approximately 1.8 W) when operating at atmospheric pressure. - °... 

Murase, Akira, Roberts, Howard L., and Converse, Alvin O., Optimal thermal design of an autothermal ammonia synthesis reactor, l EC Proc. Des. Dev. 9(4), 503 (1970). 

Modem ammonia synthesis reactors operate at -200 atm at -350°C and produce nearly the equihhrirrm conversion ( 70%) in each pass. The NH3 is separated from unreacted H2 and N2, which are recycled back to the reactor, such that the overaU process of a tubular reactor plus separation and recycle produces essentially 100% NH3 conversion The NH3 synthesis reactor is fairly small, and the largest components (and the most expensive)... 

Figure 3-17 Plot of eqdlibrimn convereion Xg vasus terr5)er-ature for ammonia synthesis starting with stoichiomeh ic feed. While the equilibrium is favorable at anbient tar5)erature (where bactaia fix N2), the convasion r dly falls off at elevated temperature, and commercial ammonia synthesis reactors operate with a Fe catalyst at pressiues as high as 300 atm to att 2 high equilibrium conversion.

To study the kinetics a flow-recirculating technique was employed, with a part of the experiments carried out in a differential reactor (at low ammonia conversions). 

In most radial-flow converters, the upper portion of the bed is sealed with excess, unused catalyst. This design prevents feed gas from by-passing the reaction section when the catalyst settles. The KAAP reactor uses a proprietary sealing system to overcome this problem. This sealing system avoids the catalyst maldistribution that can lead to formation of hot spots in the catalyst bed. The system also allows 100% of the loaded catalyst volume to be utilized for the ammonia conversion reaction203. 

The effect of feed composition cycling on the time-average rate and temperature profile was explored in the region of integral conversion in a laboratory fixed bed ammonia synthesis reactor. Experiments were carried out at 400°C and 2.38 MPa over 40/50 US mesh catalyst particles. The effect of various cycling parameters, such as cycle-period, cycle-split, and the mean composition, on the improvement in time-average rate over the steady state were investigated. 

Perhaps the first published analysis of an RFBR was by Raskin et al. (4), who developed a qua si continuum model for a radial ammonia synthesis reactor and later applied it to carbon monoxide conversion (5). 

Whether and how much a component in the entering reactant stream has any effects depend on its role in the reaction. In a study of ammonia decomposition in a counter-current microporous packed-bed membrane reactor, the inlet concentration of hydrogen greatly influences the decomposition rate. As expected from Figure 11.15, ammonia conversion increases as the hydrogen concentration in the feed stream decreases at a given temperature [Collins et al., 1993). On the contrary, the inlet nitrogen concentration... 

Another measure of the efficiency of ammonia conversion is the space velocity which may be used. Space velocity refers to the volume of reactants fed to a reactor per hour, divided by the volume of the reactor. For liquid reaction streams this relationship is straightforward. For gases, however, the space velocity is defined as being the volume of gases corrected to 0°C and 760 mm Hg (1 atm) passing through the reactor (or catalyst) volume/hour. This amounts to a measure of the gas-catalyst contact time for heterogeneous reaction (Eq. 11.7). 

The process takes hydrogen and nitrogen (in a 3 1 ratio) to make ammonia. The reactor is limited by equilibrium you will prepare the spreadsheet in stages to aid troubleshooting. Thus, first prepare a spreadsheet as shown in Figure 5.8, using 25 percent conversion per pass in the reactor. 

SYN 6.51 35 high-pressure ammonia synthesis reactor heat loss 1.09 MW the reactor is assumed to produce the total pressure drop of the ammonia plant i.e. from stream 32 to 1 2 the actual conversion is 1 6.3 of the real gas equilibrium at 673 K and 2l 0 bar... 

Urea melt is fed into the reactor and is atomized by spray nozzles with the aid of high-pressure ammonia. The reactor is a fluidized bed gas reactor using silica/aluminium oxide as catalyst. The reaction offgas, an ammonia and carbon dioxide mixture, is preheated and is used as fluidizing gas. Conversion of urea to melamine is an endothermic reaction the necessary heat is supplied via heated molten salt circulated through internal heating coils. 

The NEC (Nitrogen Engineering Co.) and TVA (Tennessee Valley Authority) —ammonia synthesis reactors are practical realizations of the above principles. Figure 11.3-5 of Sec. 11.3 schematically represents a TVA reactor. "ITie corresponding temperature profiles inside the tubes and in the catalyst bed section, calculated by Baddour, Brian, Logeais, and Eymery [26] are shown in Fig. 11.5.e-9. Reactor dimensions for the TVA converter simulated by Baddour et al. and also by Murase, Roberts and Converse [27] are... 

Experimental evidence of 100% conversion at 320 00 °C and hydrogen production in Pd-membrane reactors are reported. Simulation confirms that ammonia conversion in the membrane reactor increases with increasing pressure in the lower pressure range, temperature, flow rate of sweep gas, and reducing membrane thickness. ... 

Figure 18.7 (symbols) shows the ammonia conversions measured feeding to the reactor 500 ppm of NH3 and 500 ppm of NO2 while flowing oxygen (8 % v/v), water (8 % v/v), and balance helium. Experimental results are also compared with those obtained in the absence of NO2 in the feed stream. 

Figure III.3 Equilibrium conversion, constant rate, and energy balance curves for an adiabatic ammonia synthesis reactor (a) intermediate cooling and (b) cold feed injection.

T/year. Such a spectacular rise in reactor capacity is evidently tied to the growing market demand, but its realization undoubtedly also reflects progress in both technological and fundamental areas, pressed by the booming construction activity of the sixties and early seventies. Saturated markets and the construction of production units in newly industrialized countries have slowed down this capacity increase in the eighties. The present decade saw new spectacular developments. The utilization of remote natural gas and the associated transport problems has provided a new impetus to the development and construction of giant reactors for its conversion near the production sites methanol and ammonia synthesis reactors with a capacity of 1,600,000 T/year are now in use. 

Obviously, with a heat-exchanging line (c "), no intersection with (a) is possible, except at very low conversion, which is of no practical interest. The sensitivity of an ammonia synthesis reactor is well known to its operators. Thus, point Iir is chosen as a reasonable compromise. 

Perhaps the first published analysis of an RFBR was by Raskin, et al. ( ), who developed a quasicontinuum distributed parameter model for a radial ammonia synthesis reactor. General conclusions were limited, however, since the model was specifically concerned with ammonia synthesis and later carbon monoxide conversion ( ), where both processes are second order and reversible. However, these authors did note that "radial reactors are anisotropic", i.e., they observed higher ammonia yields for centripetal radial flow (CPRF " periphery to the center) than for centrifugal radial flow (CFRF — center to periphery) ( ). ... 

Reactor pressure an increase in total pressure increases the partial pressure of both hydrogen and ammonia. Conversion is enhanced by increasing hydrogen partial pressure and is lowered by increasing ammonia partial pressure. The hydrogen effect is greater than the ammonia one, and the net effect of raising total pressure is to increase conversion. 

The conversion reactor is selected from the object palette in Hysys. The percent conversion of ammonia is set to 100% as stated in the problem statements. The heat flow from the conversion reactor is shown in Figure 3.39. Peng Robinson EOS is used for property measurement. 

In a new case in PRO/II, the components involved are selected ammonia, oxygen, nitric oxide, and water. From the Thermodynamic Data in the toolbar, Peng-Robinson EOS is selected from the Most Commonly Used property calculation system. The Conversion Reactor is selected from the palettes in the PFD. A feed... 

From these values it is clear that if we could reach equilibrium at 1 atm and room temperature, we would have almost complete conversion to NH3 the equilibrium is very favorable for the reaction. Alas, the reaction rate at this temperature is fsO, and no catalyst is known that will make the reaction go at temperatures below about 300°C. (Fame and fortune await the student who can find one ) Most industrial ammonia synthesis reactors operate in the temperature range 350-520°C, at which the rates of the reaction are satisfactorily rapid (in the presence of a catalyst). At this temperature and 1 atm the calculated equilibrium concentration of ammonia is small enough to make the reaction completely impractical. Industrially, the reaction is conducted at high pressures, as discussed below. 

The temperature rise in the reactor depends on MeOH conversion and selectivity. The reactor exit temperature is typically at 400 to SOO C. The reactor effluent gases are condensed and stored for refining. Small amounts of noncondensablc CO, H2, and CH4 are vented from the condenser. The yield of the reactions is over 90 percent for both ammonia and methanol. Although the MeOH conversion is controlled at close to 100 percent, the ammonia conversion is dependent on the N/C ratio. The ammonia conversion is typically at 10 to 40 percent. The crude product in a conventional process consists of ... 

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