First catalyst bed

Fresh feed that has the proper hydrogen carbon monoxide ratio (i.e., slightly above the 3 1 minimum stoichiometric ratio) is mixed with recycle gas and sent through a heat exchanger and into the first catalyst bed, Stage I. The space velocity in Stage I is controlled so that all of the carbon monoxide fed to it is completely converted. The inlet gases are... 

Catalyst bed exit gas temperatures are also measured. They are indicative of each bed s S02 oxidation efficiency. First catalyst bed exit gas temperature is especially important. This bed s catalyst may overheat and degrade near the bottom of the bed. 

The calculations of this chapter are all based on feeding 1 kg-mole of dry gas into the acid plant s first catalyst bed. The kg-mole of each component (e.g. S02) in this feed gas are calculated by equations like ... 

The major part of the gas enters the vessel at the top and flows down as shell cooling gas. It then passes through the feed-effluent heat exchanger and flows upwards through a central pipe to the first catalyst bed, which is traversed from the inside to the outside. After the effluent from the first bed has been quenched with cooler recycle gas, it enters the second bed and passes through it in the inward direction. The cold gas enters through the bottom of the vessel and is mixed with the inlet gas to the first bed for temperature control. 

Further development of the radial flow concept used in the quench converter Topsoe Series 100 has led to the successful launch of the Topsoe Series 200 converter [623], [874], [898] - [904] designed for indirect cooling. Two versions are shown in Figure 92, with and without a lower internal heat exchanger. A cold shot ahead of the first catalyst bed is installed for temperature adjustment. In the converter without a lower... 

The trend followed in newer plants is to increase conversion per pass with the result of higher ammonia outlet concentrations and lower outlet temperatures from the last bed. However, as optimum energy efficiency of the whole ammonia plant requires maximum high-pressure steam generation, part of the heat must be recovered before the reaction is completed in the reactor system. This can be accomplished [900], [901], [930], [931] by using three catalyst beds in separate pressure vessels with boilers after the second and the third vessel and an inlet - outlet heat exchanger for the first catalyst bed. 

The Lurgi LPM process involves the same basic steps as the ICI processes. The two processes differ mainly in their reactor designs and the way in which the produced heat is removed as shown in Figure 12.18. The ICI design consists of a number of adiabatic catalytic beds, and cold gas is used to cool the reactant gases between the beds. The highest temperature is reached in the first catalyst bed. The Lurgi... 

A typical catalytic reforming unit consists of a number of fixed-bed reactors, frequently four, in series. The naphtha feedstock is vaporized and heated to the desired reaction temperature, then admitted to the first reactor. As the components in the naphtha undergo reaction during passage through the catalyst bed, the temperature of the vapor stream decreases by 70-100 C due to the endothermicity of the reaction. The major reaction occurring in the first catalyst bed is the dehydrogenation of cycloalkanes to aromatics. 

The optimum temperature of the second catalyst bed was determined with the first catalyst bed operating at 430°C but with 7% rather than 3% water vapor. The effect of the second reactor temperature on the sulfurous content of the final exhaust gases is shown in Figure 7, curves a and b. The results indicate that this second catalyst is more... 

Additional tests with 20 g of Surinam red mud in the double-bed catalyst were conducted with sulfur dioxide-rich gases, simulating a smelter gas. The temperature of the first reactor was 475 °C and that of the second was 230 °C. The inlet gas into the first catalyst bed contained 3.15% sulfur dioxide, 5.97% carbon monoxide, and 3% water vapor in helium. After several hours, the exhaust gas analyses from the sec-... 

The gas leaving the first catalyst bed may be at a temperature of 580 -600 C and must be cooled to a range of 420 -450 C to promote efficient conversion in the second bed because of unfavorable equilibrium at higher temperatures. Cooling may be done by injecting cool air or by heat exchange to produce more steam. Likewise, cooling between the second, third, and successive beds is required, but the temperature rise is less than that of the first bed. 

The filtration of molten sulphur is necessary in order to remove the small amount, less than 0.1 per cent, of solid matter. Any solid matter left may lead to deposits in the combustion chamber and the waste heat boiler that follows it. However the resultant ash is mainly deposited on the first catalyst bed in the form of very fine solids. These gradually accumulate and the resultant rise in pressure... 

If pressure drop is normal through the catalyst beds, this will be a tough question. With adequate instrumentation, you can obtain a vertical temperature profile through the first catalyst bed and then develop data to make a firm decision. Figure 5-2 illustrates the method. For catalyst that is in good condition, 90 + % of the heat of reaction is released in the top 6 in. If catalyst activity is impaired, the reaction is shifted down the bed. 

The carbon black deposited on the top of the first catalyst bed. Gas flow was restricted, and high pressure drop resulted. Providing sufficient combustion air to the reaction furnace could have prevented this incident. 

Burning a hydrocarbon with insufficient air produces sooty smoke. The soot deposits on the first catalyst bed. To do a thorough job of plugging a bed with this technique takes about eight hours. 

The structural parameters for S-200 type radial flow ammonia synthesis reactor with two beds of indirect heat exchange between beds and capacity of 1,000 t/d are as follows For the first catalyst bed the internal diameter, outer diameter and height are, 1.17m, 2.946 m and 3.425 m, respectively with the volume of prereducted catalyst Fri of 19.6m for the second bed the corresponding values are, 0.650m, 2.946 m and 7.925 m, respectively with the volume of imreduced catalyst Vr2 of 51.4m . The particle sizes of the catalysts are 1.5mm-3.0mm. The direction of gas flow is from outer to center. 

Table 8.8 Relationships of the temperature of inlet and outlet, and net yield of ammonia and adiabatic temperature rise at first catalyst bed for the Tops0e S-200 type radial-fiow converter using ZA-5 catalyst...

In an adiabatic fixed bed, the temperature at the outlet of the bed is determined by the temperature at the inlet, and hence the inlet temperature of first catalyst bed is particularly important. For example, based on computer simulation calculations, the relationships between the temperature at the inlet and outlet and net yield of ammonia and adiabatic temperature rise in first catalyst bed for the Topspe S-200 type converter using ZA-5 catalj t are shown in Table 8.8. The change in bed temperature with the temperature of inlet in the first bed is shown in Fig. 8.8. 

Hydrotreating catalyst particles are surprisingly small, with diameters of 1.5 to 3.0 mm and length/diameter ratios of 3 to 4. In many units, ceramic balls and/or successively larger catalyst particles are loaded on top of the first catalyst bed. This graded bed protects the bulk of the catalyst by filtering particulate matter out of the feed. 

The recycle compressor cannot overcome pressure drop across the unit. The overall pressure drop is the difference in pressure between the recycle compressor suction and the recycle compressor discharge. At start-of-run, the pressure drop across the catalyst is low - 3 to 10 psi (0.2 to 0.7 bar) for each bed - but it increases as the run proceeds. Usually, the increase is largest in the first catalyst bed, which is most susceptible to fouling. Attempts to continue rurming a unit despite very high pressure drop can deform the quench-deck support beams inside a reactor. 

Fig.10. Ammonia Synthesis. Effectiveness Factor (n) end NH3 Concentration in the Bulk (NH3,b) and in Centre of Catalyst Pellet (NH3,c) in First Catalyst Bed with 2.5-3mm Particles (cfr. Table 2, Case 1) ...

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