Normalized space velocity

Space Velocity. The space velocity is the ratio of the volumetric rate of gas at standard conditions to the volume of the catalyst. Generally, the percentage of ammonia in the existing gas decreases as space velocity increases however, the same volume of catalyst at the increased space velocities is capable of producing more ammonia (Fig. 4) (27). Normally space velocities for commercial operations are between 8,000 and 60, 000 h . ... 

In computer operations with other kinetic systems, Equation 8 may be used, and all the unique features of the kinetic system may be incorporated into the value of Q which may of course be a very complex expression. This technique is of interest only in that it simplifies the work necessary to analyze data using any specific kinetics for a chemical reaction. The technique requires sectioning the catalyst bed in most cases with normal space velocities, 50-100 sections which require 2-3 min of time on a small computer, appear to be sufficient even when very complex equations are used. 

An appropriate figure of merit to compare the performance of electrochemical reactors for effluents treatment is the normalized space velocity, which depends on the model assumed for the equipment. Thus, for a continuous stirred tank is given by... 

Resistance of electrical circuit, including busbars Linear polarization resistance Space-velocity Normalized space-velocity... 

Reforming Conditions. The main process variables are pressure, 450—3550 kPa (50—500 psig), temperature (470—530°C), space velocity, and the catalyst employed. An excess of hydrogen (2—8 moles per mole of feed) is usually employed. Depending on feed and processing conditions, net hydrogen production is usually in the range of 140—210 m /m feed (800—1200 SCF/bbl). The C —products are recovered and normally used as fuels. 

If using GHSV = 10,000 h" , the feed is, F = V GHSV = 20 (104) cm or 200 liters/h. Therefore, the 12.600 normal liters in the cylinder will be enough for 60 hours of operation. During these 60 hours, effects of temperature and conversion (by changing space velocity) can be studied at the one, given gas composition in the cylinder. 

Vapor space velocities normally should not exceed 100% of critical experience demonstrates that this keeps liquid entrainment into the flare line within acceptable limits. However, a velocity of 175% of critical is permitted when one is applyingthe 1.5 times Design Pressure Rule to remote contingencies,... 

For gaseous feeds, space velocity SV is normally determined in terms of volumes measured at standard conditions T = 25°C and P = 1.013 bar. 

Normally, catalytic reformers operate at approximately 500-525°C and 100-300 psig, and a liquid hourly space velocity range of 2-4 hr" Liquid hourly space velocity (LHSV) is an important operation parameter expressed as the volume of hydrocarbon feed per hour per unit volume of the catalyst. Operating at lower LHSV gives the feed more contact with the catalyst. 

Fig. 27. Effect of space velocity, cycle period, normality of the flushing liquid, and flush duration on S02 scrubbing from a simulated stack gas at 21°C employing a bed of BPL carbon (a) S02 removal, (b) S02 conversion to H2S04. (Figure reproduced from Metzinger et al., 1994, with permission, 1994 Elsevier Science Ltd.)...

NHSV Normal hourly space velocity [Nm3/h/m3 catalyst bed]... 

Frequently, particularly from the viewpoint of the technological application of a heterogeneous catalytic reaction, the conditions of experiments in a flow reactor are characterized by space velocity or contact time values. Space velocity, V, is the ratio to the volume of the catalyst bed of the volume of a gas mixture, reduced to the normal conditions (0°C, 760 Torr), passed through the reactor per hour. If the reaction involves a volume change, inlet and outlet space velocities should be distinguished. The reciprocal of V is of the dimension of time. Contact time ( conventional contact time), rc, is a value proportional to V l. It is defined as the ratio of the catalyst volume to the volume of the gas mixture passed per unit time, the gas volume being not under normal conditions but at temperature and pressure in the reactor. Usually, tc is expressed in seconds. It follows from the definitions given that... 

The space velocity for a given conversion is often used as a ready measure of the performance of a reactor. The use of equation 1.25 to calculate reaction time, as if for a batch reactor, is not to be recommended as normal practice it can be equated to VJv only if there is no change in volume. Further, the method of using reaction time is a blind alley in the sense that it has to be abandoned when the theory of tubular reactors is extended to take into account longitudinal and radial dispersion and other departures from the plug flow hypothesis which are important in the design of catalytic tubular reactors (Chapter 3, Section 3.6.1)... 

Mass-related reaction rates, tm, were determined at normal pressure for the following ranges of operating conditions T = 473 to 503 K, xc6h12 = 2-6 vol%, normal pressure conditions at both membrane sides, gas hourly space velocity (GHSV) 400-1000 h-1. The composition of the effluent was measured under steady-state conditions using gas chromatography (GC). 

Although multiplicities of the effectiveness factor have also been detected experimentally, these are of minor importance practically, since for industrial processes and catalysts, Prater numbers above 0.1 are less common. On the contrary, effectiveness factors above unity in real systems are frequently encountered, although the dominating part of the overall heat transfer resistance normally lies in the external boundary layer rather than inside the catalyst pellet. For mass transfer the opposite holds the dominating diffusional resistance is normally located within the pellet, whereas the interphase mass transfer most frequently plays a minor role (high space velocity). 

The application of the model of Wise et al. (195, 233) to determining deactivation rate constants encounters rather serious experimental limitations in that at low poison concentrations and space velocities, the breakthrough curves are very slow to appear, and the accurate measurement of sulfur concentrations in the ppm or ppb range is difficult. If activity decline of the catalyst for the reaction of interest could be related to the loss of sites by poisoning, a more direct measurement of deactivation rate would be realized. Bartholomew and co-workers (113, 140, 161) extended this model by expressing the rate of deactivation in terms of normalized activity a ... 

Determine column dimensions, pressure drop, and backwash requirements. In conventional water softening, an acceptable space velocity is usually between 1 and 5 gal/(min)(ft3) [8 and 40 m3/(h)(m3)]. In the present case, space velocity is (100 gal/min)/70 ft3 = 1.43 gal/(min)(ft3), which is within the normal range and thus is acceptable. 

If either space velocity or linear velocity had been considerably greater than the normal ranges, it would have been necessary to assign more resin. 

The volume hourly space velocity, in comparison with the vaporized hydrocarbon feedstock, is normally around 1600 to 2000 h for primary reforming. In high-pressure treatment (2.5 to 3.10 Pa absolute), they reach 5000 In post-combustion, which serves to reduce the quantities of residual methane in the dry gas to 0.1 to 0.3 per cent, the volume hourly space velocities range from about 2500 to 3000... 

The long chain ammonium salt and amine surfactants showed better selectivity and calculated MON s. The improvement in MON ranged from about 0.4 at an OSV of 0.08 V/Hr/V to more than 2 at 0.7 V/Hr/V. The space velocity was normally 0.077 and was cycled during the course of a run between this value and higher rates which were held until the product quality was steady. A comparison of selectivity to Cg s in the C fraction is shown in Figure 16. Octylamine was intermediate in its ability to improve selectivity while two of the surfactants which were anionic (FC-95 and FX-161), showed no improvement under well mixed conditions. In addition the tetramethylammonlum ion which is not surface active was also an ineffective additive. 

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