Volumetric hourly space velocity

VHSV = volumetric hourly space velocity WHSV = weight hourly space velocity... 

Both catalyst space velocity and bed geometry play a role. The gas hourly space velocity (GHSV) is used to relate the volumetric flow rate to the catalyst volume. GHSV has units of inverse hour and is defined as the volume flow rate per catalyst volume. 

The reactor feed may be preheated and the feed pressure may alter. The volumetric flowrate of gases depends on the reactor temperature and pressure at fixed mass flowrate. In many cases, the feed is liquid at room temperature, while the reaction mixture is a gas at the higher temperature in the reactor. In these instances, the performance of the reactor is represented as conversion and selectivity against the liquid hourly space velocity (LHSV). This is defined as... 

Note Typically in reformer design, liquid hourly space velocity (LHSV) is defined as fresh liquid charge volumetric flow rate divided by catalyst volume. Catalyst volume includes the void fraction and is defined by WJpp( — e).]... 

GHSV (gas hourly space velocity) = the volumetric flow rate of the product gases reduced to 25° C and 1 atm, divided by the bulk volume of the catalyst. ... 

As an aside, some authors use the term space velocity" such as, the liquid hourly space velocity, LHSV, the gas hourly space velocity, GHSV, the mass hourly space velocity, WHSV, or mol-volume space velocity, mol feed/hour litre of catalyst, MvolHSV. Unfortunately, the flowrates used in space velocity data are defined at conditions different from the typical reaction conditions. Thus, LHSV is measured at 20 °C GHSV, at 15 °C and 0.1 MPa. As an approximation, we can convert space velocity to residence time, in seconds, = 3600/(the hourly space velocity corrected to volumetric conditions using the temperature and pressure to reactor inlet conditions). 

GHSV Gas hourly space velocity it is used for gaseous feed stream with the volumetric flow rate expressed in term of volume per hours, thus GHSV has units per hour Glassy state A dense monolithic amorphous soUd state in which the atoms or molecules are not arranged in any regular order, as in a crystal, and which crystallizes only after an extremely long time... 

In industrial practice, the terms WHSV (weight hourly space velocity), LHSV (liquid hourly space velocity), and GHSV (gas hourly space velocity) are also used -defined as the ratio of the mass flow (WHSV) or volumetric flow (LHSVand GHSV, usually at STP) of the liquid or gaseous feed per volume of reactor. 

The operating conditions are represented by the Gas Hourly Space Velocity (GHSV) which is defined by the ratio of the volumetric flowrate at feed temperature to the volume of the monolith. 

Like the definition of the space time, the definition of the space velocity involves the volumetric flow rate of the reactant stream measured at some reference condition. A space velocity of 10 hr-1 implies that every hour, 10 reactor volumes of feed can be processed. 

The units of space velocity are the reciprocal of time. Usually, the hourly volumetric feed-gas flow rate is calculated at 60 °F (15.6 C) and 1.0 atm (1.01 bar). The volumetric liquid-feed flow rate is calculated at 60 F (15.6 °C). Space velocity depends on the design of the reactor, reactor inlet conditions, catalyst type and diameter, and fractional conversion. Walas [7] has tabulated space velocities for 102 reactions. For exanple, for the homogeneous conversion of benzene to toluene in the gas phase, the hoiuly-volumetric space velocity is 815 h . This means that 815 reactor volumes of benzene at standard conditions will be converted in one hoiu. Although space velocity has limited usefulness, it allows estimating the reaction volume rapidly at specified conditions. Other conditions require additional space velocities. A kinetic model is more useful than space velocities, allowing the calculation of the reaction volume at different operating conditions, but a model requires more time to develop, and frequently time is not available. 

In studying the kinetics of the homogeneous gas-phase reaction between sulfur vapor and methane, Fisher reported conversions for various space velocities. These space velocities were deflned as the volumetric flow rate in milliters per hour divided by the total volume of empty reactor in cubic centimeters. The flow rate is based on all the sulfur being considered S2 and is referred to 0°C and 1 atm pressure. 

Catalyst activity may be resided practically as the rate at which the reaction proceeds on the catalyst volnme charged to a reactor. The turnover number, or frequency, is the number of molecules of product produced by each active site per unit time under standard conditions. Because it is not practicable to calculate the active sites on a commercial catalyst, it is easier to measure the space-time yield (the quantity of product produced per unit volrrme of catalyst per unit time) during industrial operations. The space-time yield, or activity of a catalyst, determines the reactor size for a particular process. The ratio of volumetric gas flow per hour to catalyst volume under the design conditions chosen is known as the space velocity through the catalyst bed. 

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