Q & A > Question Details
How do you calculate weight hour space velocity (WHSV)?
16/07/2009 A: Kavirayani R Murthy, K R Murthy Consultants, krmurthy_ipcl@yahoo.com
Weight hourly space velocity (WHSV) is defined as the weight of feed flowing per unit weight of the catalyst per hour. Since weight of the catalyst charged in to the reactor is not varied and always same, so any variation in flow of liquid per hour will change the WHSV. Inverse of the space velocity is contact time, i.e. how much time the liquid is in contact with the catalyst under the conditions of operation.
We know the quantity of the catalyst charged in to the reactor. For simplification of calculation, take 1 Ton = 1000 kg of catalyst . If 1000 kg of water is flowing through the reactor per hour then
WHSV = 1000 kg of feed per hour / 1000 kg of catalyst in the reactor = 1.0 i.e. WHSV is 1.0
Mostly when we deal with hydrocarbons, the density of hydrocarbons is less than 1.0
When we deal with Naphtha, density is 0.76 kg/kg
For Calculating WHSV 1.0, using naphtha as feedstock instead of water then 760 kg of naphtha flows over 1000 kg of catalyst (760 kg/ 0.76 density = 1 M3 per hour Naphtha). So WHSV =1
15/07/2009 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
WHSV is defined as the weight of feed per hour per unit weight of catalyst loaded in the reactor. If the feed rate is 100 tons per hour to the reactor having 100 tons of catalyst loaded in the reactor, WHSV is 1.0
WHSV= (Charge stock weight per hour/ Cat weight loaded in the reactor)
15/07/2009 A: Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
For hydrotreaters and hydrocrackers, space velocity is defined either in terms of LHSV [liquid hourly space velocity] or WHSV [weight hourly space velocity].
LHSV is calculated by converting rated BPSD into equivalent ft3@60F per hr, i.e. (BPSD times 5.615) divided by 24 hours per stream day. Next, the total volume of ACTIVE catalysts in the reactors is determined, also in ft3 generally by taking the cross-sectional area(s) of the reactors times sum of vertical heights of catalyst beds excluding top dressings and alumina support balls.
LHSV is determined by first converting BPSD into "metric tons per hour", i.e. BPSD divided by 6.29 times oil specific gravity at 60F [or with trivial error 15C] divided by 24 hrs per stream day. The ft3 of active catalyst is converted into metric tons by multiplying the loaded density of the catalyst in lbs per ft3 times ft3 of active catalyst and dividing by 2204 lbs per ft3. Naturally, this calculation can also be done in m3 active catalyst times loaded bulk specific gravity of the active catalyst. Typical loaded density depends upon whether sock loading or dense loading, with modern highly active and porous catalysts tending to fall between 45 lbs per ft3 sock loaded to 50 lbs per ft3 dense loaded. Some special catalysts may be less porous with "back-bone" other than silica-alumina and may have higher loaded densities.