Q & A > Question Details
How H2/HC ratio is calculated? Our design value(in VGO Hydrocracker) is 843 at hydrotreater inlet .Is it just a ratio of H2 gas flow to VGO flow at hydrotreater inlet mixing point.
Shouldn't there be any factor of purity of recycle gas to be incorporated?
Is H2 gas flow & VGO flow should be temp. corrected values or it is just a ratio of the tags showing in DCS without temp. correction.
25/01/2014 A: Prabhakar Reddy Seerapu, SATORP, redi_nfcl@yahoo.co.in
Regarding the gas to oil ratio calculation,yes it is must to consider the H2 concentration in the recycle gas to calculate the ratio.we consider gas flow and get it multiplied with the H2 actual concentration available(online H2 analyzer) so as to calculate the gas to oil ratio.Generally it is expresses as NM3of H2/M3 of liquid feed.I am not sure of temperature compensation for flows, but for us we don't have any temperature compensation. We just take H2 purity,feed flow, Recycle gas flow and calculate the ratio.
13/11/2013 A: Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
Hydrogen to Hydrocarbon Ratio or Hydrogen Index should have been computed as moles per hour of contained hydrogen per mole per hour of oil entering the principal hydrotreater reactor inlet and hydrocracking reactor inlet.
Hydrogen Index really must be derived via building computer simulation model for at least the high pressure reactor section(s) and calibrating or validating this model against actual histypical operations.
Concurrently, this same model will yield vapor phase y,h2 at reactor inlets and outlets, taking into consideration chemical hydrogen uptakes. y,h2 is necessary for determining and then assessing actual hydrogen partial pressures at operational measured total pressure profiles.
Once the relationships among routinely measured parameters and Hydrogen Index and H2 PP are determined for typical operation, then approximation correlations might be generated based on available DCS outputs.
13/11/2013 A: Prashant Parihar, BPCL, pariharprashant@bharatpetroleum.in
H2/HC ratio referred as Gas/Oil ratio is calculated based on normal reference conditions of temperature and pressure (NTP) for expressing gas volumes (0 °C and 101.325 kPa) through ideal gas law.
Gas/Oil ratio = (Total gas to reactor)/(Total feed to reactor) [ (nm3/hr)/m3/hr]
H2 availability norms for hydrotreater suggest H2 availability expressed as (Gas/Oil ratio) / (Chemical H2 Consumption) should be > 6.
Increasing gas-to-oil ratio raises H2Partial pressure, reduces reactor outlet H2S concentration, increases unit activity and increases reactor pressure drop (ΔP).
13/11/2013 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
For the reactor inlet ratio:
1. Using the composition and flow rate of the combined hydrogen at the reactor inlet, calculate the moles / hour of pure hydrogen.
2. Estimate the molecular weight of the fresh feed by using specific gravity and points along the distillation curve.
3. Calculate moles / hour of fresh feed.
4. Calculate moles hydrogen per mole of fresh feed.