24 replies to this topic

[Arsal]

Is cetane number/cetane index improve form the distillation column by adjusting the draw off rate and temperature??

 

If cetane Index obtained form the distillation column is 45.Is any method to improve cetane index without adding improvers.

 

 

 

[gegio1960]

you can obtain a cetane improvement by optimizing the "diesel" extraction. of course, you have to take care of the other quality modifications, not only in diesel but also in the adjacent products of the tower.

you can improve the cetane of your tower cut only by further processing (eg de-aromatization, de-waxing).

maybe some else can be envisaged if you add operating info to your questions.

good luck

[P.K.Rao]

It all depends on the hydrocarbon type and nature of the crude mix (that is processed) and the fractions. Please find out the Cetane Index of Kerosene. If it has a CI of above 50, you can try blending in the diesel keeping a check on the flash point and kin viscosity requirements. If you are processing a mixture of crudes, find out which is crude is contributing to low CI and reduce its percent in the mix. Crude oils above 38 API yield diesels having 45+ CI. Hydrotreatment also improves CI. If you have high IBP paraffinic material (such as raffinate from xylene reformate) you can blend to improve the VI. Ofcourse, you have to keep a watch on  flash point and KV.

 

Alternately you can resort to extraction (NMP) as suggested.by  Gegio above (de-aromatization).

De-waxing .will reduce CI.

[gegio1960]

just a little clarification about dewaxing. I was referring to Catalytic Dewaxing, that is obtained thru hydrogen addition at relatively high pressure. the total effect, on a couple of plants working on North African crudes, that I've personally followed for years (as process designer, not as operator) is an increase of about 2 points on Cetane Index.

also de-aromatization is obtained with catalytic hydroprocessing at high pressures.

[P.K.Rao]

Yes, Gegio. Catalytic dewaxing (if it means converting aromatics to saturates/naphthenes) could help in improving CI. Solvent dewaxing reduces CI.

Edited by P.K.Rao, 22 September 2015 - 01:36 AM.

[Arsal]

Thankyou very much gegio and P.K rao.

 

Normally the cetane index of kerosene is found in the range of 43-45 while diesel have a CI of 50.As EURO 4 spec of diesel is 52(min).

 

so i have asked this question in this context that either we can obtained or improve CI without further processing.?

 

now i understand that if kerosene injection/blending reduces in the diesel then it might be helpful to increase CI.am i right or not??

[P.K.Rao]

Please, let it be clear. If the diesel blend (SR Gas oil + other components like kerosene) is having 50 CI, and kerosene is having 40-45 CI,  then lowering kerosene component in the blend will increase CI of the blend. However, if the diesel (ie, the SR gas oil component) has itself 50 CI, then lowering kerosene component in diesel blend will not be useful to improve CI of the diesel blend.

 

Please note that diesel can be a blend of several components like SR Gas oil, kerosene, LCO, heavy naphtha, etc. You can put any component in the blend provided the blend meets the requirements/specifications.

[P.K.Rao]

I will add a little more. If he diesel is a blend of several components, and you want to increase the CI of the blend, determine the CI of each component and reduce the quantity of the component having lowest CI in the blend.

[gegio1960]

rao arsalan,

could you kindly tell us the way you produce your 50 CI (or 45) diesel?

directly from an atmospheric distillation column?

from which crude?

how much is the yield of diesel with respect to crude fed to the tower?

do you combine/blend more than one cut?

[Arsal]

Crude is Arab light,

Diesel Yield : 22-23 %

Yes blending of kerosene and diesel has carried out to meet some specs.

 

I am also working how 50 CI of diesel obtained from tower. Normally i have studied that CI found in the range of 45-46 from arab light crude.whenever i found result of my study then i will be share with u.

[gegio1960]

Apart from CI, you can't obtain Euro4 diesel from the simple distillation of Arabian Light.

Your Straight Run Light Gasoil (SRLGO) cut will have a Sulphur content higher than 50 ppm.

So, I assume you will hydrodesulfurize your SRLGO, with a limited benefit on CI.

 

From an old ARL (simple) crude assay (2002), I can see a 22% yield on crude for a 220-340°C cut (approximate figures).

The relevant CI should be around 52.

Edited by gegio1960, 23 September 2015 - 03:37 AM.

[Arsal]

thankyou.i have find the results that the final product have a CI 52 and this is obtained after the blending of kerosene/HSD and LDO.however if i calculted the CI of pure diesel from distillation column it could be approximately 46 CI.As in CI corelation,it totally depends upon the 50 % boiling point and specific gravity.

[Napo]

Rao Arsalan,

 

Your quotation :" As CI correlation, it totally depends upon the 50% boiling point and specific gravity" is true for ASTM D-976, but if you employ ASTM D-4737, CI is function of four variables and sulphur content.

 

Napo.

[PingPong]

Rao Arsalan,

 

I think you are mixing up Cetane Number (CN) and Cetane Index (CI).

 

CN of a gasoil/diesel can be increased by adding improvers, however its CI cannot be improved that way, but only by hydrotreating. Hydrotreating also improves CN.

If the diesel CI from your existing HDS is too low then you need to revamp the HDS unit to increase CI.

 

However the CI spec of EURO 4 Diesel is not 52 but lower. Even CN spec is lower than 52. Get a copy of the spec that your diesel has to meet.

 

And as Napo already pointed out: you are using an old outdated (Two Variable Equation) method to calculate CI.

For EURO diesel you need to use EN ISO 4264 which is a Four Variable Equation, equivalent to ASTM D4737.

Edited by PingPong, 23 September 2015 - 01:52 PM.

[MJ94]

Dear Pingpong , Can you please explain why Cetane improver does not improve Cetane Index.

 

Also how is Cetane Index calculated? What is the relationship b/w CI and CN?

[P.K.Rao]

The property that governs the performance of diesel  in the engine is Cetane Number. Cetane number is determined with the help of CFR  Cetane Engine. Every country has a minimum specification for Cetane Number for the diesel matketed in their country. If the CN of straight Run diesel  or blend of diesel does not meet the specification, there are additives which can boost CN, like Iso Propyl Nitrate or Iso Amyl Nitrate.

Cetane Index is calculated from ASTM D 86 distillation and density and correlates with CN of diesel not containing cetane improver. Please see ASTM D 4737 Sections 1 and 4.

If cetane improver is added, Cetane Number will increase, but ASTM D 86 distillation and density results will not change. So Cetane Index will remain same as before but Cetane Number will increase because very small quantities of Cetane Imrover are enough  to increase Cetane Number but will not effect distillation and density.

That is the reason why Cetane Index is not effected by addition of Cetane Improver while Cetane Number increases.

[ioclanirban]

Dear P.K.Rao-sir, 

 

You wrote that "Cetane Index is calculated from ASTM D 86 distillation and density and correlates with CN of diesel not containing cetane improver."

 

My queries on this aspect are as under:

 

a) How does CN correlate with CIx? Is there a correlation? Could you please share the same?

How to find the CIx of a blend? Can we use linear blending method?

 

Thanks!

[gegio1960]

ioclanirban,

I assume your question is related to LP model developments (but it should be better you directly declare your scope)..

In this environment (after taking into account the explanations of PK Rao):

- you can assume CN = CI +2 (it's a rule of thumb derived by field observations)

- you can't blend linearly

[Nikolay_]

You can try equestion of blend's cetane index (CBI) 16.7+0.0571*CEI+0.01076*CEI^2 to build LP model. It's from PIMS reference, but I'm not sure if it's wrong or right because didn't use this.

[gegio1960]

Nikolai,

thank you for sharing the formula.

Anyway, are the CBIs blended by volume?

[gegio1960]

Just to add another refernce:

The book "Petroleum Refinery Process Economics" by R. Maples, reports the following correlation between CI and CN (referenced to Ethyl Corporation and to an ASTM research):

CN = 5.28 + 0.37*CI + 0.0112*(CI)²

Both this book and "Petroleum Refining - Technology and Economics" by Gary & Handwerk suggest a linear volumetric blending for CIs (as well as GRTMPS, the competitor of PIMS).

[Napo]

Hi,

 

Another reference:

 

Cetane Number = 7.624 + 0.841 Cetane Index

 

From:  "Diesel fuel quality and its relationship with emissions from diesel engines", Prepared for the CONCAWE Automotive Emissions Management Gropup" (search in the web).

 

Napo.

[Nikolay_]

Nikolai,

thank you for sharing the formula.

Anyway, are the CBIs blended by volume?

Hi,

 

I think by volume.

[robrt2]

Does anyone have this Maples correlations for Hydrotreatingunits

 

Just to add another refernce:

The book "Petroleum Refinery Process Economics" by R. Maples, reports the following correlation between CI and CN (referenced to Ethyl Corporation and to an ASTM research):

CN = 5.28 + 0.37*CI + 0.0112*(CI)²

Both this book and "Petroleum Refining - Technology and Economics" by Gary & Handwerk suggest a linear volumetric blending for CIs (as well as GRTMPS, the competitor of PIMS).

[Bobby Strain]

I'm sure if you search the web you will find what you seek.

 

Bobby