This topic contains 6 replies, has 3 voices, and was last updated by Anonymous 11 years, 2 months ago.
November 4, 2010 at 1:54 am #2474
Please help me with some information regarding the possibility for density analyze on green coke. Our Lab personal say that is very difficult to determine the Coke from Delayed Coker Unit.(I really don’t think so?!)
What method is used for coke density determination? A link, a description of a method will be much appreciated.
Thank you very much in advance!
All the best,
November 4, 2010 at 11:53 pm #5422
ASTM-941-88, why you dont asking to the company that spent the coke?
November 25, 2010 at 8:52 pm #5389
D-4292, D-2638, D-6454 take a look
December 1, 2010 at 7:22 pm #5381
I belive the ASTM 941-88 is for spent coke off catalysts and doesnt relate to green delayed coke test. Since most coke on catalysts is burnt off to regenerate the catalysts about the only use would be to identify the stream coking out and spending the catalysts.
Delayed petcoke often runs both Bulk Density (~0.8 gm/cm3) – often called VBD for Vibrated Bulk Density, and Real Density (~2.06 gm/cm3) on Calcined Delayed Coke (~Anode or Sponge type and Needle coke is similar). I am not sure what purpose it would serve to run this test on green petcoke (both VM & HGI often correlate well with Bulk Densities).
Previous guest is right and ASTM D4292 is what is currently has been used for VBD but I understand this years TMS 2011 is presenting a paper on the ASTM D7454 that was approved by ASTM in 2008. It was proposed by Rio Tinto and uses semiautomatic equipment and tighter controls on sample prep.
The delayed coke particle size and crushing size have a strong effect on the VBD/Real Density results. Natural occuring particles tend to have higher packing density compared to particles crushed to same size. And most refinery crushing for green coke only goes to 6inches and down because every handling step tends to grind up big particles and customers dont want dust. Whereas CPC Anode/other applications often require controlled particle size with lots “fresh” crushed surface showing.
Both VBD/Real density test for CPC are really just indicators for Delayed Calcined Petroleum Coke (CPC) strength and porosity which determine how strong the baked anode for use Aluminum/other industries will be and also how much pitch it will soak up to make the prebaked anode block (usually about 60% CPC & 40% Pitch ratio). The higher porosity (ie holes left by Volatile Matter or Sulfur or Moisture being driven off from heat/calcining) means more pitch it will soak up. Now if you try do green cokes these poors will likely be filled with either uncooked resid or volatile matter which will go away when its calcined and hence give false or bad indication (also reason VM and HGI tend correlate). Also reason it isnt done on fuel cokes other than that market only cares about the BTU value – is that higher sulfur delayed cokes have higher decrease in density due lose of some sulfur on calcining that isnt seen on the -3.5% Sulfur CPC Anode cokes because most that sulfur is bound in petcoke matrix insteadk of fuel cokes where some exist as possible radical attached to matrix.
So your original statement is right – it wouldnt be that difficult to do a VBD/Real density test. The question is what use is it ? ……sort like putting doors on a motorcycle you can but why hell would you want to?
December 5, 2010 at 2:41 am #5371
Thank you for your input. So, if my understanding is correct there isn’t a real standard for determination of the green coke density. The only thing will remain to use a pycnometer, and to test the density of coke. Classic method for determine the solid matter with pycnometer.
I will make 20-30 density determination using this method on various piece of coke and I will make an average density for green coke that can be applied in our refinery.
The reason that I’m doing this is because I developed an automatic calculation for the coke mass and for be more accurate in my results I need two things:
1. A good measurement of the “empty of the coke drum”
2. A good density reference that will depend about the quality of the feed, parameters an other things like that.
@Charlie Randall, thank you for your post.Now I’m hoping to understand me why I need this sort of things.
All the best
December 5, 2010 at 5:00 am #5370
Again let me say slowly so you get it – there isn’t a standard and the test isnt ran because getting green coke density is ~ meaningless number. Yes, most solids from coal to natural & synthetic graphite to green petcoke ect can yield a density value from pycnometer but its not going to have reproducibility or repeatability for coking unit. You need to understand the materials property and operation a lot better before you use some half-cooked value to plug into calculation. There are enough screwed up LP models in this world already from engineers that have no idea what process or product is like.
The one thing I can guarantee is that your going to have meaningless number that wont help calculate whatever your trying to plug that number into & for whatever reason (doesnt sound like you even know what you want to use it for either).
If your just looking for a bulk density number to try calculate tons made in drum during cycle then you can use rough estimates of sponge coke at 46-52 lb/ft3 (on 10.0 mm average size particles), or shot coke at 52-65 lb/ft3 (on 1.0mm average size particles) or fluid coke at 63-72 lb/ft3 (on 0.1 mm average size particles) – I use these with angle repose to get max tons in petcoke storage piles as estimate.
Back to trying do green coke test – whenever someone wants get real values on petcoke for shipment or sales they take running sample from conveyor or loading method and then they composite & reduce it down and run test for metals, sulfur & ect. Lot times in refineries they just do grab samples off top truck/rail car/barge & do composite (its better nothing but just barely) – its ballpark for big problems but it isnt going be representative & most times clients take delivered samples or off vessel loading by independent surveyor & lab. So you just grabbing some different size coke particles isnt going to work & there can be lot difference from big pieces from coke packed in middle drum vs fluff small size particles at top vs average particles between. Every coke drum has distribution curve range on sulfur, volatile matter and hardness that is different, these and particle size affect petcoke density.
Let’s say the average works for your purpose – it isnt going to tell you much of anything about the next drum because the operating conditions, crude mix, run length and dozen other variables are going to shift the final VM, Sulfur and hardness. If your plant is lucky one with just couple crudes that are very consistent (most crudes are actually blends these days even ones like WTI or Brent), and you have big coker for size of Vacuum unit so it isnt pushed and same with your furnace – the average just might work……but you would be 1 in 100 plants.
There have been lots studies by calciners looking to use green density to get better control on calcined densities, there have been lots research groups looking at impact of changes in sulfur, VM and HGI upon final calcined densities and correlations were too fuzzy to use for controls. They often had better results using the VM & HGI values.
May 16, 2011 at 2:52 am #5091
Ask the company that spent the coke
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