Introduction

Hydrogen is essential for the upgrading of bitumen and heavy oil. These heavy crudes are hydrogen deficient (or carbon rich) and require significant modification to their molecular structure and hydrogen to carbon ralio to be useful as refinable crude oil or transportation fuels. This is best illustrated by Figure 1 which shows the distribution of hydrogen/carbon (H/C) ratios for various hydrocarbons. The important numbers for us are oil sands bitumen and heavy oils at 1.5, conventional light crudes and synthetic crude at 1.6 to 1.7 and transportation fuels at 1.9 to 2.0. Somewhere in the processing of bitumen this H/C ratio must be raised from 1.5 to almost 2.0. This is generally done through combinations of processing steps involving hydrogen addition carbon rejection. Because of the yield penalties with carbon rejection, this H/C ratio adjustment is best achieved through hydrogen addition.

A few simple calculations can be used to illustrate the hydrogen requirements in upgrading. These calculations are not meant to substitute for proper elemental mass balances based on actual yield data but they are an excellent way of putting the chemistry in perspective. The hydrogen addition required to raise the H/C ration from 1.5 in the feed to 1.9 in the products is 2 wt% or 1330 scf/bbl.

Equations (available in full paper)

To achieve the same H/C ratio by carbon rejection would result in rejecting 21 wt% of the carbon in the feedstock.

Equations (available in full paper)

In real upgrading processes the chemistry is not quite as simple. Coke and pitch residues are carbon rich and also contain unreacted sulphur oxygen and nitrogen so the hydrogen consumption is somewhat less for this fraction than the average calculated above. Conversely the hydrocarbon gases produced by the cracking reactions are hydrogen rich and consume a disproportionate amount of hydrogen.

If we assume that the typical hydrocarbon gas make of 5 wt% is equally distributed between C1, C2 and C3 saturates, the average H/C ration is 3.22. A 5 wt% gas make would consume a further 610 scf/bbl.

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These simple generalized calculations illustrate Why high conversion hydrocracking processes typically consume over 2230 scf/bbl or 3.4 wl% hydrogen. This number will be lower for lower conversion carbon rejection processes or lower quality synthetic crude oil. Hydrogen consumption will increase with lower H/C feedstocks such as coal or wilh the higher gas make rom extensive hydrocracking of products or very high conversion levels.

Can you upgrade without hydrogen addition﹖ Yes, but you get what you pay for. Partial upgrading with no hydrogen addition generally provides low conversion of residue, iow liquid yield and poor qualily products. Table 1 lists the yields and conversion for a number of low or no hydrogen addition processes.

Equations (available in full paper)

There may be advantageous niches for such processes. For example the viscosity reduction may allow direct pipeline shipment to a specific refinery.

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