Encyclopedia of Environmental Science and Engineering, Volume I and II

414 FOSSIL FUEL CLEANING PROCESSES

schematically represents a general fl owsheet for crude oil pro-

cessing. Crude oil, as received from the source is fi rst atmo-

spherically distilled. Light ends and mid-distillates from this

operation are further processed to yield gasolines and kero-

sene. Atmospheric residuum can be directly used for No. 6

fuel oil, or further fractionated ( in vacuo ) to produce vacuum

gas oil (vacuum distillate) and vacuum residuum. After atmo-

spheric distillation, the average crude contains about 50% of

atmospheric tower bottoms, which is nominally a 650F^ ^ oil.

The vacuum distillation yields roughly equal parts of vacuum

gas oil and vacuum residuum. The bottoms from this unit is

nominally a 975F^ ^ oil, although the exact cut point will vary

for each vacuum unit.

Desulfurization of vacuum residuum would be appli-

cable where a refi nery has use for the virgin vacuum gas

oil other than fuel oil, and sulfur restrictions or increased

prices make desulfurization of vacuum bottoms attractive.

Another situation is where desulfurizing the vacuum gas oil

and blending back with vacuum bottoms no longer produces

a fi nal fuel oil meeting the current sulfur specifi cation.

Present in the residuum (vacuum) is a fraction known

as asphaltenes. This portion is characterized by a molecu-

lar weight of several thousand. The majority of the organo-

metallic compounds are concentrated in the asphaltene

fraction. Although many of the metals in the periodic table

are found in trace quantities, vanadium and nickel are usu-

ally present in by far the highest amounts. Residual oils from

various crudes differ from each other considerably in regard

to hydrodesulfurization. These differences reside to a great

extent in the asphaltene fraction.

Light Oil Desulfurization

The G O-Fining Process The G O-Fining process is designed

for relatively complete desulfurization of vacuum gas oils,

thermal and catalytic cycle oils, and coker gas oil. It represents

an extremely attractive alternative where a lesser degree of

sulfur removal from the fuel oil pool and/or a very low sulfur

blending stock is required. The feed to the G O-Finer System

is atmospheric residuum. This stream is vacuum fractionated

and the resulting vacuum gas oil (VGO) is desulfurized using

a fi xed bed reactor system. Resultant VGO is then reblended

with vacuum bottoms to yield a desulfurized fuel oil or used

directly for other applications. Figure 2 shows quantitative

breakdown of various process streams for a 50,000 barrel per

stream day (BPSD) operation utilizing a 3% sulfur Middle

East atmospheric residuum feed. The process has the capa-

bility of producing 49,700 BPSD of 1.72% S fuel oil.

There are currently a number of G O-Fining units in

commercial operation.

Investment and operating costs will vary depending on

plant location and crude stock characteristics, but for many

typical feedstocks (basis 50,000 BPSD) total investment is

about 16.3 million dollars and operating costs average out at

60¢/barrel fuel oil (1989).

UOP ’ s gas desulfurization process Another light oil desul-

furization process is UOP’s gas oil desulfurization scheme.

Unlike the previously discussed G O-Fining process, UOP’s

scheme (already commercial) is designed for almost complete

(
90%) desulfurization of a 630 to 1050; F blend of light and

vacuum gas oils (approximate sulfur content of feed—1.5%).

Vacuum residuum is neither directly nor indirectly involved

anywhere in the process.

In almost all other respects, however, UOP’s process

parallels G O-Fining. The current plant facility is of 30,000

BPSD capacity with above mentioned feed.

Comparison of UOP and G O-Finer costs show that both

are of the same order of magnitude and differ markedly only

in initial capital investment. This is in part attributable to the

fact that a G O-Fining facility requires atmospheric resid-

uum fractionation whereas UOP’s does not.

Stocks of high-sulfur content are diffi cult to crack cata-

lytically because all or most of the catalysts now in com-

mercial use are poisoned by sulfur compounds. In recent

years the trend has been toward processes that remove these

sulfur compounds more or less completely. The high sulfur

1100°F Vacuum Bottoms

16,600 BPSD

4.2 wt % s

A B

700–1100°F VGO

33,400 BPSD

2.33 WT % S

MIDDLE EAST

700°F + RESID

50,000 BPSD

3.0 WT % S

33,100 BPSD

0.3 WT % S

400°F +

Desulfurized

Fuel Oil

1.72 WT % s

THE GO–FINING PROCESS

FIGURE 2

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