Chemical Engineering May 2010 - 22

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asphaltenes) to about 50% diesel fuel,
15% naphtha and 30% vacuum gas-oil.
In the first stage, feed is slurried with a
proprietary nonmetallic additive in an
ebullated bed at 180-200 bar and more
than 400°C. The second stage employs
a standard nickel-molybdenum hydrotreating
catalyst in a fixed bed.
In contrast, conventional ebullatedbed
hydrocrackers achieve less than
80% conversion, and most fixed-bed
resid hydrocrackers obtain only about
20% conversion, says Anand Subramanian,
KBR's vice president of refining.
He adds that another advantage of
the VCC slurry-phase method is that
it avoids the fouling problem seen in
conventional ebullated-bed and fixedbed
hydrocrackers.
The economic threshold for VCC is a
crude price of $60/bbl, says Subramanian,
" and we believe the pressure on
crude prices will be only higher in the
future because of [tighter] supply and
demand. The technology was probably
invented way before its time, but now
its time has come. "
New process improvements
Despite the turndown and the decline
in the supply of heavy crude oil, the demand
for hydrogen has continued to be
robust, says David Burns, director of
global business development for hydrogen
with Praxair Inc. (Danbury, Conn.;
www.praxair.com). " The market for hydrotreating
has continued to increase
and we anticipate good future growth
for that market, " says Burns, who is located
in Houston. (For more on hydrogen,
see cover story, pp. 34-38.)
A relatively simple modification
that allows a refiner to increase H2
production from an existing steam
methane reformer (SMR) without
adding capacity is available from
Praxair.
Praxair's solution,
called
oxygen enhanced reforming (OER),
involves the injection of oxygen into
the SMR furnace to increase the O2
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22 ChemiCal engineering www.Che.Com may 2010
concentration in the combustion air
to 22-23%. This boosts the furnace
firing rate without exceeding process
limits and increases H2 production by
10-15%, says Gregory Panuccio, a development
associate with Praxair.
The additional O2 may be premixed
with the combustion air by a sparger
or injected into the furnace's combustion
zone by lances (usually one lance
per burner - see Figure 2). A sparger
requires a single penetration into the
air ductwork, whereas lances require
multiple penetrations into the furnace,
says Panuccio. However, a sparger
" slightly increases " the production
of thermal NOx (oxides of nitrogen),
while a lance installation will not.
Either system can be installed with
a one-day plant outage at a cost of
$500,000-$1.5 million, depending on
the configuration of the SMR. This
compares with $7-10 million for a prereformer
retrofit for a 100-million-scf/d
SMR, says Panuccio. The cost of incremental
H2 is similar to the baseload
H2 cost. Praxair has field-tested the
process on a 5-million-scf/d SMR and
plans to start up the first commercial
system, of similar size, next year.
In a related development, Praxair is
ready to commercialize a refinery gas
processor (RGP) that conditions refinery
fuel streams for the production of
H2 from an SMR. Panuccio notes that
refinery gases are often not suitable
for SMR feed without further processing
because their olefin content causes
coking of the SMR catalyst. The olefins
may be hydrogenated to paraffins
before going to the SMR, he says, " but
if the olefin content is 6% or more you
can't use traditional hydrotreating because
of the exotherm. "
Praxair's RGP solves this problem by
using a noble metal-based catalyst to
hydrogenate the olefins. The catalyst
can tolerate temperatures of more than
1,000°F, versus 700-800°F for a conventional
hydrogenation catalyst, says
Panuccio. The process has been tested
in a refinery at a scale of 5,000 scf/h, he
says, and the company is negotiating
with several potential customers.
Meanwhile, Air Liquide and its
Lurgi subsidiary are offering a new
generation of steam methane reformers,
designed to capture more CO2
from the offgas. The new SMRs will
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Chemical Engineering May 2010

Table of Contents for the Digital Edition of Chemical Engineering May 2010
