Hydrocarbon Processing - June 2022 - 23

Process Optimization
Lower traffic in the VPI process also
results in significantly lower xylene
losses. Overall energy credits and material
balance credits are summarized in
TABLE 1. In the base case, prior to adding
the LPI process, the complex operates
with EB-reforming VPI only at design
capacity. When LPI is added, the EBreforming
VPI process is set at turndown
capacity to maximize the benefits
of LPI implementation, which sets the
size and feed processing capacity of the
LPI unit. At constant PX and orthoxylene
production, the xylene-loop feed
consumption is cut by ~3%. Another
way to substantiate this improvement
would be to increase PX production by
~3% at constant feed consumption. Further,
and still at constant PX production,
electricity consumption decreases by 6%
and fuel gas consumption decreases by
2%. The overall PX production cost is
reduced by 4% on a $/t basis, and GHG
emissions are decreased by 11% on a
1 t CO2
equivalent/t PX basis. It is worth
pointing out that, in an existing facility
such as in Case Study 1, the low capital
expenditure investment for the LPI addition
can be further reduced by revamping
onsite equipment, such as converting
a clay treater into an LPI reactor or by reusing
the previous heat exchanger and/
or feed heater, if available. Another important
fact is that, at constant PX production,
the benefits (such as reduced
energy consumption in the reformer and
reduced reformate splitter duty) extend
well beyond the xylene-loop improvements
listed in TABLE 1.
Case Study 2: Process flow scheme
integrating an EB-reforming VPI process
and LPI process in the design
of a grassroots aromatics complex.
The flow scheme of this planned facility
is depicted in FIG. 3. One of the main
objectives for the proposed plant was to
minimize benzene production-therefore,
EB-reforming VPI was suggested to
maximize PX. Reformate and transalkylate
feed a single xylene loop comprising
a xylene column, an adsorption unit and
TABLE 1. Feed consumption and energy consumption reduction achieved by the
addition of two LPI units in an existing facility operating two xylene loops in parallel
Case Study 1
Xylene loop feed consumption
(reformate, transalkylate)
PX production
Orthoxylene production
Electricity consumption
Fuel gas consumption
PX production cost, $/t
GHG emissions, 1 t CO2 equivalent/t PX
EB-reforming VPI only
Base
Base
Base
Base
Base
Base
Base
EB-reforming VPI + LPI
97%
100%
100%
94%
98%
96%
89%
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Hydrocarbon Processing | JUNE 2022 23

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Hydrocarbon Processing - June 2022

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