Hydrocarbon Processing - May 2022 - 30

Biofuels, Alternative Fuels and Green Petrochemicals
the industry can reduce the demand for
fossil fuels and reduce CO2
sulting companyb
emissions,
making the overall energy supply more
sustainable and cost-efficient.
Mechanical vapor recompression.
Dow Chemical participated in the " Power
to Products " project and chose to focus
on MVR. MVR, or in this case steam recompression,
is a good example of the
electrification of industrial energy demand.
It is also highly energy-efficient
because the residual heat is upgraded to
high-quality heat.
Dow Chemical was drawn to MVR
technology because of the availability of
low-pressure steam at its Terneuzen polyethylene
processing plant, even though
the supply is not constant-especially
during winter, when it is needed to heat
buildings and for steam tracing. In contrast,
there is excess when the plant is running
steam turbines or when buildings are
not heated during the summer. Typically,
Dow Chemical condenses excess lowpressure
steam, and the water is sent to
the boiler to create high-pressure steam.
In 2015, Dow Chemical collaborated
on a feasability study, executed by a conParameter
Capacity
P1
T1
P2
T2
Case
1
10
bara
°C
4.2
150
13.3
240
to use MVR to convert
heat from condensation to efficient energy.
Research revealed that there were
companies that already used MVR but at
a low-pressure level (1 bar-2 bar), such
as in the food or paper industries for heat
recovery. In most cases, the companies
used blowers. However, the Terneuzen
plant required higher pressures than these
blowers could achieve.
Dow Chemical contacted several
compressor manufacturers to explore
the potential of supplying the requisite
equipment for MVR. The equipment
partners suggested were between bearing
centrifugal compressors, reciprocating
compressors and integrally geared centrifugal
compressors (IGC). As a result
of these preliminary investigations, various
alternative feasibility studies were
conducted to analyze technical and economic
potential (FIG. 1).
The polyethylene (PE) plant at Terneuzen
uses water for reactor cooling. At
the end of the process, the cooling water
becomes low-pressure steam. Especially
during the summer, the demand for heating
is lower, which in some periods means
that part of the low-pressure steam from
TABLE. 1. Five potential cases for a future pilot from the 2015-2016 feasibility study
Units
tph
bara
°C
Case 2
50
4.2
150
13.3
240
Case 3
50
13
195
36
340
Case 4
50
4.2
150
36
340
Case 5
10
4.2
150
36
340
the PE plant cannot be used and must
be sent to the atmosphere or condensed.
During the initial research phase, it became
clear that MVR could be a good
solution to avoid this waste of energy by
uprating the steam to 12.5 barg or 35 barg.
Considering the low energy prices at
that time, the result of the 2015-2016
feasibility study showed that the MVR
project was less economically feasible for
the smaller flowrates, such as with Case 1
at 10 tons per hour (tph) (TABLE 1). From
an economic viewpoint, the most viable
case studies were those with 50 tph,
with Case 3 typically representing the
most feasible. However, Dow Chemical
wanted to test the MVR technology on a
small scale, with the prospect of possibly
including the technology in future PE
expansion projects.
Therefore, the key to deciding which
of the many case studies to use for the
MVR pilot project was to base the selection
on the preferred steam pressure level
rather than a more attractive flowrate. In
this case, it meant using the low-pressure
steam from the reactor cooling water that
supplies the 3.5 barg grid. This is used primarily
for process heating purposes and
upgrading it to the lowest pressure level,
which would result in less firing of the
auxiliary boilers and reduce fossil-fuel usage.
For this reason, even though 3.5 barg
(10 tph) was economically less attractive,
the lower pressure provided the best conditions
for the pilot's primary aim. The
MVR pilot project got underway in 2018.
Selecting integrally
geared compression
for MVR. MVR is an open-heat
pump system, and it requires a relatively
small amount of energy to increase compression
pressure and temperature. Several
compressor manufacturers mentioned
in the feasibility study could produce a
suitable compressor, but after a detailed
evaluation, the co-authors' companya
awarded the order. The companya
was
has
more than 30 yr of experience in the steam
compressor field and can design each
compressor to meet specific process and
control requirements.
The companya
was chosen primarily
FIG. 4. The compressor installation inside the Terneuzen plant.
30 MAY 2022 | HydrocarbonProcessing.com
for its proposed solution for an integrally
geared centrifugal compressor, with its key
characteristic of an overhung arrangement
of the impellers on the pinion shaft ends.
One pinion shaft is designed for one or
two opposing compressor stages. In this ar
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