Hydrocarbon Processing - December 2020 - 24
Plant Design, Engineering and Construction
autothermal-only reforming plant. The plant-which originally
required a feedstock provided by nearby conventional steam re-
A plant originally dependent on a
hydrogen-rich feed from a nearby steam
methane reforming facility can now
operate independently through minimal
investment modification.
forming facilities (an imported hydrogen-rich stream) and fresh
natural gas-is now capable of operating in a standalone condition; specifically, this plant has become independent of any
feedstock from the nearby conventional reforming facility, and
the design change applied is unique among plants of this kind.
Chile 4 original design. Chile 4 is a 2,400-metric-tpd, oxygen-based methanol plant at Cabo Negro, Punta Arenas, Chile.
The plant has four main processing units, including:
* Natural gas preparation and reforming: Natural gas
compression, feed gas hydrogenation and desulfurization,
saturation and reforming (via an oxygen-fed autothermal
reformer)
* Methanol synthesis: Makeup and recycle compression,
methanol reactors and outlet gas cooling
* Methanol distillation: Degassing, topping column and
refining distillation columns
* Air separation unit: A 1,600-metric-tpd (99.5% purity)
oxygen plant.
In the reforming unit, synthesis gas is produced from natural
gas and purge gas from the adjacent Chile 1-3 methanol plants
(hydrogen-rich stream). The availability of external purge gas as
additional process feed allows the application of a single autothermal reformer-only reforming step to produce the synthesis
gas (FIG. 2).
Oxygen
Natural gas
Synthesis
gas
Reforming
Synthesis
Crude
methanol
Distillation
Methanol
product
Imported purge gas from
Chile 1, 2 and 3 methanol plants
FIG. 2. Integrated methanol production in Chile 4 (original design).
Natural gas
Hydrogen
Synthesis
gas
Reforming
Tail
gas
Synthesis
gas
Synthesis
Crude
methanol
Distillation
Methanol
product
Purge
gas
Pressure swing
adsorption
FIG. 3. Chile 4 standalone methanol production (adapted) block flow
diagram.
24
DECEMBER 2020 | HydrocarbonProcessing.com
Chile 4 plant modification. This plant incorporates design
features that result in a very efficient plant in terms of natural
gas consumption, but it does require additional feedstock imported from a nearby conventional steam
reforming plant (i.e., Chile 1). This extra feedstock
is a portion of the synthesis loop purge gas, which
is a hydrogen-rich stream. This additional hydrogen
allows the Chile 4 plant to achieve a stoichiometric
ratio higher than (and close to) a value of 2. This
characteristic of the Chile 4 plant made it unable to
operate in an autonomous manner.
However, the modification in FIG. 3 was applied,
which enabled the Chile 4 plant to operate in a standalone condition. This was achieved by purifying two streams from its own
process, namely:
* The purge gas stream coming from the synthesis loop
unit of Chile 4
* A portion of the reformed gas stream coming from the
exit of the reforming unit of the Chile 4 plant.
The solution (added to the Chile 4 flowsheet/plant), which
allowed standalone operation, incorporated a pressure swing
adsorption (PSA) package. The PSA separates hydrogen from
carbon compounds in the purge gas and reformed gas streams.
This high-purity hydrogen stream produced from the PSA
unit can then be fed to the front-end reforming section of the
Chile 4 plant, creating a synthesis gas that complies with the
stoichiometric design requirement of the synthesis loop and
eliminates the need for imported (hydrogen-rich) purge gas
from the Chile 1 plant.
The most interesting aspect of this project is related to the
modification of an existing plant that was not designed to operate with a PSA unit. Although some plants operate using their
own purge gas, Chile 4 purge gas had insufficient hydrogen to
reach the required stoichiometric ratio for methanol synthesis.
Therefore, an extra supply of " impure hydrogen " was required
to feed the PSA and to bridge the shortfall of hydrogen required to achieve the necessary stoichiometry ratio of feed gas
to the methanol synthesis unit. The synthesis gas stream (i.e.,
feed or makeup gas to the methanol synthesis unit) became the
solution to provide the additional hydrogen required for the
methanol synthesis unit. Feeding a certain percentage of the
synthesis gas stream, in addition to the synthesis loop purge
stream, to the PSA unit enabled the production of sufficient
extra hydrogen to meet the design stoichiometry target (> 2)
in the feed stream to the methanol synthesis unit.
The project also managed to recover compounds rejected
by the PSA after the hydrogen-rich stream was returned to the
process. The rejected stream (noted as tail gas in FIG. 3) is a carbon-rich stream and is returned as a fuel source to the existing
heating furnace. As such, no stream was wasted in this design,
and returning the tail gas as a fuel source allowed the plant to
maintain a high overall process efficiency level. When operating
in standalone mode, the efficiency level achieved on the Chile 4
plant was comparable and competitive with the efficiency level
of most of Methanex's remaining plants around the world.
Startup modification of the redesigned plant. In addition to the installation and connections required to install a PSA
package, a minor modification of the Chile 4 plant's startup was
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Hydrocarbon Processing - December 2020
Table of Contents for the Digital Edition of Hydrocarbon Processing - December 2020
Contents
Hydrocarbon Processing - December 2020 - Intro
Hydrocarbon Processing - December 2020 - Cover1
Hydrocarbon Processing - December 2020 - Cover2
Hydrocarbon Processing - December 2020 - Contents
Hydrocarbon Processing - December 2020 - 4
Hydrocarbon Processing - December 2020 - 5
Hydrocarbon Processing - December 2020 - 6
Hydrocarbon Processing - December 2020 - 7
Hydrocarbon Processing - December 2020 - 8
Hydrocarbon Processing - December 2020 - 9
Hydrocarbon Processing - December 2020 - 10
Hydrocarbon Processing - December 2020 - 11
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Hydrocarbon Processing - December 2020 - 18
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Hydrocarbon Processing - December 2020 - 20
Hydrocarbon Processing - December 2020 - 21
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Hydrocarbon Processing - December 2020 - 26
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Hydrocarbon Processing - December 2020 - 42
Hydrocarbon Processing - December 2020 - 43
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Hydrocarbon Processing - December 2020 - 79
Hydrocarbon Processing - December 2020 - 80
Hydrocarbon Processing - December 2020 - 80A
Hydrocarbon Processing - December 2020 - 80B
Hydrocarbon Processing - December 2020 - 81
Hydrocarbon Processing - December 2020 - 82
Hydrocarbon Processing - December 2020 - Cover3
Hydrocarbon Processing - December 2020 - Cover4
Hydrocarbon Processing - December 2020 - GP-1
Hydrocarbon Processing - December 2020 - GP-2
Hydrocarbon Processing - December 2020 - GP-3
Hydrocarbon Processing - December 2020 - GP-4
Hydrocarbon Processing - December 2020 - GP-5
Hydrocarbon Processing - December 2020 - GP-6
Hydrocarbon Processing - December 2020 - GP-7
Hydrocarbon Processing - December 2020 - GP-8
Hydrocarbon Processing - December 2020 - GP-9
Hydrocarbon Processing - December 2020 - GP-10
Hydrocarbon Processing - December 2020 - GP-11
Hydrocarbon Processing - December 2020 - GP-12
Hydrocarbon Processing - December 2020 - GP-13
Hydrocarbon Processing - December 2020 - GP-14
Hydrocarbon Processing - December 2020 - GP-15
Hydrocarbon Processing - December 2020 - GP-16
Hydrocarbon Processing - December 2020 - GP-17
Hydrocarbon Processing - December 2020 - GP-18
Hydrocarbon Processing - December 2020 - GP-19
Hydrocarbon Processing - December 2020 - GP-20
Hydrocarbon Processing - December 2020 - GP-21
Hydrocarbon Processing - December 2020 - GP-22
Hydrocarbon Processing - December 2020 - GP-23
Hydrocarbon Processing - December 2020 - GP-24
Hydrocarbon Processing - December 2020 - GP-25
Hydrocarbon Processing - December 2020 - GP-26
Hydrocarbon Processing - December 2020 - GP-27
Hydrocarbon Processing - December 2020 - GP-28
Hydrocarbon Processing - December 2020 - GP-29
Hydrocarbon Processing - December 2020 - GP-30
Hydrocarbon Processing - December 2020 - GP-31
Hydrocarbon Processing - December 2020 - GP-32
Hydrocarbon Processing - December 2020 - GP-33
Hydrocarbon Processing - December 2020 - GP-34
Hydrocarbon Processing - December 2020 - GP-35
Hydrocarbon Processing - December 2020 - GP-36
Hydrocarbon Processing - December 2020 - GP-37
Hydrocarbon Processing - December 2020 - GP-38
Hydrocarbon Processing - December 2020 - GP-39
Hydrocarbon Processing - December 2020 - GP-40
Hydrocarbon Processing - December 2020 - GP-41
Hydrocarbon Processing - December 2020 - GP-42
Hydrocarbon Processing - December 2020 - GP-43
Hydrocarbon Processing - December 2020 - GP-44
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