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A technique known as pressure swing adsorption (PSA) has been employed in a novel way to concentrate a lean amount of helium present in natural gas through selective physical elimination of N2, CO2, CH4 and C+2 (heavier hydrocarbons) in a stepwise cycle sequence at preset time intervals. The PSA-based helium pilot plant consists of four stages, with each stage composed of three parallel adsorber beds (vessels packed with adsorbents). The plant has been designed and operated for purifying helium to a level of better than 99.0 vol% from a feed natural gas containing helium to the tune of 0.06 vol%. The normal feed pressure range is 4–5 bar (abs). The overall recovery of the pilot plant is around 61%. The features of the PSA system are described here with a detailed description of the operating parameters of the helium pilot plant.
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TECHNICAL NOTE
CURRENT SCIENCE, VOL. 95, NO. 12, 25 DECEMBER 2008
1684
Purification of helium from natural gas by pressure swing adsorption
Nisith K. Das, Hirok Chaudhuri, Rakesh K. Bhandari, Debasis Ghose, Prasanta Sen and Bikash Sinha
A technique known as pressure swing adsorption (PSA) has been employed in a novel way to concentrate a
lean amount of helium present in natural gas through selective physical elimination of N2, CO2, CH4 and C+
2
(heavier hydrocarbons) in a stepwise cycle sequence at preset time intervals. The PSA-based helium pilot
plant consists of four stages, with each stage composed of three parallel adsorber beds (vessels packed with
adsorbents). The plant has been designed and operated for purifying helium to a level of better than
99.0 vol% from a feed natural gas containing helium to the tune of 0.06 vol%. The normal feed pressure
range is 4–5 bar (abs). The overall recovery of the pilot plant is around 61%. The features of the PSA system
are described here with a detailed description of the operating parameters of the helium pilot plant.
Large-scale extraction of helium is con-
ventionally realized from helium-bearing
natural gas existing in selected geographi-
cal locations across the world. Natural
gas is made up of a composite mixture of
diverse gaseous components, including a
substantial level of heavy hydrocarbons
apart from methane, nitrogen and helium
in variable amounts. A two-stage pres-
sure swing adsorption (PSA) process was
earlier developed by Knaebel and Rein-
hold1, and D’Amico et al.2. Their feed
gas contained about 2–4 vol% helium and
70 vol% nitrogen and concentrated helium
to a level of greater than 98 vol% from
the feed natural gas. The process involved
two stages of PSA used in series that
sequentially undergo a seven-step cyclic
separation process.
Helium stands out to be indispensable
in frontier technologies involving space,
atomic energy, defence, power, medicine,
welding and in many advanced research
activities, including fusion and behaviour
of materials at very low temperatures. In
view of any unforeseen scarcity in this
strategic element (even today India im-
ports almost 100% pure helium for its
domestic consumption), a stand-by meas-
ure for indigenous sources of helium is
deemed worthwhile in the country.
In India, effort towards exploration of
helium from different sources has led to
discovering helium, in small amounts, in
natural gas discharged through the natu-
ral gas wells in GCS Kuthalum, Nagapat-
tinam District, Tamil Nadu. Besides the
conventional way of helium recovery utili-
zing cryogenic separation which is an en-
ergy-expensive process, a non-cryogenic
helium purification system has been deve-
loped, with the help of Adsorption
Research Inc., Dublin, Ohio, USA, to
separate out helium from natural gas
stream by means of the PSA process. The
helium plant based on PSA produces a
constant stream of helium having a con-
centration of around 99.0 vol% from
natural gas feed stream bearing helium
content to the tune of 0.06 vol%, with an
overall recovery rate around 61%.
The developed PSA system for helium
purification involves three distinct com-
ponents: (a) pretreatment of feed gas, (b)
recovery of methane (CH4) and (c) sepa-
ration of helium. The multi-component
gas available from wellheads of the natu-
ral gas field at GCS Kuthalam, predomi-
nantly contains methane besides heavy
hydrocarbons, CO2, nitrogen and helium.
The raw natural gas is collected in the
gas storage vessel at a pressure of 16 bar.
The gas leading to the pilot plant is taken
at a reduced pressure of 4–5 bar and is
routed through a refrigerated gas dryer to
remove the bulk moisture content present
in the feed stream, and fed into the sys-
tem at about a feed pressure of 4.5 bar. A
preliminary conceptual process of the
plant was presented in an international
seminar3. Unlike in the previous works1,2,
where the feed gas contains about 2–
4 vol% helium, the present feed stream
contains helium approximately 0.06 vol%,
which makes the system more challeng-
ing and involves four stages instead of
two.
Process description
The pilot plant has four stages, with each
stage consisting of three adsorber beds.
The complete system comprises of a net-
work of piping, valves with associated
instrumentation and control equipment
that are integrated with the plant. The
number of adsorber beds used is an eco-
nomic balance between the capital cost
of the pilot plant and the desired product
quality. Stage I is adopted to remove the
heavier hydrocarbons and carbon dioxide
from the feed stream allowing methane,
nitrogen and helium to flow and continue
onto stage II. In stage I, the heavy com-
ponents include carbon dioxide (CO2),
ethane (C2H6), propane (C3H8) and butane
(C4H10) and are preferentially retained on
the adsorbent, while the less adsorbable
effluent gas comes out through the exit
end. Stage II adsorbs and rejects methane
as the heavy product, allowing nitrogen
and helium to flow and move onto stage
III. The methane-rich heavy product from
stage II is partially recycled for use in
stage I as purge gas for the purpose of
regeneration. Methane of high purity
from the waste gas is recovered as the
secondary product in this stage. Stage III
adsorbs and removes most of the nitro-
gen and allows a helium-rich mixture to
pass through and advance to stage IV.
The nitrogen-rich heavy product repre-
sents the third and final waste stream.
Stage IV operates similar to the stage III;
it adsorbs and cast-offs residual nitrogen,
allowing purified helium to pass through
as the final light product. The heavy
product (which is a mixture of nitrogen
and a little helium) from stage IV is
compressed and optionally recycled to
the inlet of stage III for the purpose of
boosting the overall helium recovery.
The entire process is controlled by
microprocessor based logic controllers
(PLCs). Figures 1–3 show some of the
components of the helium pilot plant. In
the present case, the absorbents used are
silica gel in stage I, activated carbon in
stage II, and zeolites in stages III and IV.
The adsorption system operates by a
sequence of steps, called a PSA cycle.
Each stage in the purifying system has an
associated cycle. The adsorber beds in
each stage sequentially undergo the fol-
TECHNICAL NOTE
CURRENT SCIENCE, VOL. 95, NO. 12, 25 DECEMBER 2008 1685
Figure 1. Network of adsorber vessels in stages I and II.
Figure 2. Partial view of stage II showing the methane compressor, vacuum pumps,
flow controller, etc.
Figure 3. Stages III and IV.
lowing seven steps: I, Adsorption (Fd);
II, Co-current depressurization for pres-
sure equalization (PEd); III, Blow down
to atmospheric pressure (Bd); IV, Eva-
cuation to the lowest pressure (Ev); V,
Purge with product at the lowest pressure
(Pu); VI, Counter-current pressurization
by pressure equalization (PEu), and VII,
Re-pressurization with product to a feed
pressure (Rp).
Adsorption primarily occurs during the
feed step. When the more strongly ad-
sorbed components reach the top of the
adsorber bed, and are about to contami-
nate the product, gas feed flow is discon-
tinued and switched to the second adsorber
bed. The first adsorber bed then under-
goes regeneration by depressurization
(called the blow down and evacuation
step) followed by the purge step. During
the purge step, the enriched heavy com-
ponent(s) are desorbed from the adsorber
bed at low pressure by admitting the
light component(s), instead of relying on
evacuation (vacuum) alone. These steps
induce desorption and release of the
‘heavy’ product. The heavy product will
contain both of the more adsorbable
components, which are enriched (relative
to the feed) by the adsorber bed, and
some of the less strongly adsorbed com-
ponents released from the voids. The
pressurization step, in which light prod-
uct is used to repressurize and adsorb,
can be thought of as regeneration, since
it tends to displace the more strongly ad-
sorbed constituents as it enters the
adsorber bed. It can also be viewed as an
adsorption step, since as pressure in-
creases, the light components also get
adsorbed to a greater extent. Pressuriza-
tion with feed causes some of it to be ad-
sorbed, while some feed remains in the
gas-phase to increase the column pres-
sure. The process flow diagram showing
the schematic flowsheet of P & I diagram
of each stage is given in Figure 4. Stages
I and III include equalization steps, during
which one adsorber bed depressurizes
into a parallel adsorber bed, partially pre-
ssurizing it. There are two equalization
steps per adsorber per cycle, because
each adsorber bed releases gas to one
adsorber bed and receives gas from an-
other adsorber bed. For example, stage I
delivers gas to stage III, but stage I also
receives gas from stage II.
Results and discussions
Figure 5 presents the chromatogram of
the composition of the feed natural gas at
TECHNICAL NOTE
CURRENT SCIENCE, VOL. 95, NO. 12, 25 DECEMBER 2008
1686
Table 1. Composition of feed and product gases at respective stages of the pressure swing adsorp-
tion (PSA) helium pilot plant
Product of Product of Product of
Feed of stage I/feed of stage II/feed of stage III/feed of Product of
Composition stage I vol% stage II vol% stage III vol% stage IV vol% stage IV vol%
He 0.06 0.08 1.40 15.65 99.00
N2 1.18 1.27 16.10 72.03 1.00
CH4 88.50 98.42 82.50 12.32 0.00
CO2 0.40 0.00 0.00 0.00 0.00
C+
2 9.86 0.23 0.00 0.00 0.00
Table 2. Operating parameters of four stages of PSA helium pilot plant
Parameter Stage I Stage II Stage III Stage IV
Feed pressure (bar) 4.50 4.50 2.25 2.00
Feed flow rate (slpm) 820.00 600.00 60.00 4.90
Product pressure (bar) 4.50 2.25 2.00 1.50
Product flow rate (slpm) 600.00 60.00 4.90 0.90
Regeneration pressure (bar) 1.3 (blowdown) 1.25 (blowdown) 1.1 (blowdown) 1.1 (blowdown)
75 m bar (evacuation) 75 m bar (evacuation) 60 m bar (evacuation) 60 m bar (evacuation)
Purge amount (slpm) 81 425 (rinse flow rate) 0.6 0.5
Helium in feed (vol%) 0.06 0.08 1.40 15.65
Helium in product (vol%) 0.08 1.40 15.65 99.00
PSA cycle time (min) (three-bed cycle) 24.00 4.50 6.75 36.00
Bed composition (kg/bed) Silica gel (~198) Activated carbon (~38) Zeolite 13 X (~3) Zeolite 13 X (~3)
Column dimensions (H, Height (cm); H = 129.54 H = 104.14 H = 152.40 H = 152.40
OD, Outer diameter (cm)) OD = 50.80 OD = 30.48 OD = 6.35 OD = 6.35
the GCS Kuthalam site. It is observed
that the major constituent of the feed
stream is methane, while helium content
is as low as 0.06 vol%. The composition
of the feed and product gases in four
stages of the PSA are shown in Table 1.
Figure 4. Schematic flowsheet of P&I diagram of each stage.
Figure 5. Feed gas composition.
Figure 6. Composition of the stage I
product gas as also feed of stage II.
Figure 7. Composition of the stage II
product gas as also feed of stage III.
TECHNICAL NOTE
CURRENT SCIENCE, VOL. 95, NO. 12, 25 DECEMBER 2008 1687
Figure 6 shows the product gas composi-
tion of stage I after removal of majority
of the heavy hydrocarbons and carbon
dioxide. This product is primarily meth-
ane with marginal increase in helium and
nitrogen concentrations, and it is also the
feed gas of the stage II. Figure 7 displays
the product gas composition of the stage
II as also the input gas of stage III. Fig-
ure 8 presents the product gas of stage
III, which is also the feed gas of stage
IV. The output gas of this stage III con-
sists of nitrogen and helium, accompany-
ing a small quantity of methane. Figure 9
shows the final product quality of stage
IV. Any residual methane is completely
removed from the gas stream and almost
all the nitrogen is eliminated, essentially
leaving purified helium as the yield of
stage IV. Table 2 provides the operating
parameters of the four stages of the PSA
helium pilot plant. The plant intake is a
constant feed of 50 NM3/h of natural gas
containing 0.06 vol% helium. The output
is a constant stream of helium (>99.0 vol%)
at approximately (18 l/h). Practical im-
plementation of this new system brings
out the fact that loss of helium in stages
II and III needs to be minimized through
more precise cycle times and further fine
tuning to optimize the pressure ratios.
The helium recovery from the four stages,
as observed, are: stage I ~97%, stage-II
~87%, stage-III ~81% and stage IV ~87%.
The overall helium recovery from the pi-
lot plant is ~61%.
The helium pilot plant presented above
was installed at the GCS Kuthalum site
during 2007 and commissioned in early
2008. The plant was formally inaugu-
rated and dedicated to the nation on 11
May 2008.
Conclusion
To the best of our knowledge it has been
demonstrated for the first time that, al-
though on a pilot scale, employing the
non-cryogenic PSA technique, helium
has been purified to a level better than
99.0 vol% starting from a level as low as
0.06 vol% present in the feed natural gas.
The system is completely automated and
separation has been achieved at room
temperature. This enables considerable
savings in energy and manpower com-
pared to the low-temperature separation
process. We are of the opinion that ex-
ploration of existing natural gas reserves
in India, on a commercial scale, would
be able to meet the requirement for the
domestic consumption of pure helium
through the scaling-up of such pilot
plants.
1. Knaebel, K. S. and Reinhold, H., Proceed-
ings of Fundamental of Adsorption (ed.
Meunier, F.), Elsevier, 1998, pp. 763–767.
2. D’Amico, J. S., Reinhold, H. and Knaebel,
K. S., US Patent No. 5542966 dated 6 Au-
gust 1996.
3. Das, N. K., Bhandari, R. K., Sen, P. and
Sinha, B., Proceedings of International
Seminar on Gas Technology, Kolkata, 19–
20 November 2004, pp. 252–256.
ACKNOWLEDGEMENTS. We acknow-
ledge the financial and infrastructural support
of ONGC, GCS Kuthalam, Tamil Nadu and
thank the Department of Atomic Energy, and
the Department of Science and Technology,
Government of India for sponsoring the pro-
ject.
Received 11 June 2008; revised accepted 20
November 2008
Nisith K. Das, Rakesh K. Bhandari and
Bikash Sinha are in the Variable Energy
Cyclotron Centre, 1/AF, Bidhannagar,
Kolkata 700 064, India; Hirok Chaud-
huri, Debasis Ghose, Prasanta Sen* and
Bikash Sinha are in Saha Institute of Nu-
clear Physics, 1/AF, Bidhannagar, Kol-
kata 700 064, India.
*e-mail: prasanta.sen@saha.ac.in
Figure 8. Composition of the stage III product gas as also feed of stage IV.
Figure 9. Stage IV product gas composition.
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