Nitrogen Generation by Pressure Swing Adsorption - Linde-India

Nitrogen Generation
by Pressure Swing
Adsorption

2
Contents.
3 Introduction
4 The process
PSA process cycle
Plant control and turn down
Start-up and shut-down
Turndown operation
Operation and maintenance
Safety aspects
Safety, health, environment and quality (SHEQ)
Building / shelter
8 G- series nitrogen PSA
The advantages of Linde N 2-PSA
10 A- series nitrogen PSA
The N 2-PSA layout
The scope of supply
Contact
Cover page: N2 PSA Plant / El Chacay / Chile / Minera Los Pelambres

Introduction.
The experience
The use of the Pressure Swing Adsorption (PSA) process
has seen tremendously growth during the last decades
mainly due to its simplicity and low operating costs. Major
applications have been the recovery of high purity hydrogen,
methane and carbon dioxide as well as the generation of
nitrogen and oxygen. In addition, it has gained significance
for the bulk removal of carbon dioxide from direct reduction
top-gases.
Linde as the world leader in adsorption technology has
designed and supplied more than 500 PSA plants - including
the world´s largest units and units with highest availability.
The Linde nitrogen PSA generators
The Linde nitrogen PSA generators are designed
for onstream applications, where there is need
for clean, dry nitrogen of high purity for inerting,
blanketing and purging.
The capacities of the Linde nitrogen PSA generators
range from small plants with product
requirements of only several Nm³/h, up to
large-scale plants with several thousand Nm³/h
nitrogen product flows.
Depending on client needs, the PSA plant can
be designed for nitrogen product purity in the
range of a few percent oxygen content or with
oxygen content in the ppmv level.
Linde N 2-PSA systems are available
in two plant series:
– The G-series, fully standardized with a range
of 26 capacity types.
– The A-series, a tailored modular plant series
that features highest capacities and purities.
This series can be supplied to the needs of
customer‘s specifications.
The nitrogen product is normally delivered
between 4 barg to 9 barg (60 psig to 130 psig).
In case a higher product pressure is required
a downstream nitrogen compressor will be
applied.
Linde´s PSA systems have proven to be successful
in cases where performance, flexibility,
availability and reliability are the determining
factors. High quality and easy accessibility to
all components minimize and facilitate maintenance
to the maximum extent.
3
3

4
The process.
The separation of nitrogen and oxygen from
air takes place in an adsorber vessel filled with
carbon molecular sieve.
This is based on the fact of faster kinetic diffusion
of oxygen molecules into the pore structure
of the carbon molecular sieve than for
nitrogen molecules.
Pressure time diagram for nitrogen PSA process Carbon molecular sieve
Pressure
A
B
Adsorber A
C
Adsorber B
D
E
Time
A:
B:
C:
D:
E:
Pressure equalization
Back purge step
Nitrogen production
Pressure equalization
Depressurization

Air
Air
compressor
PSA process cycle
The PSA process cycle consists of two key
mechanisms:
– Pressurisation/adsorption
– Depressurisation/desorption
Compressed air alternately pressurises each
of two identical adsorber beds. Beginning at
a point in the cycle where one adsorber bed (A)
is being pressurised and the other adsorber bed
(B) is undergoing depressurisation, the description
of the PSA process cycle is as follows:
As compressed air enters adsorber bed A, moisture,
oxygen, and carbon dioxide are adsorbed.
After operating pressure is reached, nitrogen
to
atmosphere
Waste
Adsorber A Silencer
Adsorber B
product flows from adsorber bed A into a nitrogen
product receiver prior to entering the product
piping. Simultaneously, adsorber bed B is
depressurised to atmospheric pressure.
Upon completion of nitrogen production from
adsorber bed A, an equalisation step occurs.
Adsorber bed B (atmospheric pressure) is pressurised
to an intermediate pressure as the gas
remaining in adsorber bed A (at operating pressure)
flows into adsorber bed B. During this step,
air is not consumed nor is product gas generated.
Therefore a nitrogen receiver is applied to allow
for a constant flow, purity and pressure of the
nitrogen product throughout the PSA cycle.
Adsorber bed A then undergoes depressurisa-
PSA N2-buffer
O2-analyzer
AE
Compressed air
Nitrogen
Waste gas
Nitrogen
Typical process flow diagram of a
Linde nitrogen PSA plant
tion and the oxygen enriched waste gas is
vented to the atmosphere. Depressurisation
permits the release of oxygen, carbon dioxide,
and water vapor previously adsorbed during
nitrogen production from adsorber bed A. At the
same time, adsorber bed B is brought to operating
pressure, and begins its nitrogen production
portion of the cycle.
Following nitrogen production, adsorber bed B
undergoes equalisation and subsequent depressurisation.
The cycle continues at the point
where adsorber bed A undergoes pressurisation
and adsorber bed B is depressurised.
5

6
Plant control and turn down
The N 2-PSA plant is controlled by a programmable
logic controller (PLC).
Its main control features include:
– Automatic operation of the entire N 2-PSA
plant
– Supervision of process parameters with safety
shut down and alarm in case of abnormal
plant operation
– Control of the process values on a display
– Sophisticated plant diagnostics
The (im)purity of the product is being checked
continuously by an automatic online O 2-analyzer.
Typical A-series nitrogen PSA
Start-up and shut-down
The start-up of the plant is a simple push button
operation. The product is being delivered within
a short time from start-up.
At shut-down of the plant, a precisely defined
programme cycle continues to run for a few
minutes before complete shut-down is reached.
The adsorbers are then in regenerated conditions
and prepared for restart of operation. After
restart product in accordance with specification
can be produced within a few minutes.
Turndown operation
The plant flowrate can be reduced by inserting
an “idle” step in the cycle thus saving plant
power.
This is performed automatically by the PLC.
The PLC program adjusts process parameters
accordingly.

Petrochemical
Glass
Treating
Storing
Operation and maintenance
The LINDE N 2-PSA plant is designed to run unattended
during normal operation. The plant
requires a minimum of operating and maintenance
attention. The N 2-PSA will be designed
and constructed to provide proper flexibility and
easy accessibility for operation and maintenance
of the machinery, valves and instrumentation.
Refinery
Purging Preserving
LINDE N2-PSA
APPLICATIONS
Safety aspects
The plant operates at moderate temperatures
and pressures. All necessary safety devices to
avoid increased pressures, excessive or insufficient
temperature or other failure functions
are provided.
Safety, health, environment and quality (SHEQ)
Controls relating to safety, health, environment
and quality are a pre-requisite for the Linde
work processes.
Metals
Spinning
Inerting
Chemical Food
Electronics
Blanketing
Filling
Oil & gas
Application of PSA generated Nitrogen
Building/shelter
Due to the severe ambient conditions and in order
to protect the PSA unit from driving rain and
direct sunlight, it is strongly recommended to
install the PSA unit in a closed shelter, at least a
roof covering the valve skid and the compressor
shall be supplied.
7

8
G-series nitrogen PSA.
The G-series comprises fully standardized
nitrogen PSA generators with 26 plant sizes
and hence providing optimal solution within
its product range and purity.
Particular features of G-series nitrogen PSA
– Fully standardized
– Low investment
– Compact arrangement
– Existing standard documentation
– Short delivery, installation and
commissioning time
The product ranges for the G-series plants are:
N 2-product range 50 - 1,500 Nm³/h
Nitrogen (N2 +Ar) purity 97 - 99.9 %
Oxygen impurity 3 - 0.1 %
Typical G-series nitrogen PSA plant for the generation of
nitrogen, 310 Nm³/h, 0.5% O 2

A-series Nitrogen PSA
The A-series comprise fully tailored nitrogen
PSA generators. With its A-series PSA plants
Linde is able to follow individual customers
project specifications, standards and requirements.
(e.g. for refineries etc.)
Particular features of A-series nitrogen PSA
– Tailor made according to individual project
specifications and requirements
– High capacity and purity range
– Modular and prefabricated design
The product ranges for the A-series plants are:
N 2-product capacity 50 - 5,000 Nm³/h
Nitrogen (N2 +Ar) purity 97 - 99.9999 %
Oxygen impurity 3 % - 1 ppm
9
A-series nitrogen PSA plant designed according to
individual project specification

10
The advantages of Linde N 2-PSA
The Linde PSA process for the generation of
nitrogen provides remarkable advantages:
First quality
– Only components are used which have proven
highest durability.
Low nitrogen product cost
– The Linde PSA system produces high purity
nitrogen at lowest cost compared to convent-
ional cryogenic units or liquids supplied from
outside.
Typical G-series nitrogen PSA plant
mounted in a container
Highest reliability
– The PSA system provides highest reliability.
The control system allows for the production
of nitrogen at the specified flow and purity
within minutes of demand using simple push
button.
Easy turn-down
– Excellent flexibility to match actual client
needs are achieved with the PSA system as
it provides a turn-down ratio between 0%
and 100% at unchanged purity and at nearly
proportional energy consumption.
Fully automatic operation
– The PLC based control system controls the
purity and the flow by automatically adjusting
the cycle time of the PSA system.
A modbus port for the communication with a
plantwide DCS and/or a communication board
for the remote control by a modem can be
supplied as an option.
Modular skid design
– The shop fabricated valve skid design reduces
the on-site costs for erection and commissioning.
Easy maintenance
– Only routine maintenance is required.
All components are easily accessible.

The N 2-PSA layout
All components on the skid – including nitrogen
product analyzer and control system – are completely
piped and wired for quick assembly at
the job site.
The Linde N 2-PSA nitrogen generators can be
designed for indoor or outdoor installation.
The scope of supply
The scope of supply mainly comprises the
following material and equipment:
– Air compressor, if required
– Adsorber vessels
– Specially selected adsorbent material
– PSA buffer drum
– Valve skid
– Control system
– Nitrogen product O 2-analyzer
– Nitrogen product compressor, if required
Heavy industrial standard for LINDE nitrogen PSA plants
11
A-series nitrogen PSA plant with high pressure
nitrogen storage

Designing Processes - Constructing Plants.
Linde´s Engineering Division continuously develops extensive process engineering know-how in the planning,
project management and construction of turnkey industrial plants.
The range of products comprises:
− Petrochemical plants
− LNG and natural gas processing plants
− Synthesis gas plants
− Hydrogen plants
− Gas processing plants
− Adsorption plants
− Air separation plants
− Cryogenic plants
− Biotechnological plants
− Furnaces for petrochemical plants and refineries
Engineering Division headquarters:
Linde AG
Engineering Division, Dr.-Carl-von-Linde-Str. 6-14, 82049 Pullach, Germany
Phone +49.89.7445-0, Fax +49.89.7445-4908, E-Mail: info@linde-le.com, www.linde.com
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− Coil-wound heat exchangers
− Plate-fin heat exchangers
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More than 3,800 plants worldwide document the leading position of the Engineering Division in international plant construction.
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