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ICCEECON 2K16 CHRIST KNOWLEDGE CITY 5 March 2016
NITROGEN PLANT AUTOMATION USING PLC
AND SCADA
Ms. Nicy V B
Asst. professor
Dept.of AEI
RCET, Thrissur
om
Sudheesh S
U G scholar
Dept.of AEI
RCET, Thrissur
sudheesh.s@hot
mail.com
Ajeesh V N
U G scholar
Dept.of AEI
RCET, Thrissur
vnajeesh@gmail
.com
Pranav
Ramachandran
U G scholar
Dept.of AEI
RCET, Thrissur
n6pranav@gmai
l.com
Jamsheer M I
U G scholar
Dept.of AEI
RCET, Thrissur
jamsheer1017@
gmail.com
Abstract—This paper deals with Nitrogen plant automation
using PLC and SCADA. A programmable logic controller (PLC)
is a digital computer used for automation of electromechanical
processes, such as control of machinery on factory assembly lines,
amusement rides, or light fixtures.
The entire process of extracting nitrogen gas from the
atmosphere by a system that consists of following device like
solenoids valves, air compressor, air filter regulator, rotameter,
bourdon tube, and pressure switch etc. atmospheric air with
various impurities admitted and compressed through air
compressor and send to an air receiver, then to the system.
PLC—Programmable Logic Controller
SCADA—Supervisory Control & Data Acquisition
I. INTRODUCTION
Unlike general –purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control are typically stored in battery – backed –up or non-volatile memory.
The entire processes of extracting nitrogen gas from the atmosphere by a system that consists of following device like solenoids valves, air compressor, air filter regulator, rotameter, bourdon tube, and pressure switch etc. atmosphere air with various impurities admitted and compressed through air compressor and send to an air receiver, then to the system. Plant has two tanks of similar capacity constituting with different solenoid valves and other associated paraphernalia. When the pressure in compressor exceeds 7 kg/cm 2 , it admits to the first tank through appropriate valves. Now, oxygen and other impurities are adsorbed by the CMS (carbon molecular sieve) and nitrogen is separated. The first tank works for 58seconds, meanwhile, the second one regenerates. Within another two seconds both tank equalize the pressure. Nitrogen generated in first tank pass to the storage tank, through
appropriate solenoid valves and surge vessel by releasing the impurities. Then the operation repeated in the second tank. Both tanks operate simultaneously one after another with an interval of 58 second. So that process is continued and nitrogen storage tank is filled as required. A nitrogen storage tank is installed after nitrogen surge vessel for storage of nitrogen gas at pressure of 5.0 kg/cm 2. Two manual valves are provided at inlet and outlet of tank. The plant is made to trip, by high pressure switch, when pressure of gas in the tank goes up to 5.0 kg/cm 2.
II. HARDWARE DESCRIPTION
A. BLOCK DIAGRAM AND EXPLANATION
The main blocks of PSA nitrogen generator includes air compressor, air receiver tank, pressure switch, two towers, surge vessel, oxygen analyzer and nitrogen storage tank. Nitrogen is produces from the air taken from the atmosphere.
Figure 1: Block diagram of proposed system
ICCEECON 2K16 CHRIST KNOWLEDGE CITY 5 March 2016
B. AIRCOMPRESSOR
An air compressor is a device that converts power (usually from an electric motor, a diesel engine or a gasoline engine) into kinetic energy by compressing and pressurizing air, which, on command, can be released in quick bursts. There are numerous methods of air Compression, divided into either positive-displacement or negative-displacement types.
Figure 2: Reciprocating air compressor
C. AIR RECEIVER TANK
Air receivers are tanks used for compressed air
storage and are recommended to be in all compressed air
systems. Using air receivers of unsound or questionable
construction can be very dangerous
Fig 3: Air receiver tank
D. PRESSURE SWITCH
A pressure switch for sensing fluid pressure contains a capsule, bellows, Bourdon tube, diaphragm or piston element that deforms or displaces proportionally to the applied
pressure. The resulting motion is applied, either directly or through amplifying levers, to a set of switch contacts. Since pressure may be changing slowly and contacts should operate quickly, some kind of over-center mechanism such as a miniature snap-action switch is used to ensure quick operation of the contacts. One sensitive type of pressure switch uses mercury switches mounted on a Bourdon tube; the shifting weight of the mercury provides a useful over-center characteristic.
E. TOWER-1 & TOWER-2 or PSA UNIT
There are 2 towers filled with special grade carbon
molecular sieves (CMS) to absorb o2, co2 & moisture present
in the air. At the bottom of each tower a perforated plate is
welded to hold the activated alumina & CMS. Just above the
plate, ceramic balls are put to as a holding bed for activated
alumina. Lumina are used to remove the moisture of the air
entering the CMS. The dry air is also tapped to operate the
actuators and valves.
Above the alumina, the CMS is filled up to the
straight portion of tower. A perforated plate on the top
prevents CMS from flowing out by the wire mesh. A 50mm
thick loose coconut fiber is packed in the top above CMS to
fix the absorbing bed. The upper perforated plate compresses
absorbent fill to avoid undesired void. The coconut fiber is
squeezed together when the cover is tightened. Cycle time of
PSA unit is 1 minute + 1 minute.
Each tower has air inlet valve (v1 & v2) bottom, gas
outlet valve (v7 & v8) at top and exhaust outlet valve (v3 &
v4) at bottom. Besides these, a valve v6 is for equalization at
the top and a valve v5 after exhaust valve (v3 & v4) at the
bottom. The air inlet line from air receiver has a global valve
v9 to control the flow of air, so that the pressure in the
absorbing tower goes up to 7.0kg/cm^2g maximum.
F. NITROGEN SURGE VESSEL
Nitrogen from PSA unit will have varying purity in 1
minute cycle time. This surge vessel gives nitrogen at constant
pressure with a constant average purity. For analyzing oxygen
percentage in the nitrogen gas, one needle valve for sampling
is provided in this vessel.
G. OXYGEN ANALYSER
An online oxygen analyzer continuously monitoring
oxygen percentage in surge vessel. Whenever oxygen
percentage goes above the set valve, vent valve open. For
more details please refer percentage oxygen analyzer manual.
H. NITROGEN STORAGE TANK
A nitrogen storage tank is installed after the nitrogen
surge vessel for storage of nitrogen gas at pressure of
ICCEECON 2K16 CHRIST KNOWLEDGE CITY 5 March 2016
5.0kg/cm 2 g. Two numbers manual valves are provided at
inlet and outlet of tank. The plant is made to trip, by high
pressure switch, when pressure of gas in tank goes up-to
5.0kg/cm 2 g.
III. FLOW CHART
Figure 4: Flowchart of nitrogen plant
Flow-chart diagrammatic is been shown in the Fig.4. This
flow-chart gives the entire idea for the working principle of
the automation. Initially process starts from the air receiver
tank. When pressure in the air receiver tank exceeds 7kg/cm2
the valve V9 opens and it starts operation. The PSA process
cycle consists of 2 key mechanisms:
Adsorption
Desorption
When first tank 1 works for 40 seconds the second one
regenerates. At this time adsorption take place for tank 1 and
valves V1, V4 and V7 were open. Simultaneously all other
valves gets closed for the process to take place. Nitrogen
generated in first tank pass to the surge vessel for a temporary
storage. Within another 10s both tank equalize the pressure
with valves V5 and V6 were open. Next 40s adsorption take
place for tank 2 and at this time first tank regenerated and the
impurities gets released through the silencer. Nitrogen
generated in tank 2 reaches the storage tank through valves
V2, V3 and V8.Next 10s both tank equalize the pressure
similarly as above. This operation alternatively repeated in
both tanks. After the process of storing in the surge vessel it
gets transferred to the main storage tank. But in between these
surge vessel and storage tank there is a special device known
as the oxygen analyzer for analysis of oxygen content in the
purified product. When the amount of oxygen is less than
0.7%, it reaches the storage tank. Otherwise it is vented back
to air. Then from storage tank it is used for further uses.
IV. CIRCUIT DIAGRAM
Figure 5: Circuit diagram
Plant has two tanks of similar capacity constituting with
different solenoid valves and other associated paraphernalia.
When the pressure in air receiver tank exceeds 7 kg/cm^2 , it
admits to first tank through appropriate valves. Now, oxygen
and other impurities are absorbed by the CMS (Carbon
Molecular Sieve) and nitrogen is separated. When first tank
works for 40 seconds the second one regenerates then within
another two seconds both tank equalize the pressure nitrogen
generated in first tank pass to the storage tank, through
appropriate solenoid valves and surge vessel by releasing the
impurities. Then the operation repeated in the second tank.
ICCEECON 2K16 CHRIST KNOWLEDGE CITY 5 March 2016
Both tanks operate simultaneously one after another with an
interval of 10 seconds. So that process is continued and
Nitrogen storage tank is filled as required. A nitrogen storage
tank is installed after nitrogen surge vessel for storage of
nitrogen gas at pressure of 5.0 kg/cm2 g. And there is an
oxygen analyzer and a three way valve in between the
nitrogen storage tank and surge vessel. The oxygen analyzer
will check the amount of oxygen in the gas. If oxygen content
exceeds 0.7% the three way valve will direct that gas to air.
Else it is stored in the nitrogen storage tank. Nitrogen
generates are based on well proven technology using carbon
molecule sieves (CMS) developed and supplied by Carbotech-
Germany. CMS is an absorbent having infinite number of
small pores. Nitrogen generates are based on well proven
technology using carbon molecule sieves (CMS) developed
and supplied by Carbotech- Germany. CMS is an absorbent
having infinite number of small pores. An oxygen molecule
having a smaller diameter than a Nitrogen molecule
.Therefore, the nitrogen is removed to a higher degree while
almost all the oxygen is adsorbed. Plant has two tanks of
similar capacity constituting with different solenoid valves and
other associated paraphernalia. When the pressure in air
receiver tank exceeds 7 kg/cm2 , it admits to first tank through
appropriate valves. Now, oxygen and other impurities are
absorbed by the CMS (Carbon Molecular Sieve) and nitrogen
is separated. Both tanks operate simultaneously one after
another with an interval of 10 seconds. So that process is
continued and Nitrogen storage tank is filled as required.
V. SCADA
Figure 6: SCADA Implementation
The SCADA system was designed with a software package
that has helped to ensure future upgrade capability and
compatibility. The controlling is being done using mainly 10
types of valves, also consist of receiver tank, surge vessel, and
main storage tank. In the given figure, the green color indicate
the flow of nitrogen and the red color indicates the waste gas.
VI. CONCLUSION
As per the paper “nitrogen plant automation using
PLC & SCADA” highlights the process of
manufacture and quantity control with the automation
process in the industry. Nitrogen is valued both as a
gas for its inert properties and as a liquid for cooling
& freezing. Virtually any industry can benefit from
nitrogen’s unique properties to improve yields,
optimize performance, product quality and make
operations safer.
Adsorption and other technologies for air separation
continue to advance as more efficient, highly
packaged, and compact gas generators are developed.
Increased power efficiency in PSA nitrogen
generators is being driven both by process
improvements and enhanced adsorption materials.
Nitrogen users will benefit from these advances as
they evaluate supply options for nitrogen facilities and
manage increased demand at existing plants.
REFERENCES
[1] Svetlana Ivanova, Robert Lewis,” Producing
Nitrogen via Pressure Swing Adsorption- Reactions
and Separations”.
[2] “Memo 3 preliminary design of nitrogen
processes: PSA and Membrane systems” CARNEGIE
MELLON UNIVERSITY CHEMICAL
ENGINEERING DEPARTMENT. Retrieved 9
January 2012.
[3]A review of air separation technologies and their
integration with energy conversion processes, A.R.
Smith, J. Klosek Stabilityanaly sis of a pressure swing
adsorption process, C. Bechaud,S. Melen, D. Lasseux,
M. Quintard, C. H. Bruneau
[4] T.C. Golden, P.J Battavio., Y.C. Chbn, T.S. Farrjs
and JN. Armor , Gas Separation and
Purification, vol VII, nr. 4, 1993, p. 274
[5] J.N. Armor, Molecular Sieves for Air Separation
Materials Chemistry; An Emerging Discipline
- American Chemical Society 1995
[6] Shivaji, Sircar, Pressure Swing Adsorption;
Research Needs by Industry, Proceedings of 3rd
International Conference of Fundamentals of
Adsorption, Germany, 1991, p. 815
[7] G.H. Baron, Industrial Gas Separation Using PSA
- in Separation Technology, p. 201 edited by
E.F. Vansant, Elsevier Science B.V. Amsterdam 1994
ICCEECON 2K16 CHRIST KNOWLEDGE CITY 5 March 2016
[8]Shivaji, Sircar, Gas Separation and Purification,
vol VII, nr. 2, 1993
[9] H.J. Schroter - Gas separation and Purification, vol
VII, nr. 4, 1993, p. 247
[10]V. Stanciu, E. David, D. Ştefănescu, Chem. Rew.
(Bucharest), vol 46, nr. 4, 1995, p. 34