NITROGEN PLANT AUTOMATION USING PLC

AND SCADA

Ms. Nicy V B

Asst. professor

Dept.of AEI

RCET, Thrissur

nicy.vb@gmail.c

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

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

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.

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

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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.

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integration with energy conversion processes, A.R.

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M. Quintard, C. H. Bruneau

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and JN. Armor , Gas Separation and

Purification, vol VII, nr. 4, 1993, p. 274

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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

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E.F. Vansant, Elsevier Science B.V. Amsterdam 1994

[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.

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