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The Principle Of Liquefaction Engineering Essay

Liquefaction of gases is ever accomplished by refrigerating the gas to some temperature below its critical temperature so that liquid can be formed at some suited force per unit area below the critical force per unit area. Thus gas liquefaction is a particular instance of gas infrigidation and can non be separated from it. In both instances, the gas is foremost compressed to an elevated force per unit area in an ambient temperature compressor. This high-pressure gas is passed through a rip recuperative heat money changer to a restricting valve or enlargement engine. Upon spread outing to the lower force per unit area, chilling may take topographic point, and some liquid may be formed. The cool, low-pressure gas returns to the compressor recess to reiterate the rhythm. The intent of the rip heat money changer is to warm the low-pressure gas prior to recompression and at the same time to chill the high-pressure gas to the lowest temperature possible prior to enlargement. Both iceboxs and liquefiers operate on this basic rule.

In a uninterrupted infrigidation procedure, there is no accretion of refrigerant in any portion of the system. This contrasts with a gas liquefying system, where liquid accumulates and is withdrawn. Therefore, in a liquefying system, the entire mass of gas that is warmed in the rip heat money changer is less than that of the gas to be cooled by the sum liquefied, making an instability mass flow in the heat money changer. In a icebox the warm and cool gas flows are equal in the heat money changer. This consequences in what is normally referred to as a “ balanced flow status ” in a icebox heat money changer. The thermodynamic rules of infrigidation and liquefaction are indistinguishable. However the analysis and design of the two systems are rather different because of the status of balanced now in the icebox and imbalanced now in liquefier systems.

The Joule-Thomson coefficient is a belongings of each particular gas, is a map of temperature and force per unit area, and may he positive, negative, or nothing. For case, H, He, and neon have negative J-T coefficients at ambient temperature. Consequently, to be used as refrigerants in a restricting procedure they must foremost be cooled either by a separate pre coolant liquid. Merely so will restricting do a farther chilling instead than a warming of these gases.

Another method of bring forthing low temperatures is the adiabatic enlargement of the gas through a work-producing device such as an enlargement engine. In the ideal instance, the enlargement would be reversible and adiabatic and hence isentropic. In this instance, we can specify the isentropic enlargement coefficient which expresses the temperature alteration due to a force per unit area alteration at changeless information. An isentropic enlargement through an expander ever consequences in a temperature lessening. Whereas an enlargement through an enlargement valve may or may non ensue in a temperature lessening. The isentropic enlargement procedure removes energy from the gas in the signifier of external work, so this method of low-temperature production is sometimes called the external work method.

1.2 Requirement of N liquefier

Nitrogen liquefier used to bring forth liquid N. Because of its low production cost and comparatively higher degrees of safety is the most common chilling medium in the cryogenic temperature scope above 77 K. The application covers such diverse countries as:

Pre coolant in production of liquid He and low temperature iceboxs

Cryotreatment of critical metallic constituents such as hubs, milling cutters, knives, rollers, acerate leafs, dies and clouts, bearings and preciseness measurement equipment,

Preservation of unrecorded biological stuff as blood, animate being and human sperms, embryos, bacterial civilizations etc

Cold trap in vacuity systems and in surface assimilation pumps, and

Assorted research lab and industrial applications.

1.3 Production of Liquid Nitrogen

In some parts of our state, it is possible to purchase liquid N from majority providers at low cost. But in most instances, including some major metropolitan countries, a research lab needs to run its ain liquid N generator. There are three major international providers of N liquefiers in our state:

Stirling Cryogenicss of Netherlands,

Linde AG, Germany, and

Consolidated Pacific Industries, USA.

The liquefier from Stirling Cryogenics is based on the built-in Philips-Stirling Cycle, while the latter two usage turbine for cold production. The Linde turbine uses gas bearings, while the CPI machine uses antifriction bearings. The workss are tremendously expensive to purchase and to keep and proprietors are frequently forced to purchase new workss due to non-availability of proprietary spares. It is imperative that our state develops an autochthonal N liquefier of capacity in the scope 10 to 50 l/hour. Hence a N liquefier is to be designed.

1.4 Aims of the work

Prior to the devising of the turboexpander based nitrogen liquefier, the thermodynamic procedures is to be designed and each equipment specifications are to be determined. A system runs continuously when it follows definite procedures in a cyclic way. Process design means, finding of the type of thermodynamic procedures included in the thermodynamic rhythm and repairing the points i.e. force per unit area and temperature. While planing the procedure, equipment handiness, restraints and cost should be kept in head. Process design besides includes the puting the parametric quantities up to the optimal status that maximal sum of liquid will be obtained.

Chapter 2

Literature Review

2. LITERATURE REVIEW

2.1 History of Liquefaction

Before 1877, a figure of workers had discovered by ocular observation in thick-walled glass tubings that the lasting gases, including H, N, O and C monoxide, could non be liquefied at force per unit areas every bit high as 400 standard pressure. At foremost in 1877 O gas is liquefied by Cailletet and Pictet. It is the first lasting gases to be liquefied. The term ‘permanent ‘ arose from the by experimentation determined fact that such ‘permanent ‘ gases could non be liquefied by force per unit area entirely at ambient temperature, in contrast to the non-permanent or condensable gases like Cl, azotic oxide and C dioxide, which could be liquefied at rather modest force per unit areas of 30-50 standard pressure.

Fig. 2.1 Cailletet ‘s gas compressor and liquefaction setup

Figures 2.1 show the setup which Cailletet used to bring forth a fleeting fog of O droplets in a midst walled glass tubing. The O gas was compressed utilizing the petroleum Natterer compressor in which pressures up to 200 standard pressures. were generated by a non-automatic prison guard doodly-squat. The force per unit area was transmitted to the O gas in the glass tubing by hydraulic transmittal utilizing H2O and quicksilver. The gas was cooled to – 110A°C by enveloping the glass tubing with liquid ethene, and was so expanded all of a sudden by let go ofing the force per unit area via the manus wheel. A fleeting fog was seen, and the process could so be repeated for other perceivers to see the phenomenon.

Simultaneously at the first liquefaction of O by Cailletet, Pictet besides liquefied O in the same twelvemonth 1877.

Fig 2.2 Pictet ‘s cascade infrigidation and liquefaction system

Figure 2.2 shows the cascade infrigidation system of Pictet, in which O was foremost cooled by sulfur dioxide and so by liquid C dioxide in heat money changers, before being expanded into the ambiance by opening a valve. The enlargement yielded a ephemeral jet of liquid O, but no liquid could be collected from the high speed jet. The figure shows how Pictet used braces of compressors to drive the SO2 ( -20A°C ) and CO2 ( -60A°C ) refrigerant rhythms on a uninterrupted footing, and this is likely the first illustration of a cascade infrigidation system runing at more than one temperature degree. his usage of the cascade system inspired others like Kamerlingh Onnes and Dewar.

In 1883, the Polish scientists Olzewski and Wroblewski, at Cracow, had improved Cailletet ‘s setup by:

Adding an upside-down Uracil to the glass tubing ; and

Rreducing the ethylene temperature to – 136A°C by pumping it below atmospheric force per unit area.

These betterments enabled them to bring forth little measures of liquid O in the U tubing and to liquefy C monoxide and N for a few seconds.

From first liquefaction of O to 1895, there was small advancement in the developments of liquefiers. Then in 1895, Hampson in London and Linde in Munich at the same time patented compact and efficient air liquefiers which used self-intensive or regenerative chilling of the high force per unit area air by the colder low force per unit area expanded air in long lengths of coiled heat money changer. In this simple manner, the complications of cascade precoolers using liquid ethene and other liquid cryogens were removed. A farther advantage of this simple liquefier was the absence of traveling parts at low temperature, the chilling being produced by Joule-Thomson enlargement through a nose or valve. Carl von Linde made rapid advancement in developing this technological discovery. He was a professor and research worker at the University of Munich, and he had his ain company building infrigidation works.

The Linde-Hampson is the simplest of all the liquefaction systems. A schematic of the Linde-Hampson system is shown in Fig. 2.3 and the rhythm is shown on the T-s plane in Fig. 2.4.

Fig. 2.3 Linde air liquefaction system Fig. 2.4 T-S Diagram of Linde rhythm

Procedure 1 to.2 would really be two procedures: an irreversible, adiabatic or polytropic compaction followed by an after chilling to take down the gas temperature back to within a few grades of ambient temperature. The gas following passes through a constant-pressure heat money changer ( ideally ) in which it exchanges energy with the surpassing low force per unit area watercourse to indicate 3. From point 3 to indicate 4, the gas expands through an enlargement valve to P4. At point 4, some of the gas watercourse is in the liquid province and is withdrawn at status degree Fahrenheit ( saturated-liquid status ) , and the remainder of the gas leaves the liquid receiving system at status g ( saturated-vapor status ) . This cold gas is eventually warmed to the initial temperature by absorbing energy at changeless force per unit area ( ideally ) from the incoming high-pressure watercourse. The liquid air produced is really less.

By 1898, Charles Tripler, an applied scientist in New York, had constructed a similar but much larger air liquefier, driven by a 75 kilowatt steam engine, which produced literally gallons of liquid air per hr. Tripler discovered a market for liquid air as a medium for driving air enlargement engines ( the internal burning engine was still undependable at that clip ) and succeeded to establish his Liquid Air Company.

Fig. 2.5 Tripler ‘s research lab demoing 175 kW steam driven

multistage air compressor and 25 dm h- air liquefier

In the twelvemonth, 1902, a immature Gallic advanced applied scientist Georges Claude, with broad connexions in the scientific universe of Paris, had succeeded in bring forthing a Piston enlargement engine working at the low temperatures required for the liquefaction of air. The addition in chilling consequence over the Joule-Thomson nozzle enlargement of the Linde, Tripler, and Hampson designs was so big as to represent a 2nd technological discovery. Claude developed air liquefiers with Piston expanders.

Fig. 2.6 Claude air liquefaction system Fig. 2.7 T-S Diagram of Claude Cycle

The enlargement through an enlargement valve is an irreversible procedure, thermodynamically talking. Therefore if we wish to near closer to the ideal public presentation, we must seek a better procedure to bring forth low temperatures. In the Claude system, shown in Fig. 2.6, energy is removed from the gas watercourse by leting it to make some work in an enlargement engine or expander.

The Claude rhythm is shown on the T-s plane in Fig. 2.7. If the enlargement engine is reversible and adiabatic ( which we shall presume to be true for this analysis ) , the enlargement procedure is isentropic, and a much lower temperature is attained than for an isenthalpic enlargement, In the Claude system, the gas is foremost compressed to force per unit areas on the order of 4 MPa ( 40 standard pressure or 590 psia ) and so passed through the first heat money changer. Between 60 and 80 per centum of the gas is so diverted from the mainstream, expanded through an expander, and reunited with the return watercourse below the 2nd heat money changer. The watercourse to be liquefied continues through the 2nd and 3rd heat money changers and is eventually expanded through an enlargement valve to the liquid receiving system. The cold vapour from the liquid receiving system is returned through the heat money changers to chill the entrance gas.

In 1882, Kamerlingh Onnes embarked on edifice up a cryogenic research lab at the University of Leiden in the Netherlands. The inspiration for his research lab was provided basically by the systematic work of Van der Waals at Amsterdam and later at Leiden on the belongingss of gases and liquids. In 1866, Van der Waals had published his first paper on ‘the continuity of liquid and gaseous provinces ‘ from which the physical apprehension of the critical province and of liquefaction and vaporization was to turn. Although slow to acquire started, Onnes was the first individual to develop the trigon of interaction between research, preparation and industry. He operated an unfastened door policy, promoting visitants from many states to see, learn and discourse. As a consequence, he developed a broad scope of contacts and a turning path record of success, so that from the bend of the century his Leiden research lab became the taking Centre for cryogenies for about 50 old ages, surely until the mid-1930s. For illustration, in 1908 he won the race with Dewar to liquefy He and went on to detect superconductivity in 1911 ( Table 2 ) .

Kapitza ( 1939 ) modified the basic Claude system by extinguishing the 3rd or low-temperature heat money changer, as shown in Fig. 3.20. Several noteworthy practical alterations were besides introduced in this system. A rotary enlargement engine was used alternatively of a reciprocating expander. The first or high-temperature heat money changer in the Kapitza system was really a

set of valved regenerators, which combined the chilling procedure with the purification procedure. The incoming warm gas was cooled in one unit and drosss were deposited at that place, while the surpassing watercourse ~armed up in the other unit and flushed out the frozen drosss deposited in it. After a few proceedingss, a valve was operated to do the high- and low-pressure

watercourses to exchange from one unit to the other. The Kapitza system normally operated at comparatively low pressures-on the order of 700 kPa ( 7 standard pressure or 100 psia ) .

Around 1942 Samuel C. Collins of the section of mechanical Engineering at Massachusetts Institute of engineering developed an efficient liquid He research lab installation. He developed Collins He cryostat consequences economical and safe production of liquid He.

3.B. Heyiandt system

Helandt ( Davies 1949 ) noted that for a high force per unit area of about 20 MPa ( 200 standard pressure ) and an expansion-engine flow-rate ratio of appro ximately 0.60, the optimal value of temperature before enlargement through the expander was close ambient temperature. Therefore, one could extinguish the first heat money changer in the Claude system by compacting the gas to 20 MPa. Such a modified Claude system is called the Heylandt system, after its conceiver, and is used ext~nsively in hard-hitting liquefaction workss for air. The system is shown schematically in Fig. 3.21. The advantage ofthe Heylandt system is that the lubrication jobs in the expander are non hard to get the better of. In the air-liquefaction system, the gas enters the expander at ambient temperature and leaves the expander at about 150 K ( -190A°F ) so that light lubricators can be used. In the Heylandt system, the expander and the enlargement valve contribute about every bit in bring forthing low temperatures, whereas in the ordinary Claude system, the expander makes by far the largest part, as one will observe from Example 3.4.

Chapter 3

Procedure Design

3.1 Modified Claude Cycle for Nitrogen Liquefier

A modified Claude rhythm is taken into consideration to plan nitrogen liquefier to take the advantage of both the turboexpander and JT valve. Alternatively of three heat money changers as in the Claude rhythm, two Numberss of heat money changers are used in this liquefier. Last two heat money changers of the Claude rhythm are combined to a individual heat money changer to cut down the cost of the liquefier.

A turbo expander based nitrogen liquefier consists of following parts:

Compressor

Heat money changers

Turboexpander

JT Valve

Phase centrifuge

Cold box

Shrieking

Instrumentality

A prison guard compressor will be installed to supply the tight N gas. Heat money changers are critical constituents of any cryogenic icebox. To interchange high heat in little country home base five compact heat money changer are used. The turboexpander is the bosom of the liquefier and it can used take downing the temperature to expectable sum adiabatically. JT valve is used for isenthalpic enlargement. Phase centrifuge is used to divide liquid and gas. Piping and other instrumentalities are required to link and command the systems. Whole thing is kept inside the cold box.

Fig.3.1 shows the procedure diagram of the N liquefier. At atmospheric temperature and force per unit area at 1.1 saloon the pure N gas is feed into the prison guard compressor and compressed up to 8 bars. The tight gas is passed through the first heat money changer i.e. HX1. Then some mass is diverted through the turboexpander and remain base on ballss through the 2nd heat money changer i.e.HX2 for liquefaction. For easy computation HX2 split into two parts i.e. HX2a and HX2b. From the HX2, isenthalpic enlargement takes topographic point by utilizing JT valve which consequences liquid N. Liquid N taken out and stay vapor nitrogen meet with the isentropic expanded N by the turboexpander and provender once more to the compressor by go throughing through the HX2 and HX1.

Fig. 3.1 Process Diagram Nitrogen Liquefier

3.2. Stairss of the procedure design computations

I. Known values

Pure N provender to the prison guard compressor at temperature, 300 K and force per unit area 1.1 bars. Isothermal compaction is considered but in existent instance, temperature is increased. Let it is increased to the temperature 310 K and force per unit area is 8 bars.

By and large maximal force per unit area bead in both the heat money changers is taken as 0.05 bars. Hence the force per unit area of high force per unit area watercourse after the HX1 is 7.95 bars. Similarly after HX2, the force per unit area is 7.9 bars. Passing through the HX2 Nitrogen in the high force per unit area watercourse comes to two stage province. The concentrated temperature at 7.9 bars is 100.13 K.

The force per unit area inside the stage centrifuge should be merely higher than the atmospheric, so that the liquid will come out of the cold box. So phase centrifuge force per unit area is fixed to 1.2 bars. Saturated temperature of N at 1.2 bars inside stage centrifuge is 78.8 K.

Between HX2 and stage centrifuge, JT Valve is placed for isenthalpic enlargement of N from 7.9 bars to 1.2 bars.

The fraction of mass flow through the turboexpander expanded to the force per unit area 1.3 bars to keep the force per unit area ratio of 6.

Then from mixture comes out at 1.2 bars and return to compressor at 1.1 bars by force per unit area bead of 0.05 bars at each heat money changer. Pressure difference is maintained at all equipments so flow will happen cyclically.

two. Parameters:

The parametric quantities, by altering which, the sum of liquid N effected or by commanding which we optimize the end product are:

Effectiveness of heat money changer 1, i??1

Pinch point for heat money changer 2, P

Efficiency of turbo expander, i??t

Mass flow ratio diverted through Turbo expander, i??

three. Initial Valuess:

Some initial value of Yield, y and low force per unit area watercourse mercantile establishment heat content from HX1, should be taken.

four. Unknown Variables:

Following are the unknown variables which value are to be determined.

Heat content at the issue of first heat money changer, h3

Heat content at the issue of 2nd heat money changer, h4

Heat content at the issue of JT valve, h5

Heat content at the issue of turboexpander, h6

Heat content at the issue of turboexpander ( Isentropic enlargement ) , h6s

Heat content at after blending from stage centrifuge and issue of turboexpander, h7

Heat content at the recess to the 2nd heat money changer, h8

Heat content at the recess to the first heat money changer, h9

Dryness fraction in the stage centrifuge, x5

Ratio of mass of liquid produced to mass of gas compressed, output, Y

Heat content at the pinch point temperature of low force per unit area watercourse of 2nd heat money changer, horsepower

v. Pinch point specification of Heat exchanger2

Dividing the HX2 into two parts, First heat money changer being the one where the hot N gas is cooled up to the impregnation temperature of 100.13 K & A ; the 2nd portion being the distilling portion. The minimal temperature difference occurs at the point where the condensation Begins and is called as pinch point.

For the specified pinch value P, for HX2, we have

( 3.1 )

We can acquire enthalpy horsepower, at that pinch temperature and force per unit area.

six. Heat Exchanger 1

For the specified value of effectivity of heat money changer 1 and the pinch point specification for heat money changer 2, h8, h3 and h9 calculated from the effectivity definition and energy balance between hot and cold fluids for HX1 and HX2a.

Assume

( 3.2 )

( 3.3 )

( 3.4 )

The updated value of h9 is calculated. It should be checked with the old value. This loop should be done until both are equal.

seven. Turbo-expander

From the Fig. 3.2, it is clear that 3-6s is the isentropic enlargement and 3-6 is the existent enlargement.

From belongings tabular array, information at 3, i.e. s3, can be found out at h3 and p3.

The heat content at the terminal of enlargement is found out as

( 3.5 )

h6s can be acquire from p6s and s6s.

( 3.6 ) ( 6 )

3

6s

6

Fig. 3.2 Expansion in Turbo Expander

eight. Mixer

Applying energy balance equation for the sociable, heat content at mercantile establishment of sociable is

( 3.7 )

nine. Heat Exchanger 2

Heat content at mercantile establishment of hot fluid is found out by energy balance between hot and cold fluids as

( 3.8 )

x. Throttle valve:

Choking is an isenthalpic procedure. Comparing the heat contents before and after restricting

( 3.9 )

( 3.10 )

eleven. Output:

The liquid output obtained per kilogram of gas passing through the choking valve is hence ( 1-x5 ) .

For kilogram of gas passing through the choking valve is

( 3.11 )

Again look into the deliberate value of Y with the false one and calculated h9 with false h9. Replace it with the new value of h9 and Y and calculate once more till both the false values match with deliberate value

3.3 Process Design Calculation Using Microsoft Excel

Working Fluid:

Nitrogen

Asumed Yeild, Y =

0.043262

Flow Through Turbo Expander, i?? =

0.94

Effectiveness of HX1 =

0.98

Efficiency of Expander =

0.5

Pinch temperature HX2 =

1

Mass Flow Rate =

296

kg/hr =

0.08222

kg/s

Assumed Enthalpy at 9 =

317.461

Points

Presssure

( saloon )

Temperature

( K )

Heat content

kJ/kg

Information

kJ/kg/K

Quality

Mass Flow Rate kg/s

1

1.1

300.00

311.44

6.8194

0.08222

2

8

310.00

320.44

6.2602

0.08222

2*

1.1

310.00

321.85

6.8535

A

3

7.95

120.52

114.76

5.2269

0.0772868

4

7.9

100.13

-64.24

3.4653

0.0541

0.0049332

4f

7.9

100.13

-72.91

3.3788

0.0000

A

4g

7.9

100.13

87.39

4.9786

1.0000

A

5

1.2

78.78

-64.24

3.5678

0.2790

0.0049332

5f

1.2

78.78

-119.19

2.8708

0.0000

0.003557

5g

1.2

78.78

77.78

5.3693

1.0000

0.001376

6s

1.3

79.49

68.24

5.2269

0.9487

A

6sf

1.3

79.49

-117.72

2.8892

0.0000

A

6sg

1.3

79.49

78.29

5.3533

1.0000

A

6

1.3

90.81

91.496

5.5090

& gt ; 1

0.0772868

7

1.2

90.40

91.26

5.5293

0.078663

Phosphorus

1.15

99.13

100.77

5.6420

A

8

1.15

100.73

102.48

5.6592

0.078663

9

1.1

305.78

317.461

6.8393

A

0.078663

Calculated Yeild, Y in Phase Separator =

0.043262

Energy Balance =

0.043261

Temperature Drop in Turbo Expander =

29.71

Accumulative UA for Hx 1 =

1.8787

kW/K

Accumulative UA for Hx 2 =

0.2032

kW/K

Liquid Nitrogen Produced

12.805206

kg/hr

* Note: Text written indoors double lined boundary line are the input values

Fig. 3.3 T-S Diagram of Nitrogen Liquefier

3.4 Process Design Using Aspen Hysys

I. Introduction to Aspen Hysys

Aspen Hysys is a procedure simulation environment designed to function many treating industries particularly Oil & A ; Gas and Refining. With Aspen Hysys one can make strict steady province and dynamic theoretical accounts for works design, public presentation monitoring, trouble-shooting, operational betterment, concern planning, and plus direction. Through the wholly synergistic Aspen Hysys interface, one can easy pull strings procedure variables and unit operation topology, every bit good as to the full custom-make your simulation utilizing its customization and extensibility capablenesss. The procedure simulation capablenesss of Aspen Hysys enables applied scientists to foretell the behaviour of a procedure utilizing basic technology relationships such as mass and energy balances, stage and chemical equilibrium, and reaction dynamicss. With dependable thermodynamic informations, realistic operating conditions and the strict Aspen Hysys equipment theoretical accounts, they can imitate existent works behaviour. Some of the of import Aspen Hysys characteristics are listed below:

WindowsA® Interoperability: Interface contains a procedure flow sheet position for graphical layout, informations browser position for come ining informations, the patented Next expert counsel system to steer the user through a complete and consistent definition of the procedure flow sheet.

Plot Wizard: Hysys enables the user to easy make secret plans of simulation consequences.

Flowsheet Hierarchy and Templates: Collaborative technology is supported through hierarchy blocks that allow sub-flowsheets of greater item to be encapsulated in a individual high-ranking block. These hierarchy blocks can be saved as flowsheet templets in libraries.

Equation-Oriented Mold: Advanced specification direction for equation oriented theoretical account constellation and sensitiveness analysis of the whole simulation or specific parts of it. The alone combination of Sequential Modular and Equation Oriented solution engineering allows the user to imitate extremely nested procedures encountered typically in the chemical industry.

Thermo physical Properties: Physical belongings theoretical accounts and informations are cardinal to bring forthing accurate simulation consequences that can be used with assurance. Aspen Hysys uses the extended and proved physical belongings theoretical accounts, informations and appraisal methods available in Aspen Propertiesa„? , which covers a broad scope of procedures from simple ideal behaviour to strongly non-ideal mixtures and electrolytes. The constitutional database contains parametric quantities for more than 8,500 constituents, covering organic, inorganic, aqueous, and salt species and more than 37,000 sets of binary interaction parametric quantities for 4,000 binary mixtures.

Convergence Analysis: to automatically analyse and propose optimum tear watercourses, flowsheet convergence method and solution sequence for even the largest flowsheets with multiple watercourse and information recycles.

Sensitivity Analysis: to conveniently generate tabular arraies and secret plans demoing how process public presentation varies with alterations to selected equipment specifications and runing conditions.

Design Specification: capablenesss to automatically cipher operating conditions or equipment parametric quantities to run into specified public presentation marks.

Data-Fit: to suit procedure theoretical account to existent works informations and guarantee an accurate, validated representation of the existent works.

Determine Plant Operating Conditions that will maximise any nonsubjective map specified, including procedure outputs, energy use, watercourse purenesss and procedure economic sciences.

Simulation Basic Manager: This characteristic available in Aspen Hysys for utilizing different fluids like N, air, ethyne as per demand. Besides several fluid bundles like BWRS, MWRS, and ASME are provided to cipher belongingss at different provinces.

two. Procedure of Process Design in Aspen Hysys

To make a new instance, From the File bill of fare, choice New. In the sub-menu, choice Case. The Simulation Basis Manager window will look.

The Simulation Basis Manager is the chief belongings position of the Simulation environment. One of the of import constructs that HYSYS is based upon is Environments. The Simulation Basis environment allows you to input or entree information within the Simulation Basis director while the other countries of HYSYS are put on clasp avoiding unneeded Flowsheet computations. Once you enter the Simulation environment, all alterations that were made in the Simulation Basis environment will take consequence at the same clip. Conversely, all thermodynamic informations is fixed and will non be changed as uses to the Flowsheet take topographic point in the Simulation environment. The minimal information required before go forthing the Simulation Basis director is atleast one installed Fluid Package with an affiliated Property Package and At least one constituent in the Fluid Package.

The Components Manager is located on the Components check of the Simulation Basis Manager. This check provides a location where sets of chemical constituents being modeled may be retrieved and manipulated. These component sets are stored in the signifier of Component Lists that may be a aggregation of library pure constituents or conjectural components.The Components Manager ever contains a Master Component List that can non be deleted. This maestro list contains every constituent available from “ all ” constituent lists. If you add constituents to any other component list, they automatically acquire added to the Master Component List. Besides, if you delete a constituent from the maestro, it besides gets deleted from any other component list that is utilizing that constituent.

In HYSYS, all necessary information refering to pure component flash and physical belongings computations is contained within the Fluid Package. This attack allows you to specify all the needed information inside a individual entity. There are four cardinal advantages to this attack:

All associated information is defined in a individual location, leting for easy creative activity and alteration of the information.

Fluid Packages can be exported and imported as wholly defined bundles for usage in any simulation.

Fluid Packages can be cloned, which simplifies the undertaking of doing little alterations to a complex Fluid Package.

Multiple Fluid Packages can be used in the same simulation.

The Fluid Package Manager is located on the Fluid Pkgs check of the Simulation Basis Manager. This check provides a location where multiple fluid bundles can be created and manipulated. Each fluid bundle available to your simulation is listed in the Current Fluid bundles group with the undermentioned information: name, figure of constituents attached to the fluid bundle, and belongings bundle attached to the unstable bundle. From the Fluid Pkgs check of the Simulation Basis Manager chink either the View or Add button to open the Fluid Package belongings position. Make certain you select the proper fluid bundle when utilizing the position option. Click on the Set Up check. From the Component List Selection drop-down list, select the constituents you want to utilize in your unstable bundle.

Here Benedict-Webb-Rubin-Starling ( BWRS ) fluid bundle was used. This theoretical account is normally used for compaction applications and surveies. It is specifically used for gas stage constituents that handle the complex thermodynamics that occur during compaction, and is utile in both upstream and downstream industries.

After choosing fluid bundles and constituents, a procedure flowsheet window will apear on which the unit opearations can be installed. There are a figure of ways to put in unit operations into your flowsheet. Many unit operations are available in the flowsheet pallet. All information refering a unit operation can be found on the check and pages of its belongings position. Each check in the belongings position contains pages, which pertain to a certain facet of the operation, such as its watercourse connexions, physical parametric quantities ( for illustration, force per unit area bead and energy input ) , or dynamic parametric quantities such as vas evaluation and valve information. Material and energy watercourses transfer process information between operations. The Process Flow Diagram is the default belongings position when you foremost enter the Simulation environment. The PFD provides the best representation of the flowsheet as a whole. Using the PFD gives you immediate mention to the advancement of the simulation presently being built, such as what watercourse and operations are installed, flowsheet connectivity, and the position of objects. In add-on to graphical representation, you can construct your flowsheet within the PFD utilizing the mouse to put in and link objects. A full set of use tools is available so you can shift watercourses and operations, resize icons, or reroute watercourses. All of these tools are designed to simplify the development of a clear and concise graphical procedure representation.

The PFD besides possesses analytical capablenesss. You can entree belongings positions for watercourse or operations straight from the PFD, or put in custom Material Balance Tables for any or all objects. Complete Workbook pages can besides be displayed on the PFD and information is automatically updated when alterations are made to the procedure.

Input values in hysys

From simulation footing director in the constituent pure N is taken as material watercourse. Then enter into the simulation environment. There all unit operations are arranged in order and linked by material watercourses. For each unit operations follwing input values are entered.

1. Compressor

Mass flow rate =296 kg/hr

Inlet temperature = 300 K

Inlet force per unit area = 1.1 saloon

Outlet force per unit area =8 saloon

2. Cooler

Outlet temperature = 310 K

Outlet force per unit area =8 saloon

3. Heat exchanger 1

Minimum Approach = 4.15 K

Pressure bead in both watercourses =0.05 saloon

4. Tee

Flow ratio through turbo expander = 0.94

5. Turbo expander

Efficiency of turbo expander = 50 %

Outlet force per unit area =1.3 saloon

6. Heat exchanger 2

Minimum Approach = 1 K

Pressure bead in both watercourses =0.05 saloon

7. JT Valve

Outlet force per unit area = 1.2 saloon

OUTPUT VALUE

Sum of liquid yeild can be seen in the liquid watercourse of the stage centrifuge. It comes 12.392 kg/hr.

Fig. 8 Process Flow Diagram of Nitrogen Liquefier

Chapter 4

Consequences and Discussion

4. RESULTS AND DISCUSSION

4.1 Performance Analysis

The consequence of parametric fluctuation is done on the liquefaction system gives the optimal public presentation. This analysis besides depicts the off design public presentation analysis. The parametric quantities are

Effectiveness of heat money changer 1, i??1

Pinch point for heat money changer 2, P

Efficiency of turbo expander, i??t

Mass flow ratio diverted through Turbo expander, i??

4.1.1 Effect of Variation of expander flow ratio, i??

The value of turbine efficiency, effectivity of heat exchanger-1, and pinch point of heat exchanger-2 are kept changeless. The consequence of output with the fluctuation of mass flow ratio through turboexpander is studied as shown in figure. This indicates that there is an optimal output at a peculiar mass flow ratio through the turboexpander.

Table 4.1 Effect of fluctuation of expander flow ratio

Turbo expander

flow ratio, i??

Output ( Excel )

Output ( Hysys )

Compressor work

per kilogram of liquid

produced

in kJ/kg ( Excel )

Compressor work

per kilogram of liquid

produced

in kJ/kg ( Hysys )

0.94

0.04278

0.04211

210.36

213.75

0.90

0.04096

0.04030

219.71

223.32

0.85

0.03870

0.03804

232.58

236.59

0.80

0.03644

0.03585

246.98

251.08

0.70

0.03197

0.03128

281.55

287.77

0.60

0.02756

0.02704

326.52

332.86

0.50

0.02327

0.02249

386.76

400.16

0.40

0.01917

0.01827

469.53

492.70

0.30

0.01543

0.01459

583.39

616.91

0.20

0.01251

0.01091

719.25

824.59

Fig. 4.1 Variation of output with expander flow ratio

Fig. 4.2 Variation of compressor work per kilogram of liquid with expander flow ratio

4.1.2 Effect of Variation of effectivity of HX1, i??1

The value of turbine efficiency, mass flow ratio through turboexpander, and pinch point of heat exchanger-2 are kept changeless. The consequence of output with the fluctuation of effectivity of heat exchanger-1 is studied as shown in figure.

Table 4.1 Effect of Variation of effectivity calculated by Excel and Hysys

Effectiveness of

Heat money changer 1, i??iˆ±

Output ( Excel )

Output ( Hysys )

0.98

0.04278

0.04211

0.97

0.03838

0.03784

0.96

0.03395

0.03365

0.95

0.02948

0.02937

0.94

0.02499

0.02503

0.92

0.01591

0.01628

0.90

0.00671

0.00756

0.89

0.00206

0.00304

Fig. 4.3 Variation output with effectivity of HX-1

4.1.3 Effect of Variation of pinch point of 2nd heat money changer

The value of turbine efficiency, mass ratio through turboexpander, and effectivity of first heat money changer are kept changeless. The consequence of output with the fluctuation of pinch point of 2nd heat money changer is studied as shown in figure.

Table 4.1 Effect of Variation of pinch point of HX-2 calculated by Excel and Hysys

Pinch Temperature

Of heat money changer 2

Output ( Excel )

Output ( Hysys )

Temperature bead

in turboexpander,

DTex ( Excel )

Temperature bead

in turboexpander,

DTex ( Hysys )

1.00

0.04326

0.04258

29.71

30.51

2.00

0.04278

0.04211

29.63

30.42

3.00

0.04231

0.04162

29.57

30.35

4.00

0.04185

0.04123

29.50

30.28

8.00

0.04005

0.03944

29.25

30.06

12.00

0.03836

0.03783

28.96

29.94

Fig. 4.4 Variation output with Pinch temperature of HX-2

4.1.4 Effect of Variation of turbo expander efficiency i??

The consequence of fluctuation of turbo expander efficiency on output, temperature bead in turbo expander and temperature difference in mixture is studied at changeless effectivity of first heat money changer, mass fraction through turbo expander and pinch point of 2nd heat money changer.

Table 4.1 Effect of Variation of pinch point of HX-2 calculated by Excel and Hysys

Turbo

expander

efficiency, i??

Output ( Excel )

Output ( Hysys )

Temp. bead

in turbo

expander,

DTex

( Excel )

Temp. bead

in turbo

expander,

DTex

( Hysys )

Temp.diff

At mixture,

DTmix

( Excel )

Temp. diff

At mixture,

DTmix

( Hysys )

0.40

0.03215

0.03172

25.37

26.032

13.40

12.77

0.50

0.04278

0.04211

29.63

30.415

11.14

10.37

0.60

0.05385

0.05186

34.08

34.741

8.81

6.32

Fig. 4.4 Variation output with Turboexpander efficiency

4.2 Variable Specific Heat Analysis of Heat Exchanger

NTU-effectiveness relationships, was integrated with the limitation that the specific heats of the fluids was changeless. The fluid belongingss do vary well in the close critical part, and cryogenic heat money changers may run in this government. The specific heat besides varies significantly in a capacitor in which the fluid enters as a superheated vapor.Chowdhry and Sarangi ( 1984b ) examined the consequence of variable specific heats on the public presentation of H heat money changers. Oonk and Hustevedt ( 1986 ) examined the same consequence for He heat money changers. Soyars ( 1991 ) examined the consequence of variable fluid belongingss on the truth of analysis of He heat money changer public presentation in the temperature scope below 15 K.Their consequences indicated that noticeable mistakes result for He heat money changers in infrigidation systems if the He specific heat was treated as a changeless below 15 K.

Fig. 19 Heat money changer divided into five parts

A technique similar to the finite component attack will be used ; the heat money changer will be subdivided into little elements, in which the particular heat fluctuation is comparatively little and may be treated as changeless. In the heat money changer 2, Temperature of the hot fluid was divided into five parts and their heat contents found out by utilizing Allprops. The figure of Transfer units for each component is found out as follows:

Enthalpy of cold fluid at recess of component 1 is found out from energy balance between hot and cold fluids as

( 1 )

Heat capacities of cold and hot watercourses are found as

( 2 )

( 3 )

The effectivity of Heat money changer 1 is found out as

( 4 )

Or else,

( 5 )

The figure of transportation units for each component is found out as

( 6 )

( 7 )

4.2. Analysis of Heat exchanger-1

Table:

Element No. from hot terminal

Temp. in Cold watercourse ( K )

Enthalpy in Cold watercourse ( kJ/kg )

Enthalpy in Hot watercourse ( kJ/kg )

Temp. in Hot watercourse ( K )

Heat Capacity of cold watercourse ( kJ )

Heat Capacity of cold watercourse ( kJ )

Heat capacity ratio ( Cr )

Effectiv

-eness

Ntu

UA in kW/K

0

305.78

317.45

320.44

310.00

1

285.28

296.11

300.02

290.59

0.0819

0.0865

0.9468

0.8294

4.3239

0.3541

2

264.77

274.76

279.60

271.21

0.0819

0.0867

0.9446

0.7943

3.4992

0.2866

3

244.27

253.40

259.15

251.88

0.082

0.0869

0.9436

0.7611

2.9299

0.2402

4

223.76

232.00

238.68

232.60

0.0821

0.0873

0.9404

0.7294

2.4997

0.2052

5

203.26

210.57

218.18

213.40

0.0822

0.0878

0.9362

0.6989

2.1646

0.1779

6

182.75

189.10

197.64

194.31

0.0824

0.0885

0.9311

0.6691

1.8931

0.156

7

162.25

167.58

177.05

175.37

0.0826

0.0894

0.9239

0.6396

1.6647

0.1375

8

141.74

145.99

156.39

156.66

0.0828

0.0908

0.9119

0.6098

1.4642

0.1212

9

121.24

124.31

135.65

138.32

0.0832

0.093

0.8946

0.5789

1.2838

0.1068

10

100.73

102.48

114.77

120.59

0.0837

0.0969

0.8638

0.5456

1.1121

0.0931

0

0

Cum. UA =

1.8787

350

350

Avg Cc =

0.0825

Avg Ch =

0.0893

NTU=

22.782

Fig. 16 Operating Temperature Line for Heat money changer 1

Table: Accumulative heat content analysis for HX-1

( a ) L.P. side

Temp. ( K )

L P side ( 1.1 saloon ) Cp

Change in Temp

Average Cp

Mass Flow Rate

Change in Enthalpy

Cum Enthalpy

305.78

1.0404

0.00

1.04036

0.07866

0.000

0.000

280

1.0409

25.78

1.0406

0.07866

2.110

2.110

260

1.0417

20.00

1.0413

0.07866

1.638

3.748

240

1.0428

20.00

1.0423

0.07866

1.640

5.388

220

1.0443

20.00

1.0436

0.07866

1.642

7.030

200

1.0461

20.00

1.0452

0.07866

1.644

8.674

190

1.0471

10.00

1.0466

0.07866

0.823

9.497

180

1.0483

10.00

1.0477

0.07866

0.824

10.321

170

1.0496

10.00

1.0489

0.07866

0.825

11.146

160

1.0510

10.00

1.0503

0.07866

0.826

11.972

150

1.0526

10.00

1.0518

0.07866

0.827

12.799

145

1.0535

5.00

1.0531

0.07866

0.414

13.213

140

1.0545

5.00

1.0540

0.07866

0.415

13.628

135

1.0556

5.00

1.0551

0.07866

0.415

14.043

130

1.0568

5.00

1.0562

0.07866

0.415

14.458

125

1.0582

5.00

1.0575

0.07866

0.416

14.874

120

1.0597

5.00

1.0590

0.07866

0.416

15.290

115

1.0615

5.00

1.0606

0.07866

0.417

15.707

110

1.0636

5.00

1.0626

0.07866

0.418

16.125

105

1.0662

5.00

1.0649

0.07866

0.419

16.544

100.73

1.0690

4.27

1.0676

0.07866

0.369

16.913

( B ) H.P. side

Temp. ( K )

H P side ( 8 saloon ) Cp

Change in Temp

Average Cp

Mass Flow Rate

Change in Enthalpy

Cum Enthalpy

310.00

1.0507

0.00

1.0507

0.08222

0.000

0.000

300.00

1.0516

10.00

1.0512

0.08222

0.864

0.864

280.00

1.0541

20.00

1.0529

0.08222

1.731

2.595

260.00

1.0577

20.00

1.0559

0.08222

1.736

4.331

240.00

1.0624

20.00

1.0600

0.08222

1.743

6.074

220.00

1.0688

20.00

1.0656

0.08222

1.752

7.826

200.00

1.0778

20.00

1.0733

0.08222

1.765

9.591

190.00

1.0836

10.00

1.0807

0.08222

0.889

10.480

180.00

1.0907

10.00

1.0871

0.08222

0.894

11.374

170.00

1.0995

10.00

1.0951

0.08222

0.900

12.274

160.00

1.1107

10.00

1.1051

0.08222

0.909

13.183

150.00

1.1254

10.00

1.1181

0.08222

0.919

14.102

145.00

1.1345

5.00

1.1300

0.08222

0.465

14.567

140.00

1.1453

5.00

1.1399

0.08222

0.469

15.036

135.00

1.1582

5.00

1.1518

0.08222

0.474

15.510

130.00

1.1740

5.00

1.1661

0.08222

0.479

15.989

125.00

1.1937

5.00

1.1838

0.08222

0.487

16.476

120.52

1.2163

4.48

1.2050

0.08222

0.444

16.920

Fig. 17 Accumulative enthalpy- Temp Diagram for Heat Exchanger 1

4.3. Analysis of Heat exchanger-2

Element No. from hot terminal

Temp in Hot watercourse ( Th )

Enthalpy in Hot watercourse ( hh )

Enthalpy in Cold watercourse ( hc )

Temp in Cold watercourse ( Tc )

Heat Capacity of cold watercourse ( Cc )

Heat Capacity of hot watercourse ( Ch )

Heat capacity ratio ( Cr )

Effectiv

east northeast

Ntu

UA in ( kW/K )

0

120.52

114.76

102.48

100.73

1

116.44

109.75

102.17

100.44

0.0842

1.1327

0.0743

0.0145

0.0146

0.0012

2

112.36

104.61

101.85

100.14

0.0842

1.1620

0.0725

0.0183

0.0185

0.0016

3

108.28

99.28

101.52

99.83

0.0843

1.2057

0.0699

0.0246

0.0249

0.0021

4

104.20

93.61

101.16

99.50

0.0843

1.2816

0.0658

0.0383

0.0391

0.0033

5

100.13

87.39

100.77

99.13

0.0843

1.4106

0.0598

0.0718

0.0747

0.0063

6

100.13

-64.24

91.26

90.31

0.0848

0.0000

0.8985

2.2872

0.1940

Cum. UA=

0.2084

Fig. 16 Operating Temperature Line for Heat money changer 2

Table: Accumulative heat content analysis for HX-2

( a ) L.P. side

Temp. ( K )

L P side 1.15 saloon Cp

Change in Temp

Average Cp

Mass Flow Rate

Change in Enthalpy

Cum Enthalpy

100.73

1.0705

0.00

1.0705

0.0787

0.000

0.000

99.00

1.0720

1.73

1.0713

0.0787

0.146

0.146

98.00

1.0730

1.00

1.0725

0.0787

0.084

0.230

97.00

1.0741

1.00

1.0735

0.0787

0.084

0.315

95.00

1.0766

2.00

1.0754

0.0787

0.169

0.484

93.00

1.0800

2.00

1.0783

0.0787

0.170

0.653

90.40

1.0865

2.60

1.0833

0.0787

0.221

0.874

( B ) H.P. side

Temp. ( K )

H P side 7.95 saloon Cp

Change in Temp

Average Cp

Mass Flow Rate

Change in Enthalpy

Cum Enthalpy

120.52

1.0425

0.00

1.0425

0.00493

0.000

0.000

118.00

1.0423

2.52

1.0424

0.00493

0.013

0.013

116.00

1.0422

2.00

1.0422

0.00493

0.010

0.023

112.00

1.0419

4.00

1.0420

0.00493

0.021

0.044

110.00

1.0417

2.00

1.0418

0.00493

0.010

0.054

108.00

1.0415

2.00

1.0416

0.00493

0.010

0.064

106.00

1.0413

2.00

1.0414

0.00493

0.010

0.075

104.00

1.0412

2.00

1.0412

0.00493

0.010

0.085

101.00

1.0408

3.00

1.0410

0.00493

0.015

0.100

100.13

1.0407

0.87

1.0408

0.00493

0.004

0.105

100.13

PHASE CHANGE

0.00493

0.748

0.873

Fig. 18 Accumulative enthalpy- Temp Diagram for Heat Exchanger 2

Chapter 5

Decisions

Decision

Two heat money changers are required, one with maximal effectivity of 0.98 and other heat money changer with pinch point of 1 or 2 K.

In the heat exchanger the force per unit area bead must be less than or equal to 0.05 Bar.

The turbo expander must be able to spread out so that 30 K will be decrease in temperature.

The JT valve should able to cut down force per unit area from 7.95 saloon to 1.2 saloon.

In the stage centrifuge liquid N of 12.39 kg/hr will be collected.

Chapter 6

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