Study of Cryogenic Cycles

with ASPEN HYSYS Simulations

By: SURAJ SINGH PATWAL (11338)

PRADEEP MEENA (11339)

ASHISH ARYA (11361)

UDAYAVEER SINGH (11371)

ANURAG NEOTIA (11372)

RAVI KUMAR (10339)

Cryogenics

Cryogenics is the science that addresses the

production and effects of very low

temperatures. (generally temperatures less

than -150oC)

The word originates from the Greek words

'kryos' meaning "frost" and 'genic' meaning

"to produce.“

Liquefaction

The process of refrigerating a gas to a temperature below its critical

temperature so that liquid can be formed at some suitable pressure, also

below the critical pressure.

Gas Critical Temperature

(oC)

Critical Pressure (atm)

NH3 132.4 113.5

CO2 31.0 73.8

He -267.96 2.27

CH4 -82.6 46.0

N2 -146.9 33.9

H2O 374.0 217.7

Applications of Liquefied Gases

Uses of liquid Nitrogen (N2) in cryotherapy for removing unsightly or potentially malignant skin lesions such as warts and

actinic keratosis

to store cells at low temperature for laboratory work

in cryogenics

as a source of very dry nitrogen gas

for the immersion, freezing, and transportation of food products

for the cryopreservation of blood, reproductive cells (sperm and egg), and other biological samples and materials

to preserve tissue samples from surgical excisions for future studies

as a method of freezing water and oil pipes in order to work on them in situations where a valve is not available to block fluid flow to the work area, method known as "ice plug" – nowadays replaced by electrical heat pumps (for small pipe diameters)

to shrink-weld machinery parts together

Uses of liquid Oxygen (O2) (LOX)

Liquid oxygen is a common cryogenic liquid oxidizer propellant for

spacecraft rocket applications, usually in combination with liquid

hydrogen, kerosene or methane .

Liquid oxygen is used to create vitamin supplements.

Liquid oxygen is also used to manufacture certain oxygen therapy

sprays. These are used topically to heal wounds, bug bites and

various skin conditions.

Uses of liquid carbon-dioxide (CO2)

Carbon dioxide (CO2) is used as a key cryogenic agent in cooling,

chilling and freezing applications — protecting the taste and

texture of food products by maintaining proper temperature

control.

Carbon dioxide is most often mixed with argon as a shielding gas

used to prevent atmospheric contamination of molten metal in

electric arc welding processes.

A safe alternative to mineral acids, carbon dioxide replaces

chemicals used in pH reduction.

Liquefaction Cycles

Some of the commonly used thermodynamic cycles for liquefaction of

gases are :

(i) Ideal liquefaction Cycle

(ii) Linde-Hampson Process

(iii) Claude Cycle

(iv) Kaptiza Cycle

(v) Heylandt Cycle

(vi) Cascade System

Joule-Thomson effect

In thermodynamics, the Joule–Thomson effect describes the

temperature change of a gas or liquid when it is forced through a

valve or porous plug while kept insulated so that no heat is

exchanged with the environment. This procedure is called a

throttling process or Joule–Thomson process. At room temperature,

all gases except hydrogen, helium and neon cool upon expansion

by the Joule–Thomson process.

If J-T coefficient is +ve then a gas

cools down on expansion and if it is -ve

then the gas heats up.

Joule Thomson Inversion Curve

Maximum Inversion temperatures of

some gasesGas Max. Inversion Temperature (oC)

Air

Carbon-Dioxide

330.15

1227

Nitrogen 347.93

Oxygen 491

Hydrogen -77.63

Neon -23

Helium -249.85

Methane 695

Liquefaction Cycles

Ideal liquefaction Cycle :

It is the most basic liquefaction cycle which includes an isothermal

compression process and an isentropic process as shown in fig.

Linde-Hampson Process

It was developed by William Hampson (1895) and by Carl von Linde (1895),

in which the gas was recirculated through a heat exchanger in order to

lower the temperature of incoming gas.

Linde–Hampson Process (Contd.)

T-s Diagram for Linde-Hampson Process

1—2 : is the isothermal compression

2—3 : is Isobaric cooling occurring in Heat Exchanger

3—4 : is isenthalpic expansion (throttling) which results

in cooling due to Joule-Thomson effect .

Finally liquid and gaseous phases are separated in

separator.

Claude Cycle

Gases can also be liquefied by Claude's process in which the gas is

allowed to expand isentropically. While expanding, the gas has to do work

as it is led through an expansion turbine. Final liquefaction takes place by

isenthalpic expansion in a Joule-Thomson-Valve.

Claude Cycle (Contd.)

T-s diagram for Claude Cycle

Performance Parameters

These are the functions which are used to indicate the performance of a

liquid system. There are mainly four process parameters :

(i) Work done per unit mass of gas compressed (W/m)

(ii) Work done per unit mass of gas liquefied (W/mf )

(iii) Yield: It is the mass of liquid gas produced per unit mass of gas

compressed .

(iv) Figure of Merit(FOM) : It is the ratio of minimum work required to the

actual work needed to liquefy the gas.

Aspen HYSYS

Aspen HYSYS is a Process modeling tool for steady-state simulation design,

performance monitoring, optimization.

Automatically integrate process models with your engineering knowledge

databases, investment analyses, production optimization and numerous

other business processes.

System simulation is the calculation of operating variables such as pressure,

temperature, and flow rates, energy of fluids in a thermal system operating

in a steady state.

It is generally use in chemicals, specialty chemicals, petrochemicals and

metallurgy industries.

Benefits of ASPEN HYSYS

To predict the behaviour of a process using basic engineering relationships

such as mass and energy balances, phase and chemical equilibrium, and

reaction kinetics.

With Aspen HYSYS, companies can design, simulate, troubleshoot and

manage profitable process plants.

To avoid production delays, downtime or off-spec product, cost effective

tools.

Interface of ASPEN HYSYS

Simulation on ASPEN HYSYS

Different components used

Ideal Liquefaction Cycle

Variation of various parameters with

pressure ratio for Ideal Liquefaction

Cycle

Variation of various parameters with pressure ratio for Ideal Liquefaction Cycle

(contd.)

Variation of various parameters with pressure ratio for Ideal

Liquefaction Cycle

Variation of yield with

pressure ratio of compressor

NON-RGENERATIVE LIQUFACTION CYCLE WITH THROTTLING EXPANSION.

Case study 1

Variation with pressure ratio

Molar flow with cooler E101 outlet temperature

Linde’s Cycle with properties given at

different states

Properties at different points in Linde’s cycle

MOLAR FLOW

Worksheet of HEX E101 in Linde’s Cycle

Pressure and temperature across HEX -101Variation of Enthalpy and Temperature across shell and tube

Claude’s Liquefaction Cycle

Properties at different points in Claude’s Cycle

HEX-101

HEX-101 : Ratings

Heat flow across shell and tube

HEX - 102

HEX – 102

HEX-103

HEX -103 : CHARACTERISTICS

CONCLUSION

In case of ideal thermodynamic cycle, since it a non – regenerative ideal cycle, with efficiency of 100%, so we observed that molar flow of liquefied gas increases with pressure ratio in compressor, and it reaches 100 kg mol/h of molar flow of liquefied gas at the min pressure of 28Gpa or 2.8*10000000 kpa , start at the pressure of 8720Kpa.

In case of NON-RGENERATIVE LIQUFACTION CYCLE WITH THROTTLING EXPANSION,molar flow first remains zero for the pressure ratio range ( 0 – 237 ), and it starts giving liquefied air from the pressure ratio of 237 and then there is increase in the value of liquefy gas upto the ratio of 342 at this ratio we get molar flow of 1.727 Kgmol/h for the inlet of 100 Kg mol/h of gas, and after that it decreases to zero at the ratio of 498 , Since max. molar flow is 1.727Kg mol/h which is quite low in value that is the reason, why we never use cooler as a temperature reducing device instead of this we use heat exchanger, (efficiency of compressor is 80%).

In case of simple Linde’s cycle, due to the use of the heat exchanger, we can’t be able to do case studies because it requires certain value of the flow of regenerative stream which gains heat and provide cooling to the compressed air , so here we made a simulation in which outlet kept fix having a value of 2 Kg mol/h for the inlet of 100Kg mol/h, with the pressure ratio of 460, inlet temperature of 25degree C , and outlet temperature is -195 degree C, also obtain rating, design characteristics, parameters related to heat exchanger,with value of FOM= .21.

Finally in case of Claude cycle, same reason is there for not getting the case study, so we need to fix its value to 40% and determine the various parameters like in Linde’s cycles for all the 3 heat exchangers.

Thank You!!!.