Percentage deviation of calculated heat flows for a simulated overcritical multi-stage LNG evaporation process

F. Dauber and R. Span

•

(including the vapor-liquid phase boundary)

Thermal and caloric properties can be calculated with the highest accuracy possible (reference quality) for natural gases and other multi-component mixtures consisting of any of the 18 natural gas components

In the liquid region the uncertainty in density for natural gases is: D= 0.1% 0.5%

Kunz, O.; Klimeck, R.; Wagner, W.; Jaeschke, M.: The GERG-2004 Wide- Range Equation of State for Natural Gases and Other Mixtures: GERG Technical Monograph 15 (2007) and Fortschr.-Ber. VDI, Reihe 6, Nr. 557, VDI Verlag, Düsseldorf 2007

• Covers wide ranges of temperature, pressure and composition

• Valid in the gas phase, in the liquid phase, in the supercritical region and for the vapor-liquid equilibrium

• Developed using only data of binary mixtures

•

•

• Formulated as a fundamental equation in terms of the reduced Helmholtz energy as a function of temperature, density and composition, the GERG-2004 model allows for calculations of thermal and caloric properties just by combination of derivatives of the Helmholtz energy

r/r -

GERG-2004 Equation of State

• The GERG-2004 has been implemented successfully in Aspen-Plus, Aspen Hysys, ChemCAD, Pro/II and in several other simulations tools using the CAPE-OPEN Standard

• Research of the property models influence on the design data of LNG processes • simulation of a simplified LNG evaporation terminal • simulation of a complex natural gas liquefaction process (C3MR) - most widely used liquefaction process - cooling with propane (C3) and a mixed refrigerant (MR)

Simulation of LNG-Processes

equations of state:

Peng-Robinson

Revised Klosek-McKinley (

• Comparison of LNG densities calculated with the GERG-2004 and other

• Redlich-Kwong-Soave (Redlich and Kwong (1949), Soave (1972)); (Peng and Robinson (1976)) - cubic equations of state - valid for the whole fluid region

• Lee-Kesler-Plöcker • empirical (BWR-Type) equation of state (Lee and Kesler (1975)) • also describing asymetric mixtures with an extended corresponding-states approach (Plöcker et al.(1978)) • valid for the whole fluid region

• McCarty (1980)) • for calculations of densities only • only valid in the liquid region • calculation of densities without taking the compressibility into account

• fitted to experimental saturated liquid densities of natural gases • industrial standard for the accounting of LNG

Comparison of different Property Models

Natural gas liquefaction process ( as displayed on the graphical user interface of Aspen-Hysys

C3MR)

-10

-5

0

5

10

100 120 140 160 180 200 220 240 260 280

100

*à

Q/Q

GERG-2004 Peng-Robinson Redlich-Kwong-Soave

Temperature [K]

Percentage deviation of calculated LNG densities for p = 1.01325 bar

GERG-2004 Peng-RobinsonRedlich-Kwong-Soave

phase boundary

-1.0

0,0

1.0

Revised Klosek-McKinley

Temperature [K]

• Significant differences for the modeled design data of the LNG processes are based on the uncertainties of the cubic equations and the Lee-Kesler-Plöcker equation in the vapor-liquid equlibrium

• The influence of property models with different qualities on the simulation of processes in the natural gas industry should not be underestimated

• Data for operating liquefaction processes are required to prove the advantages expected for the application of the GERG-2004 model in process simulations

• High expectations regarding economic efficiency, product quality and environmental safety lead to increasing demands on the LNG vaporization and liquefaction processes

New highly accurate equations of state for natural gas and LNG represent an unused potential for accurate process modelling

• Fundamental contributions to optimization and operation of a system are expected from the simulation of processes

• Accurate representation of thermophysical properties and energy balances of the simulated process are essential

•

GERG-2004*

Haynes (1982)Hiza & Haynes (1980) Haynes (1982) Haynes (1982)

Haynes (1982) Haynes (1982) Hiza & Haynes (1980)

Temperature [K]

-0.5

0.5

0,0

10

0 Dr’ / r’

0.5

0.0

Revised Klosek-McKinley (1980)*

Peng-Robinson (1976)

-15

15

0

• • The GERG-2004 has the same range of validity as the

• With the GERG-2004 even calcoric properties can be calculated easily and with high accuracy

GERG-2004 shows similar accuracies for the density of LNG as the Revised Klosek-McKinley equationcubic equations and the extended corresponding-states model

Ruhr-Universität Bochum

Prozentuale Abweichung gemessener LNG-Siededichten von berechneten Werten

Thermodynamics, Contact: F.Dauber@thermo.rub.de, Tel. +49 (0)234 / 32-26395

Ruhr-University Bochum, D-44780 Bochum

95 100 105 11090 115

Percentage deviation of measuredsaturated LNG densities from calculated data

115

Temperature [K]

100 105 110 120 130125 135

115

GERG-2004 *

Haynes (1982)Hiza & Haynes (1980) Haynes (1982) Haynes (1982)

Haynes (1982) Haynes (1982) Hiza & Haynes (1980)

Temperatur [K]

-0,5

0,5

0,0

-0,5

0,5

0,0

Revised Klosek-McKinley (1980) *

Peng & Robinson (1976)

-15

15

0

Lee Kesler Plöcker (1978)

-0,8

0,8

0

100 105 110 120 130125 135

Prozentuale Abweichung gemessener LNG-Siededichten von berechneten Werten

10

0 (

- r

be

r.)

/ r

ex

p.

r

.exp

10

0 D

Q / Q

10

0 Dr / r

• Comparison of the GERG-2004 with the cubic equations and the equation of state of Lee-Kesler-Plöcker for calculated design data of a C3MR process:

power of the compressors: - 1.7 % - 1.7 % + 0.9 %

UA / Cryogenic Heat Exchanger: - 1.1 % + 5.2 % - 5.6 %

Lee-Kesler-Plöcker Redlich-Kwong-Soave Peng-Robinson

* prädiktive Beschreibung der dargestelten Daten

* angepasst an die dargestelten Daten

This work is carried out as part of the "competence centre thermodynamics ofgases" initiative jointly financed by e.on Ruhrgas and by the Ministry of Innovation,Science, Research and Technology of North Rhine-Westphalia.

-0.5

1

0

-1

Lee-Kesler-Plöcker (1978)

115100 105 110 120 130125 135

*predicitve description of the presented data

*fitted to the presented data

Influence of Thermodynamic-Property Models on theSimulation of LNG Evaporation and Liquefaction Processes

10

0 D

A / A

Percentage deviation of calculated heat transfer areas fora simulated multi-stage flash LNG evaporation process

GERG-2004 Peng-Robinson Redlich-Kwong-Soave

Temperature [K]

-8

-4

0

4

8

110 120 130 140 150 160 170

-8

-4

0

4

8

110 120 130 140 150 160 170

-15.0

0,0

15.0

10

0 Dr / r

Acknowledgment

Conclusion

partial mass flows of the mixed refrigerant: - 15 % + 1.7 % - 1.2 %

Category: LNG