gpa2286 porac-pac resumen

APPLICATION NOTE

USA FRANCE GERMANY NETHERLANDS UAE RUSSIA CHINA SINGAPORE SOUTH KOREA THAILAND INDIA

www.paclp.com

GPA2286: Extended Analysis for Natural Gas and Similar Gaseous Mixtures by Temperature programmed Gas Chromatography

• Analysis time under 30 minutes

• High sensitivity, linearity, accuracy

and precision

• GasXLNC software for flexible and

easy reporting

Keywords:

GPA 2286, Extended NGA, Micropacked ,

Natural Gas Analyzer

INTRODUCTION

Natural gas is a part of a continuum of hydro-

carbons, ranging from methane to the heaviest end

of oil, that are found in geological accumulations. By

far, the largest use of natural gas is as a fuel; other

uses are as a chemical feed stock or as a source of

pure single hydrocarbon gases. Gas separated from

a natural gas field will burn in that form but is

usually treated to remove or to control traces of

particular components for regulatory compliance or

for quality control. Hydrogen sulfide is a toxic and

corrosive gas; therefore, natural gas is subject to

very low specification limits of hydrogen sulfide.

Figure 1: The largest use of natural gas is as a fuel

The value of an individual natural gas is related

primarily to the amount of thermal energy it

contains, British Thermal Units (BTU) or Calorific

Value (CV), and certain other physical properties,

such as liquid content, burning characteristics, dew

point, density, and compressibility. The composition

of an individual natural gas varies depending on its

source and, therefore, its value will vary.

This application note describes GPA 2286-02

Extended using the AC Natural Gas Analyzer with

micropacked columns. This method is an extension

of GPA 2261-00.

SOLUTION

The AC NGA GPA 2286 system consists of an

Agilent 7890A Series GC optimized for GPA 2286

natural gas analysis. The AC NGA GPA 2286

system determines hydrocarbons from C1 up to

C14+, carbon dioxide, nitrogen, oxygen, and

hydrogen sulfide. The AC NGA GPA 2286 system

complies with the GPA standard 2286-02 for natural

gas analysis and incorporates a high level of

automation. Calibration, reporting and specific

calculations are all performed with the GasXLNC

software.

Figure 2: Flow diagram NGA system

Carbon dioxide is a less acidic gas but is still

potentially corrosive at pressures used for gas

transmission, and its concentration is also

controlled to very low percentage levels.

APPLICATION NOTE


www.paclp.com

TCD. The second channel utilizes a gas sampling

valve, a split/ splitless injector, a capillary column,

and an FID. This channel analyzes the individual

components of the C6+ fraction. The sample is

injected on both channels at the same time.

Figure 3: Micropacked column separation on TCD channel

ANALYSIS

The AC NGA GPA 2286 system consists of two

channels. One channel contains a gas sampling

valve and four columns: a stripper Pre-Column and

three analysis columns. Detection is done by a

The stripper Pre-column separates the C6+ fraction

from the other components. The C6+ fraction is

back flushed to the detector. By using multiple

valves and columns, the other components are

divided into different fractions, further separated

and detected by the TCD. The second channel

splits the sample utilizing the split inlet and the gas

sampling valve. The capillary column separates the

C5–C14+ components. The GasXLNC software

integrates the analyses results of both channels

utilizing i-pentane and n-pentane as bridge

components.

The micropacked columns are located in a separate

isothermal column box. This allows running both

channels simultaneous, resulting in total analysis

runtime of less than 30 minutes.

Figure 4: Capillary Column Separation on FID Channel

-50

450

950

1450

1950

2450

2950

3450

3950

0 5 10 15 20 25 30

Sig

an

l (p

A)

Time (min)

TCD Channel

C6

+ Pro

pane

i-B

uta

ne

n-B

uta

ne

neo-P

enta

ne

i-P

enta

ne

n-P

enta

ne

Carb

ondio

xid

e

Eth

ane

Oxygen

Nitro

gen

Meth

ane

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

3 3.5 4 4.5 5

Sig

an

l (p

A)

Time (min)

FID Channel

Hexane

Pro

pane

i-B

uta

ne

n-B

uta

ne

neo-P

enta

ne

i-P

enta

ne

n-P

enta

ne

Eth

ane

Meth

ane

APPLICATION NOTE


www.paclp.com

VALIDATION

The system and methodology of the AC NGA GPA

2286 system are thoroughly tested to comply with

GPA 2286-02 Extended. Repeatability, Linearity,

Discrimination, Detection levels and Critical

Separation of H2S / Propane will be discussed

further.

REPEATABILITY

Area and retention time are the two primary

measurements in Gas Chromatography. The

precision (repeatability) in which they are measured

ultimately determines the validity of the generated

quantitative data.

Table 2: Area repeatability using NGA calibration

gas

Retention time and area precision require that all

parameters (temperatures, pressure, flow, injection)

are controlled to exacting tolerances. For active

compounds, the inertness of the flow path can

dramatically affect area precision, especially at low

levels.

Area and retention time repeatability for the AC

NGA GPA 2286 system are measured for 20 runs

(table 1 and 2). Very good repeatability values are

obtained, which is possible because of the excellent

stability of the Agilent 7890 Series GC electronic

pneumatics control, the precise temperature control

of all heated zones, the stable control of the

injection volume by the gas sampling valve and the

inertness of the entire flow path.

Table 1: Retention time repeatability using NGA

calibration gas

Component Ret. time

Average

Ret. time

Stdev (n=20)

FID i-Pentane 4.88 ± 0.0001

FID n-Pentane 4.97 ± 0.0001

TCD Propane 5.36 ± 0.0074

FID n-Hexane 5.50 ± 0.0001

TCD i-Butane 6.63 ± 0.0153

TCD n-Butane 7.64 ± 0.0227

TCD Neopentane 8.15 ± 0.0263

TCD Carbondioxide 16.15 ± 0.0096

TCD Ethane 19.24 ± 0.0353

TCD Oxygen 20.92 ± 0.0064

TCD Nitrogen 21.81 ± 0.0121

TCD Methane 23.54 ± 0.0222

Component Average

Concentration

Concentration

Stdev (n=20) RSD

FID i-Pentane 0.201% ± 0.001 0.447%

FID n-Pentane 0.397% ± 0.002 0.447%

TCD Propane 1.000% ± 0.002 0.245%

FID n-Hexane 0.050% ± 0.000 0.456%

TCD i-Butane 0.400% ± 0.001 0.239%

TCD n-Butane 1.000% ± 0.002 0.233%

TCD Neopentane 0.099% ± 0.001 0.731%

TCD Carbondioxide 3.040% ± 0.009 0.281%

TCD Ethane 3.010% ± 0.007 0.233%

TCD Oxygen 0.201% ± 0.002 0.930%

TCD Nitrogen 9.000% ± 0.029 0.324%

TCD Methane 81.600% ± 0.171 0.210%

100.00%

APPLICATION NOTE


www.paclp.com

LINEARITY

The linearity of the system is checked using dynamic

dilutions of a representative NGA calibration gas with

helium. 7 levels of the diluted NGA gas are used to

perform an injection by the GSV. For each

component the concentrations in the dilutions are

calculated, and linearity plots are created (see

examples below). All calibration lines have a linearity

correlation > 0.999.

Figure 5: Examples of linearity plots on both FID and TCD channel

Table 3: Dilution table

Amount[%]0 50

Area

0

20000

40000

60000

80000

100000

76 5

43

2

1

TCD Methane, TCD2 B

Correlation: 0.99996

Rel. Res%(3): 7.8402e-1

Area = 1275.5887*Amt +500.98275

Amount[%]0 5

Area

0

2500

5000

7500

10000

12500

15000

76 5

43

2

1

TCD Nitrogen, TCD2 B


Rel. Res%(4): 9.0893e-1

Area = 1703.05191*Amt +12.780395

Amount[%]0 0.1

Area

0

50

100

150

200

250

300

76 5

43

2

1

TCD Oxygen, TCD2 B


Rel. Res%(5): -5.9927e-1

Area = 1510.25687*Amt -0.360469

Amount[%]0 0.2

Area

0

200

400

600

800

1000

1200

1400

76 5

43

2

1

TCD n-Pentane, TCD2 B


Rel. Res%(4): 5.3125e-1

Area = 3586.39408*Amt +2.5398637

Amount[%]0 0.02 0.04

Area

0

20

40

60

80

100

120

140

76 5

43

2

1

FID n-Hexane, FID1 A


Rel. Res%(2): -1.563

Area = 2983.40688*Amt -0.2739378

Amount[%]0 0.2

Area

0

200

400

600

800

1000

76 5

43

2

1

FID n-Pentane, FID1 A


Rel. Res%(5): 3.1504e-1

Area = 2505.67456*Amt -0.1470738

Dilution Level 1 2 3 4 5 6 7

Cal Gas (ml/min) 19.50 10.10 7.10 4.00 3.00 1.80

Helium (ml/min) 19.90 20.00 20.10 20.20 20.40 20.40

Dilution factor neat 2.02 2.98 3.83 6.05 7.80 12.33

APPLICATION NOTE


www.paclp.com

DISCRIMINATION CHECK

Using a microliter syringe, 0,5 µl of a hydrocarbon

test mix is injected on the front channel, using the

correct split ratio and temperature program settings

(see figure 6 for the chromatogram). The peak

retention times and peak areas are recorded by the

FID. Response factors are calculated using the

exact concentrations of the components.

Figure 6: Chromatogram discrimination check reference sample

Table 4: Results discrimination test mix

Component Percentage Weight

(gram)

Peak Area

pA*s

Area % Response

factor

Resp. factor

relative to C5

Theoretical

Resp. Factor

(rel. to C5)

Pentane 1.06% 0.32 709.25 1.046 1.50E-05 1.00 1.00

Hexane 1.06% 0.32 712.15 1.050 1.49E-05 1.00 1.00

Benzene 2.06% 0.62 1,541.53 2.272 1.34E-05 0.89 0.90

Heptane 86.54% 26.11 58,389.14 86.071 1.48E-05 0.99 0.99

Toluene 2.05% 0.62 1,518.70 2.239 1.35E-05 0.90 0.91

Octane 1.03% 0.31 709.39 1.046 1.46E-05 0.97 0.99

Nonane 1.02% 0.31 703.18 1.037 1.46E-05 0.97 0.99

Decane 1.02% 0.31 705.61 1.040 1.45E-05 0.97 0.99

Undecane 1.06% 0.32 726.57 1.071 1.46E-05 0.97 0.99

Dodecane 1.03% 0.31 708.19 1.044 1.45E-05 0.97 0.98

Tridecane 1.01% 0.31 692.39 1.021 1.46E-05 0.98 0.98

Tetradecane 1.05% 0.32 722.30 1.065 1.45E-05 0.97 0.98

Finally the measured response factors are

compared with the theoretical response factors

(table 4). It can be concluded that all determined

Response Factors are comparable with the

theoretical response factors (maximum deviation

0,02).

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30

Sig

anl (p

A)

Time (min)

C14

C13

C12

C11

C10

C9 C

8

C7

Benzene

C6 C

5

To

luene

APPLICATION NOTE


www.paclp.com

DETECTION AND QUANTIFICATION

LIMIT

Detection and quantification limit of each

component is calculated using the chromatogram of

level 7 (≈ 12 x diluted) NGA gas. LOD is defined as

3 * standard deviation of the noise, LOQ is defined

as 10 * standard deviation of the noise.

𝐿𝑂𝐷 = 3 ∗ 𝑁 ∗ 𝐶 ∗ 𝑊

𝐴

𝐿𝑂𝑄 = 10 ∗ 𝑁 ∗ 𝐶 ∗ 𝑊

𝐴

Where:

N = Noise of signal (pA) C = Concentration of component (ppm) W = Peak width (s) A = Area (pA*s)

Figure 7: Overlay of H2S and Propane in Natural gas

Table 5: LOD and LOQ for major Natural gas

components

Component

LOD

(3x N)

Range/Scope covered

GPA 2286

FID i-Pentane < 0.001% 0.001-100 %

FID n-Pentane < 0.001% 0.001-100 %

FID n-Hexane < 0.001% 0.001-100 %

TCD Propane < 0.001% 0.001-100 %

TCD i-Butane < 0.001% 0.001-100 %

TCD n-Butane < 0.001% 0.001-100 %

TCD Neopentane < 0.001% 0.001-100 %

TCD Carbondioxide < 0.001% 0.005-100 %

TCD Ethane < 0.001% 0.001-100 %

TCD Oxygen < 0.001% 0.005-100 %

TCD Nitrogen < 0.001% 0.005-100 %

TCD Methane < 0.001% 0.001-100 %

SEPARATION H2S/PROPANE

H2S elutes just before Propane. The resolution is

calculated between the two peaks, based on the

retention time’s en peak width at half height

reported by ChemStation. Specification ≥ 1.5

(baseline separation).

𝑅𝑠 = 𝑅𝑡2 − 𝑅𝑡1

𝑊1 + 𝑊2

Where:

Rt1 = Retention time H2S (min.) Rt2 = Retention time Propane (min.) W1 = Peak width at half height of H2S (min.) W2 = Peak width at half height of Propane (min.)

𝑅𝑠 = 4.346 − 3.871

0.1136 + 0.1069

𝑅𝑠 = 2.15

-50

50

150

250

350

450

550

2.7 3.7 4.7

Sig

anl (p

A)

Time (min)

Separation H2S / Propane

4.3

46

Pro

pane

3.8

71

H2S

APPLICATION NOTE


www.paclp.com

AC Analytical Controls® has been the recognized leader in chromatography analyzers for gas, naphtha and gasoline streams in crude

oil refining since 1981. AC also provides technology for residuals analysis for the hydrocarbon processing industry. Applications cover

the entire spectrum of petroleum, petrochemical and refinery, gas and natural gas analysis; ACs Turn-Key Application solutions

include the AC Reformulyzer ® , DHA, SimDis, NGA, Hi-Speed RGA and Customized instruments.

00.00.191 2012/1 - © Copyright 2012 PAC L.P. All rights reserved

CONCLUSION

The AC NGA GPA 2286 system is a specialized solution for Natural Gas stream composition analysis.

Its performance exceeds GPA 2286-02 Extended, which allows for very accurate value determination.

The dedicated GAS XLNC software automates analysis and calibration functions and facilitates simple

reporting of individual component concentrations and a variety of physical properties, reducing errors and

increasing laboratory productivity.

CALCULATIONS

The AC NGA GPA 2286 system defines many

calculations for the analyst, including calculations

established in ASTM D 2421, D 2598, D 3588,

ISO 6976 and GPA 2172. Table 6 lists a subset

of standard calculations that can be performed

using GasXLNC software.

To reduce operator involvement, the software

contains a standard database of component

constants and formulas. A user-friendly edit

mode allows authorized users to edit the

database. The GasXLNC software includes

several standard report formats. In addition, a

user can easily create customized reports.

Parameter

Liquid volume

Liquid vapor pressure

Relative density of liquefied petroleum gas (LPG)

Compressibility of mixture

Real specific gravity at 15.55°C (60° F)

Real BTU

GPM

Ideal calorific value on molar basis (inferior and superior)

Ideal calorific value on mass basis (inferior and superior)

Ideal calorific value on volume basis (inferior and superior)

Real calorific value on volume basis (inferior and superior)

Ideal & Real wobbe index (superior)

Density

Table 6: Some of the standard gas calculations available

in GasXLNC software

Figure 8: Unknown Natural Gas, FID Channel

-10

90

190

290

390

490

3 4 5 6 7 8 9 10

Siga

nl (

pA

)

Time (min)

FID Channel

Pro

pane

i-B

uta

ne

n-B

uta

ne

meth

yl cyclo

penta

nte

i-P

enta

ne

n-P

enta

ne

n-H

exane

Eth

ane

Cyclo

hexane

Benzene

Meth

ane

iso-O

cta

ne

meth

yl c

yclo

hexane

n-H

epta

ne

To

luene

n-O

cta

ne

eth

yl benzene

para

-xyle

ne

meta

-xyle

ne

ort

ho-x

yle

ne

n-n

onane

gpa2286 porac-pac resumen

Documents