Determination of Argon in Ammonia Plant Process Gas Streams by Gas Chromatography

GBH Enterprises, Ltd.

Plant Analytical Techniques
GAS ANALYSIS:

Determination of Argon in Ammonia Plant
Process Gas Streams by Gas
Chromatography

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Gas Analysis:

1

Determination of Argon in Ammonia
Plant Process Gas Streams by Gas Chromatography

SCOPE AND FIELD OF APPLICATION
This document is a method for the determination of argon in process gas
streams in the range 0-10% v/v.

2

PRINCIPLE
The gas sample will be injected automatically by a ten port valve onto the
poraplot U column. The unsplit hydrogen, argon, nitrogen, methane and
carbon monoxide will elute first and be switched to the mole sieve column.
The molsieve column will be isolated and the poraplot column will elute
any carbon dioxide and ethane present via a restrictor column to the
detector.
After the elution of the carbon dioxide and ethane the poraplot column will
be back flushed to remove any C3 and higher hydrocarbons from the
system. Then the separated hydrogen, argon, nitrogen, methane and
carbon monoxide will be allowed to elute from the mole sieve column (see
figure 1).
A micro T.C.D. is used which depends on keeping one resistance filament
as a reference and the second as an analyzer resistance filament.

3

MATERULSRFQUIRED
3.1 Carrier Gas
3.1.1 Helium at not less than 100 kpa pressure.
3.2 Materials for the Preparation of Standards
3.2.1 Argon
3.2.2 Hydrogen

HYDROGEN IS EXPLOSIVE WHEN MIXED WITH AIR AT CONCENTRATION
RANGING APPROXIMATELY FROM 4% TO 75% (V/V). CHECK FOR LEAKS.


4

APPARATUS
4.1 General Description
4.1.1 Gas chromatographic system, the system comprises a gas
chromatograph with a thermistor detector. A chrompack 9000 G.C.
is suitable.
4.1.2 Characteristics of the Assembly
4.1.2.1 Column temperature, isothermal temperature control
range 30°C-50°C to within + 0.50oC.
4.1.2.2 Detector temperature, should be within the range
80oC-120oC to within +0.50oC.
4.1.3 Gas Controls and Flow Measurement
4.1.3.1 Pressure regulators, supplied by manufacturers of
the gas chromatographic equipment.
4.1.3.2 Bubble flow meter, which can be used over a range
of 0.1 to 50ml/MIN.
4.2 Injection Equipment
4.2.1 Injection system comprising a ten port gas sampling valve
with a 50 µl sample loop.
4.3 Columns
4.3.1 Three columns are required.
4.3.1.1 Poraplot U Column (Quartz/Capillary) 10 m x
0.32mm t 5 m x 0.32 mm (Particle/Trap).
4.3.1.2 Mole sieve Column (Quartz Capillary). 4 m x 0.32mm
t 2 5 m x 0.32mm deactivated fused silica.
4.3.1.3 Restriction Capillary Column. 10 m x 0.32mm
deactivated fused silica.


4.3.2 Conditioning

4.3.2.1 The mole sieve column is conditioned by passing
helium through the column for 12 hours with the oven set at
17OoC.
4.3.3 Resolution
There shall be full resolution from peak height to base line between
all peaks as shown on the typical chromatograph (see Figure 2).
4.4 Detector
The micro thermal conductivity detector is a dual channel device with a
reference flow of carrier gas through the second channel. The detector
measures the difference in thermal conductivity between two gas streams
when a sample passes through one of the channels. Make-up gas is
required.
4.5 Recorder
Having the following characteristics.
4.5.1 Suitable for a chart speed of l0 mm/min.
4.5.2 Single span lmv measuring range.
5

SAMPLE
5.1 The gas sample to be analyzed is collected in glass aspirator bottles.
(See sampling procedure S3/1/1).
5.2 Preparation of Test Portions
Approximately lOOm1 of the sample shall be purged through the sample
loop, before turning the sample into the chromatograph.


6

PROCEDURE
6.1 Setting up the Apparatus
6.1.1 Oven and Columns
6.1.1.1 Oven Temperature - 40°C.
6.1.1.2 Detector Temperature 100°C
6.1.1.3 Helium Carrier.
P.l. Pressure 70 KPA
P.2. Pressure 45 KPA
P.3. Pressure 45 KPA
6.1.1.4 Helium Carrier to detector 4.5ml/min.
6.1.1.5 Helium Carrier M.U.G. 45 ml/min.
6.2 Calibration
6.2.1 Calibrate by external calibration.
6.2.2 Standard mixtures.
6.2.2.1 Purity of components. The purity of the gases used
to make standard blends shall not be less than 99.5%
6.2.2.2.1 Calibration gas mixtures are produced using a gas
blending instrument, a Wosthoff Gas proportioning pump or
a signal gas blender are suitable.

The composition of the calibration mixtures % v/v is:
Argon 5%
Argon 10%

Hydrogen 95%
Hydrogen 90%

(HYDROGEN BEING THE LARGEST COMPONENT OF THE PROCESS GAS
TO BE ANALYZED).
6.2.2.2 The calibration mixtures are passed directly into the
sample loop (see 5.2).

6.2.3 Presentation of the calibration data. The calibration
results are presented in the form of a graph. (Figure 3 and
Figure 4).
6.3 Test
6.3.1 Preparation of the Test Portion
Collect gas sample as described in (5.1).
6.3.2 Introduction of the Test Portion
Purge 100 ml of sample through the 10 port valve, with the valve
set in the purge position. Disconnect the sample bottle, then turn
the valve to the sample position.
6.4 Examination of the Chromatogram
6.4.1 A typical chromatogram for the analysis is shown in Figure 2.
6.4.2 Identification
The argon is identified by comparing the retention times of the
sample chromatogram against the argon standard retention time.
6.4.3 Quantitative Analysis
Calculate the amount of argon by using the graph. Draw in the peak
base and measure the peak height in mm and read the %v/v
directly from the graph.

7

EXPRESSION OF RESULTS
7.1 The concentration of the gas analysed as a percentage by volume, to
the nearest 0.1%.


8

REPEATABILITY
The following data was obtained by the analysis of gas samples produced
on a proportioning pump (see 6.2.2.2.1).
Injection No.
1
2
3
4
5
6
7
8
9
10

6.0
6.0
6.0
6.0
6.1
6.1
6.0
6.0
6.1
6.1

%An.

11
12
13
14
15
16
17
18
19
20

6.0
6.0
6.0
5.9
6.0
6.0
6.0
6.0
6.0
6.0

MEAN
STD DEVIATION
% RSD

6.015
0.049
0.8


Determination of Argon in Ammonia Plant Process Gas Streams by Gas Chromatography

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