Endress+Hauser SpectraSensors J22 TDLAS, Руководство по эксплуатации

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J22 TDLAS Gas Analyzer Operating Instructions
Hauser 149
14.2 MDP calculation
Three methods are described below for calculating moisture dew point given moisture concentration and process
pressure. The methods described are industry-accepted publications which are available from the respective
organizations.
14.2.1 Methods for MDP calculation
ASTM D1142
This method has two equations.
•
Equation 1 (ASTM1): Range 0 to 100 °F (-18 to 38 °C)
• Equation 2 (ASTM2):
• Range -40 to 460 °F (-40 to 238 °C)
• Originally from IGT-8 (1955)
• The equations do not consider stream composition
ISO 18453
• Considers stream composition, molar ratios are inputs to the equation.
• Stream composition must be entered into the analyzer.
The ISO 18453 method is applicable to natural gas mixtures with compositions within the limits listed in the table
below. Dew point temperatures calculated from water contents were validated to be generally within ± 2 °C for
pressures 0.5 ≤ P ≤ 10 MPa and dew point temperatures 258.15 ≤ T ≤ 278.15K [14]. Due to the solid thermodynamic
basis on which the method was developed, an extended working range of 0.1 ≤ P ≤ 30 MPa and 223.15 ≤ T ≤ 313.15 K
is also considered valid [10]. Beyond the extended working range, however, the uncertainty in calculated dew point
temperature is unknown.
Compound mol %
Methane (CH
4
) ≥ 40.0
Ethane (C
2
H
6
) ≤ 20.0
Nitrogen (N
2
) ≤ 55.0
Carbon Dioxide (CO
2
) ≤ 30.0
Propane (C
3
H
8
) ≤ 4.5
i-Butane (C
4
H
10
) ≤ 1.5
n-Butane (C
4
H
10
) ≤ 1.5
neo-Pentane (C
5
H
12
) ≤ 1.5
i-Pentane (C
5
H
12
) ≤ 1.5
n-Pentane (C
5
H
12
) ≤ 1.5
Hexane/C
6
+ (C
6
H
14
) ≤ 1.5
In summary, for moderate to high water contents at low pressures, all three correlations produce acceptable results.
Although somewhat more difficult to implement, the ISO method is arguably the more accurate of the methods
(especially for low water contents and high pressures).