GB/T 17283.1-2025 (GB/T 17283-2014) PDF English
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Natural gas - Determination of moisture - Part 1: Determination of water dew point by cooled surface condensation hygrometers
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Determination of the water dew point of natural gas -- Cooled surface condensation hygrometers
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| GB/T 17283-1998 | English | 359 |
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Determination of the water dew point of natural gas--Cooled surface condensation hygrometers
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GB/T 17283-2014: Determination of the water dew point of natural gas -- Cooled surface condensation hygrometers
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GB
NATIONAL STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
ICS 75.060
E 24
Replacing GB/T 17283-1998
Determination of the water dew point of natural gas -
Cooled surface condensation hygrometers
(ISO 6327.1981, Gas analysis - Determination of the water dew point of natural
gas - Cooled surface condensation hygrometers, MOD)
Issued on: DECEMBER 05, 2014
Implemented on: MAY 01, 2015
Issued by. General Administration of Quality Supervision, Inspection and
Quarantine of the People's Republic of China;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Principles ... 4
3 Performances of apparatus ... 5
4 Sources of error - General precautions for operation ... 8
5 Elimination of hydrocarbon condensates ... 10
6 Accuracy... 11
Appendix A (Informative) Structure changes of this standard as compared with
ISO 6327.1981 ... 12
Appendix B (Informative) Correction of water dew point ... 14
References ... 15
Foreword
This standard was drafted in accordance with the rules given in GB/T
1.1-2009.
This standard replaces GB/T 17283-1998 “Determination of the water dew
point of natural gas - Cooled surface condensation hygrometers”. As
compared with GB/T 17283-1998, the main technical content the same.
This standard, through re-drafting method, modifies and adopts ISO
6327.1981 “Gas analysis - Determination of the water dew point of natural gas
- Cooled surface condensation hygrometers”; AND ISO 6327 had confirmed
this in 2011.
This standard has a greater structural adjustment as compared with ISO
6327.1981, AND in Appendix A it provides the clause number comparison list
between this standard and ISO 6327.1981.
The main technical differences between this standard and ISO 6327.1981 and
the causes are as follows.
- MODIFY the scope of application of standard; based on the scope of
application of ISO 6327.1981 “The water dew point generally ranges from
-25 °C ~ 5 °C”, ADD that “Under special environment, the water dew point
range may be widened”; AND expand the scope of application of this
standard for the purposes of adapting to the actual conditions of the
natural gas production in China.
This standard was proposed by China National Petroleum Corporation.
This standard shall be under the jurisdiction of the National Natural Gas
Standardization Technical Committee (SAC/TC 244).
The main drafting organizations of this standard. China National Petroleum
Corporation Southwest Oil and Gas Field Branch Natural Gas Research
Institute, Chengdu Tianke Oil and Gas Engineering Co., Ltd.
The main drafters of this standard. Zeng Wenping, He Bin, Gao Xiaogen.
This Standard replaces the standard previously issued as follows.
- GB/T 17283-1998.
Determination of the water dew point of natural gas -
Cooled surface condensation hygrometers
1 Scope
This standard specifies the method of using the cooled surface condensation
hygrometers to determine the water dew point of natural gas.
This standard applies to the determination of the water dew point of natural
gas and similar gases. The water dew point of the treated natural gas is
generally in the range of -25 °C ~ 5 °C. Under the corresponding gas pressure,
the water content range (volume fraction) is 50 × 10-6 ~ 200 × 10-6. In special
circumstances, the water dew point range may also be wider.
2 Principles
2.1 Principle of the apparatus
With this type of apparatus, which determines the water content of a gas by
measuring the corresponding dew point, a surface (generally a metallic mirror),
the temperature f which may be artificially lowered and accurately measured,
is exposed to a sample of the gas being tested. The surface is then cooled to a
temperature at which condensation occurs and is observed as dew.
Below this temperature, condensation increases with time, whilst above it,
condensation decreases or does not occur. This surface temperature is then
(for practical applications) taken as the dew point of the gas flowing through
the apparatus.
2.2 Determination of water vapor pressure
The partial water vapor pressure in the gas samples is the saturated vapor
pressure corresponding to the observed dew point, provided that the gas in the
hygrometer is at the same pressure as the gas at the time of sampling.
REFER to the relevant manual for the relationship between saturated water
vapor pressure and temperature.
It shall be noted that if methanol is present, this method determines the
methanol in addition to water. However, if the methanol content is known, the
The manual device can involve observation of condensation with the naked
eye; if a photoelectric cell is used, the mirror is illuminated by a light source
built into the test cell. The lamp and photoelectric cell can be arranged in
various ways, provided that diffusion in the direction of the light source from
the mirror is reduced by the polishing of the mirror. In any case, the mirror must
be clean before use.
In the absence of any condensation, the diffused light falling on the photocell
must be reduced. The effects of light diffused from internal surfaces of the cell
can be reduced by blackening these surfaces AND this precaution can be
supplemented by an arrangement of the optical system so that only the mirror
is illuminated AND the photocell views only the mirror.
3.4 Methods for cooling the mirror and controlling its temperature
3.4.1 General
The following methods are used for reducing and adjusting the mirror
temperature. The methods described in 3.4.2 and 3.4.3 require constant
attention from the operator AND are not suitable for automatic devices. For
automatic devices, two cooling methods are used. indirect contact with a
coolant OR cooling by the thermoelectric (Peltier) effect as described in 3.4.4
and 3.4.5. In any case, the rate of cooling of the mirror shall not exceed
1 °C/min.
3.4.2 Solvent evaporation
A volatile liquid in contact with the rear face of the mirror can be evaporated
AND cooled by an air flow. Hand bellows are generally used for this purpose,
BUT an adjustable source of low pressure compressed air or any other
suitable pressurized gas is preferable. The liquid used can be ethylene oxide,
a very efficient liquid giving cooling of the mirror of approximately 30 °C,
without effort, when hand bellows are used. However, if toxicity is a risk,
acetone can be used to obtain cooling of approximately 20 °C with hand
bellows OR even greater cooling with compressed air or other suitable
pressurized gas.
3.4.3 Gas cooling by adiabatic expansion
The mirror can be cooled by discharging onto its rear face a gas which has just
expanded through a nozzle. Compressed carbon dioxide, available from small
cylinders, is often used for this purpose, BUT other gases such as compressed
air, compressed nitrogen, propane, or halogenated hydrocarbons can also be
used. Mirror temperatures of at least 40 °C below the gas sample temperature
can be obtained.
introduced into the test cell, can also induce an observed dew point different
from the dew point which would correspond to the actual water vapor content.
4.1.2 Solid impurities
If solid impurities are absolutely insoluble in water, they do not modify the
observed condensation temperature, BUT can hinder condensation
observation. In an automatic device, without a compensation device for such
impurities, these tend to obstruct the operation of the device if the amount of
condensate is low. Defects resulting from an excess of solid impurities on the
mirror generally result in an unexpected increase of the mirror temperature for
a few minutes AND call for dismantling of the device AND cleaning of the mirror.
(It is essential for this purpose that the hygrometeric cell can be rapidly
dismounted). It may be desirable to remove solid impurities by using a
non-hygroscopic filter to avoid such difficulties.
If a filter is used, even if it is stated to be non-hygroscopic, it shall be in
equilibrium water the water vapor content of the gas; this is obtained by
allowing gas to flow through it for a period of time before the test at a rate
considerably higher than that to be used during the test.
To prevent the influence of dust particles, some automatic devices are fitted
with a “calibration sequence”. This consists of an optional superheating of the
mirror, so as to remove all condensate, water and hydrocarbons, followed by a
rebalancing of the measuring bridge.
4.1.3 Impurities in vapor form
Hydrocarbons can condense on the mirror. In principle, these do no interfere
because hydrocarbon surface tension is very different from that of water. They
spread on the mirror AND form a continuous layer which does not diffuse light.
Manual detection of condensates is, nevertheless, not easy because although
the dew point is very much lower than the condensation temperature of
hydrocarbons, only a few water droplets can be detected in a large
hydrocarbon ...
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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