水合物基础知识

Organic inhibitors have methanol and glycol compounds, and inorganic inhibitors have calcium and sodium chloride, etc. ③ Gas airtight gathering and transportation mainly adopts organic inhibitors. The most commonly used inhibitors are methanol and glycol.
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Methane hydrate simulation diagram
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The internal cage structure Flammable ice源自2014-5-59
Gas hydrate
水-水：氢键 (hydrogen bond) Water molecules “笼子 (cavity)”
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TABLE OF CONTENTS
1. 2. 3. 4. The basic characteristics of gas hydrate The formation of gas hydrate How to inhibit or prevent hydrate The application of gas hydrate
Type II:
136
Type H:
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2. The conditions of Gas hydrate
2.1 Necessary conditions: ① Natural Gas and free water. ② The recognized formation condition: Temperature condition:2.5~25 °C. Pressure condition：5~40Mpa。
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2.5 The influence of natural gas hydrate formation because of the gaseous impurities
① There are hydrogen sulphide and carbon dioxide containing
in natural gas, in the condition of constant pressure, the hydrate formation temperature will increase; Under the condition of invariable in temperature will reduce the pressure of hydrate formation .
② Namely, natural gas contains hydrogen and carbon dioxide,
more easy to generate hydrate.
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2.6 The influence of CO2 in natural gas
In the process of gas processing, when there is more carbon dioxide existing in gas, it will appear in the following two aspects: ① At low temperature and under high pressure, carbon dioxide and water will form the solid hydrate, plug equipment and pipe, ② When gas temperature low (general < - 57 degrees Celsius), carbon dioxide, also can form ice itself, and can plug equipments and pipelines, especially in the inlet of expander and the top of contact tower. Removal of water can prevent CO2 and H2O to format gas hydrate, remove carbon dioxide from natural gas can prevent generating dry ice. 2014-5-5 18
3. Hydrate prevention
Because gas hydrate is a crystalline solid substances, once gas hydrate formation, it will plug in the valve, the inlet of separator, pipelines, elbow, tee etc. It also affect gas collection and transportation, therefore, measures must be taken to prevent it. Usually, the method of heating or Injecting inhibitors is used to prevent gas hydrate formation in natural gas airtight gathering and transportation system.
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Natural gas hydrate
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Gas hydrate structure similar crickets cage
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1.1 The structure of natural gas hydrate
Gas hydrate is a kind of squirrel-cage clathrate , each water molecule under the action of hydrogen grid combines with together to form a cage, gas molecules by the action of the Van der Waals force are surrounded in the clathrate.
外观为类冰晶体 非化学计量的 包合物 (clathrate)
Gas molecules：CH4, C2H4, C2H6, C3H8, N2, H2S, CO2, Ne, Ar, Kr, Xe,
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1.2 The type of gas hydrate
Number of
Types of clathrate
formation
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2.2 Auxiliary conditions
Auxiliary conditions: Pressure fluctuations High speed gas flow The flow speed for the agitation The existence of a crystal chips A specific physical location (such as elbow, orifice plate, valves, coarse of wall, etc.)
②
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3.3 Performance comparison of methanol and glycol inhibitors
① The low cost of investment is methanol inhibitors but loss a lot in gas, so the high cost of operation; ② The high cost of investment is glycol inhibitors, but low operation cost; ③ The best effect inhibitor is methanol, secondly is
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3.1 Heating method
To increase gas temperature before throttling, or laying a hot water pipeline with the gas pipeline in parallel that keep the temperature of gas flow above its dew point, so this is the effective method to prevent gas hydrate formation.
Name
Gas hydrate formation of critical temperature/℃
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C2
C3
I-C4 N-C4 CO2 2.5 1 10
H2S 29
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2.4 Prediction of hydrate formation pressure and temperature curve
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1. The basic characteristics of gas
hydrate
In a certain temperature and pressure， some components of the natural gas with liquid water can form gas hydrate. Gas hydrate is a kind of white crystalline solid， looking similar to the ice or density loose snow, density of 0.88 ~ 0.9 g/cm3.