NATURAL GAS ICING

Natural gas is an alternative source of energy for oil and is characterized by its low environmental emissions, as well as its importance in many industrial and commercial sectors. As global demand for natural gas increases and prices rise due to political problems, it has become important to keep its pipes safe.

Natural gas can be referred to as concomitant gas which is the gas produced with oil during the extraction process from oil tanks, or unaccompanied gas produced from gas tanks. To maintain the safety of gas pipes, we must be aware of potential problems that may lead to disruption or disruption of pipes containing natural gas and actions that can be taken to predict and reduce these costly conditions.

Among the most significant problems that occur to gas pipes are formation of hydrates, corrosion in gas pipeline, icing. Our article will address the issue of gas icing and the methods for preventing it.

Definition of natural gas icing:

Natural gas icing is a widespread phenomenon that constitutes a major and widespread challenge in the field of the oil industry.

Natural gas icing is the formation of ice in natural gas pipelines or processing facilities due to the presence of water vapor and low temperatures. This phenomenon can lead to operational issues such as blockages and increased pressure, posing risks to the integrity of the pipeline. The presence of water vapor in natural gas can condense and freeze under low temperatures, causing ice to form within the pipeline. This can impede the flow of natural gas and lead to mechanical issues.

Natural gas icing causes:

Fig 1: Example of Icing on Lift Gas Injection Line Downstream of Lift Gas Choke. [1]

The icing of natural gas can be caused by several factors, such as:

High humidity: when water contacts natural gas can create ice blockages.

The Presence of water vapor or hydrocarbon liquids: Water vapor found in natural gas can freeze at high pressures and low temperatures.

Other factor is Pressure drops in the gas stream (Joule–Thomson effect): Expansion of natural gas during distribution causes it to cool down, increasing the likelihood of moisture condensation.

Joule–Thomson effect: By being throttled, the gas undergoes a pressure reduction and under certain conditions its temperature decreases. The phenomenon is called the Joule–Thomson effect and is accompanied by a temperature change of the gas. If the process occurs within a temperature and pressure range that ensures that the effect is positive (the gas temperature decreases as its pressure is reduced)

Effects of natural gas icing:

Natural Gas Icing can have several undesirable effects including:

Low gas pressure This is when the gas freezes inside the pipe, it occupies less volume than natural gas. Icing can disrupt gas supply, and this can be a serious problem especially when winter when the need for gas is high. Increase internal pressures and pipe damage and equipment when ice forms on the surface of the pipe, it can exert pressure on the pipe which can lead to it cracking or breaking. This can lead to gas leakage, posing a safety hazard. It is important to take measures to reduce those effects.

Prevention the formation of natural gas icing:

To prevent the icing of gas pipes, the temperature of the tube must be maintained above the icing point by:

Thermal insulation of pipes as the use of insulating materials for pipelines reduces heat loss, which reducing the chance of gas icing during transport. Also The placement of heaters helps maintain the temperature of the gas and prevent its icing, such as the using of oil pipes to heat the gas in the oil fields. This is done by placing oil pipelines in a spiral around the gas pipelines. When hot oil flows through oil pipelines, it transfers heat to the gas pipelines, which helps prevent icing.

Drying and dehumidifying natural gas through drying operations helps prevent ice being inside pipelines. Tubes of antifreeze-resistant materials such as stainless steel can also be used to prevent icing.

De-icing of natural gas icing in pipelines:

Chemical De-icers such as Ethylene Glycol (MEG, DEG, TEG) are commonly used for de-icing and anti-freezing, these glycols reduce the degree of water icing. When mixed with water, they form a solution that remains in liquid condition at temperatures below water alone. This prevents the formation of ice on surfaces.

Other Mechanical methods such as steam or ice breaking are commonly used to remove ice. These methods depend on breaking ice by scraping or releasing energy from shock waves or vibrations to break ice or use heat to melt ice.

References:

1.Hydrate Mitigation and Flare Reduction Using Intermittent Gas Lift in Hassi Messaoud, Algeria. SPE Annual Technical Conference and Exhibition, Dallas, Texas, USA, September 2018.