Gas drying: definition, characteristics, methods and types of work, application of installation and special equipment

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Today, a wide variety of impurities are known. For example, it can be mechanical pollution. They are found both in compressed air and in natural gas itself. After these impurities enter installations, for example, in gas pipelines, all devices operating in this place are exposed to these particles. This leads to the fact that their wear is greatly increased.

Moisture as an impurity

Naturally, you need to understand that mechanical impurities are not the only problem. A rather large danger is borne by such a substance as an ordinary liquid, water. No matter how strange it may sound, but it is during the extraction of natural gas that the problem with water is quite acute. This is expressed in the fact that the formation of water vapor is possible. Their occurrence, as well as the density, depends on the location of the extraction site. Although it is important to note here that vapors of this type are present in any case, their concentration may simply be different.

What is dangerousmoisture?

The reason is quite obvious - corrosion of the metal pipes through which the gas moves. Basically, all devices, like pipelines, consist of iron alloys. The presence of moisture inside such a pipe will lead to the formation of hydrates. In addition, the formation of ordinary ice is not excluded. The presence of any of these impurities will lead to the following effect: a plug will form inside, which will prevent the transportation of natural gas. In addition, the appearance of hydrates disrupts the work of most regulatory bodies responsible for maintaining proper pressure.

From all this it follows that gas drying is a procedure for removing such impurities as moisture. This problem is most acute in the transportation of blue fuel. It is also worth adding here that most installations for the extraction of volatile matter are located far from infrastructure, in the Far North. For these reasons, all installations must follow certain rules. The first and most important requirement is the ability to function at a sufficiently wide range of external temperatures, including the lowest ones. The second important requirement is the reliability of the installations, and the third is the availability in operation and maintenance.

Drying methods

Gas drying is a method that allows you to get rid of the formation of hydrates or ice plugs. Currently, there are four main methods for carrying out this operation.

1. Cooling. In this case, cold is used, both natural andartificially created.
2. The absorption method uses liquid scavengers.
3. The adsorption method is carried out using an already solid absorber.
4. Another way is combined. For example, absorption and cooling can be used.

Gas cooling method

The first way to dry gas is cooling. The method is based on the fact that the humidity of the gas varies depending on the ambient temperature. For example, if you cool a gas that was previously warm, then some of the wet vapor will condense. The condensate that will fall out in this case can be simply removed, and the gas itself will have a lower dew point. In order to achieve the necessary drying of the gas in this way, it is necessary that it be cooled to a temperature that will be slightly lower than the minimum value in the pipeline.

As for free cooling, it is possible during the winter period and if the pipeline was laid above the ground. Also, the air temperature should be lower than the soil. There is another way you can use. To do this, it is necessary that the field has reserves of natural and petroleum gas. In this case, it becomes possible to cool the oil gas with cold in the heat exchanger. Cold is taken in it after the natural fuel throttling procedure. Cooling can also be carried out by throttling oil gas.

There is another cooling method that is often used in various gas processing plants. The artificial method is carried out using ammonia or propane. For this, the evaporation of these substances is carried out. Thus, it is worth noting that drying natural gas by cooling will in any case partially remove substances such as heavy hydrocarbons.

Liquid absorbers

Absorption gas drying, or rather its essence, lies in the fact that some liquid substances are able to absorb moisture from the air. In order for a substance to be used as such an absorbent, it must meet several requirements:

• moisture capacity of the substance must be very high;
• absorbent must not be toxic;
• stability;
• item must not have corrosive characteristics;
• solubility of the absorber in a substance such as a gas or liquid hydrocarbon should be minimal;
• absorber regeneration - simple.

The best substances that fit this description are DEG and TEG. They are deciphered as diethylene glycol and triethylene glycol. If we consider mainly only Russian places and methods of production, then DEG is most often used. As a substance, a chemical reagent such as calcium chloride is used.

Solid Type Absorbers

Adsorptive gas dehydration is built on approximately the same principle as the previous method, but solid materials are used instead of a liquid substance. In this case, these items are called adsorbents. They differ in thattheir area is quite large, besides, it is covered with many capillary pores. Raw materials such as activated alumina, bauxite, florite and several other substances can be successfully used as such materials.

It is very important to note here that if the gas is not previously purified from some other impurities, such as heavy hydrocarbons or hydrogen sulfide, then the ability of adsorbents to absorb moisture will be significantly reduced. This suggests that the gas drying circuit cannot be used as an independent system. To regenerate solid absorbents, either dry hot gas or air must be used.

Design of drying plants

Drying equipment consists of several prefabricated elements, they are equipped with all the controls and controls to perform the operation. All of this equipment has the following features:

• the regeneration process is carried out in a completely closed circuit, moreover, without the consumption of natural fuel;
• incorporated automatic type logic circuits responsible for the management and control of the entire system;
• base frame for this fixture is separate;
• maintenance and use of such installations is as simple as possible;
• station flexibility and reliability are quite high;
• when assembled, they are made in such a way that the equipment can function at 100% under conditions of very low temperatures.

Devices with liquid absorbers

If absorption was chosen as the gas drying method, then in this case the absorber will be the main apparatus. This is quite understandable. The gas drying plant has other elements, but this one is the most important. The absorber is a bubble column used as a mass transfer. There are also special plates that have round or conical caps. They will be responsible for ensuring that the required level of liquid is always maintained on the plates.

Using drying methods

As you can see, there are a number of different methods for drying gas, but it should be added that they are not always possible to use. When choosing a method, it is very important to take into account the area where the mining is carried out and, of course, the economic costs and benefits.

Thus, in laboratories, only one is most often used - the chemical method of drying. It is important to understand here that in fact there are a lot of substances that can act as absorbents or adsorbents.

While the problem is that the use of chemicals is a one-time process, this fact means that it is not entirely cost-effective on an industrial scale. Given the rather large volumes of the gas industry in Russia, we can conclude that this will be very costly. All this has pushed the industry towards the development of completely physical drying methods. In the endone has only to add that in terms of economic costs, as well as the complexity of technical implementation, the absorption method is much simpler and cheaper than adsorption, which led to the spread of liquid absorbers.