Why must natural gas be processed before it can be used?

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With the ongoing advancement of the nationwide project to replace coal with natural gas, it has now reached thousands of households. So, for those new to gas, do you know what processing steps natural gas goes through before it reaches people’s homes? Today, let’s learn together about * natural gas resources. There are mainly three types: reservoir gas, associated gas, and condensate gas. Atmospheric gas is natural gas extracted from gas reservoirs ； Associated gas is the natural gas that is produced alongside crude oil during its extraction from oil reservoirs ； The gas in condensate gas reservoirs refers to gas that is stored in the reservoir under its original geological conditions; however, during extraction, as pressure decreases, some of the heavier hydrocarbons in the natural gas condense into a liquid state. Some of this liquid remains underground, while another portion is brought to the surface along with the natural gas. At present, most of the natural gas used around the world is reservoir gas; for example, gas fields in Sichuan and Changqing in China mainly produce reservoir gas. The Dagang oil field produces a significant amount of condensate gas, while the natural gas from other oil fields is mostly associated gas. It can be seen that natural gas extracted from the wellhead or from the oil and gas separator in the field contains varying amounts of heavier hydrocarbons, as well as non-hydrocarbon gases such as water vapor, sulfides (such as hydrogen sulfide), carbon dioxide, nitrogen, and helium; this is what we refer to as crude natural gas or wet gas. This type of natural gas is generally not suitable for direct use by most users; it needs to be specially processed to remove hydrogen sulfide, water vapor, condensed hydrocarbons, etc., before it can be supplied to users as commercial natural gas. Why is it necessary to remove water from natural gas? As is well known, natural gas is transported through pipelines, and it usually contains saturated water vapor. When the temperature of the medium surrounding the pipeline is lower than that of the gas, the water vapor will condense into a liquid, or even freeze or form hydrates, which can severely block valves or pipelines. As for the acidic gases contained in natural gas, such as carbon dioxide and hydrogen sulfide, they are even more harmful; the presence of water converts these gases into acids, thereby accelerating corrosion of the pipe walls and shortening the service life of the pipelines. When natural gas is used as fuel, it can endanger people’s lives. When used as chemical raw materials, these acidic gases can also poison the catalysts, reducing their catalytic efficiency or even rendering them ineffective, which affects the quality of the products. Even after natural gas has been dehydrated and desulfurized, it still cannot be used directly as fuel gas or a raw material for chemical industries. It is necessary to separate the thiol compounds and heavier hydrocarbons from the natural gas in accordance with certain standards and requirements; primarily, hydrocarbons with 3 carbon atoms or more (components with more than 3 carbon atoms) need to be liquefied and recovered. In this way, it not only avoids the many issues related to instability that can arise from the formation of condensate during natural gas transportation, but also purifies the natural gas, eliminating numerous hazards for users during its use. At the same time, after separating the components above C3, the calorific value of natural gas increases significantly; moreover, these components above C3 can be turned into qualified liquefied gas and light oils, yielding good economic benefits. The process flow for natural gas processing can vary in many ways, but the basic sequence remains the same: natural gas purification—compression—cooling—fractionation. Cooling is further divided into expansion refrigeration or refrigerant refrigeration; currently, most natural gas processing units in China are of the shallow cooling type. Typically, after natural gas enters the centralized treatment plant, it is first passed through a separator to remove the accompanying condensate, water, and solid impurities. It is then compressed by a compressor to the desired pressure, and after cooling and separation, it is sent to desulfurization towers and dehydration towers so that the dew point of the dehydrated gas meets the requirements for low-temperature processing. Then, it passes through the rich-poor gas heat exchanger, the propane refrigerator, and the plate-fin heat exchanger in sequence to bring the temperature of the feed gas to the required level. Finally, a qualified natural gas is obtained through distillation in a distillation tower, while by-products such as liquefied gas and light oils are produced as well. Natural gas is widely used as a fuel for industrial and domestic purposes due to its convenience, cost-effectiveness, cleanliness, and high calorific value, and it is also an important raw material for the petrochemical industry. The first step in producing petrochemical products is the cracking of gas to generate basic chemical raw materials such as ethylene, propylene, butadiene, benzene, toluene, and xylene ； The second step is to produce a variety of organic chemical raw materials and synthetic materials from basic chemical raw materials. It can be seen that natural gas is both an important fuel and a valuable industrial raw material, but untreated natural gas cannot be used directly.