Discussion on LPG purification process


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Discussion on purification process of liquefied petroleum gas

Article source: AI Yi Technology popularity: - Time of publication: 10:34:00, September 23, 2016

As a kind of industrial raw material and civil fuel, liquefied petroleum gas (LPG) has been widely used and achieved great economic and social benefits. In history, the first market of liquefied petroleum gas (LPG) was used as fuel, and it is still an important market today. However, with the rapid development of petrochemical industry, liquefied petroleum gas (LPG), as the raw material of chemical industry and civil gas industry, has broad prospects for its production and application, especially today's fine chemical production is more inseparable from LPG. For example, in spray, cleaning agent, rust remover, release agent, plastic foam and other industries as propellant, propellant, foaming agent has an irreplaceable role. However, due to a certain amount of impurities in general petroleum gas, it must be purified as chemical raw materials. Therefore, as a purification process, treatment methods and operations are very important.

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There are two main sources of LPG: one is from oil field associated gas or natural gas, the other is from petroleum refining.

2.1 to separate and recover the by-product associated gas in the process of oil production from oil and gas fields. After proper treatment measures such as oil and gas separation, high-quality liquefied petroleum gas with high propane purity and low sulfur content can be obtained.

2.2 the extraction of petroleum gas from refineries and by-products of petrochemical plants is usually carried out by atmospheric distillation, vacuum distillation, thermal cracking, catalytic cracking and catalytic reforming in petroleum refineries. Thermal cracking and catalytic cracking are the main sources of domestic petroleum gas production. Petroleum gas contains a lot of sulfides such as ISO alkanes, olefins and hydrogen sulfide, and often contains oil components that are difficult to separate.

Main components and impurities of LPG

3.1 at present, the petroleum gas supplied in the domestic market mainly comes from refinery gas, and the main components are propane (C3H8), propylene (C3H6) and butane (c4hl0).

3.2 impurities mainly include: 3.2. Sulfur, carbon oxysulfide, hydrogen sulfide and dimethyl sulfide, etc. in the process of petroleum production, the petroleum gas reacts with the inner walls of pipelines and storage tanks to form iron sulfide and ferrous sulfide; Sweeteners (mainly composed of methyl mercaptan CH3SH and ethanethiol C2H5SH) are prepared by artificially adding sulfur-containing compounds such as mercaptan and thioether in the sales process of petroleum gas.

3.2.2 petroleum gas refining process contains sediment and iron filings (rust) which are not completely removed. Although the petroleum gas is desalinated and dehydrated, it still contains a small amount of water. Water usually exists in two ways in petroleum gas: one is free water, the other is dissolved water, and the content of dissolved water in petroleum gas changes with the state and temperature of petroleum gas. Let's take propane as an example to see its changes: the water content of liquid propane at different temperatures: it can be seen that at 35 * C, it propane dissolves about 5kg of water.

At the same temperature, the water content of gaseous propane is much higher than that of liquid propane.

3.2.4 aromatic hydrocarbons and product oil: mainly those that are not cleaned during refining in refinery.

4 LPG purification process

4.1 selection of gas source: the quality requirements of fine chemical products for petroleum gas are much higher than that for ordinary petroleum gas. The selection of high-quality gas source can greatly improve the purification speed of basket, shorten the production cycle, reduce the production cost and improve the economic benefits. The later purification of petroleum gas mainly focuses on water, sulfide, sediment and oil composition, and the content of sulfide and the degree of oil smell have a great impact on the deodorization effect. The selection of gas source is determined from three aspects as follows:

4.1.1 the quality test reports of suppliers and authoritative departments mainly include pressure, temperature, specific gravity, chemical composition, sulfide content, free water content and residue content.

4.1.2 based on the experience of the staff, the "nose sniffing method" is adopted to determine the content of oil components according to the light and heavy weight of the oil in the LPG. This method is simple and easy, but it needs some work experience.

4.1.3 use "gas chromatography" to analyze the components of petroleum gas. The data obtained by this method are accurate, but the operation is complex.

Generally speaking, although the petroleum gas produced by refineries is the main source of domestic market, it is difficult to process because of its complex composition and many impurities, especially the oil components which are difficult to treat. For the associated gas separated from oil and gas, the purification requirement is low and it is the first choice of gas source.

4.2 main equipment and process flow since liquefied petroleum gas (LPG) belongs to flammable and explosive dangerous goods, the purification treatment equipment must be selected and operated according to its nature and function.

4.3 principle of petroleum gas purification and selection of deodorizing materials. Although crude oil is filtered and desalted in the refining process, there is still a small amount of sediment and iron shoulder (rust) in the process of refining petroleum gas. In the purification process, the precipitation method can be used first, and then the purification effect can be achieved by adsorption of adsorbent (activated carbon). In this process, activated carbon particles are the main raw materials, which are made of carbonaceous materials such as wood, coconut shell, fruit shell, coal and so on. The selection of activation degree of raw materials for manufacturing activated carbon has great influence on the surface chemical properties, volume and surface area of activated carbon. Therefore, the selection of appropriate activated carbon and carbon particle degree has a great influence on the purification quality of basket.

4.3.2 dehydration and dryness: if the moisture content of LPG exceeds a certain amount, under a certain temperature and pressure, water can form crystalline hydrate <: * > * xh20 hydrate with C2, C3, (: 4) in liquefied petroleum gas, which is white crystal or rust colored under aggregation state. Because the formation of hydrate will reduce the flow section of the pipeline, and even block the pipeline, valves, instruments and equipment, the excessive water content of petroleum gas in chemical products (especially in the gas phase state) will affect the product quality.

B. treatment measures since there are two existing ways of water in petroleum gas: one is free water, the other is dissolved water. Generally, for the former form, the "sinking drainage method" can be adopted, that is, water treatment is conducted in the lowest water condenser in the cylinder, which is also the most economical way.

For the dissolved water, in addition to the "sinking and drainage method", the main drying method is to use absorbent silica gel for drying. Its essence is the process of LPG absorbing water and filtering through solid silica gel (435mm).

Liquefied petroleum gas (LPG) contains sulfide, which is not only corrosive, toxic, but also has a special odor. This odor directly affects the quality of chemical products. Therefore, deodorization is an important part in the purification process. Copper molecular sieve can be used for adsorption to produce physical and chemical reaction with sulfide in petroleum gas to achieve the purpose of sulfur removal.

4.4 process treatment and operation

4.4.1 although the content of impurities in LPG is very small, it has a great impact on the quality of purification. Therefore, the storage tanks and pipelines of the purified LPG after loading and transportation must be polished before use, and then cleaned and blown to ensure that there is no corrosion, dust and moisture, and they can be put into use after replacement treatment.

4.4.2 the existence mode of petroleum gas is gas-liquid coexistence, which can be fully purified only in the liquid phase state. In the purification process pipeline, the pressure at any point shall not be lower than the saturated vapor pressure of petroleum gas at corresponding temperature, so as to avoid "gas blockage" caused by LPG gasification in the pipeline.

4.4.3 check the purification effect. In the process of purification, pay close attention to the changes of pressure and flow, and regularly check the purification effect through the inspection port. The main examination methods are "nose olfactory method" and "detector detection method". On the one hand, the flow rate and flow rate are regulated by pipeline valves. If the quality of gas source is good, the flow can be appropriately enlarged; if the quality of gas source is general, it should be controlled to operate under the state of small flow; on the other hand, it is necessary to determine the reasonable dressing change period to ensure the purification quality.

Conclusion through the actual operation of the purification process equipment, it is possible to achieve good purification effect by selecting the appropriate gas source, removing impurities and adopting the correct purification process. Source: China education equipment procurement network

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