Discussion on purification process of liquefied petroleum gas

1 Overview Liquefied petroleum gas (LPG) has been widely used as an industrial raw material and civil fuel, and has achieved great economic and social benefits. Historically, the first sales of LPG was used as fuel, and today it is still an important market. However, with the rapid development of the petrochemical industry, liquefied petroleum gas (LPG), as a raw material for the chemical industry and the civil gas industry, has broad prospects for its production and application, especially today's fine chemical production is inseparable from liquefied petroleum gas. Such as spray, cleaning agent, rust remover, mold release agent, plastic foam and other industries as a propellant, propellant, foaming agent, etc. have an irreplaceable role. However, since the general petroleum gas contains a certain amount of impurities, it must be purified as a chemical raw material. Therefore, as a purification process and operation is very important.

2 Production route of liquefied petroleum gas There are two main sources of liquefied petroleum gas: one is to extract from associated oil or natural gas in oil fields, and the other is to extract from petroleum refining.

2.1 Separation and recovery from oil and gas fields In the process of oil extraction, the associated gas of by-products, through appropriate treatment measures such as oil and gas separation, can obtain high-quality liquefied petroleum gas with high purity and low sulfur content.

2.2 Extraction from petroleum refining Extraction of petroleum gas from refineries and from by-products of petrochemical plants is usually carried out in petroleum refineries using atmospheric distillation, vacuum distillation, thermal cracking, catalytic cracking and catalytic reforming, while thermal cracking and catalysis. The cracking process is the main source of domestic LPG production. Petroleum gas contains a large amount of sulfides such as isoparaffins, olefins, hydrogen sulfide, etc., and often contains oil components that are difficult to separate.

3 Liquefied petroleum gas main components and impurities 3.1 The current domestic supply of LPG is mainly from refinery gas, the main components are propane (C3H8), propylene (C3H6) and butane (C4H10).

3.2 Impurities mainly include: 3.2. Sulfur-containing compounds In the petroleum production process, sulfur, carbon oxysulfide, hydrogen sulfide and dimethyl sulfide are contained in the petroleum production process: the petroleum gas reacts with the inner wall of the pipeline and the storage tank to form iron sulfide and sulfurized Iron; LPG is artificially added with a odorant prepared by a sulfur compound such as mercaptan or thioether (the main component is methyl mercaptan ch3sh, ethanethiol c2h5sh).

3.2.2 During the LPG refining process, the sediment and iron filings (rust), which have not been completely removed, are still dehydrated and dehydrated during the refining process, but still contain a small amount of water. There are usually two ways in which water can exist in LPG: one is free water and the other is dissolved water, and the content of dissolved water in LPG varies with the state and temperature of LPG. (See Tables 1 and 2) Take propane as an example to see the change: Table 1: Liquid propane at different temperatures. Temperature: * Water 倨 (%) As can be seen from the table, dissolved in 35*C, It is dissolved. There is about 5kg of water.

Table 2 The ratio of the water content of gaseous propane and liquid propane at different temperatures. The ratio of the water content at the same temperature, the gaseous water content will be much higher than the liquid water content.

3.2.4 Aromatic hydrocarbons and refined oils: mainly unrefined during the refinery refining process.

4 Liquefied petroleum gas purification treatment process 4.1 Selection of gas source Because the quality requirements of fine chemical products for LPG are much higher than ordinary LPG. Choosing a high-quality gas source can greatly improve the purification speed, shorten the processing cycle, and improve economic efficiency while reducing production costs. The later purification of petroleum gas is mainly for water, sulfide, sediment and oil components, and the content of sulfide and the weight of oil taste have a great influence on the deodorization effect. The selection of gas source is determined from three aspects: 4.1.1 The quality inspection report of suppliers and authoritative departments is mainly pressure, temperature, specific gravity, chemical composition, sulfide content, free water content and residue content. .

4.1.2 Based on the experience of the staff, adopt the “nose sniffing method” to determine the content of the oil component based on the lightness of the oil in the LPG. This method is simple and easy, but requires some work experience.

4.1.3 Analyze the components of LPG by "Gas Chromatography". The data obtained by this method is accurate, but the operation is complicated.

* Generally speaking, although the LPG produced by the refinery is the main source of the domestic market, it is difficult to handle due to its complex composition and high impurities, especially the oil components that are difficult to handle. The associated gas from the separation of oil and gas, the purification requirements are lower, is the first choice for gas source.

4.2 Main equipment and process flow Since liquefied petroleum gas is a flammable and explosive dangerous product, the purification treatment equipment must be selected and operated according to its nature and function. The main process flow chart is as follows: the smell storage tank I4.3 LPG purification principle and the selection of deodorant materials. Although the crude oil is filtered and desalted during the refining process, it still contains a small amount of silt iron during the process of refining LPG. Shoulder (seduction). In the purification process, the precipitation method can be firstly used, stepwise elimination, and then adsorbed by the adsorbent (activated carbon) to achieve purification. In this process, activated carbon granules are the main raw materials. They are made from carbonaceous materials such as wood, coconut shell, husk, coal, etc., which are made by carbonization and activation. The raw materials for the production of activated carbon, the degree of activation is selected on the surface chemical properties of activated carbon. , volume and surface area have a great impact. Therefore, choosing the appropriate degree of activated carbon and carbon particles has a great relationship with the quality of purification.

4.3.2 Dehydration and dryness If the liquefied petroleum gas contains more than a certain amount of water, under certain temperature and pressure, water and liquefied gas in C2, C3, (: 4 crystallized hydrates <:*>*XH20 hydrated In the aggregate state, it is white crystal or rust-colored. Because the formation of hydrates will reduce the flow cross section of the pipeline, and even block the pipelines, valves, instruments and equipment, the petroleum gas in the chemical products has too much water content (especially In the gas phase) will affect the quality of the product.

b. Treatment measures Because water has two ways of existence in LPG: one is free water and the other is dissolved water. Usually for the former form, the “sinking method” can be used, which is the lowest position in the cylinder. The condensate is also the most economical way to treat water. (Go to page 46) Now there are no defects in the eight years. Jl. has two changes in the following aspects.

Fundamentally realized the safety management mode from "post-event" to the establishment of "hazard identification, risk assessment control procedures", various types of emergency preparedness and response measures, so that each production activity "predicted before operation, there is prevention in operation , can control when emergency."

It has created a “human security” environment, and the traditional safety management has changed among the employees only the safety department.

Now, according to the system documents established by the standards, the trade unions, technology, equipment, publicity and other departments are organically included. In the operation of the system, each tl can perform management according to the principle of “doing according to standards and following procedures”. Function. Really the safety production department has the responsibility, everyone participates in the standards according to the standards, the company has carried out safety training for various types and levels of personnel, through training to enhance the safety awareness of the staff, to do a good job of the company's safety: It is necessary to establish an advanced safety management idea of ​​"prevention first, control process, guarantee results, and stay in K witness", and a consensus has been formed in the majority of the staff.

At present, the company is working hard to improve the system in a footstep, and strive to achieve new achievements in occupational safety and health management T.

For the dissolved water, in addition to the "sinking method", the main use of water-absorbing silica gel for drying, the essence is that the liquefied petroleum gas through the solid silica gel (435mm) for water absorption, diafiltration process.

Liquefied petroleum gas will contain sulfides, which are not only corrosive, toxic, but also have special odor. This odor directly affects the quality of chemical products. Therefore, deodorization is an important part of the purification process. Copper is usually used. The molecular sieve adsorbs and reacts with the sulfide in the petroleum gas to achieve the purpose of sulfur removal.

4.4 Process treatment and operation 4.4.1 Although the content of impurities in liquefied petroleum gas is small, it has a great influence on the purification quality. Therefore, the storage tanks and pipelines of the purified LPG must be polished before use. It is cleaned and purged to achieve no corrosion, no dust, no moisture, and can be put into use after being replaced. 4.4.2 The existence of LPG is the coexistence of gas and liquid, which can only be fully purified in the liquid phase. In the purification process pipeline, the pressure at any point shall not be lower than the saturated vapor pressure of the LPG at the corresponding temperature to avoid "gas blockage" caused by gasification of LPG in the pipe. 4.4.3 Checking the Purification Effect During the purification process, the changes in pressure and flow rate should be carefully observed, and the cleaning effect should be checked regularly through the inspection port. The inspection methods mainly include "nose sniffing method" and "detector inspection method". On the one hand, relying on pipeline valves to regulate the flow rate and flow rate, if the quality of the gas source is good, the flow can be appropriately amplified. If the quality of the gas source is generally controlled, it should be controlled to operate under a small flow state; on the other hand, it is reasonable to determine the dressing cycle to ensure Purify the quality.

5 Conclusion By looking at the actual operation of the purification process equipment, selecting a suitable gas source, removing impurities and taking the correct purification process can achieve a good purification effect.

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