Refining of high-acid oil

High-acid corrosion refers to naphthenic acid corrosion; it typically occurs at temperatures above 240°C. The main areas affected are those in atmospheric and vacuum distillation units, and many refineries use high-temperature corrosion inhibitors to mitigate corrosion in these areas.

However, the acid value is very high; units for atmospheric and vacuum distillation should pay special attention to corrosion protection in the high-temperature areas. Corrosion inhibitors should be used, monitoring should be intensified, and the dosage of these inhibitors should be adjusted promptly based on the monitoring data.

High-temperature corrosion usually occurs, so it is necessary to consider adding corrosion inhibitors to prevent it; it is recommended to use Nalco’s Scorpion high-temperature corrosion protection solution.

It is best not to refine it alone; blending it with other materials is recommended. Production arrangements can be made carefully.

Naphthenic acid corrosion and perforation interact with high-temperature S corrosion; it is possible to conduct a survey of the materials used in the pipelines and equipment of the installation to determine which areas are prone to corrosion. Generally, 316L or 317 is used, while carbon steel can be employed in areas with low temperatures, with no problems in the short term.

Corrosion by naphthenic acids: Naphthenic acids (RCOOH), where R is a naphthyl group, are a mixture of various acids present in crude oil, with molecular weights ranging over a wide range (180–350). The corrosivity of naphthenic acids is affected by temperature. Naphthenic acid does not cause corrosion below 220°C; as the temperature rises, corrosion increases gradually, reaching its maximum at 270–280°C, after which it decreases again with further increases in temperature. However, corrosion increases sharply around 350°C, and there is no corrosion above 400°C. At this point, the naphthenic acids in the crude oil have been essentially completely vaporized. The concentration of acidic substances in the airflow decreases. Naphthenic acid corrosion occurs in the liquid phase. If no condensate is formed in the gas phase and no mist is entrained, gas-phase corrosion is minimal. If the gas is at its dew point or if mist is present, corrosion is exacerbated. Naphthenic acid corrosion products are soluble in crude oil; as a result, the corroded metal surface remains smooth without scales, showing grooved corrosion. Generally, the acid value in crude oil is used to determine the content of naphthenic acids; when the acid value of crude oil exceeds 0.5 mgKOH/g, it can cause corrosion of equipment. The domestic crude oils containing naphthenic acid include Liaohe crude oil (acid value of 0.86–1.64 mgKOH/g), Luning pipeline crude oil (acid value of 0.96–1.96 mgKOH/g), Xinjiang crude oil (acid value of 0.76–5.64 mgKOH/g), and Shengli crude oil (acid value of 0.24–1.18 mgKOH/g). It is recommended to… ； Typical designs do not take high-acid crude oil into account, and the materials used for equipment and pipelines do not meet the requirements for handling such crude; therefore, processing high-acid oil separately carries a high level of risk. It’s best not to refine it alone, as the benefits do not outweigh the costs and safety risks are high.

Processing acidic crude oil presents the following problems: 1. Desalination and dewatering – Cyclic carbonates are strong surfactants, and emulsification easily occurs during desalination, making it difficult to separate oil from water. As a result, the water content in the crude oil after desalination and the oil content in the wastewater fail to meet the specified standards. 2 Corrosion of equipment; the main component of petroleum acid in acidic crude oil is naphthenic acid, which often causes severe corrosion in the heating furnaces, atmospheric and vacuum distillation towers, as well as various equipment pipelines in processing units. 3 Emulsification that occurs during the purification of distillate oils at atmospheric pressure (mainly diesel); 4 Impacts on downstream facilities. Measures to be taken when processing crude oil with high acid content: 1 Establish corrosion control procedures; 2 Blend it with crude oil having a low acid value. It is advisable to keep the acid value of the blended crude oil below 0.5 mgKOH/g. 3 Process alternately with crude oils of low acid value. When processing crude oils with low acid values, a protective film or thin layer of char may form in the high-temperature areas; these can reduce the corrosive effect of naphthenic acids. When processing high-acid-value crude oil subsequently, the protective film is damaged; before it is completely destroyed, processing is switched to low-acid-value crude oil in order to reduce the corrosion caused by naphthenic acids. This method has been used at the Dushanzi Refinery and the Jinxī Petrochemical Complex, with good results. You can process high-acid oil for a while first, and then process low-acid oil for a while once it arrives. 4 Use high-temperature corrosion inhibitors 5 Deacidification of crude oil Last edited by myzfs on 2009-4-10 12:48]

(1) Processing of acid-containing crude oil: To address the problems encountered by various units in processing low-quality crude oil, a petrochemical company took measures such as crude oil blending, distillation without producing residue, increasing the frequency of catalyst replacement in catalytic cracking, and reducing production volumes, which helped to resolve some of these issues. Through analysis and research on the characteristics of processing sour crude oil at a certain petrochemical subsidiary, the corrosion caused by sour oil and its patterns, measures for preventing acid corrosion, as well as issues related to plant operation, a preliminary understanding of the processing of sour crude oil has been gained, along with some recommended measures. Processing acid-containing crude oil requires solving 3 main problems: corrosion of the distillation equipment ； The impact of emulsification and VGO in the refining of atmospheric distillation products (mainly diesel) on downstream units. Therefore, it is recommended to adopt the following countermeasures and measures: 1) Strengthen the evaluation of crude oil and pay attention to its changing trends. For example, Duba crude oil has a high acid value and high salt content, and it has never been processed; production plans should be formulated accordingly, taking into account the information on the crude oil provided by the supplier. 2) Improvement of processing technology. Improvements can be made to processes such as electrical desalting of crude oil and electrochemical refining of diesel; if necessary, pre-deacidification or pre-hydrogenation refining of vacuum distillate oils can also be carried out. 3) Explore new intermediate quality control indicators to meet the requirements of secondary processing equipment. 4) Further optimize the current planning principles for crude oil blending and tanking. For example, ensuring that the light and heavy fractions of crude oil processed by the same distillation unit have similar properties. 5) Draw on some measures from other factories to reduce the impact of processing acid-containing oils from various aspects. For example, blending with crude oil of low acid value; processing it in alternation with crude oil of low acid value; injecting appropriate high-temperature corrosion inhibitors at suitable locations, etc. 6) Employ equipment anti-corrosion and hydrogenation technologies. The most effective method for preventing corrosion in equipment used to process crude oil with high acid content is to replace it with appropriate corrosion-resistant materials, while the effective processing technique is hydrogenation. Therefore, in the long run, to fundamentally solve the processing corrosion problem associated with low-quality acidic crude oil, it is necessary to use corrosion-resistant materials and build hydrogenation units.

When the acid value is too high, special plans are required for the processing of high-acid crude oil. High-temperature corrosion inhibitors must be used, and the relevant equipment and materials need to be upgraded; otherwise, processing high-acid crude oil blindly is a very dangerous practice. Pipeline corrosion and leaks can occur, fires are likely to break out in areas exposed to high temperatures, and the packing in the pressure-reduction components suffers severe corrosion.

Attention to the poster: Whether a vacuum distillation unit can process high-acid crude oil depends on the actual material quality of the equipment. . . 1. If your atmospheric pressure towers are made of 16Mn or 20R, then you must implement proper anti-corrosion measures for the areas exposed to low temperatures, by injecting ammonia and neutralizing corrosion inhibitors. . . Enhance electrodesorption operations; from the second line downward to above the feed section, add high-temperature corrosion inhibitors. . . 2. Pressure reduction towers generally use material 321; at the very least, they use material 304, or steel plates lined with either of these two materials. Such a vacuum distillation column, combined with the use of high-temperature corrosion inhibitors, is generally sufficient to handle high-acid crude oils with an acid number of 2–4. . . You can consult CNOOC Asphalt as well as the various refineries under CNOOC; they have the most experience in processing high-acid marine crude oil. . . :lol