Research and Application of Non-stop Chemical Cleaning Technology for Cleaning Global Cleaning Equipment Zhang Qiyu Li Minming (Tuha Oilfield Drilling and Production Technology Research Institute, Shanshan 838202, Xinjiang) Zhang Yimin (Blue Star Cleaning Co., Ltd. Beijing Branch, Beijing 101318) successfully used The high-pressure equipment was cleaned without stopping, and the development process and application examples of HX-5 from Beijing Bluestar Cleaning Company and Tuha Oilfield were introduced. Chemical cleaning is a method of removing dirt from the surface of an object using one or several chemicals (or an aqueous solution thereof). It uses the cleaning agent to chemically transform, dissolve and peel off the surface contaminants or coatings to achieve degreasing, descaling and decontamination. Physical cleaning uses a variety of mechanical external forces and energy to make the dirt pulverize, decompose and peel off the surface of the object to achieve the cleaning effect. Due to the particularity of the oilfield equipment environment, the aging of high-voltage equipment and the instability of water quality, the metal ions such as calcium, iron and magnesium in the source water are seriously exceeded and the continuous operation for a long time, iron, calcium, etc. are formed in the equipment cooling system. Magnesium ion compounds and some microbial sludge cause the temperature of the equipment cooling system to rise. Under normal circumstances, the scaling equipment is shut down and cleaned during the inspection period. Generally, the combination of chemical cleaning and physical cleaning can achieve the desired cleaning effect. However, the formation of the industrial chain of light hydrocarbon equipment and the petrochemical equipment in Tuha Oilfield is closely related and inseparable. Especially in the past two or three years, the maintenance period is not yet available. The scale of light hydrocarbon equipment in the oil production plant has been severely cooled. Elevation, gas treatment can not meet the capacity and technical requirements, often passive production stoppages, shutdown maintenance not only affects normal production, but each production plant stops production loss of about 150,000 yuan per day (according to the 15 days of maintenance of each factory, 6 oil production plants) Total loss 1 In view of the above situation, our company conducts research on the non-stop descaling technology of refinery and light hydrocarbon equipment: first, investigate from the equipment environment, and then make corresponding technical countermeasures. Equipment investigation Light hydrocarbon equipment is mainly air cooling and heat exchange equipment. Air cooling equipment is mainly composed of air cooling and water cooling. The medium is mainly air and water, and it is in open air operation. Due to the harsh natural environment all the year round, dust storms often occur, causing serious metal ions such as iron, calcium and magnesium in the source water. In the cooling water circulation system, some microorganisms causing fouling are often generated and deposited on the surface of the device together with high temperature of metal ions such as iron, calcium and magnesium in the water, thereby forming a hard mixed scale. The medium contacted by petrochemical equipment is mostly corrosive medium, such as water, acid, alkali, salt, organic solvent, catalyst and so on. Once the equipment is fouled, the scale layer is close to the wall of the equipment. The scale layer wetted by the corrosive medium is highly corrosive. The scale metal has a large concentration gradient due to the mass transfer rate, which makes the surface of the equipment corroded. There is a potential difference in the medium, and the local corrosion rate is accelerated, which reduces the service life. The fouling of the heat transfer equipment will inevitably affect the heat transfer. The medium to be cooled will not be properly cooled, so that the heated medium will not be properly heated, the heat transfer efficiency will decrease, the production cost will increase, and the scale will easily cause the equipment. Corrosion, perforation, bursting. For petrochemical production, due to the corrosion of equipment and pipelines, the flammable, explosive, toxic and harmful materials run, run, drip, and leak, which makes the equipment safety and personal safety seriously threatened and increases environmental pollution. . Due to the long-term high temperature and high pressure operation of the equipment, the scale attached to the surface of the equipment causes the air cooling and water cooling effects to be poor, and the process performance is unstable, which seriously affects the output. Take the Shenquan centralized treatment station of Turpan Oil Production Plant as an example. Under normal circumstances, the daily gas handling capacity is 53.6t and the equipment set temperature is 28°C. After the surface of the equipment is fouled, the gas treatment volume is only 40% of the original, and the cooling effect is not Well, the temperature of the equipment rises to 46 ° C. It seriously affects the normal operation of production. Table 1 is a survey of the operation of light hydrocarbon equipment in the Tuha Oilfield. Table 1 Light hydrocarbon equipment survey The number of years of use Environmental scale fouling thickness Water quality / set / year situation Hilly oil production plant difference Wenmi oil production plant Turpan oil production plant difference 鄯 good mining oil plant difference Bakahara stable factory difference Qiudong processing plant difference In response to the above investigations, we began to study from the following aspects: cleaning mechanism research, cleaning agent screening, cleaning process research. 2.1 Principle of cleaning Since the substances to be cleaned are present in a specific medium environment, there are inevitably three substances in the cleaning process: the solid matter to be cleaned, the dirt present on the solid surface, and the medium to be cleaned. There must be a certain force between the three substances in order to make the cleaning process happen. We call this force the cleaning force. The cleaning system consists of four elements, namely the object being cleaned, the dirt, the cleaning medium and the cleaning force. Therefore, the cleaning must be carried out under a certain medium environment under the action of the cleaning force, so that the dirt on the surface of the object can be removed and recovered, and the surface of the object can be restored. 2.2 Research on the mechanism of cleaning agent The development of chemical cleaning technology is closely related to the progress of cleaning agent. The progress of cleaning agent has gone through the development stages of simple type and combination type. The cleaning agent used in the first stage is mainly strong acid and alkali which are highly corrosive, such as hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid and sodium hydroxide. At that time, due to the small variety of pickling inhibitors and poor performance, it was only suitable for the corrosion control of a certain acid and a certain metal material, and the corrosion inhibition performance of various metal materials and their components was poor, which limited the chemical cleaning. The scope of application. The second stage is mainly a combination cleaning agent. With the appearance of multi-functional pickling corrosion inhibitor, the same corrosion inhibitor has good combination of more than ten kinds of acid and common metal materials. Corrosion inhibition performance not only can effectively control the uniform corrosion of metal, but also has a good inhibitory effect on pitting corrosion, stress corrosion and hydrogen permeation corrosion. At the same time, organic acids, complexing agents and chelating agents replace strong acid and alkali, and combined weak acid complex cleaning agents and neutral detergents dominate. It has a strong reaction, dispersing or dissolving ability to remove dirt, and it can remove dirt more thoroughly during a limited period of time. 2) The damage to the cleaning object should be within the limits of the production permit, and the corrosion caused by the metal should be correspondingly inhibited. 4) The cleaning agent is non-toxic or low-toxic to organisms and the environment, and the exhaust gas, waste liquid and waste residue should be able to be processed to meet the requirements of relevant national laws and regulations. 5) The cleaning conditions are mild and try not to rely on additional strengthening conditions. 6) The cleaning process does not leave insoluble matter on the surface of the cleaning object, does not produce new stains, and does not form a new cover layer which is harmful to the subsequent process. According to the cleaning mechanism, technical requirements and the principle of cleaning agent screening, we screen the non-stop chemical cleaning agent. We evaluated the performance of several commonly used cosolvents. The results are shown in Table 2. Table 2 Evaluation of Cosolvent Performance Name Mass Fraction Basic Reaction Formula 2.3 Cleaning Agent Screening The principle of screening cleaning agent is as follows. It can be seen from the data in Table 1 that NaF has strong solvent-dissolving ability at the same temperature, the corrosion rate is within the standard range, and the price is low, which is the preferred co-solvent. Screening of cleaning main agent Through the comparison of Table 3 and Table 4, we chose solid cleaning agent as the main cleaning agent, which is mainly composed of organic acid, solid organic acid is easy to store and transport, easy to use; and organic acid cleaning agent is in cleaning. The main mechanism is its own oxidizing property, acidity, and excellent chelating ability of the active group, plus the cleaning of the compound surfactant, slow-table 3 solid organic cleaning agent and other pickling agents. Effect comparison cleaning solution mass fraction scaling amount dissolution amount dissolution rate time solid organic acid cleaning agent Table 4 solid cleaning agent and other pickling agent corrosion rate comparison of different materials, / 2, cleaning liquid cast iron carbon steel aluminum stainless steel copper Brass solid organic acid cleaning agent (10%) etchant, penetrant, etc., the oxide barrier layer attached to the metal surface is stripped, infiltrated, dispersed, and sequestered into the washing liquid to achieve the purpose of cleaning. The cleaning main agent we need should have strong complexing ability and good corrosion inhibition ability, not only good chelating function for metal ions such as Ca2+, Mg2+, Fe2+, etc., even for the inorganic salts CaS4 of these metals, MgSi3 and the like also have a good cleaning effect. 2.3.3 Screening of Corrosion Inhibitors During the entire chemical cleaning process, the dissolution of the scale layer is accompanied by corrosion of the base metal due to contact of the acid with the base metal. During the cleaning process, after the surface of the object to be cleaned is immersed in the cleaning liquid, corrosion begins at the crack of the rust and scale. As the scale layer is removed, the area in which the acid contacts the substrate becomes larger and larger, and the corrosion caused is also more and more serious. The metal corrosion process is the process of forming an electrochemical reaction on the metal surface. Slowing the metal corrosion is inevitably a process that affects the electrochemical reaction rate of the metal surface. The corrosion inhibitor suppresses the metal corrosion by the active region on the metal surface. It is carried out by means of atomic or molecular adsorption, and because of the adsorption characteristics of the corrosion inhibitor, it is possible to receive a very significant corrosion inhibition effect with a small amount of additives. Therefore, the selection and application of corrosion inhibitors is one of the most important aspects. It not only directly affects the effect of chemical cleaning, but also affects the safety and longevity of the objects being cleaned. Through comparison of various materials corrosion inhibition rate, we choose Lan-826 corrosion inhibitor, see Table 5. Table 5 corrosion inhibitor corrosion inhibition effect cleaning liquid cast iron carbon steel aluminum stainless steel copper brass Note: solid organic acid cleaning agent quality The score is 10% and the temperature is normal temperature. 2.3.4 Screening of reducing agent During the pickling process, Fe3+ in the pickling solution increases with the dissolution of scale and rust. Since Fe3+ is an effective cathodic polarizing agent, when it is reduced to Fe2+ in the cathode region, the corresponding metal is corroded in the anode region. The reaction formula is as follows: in order to reduce the concentration of Fe3+, thereby reducing the corrosion rate. The reducing agents commonly used to reduce Fe3+ to Fe' are Na2S3, SnCl2, H3P4, N2H4. The performance of the reducing agent is shown in Table 6. Table 6 Evaluation of Reductant Performance Ag.L-1f Reducing Agent Addition amount/gx Corrosion ~ Corrosion inhibition effect is as good as the beginning. Basically good corrosion Corrosion Bright as initially Corrosive Corrosion Corrosion During the chemical cleaning process, the purpose of the reducing agent is to suppress Fe3+, reduce the corrosion rate and avoid the occurrence of pitting. by. 4 Determination of the construction plan Cleaning step: make the circulating cooling water system and the auxiliary pipeline form a circulation loop, and the liquid level of the suction pool is normal. The inlet valve for circulating cooling water is controlled, and the formulated cleaning liquid is added to the sink at 0.56 kg/L. Adjust the pH of the cleaning solution to a range of 2.6 ~ 3.4 with a pH adjuster, perform a full-system chemical cleaning at room temperature, and hang a new test piece and the old test piece in the sink. After 24 hours, add a pH adjuster. After 36 hours, The pH is naturally stable and the displacement is discharged. The quality control cycle and time control indicators in chemical cleaning are shown in Table 9. Table 9 Chemical cleaning quality monitoring cycle and time control index Project test cycle control index (0~24h) Control index 9 Turbidity tends to steady temperature Normal temperature Total iron cleaning fluid mass fraction /% After our research, we believe that the auxiliary flow is added to the overflow pipe at the side of the suction pool, the cleaning liquid is circulated to the air-cooled part, and four jet tubes are set in the air-cooled part so that the cleaning liquid is evenly sprayed to the air-cooled scale. Uniform cleaning is possible. At the same time, the cleaning liquid flows down to the water-cooled part to clean and remove the scale of the water-cooled part, thereby achieving the purpose of cleaning. The conventional cleaning must be stopped, and the water-cooled and air-cooled parts need to be cleaned separately. 5 Application effect analysis 5.1 Cleaning effect During the cleaning process, we hang I-type and type test pieces in the liquid returning place. The type I test piece is a test piece type which is hanged into the sink without pre-treatment and naturally rusted for two months. The test piece was immersed in dilute hydrochloric acid, and then placed in air for watering, and the test piece was etched for 7 days. The purpose of the test piece is to observe the descaling rate and corrosion of the equipment, and to suspend two pieces of stainless steel test piece and two pieces of aluminum test piece at the liquid return point in order to detect corrosion and passivation film formation of the equipment after cleaning. Two pieces of type I and type test pieces are suspended at the liquid return. 12h before the cleaning process, the rust of the hanging piece was completely removed, the removal rate was 90%, and the change of rust was not obvious; the rust removal rate of the 24hi type test piece was about 90%, and the rust removal rate of the type test piece was 85%; 24h After that, most of the rust-removing surface becomes light gray-brown, and metallic luster is visible. Two pieces of stainless steel test piece and two pieces of aluminum test piece suspended in the liquid inlet have no obvious change during the cleaning process, and the surface is clean, and the metallic color is visible. After 24 hours, the surface color becomes lighter, and a gray-colored passivation film is formed and cleaned. At the end of the test, the corrosion rate of the new test piece is shown in Table 10. Table 10 Corrosion rate of the new test piece after the chemical cleaning is finished. Material cleaning time flow rate Stainless steel aluminum According to Table 10, the corrosion rate of each test piece is less than the cleaning effect 5.2. After the non-stop cleaning of the light hydrocarbon high-pressure air cooler, although the high temperature season in June and July, the cooling effect is significantly higher than before the cleaning, the average temperature is 14~16 °C lower than before the cleaning, and the operating set temperature is reached. The requirements ensure the normal operation of the production and solve a process problem that has plagued the oil production plant for many years. 5.3 Economic effect Due to the improvement of the cooling effect of the air cooler, the production load in the high temperature season is increased by 15%, the production of liquefied gas is 32t/d, and the total economic benefit is 13.5 million yuan (the loss of production is 150,000 yuan per day for maintenance and repair, according to the maintenance of each factory) Period 15 days). Saving maintenance costs of 400,000 yuan. 6 Conclusions The application of chemical cleaning technology for light hydrocarbon equipment is successful. The average corrosion rate of the new film is 0.46g/(m2h), which is far below the national standard of 6g/(m2h), forming a good passivation film. It has achieved the requirements of strong descaling ability, less sediment formation, easy handling, less corrosive to metal matrix, high safety and suitable for various metal materials. It can be used for a cleaning agent to achieve descaling and passivation at the same time. The requirements for chemical cleaning are not discontinued. The first application of non-stop chemical cleaning technology to the field has been highly evaluated by the client. This technology fills another gap in the chemical cleaning field of Tuha Oilfield. Although there are some unparalleled advantages of inorganic acid cleaning in organic cleaning applications, there are some shortcomings, such as cleaning of hard, thick, layered silicates and sulfate scales that have not been cleaned for many years. The ability is weak; if the concentration is low, the cleaning effect is not good; if the concentration is high, the cost is higher than the inorganic acid cleaning agent. In addition, it is more complicated to judge and measure the end point of system cleaning than inorganic acid. With the continuous development of cleaning technology, along with the continuous development and application of organic cleaning agents, we believe that the application prospects of high-pressure equipment non-stop chemical cleaning technology will become more and more broad. Wenzhou Vigorous Pet Products Co.,Ltd , https://www.vigorouspet.com
Research and application of non-stop chemical cleaning technology for high-voltage equipment