Proposal for Chemical Cleaning Tasks Prior to the Commissioning of Methanol Plant 《Reposted》
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Recommendations for Chemical Cleaning Before the Commissioning of Alcohol Production Facilities I. Overview of the Development of the Methanol Industry at Home and Abroad Methanol is a colorless liquid that is toxic! Pure methanol has an alcoholic odor, while crude methanol has a strong, irritating smell. When burned in air, methanol produces a faint blue flame. It is an excellent solvent, capable of dissolving various inorganic salts, as well as mixing well with water and most organic solvents such as ether and benzene. Its specific gravity is 0.7913, its boiling point is 64.7°C, and its melting point is -97.1°C. In the field of organic synthesis, methanol is an important basic organic raw material, second only to olefins and aromatics. With further advancements in science and technology, new applications for methanol have been developed. Not only is methanol an important chemical raw material, but it is also a highly efficient, clean, energy-saving, and environmentally friendly green energy source. The development of methanol fuels can help reduce pollution in the atmosphere, promote sustainable development in terms of energy and the environment, and ensure energy security. Therefore, as environmental protection measures are implemented more strictly, demand for methanol across various industries will increase, thereby having a significant impact on the methanol market. The chemical industry that uses methanol as a raw material will thus gain new vitality. According to reports from American publications such as “European Chemical News” and China’s “China Chemical Industry News”, China’s consumption of methanol is increasing at a rate of 10%–15% per year. By 2005, the demand is expected to exceed 3 million tons, and currently there is a significant gap in methanol production in China. In the coming years, our country will also build several large and medium-sized methanol projects to meet the needs of various industries. II. Current status of cleaning large and medium-sized chemical production facilities in China. Abroad, great emphasis is placed on the cleaning of equipment and pipelines, with specialized research institutions dedicated to this field. Abroad, the design firms took cleaning into account when designing the chemical process flows and requirements, and prepared estimates and cost projections. Cleaning methods have also evolved from the simple hydrodynamic cleaning to chemical cleaning, mechanical cleaning, and so on. The organizational forms of the cleaning industry vary around the world; ranging from the cleaning of individual parts to that of entire devices, there are both specialized chemical cleaning companies as well as cleaning teams organized by enterprises themselves. Some equipment, pipelines, and components require regular cleaning, and some production equipment is equipped with built-in cleaning devices; significant progress has been made in the application of cleaning technologies. There are various processes for producing methanol. While developing new technologies and carrying out technical upgrades, manufacturers strive to reduce energy consumption by cleaning their equipment, thereby increasing its operational efficiency and extending its lifespan, so as to produce more products with the lowest possible energy use. In the past, China lacked an adequate understanding of equipment cleaning; it was not until the 1970s, with the introduction of 13 large-scale fertilizer production units, 8 petrochemical plants, as well as large-scale steelmaking and generator equipment, that foreign cleaning companies came to China to undertake cleaning tasks for these projects. This was what drew the attention of relevant manufacturers and regulatory authorities. China Blue Star Chemical Cleaning Company was the first to break the monopoly held by foreign cleaning companies in China’s cleaning industry. The ammonia and urea production facilities in Nanjing Yangzi, Beijing Dongfang, Lanhua, Tianjin, Dushanzi, Zhongyuan, Maoming, Guangzhou, Jihua, as well as those at Wushi Petrochemical, Ninghua, Weihua, Shanhua, Jiujiang, Dalian, and Inner Mongolia, were all subjected to systematic chemical cleaning by domestic cleaning companies prior to being put into operation, with excellent cleaning results achieved in each case. III. The significance of chemical cleaning before the commissioning of a methanol plant Equipment and pipelines in newly built chemical plants accumulate a large amount of contaminants during manufacturing, storage, transportation, and installation. These contaminants mainly include: forged scales, iron oxide rust, sediment, welding slag, flux, rust preventive oil, and surface coatings. The main components of slag and flux are metal oxides such as titanium, manganese, chromium, and iron, whereas rust preventive oils and surface coatings are various polymer organic substances. Second-hand equipment imported often develops some type of material scale during the production process. After being taken off the original production line, pipes and towers may accumulate varying amounts of dirt and rust during transportation. To ensure the smooth operation of new installations and the reactivation of second-hand ones, it is necessary to remove dirt, rust, and other contaminants from the pipes and equipment in order to meet the requirements of the production process. Chemical cleaning is performed on newly installed equipment; not only is grease removal carried out, but chemical cleaning is also required. With the development of corrosion inhibition technologies, the corrosion losses of metal equipment during chemical cleaning have been reduced to a minimum, and the final passivation treatment will help to minimize corrosion during equipment operation. Furthermore, compared to corrosion during pickling, equipment operation failures caused by rolling scales, iron oxide rust, sediment, slag, rust preventive oils, and coatings are even more dangerous. Since a clean metal surface is obtained after chemical cleaning, it becomes possible to produce qualified products more quickly; as a result, the economic benefits gained by the factory will **exceed the investment cost of the cleaning process. Currently, all newly installed equipment, especially high-temperature and high-pressure devices, large-scale equipment, as well as those with high requirements in terms of production processes, must undergo chemical cleaning before being put into operation. Not only must the equipment itself be cleaned, but also other pipes and devices connected to the equipment that could introduce dirt must be cleaned as well. In recent years, our country has successively imported many large-scale chemical processing units from abroad, and the foreign manufacturers require that these units be chemically cleaned before being put back into operation. Many domestic cleaning companies have successfully carried out chemical cleaning of multiple large-scale chemical plants. Similarly, we believe that chemical cleaning of large and medium-sized chemical plants is also highly necessary. The necessity of chemical cleaning for medium-pressure methanol synthesis plants is discussed as follows: 1. Introduction to the methanol synthesis process: After being desulfurized through a gas purification system, natural gas is fed into a steam reformer, where the methane contained in the gas is converted, under the action of nickel-based catalysts, into syngas containing carbon monoxide, carbon dioxide, hydrogen, and other substances. After being cooled, the syngas is fed into a centrifugal turbine compressor, where it is compressed to 100–270 atm before being sent to the synthesis tower. In the synthesis tower, syngas reacts under the action of a copper-based catalyst to produce methanol. The heat of reaction in methanol synthesis is used to produce high-pressure steam, which serves as power for the turbine compressors. The gas containing methanol at the outlet of the synthesis tower is cooled in a condenser to condense the crude methanol, which is then separated in a separator. The condensed crude methanol is flashed in a flash tank and then sent to a distillation tower for purification, resulting in the final refined methanol product. 2. The significance of chemical cleaning in the purification system: Gas purification in the methanol production process mainly refers to the removal of sulfur-containing impurities from natural gas. The contaminants remaining in the pipes and equipment contain components that readily react with the desulfurization liquid, thereby affecting the purification efficiency of the feed gas. If the sulfur-containing gases in natural gas are not removed properly, it will be extremely harmful to the further conversion of the gas and subsequent synthesis. Specifically, the hazards include corroding equipment and pipelines, as well as poisoning the catalysts used in conversion synthesis. Therefore, the gas purification system of the methanol production plant must undergo chemical cleaning to keep its surfaces clean and free from contaminants, thereby obtaining clean natural gas feedstock and laying a solid foundation for methanol production. Not only that, but all the pathways through which natural gas passes, from the purification system to the subsequent processing steps, need to be cleaned. Otherwise, contaminants in the pipelines and equipment can mix into the already purified gas, causing secondary pollution that affects the production in subsequent steps as well as the purity of the product.
Could you provide the cleaning method and implementation plan?
That's right, cleaning process equipment is of great significance!
3. The significance of chemical cleaning for conversion and synthesis systems: The thermal conductivity of certain types of contaminants compared to carbon steel is as follows: Parameter – Thermal conductivity (kcal/m·h·°C): Carbon steel: 40–50; Ordinary scale: 1–2; Sulfate scale: 0.52; Carbonate scale: 0.4–0.6; Silicate scale: 0.2–0.4; Oil films: 0.1; Bituminous coal: 0.05–0.1; Air: 0.04. The thermal conductivity of dust and oil films is very low; their presence reduces the efficiency of heat transfer. This also means that a lot of fuel is wasted, and manufacturers have to incur additional unnecessary costs as a result. More importantly, in the conversion and synthesis systems, the high-temperature and high-pressure equipment, as well as the high-, medium-, and low-pressure steam pipelines and material transfer pipelines, have uneven distributions of anti-rust coatings, oil films, and dust. This leads to uneven temperature distributions in these devices, and even localized overheating. This requires the material of the equipment to have higher temperature and pressure resistance; otherwise, the strength of the metal equipment will be significantly reduced. When the fuel, flue gas, reactants, etc. remain constant, local overheating also implies local undercooling within the equipment, with serious consequences such as low conversion rates and stress corrosion of the equipment. Furthermore, if these contaminants are not removed, they will affect the quality of the materials, syngas, and steam, and may also poison the catalyst. This in turn affects the quality and yield of the product. Furthermore, certain components in the contaminants can accelerate the corrosion of sulfur-containing gas impurities on equipment and pipelines at high temperatures. Thoroughly removing debris from equipment and pipelines is highly beneficial for both the equipment, the pipelines, and the products. The turbo compressor is one of the most important devices in this system; as the gas is compressed, its pressure increases, and its temperature rises as well, which in turn raises the temperature of the compressor itself. To ensure the proper operation of the compressor, cooling water must be circulated through its jacket to remove the large amount of heat generated during operation. However, during processing, transportation, and installation, the heat exchange surfaces within the compressor jacket inevitably accumulate heat-insulating contaminants such as dust, impurities, and oil films. If the heat generated during compression is not removed in a timely manner, the increased temperature of the compressor itself causes the cylinders to expand due to heat, leading to wear. It also reduces the quality of the compressor’s lubricating oil, resulting in wear of the bearing shells and thus abnormal operation of the compressor. Therefore, the compressor jacket must be thoroughly cleaned, and it also needs to be cleaned regularly during subsequent production processes; this is very important for the proper operation of the equipment. 4. The significance of chemical cleaning in the distillation system: During the entire distillation process of methanol, the operating temperature plays a very important role in determining the quality and yield of methanol. The heat exchange equipment in each tower determines that they operate at appropriate operating temperatures. Since heat exchangers inevitably accumulate contaminants on their heat transfer surfaces during processing, manufacturing, storage, transportation, and installation – particularly oil and dust – this will **reduce the equipment’s heat transfer efficiency**. Therefore, it is necessary to chemically clean the heat exchange surfaces of the heat exchanger to keep the equipment in good working condition, so as to maintain the temperature of the distillation tower within an optimal range and thus ensure the quality and yield of the product. During the manufacturing, storage, transportation, and installation of components such as the separators, flash tanks, internal parts of the three columns, connection pipes between columns, the shell side of heat exchangers, return troughs, storage tanks, and export pipelines in this system, their inner surfaces accumulate a considerable amount of dirt. If this dirt is not removed in time, it can contaminate the semi-finished and finished products. In mild cases, it affects the color and turbidity of the product ； In severe cases, certain components in the impurities may react chemically with the product to form other substances. Moreover, using this substance as a raw material for other products will lead to many technical problems. Therefore, the aforementioned equipment and pipelines must undergo chemical cleaning to thoroughly remove contaminants from the metal surface in order to produce qualified products. 5. The significance of chemical cleaning for process water and cooling water systems: Heat exchangers play a significant role in the methanol production process. The heat transfer media used include process gas, steam, and industrial water (process water, circulating cooling water, and chill water). Industrial water often contains calcium and magnesium ions, bicarbonate ions, dissolved oxygen, and various microorganisms. Their presence often leads to equipment corrosion, scaling, and the attachment of microbial sludge. Water treatment techniques and chemical priming methods are commonly used to prevent corrosion, scaling, and the attachment of microbial sludge to equipment. However, the contaminants remaining in the water delivery pipes can easily react with the water quality stabilizers and priming agents used, thereby affecting the effectiveness of water treatment and priming. As a result, the efficiency of the heat exchanger decreases; it may even become corroded or clogged, causing the water pump to generate higher pressure while reducing flow rate, and an accidental shutdown may also occur. Therefore, it is highly necessary to perform chemical cleaning of the inner surface of the heat exchanger and the water delivery pipelines before driving. Furthermore, during subsequent production processes, the heat transfer surfaces of the heat exchangers should be chemically cleaned on a regular basis to ensure smooth operation. Following the methanol production process, and taking into account the towers, buildings, furnaces, containers, heat exchangers, pumps used in methanol production, as well as the pipelines that connect them and the steam generation systems, we believe that chemical cleaning has a direct impact on the success rate of starting up methanol production facilities, and it even affects the safety and stability of their operation in the future. IV. Comparison between chemical cleaning and steam purging before plant commissioning. Before the 1960s, to ensure cleanliness inside the equipment and pipelines, manufacturers would purge the pipeline systems before starting up the plant. The following compares the advantages and disadvantages of steam purging and chemical cleaning from several aspects: 1. Comparison of the time required for chemical cleaning and steam purging. Steam purging involves segmented purging, repeated purging, as well as alternating phases of temperature increase, constant temperature, and temperature decrease, which results in a longer purging time; for large-scale installations, this period is at least 1–2 months. Some pipelines, due to excessive residues from the manufacturing and production processes, have dirty inner surfaces, and it takes as long as half a year for them to meet the quality standards required for use. Chemical cleaning features rapid scale removal, short processing time, and a brief project duration. Under normal circumstances, cleaning a 100-cubic-meter system requires only three days for chemical cleaning. The duration of steam purging is not only determined by the characteristics of the steam purging process itself, but also constrained by the rated steam output of the steam generation system; it is generally difficult to reduce this duration further. A fertilizer plant compared its 300,000 tons per year ammonia synthesis unit and 520,000 tons per year urea production unit during chemical cleaning and steam purging. The equipment and pipelines that underwent chemical cleaning passed the inspection after just a few days, whereas those that were not chemically cleaned took about 27 days of steam purging before meeting the required standards. In other words, equipment and pipelines that have undergone chemical cleaning can be put into operation 20 days earlier. Therefore, chemically cleaning is faster and more time-efficient than steam purging in terms of time. The economic benefits of driving ahead of time are considerable, far exceeding the cost of cleaning. 2. Comparison of the application ranges of chemical cleaning and steam purging: Steam purging is generally used for pipes and process pipelines, while chemical cleaning has a wider range of applications; it can be used for pipes, process pipelines, heat exchangers, as well as reactors and containers. In particular, for certain large containers and spherical tanks, chemical cleaning using the spraying method can also yield satisfactory results. And these are incomparable to steam purging. 3. Comparison of the effects of chemical cleaning and steam purging: Steam purging only removes loose and free impurities and contaminants remaining in the pipelines; it cannot eliminate welding slag, flux, weld beads, and similar substances that are stuck inside the pipes. Chemical cleaning, on the other hand, can completely remove slag, spatter, and flux, while forming a dense passivation layer on the metal surface. Furthermore, adding acid cleaning inhibitors during the chemical cleaning process provides protection for the metal surface. Therefore, chemically cleaning the device is not only fast and thorough, but also very safe. 4. Comparison of economic benefits between chemical cleaning and steam purging: For manufacturers, time is equivalent to profit. Chemical cleaning is more time-efficient than steam purging, which means it enables faster realization of benefits. For a plant with a refining capacity of 180,000 tons per year, producing one day earlier allows for an additional 500 tons of refined methanol to be produced (based on the designed capacity), worth 1 million yuan in terms of monetary value (at 2,000 yuan per ton). Moreover, in general, production can start 10 or more days earlier, or even sooner; when these benefits are compared to the costs of chemical cleaning, they are certainly very cost-effective. In this sense, chemical cleaning is more economical than steam purging, offering significant benefits to manufacturers. 5. Comparison of chemical cleaning and steam purging in other aspects: Steam purging uses steam as the medium, which undoubtedly requires a large amount of high-quality steam; for manufacturers, steam purging entails significant energy consumption. At the same time, since steam purging requires a large amount of steam, for steam generation units with a fixed steam output, it is necessary to reduce the steam supply to other users, which affects the normal progress of production in those areas; chemical cleaning does not have such problems. Advanced chemical cleaning techniques have advantages over traditional steam purging methods, but steam purging also has its advantages in certain aspects. If it is possible to leverage the strengths of both approaches and integrate them effectively, by carrying out chemical cleaning of the entire system before starting up the plant, while simultaneously performing steam purging on individual pipelines in a targeted manner, along with physical cleaning, then the cleaning process prior to plant startup can be made as perfect as possible. V. Scope of chemical cleaning for methanol plants Depending on the specific production process for methanol, the cleaning tasks prior to the commissioning of a methanol plant generally cover the following areas: 1. Boilers used in operation 2. Heat exchangers 3. Steam pipelines 4. Water system pipelines 5. Pipelines carrying materials for which high process requirements apply 6. Vessels of various types 7. Devices used in the production of methanol derivatives. In theory, it is necessary to clean those equipment, pipelines, and vessels that directly affect product quality and yield, influence production efficiency, or are crucial for the safe, stable, and proper operation of the plant. However, in actual production, manufacturers can clean the equipment in a targeted and selective manner based on their own specific circumstances, and can still achieve good results. VI. Chemical cleaning process: The general cleaning process for chemical processing units is as follows: water flushing and pressure testing – alkali washing – acid washing – water flushing – rinsing – neutralization and passivation – treatment of waste liquids. For methanol production units, the cleaning processes vary depending on the specific equipment, and include: 1. Cleaning process before the unit is put into operation; 2. Cleaning process for units that are already in operation; 3. Cleaning process for the compressor oil system; 4. Cleaning process for steam pipelines