Chemical cleaning

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1 Purpose This trial operation guide describes the chemical cleaning process of components. It also describes the scope of cleaning, that is, which parts of which devices must be cleaned and the possible cleaning methods. This trial operation guide is intended for those responsible for the equipment under trial operation. This operation manual is issued by the manufacturer of the priority device components. Contractors usually carry out chemical cleaning. Therefore, its process description and cleaning procedures must be examined, including the specific safety, health, and environmental risks associated with the handling of chemicals. 2 Definition: Alkaline washing process (boiling); alkaline scouring process. Boiling refers to the process of using alkaline agents to clean a system, with pressure being adjusted to enhance the effectiveness. Along with the system’s “breathing” (pressure changes), the chemicals used remove the loose iron oxide coating and carry the dust particles into the suspended emulsified oil and lubricant. Rinsing and cleaning: Rinsing refers to the use of a boiler feedwater cleaning system. Acid leaching: Use an acid leaching solution to clean the system. Passivation: The exposed inner surface of the pipe is passivated using a passivation solution. Protective coating: In the protective coating process, a thin layer of magnet is created inside the pipe. This magnet coating protects the surface from corrosion. It is the responsibility of the personnel in charge of the trial operation process to ensure that chemical cleaning activities are carried out in accordance with the following guidelines, and to verify this. To ensure the proper operation of the system, it is necessary to thoroughly clean the high-pressure steam and feedwater systems as well as the suction pipes of the piston compressor and the expansion turbine before the trial run. Start with a thorough rinsing of the system to remove loose dust, rust, scale, and impurity particles. After rinsing, alkaline degreasing or acid pickling is carried out. Without a rinsing system or insufficient rinsing, damage and blockages can occur at any time during the boiling and acid soaking processes. The formation of the magnet protection layer slows down, and the steam cannot reach a pure standard within the time it takes to expand. 3.1 Cleaning range: The existing condensation lines can be used for cloud ring cleaning solution. Otherwise, a temporary wire must be used. Basically, the following equipment components must be chemically cleaned: a) the boiler feedwater high-pressure system (HP-BFW) – the boiler feedwater system includes the deaerator, as well as the steam drums of the cracker and the steam boilers, the boiler feedwater control station, and the feed lines of the high-pressure steam superheater and desuperheater; it does not include the boiler feedwater pump (only the suction pipe and discharge pipe). - Boiler feed water pipe to the steam deceleration station b) High-pressure steam system of the cracker – pipes from the boiler feed water control station to the inlet of the feed water preheater. - The transfer pipe switch and steam tank include a rising device and an overflow pipe. - Water preheater and high-pressure steam superheating equipment. - High-pressure steam pipe and high-pressure steam shut-off valve. c) High-pressure system of steam boilers – Steam boilers include a feedwater preheater, a steam generator (partition), a superheating device, and a steam drum that comprises an overflow pipe and a rising pipe. - Pipes from the boiler feedwater control station to the inlet of the boiler feedwater preheater. - The pipeline from the end superheater device to the high-pressure steam shut-off valve. d) High-pressure steam system – High-pressure steam shut-off valves located at the cracking furnace steam tank and steam boilers; the connections to the high-pressure steam pipes include the start-up line outlet. - High-pressure steam pipes and turbines. - High-pressure steam pipelines and reduction stations from high pressure to medium pressure. e) The inlet pipe of the piston compressor and the expansion turbine: The machine department specifies the scope of delivery for piston compressor components and expansion turbines as follows: Pulsation dampers and prefabricated gas pipes must be acid-treated, neutralized, and properly protected before being delivered to the site. The machine manufacturer specified the applicable acid leaching process and protective measures. The machine pipes for guiding the process gas, as well as those pipes that cannot be fully prefabricated in the machine manufacturer’s factory, are acid-treated or cleaned after being welded on-site. The machinery department relies on the acid leaching range table to identify the pipes in the PI diagrams, and passes them on to the department process diagrams and operations. On-site construction and commissioning supervision inspected the acid-treated pipes before their assembly and connection to piping (pulsation dampers, heat exchangers, etc.). If the system is not clean enough, additional measurements should be taken. In the case of very long pipes (>100m) and large-diameter pipes, the range of acid immersion depends on the location upstream of the piston compressor; it is recommended to install a pipe-type filter at the suction end. The installation of such filters should be inspected by the relevant machine department, in accordance with the department’s process diagrams and operating procedures. See the PI chart for details. The precise cleaning procedure is drafted by the designated cleaning company, taking full account of the supplier’s guidelines. Good cleaning results can only be achieved by following these points: – Plan and prepare the acid immersion process as early as possible. - Define the acid leaching range. - Define the acid leaching process and acid leachers. - Define materials that cannot be related to acid leaching agents. - Remove these components or take preventive measures. - Provide accurate cleaning nozzles in sufficient quantity. The cleaning procedure should include the following key points: – The circulation system to be used. - Information on chemicals and their properties (see the relevant accident prevention regulations and list of hazardous materials). - PI charts for loop stations and temporary pipelines. - List of pipeline components to be removed. - Information on the treatment/disposal of cleaning chemicals, etc. 3.2 Alkaline washing (boiling) Used with a boiling alkaline solution. Including: - 1 kg of solid sodium hydroxide per cubic meter of water, or 1.31 L of hydrated caustic soda (50%). - About 20% P2O5 is contained in 1 kg of flaky trisodium phosphate per cubic meter of water. In the case of surface rust, a good treatment method is to add oxygen-based resin adhesives to each m3 of water, such as 0.2 liters of hydrazine or 150 or 100 grams of sodium sulfite. There are two methods for bringing it to a boil: A) System ventilation – the system pressure is increased to about 50% of the rated pressure and the temperature is raised to about 250°C. This pressure is maintained for 2–4 hours, after which it is reduced to 25% of the calibrated pressure. After the pressure is reduced, the system cools down to about 120°C. Repeat this process 2 or 3 times. B) System circulation: Boiled solution is circulated within the system using temporarily installed pipes and pumps. The system pressure increases to about 50–60% of the calibrated pressure and remains at that level ； Increase the temperature (see QPB 09.02.01) by approximately 50 hours. A magnet coating is formed during the boiling of this type. Process: Before boiling or acid leaching can begin, the system must be inspected for leaks, undergo pressure testing, be rinsed, and have its oil removed using alkali. Pre-rinse the system using boiler feed water and a temporary centrifugal pump at a flow rate of 1–1.5 m/s. The debris was discharged at the intermediate discharge point. The turbidity (disappearance) of the rinsing water is photometrically measured at each intermediate discharge point. Once the turbidity value is satisfactory, it can be moved down to the rinsing section. Pre-rinsing is completed when the turbidity at the end of the system is almost the same as that upon entry into the system. The subsequent degreasing process is carried out using an alkaline degreasing agent. When circulating the alkaline solution, strive to achieve a water flow rate of 0.2–0.5 m/s. The processing temperature should be around 90°C. Refer to the manufacturer’s or chemical cleaning contractor’s operating instructions for details on how to prepare alkaline feed water. During the degreasing period, the phosphate content, pH value, and conductivity were measured at defined intervals. When the phosphate is no longer depleted, the cycle stops, and the cycle solution is optically clean. The alkaline solution was then removed from the system. With a steam drum and evaporator, this can be accomplished through drainage, and with pipes and heating surfaces, it is done by injecting boiler feedwater. For system components that will not be boiled or acid-treated subsequently, the alkaline degreasing method should be repeated one to two times or more (i.e., high-pressure steam and condensation line). The remaining alkaline solution should be collected and neutralized using hydrogen chloride or sulfuric acid. For refined boiler and furnace steam tanks, before starting the manufacturing process of the equipment components, it is necessary to ensure that the relevant components (boilers, furnaces) required for igniting the burners are ready, that the operation protocols are prepared, and that these protocols are established and issued. Isolate the boiling system from the rest of the equipment. The boiling process should be carried out in accordance with the manufacturer’s instructions, which specify the maximum operating pressure and temperature, the duration of boiling, and the concentration of chemicals used for boiling. Fill the boiler or furnace steam tank with boiler feed water from the degasser until the visible level is reached, then use a pump to add chemicals to the appropriate locations. Continue to fill the steam tank to the normal level, then close the boiler’s feed water inlet pipeline. Light the burner (with the available fuel) and increase it according to the manufacturer’s instructions. Important: During trial operation, the linings of furnaces and boilers are usually dried as part of the boiling process. If done this way, it should be ensured that the minimum temperature increase rate of the heating curve is applicable. (The drying curve represents the lining layer, or the thermalization curve represents the alkaline boiling process). It shows the alkaline boiling process of the transfer pipe switch/steam tank unit. It must be boiled for at least 48 hours, and the first precipitation should occur approximately 6 hours after boiling at a pressure of 4 bar. Heating causes the water level in the tank to rise. The condensation process is carried out using predefined pressure stages and outlets. The boiling process is monitored through analysis ； Measure the phosphate content, pH value, conductivity, and turbidity of the boiler water within the defined time interval. If the phosphate level drops to half of the current value, the installed pump can be used to increase the phosphate level. The pressure should not be increased during the condensation process. The manufacturer should specify the boiling process, pressure increase rate, residence time, condensation period, and maximum allowable condensation pressure. Once the phosphate level remains constant for several hours and the boiled solution is optically clean, the boiling process can be stopped. After boiling, all contents in the transfer pipe switch must be drained, and the system must be rinsed with boiler water at least 4–5 times. The rinsing process can be stopped when the distance of the discharged water from 0.1 mval/L of corrosive agent is reached, or when the pH value and conductivity of the discharged water are similar to or identical to those of fresh rinsing water. The discharged water should also be optically clean. Continue by opening the steam boiler tank and removing all dust found. Check the accessories inside the tank. If the system becomes very dirty after long periods of idleness or transportation, the aforementioned boiling process must be repeated several times. The caustic solution discharged before and after boiling has a pH of 12–14; it must be cooled and neutralized with acid before being fed into the biological treatment plant. Before starting the boiling process, the system operator should take the necessary steps for this purpose. If the system is not to be used immediately after boiling, it must be stored in accordance with the manufacturer’s instructions. When inspecting the steam tank, a layer of magnet formed (black to blue-black) can be seen. During subsequent operations, the magnet layer will become thicker. If it is certain that the boiling process was successful and the boiler or furnace can be operated, it proves that the lining of the furnace or boiler is completely dry. 3.3 Acid leaching is another method used to prepare for the operation of high-pressure steam and boiler feedwater systems. Acid leaching is carried out using a mild acid (i.e., citric acid) at a temperature of around 90°C. Similar to boiling, acid soaking must be carried out before rinsing. If necessary or for protective purposes, the system must be passivated immediately thereafter. Acid leaching has the following advantages: – No operational preparation is required for the ignition and steam heating systems. - If the system is cleaned more thoroughly, the trial run will be faster. - Since acid leaching exposes the metal surface, a uniform magnet coating can be applied after acid leaching. Disadvantages of acid leaching: - The disposal of the acid leaching solution is usually quite difficult. Acid leaching of boilers and pyrolyzers: If acid leaching is intended to replace boiling, it must be kept in mind that it involves numerous technical and chemical issues. Accordingly, acid leaching can only be carried out by specialized companies. This company must have several years of experience using acid leaching processes, acid leaching reagents, and additives. Therefore, these descriptions only include various stage descriptions of acid leaching. At the start of the acid leaching process, the company carrying out it must ensure that all joint connections, gaskets, etc., do not leak, and that the acid leaching solution does not damage anything. The surface subjected to acid leaching should be thoroughly inspected, and the scale coating as well as its solubility should be assessed. High-pressure valves should remain open to prevent impurity particles from damaging the base surface and to protect the packing from being eroded by the pickling solution. During acid leaching, if certain valves are about to be closed, their bases should be removed and cleaned, and the packaging should be replaced. The acid leaching process can be divided into 11 stages: 1. Rinse with water to remove loose dust. 2. Perform alkaline degreasing at a temperature of about 80–90°C for 8 hours. 3. Empty and neutralize. 4. Rinsing of the system. 5. Acid leaching of the system is carried out at a temperature of approximately 85–90°C for 15–18 hours. The acid leaching solution should remove impurities, especially iron oxide, so that the surface is clean and shiny. The addition of appropriate inhibitors will limit the corrosive effect of acid on metals (maximum material loss: < 20 g of iron/m2 = < 0.0025 mm). If the iron content in the acid leaching solution changes by no more than +0.2 g Fe/l over 2 hours, then the properties of this solution may change. 6. Empty and neutralize. (If an ammonia solution is used) 7. Rinse with boiler feed water. 8. A second acid leaching is carried out at 60°C for about 8 hours. One of the purposes of this step is to remove the rust formed in steps 6 and 7. To prevent further corrosion, steps 8 through 11 should be carried out continuously. Secondary acid leaching is complete when the iron content in the acid leaching solution remains almost constant and does not exceed 0.5 g Fe/l. After acid leaching, all leached surfaces should be clean, free of rust and loose magnets. Due to acid leaching, the material loss should not exceed 20 g/m2. Checking can be done by installing a typical piece of iron before acid leaching. 9. Adjust the pH of the acid leaching solution to about 10 by adding a solution such as 25% ammonium solution. The temperature is about 50°C. 10. Passivate the surface with a circulating alkaline solution. 11. Continuation: At a temperature of 80°C, the cycle lasts for about 12 hours. The pH value remains between 9.5 and 10. Drain the system and neutralize the passivation solution. The acid leaching process of the rinsing system is now complete. After being completely emptied, the system should be used for operations immediately or stored dried using nitrogen, as specified by the manufacturer. 3.4 Blunting: Fill the system with boiler feed water of a specified mass to increase the concentration of Levo*n (activated hydrazine hydrate) to 0.1% and the concentration of ammonia to 2%. The solution passivation temperature should be around 95°C. Then, the passivation solution with a pH value of 9.5 to 10 was pumped into the system under the normal system pressure generated by the auxiliary pump, and left there for 12 hours. Use pressurized nitrogen to purge the passivation solution from outside the tank and pipeline system, and cool it to 50°C before it enters the wastewater treatment system. Clean the drying system with nitrogen. 3.5 Inspection of the system after cleaning Before starting the inspection process, air (100% free of oil and water, instrument-grade gas) is used to remove the nitrogen that was introduced into the instrument during passivation. Random sampling inspections are carried out. Check the low points in the pipes: experience shows that sediment accumulates at these points and around valves. These precipitates must be completely removed. In the waste heat area, it may be necessary to cut off the test section in order to inspect the surface condition. The inspection nozzles on the distributor and head are suitable for this purpose. Re-welding and 100% X-ray inspection are the responsibilities of the installation company, and must be included in their contract accordingly. 3.6 Storage We distinguish between dry storage and moist storage. When stored in a dry condition (< 30% relative air humidity), the system is filled with nitrogen. To achieve this, the system must be completely dry, and pure nitrogen must be used. Under humid storage conditions, fill the system with degassed boiler water. Oxygen insect gum adhesive (i.e., hydrazine (100–300 mg/l)) can also be added to the boiler feed water. 3.7 Protective coating process: After the circulation system is cleaned, the system is heated to above 500°C, and a thin protective magnet coating is applied to the inner surface of the pipes. The oxygen required to form Fe3O4 is extracted from water, leaving 5 to 10 ug/l of hydrogen to condense after 2 days at normal steam concentrations. Iron and iron oxide are brought into the system by the boiler feed water (along with some iron on the pipe walls) and continue to be converted into magnets during operation ； Its scope depends to a large extent on how the equipment operates. The hydrogen level is approximately 5 ug/l, corresponding to 100 ug/l for Fe3O4 conversion. Note: If NaNO2 or KNO2 is used for passivation (which is more expensive), a magnet coating will begin to form during the passivation process. No additional protective coating process is required. 3.8 For the suction pipe between the piston compressor and the expansion turbine, if its internal diameter is small, the best approach is to remove the suction pipe, clean it mechanically and remove any oil from it, and then place it in an acid cleaning tank. If the inner diameter is large, use a cover to isolate the other parts of the system that need to be cleaned before starting work. Then the pipe is mechanically cleaned, degreased, and pickled. 3.9 Treatment of rinsing media and solutions As mentioned above, before introducing them into the operator’s wastewater treatment system, all rinsing media and solutions must be collected and neutralized. It is very important for the operator, Linde, and the cleaning company to make the necessary arrangements together in advance. Alkaline and antacid condensation tanks are more suitable for collecting solutions ； Sometimes rainwater collection tanks and gravel storage tanks are also suitable. Local laws and regulations regarding safety, health, and environmental protection (disposal) must be complied with. 4 Other applicable documents and precautions – P&I charts – Operation manual – Summary table – Mechanical completion transfer report – Manufacturer’s operating instructions – Cleaning procedures of the contracted cleaning company – Technical specifications for chemical cleaning of high-pressure steam and feedwater systems. - Relevant protection and safety measures when handling chemical substances (accident prevention regulations, information on hazardous materials). - Operation report for the furnace and boiler, including a list of the trial operation preparations that have been completed (applicable only to boiling requirements).