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XX Power Plant’s 2 × 300MW boilers are subcritical intermediate-reheat natural-circulation drum boilers. Before supplying steam to the turbine, the newly installed boiler unit will adopt a combined oxygen flushing scheme using both the superheater and reheater in order to reduce the number of cleaning operations while ensuring high quality cleaning; this approach is intended to shorten the overall project duration and lower the fuel consumption during the commissioning phase. The combined oxygen injection blowing method for the superheater and reheater in one stage involves installing a granulator behind the temporary blowing control valve, which connects the cold sections of the superheater and reheater. The impurities removed from within the superheater tubes can be collected by this granulator and discharged through the drain pipe, thereby preventing these impurities from reaching the reheater tubes. The steam that passes through the granulator can then continue to clean the reheater tubes ； At the same time, during the blowing process, pure oxygen is added to the high-temperature steam at the oxygen injection point; this helps to remove impurities from the surface of the furnace tube and promote the formation of a protective film. 1 Purpose and Principle of Steam Oxygen Blasting Nozzles 1.1 Purpose Before supplying steam to the turbine, newly installed boiler units must have their steam pipelines cleaned. This is necessary to remove various impurities that may have remained in the superheated and reheat steam systems as well as in the steam pipes during manufacturing, transportation, and installation – such as sand particles, stones, weld slag, rust, iron oxide scale, etc. – by using high-speed steam streams, thereby ensuring the safe and reliable operation of the unit. 1.2 Principle: When high-temperature steam carrying pure oxygen flows over the surface of the furnace tubes contaminated with oxides, the diffusion reaction of oxygen, combined with the differences in the thermal expansion coefficients of various materials, alters the phase state of the adhering substances. This reduces the strength of the bond between the corrosion products and the furnace tube surface, allowing these impurities to be stripped off from the surface of the furnace tubes under the action of the high-temperature steam flow and thus removed from the system ； At the same time, the cleaned metal surface forms a high-strength protective film due to the action of the oxidant, which protects the tube. By using these two approaches simultaneously, it is possible to **reduce the number of blowing operations, save fuel, and shorten the project duration. The chemical reaction equations are as follows: 4FeO + O2 → 2Fe2O3; 6FeO + O2 → 2Fe3O4; 6Fe(OH)2 + O2 → 2Fe3O4 + 6H2O. For the passivation reaction: Inner layer film: 3Fe + 2O2 → Fe3O4; Outer layer film: 4Fe + 3O2 → 2Fe2O3. Scope and process of steam-oxygen cleaning: 3.1 Cleaning scope: Includes the superheater, main steam pipes, tubes in the hot and cold sections of the reheater, the reheater itself, as well as the temperature-reduction pipes for the superheater and reheater. 3.2 Main purging procedures: 3.2.1 Phase-one combined oxygen injection purging procedure: O2 drum – ceiling superheater – shell wall superheater – partition wall superheater – primary superheater – O2 primary desuperheater – screen superheater – secondary desuperheater – secondary superheater – main steam pipe – high-pressure main steam valve – temporary O2 pipe – temporary throttle valve – temporary pipe – particle collector – cold section tubes of the reheater – low-temperature reheater – high-temperature reheater – hot section tubes of the reheater – medium-pressure main steam valve – temporary pipe – target plate – exhaust vent. 3.2.2 The tubes for superheaters, reheaters, and desuperheaters are purified using a pressure-stabilized flushing method. 4. In accordance with Standard 3.1 \"Regulations for the Commencement and Completion Inspection of Thermal Power Plant Construction Projects (1996 edition) and Related Regulations\", 3.2 DL/T5047-95 \"Technical Specifications for Power Plant Construction and Acceptance – Boiler Units\", 3.3 the 1996 edition of \"Quality Inspection and Evaluation Standards for Commissioning and Testing of Thermal Power Projects\", and 3.4 the 1998 edition of \"Guidelines for Steam Purging during the Startup of Thermal Power Units\". 5. Quality control points: 5.1 During the steam purging process, the commissioning personnel are responsible for all commissioning tasks within their team; they must carefully fill in the original records for each stage and sign them. The person in charge of boiler-related commissioning tasks is responsible for verifying these records and signing them as well ； 5.2 Quality control point: The target plate used to verify the effectiveness of the cleaning process can only be used to conclude the steam cleaning work for the superheater and reheater of #3 furnace after it has been inspected and approved by the relevant departments in accordance with applicable regulations ； 5.3 Inspection method: 5.3.1 During blowing, the momentum of the steam used for blowing should be greater than that of the steam operating under the unit’s rated conditions (i.e., the momentum coefficient K > 1). Two consecutive tests on the aluminum target are conducted; there should be no impact marks on the target larger than 0.5 mm. For marks ranging from 0.2 to 0.5 mm in size, there should be no more than 5 such marks on the first target, and the number of marks on the second target should be less than that on the first target. Additionally, the target surface should exhibit a metallic luster typical of aluminum. 5.3.2 If necessary, select some superheater and reheater tubes for tube cutting inspection; observe the condition and color of the passivation film on the surface of the sample tubes, and conduct copper sulfate drop tests as well as scale amount analysis tests, recording the time of color change and the remaining scale amount. 5.4 If a device issue is detected during the blowing process, the maintenance technician shall fill out a maintenance request form, and the relevant department shall provide feedback on the results of the maintenance. 6 Division of Responsibilities 6.1 The boiler commissioning technicians participate in the operation shifts, and are responsible for directing and coordinating each shift throughout the tube blowing process; they provide guidelines regarding equipment operation and technical support for the tests, while also carrying out testing and recording tasks for the entire tube blowing process ； All the technicians who participated in the test held the corresponding qualification certificates. 6.2 Chemical supervisors work on rotating shifts alongside the operation. 6.3 During the blowout process, the operators are responsible for operating the equipment in accordance with the blowout plan and the requirements of the commissioning personnel. 6.4 The installation unit is responsible for installing the temporary facilities required for the tube blowing process, cleaning the granulators, carrying out oxygenation operations, and maintaining the equipment. 7 Control parameters for steam-oxygen purging 7.1 Purging pipe parameters: 7.1.1 The purging pipe utilizes a method that combines oil injection with fire suppression, as well as pressure stabilization and reduction. 7.1.2 Stable pressure purging: pressure of 3.0 MPa, temperature not exceeding 450 ℃ ； 7.1.3 Pressure reduction purging: The initial pressure is 5.8 MPa, the final pressure is 3.0 MPa, the temperature shall not exceed 450 °C, and the pressure drop during purging is determined by ensuring that the saturated temperature in the drum does not drop by more than 40 °C. 7.2 Oxygenation parameters: The amount of oxygen added is 0.3 to 1 ‰ of the steam volume; oxygenation takes place simultaneously with the blowing process, and it stops when the blowing process ceases. 8 Temporary measures for the soot blowing system 8.1 Temporary control electric doors for soot blowing 8.1.1 Two temporary control electric doors (DN300, PN25) are required for the oxygen-enriched soot blowing operation in the superheaters and reheaters. It is recommended to use electric doors with rapid opening and closing that are imported from Japan; the opening time should be less than 1 minute, they should be able to stop at an intermediate position, and they must be capable of withstanding the differential pressure forces generated during opening or closing, so as to prevent the valve element from shifting due to high differential pressures. For ease of operation, the temporary door control device should be located in the main control room. 8.1.2 A bypass pipe with dimensions of Φ76×8 shall be installed at the temporary control valve, along with a manual stop valve used to control the speed of pressure increase and to warm up the system; the valve model is DN50, PN25. 8.2 Temporary connection pipes 8.2.1 According to the pipeline layout, temporary pipes shall be connected behind the high-pressure main steam valve, the medium-pressure main steam valve, and the high-pressure cylinder exhaust check valve. 8.2.2 Remove the flow orifice plates from the desuperheating water and reheat water tubes, and replace them with temporary pipes; connect a temporary pipe to the desuperheating water drain pipe to vent air, thereby facilitating the cleaning of these tubes. 8.2.3 The cross-sectional area of the temporary pipe shall be no smaller than that of the permanent pipe, and its strength shall meet the requirements for blowing. 8.2.4 The temporary pipe section in front of the target plate must be descaled, and after passing strict inspection by the quality control department to ensure that there are no debris inside, it can be welded. Tungsten inert gas welding should be used for the root pass, and the welding must be carried out by qualified welders with high pressure welding skills. 8.2.5 All temporary connection pipes must be fitted with insulation. 8.3 Temporary Supports 8.3.1 To ensure that the temporary piping system can expand freely, strong fixing supports should be installed on vertical sections, while stable sliding supports should be used on horizontal sections. 8.3.2 The installation of temporary supports allows the temporary pipe to expand in the direction of the steam flow only; movement in the opposite direction is not permitted. 8.3.3 Temporary supports should meet the same design standards as those for permanent pipes, capable of withstanding the impact forces and reaction forces generated during blowing, to prevent the temporary pipes from shaking during this process. 8.4 Temporary handling of various electric and control valves on the turbine side 8.4.1 Handling of the high-pressure main steam valve and medium-pressure main steam valve: Disassemble the high-pressure main steam valve, remove components such as the valve core and valve stem, protect the valve seat with special plugs, and then connect temporary pipes at the main steam valve gland using special flanges. The treatment of the medium-pressure main steam valve is the same as that of the high-pressure main valve. 8.4.2 For the treatment of the exhaust check valve in the high-pressure cylinder, in order to prevent steam from leaking into the turbine, the valve stem of the check valve should be pressed tightly; the drain valve behind it should be kept in the open position, and its drain pipe should be led to a location where it can be easily observed. Temperature sensors installed on the cylinder wall should also be activated in order to enable monitoring. 8.4.30% For the 30% bypass section, mechanical treatment is applied; it is not involved in the tube blowing process. Treatment is carried out before the bypass is installed, and it can be installed in place only after it receives approval from the quality inspection department. During the blowing process, the high-pressure bypass temperature and pressure reduction valve is not installed; the pipeline is blocked with a plug. 8.5 Target Plates 8.5.1 Two target plates are installed on the temporary pipe section behind the joint door. To ensure the quality of targeting, the target plates should be at a distance of at least 5 to 10 times the pipe diameter from the elbow, so as to prevent steam containing impurities from separating from those impurities as it passes through the elbow, which could affect the accuracy of quality inspections. 8.5.2 The target plate is made of aluminum, with a width of ≥25 mm and a length corresponding to the inner diameter of the tube. 8.6 Temporary Oxygenation System 8.6.1 Oxygen Cylinder Sets: The blowpipe oxygenation system consists of 4 to 5 sets of oxygen cylinders, with each set containing 10 to 15 oxygen cylinders; these cylinders are secured to the cabinet rack using straps. The connection between the oxygen cylinder and the main oxygen supply pipe is made using Φ6 ×2 red copper pipes, while the connection between the red copper pipes and the oxygen cylinder is achieved through detachable threaded connectors. 8.6.2 Oxygenation pipeline: Composed of the oxygen supply main pipe, as well as the air pipe and drain pipe of the furnace body. The oxygen supply main is made of stainless steel pipes with a diameter of Φ32×3.5. 8.6.3 Sampling tube: To facilitate timely monitoring of the effectiveness of steam oxygen scouring, a sampling tube is installed in front of the target plate. The temporary sampling tube is made of stainless steel with dimensions of Φ16×2.5. Small holes with a diameter of Φ6 mm are drilled in the semi-circular surface on one side of the tube, and bevels are created at those holes. Insert the sampling tube into the temporary tube, with the small hole facing away from the direction of the steam flow (steam samples from the temporary tube are taken using static pressure), and its outlet end is connected to the sampling tube cooler. During the blowing process, steam quality is analyzed through chemical sampling. 8.6.4 Oxygenation points: Oxygen is added to the system from four locations. The first one is added from the drain pipe of the ceiling inlet header ； The second is added through the primary superheater temperature-reduction water pipe ； The third is added through the secondary superheater temperature reduction water pipe ； The fourth one is added by the reheater accident **pipe. 8.7 Granulator The granulator shall meet the following requirement: resistance less than 0.1 MPa ； The strength meets the steam parameters ； It has good performance in collecting miscellaneous items. It is recommended to adopt an external-in, internal-out structure. 8.8 Silencer: To reduce noise during blowing, a silencer must be installed at the exhaust outlet. 9 Requirements for the soot blowing pipe 9.1 The boiler must be in a condition that permits ignition and pressure building up. 9.2 The temporary system for the soot blowing pipe must be installed and pass inspection by the quality control department. 9.3 Conduct an air pressure test on the oxygen addition system at a pressure not lower than that of the oxygen cylinders (12–13 MPa) to ensure that the system is airtight and leak-free. 9.4 The main operating monitoring instruments, such as pressure, temperature, flow rate, and water level, have all been calibrated and are ready for use at any time, with accurate readings. 9.5 The temporary pressure gauges, thermometers, sensors, etc. used for the blowing pipe have been calibrated and installed; they are ready for operation and display correct readings. For ease of observation, the meters should be arranged together and kept away from temporary pipes. 9.6 The fuel system has been tuned up, and all fuel nozzles are ready to be put into operation at any time. 9.7 The turbine barring system can be put into operation at any time. 9.8 The electric feed water pump has been completed in debugging and can be put into operation at any time. 9.9 Ensure that the deaerator is operational, and strive to raise the water temperature while maintaining a high water level. 9.10 Chemically prepare sufficient demineralized water (3000 t). After ignition on 9.11, the oxygen addition pipelines must be cleaned with steam; each oxygen addition point should be subjected to pressure-stabilized cleaning for at least 1 hour to achieve degreasing and the removal of impurities. 9.12 Store 500 bottles of oxygen (40 liters, 12–13 MPa). 10 Implementation steps for the blowing pipe 10.1 Carry out the boiler startup operations in accordance with the trial operation procedures and measures for the first ignition and pressure rise trial run. 10.2 When the pressure reaches 0.5 MPa and the temperature is around 150 °C, close the exhaust valve to the atmosphere, and open the drain valves on the main steam pipeline as well as the bypass valves adjacent to the surge valve, in order to warm up the superheater and reheater systems. At the same time, the drain valves in all relevant areas should be opened to prevent water accumulation. 10. During the pipe heating for pressure boosting, check the expansion of the temporary pipes as well as the condition of their fixing supports. 10.4 When the drum pressure rises to 3.0 MPa, flush the oxygen addition pipeline. The flushing of the oxygenation pipelines is carried out using a pressure-stabilized flushing method; each oxygenation point is flushed twice, for half an hour each time. The flushing of the oxygenation pipeline must be done to a high standard to ensure thorough degreasing. 10.5 Increase the pressure to 4.0 MPa, fully open the emergency valve, and perform a pressure relief test blow of the pipeline once. When the drum pressure drops to 2.2 MPa, start closing the surge valve; by the time the surge valve is fully closed, the pressure should remain at least at 1.9 MPa. 10.6 Then check the expansion, support, and fixation of the temporary pipes; if there are no abnormalities, proceed with increasing the pressure for purging. 10.7 When the drum pressure reaches 5.8 MPa and the steam temperature does not exceed 450 °C, open the relief valve fully to reduce the pressure and perform blowdown. When the drum pressure drops to around 3.5 MPa, the relief valve can begin to be closed; it is required that the steam pressure remain at least 3.0 MPa after the relief valve is completely closed. Then, check the temporary piping system again to prepare for the next blowdown operation. 10.8 Requires that the interval between each two tube-blowing sessions be no less than half an hour. 10.9 Eight hours after starting the blowing process, the furnace is shut down for the first time to allow for extensive cooling; the entire furnace’s water is replaced, a process that takes twelve hours. 10.10 Record the boiler expansion indications under the following conditions: before water filling, after water filling, at 0.5 MPa, 3.0 MPa, and 4.5 MPa. 11 Arrangements for the cleaning system: 11.1 It is planned to carry out cleaning during the day shift, while performing large-scale cooling of the boiler and replacing all the water at night. 11.2 Before the first formal blowing, perform a pressure-stabilizing purge for half an hour. 11.3 Perform depressurization purging five times. 11.4 Perform depressurized oxygen purging ten times. 11.5 The first shutdown for major cooling lasts for twelve hours. 11.6 Perform depressurization purging about ten times; decide whether to add oxygen based on the replacement rate of the oxygen cylinder set. 11.7 Perform a pressure-stabilized oxygen purging once, for a duration of half an hour. 11.8 Major cooling during shutdown. 11.9 Repeat 11.6–11.8. 11.10 After multiple blowdowns, and based on the chemical analysis results regarding the quality of the boiler water and steam at that time, decide whether to proceed with a complete cooling down of the boiler. 11.11 Combine oxygenation with pressure reduction (or pressure stabilization) purging until the target is met. 12 Methods of Oxygenation 12.1 First, open the outlet valves of a set of oxygen cylinders; once the pressure in the main oxygen supply pipeline stabilizes, record the pressure value. 12.2 Before oxygenation, open the corresponding valves and record the pressure value. 12.3 At the start of blowing, open the corresponding valves to introduce oxygen from the first, second, or third oxygenation points, and use a control valve to keep the rate of decrease of pressure P1 within the specified range. 12.4 The oxygen addition rate is controlled at 3 to 12 kg/min, and is regulated by the pressure drop rate of the oxygen cylinder set: 3) ； During pressure stabilization blowing, oxygen is supplied by 30 oxygen cylinders from two oxygen cylinder sets. The pressure of the oxygen cylinder should be reduced from 12 MPa to 3.0 MPa, with a reduction rate of 0.3 MPa/min ； 4 )  ； When performing pressure reduction blowing, oxygen is supplied by 15 oxygen cylinders from one set of oxygen cylinder units. The pressure of the oxygen cylinder should be reduced from 12 MPa to 3.0 MPa, with the rate of pressure reduction controlled at 2.5 MPa/min. 5) ； If the pressure of the oxygen cylinder can be increased to 13–15 MPa, the concentration of oxygen added can be further raised, resulting in a more pronounced cleaning effect. 12.5 When the blowing tube stops, the corresponding valve should be closed immediately, and the oxygen cylinder set should be replaced. 12.6 Before formal oxygen addition, during the blowing process, 2 to 3 tests should be conducted in accordance with the requirements for oxygen addition control in order to find the optimal operating method. 13 Control of the blowing pipe 13.1 Pressure-reducing blowing: 13.1.1 When the drum pressure reaches the blowing pipe pressure, fully open the blowdown valve to carry out blowing. 13.1.2 To prevent boiler water deficiency accidents caused by delayed water replenishment, water supply can be started immediately after the temporary control valve is opened, with the water supply rate being increased gradually until the end of that blowdown process. 13.1.3 When the emergency shut-off valve is fully closed, the water level in the drum should be at the visible level, and accidents caused by low water level or excessive water level must be prevented. 13.2 Pressure-stabilizing purging: 13.2.1 When the drum pressure reaches 3.0 MPa, open the relevant control valves to purge the system. 13.2.2 Use hydrophobic bypass valves or other control valves to maintain the stability of the drum pressure. 13.2.3 Since the pressure in the drum changes slowly, the water makeup operation can be carried out based on the level of water in the drum. 14 Chemical monitoring during the blowing process 14.1 During each oxygen-blowing cleaning process, the quality of the steam is determined by chemical sampling. 14.2 The quality of the boiler water shall be sampled and analyzed once per hour, and it is required that its quality remain within the specified range during blowdown. PO4－3: 2 ~ 10 mg/l; Fe: ≤3000 ug/l. 14.3 When the amount of iron corrosion residues in the steam decreases sharply, notify the boiler operator to conduct a target inspection. 14.4 Target loading test when Fe in the steam is 200 ug/l. 14.5 Continuous target shooting tests shall be conducted when the Fe content in the steam is 100 ug/l. 14.6 During the oxygenation process, record the rate of pressure drop in the oxygen cylinder, the oxygenation time, and the number of oxygenation sessions, in order to guide and supervise the entire process. 15 Precautions and Safety Measures 15.1 After the boiler is started, the flue gas dampers on the reheater side should be closed completely, so that the majority of the flue gas flows through the low-temperature superheater. This not only protects the reheater but also helps to increase the temperature of the superheated steam more rapidly, thereby reducing the startup time. 15.2 Before purging, the main steam pipeline must be thoroughly warmed up and drained of water; purging of the system can only be carried out after it is confirmed that there is no water left in the system pipes, to prevent water hammer. 15.3 When blowing the tube, close attention must be paid to changes in the water level in the drum, as well as to the phenomenon of false water levels; water should be added appropriately to prevent incorrect operations. 15.4 During the pressure-reduction blowing process, the drop in the saturation water temperature of the steam drum should not exceed 40°C; under any circumstances, the temperature difference between the upper and lower walls of the steam drum should not exceed 40°C. 15.5 During the blowing process, the flue gas temperature at the reheater inlet must not exceed 540 ℃, and the steam temperature at the reheater inlet must not exceed 450 ℃; overheating should be avoided as much as possible. 15.6 The exhaust outlet of the blowpipe must not be directed at any location that could pose a risk to the safety of the equipment or personnel, and the exhaust outlet shall be under the supervision of a designated person. 15.7 The oxygen cylinder array is located at the 12.6-meter working level; a warning line must be set up around the oxygen supply system, and measures must be in place to prevent falling objects from damaging the oxygen cylinders. 15.8 Flammable and explosive materials are not allowed to be stored near the oxygenation area; welding equipment, heat treatment equipment, electrical equipment, etc., must be removed, and open flames are strictly prohibited. 15.9 A sufficient number of fire-fighting equipment must be available at the blowing tube site and in the vicinity of the oxygenation area, with fire-fighting personnel on duty. When replacing the oxygen cylinder, staff should not face it directly to avoid being injured by the airflow. 15.10 All oxygen cylinders must have safety inspection certificates. When checking for leaks in cylinders, valves, and pipelines, soap and water should be used. When moving gas cylinders, use a wheeled cart; it is strictly prohibited to drag them on concrete surfaces to prevent static electricity sparks that could cause danger. 15.11 The pressure gauge for the oxygenation system must be an oxygen pressure gauge, and it must have been calibrated successfully under oil-free conditions. 15.12 Sufficient deionized water must be available for chemical preparation (the flow rate during blowing should correspond to the water consumption at 30% load after operation starts). 15.13 Remove all scaffolding, walkways, etc. that affect the expansion of boilers and pipelines or that may lead to fires; ensure that walkways are unobstructed and that there is sufficient lighting. 15.14 Security personnel, firefighters, medical staff, and equipment maintenance personnel shall be on duty at the site; medical staff should prepare sufficient first-aid supplies in light of the characteristics of the tube-blowing work. 15.15 Since the blowing pipe generates considerable noise, it is necessary to issue public notices and take appropriate measures before using it.