Steam pipeline purging problem

You can refer to the Ministry of Electric Power's Steam Blowing Guidelines, which have very detailed instructions and steps.

Guidelines for starting steam blowing of thermal power units 1. Purpose and scope of blowpipe 1.1 Purpose of blowpipe The purging of boiler superheater, reheater and steam piping system is an important process before the operation of a new unit. Its purpose is to remove various debris left in the superheater, reheater system and steam piping (such as: sand, stones, shavings, oxide scale, etc.) to prevent the unit from bursting, reheater tubes and turbine flow parts during operation, improve the safety and economy of the unit, and improve the steam quality during operation. It should be emphasized that the blowpipe cannot be expected to remove all debris. First, the accumulation of debris should be eliminated from the manufacturing and installation process. The blowpipe can only be used as a last supplementary means. 1.2 Main scope of blow pipe 1.2.1 Boiler superheater, reheater and their systems. 1.2.2 Main steam pipe, reheated steam cold section pipe and hot section pipe. 1.2.3 High-voltage bypass system. 1.2.4 Steam source pipeline of steam-driven feed water pump. 2. Blow pipe quality standards and parameter selection 2.1 Blow pipe quality standards 2.1.1 According to the provisions of Article 10.5.8 of the "Technical Specifications for Electric Power Construction and Acceptance" (Boiler Units) (hereinafter referred to as the Boiler): The blowing coefficient of the superheater, reheater and each section of its pipelines should be greater than 1 ； Install a target plate in the temporary exhaust pipe at the end of the pipe to be purged (or at the exhaust port). The target plate can be made of aluminum plate. Its width is about 8% of the inner diameter of the exhaust pipe, and its length runs across the inner diameter of the pipe. ； Under the premise of ensuring the blowpipe system, replace the target plate for two consecutive inspections. If the particle size of the impact marks on the target plate is not greater than 0.8mm, and the visible stains on the target plate are not more than 8 points, the purge is deemed to be qualified. 2.1.2 When using the two-stage purging method, check that the main steam pipe is purged qualified, then purge the reheater and its pipes, and check that the purging quality is qualified. When using the one-stage purging method, the purging quality of the main steam and reheated steam pipelines should be checked separately to ensure that they meet the standard requirements. 2.2 Selection of blowpipe parameters 2.2.1 The blowpipe system is calculated according to the following formula: Blowing system = (steam flow rate when blowing) 2 × (steam specific volume when blowing) / (steam flow rate at rated load) 2 × (steam specific volume at rated load) 2.2.2 The following requirements should be met when purging boiler superheaters, reheaters and their steam piping systems. 2.2.2.1 The cross-sectional area of ​​all temporary pipes should be greater than or equal to the cross-sectional area of ​​the pipe being purged, and the temporary pipes should be as short as possible to reduce resistance. 2.2.2.2 The control door should be fully opened during purging ； When used for purging by heat storage and pressure reduction method, the opening time of the control door should generally be less than 1 minute. 2.2.2.3 The blowpipe coefficient everywhere in the system being purged should be greater than 1. 2.2.3 When blowing the pipe, the drum pressure in the range of 5 to 7Mpa can generally meet the requirements. 2.2.4 The resistance of the superheater, reheater and system is too large, and the upper limit of the blowpipe drum pressure should be selected. 2.2.5 When using the two-stage blowpipe method, the blowpipe pressure can be the same (see Appendix A). 2.2.6 During the blowing process, the ratio of the pressure difference of each section to the pressure difference of each section at rated load should be checked, the blowing coefficient should be checked, and the blowing pressure should be adjusted as necessary. 3． Blowing method and blowing method 3.1 Blowing method 3.1.1 Blowing method is generally divided into two stages: one-stage blowing and two-stage blowing. 3.1.2 Two-stage purging: The first stage purges the superheater, main steam pipeline and cold section reheat steam pipeline ； In the second stage, the whole system is purged (referred to as the two-step method). 3.1.3 One-stage purging: The entire system is purged at one time (referred to as the one-step method). 3.1.4 When the reheat unit adopts one-step purging method, a particle collector must be installed on the reheat steam cold section pipe. The granule collector should meet the following conditions. 3.1.4.1 The intensity meets steam parameter requirements. The design pressure is not less than 3Mpa and the temperature is 450℃. 3.1.4.2 The resistance is less than 0.1 MPa. 3.1.4.3 Good performance in collecting debris. The pore size of the filter should not be larger than 12mm, and the main air flow should not blow directly into the mesh, and there should be enough space for collecting debris. 3.1.4.4 The particle collector should be installed as close to the reheater inlet as possible. 3.1.4.5 The design of the granulator should have the characteristics of compact and reasonable structure, easy production and installation. 3.2 Pipe blowing method There are two basic methods of steam blowing: Stable pressure purge ； Pressurize and purge. 3.2.1 Key points of pressure stabilization and purging 3.2.1.1 Generally suitable for one-stage purging. 2.2.1.2 During purging, the boiler is boosted to purging pressure and the blowpipe control door is gradually opened. When the reheater does not have enough steam for cooling, the smoke temperature at the boiler furnace outlet should be controlled not to exceed 500°C or as specified by the manufacturer. 3.2.1.3 During the process of opening the blowpipe control door, try to control the amount of fuel and steam to maintain a balance. After the control door is fully opened, maintain the pressure of the blowpipe. After purging for a certain period of time, gradually reduce the amount of fuel, close the control door until it is fully closed, and the blowpipe is completed. 3. 2.1.4 The duration for each blowpipe control door to be fully opened mainly depends on the amount of water replenishment, which is generally 15 to 30 minutes. After one blow, the pressure should be reduced and cooled, and the interval between two adjacent blows should be 12 hours. 3.2.2 Key points of pressure reduction and purging 2.2.2.1 When depressurizing and purging, use the ignition fuel amount to increase the pressure to the purge pressure, maintain the ignition fuel amount or turn off the flame, and quickly open the control door to use the additional steam generated by the pressure drop to blow the pipe. 2.2.2.2 Pressure reduction purging generally uses fuel or gas, and the amount of fuel input is limited to the dry burning of the reheater without overheating. 3.2.2.3 Flushing should not exceed 4 times per hour. 3.2.2.4 When purging, avoid excessive hydration too early. 3.2.3 Due to the drastic changes in pressure and temperature during each purge, it is beneficial to improve the purge effect. However, in order to prevent the loss of drum life, the pressure drop of the drum during purging should be strictly controlled within the range of the corresponding saturation temperature drop not exceeding 42°C. 2.3.4 During each purging process, there should be at least one shutdown for cooling (more than 12 hours) to cool the superheater, reheater and their pipes to improve the purging effect. 3.2.5 During the purging process, water quality should be controlled as required. During the shutdown cooling period, the entire furnace water can be changed. 3.3 Improve the blowing effect 3.3.1 In order to improve the blowing effect, a certain amount of oxygen can be added to the basic steam blowing method, which is beneficial to the shedding of rust and the formation of protective film. 4． Installation and technical requirements of temporary facilities 4.1 Selection and installation of temporary control doors for purging 4.1.1 The temporary control door is one of the important components that affects the normal progress of the purging process. During purging, the control door will bear a greater pressure difference and torque than under rated working conditions. Purge control door should be selected: An electric gate valve with a nominal pressure of not less than 16MPa, a temperature of 450°C, and a diameter matching the main steam pipe. 4.1.2 In order to protect the temporary control door and heating pipe, a bypass door should be added with the following specifications:: The nominal pressure is not less than 10MPa, the temperature is 450℃, and the nominal diameter is not less than 28mm. 4.1.3 Temporary control doors should be installed horizontally and an operating platform should be set up. 4.1.4 Temporary control doors should be operated remotely from the main control room. 4.2 Requirements for temporary connecting pipes and exhaust pipes 4.2.1 The design pressure of the temporary connecting pipe in front of the temporary control door should not be less than 9.8MPa, the temperature should not be less than 450°C, and the pipe diameter should be the same as the main steam pipe. ； The inner diameter of the temporary exhaust pipe should be greater than or equal to the inner diameter of the pipe being purged, with a design pressure of 1.5MPa and a temperature of 450°C. 4.2.2 When it is difficult to select the temporary exhaust pipe of the hot section with the same diameter as the hot section pipe, a temporary exhaust pipe with a total cross-sectional area larger than 2/3 of the cross-sectional area of ​​the hot section pipe can be selected. 4.2.3 When the manufacturer provides high-pressure and medium-pressure automatic main steam valve protection equipment, the connecting pipe and exhaust pipe should be led out from the door cover. 4.2.3.1 When the high-voltage door cover is located in front of the temporary control door, its strength should be: Designed for pressure not less than 9.8MPa and temperature 450℃ ； Press when behind the door: Designed for pressure of 4MPa and temperature of 450℃. Medium pressure door cover can be pressed: Designed for a pressure of 1.6 MPa and a temperature of 450°C. 4.2.3.2 The quality must be ensured when installing the high- and medium-pressure automatic main steam valve blocking plates, and must be confirmed by quality inspection personnel. 4.2.4 Obvious and reliable isolation measures should be taken at the high-pressure check door of the turbine to strictly prevent steam from entering the high-pressure cylinder during purging. 4.2.5 When the hot section exhaust pipe is connected from in front of the medium pressure main steam door, other measures must be taken for the pipeline behind the door to ensure that the interior is clean and free of debris. 4.2.6 If the steam guide pipe behind the high-pressure automatic main steam valve cannot participate in purging, measures should be taken to ensure that the inside is clean and free of debris. 4.2.7 When the two-stage method is used to purge the cold section pipe as the exhaust pipe, a blocking plate should be installed at the reheater inlet, and the hot section exhaust pipe should also be installed to prevent water in the reheater from spraying out and injuring people and damaging equipment. 4.2.8 The temporary exhaust pipe should be installed horizontally, with the exhaust outlet slightly tilted upward to avoid buildings and equipment. 4.2.9 The temporary connecting pipes and exhaust pipe supports and hangers should be reasonably set up and reinforced reliably. The strength of the bracket that bears the exhaust steam reaction force should be considered as greater than 4 times the purging calculated reaction force (see Appendix C) (omitted). 4.2.10 It is not advisable to install steam flow measuring components during purging. After purging, attention should be paid to the installation process. Iron slag and oxide scale are strictly prohibited from falling into the pipe. For nozzle-type measuring elements, it is recommended to install them during the purging process and when the furnace is shut down for cooling. 4.2.11 Temporary connections for purging should be inspected before installation and constructed according to the construction technology of formal pipelines. 4.3 Technical requirements for granule vending machines 4.3.1 The granule collector should be installed horizontally. During installation, attention should be paid to the direction of steam flow and an operating platform should be set up. Please refer to Appendix B (omitted) for the structure of the granulator. 4.3.2 A pressure gauge or differential pressure gauge should be installed before and after the granule collector to monitor its resistance. 4.4 Installation of the target plate holder 4.4.1 The target plate holder is used to place the target plate. Pay attention to the structure and craftsmanship of the target plate holder, and it must have sufficient strength. Its structure should be simple, with good sealing and flexible operation. It should be safe and convenient to replace the target plate (see Appendix D) (omitted). 4.4.2 Commonly used target plate structures include flange type, straight shaft type, tandem shaft type and frame type. The first three types are internal test target plates, and the frame type is external test target plate. 4.4.3 The internal test target plate is installed in the purge connecting pipe or exhaust pipe, as close as possible to the end of the purge pipe, and on a straight pipe 4-6m away from the elbow. 4.4.4 When using the two-stage purging method, after the first stage of purging is qualified, the target plate device should be removed. When performing the second stage of purging, it is not appropriate to install the target plate in the first stage. 4.4.5 In order to correctly test the quality of the blowpipe, the target plate should be polished without visible marks to the naked eye. 4.5 Purge of the high-pressure bypass 4.5.1 When purging the high-pressure bypass, install a temporary door and postpone the installation of the adjustment door. 4.6 Purge of the steam source pipeline of the steam feed water pump 4.6.1 For the purge of the steam source pipeline of the steam feed water pump and other pipelines, temporary purge pipelines can be configured according to the specific conditions on site and in accordance with the above principles. 4.7 Precautions at the end of purging. 4.7.1 After purging is completed and the temporary system is restored, reliable measures must be taken to prevent secondary pollution. 5. Key points for the implementation of pipe blowing technology 5.1 Basic conditions before purging 5.1.1 The installation and civil construction work of the boiler unit, purging-related system equipment and temporary systems are basically completed, and the necessary on-site conditions are in place according to Article 10.1.5 of the Boiler Chapter. 5.1.2 Before steam purging of the unit, the partial trial operation, debugging and testing of the boiler ignition and pressure boosting and related equipment systems that need to be invested (including: Boiler auxiliary machinery and various ancillary systems ； Flushing of supply water and condensate pipelines ； Water supply line flushing ； Boiler chemical cleaning ； Thermal measurement, control and protection system debugging, etc.). 5.1.3 Various measures to prevent steam from entering the turbine have been implemented. Steam turbines should generally have the conditions for cranking and vacuuming. 5.1.4 Under the supervision of the trial operation headquarters, all parties involved in commissioning, trial operation, and construction have completed all preparatory work before blowing the pipe in accordance with the "Starting Height Working Regulations for Thermal Power Projects" and relevant technical documents for starting trial operation. 5.2 Key points of purging process 5.2.1 Complete comprehensive inspections and various tests in accordance with relevant procedures and measures. 5.2.2 Carry out ignition and voltage boosting according to relevant procedures and measures. 5.2.3 During the boiler ignition, pressure boosting and purging process, supervision should be carried out according to the steam and water quality requirements of the trial operation unit. 5.2.4 Before formal purging, 2 to 3 pre-purgings lower than the selected purging pressure should be carried out to check the status of the temporary purging equipment system and familiarize yourself with the control operations. Generally, the pre-purging pressure can be selected according to 30% to 40%, 50% to 60%, and 70% to 80% of the selected blow pipe pressure. 5.2.5 During the first pre-purging, the target plate can be installed and the target plate device can be put in to check the degree of dirtiness of the purging system and the performance of the target plate device. 5.2.6 During the purging process, the target plate can be put in based on the exhaust situation, steam quality or to understand the purging situation. 5.2.7 During the purging process, the differential pressure of the superheater and reheater must be monitored to ensure that when the control door is fully open, the differential pressure is greater than 1.4 times the differential pressure value under rated operating conditions. 5.2.8 The front and rear pressure of the granule collector should be monitored. Especially in the early stage of purging, inspection and cleaning of the interior of the granule collector should be strengthened. 5.2.9 The purging of other systems should generally be carried out after the purging of the main steam pipeline is completed, and the purged pipelines should be prevented from being contaminated again. 6. Safety and precautions for pipe blowing work 6.0.1 In order to prevent steam from leaking into the turbine during blowing, the turbine turning and vacuum system should be put in place. When the above conditions are not met, reliable measures must be taken to prevent steam from leaking into the turbine. 6.0.2 When the main steam and reheat steam pipes are double, it is not advisable to use a single alternate purging method. This will not only reduce the purging effect of the superheater and reheater, but also easily blow debris into the dead zone at one end of the header. 6.0.3 During purging, the steam flow from the exhaust outlet should avoid buildings and equipment. A warning area should be set up and guarded by dedicated personnel. 6.0.4 During the purging period, notices for the safety of the people should be issued and the scope of construction operations should be adjusted. High-altitude operations should not be carried out, and midnight purging should be avoided as much as possible. 6.0.5 Develop reliable fire prevention measures. Prepare enough fire-fighting equipment and have dedicated personnel to check and deal with problems in a timely manner if problems are found. 6.0.6 When blowing the boiler fuel pipe, attention should be paid to monitoring and adjusting the fuel working conditions. Inspection and maintenance of the oil gun and reasonable air distribution are necessary conditions to ensure stable and complete fuel. Be careful to prevent oil from leaking into the furnace and unburned embers oil mist accumulating at the rear, causing furnace explosion and rear combustion. Pay attention to the monitoring of the flue temperature after the air preheater, the input of the soot blower and its internal inspection. If necessary, the furnace should be shut down for flushing. 6.0.7 When using the powder injection and pressure stabilization purging method, the pulverized coal fire and combustion conditions in the furnace should be monitored and adjusted to prevent fire extinguishing and blasting. After the fire is extinguished, attention should be paid to ventilation and cleaning in the furnace. 6.0.8 The steam purging process is a process in which the hydrodynamic working conditions of the boiler change drastically. Maintaining the normal water level of the steam drum and the normal hydrodynamic working conditions is an important link to ensure the safety of the boiler. Therefore, it is very important to ensure that the boiler water supply equipment and system are reliable (including configuring backup equipment as much as possible) and operate them carefully. 6.0.9 Temporary control doors should be maintained by dedicated personnel and the power supply should be cut off when out of use. 6.0.10 Reliable safety measures must be taken when replacing target plates. 6.0.11 The heating pipe must be fully drained and protected from water and impact. 6.0.12 When there is no steam passing through the reheater, the furnace outlet smoke temperature should be strictly controlled not to exceed 500°C (or according to the manufacturer's requirements). 6.0.13 Thermal expansion inspection and recording of the first ignition and pressure increase of the boiler should be carried out according to regulations. If it is found that the expansion is blocked, the pressure increase should be stopped, the cause should be identified, and the defect should be eliminated. 6.0.14 Strictly implement the operation ticket, work ticket system and patrol inspection system, pay attention to the inspection and maintenance of operating equipment, and inspect pipeline supports and hangers and isolation systems. 6.0.15 Develop anti-accident measures. Pipe blowing operations and accident handling should be carried out in accordance with operating procedures, pipe blowing measures and accident handling measures. 6.0.16 After purging, anti-corrosion and anti-freezing measures should be determined in conjunction with relevant personnel.