Chemical plant purging is an important and indispensable part of chemical production, mainly to eliminate hidden dangers and avoid unnecessary losses in order to check the construction quality of the cleanliness of the piping system so that system operation can proceed smoothly. Today we introduce you to three common chemical plant blowing methods, their flushing principles and requirements, preparation conditions, operating points, qualified standards and precautions!
The purpose of blowing: before the start of the device, it is necessary to blow and clean the pipeline and equipment after its installation and inspection is qualified, the purpose is to use air (nitrogen), steam, water and chemical solutions and other fluids, blowing and flushing to remove residual impurities in the construction process to ensure the smooth start of the device. There are usually several methods such as water flushing, air (nitrogen) blowing and oil cleaning.
Water flushing Water flushing is a method of flushing pipes and equipment with water as the medium and under pressure by means of a pump. For example: flushing of circulating water systems.
1. Flushing principles and requirements ❶ Water flushing of pipes should be carried out at the maximum possible flow rate in the pipe or at a flow rate of not less than 1.5 m/s, with the flow direction from high to low.
❷ The water quality for flushing should meet the requirements for flushing pipes and equipment materials. General equipment and pipeline flushing is commonly used with a turbidity level of less than 10mg/L and a chloride ion content of less than 100ppm.
The water is not only used for the flushing of the pipes, but also for the flushing of the pipes.
❹ Where pipes and equipment are connected, a blind must be added to the inlet and outlet of the equipment when flushing, and only after this pipeline has been flushed and passed, can it be connected.
❺ When flushing pipelines with water, make sure that the pipe racks, hangers, etc. can withstand the load safely when full of water.
❻ Where devices such as flow meters, valves, filters etc. are encountered on the pipeline, they must be removed or a temporary short circuit added and they can only be put back on once the pipeline has been flushed.
❼ After the process line has been flushed, drain the water from the system. There should be a large top venting hole when draining to avoid forming a vacuum that could damage the equipment.
❽ Pay attention to anti-freezing work in winter flushing. After flushing, drain the water out promptly and blow dry with compressed air if necessary.
2. Preparation conditions for water flushing ❶ Before flushing the system, a flushing plan must be prepared.
❷ Equipment and piping are installed, pressure tested and checked for accuracy according to the PID diagram.
❸ Temporary flushing pipelines have been installed as required by the flushing plan.
❹ Flushing personnel must be familiar with the flushing programme.
❺ The electrical and instrumentation equipment for water flushing is put into operation normally.
3. Methods and operational points of water flushing ❺ Strictly follow the segmental flushing procedure in the water flushing programme, i.e. reset after each flushing port is qualified, before flushing the subsequent system.
4.Fill in the flushing records and acceptance records of pipe sections and equipment Air (nitrogen) purging Air blowing is a method of blowing residual debris out of the process pipeline with air as the medium, after being pressurised to 0.6~0.8Mpa by an air compressor.
1. Air (nitrogen) purging principles and requirements ❶ When air (nitrogen) is selected for purging process pipelines, sufficient gas volume should be ensured so that the flow rate of purging gas is greater than the normal operating flow rate, or at least not less than 20 m/s.
❷ The pressure of the purge gas source for the process pipeline should generally be controlled at 0.6 to 0.8 Mpa, which can be reduced or increased as appropriate.
❸ The instrumentation on the purging pipeline should be removed to prevent damage to the instrumentation components. The regulating valve should also be protected by appropriate measures and, if necessary, removed and a temporary short section added.
❹ Before blowing, blind plates must be added to the inlet and outlet of the heat exchanger, tower kettle and other equipment. Only after the upstream blowing has been passed can the subsequent system be purged.
❺ When blowing, the safety valve should be disconnected from the pipeline and a blind plate added to prevent damage to the safety valve.
2.System blowing gas source System blowing, compressed air (nitrogen) dosage, through the pipeline and the system flow rate is fast, so must ensure sufficient pressure air volume, in order to ensure the quality of blowing.
3.Air (nitrogen) purging preparation conditions ❶ The process system piping and equipment installation is completed and the strength test pressure is passed.
❷ All instruments in the purging pipeline have been properly protected.
❸ The equipment and pumps that are not to be blown have been fitted with blinders as required.
❹ Temporary piping, valves, etc. for blowing are ready to be put in place.
❺ The air compressor for the public works is in operation and the conditions for continuous air supply are in place.
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Blowdown personnel and operators are familiar with the blowdown programme. Blowdown procedures, flow directions, exhaust ports, etc. are well understood according to the blowdown schematic flow chart.
❼ Blowdown record sheets are well prepared.
4. Blowing methods and points ❶ Purge each system one by one in the order of the purging flow chart. Blow the main line and then the branch lines.
❷ Blowing is carried out in a continuous manner at each discharge port, and the pipes are continuously struck with a wooden hammer, especially at welded seams and dead ends, but the pipes must not be damaged.
❸ At the beginning of the blowdown, the system should be slowly fed with air. When there is gas discharge from the inspection port, the amount of blowdown air should only be increased to prevent the system from being over-pressurized and malfunctioning due to incorrect reasons such as blinders and valves.
❹ When blowing multiple systems, obey the unified command to avoid human and machine damage.
❺ After the end of the purge is confirmed as qualified, the system should be reset and prepared for the next stage of the gas tightness test.
5.Testing methods and blowing qualified standards Each section of the pipeline blowing whether qualified, production and installation personnel should jointly check, when the visual exhaust clean, in the exhaust port with a white cloth target plate or white lead oil target plate check, such as 5 minutes on the target plate without rust, dust, moisture and other debris and pockmarks that is qualified.
Steam blowing Steam blowing is a blowing with different parameters of steam as the medium, it has a high blowing speed, and intermittent steam blowing way, can make the pipeline through the hot and cold contraction, expansion, stripping the inner wall of the pipeline adhesion, to achieve the best blowing effect.
Note: steam blowing high temperature, high pressure, fast flow rate, pipeline expansion displacement after heating, contraction occurs after cooling, so take full account of the impact on the structure of the system to ensure that when blowing, personal and equipment safety.
1, the principles and requirements of steam blowing Steam blowing according to the parameters used in the pipeline is usually divided into high, medium and low three levels. Distillation of the steam system belongs to the low-pressure operation category, so to use <1Mpa steam, flow rate ≥ 30m / s.
When steam purging, attention needs to be paid to
Checking steam pressure and temperature.
The opening of blowdown valves.
The hydraulic characteristics of the steam pipeline.
2.Preparation conditions for steam blowing ❶ Develop a complete steam blowing program, which should include: blowing scope, blowing pressure level, blowing method, blowing sequence, identification standards and methods, as well as safety measures and precautions.
❷ Make a detailed inspection of steam pipes, pipe fittings, pipe supports, pipe brackets, etc., to confirm that they are secure and reliable.
❸ All temporary piping, valves, venting pipes, etc. have been installed as required by the purging plan.
❹ Confirm that all instrument components, regulating valves, water evacuators, etc. on the pipeline being purged have been removed and protective measures such as short section connections have been taken.
3.Methods and points of steam purging ❶ Steam blowing is usually carried out in the order of network configuration, generally first blowing high-pressure steam pipelines, then blowing medium-pressure pipelines, and finally blowing low-pressure steam pipelines. For each stage of the pipeline, from near to far, the main line should be purged first, and then the branches. Wait until the pipeline blowing is completed before installing the water separators for each section.
❷ It is advisable to adopt the method of blowing steam lines to warm up the pipes → blowing → cooling down → warming up the pipes → blowing → cooling down, and to proceed in a cyclical manner so that the adherents on the inner walls of the pipes are stripped off and a good blowing effect is achieved.
❸ Steam blowing must first warm the pipe sufficiently to drain off condensate and prevent water hammer from occurring. In the first cycle of blowing, special attention should be paid to checking the thermal expansion of the pipeline and whether the sliding of the pipeline is normal.
4.Safety precautions for steam blowing Set up a blowing cordon to prevent personnel from accidentally entering the blowing mouth range, resulting in accidents.
Blowing process, do a good job of unified deployment and arrangements, all parties should be based on the actual situation, in collaboration with the steam blowing work.
Disclaimers.
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