Operating procedures for nitrogen purging of acetylene systems

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Operating Procedures for Nitrogen Purging of the Acetylene System I. Purging of the Generation and Feeding Systems 1. Purging of the Calcium Carbide Feeding Process The scope of purification for the calcium carbide feeding system includes the raw material calcium carbide storage tank up to the weighing bin. First, seal the feed inlet of the calcium carbide storage tank for raw materials. Then, activate the equipment of the feeding system as well as the nitrogen filling valves for each silo; the nitrogen flow rate for each set must be no less than 100 m3/h, and the nitrogen filling time must be at least two hours. Relevant records must be kept. This project consists of eight units in total, with two units per group, which are replaced simultaneously. 1.1 The specific replacement steps are as follows: a. Install a blind plate (with a marking tag) at the soft connection between the calcium carbide weighing bin and the feeding bin, thereby isolating the system into two separate units. b. Sequentially open the nitrogen filling valves at the top of the raw calcium carbide storage tank, at the bottom of conveyor I, at the top of the finished calcium carbide storage tank, and at the bottom of conveyor II to fill them with nitrogen. Under nitrogen protection, feed material into the raw calcium carbide storage tank, using crude calcium carbide as a barrier to reduce nitrogen leakage. c. Depending on the pressure in the internal space, open the top vent valves of Conveyer I and Conveyer II at the appropriate time to allow venting. d. Once the nitrogen filling flow rate and time reach the target values, notify the crushing process to feed material into the calcium carbide storage tank ； e. During the production process, strict adherence to operating procedures is required to keep the acetylene content in the crushing, screening, storage, and feeding systems at ≤1.5%. 2. Purging in the acetylene generation process 2.1 Sealing the outlet of the slag discharge machine. Open the manual access door of the slag discharge machine, add coal powder with a particle size and moisture level similar to that of calcium carbide slag into the machine chamber, gradually start the slag discharge machine to create a compact material seal, and then close the manual access door. 2.2 Fill all the positive and negative water seals of the system with water, as well as the safety water seal of the system, to a level of 1 meter. Close the drain valve at the bottom of the tubular cooler, and open the nozzles at the top of the tubular cooler to create a liquid seal at the bottom of the tubes, until water starts to overflow into the main condensate pipe. 2.3 Start the supernatant transfer pump and open the spray water valves of the dust removal cooling tower in the system, ensuring a water flow rate of 2–5 m3/h in each spray water pipeline; remove the air from the clear liquid pipelines until there is overflow water at the bottom of the dust removal cooling tower. 2.4 Industrial water is injected into the tank, with the liquid level maintained at around 2/3 of its capacity. The control valve is used to implement a level interlock mechanism; the corresponding water pump in the generation system is activated. The generated water is directed to the inlet valve of the water distribution panel in that system, and from there it is discharged through the waste outlet of the distribution panel. After the air in the water pipes is removed, the waste outlet valve is closed, allowing the generated water to circulate. 2.5 Open the nitrogen pipeline valve of the generation system (pay attention to the valve opening degree to maintain the pressure in the nitrogen system), fill the generator with nitrogen, and control the generator pressure at ≤6 KPa. Open the drainage pipe at the top of the positive water seal to drain and replace the fluid; keep the generator pressure at ≥2 KPa. Repeat this replacement process until the oxygen content is ≤2%, at which point the system is considered to have been properly replaced. 2.6 Ensure that the oxygen content in the generator system is ≤2% before feeding material into it, and maintain the nitrogen pressure in the system at 2–6 KPa ； II. Purging from the main crude acetylene pipeline to the generation branch pipes 1. Inform the cleaning inspector to close the outlet valves of Wash Tower 1 (areas A and B), and open the inlet valve of Wash Tower 1. Nitrogen shall be introduced before the outlet valve of Wash Tower 1, with the pressure in the main crude acetylene pipeline kept at ≤8 KPa. The drain valve of the main crude acetylene pipeline shall be opened to carry out purging; the system pressure shall be maintained at ≥2 KPa. This process of purging shall be repeated until the oxygen content is ≤2%, at which point the system is considered to have been properly purified. 2. Sampling points for displacement analysis in this system: main acetylene pipeline, positive and negative water seal connection pipes ； 1. Gas holder replacement 1.1 Fill the water tank in the gas holder to seal it, and close the main valves for acetylene gas at the inlet and outlet of the gas holder. 1.2 Open the vent valve at the top of the gas holder to bring the bell cover and bell section of the gas holder into a horizontal position, then close the vent valve. 1.3 Open the nitrogen valve at the inlet of the gas tank and fill it with nitrogen. When the gas tank reaches a pressure level of 10–15%, close the nitrogen filling valve to stop the filling process. Then open the vent valve and take samples at the vent outlet to check whether they meet the requirements (oxygen content < 1%). Once the gas tank has reached the appropriate pressure level, close the vent valve. 1.4 Repeat step three one or two times until the sample taken from the vent port passes the analysis (oxygen content < 1%). 2. Purging of the pipelines from the gas tank to the compressor and the water scrubber tower 2.1 Close the outlet valve of the first water scrubber tower, close the main acetylene inlet valve of the gas tank, open the inlet valve of the compressor, and close the outlet valve of the compressor. 2.2 Open the nitrogen filling valve located before the inlet valve of the gas holder to fill it with nitrogen, maintaining a pressure of around 5 kPa. Then open the exhaust valve at the compressor outlet as well as the outlet valves of the washing towers for lines A and B, in order to vent the gas. Take samples to analyze the oxygen content, and repeat these steps until the oxygen content is less than 1%. After the sampling analysis shows satisfactory results, slightly open the nitrogen filling valve to maintain pressure. Note: The backup compressor must be replaced with a qualified unit before the system is started up, and nitrogen should be used to maintain pressure. 3. Replacement of the pipe from the pre-alkaline washing tower to the outlet of the neutralization tower 3.1 Raise the liquid levels in the pre-alkaline washing tower, the two water washing towers, the cleaning tower, and the neutralization tower to the specified levels; keep the upstream and downstream isolation valves of the cleaning tower open. 3.2 Open the outlet valve of the compressor, close its inlet valve, and open the nitrogen filling valve at the compressor’s inlet. Build up pressure to around 10 KPa, then take samples for evacuation before the exhaust pipe at the outlet of the neutralization tower and before the large reflux valve; a oxygen content of less than 1% is considered acceptable. After the replacement is completed, slightly open the nitrogen charging valve to maintain pressure in the system. IV. Nitrogen purging of the outer pipe of the acetylene unit 1. Inform the VCM team to close the shut-off valve before the acetylene enters the mixer; at the same time, open the nitrogen filling valves located after the neutralization towers in lines A and B to fill the outer pipe of the acetylene unit with nitrogen. Raise the pressure in this outer pipe to around 20–30 Kpa. Then instruct the personnel in the downstream VCM unit to open the drainage valve of the acetylene main pipe for drainage. Repeat this process 3–5 times, then take samples for analysis (oxygen content <1%), until the analysis results are satisfactory.