Hydrogen replacement issues during startup and shutdown of diaphragm electrolyzers
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This post was last posted by sunjl1981 on 2013-1-6 23:02. The editor would like to ask you guys how to replace the hydrogen system with nitrogen during the startup and shutdown of the diaphragm electrolyzer? This post was last edited by Captain Yang on 2008-4-29 08:05 ] # , , &
When the diaphragm electrolyzer is started and shut down, nitrogen replacement is usually carried out at the end of the hydrogen gas, and oxygen content analysis is performed to meet the specified requirements. By the way, the amount of nitrogen used is very large.
Some manufacturers do not perform nitrogen purge during normal operation and only perform a thorough purge when overhaul requires fire. Brother, do you think this is advisable? I feel like it’s not possible! But. . . . . . .
What you said is not advisable. Hydrogen containing oxygen is very dangerous, and static electricity will also be generated during gas flow. Even if there is static electricity grounding, there is still danger. Don't ignore safety for the sake of temporary convenience. If an accident occurs, the gain will outweigh the loss.
When starting and stopping, the electrolysis and hydrogen delivery systems are filled with nitrogen at the same time. Make sure there are no dead corners, and there should be vents in places where it is easy to accumulate.
It is usually filled with nitrogen in several stages: 1. Single-row nitrogen charging of the electrolyzer 2. The main pipe from electrolysis to chlorine and hydrogen must also be filled with nitrogen 3. The chlorine and hydrogen side must also be filled with nitrogen to ensure that no dead ends are left
My unit used to drive and stop without nitrogen replacement, which was relatively safe. It was air-proofed in front of the hydrogen spray tower. However, now it is replaced with nitrogen. The replacement nitrogen inlet is on the outlet pipe of the spray tower. When nitrogen is flushed, the electrolysis system and the chlorine-hydrogen system are first replaced. After passing the test, the synthesis system is replaced.
Catholyte Drainage Tank (D-2290) (See Figure A) If possible, inject water (or caustic soda) up to 90% on the LIA-2290. Pass N2 through FI-2299 to D-2290 at a flow rate of 10 Nm3/hr until the end of this section. The alkali liquid circulation tank (D-2270) and the alkali liquid high-level tank (D-2273) (see Figure B) pass through FI-2279 and pass N2 to D-2270 at a flow rate of 50 Nm3/hr for more than 20 minutes. Route: D-2270-------D-2273 ----- H2 main pipe---- PICZA-2226 ---- H2 processing section 3) Catholyte overflow line (see Figure C) Pass N2 to D-2270 through FI-2279 at a flow rate of 20 Nm3/hr for more than 10 minutes. Route: D-2270 –> NaOH main pipe –> Valve 6 –> Valve 8 –> D-290 –> Drain 4) The H2 main pipe and the top line of the catholyte circulation tank (see Figure D) pass N2 through FI-2279 to D-2270 at a flow rate of 20 Nm3/hr for more than ten minutes. Route: D-2270 –> H2 Main –> Valve 12 –> Valve 14 –> Drain from valve 56 to analyze the oxygen content of the nitrogen. If the O2/N2 ratio is less than 1%, continue to the next step. 5) The H2 main line (see Figure E) continues to flow N2 to D-2270 at a flow rate of 50 Nm3/hr. Route: D-2270 – H2 Main Pipe ----- PICA-2226 –---- H2 Processing Stage Valve S 6) The circulation line of D-2270 (see Figure F) passes NaOH to D-2270, through valve 86 on LICZA-2270 until the liquid level reaches 70%. Then set the LICZA-2270 to automatic mode and start circulating the liquid with the P-2274 A/B through valve 88 to the D-2270. 7) The DICA-2274 line starts looping to D-2270 through DICA-2274 control. (5) Confirmation of air purge by analyzing the oxygen content of nitrogen from 56 and sampling at the end of the H2 treatment section. (6) Continuous air purging If the oxygen content is less than 1%, reduce the N2 flow rate and maintain the lower flow rate until electrolysis begins. FI-2279 (to D-2270) : 10 Nm3/hr Route: D-2270–> H2 Main -------- PICZA-2226–> Exclusion FI-2299 (to D-2290) : 5 Nm3/hr FI-2249 (to drain) : 1 N m3/hr (7) Continuous air purging during short-term device shutdown in case the equipment is shut down and then started again within 24 hours. 1) Pass N2 to D-2270 through FI-2279 at a flow rate of 10 N m3/hr. Route: D-2270–>H2 Main Pipe–>PICZA-2226–>H2 Main Treatment 2) Analyze the oxygen content of the nitrogen at the end of the H2 treatment stage. 3) Confirm that the O2/N2 ratio is less than 1%.
When the diaphragm electrolyzer is started and shut down, nitrogen replacement is usually carried out at the end of the hydrogen gas. The pressure is controlled at 10-20mmH2O column, and the oxygen content is analyzed to be less than 3%. The amount of nitrogen is related to the system (generally 4 times the system volume).
Express your personal opinion: 1. If the shutdown of the diaphragm is only for a short period of time, and the hydrogen pipeline and system do not fire, there is no need to pass nitrogen. 2. Without nitrogen filling, the hydrogen should be evacuated before driving again, and hydrochloric acid synthesis can be started only after passing the analysis. 3. Unless there is a fire requirement, nitrogen filling is generally not required and can be directly replaced with air. Some manufacturers rarely use nitrogen for diaphragm electrolysis, and nitrogen is used for ion membranes. But for safety reasons, it is better to fill it with nitrogen, which is safer.