I. Common Cleaning Methods for Synthesis Furnace Burners
The conventional method for removing blockages from burners involves shutting down the furnace, dismantling the burner, and then cleaning it. Cleaning the burner necessitates stopping the furnace, severely disrupting normal production operations. The process of shutting down the furnace, cleaning the burner, and restarting the furnace carries significant safety risks, including potential fires, explosions, and casualties.
1.1 Steps and Risks of Furnace Shutdown
Upon receiving a shutdown notice from the supervisor or dispatcher, the shift leader and relevant personnel from upstream and downstream processes must be notified. The chlorine and hydrogen valve openings should be adjusted to reduce the flow rates (ensuring no excess chlorine by first reducing chlorine flow before hydrogen flow). If the furnace is producing high-purity acid before shutdown, switch to producing standard hydrochloric acid. While reducing flow rates, adjustments must also be made to other operational synthesis furnaces in the system. Once the hydrogen and chlorine flow rates of the furnace to be shut down reach 700 m³/h, open the valve connecting the furnace to the vacuum distribution platform and produce high-purity acid. Continue gradually reducing the flow rates, ensuring stable chlorine and hydrogen pressures, and continuously monitor the hydrogen chloride (HCl) purity of this and other furnaces. Adjust the chlorine-to-hydrogen ratio to maintain HCl purity between 92% and 96%, preventing excess chlorine. Close the chlorine and hydrogen valves, shut down the furnace, and post a “No Operation” sign. Shut off the hydrogen and chlorine cutoff valves. During shutdown, fluctuations in flow rates of other operational furnaces may occur, leading to system pressure instability, excess chlorine, and potential explosions in subsequent vinyl chloride processes.
1.2 Steps and Risks of Burner Dismantling
During dismantling, when only two screws remain, two workers should support the burner base while one removes the remaining screws. The three workers then slowly remove the burner assembly.
The limited workspace below the synthesis furnace and the heavy burner pose risks of injury to operators.
1.3 Steps and Risks of Furnace Restart
After confirming the status of hot water and cooling systems, start the vacuum fan to evacuate and purge the furnace. On-site personnel must verify the furnace’s negative pressure and adjust the demister valve accordingly. Connect a nitrogen hose to the hydrogen pipeline drain valve and purge the furnace for 10 minutes. Close the nitrogen valve and hydrogen drain, and continue evacuation for at least 30 minutes. Install a blind flange at the hydrogen flame arrester’s upper flange and test for hydrogen content (<0.4%). Ignite the ignition rod and place it on the burner. Remove the blind flange, secure the connection, and slowly open the hydrogen valve until combustion begins. Adjust the hydrogen flow based on flame conditions. After ignition, turn off the ignition rod and move it to a safe location. Gradually open the chlorine valve until the flame turns bluish-white, adjusting as needed. Two to three operators should collaborate to seal the furnace door. Introduce minimal absorption water to prevent HCl emissions, then stop the vacuum fan and close the absorption water valve. Gradually increase hydrogen and chlorine flow rates while ensuring HCl purity remains within specifications. Once furnace pressure reaches ≥0.02 MPa and HCl purity meets standards, notify the system for integration.
During restart, introducing the ignition rod into the quartz burner area risks explosion if hydrogen mixes improperly with residual air, potentially rupturing the quartz burner and endangering the system. Inadequate purging or inaccurate hydrogen analysis may cause burns, while poor door sealing can lead to HCl leaks and environmental contamination.
II. Online Cleaning Modification
Analysis of burner blockages revealed large amounts of white solid deposits, primarily composed of:
- Sodium (45.6% by mass, atomic weight 23)
- Chlorine (25.6% by mass, atomic weight 35.5)
- Oxygen (15.7% by mass, atomic weight 16)
- Hydrogen (6.5% by mass, atomic weight 1).
Based on chlor-alkali production materials and equipment, these solids were identified as sodium hydroxide (NaOH) and sodium chloride (NaCl), both highly water-soluble. Water rinsing proved highly effective.
A task force was established with the goal of developing an online cleaning system for HCl synthesis furnace burners to extend operational intervals between shutdowns and reduce cleaning frequency. The target was set at a minimum 6-month interval between shutdown cleanings for a single furnace.
Option 1: Industrial tap water (high impurity, low cost)
Option 2: High-purity water (low impurity, high cost)
Considering cost and system risks, high-purity water was selected as the cleaning medium.
III. Economic Benefits
The online cleaning system demonstrated significant results. Each manual burner cleaning averages 4 hours of downtime, reducing HCl output by 1,300 m³/h per furnace and affecting PVC production by 6.436 tons. After implementing online cleaning across all furnaces, with an annual reduction of two cleanings per furnace, PVC powder production increased by 231.696 tons/year. At September 2017 PVC prices (~8,000 CNY/ton), this translated to approximately 1.85 million CNY in additional annual revenue.