HCl Furnace Maintenance and Decommissioning Procedure

In chlor-alkali and basic chemical production, the hydrochloric acid synthesis furnace (HCl furnace) plays a central role in synthesizing hydrogen chloride gas from chlorine and hydrogen produced by electrolysis; its output is directly used in the production of PVC, hydrochloric acid, and downstream chloride products. Internationally, there are two mainstream designs: graphite synthesis furnaces and steel water-jacketed synthesis furnaces. The former is represented by bottom-fired or top-fired units from manufacturers such as Mersen, SGL Carbon, and Wilk-Graphite, while the latter is primarily used in small- and medium-sized plants. Graphite furnaces typically operate at temperatures above 1,500°C, and under special operating conditions, temperatures can reach 2,500°C. The burner (HCl Burner) is bottom-mounted with the flame directed upward, and a safety rupture disc is installed at the top of the furnace; in the event of overpressure, the gas is safely released upward.

The operating environment for this type of equipment is extremely harsh. HCl is highly corrosive to metals in the presence of water. Although graphite components are corrosion-resistant, they are highly susceptible to mechanical damage; impregnated graphite must undergo a complete impregnation process to withstand HCl corrosion across the full range of concentrations and temperatures. Therefore, performing regular HCl furnace maintenance is essential for ensuring the furnace’s long-term operation. The maintenance cycle is typically 36 to 48 months, but burners often require more frequent inspections—if the hydrogen-to-chlorine ratio deviates, an explosive mixture may form inside the burner. At a chemical plant in France, condensation in the hydrogen pipeline caused a decrease in hydrogen flow rate, leading to an excessive accumulation of chlorine inside the furnace, which ultimately resulted in an explosion during restart. Based on these real-world lessons, we have updated our maintenance/repair plan for HCl furnace burners. The following sections will detail the three phases: HCl Furnace Maintenance Steps, HCl Furnace Removal/Demolition Steps, and HCl Furnace Disassembly Steps.

HCl Furnace Maintenance Steps

Preparations for HCl furnace maintenance proceed along three tracks. Technical preparations involve reviewing records from the previous maintenance and analyzing the current failure symptoms to determine the replacement list for components such as the combustion head, graphite sections, and explosion-proof membranes. Material preparations involve verifying the specifications of graphite short tubes, expanded PTFE gaskets, and rupture discs; gaskets for the graphite furnace body are typically 5 mm thick and 15 mm wide. Safety and process isolation preparations are paramount—after emptying the furnace of its contents, nitrogen is purged into the furnace until oxygen and combustible gas levels meet standards; blind flanges are installed on the chlorine and hydrogen pipelines; and work may only commence after all feed lines have been shut off.

Upon entering the Disassembly and Inspection phase, first remove the sight glass to check for glass damage, then remove the burner head to inspect whether the concentric tube is clogged or burnt out; if corrosion at the end of the inner tube exceeds 20 mm in length, the part must be replaced. Next, remove the burst disc; a new burst disc must be installed during every maintenance cycle, and any disc showing deformation or corrosion must not be reinstalled. The HCl gas pipeline must be inspected for blockages and corrosion, and valves, flow meters, and temperature gauges must be checked to ensure they are functioning properly. The key focus of the furnace body inspection is wall thickness measurement; areas below the design thickness must be repaired or replaced, and the levelness deviation of the furnace base must be controlled within 3 mm.

Repair and Replacement is the most critical phase. When reinstalling the burner head, the verticality deviation must not exceed 1 mm. If minor cracks appear in the graphite section, they may be re-bonded; however, in the event of extensive cracking, the entire section must be replaced. If flange faces are damaged, they must be turned to restore them; graphite blocks with severe scale buildup on their outer surfaces must undergo acid washing. Localized corrosion on the carbon steel shell can be ground down and rewelded, but the integrity of the lining must be confirmed; otherwise, HCl penetration into the jacket layer may cause stress corrosion cracking. The Reassembly and Commissioning phase sequentially completes reinstallation, alignment, pressure and leak testing, and ignition acceptance. Graphite Furnace Special Repair involves specialized treatment for graphite furnaces, including re-bonding, replacement of graphite sections, flange face turning, and acid washing to remove scale.

HCl Furnace Removal / Demolition Steps

The first step in HCl furnace removal is shutdown and isolation. After gradually reducing the gas flow into the furnace, shut off the chlorine supply first, followed by the hydrogen supply, and purge with nitrogen until the system meets acceptance criteria. Depressurize and cool the system to below normal operating levels. After disconnecting the chlorine and hydrogen pipelines, install blind flanges using flange clamps. Disconnect the PVC pipe running from the furnace top HCl outlet to the first-stage absorber and install a blind flange to avoid interfering with subsequent hoisting operations. After disconnecting the flange connecting the graphite cooler to the synthesis furnace, hoist the entire cooler and move it to a safe area.

Piping and Auxiliary Removal should proceed in a top-down, outside-in sequence: electrical and instrumentation lines are removed first, followed by valves and process piping, and finally the equipment itself. When cutting and removing the furnace top ladders and platforms, pay attention to hot work management in explosion-hazard areas. Lifting and hoisting is the highest-risk phase of HCl furnace removal. When a certain plant dismantled a 16-meter-tall, 37-metric-ton synthesis furnace, a comprehensive survey of the work environment was conducted prior to dismantling, and a plan was formulated to identify potential risks item by item. Technical personnel provided full guidance throughout the process, and dedicated safety personnel supervised on-site for all work at height, hot work, and lifting operations. After all base bolts and flanges on auxiliary piping were removed, the furnace body was safely hoisted out with the assistance of a crane. Safety controls were implemented throughout the entire process; work permits, restricted access zones, hot work permits, and gas detection were all mandatory.

HCl Furnace Disassembly Steps

HCl furnace disassembly begins with sectional dismantling. First, remove the short graphite tubes connecting the steel furnace body to the graphite furnace body—care must be taken when removing the sealing packing groove. Only after the short tubes are removed can the connecting flanges on the upper section of the steel furnace body be disassembled. After the steel furnace body is hoisted away and placed on the ground, the graphite furnace body is dismantled section by section from top to bottom. Lifting force must be carefully controlled during the removal of each graphite section. Although impregnated graphite is corrosion-resistant, it has poor resistance to mechanical impact, and collisions can easily cause cracks.

Numbering and recording are steps in the dismantling process that are easily overlooked but have a significant practical impact. Immediately after removing each graphite section, number it and draw a sketch, noting the orientation of the flange face and the location of the sealing surface. Without proper numbering and records, if the sections are reassembled in the wrong order or orientation, the flange faces will not align, and the seal will fail. Inspection and repair are conducted section by section during disassembly, focusing on checking the inner and outer surfaces of the graphite blocks for slag pores, leaks, and cracks, as well as the flange faces for corrosion pits. Graphite blocks with severe scale buildup require acid washing; small cracks can be repaired with adhesive, while those with through-cracks or extensive damage must be replaced. 

During maintenance of the graphite cooler, the pipe openings must also be checked for blockages—the outlet temperature of the synthesis furnace is generally between 450 and 500°C. If the cooler inlet temperature falls below the hydrogen chloride dew point (108.65°C), HCl will condense into an acidic solution that corrodes the piping; conversely, excessively high temperatures will shorten the service life of the graphite cooler. Maintaining this temperature range is a key aspect of HCl furnace maintenance that is often overlooked but significantly impacts equipment lifespan. After the disassembly inspection is complete, all components are returned to their designated storage locations according to their serial numbers, awaiting reinstallation or scrapping.

During the maintenance and dismantling of the HCl furnace, some failed precious metal components may be recovered; you can contact a precious metal recycling company to have them recycled.