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Author:
Nikulin V, Head of Engineering
Nikulin V, Head of Engineering
An HCl tank vent scrubber for venting hydrochloric acid storage tanks is typically designed as a compact packed wet column made of corrosion-resistant materials. Such systems are widely used in chemical plants and storage facilities handling 30–36% HCl, as well as in petrochemical applications for acid recovery from hydrochlorination processes and in laboratory-scale installations.
Tank Vent Scrubber Animation
HCl Storage Tank Scrubber Design
Main Shell and Materials
An HCl tank scrubber is most commonly designed as a vertical packed tower made of polypropylene (PP), PVC, FRP, or other plastics resistant to 36% HCl and its vapors. The lower section of the column contains a sump with the scrubbing liquid (typically water or an alkaline solution such as NaOH), while the upper section includes the clean air outlet nozzle and a mist eliminator.
Connection to the Tank
The vent gas from the HCl storage tank scrubber is routed to the tower inlet via a vent line, typically entering the column from the top or side. The system is designed to accommodate vessel breathing and filling operations, therefore the vent line diameter and configuration are sized for maximum vapor flow rates and emission control requirements.
Contact Zone and Packing
Inside the column, a packed bed (Raschig rings, Pall Rings, Intalox saddles, etc.) provides a large gas–liquid contact surface. Above the packing, a spray header with nozzles uniformly distributes the scrubbing liquid across the column cross-section, forming a thin film on the packing for efficient absorption.
An HCl tank scrubber is most commonly designed as a vertical packed tower made of polypropylene (PP), PVC, FRP, or other plastics resistant to 36% HCl and its vapors. The lower section of the column contains a sump with the scrubbing liquid (typically water or an alkaline solution such as NaOH), while the upper section includes the clean air outlet nozzle and a mist eliminator.
Connection to the Tank
The vent gas from the HCl storage tank scrubber is routed to the tower inlet via a vent line, typically entering the column from the top or side. The system is designed to accommodate vessel breathing and filling operations, therefore the vent line diameter and configuration are sized for maximum vapor flow rates and emission control requirements.
Contact Zone and Packing
Inside the column, a packed bed (Raschig rings, Pall Rings, Intalox saddles, etc.) provides a large gas–liquid contact surface. Above the packing, a spray header with nozzles uniformly distributes the scrubbing liquid across the column cross-section, forming a thin film on the packing for efficient absorption.
Torch-Air HCl Tank Scrubber System
Liquid Circuit
A solution reservoir is located at the bottom of the column, from which a circulation pump delivers liquid to the spray nozzles. The liquid circuit includes valves and instrumentation such as flow meters, pressure gauges, level sensors, and pH / conductivity analyzers to monitor solution saturation and HCl neutralization. A portion of the liquid is periodically bled off and replaced with fresh absorbent to maintain scrubbing efficiency and control salt concentration.
Mist Eliminator and Outlet
A high-efficiency demister is installed above the packing to capture entrained droplets and return them to the column. The clean gas outlet is connected to an exhaust stack, designed to provide the required discharge velocity and height while maintaining minimal pressure drop (ΔP).
Additional Components
A typical HCl tank vent scrubber design includes access manways, a support frame or structure, piping with isolation and control valves, and—if installed outdoors—thermal insulation and heat tracing for freeze protection. Instrumentation and control systems monitor column ΔP, liquid level, pH/conductivity, and, if required, HCl concentration at the outlet using an online analyzer.
A solution reservoir is located at the bottom of the column, from which a circulation pump delivers liquid to the spray nozzles. The liquid circuit includes valves and instrumentation such as flow meters, pressure gauges, level sensors, and pH / conductivity analyzers to monitor solution saturation and HCl neutralization. A portion of the liquid is periodically bled off and replaced with fresh absorbent to maintain scrubbing efficiency and control salt concentration.
Mist Eliminator and Outlet
A high-efficiency demister is installed above the packing to capture entrained droplets and return them to the column. The clean gas outlet is connected to an exhaust stack, designed to provide the required discharge velocity and height while maintaining minimal pressure drop (ΔP).
Additional Components
A typical HCl tank vent scrubber design includes access manways, a support frame or structure, piping with isolation and control valves, and—if installed outdoors—thermal insulation and heat tracing for freeze protection. Instrumentation and control systems monitor column ΔP, liquid level, pH/conductivity, and, if required, HCl concentration at the outlet using an online analyzer.
Working Principle
Most commonly, a packed-type hydrochloric acid tank scrubber is used for HCl removal, as it provides maximum mass transfer efficiency. Laden vapors from the hydrochloric acid storage vessel enter the lower section of the column through the inlet nozzle. The absorbing solution is uniformly sprayed from the top via nozzles and flows downward as a thin liquid film over the packing (Pall Rings or Raschig rings), ensuring intensive counter-current contact with the gas stream.
HCl is physically absorbed in water (an exothermic process) or chemically neutralized by an alkaline solution, forming a dilute hydrochloric acid (typically up to 10–15%) or corresponding salts, which are collected in the bottom sump. The cleaned air passes through a demister installed in the upper section of the unit, where entrained droplets are removed, and is then discharged to the atmosphere through the exhaust stack. A circulation pump recirculates the liquid from the sump to the spray nozzles, with a portion of the saturated solution periodically bled off for regeneration or disposal, maintaining the optimal liquid-to-gas ratio (L/G) of 2–5 L/m³ and controlled pH.
HCl is physically absorbed in water (an exothermic process) or chemically neutralized by an alkaline solution, forming a dilute hydrochloric acid (typically up to 10–15%) or corresponding salts, which are collected in the bottom sump. The cleaned air passes through a demister installed in the upper section of the unit, where entrained droplets are removed, and is then discharged to the atmosphere through the exhaust stack. A circulation pump recirculates the liquid from the sump to the spray nozzles, with a portion of the saturated solution periodically bled off for regeneration or disposal, maintaining the optimal liquid-to-gas ratio (L/G) of 2–5 L/m³ and controlled pH.
Materials of Construction
HCl tank vent scrubbers are manufactured exclusively from corrosion-resistant materials capable of withstanding aggressive hydrochloric acid vapors at temperatures up to 50–60 °C.
Main Materials for Shell and Packing
Main Materials for Shell and Packing
- FRP (fiberglass-reinforced plastic with vinyl ester or chlorendic resin) — the primary material for the column, sump, and piping (resistant to up to 37% HCl).
- Polypropylene (PP) or PVDF — molded housings, spray nozzles, and packing (PP/PVDF Pall Rings, Intalox saddles).
- PVC or CPVC — used for small systems and piping (up to 20–25% HCl).
- PTFE-lined steel or titanium — for highly loaded components and extreme acid concentrations.
- PP/PVDF magnetic-drive centrifugal pumps (seal-less design).
- PVDF/PTFE diaphragm pumps for precise alkali dosing.
- PVC/PP valves with PTFE seals.
- PP mesh demisters or PVDF vane-type demisters.
- PVDF/PTFE spray nozzles for uniform wetting of the packing.
Selecting a Wet Scrubber for a Tank
Operation and Maintenance
Proper operation and maintenance of a hydrochloric acid tank vent scrubber focus on maintaining a stable flow of scrubbing liquid, controlling pH and liquid levels, and regularly inspecting for corrosion and blockages. This ensures consistent removal efficiency, prevents emissions, and prolongs equipment life.
Operating Mode
The hydrochloric acid storage tank vent scrubber must operate continuously whenever the vessel is breathing. Therefore, the circulation pump and spray system are started before any potential gas release and stopped only after the gas flow stabilizes. Liquid and gas flow rates are maintained within design limits (L/G ratio, pressure, temperature), with periodic monitoring of the scrubbing solution pH and addition of alkali or fresh water to maintain effective HCl absorption.
The sump level is controlled automatically via level sensors to prevent air entrainment by the pump or overflow. Gas line pressure is monitored with manometers; an increase in pressure drop across the packing or demister indicates blockages or salt deposition.
Operating Mode
The hydrochloric acid storage tank vent scrubber must operate continuously whenever the vessel is breathing. Therefore, the circulation pump and spray system are started before any potential gas release and stopped only after the gas flow stabilizes. Liquid and gas flow rates are maintained within design limits (L/G ratio, pressure, temperature), with periodic monitoring of the scrubbing solution pH and addition of alkali or fresh water to maintain effective HCl absorption.
The sump level is controlled automatically via level sensors to prevent air entrainment by the pump or overflow. Gas line pressure is monitored with manometers; an increase in pressure drop across the packing or demister indicates blockages or salt deposition.
Installed System Overview
Routine Maintenance
Maintenance includes periodic washing of the packing and demister (with water or mild solution) to remove salt and sludge deposits, especially when operating with alkaline neutralizing solutions. Internal surfaces, nozzles, spray headers, and fasteners are inspected for corrosion, erosion, and cracking of plastics or FRP.
Pumps are checked and serviced (bearings, magnetic couplings, mechanical components), along with valves and instruments (pH sensors, flow meters, level sensors), replacing worn seals and gaskets resistant to HCl. The solution is periodically partially or fully bled off, sludge is removed from the sump and piping, and fresh solution is added in accordance with waste management regulations.
To prevent corrosion of surrounding structures, the quality of the cleaned gas (HCl content and condensate pH after the demister) is regularly monitored, and operating conditions are adjusted if necessary. Explosion-proof and corrosion-resistant fans, along with proper grounding and ventilation of the tank farm area, reduce risks to personnel and equipment.
Maintenance includes periodic washing of the packing and demister (with water or mild solution) to remove salt and sludge deposits, especially when operating with alkaline neutralizing solutions. Internal surfaces, nozzles, spray headers, and fasteners are inspected for corrosion, erosion, and cracking of plastics or FRP.
Pumps are checked and serviced (bearings, magnetic couplings, mechanical components), along with valves and instruments (pH sensors, flow meters, level sensors), replacing worn seals and gaskets resistant to HCl. The solution is periodically partially or fully bled off, sludge is removed from the sump and piping, and fresh solution is added in accordance with waste management regulations.
To prevent corrosion of surrounding structures, the quality of the cleaned gas (HCl content and condensate pH after the demister) is regularly monitored, and operating conditions are adjusted if necessary. Explosion-proof and corrosion-resistant fans, along with proper grounding and ventilation of the tank farm area, reduce risks to personnel and equipment.
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Head of Engineering,
Vladimir Nikulin
Vladimir Nikulin
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