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Author:
Nikulin V, Head of Engineering
Nikulin V, Head of Engineering
Br₂ is produced from natural brines, bitterns, and seawater, and every recovery flowsheet ends with the same step: a carrier stream loaded with halogen vapor has to surrender it to a liquid. The bromine absorption tower performs that step. Below is where the column sits in the process, which reactions run inside it, and how to specify the internals, operating parameters, and materials.
Role of the Column in Bromine Recovery
Feed brine is acidified and oxidized with chlorine: Cl₂ + 2Br⁻ → Br₂ + 2Cl⁻. The next step depends on feed strength. Rich brines, roughly 1 g/L of bromide and above, follow the hot steaming-out route: vapors are stripped with steam and condensed directly. Lean sources, down to seawater at about 65 mg/L, run the cold blowing-out route — air strips the halogen, and the resulting stream is far too dilute to condense, so it goes to an absorber for chemical concentration. Both routes were commercialized in the 1930s and still dominate: Smackover brine plants in Arkansas, Dead Sea operations, and seawater units all run variants of this scheme.
The bromine absorption tower diagram below shows the cold-process loop: chlorination, air stripping, counter-current gas–liquid contact, then acidification of the rich liquor and steam desorption back to liquid product. In this loop the absorber works as the concentration stage of the plant, turning a stream that carries a fraction of a percent of Br₂ into a liquor ready for stripping.
The bromine absorption tower diagram below shows the cold-process loop: chlorination, air stripping, counter-current gas–liquid contact, then acidification of the rich liquor and steam desorption back to liquid product. In this loop the absorber works as the concentration stage of the plant, turning a stream that carries a fraction of a percent of Br₂ into a liquor ready for stripping.
Using Heat and Steam to Remove Volatile Contaminants
What Happens to Bromine Vapour in the Column
Plain water is a weak absorbent for this duty: solubility is about 3.4 g per 100 g at 68°F, and the dissolved halogen keeps a high backpressure over the solution. Industrial units rely on chemisorption instead. What happens to bromine in an absorption tower is set by the circulating reagent. Soda ash or caustic liquor binds Br₂ as a bromide–bromate salt solution (3Br₂ + 3Na₂CO₃ → 5NaBr + NaBrO₃ + 3CO₂); a sulfur dioxide solution reduces it to hydrobromic and sulfuric acids (Br₂ + SO₂ + 2H₂O → 2HBr + H₂SO₄); iron turnings, a route kept for small plants, yield ferrous bromide. Alkaline capture has one process advantage: the bromide–bromate liquor is stable in storage and releases Br₂ on acidification, which decouples the absorber from the stripping stage.
The main change in bromine vapour in absorption tower service is therefore chemical. The dense red-brown vapor crosses into the liquid film and is fixed as a non-volatile salt or acid, its equilibrium backpressure drops almost to zero, and the driving force stays high along the whole packed height. Heat works against capture: Br₂ boils at 138°F, and its partial pressure over the liquor climbs steeply as the solution warms, so the recirculating liquid is kept cool and reaction heat is removed.
The main change in bromine vapour in absorption tower service is therefore chemical. The dense red-brown vapor crosses into the liquid film and is fixed as a non-volatile salt or acid, its equilibrium backpressure drops almost to zero, and the driving force stays high along the whole packed height. Heat works against capture: Br₂ boils at 138°F, and its partial pressure over the liquor climbs steeply as the solution warms, so the recirculating liquid is kept cool and reaction heat is removed.
Demonstration of the process in the column.
Column Types and Contacting Media
Counter-current packed columns carry most of this duty. Random packing — ceramic saddles, PTFE or PVDF Pall rings — tolerates fouling and is simple to replace; this is the configuration of our Tornado units with random packing. Structured packing gives more transfer surface per foot at lower pressure drop, which suits large recovery trains. Spray designs have no internals to plug and accept dusty, salt-laden streams, at the price of higher recirculation rates. A venturi unit is placed upstream as a quench and first contact stage when the feed carries particulate.
The packing itself acts as the filtration medium: capture happens on its wetted surface, so material and geometry are picked for chemical resistance and film renewal rather than mechanical straining. At the outlet, a droplet separator stops carryover of corrosive liquor into the fan and stack. The full range of these configurations is in our wet scrubber catalog.
The packing itself acts as the filtration medium: capture happens on its wetted surface, so material and geometry are picked for chemical resistance and film renewal rather than mechanical straining. At the outlet, a droplet separator stops carryover of corrosive liquor into the fan and stack. The full range of these configurations is in our wet scrubber catalog.
Key Design Parameters
Superficial gas velocity is set at 60–80% of the flooding point. The liquid rate must keep every element of the bed wetted; recirculation with fresh reagent make-up is standard, dosed on ORP or pH of the liquor. Reagent strength is held below the level where crystallization starts, since bromide–bromate salts precipitating in the bed are the usual cause of channeling. Bed height follows from the transfer-unit count needed for the target slip; with a fast chemisorbent the liquid-side resistance nearly vanishes and the gas film controls, which keeps the required heights moderate. Where a single stage cannot hold the required slip, two columns in series split the duty, the second running on fresh reagent.
Slip is the controlling specification. The residual concentration of bromine vapour in absorption tower exhaust is judged against workplace limits: per OSHA, the permissible exposure limit is 0.1 ppm as an 8-hour average, and ACGIH lists a 0.2 ppm short-term value. A design basis of 99%+ capture with continuous colorimetric or electrochemical monitoring of the outlet is the conservative baseline for permitting and industrial hygiene alike.
Slip is the controlling specification. The residual concentration of bromine vapour in absorption tower exhaust is judged against workplace limits: per OSHA, the permissible exposure limit is 0.1 ppm as an 8-hour average, and ACGIH lists a 0.2 ppm short-term value. A design basis of 99%+ capture with continuous colorimetric or electrochemical monitoring of the outlet is the conservative baseline for permitting and industrial hygiene alike.
Dual Packed Bed Tower
Packed Bed Wet Scrubber Design and Types of Packing
Materials and Operation
Moist Br₂ ranks among the most corrosive services in gas cleaning. Carbon and stainless steels are unusable, and polypropylene, dependable in HCl duty, darkens and embrittles fast. Proven choices are glass and glass-lined steel, ceramics, and fluoropolymers — PTFE, PVDF, FEP — as solid parts or as liners over FRP shells. Tantalum withstands wet and dry service and is reserved for instrument wetted parts. Gaskets and expansion joints are the weak points: only fluoropolymer-faced elements last, and they belong on the inspection schedule.
Operation comes down to three checks. Reagent depletion shows up as coloring of the exhaust — the vapor is visibly red-brown far above hygiene limits, so a tinted stack means breakthrough has already happened. Salt deposits in the bed raise resistance; a rising ΔP trend at constant flow calls for a wash cycle. And since this vapor is roughly five times denser than air, leaks pool at grade around flanges and pumps, which is why detectors are mounted low, close to the equipment.
Operation comes down to three checks. Reagent depletion shows up as coloring of the exhaust — the vapor is visibly red-brown far above hygiene limits, so a tinted stack means breakthrough has already happened. Salt deposits in the bed raise resistance; a rising ΔP trend at constant flow calls for a wash cycle. And since this vapor is roughly five times denser than air, leaks pool at grade around flanges and pumps, which is why detectors are mounted low, close to the equipment.
Optimal Chemical Wet Scrubber Materials: Ensuring Durability and Efficiency
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Head of Engineering,
Vladimir Nikulin
Vladimir Nikulin
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