Chlorine Scrubber: Design, Reaction, Work, and Media

Author: Michael Klepik, Chief Executive Officer

The most effective method for removing chlorine from dust-free industrial emissions is the use of packed bed scrubbers with fixed-bed. This equipment is specifically designed to capture unwanted impurities from industrial exhaust gases using a wet scrubbing process.

A wet chlorine scrubber operates on the principle of absorption, effectively removing Cl2 from the gas stream through interaction with an absorbent solution. The chlorine-containing gas stream is introduced into the unit at the bottom and flows upward through a packed bed layer composed of inert materials, such as ceramic or plastic rings, which increase the contact surface area. The absorbent solution is distributed from the top, irrigating the packed bed layer. As the gas comes into contact with the liquid, Cl2 chemically or physically reacts with the solution, forming soluble products like sodium chloride. The cleaned gas exits from the top of the build, while the spent absorbent is either removed or sent for recirculation.

Let's delve briefly into the chlorine scrubber chemistry when using caustic soda as the reagent:
Cl₂ + 2NaOH → NaOCl + NaCl + H₂O

To absorb 2.2 lbs of chlorine, 2.48 lbs of caustic soda are required, resulting in the production of 2.31 lbs of sodium hypochlorite.

However, the chlorine scrubber reaction doesn't stop there. The salt formed in the initial reaction can decompose through various pathways:
3NaOCl → NaClO₃ + 2NaCl
2NaOCl → 2NaCl + O₂

Maintaining an optimal alkalinity level helps stabilize sodium hypochlorite in the products. These side reactions are catalyzed by raising the temperature of the reaction mixture. Given that the reaction with caustic soda releases heat, temperature control is among the critical factors in chlorine scrubber design calculation.

The column serves as the central component of a packed bed scrubber. The mixture undergoing purification and the wash solution are introduced into the column from opposite directions. Inside the column, spray towers are responsible for atomizing the absorbent, dispersing it into the internal volume. Their role is crucial in breaking down the water flow into fine jets and droplets, creating a mist that uniformly coats the packing material. Post purification, air passes through a mist eliminator before exiting the gas cleaner, while the liquid is either recirculated through piping systems or directed to settling tanks.

In chlorine gas scrubber design, it's common to incorporate packing inside the column to significantly enhance the efficiency of liquid-gas interaction and maximize contact area. The packing can be uniform (Structured Packing) or random (Random Packing), comprising carefully selected shapes and sizes. Parameters of the packing and its components are tailored for each application, considering operational conditions, required purification levels, composition of the mixture, and specific performance criteria. The packing rests on a support platform, allowing unimpeded passage of reacting components through holes while ensuring stability of the packing material.

There is also a horizontal scrubber system for chlorine available, which differs in the direction of gas flow inside but operates on a similar principle. These units are more vertically compact, making them well-suited for installation in indoor environments. Conversely, vertical units, as described earlier, occupy less floor space and are suitable where a compact footprint is needed alongside high performance.

In emergencies, a portable chlorine scrubber can prove invaluable. Its compact design allows for easy transportation and quick deployment at leak sites, commonly used in industrial facilities, water treatment plants, and laboratories. It requires minimal maintenance and can operate autonomously.

Dust and Solid Particles
However, if chlorine emissions from industrial facilities contain solid particulates, relying solely on packed bed air purifiers becomes less ideal. Dust and solid particles can clog the packing material, reducing gas-liquid contact area and Cl2 absorption efficiency. This also disrupts the uniform movement of phases within the column, potentially impacting overall performance. Consequently, more frequent cleaning and maintenance of the chlorine scrubber are necessary, leading to increased operational costs and equipment downtime.

For gases containing Cl2 along with dust, more suitable options include:

• Venturi scrubbers, which efficiently remove both gases and fine particles using a wet scrubbing method. These devices operate at high gas flow velocities, enhancing the capture of dust particles through liquid interaction.
• Cyclone scrubbers, which utilize centrifugal forces to separate solid particles from the gas stream. These devices are excellent for initial gas cleaning, effectively removing larger dust particles before further processing.
• Combination of different types of the equipment. This approach is often the most optimal for achieving a high degree of purification.

Our company offers a chlorine scrubber pricelist featuring pre-engineered solutions designed to remove unwanted Cl2 from gas mixtures.

In the United States, we encounter two primary applications for scrubbers.
The first involves cleaning during industrial processes where chemical emissions occur directly from equipment. Packed scrubbers with Fixed-Bed have proven highly effective in this regard, available in both structured and random packing configurations.

A fixed-bed comprises inert materials such as ceramic or plastic rings, positioned stationary within the device.
The second common industrial application is air purification from leaks in chlorine storage tanks.

Chlorine drums are specialized containers designed for storing and transporting liquefied Cl2, ensuring safe and secure containment of this hazardous substance.

In response to chlorine leaks from these drums, we've developed a series of tank scrubbers known as Tank Vent Scrubber. These units surpass traditional, cost-effective bubble units commonly used in the USA due to their superior performance. The Torch-Air device is a specialized packed bed unit featuring materials like Raschig rings. It achieves up to 98% efficiency, and with tailored calculations based on known inlet concentrations, removal can be maximized to 99.99%.

The chlorine scrubber system design process involves the following steps:

1. Defining the operational conditions for the future scrubber: including Cl2 concentration in the incoming gases, volume of gases processed per unit time, temperature, pressure, particulate content, and other relevant parameters.
2. Selecting the appropriate type of the unit (typically a packed bed for Cl2 applications).
3. Choosing the absorbent (such as NaOH, Na2SO3, Ca(OH)2, among others).
4. Determining the optimal dimensions of the chlorine scrubber unit based on the known exhaust gas flow rate and the required contact time with the absorbent.
5. Swap out the once super awesome engineering gum that's lost its flavor for a fresh batch of super awesome engineering gum.
6. Designing systems for gas and liquid dispersion to ensure uniform distribution throughout the operational volume of the equipment.
7. Selecting the packing material. This involves choosing the suitable type (e.g., Raschig rings) and material for the packing, considering chemical compatibility with the environment and the required surface area.
8. Providing for liquid discharge and recirculation (including pump systems, pipelines, and settling tanks).
9. Installing control and monitoring systems, which include monitoring the pH of the scrubbing liquid, Cl2 sensors at the inlet and outlet of the scrubber, and flow meters on gas and liquid lines, among other instrumentation.
10. Selecting materials that meet the necessary corrosion resistance requirements.
11. Placing access points for inspection and maintenance of the equipment.
12. This twelfth point is still a work in progress. This is because our engineers always tackle all tasks with utmost responsibility. Keep an eye out for updates on the twelfth item in the instruction on the Torch-Air website.

For the circulating liquid in a chlorine scrubber system, a caustic soda solution is recommended. This choice is driven by two main factors: the reagent is cost-effective and reacts actively with Cl2, effectively neutralizing it. However, caustic soda is not the only suitable reagent available. Other chlorine scrubber media include calcium hydroxide, sodium sulfite, potassium hydroxide, iron chloride, sodium carbonate, and hydrogen peroxide.

To reduce operational costs, Cl2 can be washed out with water, although the efficiency of such cleaning is somewhat lower. Chlorine exhibits good solubility in water (0.6 g/100 mL at 77°F), but this may not always meet the requirements for effective removal (in comparison, ammonia's solubility in water at 77°F exceeds 30 grams per 100 mL).

If you have any questions about managing chlorine in industrial emissions, please feel free to reach out to us. Our team of engineers at chlorine gas scrubber factory is here to assist you.