CO₂ Scrubber for Tanks: Applications, Operation, Calculation and Selection

Breather CO₂ scrubber for tanks containing mineral acids (HCl, H₂SO₄, HNO₃, etc.) perform two key functions:

• they purify the incoming air during tank inhalation by removing CO₂ and organic contaminants, thereby preventing side reactions and carbonate formation;
• they capture acid vapors and toxic gaseous by-products during tank exhalation, reducing corrosion of breather lines and minimizing environmental impact.

The design comprises a corrosion-resistant housing (often insulated and equipped with electric heat tracing for outdoor installation), cartridges filled with a chemical adsorbent, a bypass / relief valve, and, where required, a demister and a pre-filter to retain acid aerosols and extend the service life of the sorbent.

A CO₂ scrubber for DM water tanks is a breather adsorber installed on the vent nozzle of a demineralized water tank to remove carbon dioxide from atmospheric air and maintain stable pH and low electrical conductivity of the water.
When a DM tank is drained or cooled, a vacuum is created and air is drawn into the reservoir through the breather. As the air passes through a layer of chemical adsorbent in the scrubber, carbon dioxide is almost completely removed, and only purified air enters the reservoir. This prevents the formation of carbonic acid, an increase in dissolved solids, and accelerated corrosion.

Such scrubber filters are used on demineralized water and condensate tanks at thermal power plants, in water treatment systems for turbines and boilers, as well as in the pharmaceutical, microelectronics, and other high-technology industries where requirements for conductivity and total organic carbon are particularly stringent.

From a design perspective, a CO₂ scrubber for a DM water tank is typically a compact housing with connections for integration with the reservoir breather valve, replaceable cartridges filled with adsorbent (usually based on alkaline or amine materials), low pressure drop (ΔP), and provisions for ground-level or rooftop installation so as not to interfere with normal tank breathing.

The selection of a carbon dioxide adsorber is based on three key components: reservoir data, selection of the nominal size according to the breathing rate, and calculation of the adsorbent’s service life.

For accurate selection, the following information is required:

• Tank volume and product type (DM water, potable water, acids, reagents, wastewater) to determine the allowable CO₂ level and presence of accompanying gases;
• Breathing mode: frequency of filling/emptying, typical temperature range, maximum liquid level change rate — these factors determine the peak airflow through the breather;
• Required residual CO₂ concentration or purification efficiency, e.g., 90–99.9%, and the allowable pressure drop in the breather line.

Using the tank’s operating conditions, the maximum breathing rate — the peak airflow through the breather valve (m³/h or cfm) — is calculated. The scrubber filter nominal size is chosen so that its rated capacity meets or exceeds this airflow, with a safety margin of 10–20% and an acceptable ΔP.

For example, if the calculated maximum breathing rate is 4,500 cfm, it is reasonable to select a model rated at 6,000 cfm (such as the standard Sirocco model) to ensure unrestricted tank breathing and prevent triggering the pressure relief valve.

In such filters, the adsorbent typically consists of granular or cartridge-packed materials based on alkaline and/or amine-containing compounds capable of chemically binding carbon dioxide from air. Most commonly, this includes modified activated carbon, zeolites, or porous mineral carriers impregnated with hydroxides (NaOH, KOH, Ca(OH)₂) or amines. Through these reactions, CO₂ is irreversibly captured as carbonates, providing a high purification efficiency of up to 90–99.9% when the adsorbent is properly selected.

The replacement interval for the adsorbent is determined by the total CO₂ load: the calculation uses the average and maximum airflow, the average carbon dioxide concentration in the incoming air, and the CO₂ capacity of the adsorbent as specified in the datasheet. Based on these parameters, the theoretical service life is estimated, for example, in hours of operation or number of “breathing cycles” until saturation.

In practice, the calculated interval is refined using readings from an integrated CO₂ analyzer at the outlet: a rise in carbon dioxide concentration above a set threshold serves as a trigger for scheduled cartridge replacement. This approach allows a shift from rigid calendar-based maintenance to condition-based servicing.

Automation and performance monitoring of the adsorber are based on continuous measurement of CO2 concentration upstream and/or downstream of the unit, as well as monitoring of key parameters — airflow, pressure drop, and housing heating status.

In a typical system, a built-in CO₂ analyzer sends signals to the control panel or DCS, enabling detection of adsorbent saturation, generation of alarm and warning signals, and planning of maintenance based on actual service life rather than a fixed calendar schedule.

The installation and integration of the adsorber focus on correctly incorporating the filter into the breather line without restricting the reservoir’s normal ventilation and ensuring convenient access for maintenance.

The installation method depends on the size and configuration of the unit:

• Compact adsorbers are mounted directly on the flange of the breather valve or nozzle on the roof.
• Larger/heavier units are installed on a separate support structure near the reservoir and connected to the breather nozzle via a short piping run with minimal pressure loss and flexible joints.

During the piping design, the following considerations are included:

• Condensate drainage, especially for outdoor installations and “warm” gas streams;
• Isolation of the filter using shut-off valves for maintenance;
• Unrestricted access to lids and hatches for cartridge replacement, to the terminal box and control panel, as well as safe access via platforms and ladders for personnel.