The basics of water decarbonation, the removal of CO2 from water

the removal of carbon dioxide (CO2). The need to remove (CO2) is essential in most Aquaculture, Municipal, Industrial, and Food & Beverage Processes To understand you must familiarize yourself with Henry’s Law.

Henry's Law defines the method and proportional relationship between the amount of a gas in solution

in relationship to the gases partial pressure in the atmosphere. Often you will see and hear various terms like degasification, decarbonation, aeration, and even air stripping when discussing the removal of dissolved gases and other convertible elements from water. Understanding the impacts that Carbon Dioxide (CO2) can have on both equipment and aquatic life provides the basic reasons why the need to decarbonate water, exists. Carbon Dioxide (CO2) can exist naturally in the raw water supply or be the results of ph control and balance. In either case the the process called Decarbonation or Degasification provide the most cost effective and efficient manner to reduce or tally remove (CO2) from the water. In addition to Carbon Dioxide (CO2), water can contain a variety of other contaminants that may impact the removal efficiency of the Carbon Dioxide. A variety of elements as well as dissolved gases such as oxygen, nitrogen and carbon dioxide (CO2). A full analytical review of the water chemistry is required to properly design and size the “Water Treatment” process.

Breaking the bonds in water to release a dissolved gas

such as carbon dioxide (CO2) you must change the conditions of the vapor pressure surrounding the gas and allow the gas to be removed.  There are many variables to consider when designing or calculating the “means and methods” of the removal of carbon dioxide (CO2). When I refer to the means and methods. I am referring to the design of a decarbonator and its components. The means equals the size and type (Hydraulic load) of the decarbonator and the “method” equals the additional variables such as cubic foot of air flow (CFM) and “Ratio” of the air to water to accomplish the proportional condition needed to remove the carbon dioxide (CO2).

The need for pH control with water degasification and decarbonation in water treatment includes almost every industry and includes;

The need for pH control with water degasification and decarbonation in water treatment includes almost every industry and includes; Aquaculture, food and beverage, industrial, municipal, and even pisciculture.  In some water treatment applications, harmful gases such as Hydrogen Sulfide (H2S) are removed, while in other applications, Carbon Dioxide (CO₂) or a combination of both. In addition, there's a host of other organic and inorganic elements found in water, both naturally occurring and manmade, that require removal during some part of the water treatment process.  

In almost every application of degasification or decarbonation, you will hear or see the term pH used either by need or by the result.  If, as an example, the water treatment application requires the removal of Hydrogen Sulfide (H₂S) to be removed either as “free” gas or requires the conversion of Sulfides into (H₂S) gas. You will often also see the need to adjust the pH of the water chemistry to maximize both the removal and the conversion to increase the efficiency of the equipment being utilized to remove the hydrogen sulfide, such as a degasification tower or commonly called a degasifier.

So, what is pH?

Water pH is a term used to describe whether or not the water is “acidic” or “basic.”  pH ranges in water can be from 0-14.  0 is the most acidic, and 14 is at the far end and is the most basic, leaving “7” as the neutral state.  A pH of 7 is neither acidic nor basic. So, what causes pH to be acidic?  In nature, the most common cause of a low acidic pH in water is Carbon Dioxide (CO₂) which occurs naturally when photosynthesis, decomposition, or respiration occurs in nature.  The increase in CO₂ causes an increase in ions, producing a lower pH in a simplified explanation.

How does pH play such a significant role in degasification and decarbonation? 

As mentioned above in the example of the removal of certain harmful elements such as sulfides, sulfates, and free H₂S hydrogen sulfide gases, to maximize the removal from water utilizing a degasification tower, it is essential to maintain as close to a pH of 5 as possible.  When the pH rises above 5, the ability to convert and strip the free H₂S gas from the water diminishes.  When a degasification tower operates within this specific range and if it has been designed with the higher efficient distribution systems such as the ones utilized by DeLoach Industries, removal efficiencies of 99.999%- 100% can be achieved.   If the pH rises to seven or above, the removal process becomes much more complex, and typically, you will have much lower results.  The pH adjustment during the water treatment process is typically accomplished by adding commercially available acid, such as “sulphuric acid,” one of the most common in the municipal and food and beverage industry.

Hydrogen Sulfide Chemical Formula and the Molar mass of H2S

H2S is a naturally occurring chemical compound created in nature with the decay of organic material. Hydrogen sulfide is a chemical compound with a molecular formula comprised of (2) hydrogen atoms and (1) one sulfur atom. The formula is displayed as H2S. The gas is a colorless hydride, often known as the “Rotten egg gas.” This gas is very dangerous as it is poisonous and toxic to all life forms. It is also very corrosive and flammable. The H2S molar mass is 34.1 g/mol, with a melting point of -76 F (-60 C) and a melting point of –115.6F or (-82C).

Hydrogen sulfide gas is also created more often from a byproduct of a manufacturing process or the removal of water or wastewater treatment systems. In wastewater, as organic material decays, H2S is released, captured, and treated to protect human lives, reduce corrosion, and reduce odor complaints. Hydrogen sulfide gas is produced during the manufacturing operations at refineries, pulp mills, and mining. These high levels of H2S are released during manufacturing. They must be captured and neutralized to protect human life from unwanted health effects such as pulmonary edemaand prevent excessive corrosion to your system. You cannot even smell the gas at higher concentrations, and it is not distinguishable as the “rotten egg gas,” which makes it even more dangerous and drives the need for hydrogen sulfide scrubbers equipment, fume scrubbers, or odor control scrubbers.

According to the “Agency for Toxic Substance & Disease Registry,” those who work within certain industries are exposed daily to higher levels of hydrogen sulfide gas than the normal public. Because the gas is also heavier than air, it will settle into lower places like manholes, tanks, and basements, and it will travel across the ground filling in low-level areas. To protect the public, OSHA (occupational safety and health administration) has set guidelines and rules known as “Permissible Exposure Limits” (PEL). A PEL is a legal limit a worker may be exposed to a chemical substance. The PEL limit for hydrogen sulfide is ten parts per million (10 ppm) over eight hours.

Basics of water decarbonation for dissolved organic carbon.

The water treatment industry continues to develop and evolve and over the past two decades there have been many new developments in technology and even more refinement in existing technologies such as "Degasification". The evolution and advancement of water treatment have been driven by the constantly increasing demand from an increase in population that demand cost-effective solutions and recognition to improve safety with the implementation of NSF 61 standards.

All human cultures on our planet share a single commonality and that is the dependency on water to survive.

Many existing technologies such as "Degasification" have evolved with higher efficiency to meet the demand changes and provide safety to consumers and to the systems. Degasification refers to the removal of dissolved gases from liquids and the science to degasify water is based upon a chemistry equation known as "Henry's Law". The "proportionality factor" is called Henry's law constant" and was developed by William Henry in the early 19th century. Henry's Law states that "the amount of dissolved gas is proportional to its partial pressure in the gas". The most "cost" effective method to perform degasification is with the packed vertical tower called a "Degasifier” or “Decarbonator”.

The key words in this previous sentence for owners, operators, and engineers to focus on is "the most cost-effective" as there is no other process more cost-effective at removing dissolved gases at the lowest cost than the use of a Degasifier or decarbonator. The process of degasification is simple enough to understand. Water is pumped to the top of a vertically constructed tower where it first enters the tower through some type of distribution system at the same time there is a cross current air flowing up from the bottom by a blower located at the bottom of the tower and the air encounters the water and is exhausted at the top of the tower through an exhaust port. There are various types of distributions systems and we will explore these in later discussions. Once the water enters the top of the tower and passes through the distribution system it then travels by gravity downward. The next thing the water encounters is some type of media packing. There are various forms of media packing offered in the degasification industry and each type can offer higher performance or have the ability to deter fouling. The selection of the type, size, and volume is where the “experience, engineering and understanding of each application” comes in to play.

In the production and purification of water for industry

there are many types of different processes available to remove harmful minerals and gases from the water stream but the most effective process and most cost effective from both a capital investment and operational cost is a “Forced Draft Degasification System” (Degasifier).

Degasification is used in a wide range of water processes for industrial and municipal applications which extend from the production of chemicals to the production of semiconductors and in all applications the need to remove contaminants from the water and dissolved gases is key to achieving the end results needed in the industrial water process. Water from the ground often contains elements such as calcium carbonate, manganese, iron, salts, hydrogen sulfide, and sulfur just to name a few of the basic contaminants and these naturally occurring elements can cause serious damage and consequences to process equipment such as boiler systems, piping, membranes, and cation and anion exchange resins used in the demineralization process.

Calcium carbonate can dissolve in water under certain pH ranges forming carbonic acid and releasing carbon dioxide (CO2) gases. These gases are not only very corrosive to equipment like boiler feed systems and boiler tubes but also attack the actual resin beds found in cation and anion softening and demineralization system causing an increase in regeneration and chemical consumption and resin bed replacement.

By incorporating a Force Draft Degasification system you can remove dissolved gasses

like CO2 and hydrogen sulfide (H2S) to as low as 99.999% and improve the cation and anion system performance, extend the resin bed life, and lower the operating cost of the water treatment process.

Quite often Forced Draft Degasification is utilized “post” treatment to also remove newly formed dissolved gases prior to entering the boiler feed system to prevent corrosion damage within the tubes and feed system and pumps. These gases are easily removed with the forced draft degasifier at a much lower cost than chemical additives or liquid cell degasification that requires higher capital cost and much higher operating cost.

The Term Sour Gas

refers to any natural gas or other gas that contains high levels of hydrogen sulfide (H2S). The H2S is typically naturally occurring and found in deposits of natural gas and when there are concentrations above 5.7 milligrams per cubic meter or 4 milligrams per cubic meter when tested under standard temperature and pressure. At these levels the industry classifies the gas as “Sour.” Of course there are variations to this classification dependent upon agency an organization.

A Sour gas is not to be confused with an acidic gas 

although one could be both a sour gas is strictly defined by having large quantities of hydrogen sulfide and is usually accompanied by having mercaptans which adds to the foul smell and odor. The term is often used in the oil refinery business and when gases contain sour gas the process to remove the hydrogen sulfide and mercaptans is referred to as “Sweetening”. The most common method to “sweeten” and remove the sour gas is by processing the gas through an “amine process” which removes the harmful gas.

Would it be possible for our odor control scrubbers to communicate with us and tell us when there are problems? Or when they need service? With the new technological revolution, we are now into this is quickly becoming a reality. DeLoach Industries is rapidly changing how water treatment and odor control and air emissions are treated with new advancements in artificial intelligence and integration into proven technologies.

Most operators will tell you that to keep and maintain an odor control system whether its Biological Vs. chemical can be quite challenging depending on the type and source of the off gas to be treated and depending on the type of chemical reagents being utilized such as acid or caustic solutions. When odor control systems such as a biological scrubber are met with a varying flow rates, corrosive gases, or spiking concentrations an odor control system can be daunting to keep in balance and operating efficiency. But what if they could think or communicate with other devices or even operators for themselves? What if they could make corrections in caustic feed rates because of ammonia (NH₃) concentration spikes, order chemicals like caustic or acid for pH control, and even inform us when they anticipate a problem for either the odor control scrubber or another critical component that it depends upon? That time has now arrived that’s to DeLoach Industries new advancements to their equipment systems.

A Biological Scrubber is a wet odor control scrubber that treats and removes contaminants from an air stream. It utilizes caustic typically to control the pH of the re-circulation solution. There are several types of odor control and chemical fume scrubbers on the market today. Each plays a role in treating noxious or corrosive gases in the industry.

When evaluating off gases that need to be treated and prior to the designing of the correct type of odor control system for a project there are several key items that should be considered before making a selection. It is best to read the article called “industrial odor control the do’s and don’t’s to refresh or learn a wider prospective on odor control scrubbers and their operational challenges. 

The first question is what is the source of the off gas or odor problem and is it corrosive, dangerous, or just a noxious odor?  A design professional should fully examine what types of contaminants are in the gas air stream to identify harmful and corrosive elements such as ammonia (NH₃), hydrogen sulfide (H₂S), or even caustic (NaOH).   Is the odorous gas that is being generated a result of a “water treatment plant”, “ waste water treatment plant”, “industrial water treatment plant”, or a “manufacturing process” operation,?  Perhaps the odorous gas is being generated from a collection systemsuch as a “lift station” or “head-works” facility?  If the odorous gas is being generated as the result of the removal of hydrogen Sulfide (H2S) from a water treatment process as found at a water treatment plant then the odorous gas can be corrosive, dangerous, and noxious and it will require either treatment utilizing reagent chemicals such as caustic.  The production of hydrogen sulfide gas (H2S) typically is the residual result from treating water and removing the H2S from a water source.   

The type of Odor Control wet scrubber selected for the treatment and neutralization of Ammonia (NH3) gases depends on several variables, including the type and source of the ammonia gas and whether or not it is “Free” ammonia and or unionized. Ammonia is a very miscible and stable molecule with solid hydrogen bonds, making it very soluble in water and difficult to treat without using a properly designed and sized ammonia scrubber. The concentrations, air flow rates, temperature of the gas stream, and chemical reagents being utilized, such as caustic to remove and then treat the ammonia, all play a significant role in the efficiency of the ammonia scrubber system. Unlike other types of “odor control scrubbers,” an ammonia scrubber is much more sensitive to variables such as the gas stream temperature because of the solubility of ammonia.

the process is called the Haber Process by combining nitrogen with air and adding pressure, you can make ammonia. It takes about 200 atmospheres of pressure, and the process varies from refinery to refinery. Still, on average, you can only make approximately 15% of ammonia during each pass which takes multiple passes to achieve the 15%. The reaction to make ammonia is exothermic when produced in a refining process. 

However, ammonia is also formed in nature in smaller quantities. Most ammonia (90%) is utilized for fertilizer production, but ammonia can be found in food, pharmaceutical products, and cleaning supplies. When ammonia gas is released into the air, it has a very noxious and pungent odor that can be dangerous to inhale, so often, odor control scrubbers are required to capture and treat the ammonia gas.