Part 5 of Abating Hazardous Air Pollutants: Ammonia
What is Ammonia?
Ammonia is a compound of nitrogen and hydrogen. A colorless gas with the formula NH3, ammonia has a pungent smell. Ammonia boils at 33.34 degrees and must be stored under pressure or at a low temperature. Industrial ammonia is sold as either an ammonia liquor or as a pressurized and/or refrigerated anhydrous liquid ammonia transported in tanks cars or cylinders. In 2014 the global production of ammonia was 176 million tonnes. China is the top worldwide producer with nearly one-third of total production, followed by India, Russia and the United States.
Ammonia molecules have a trigonal pyramidal shape. The molecules shape allows for a dipole moment and makes it polar. This polarity allows the ability to form hydrogen bonds and makes ammonia highly miscible with water. The central nitrogen atom has five outer electrons with additional electron from each hydrogen atom. This makes a total of eight electrons or four electron pairs that are arranged tetrahedrally. Of these electron pairs three of them are used as bonded pairs leaving one sole pair of electrons. This long pair repels more strongly than bond pairs.
Where is Ammonia found?
Produced from nitrogenous animal and vegetable matter, ammonia is found in trace quantities in nature. In the form of ammonium salts, ammonia is also found in rainwater whereas ammonium sulfate is found in volcanic districts. Ammonia is secreted from the kidneys to neutralize acid. In the Solar System ammonia can be found on Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
Ammonia is manufactured from nitrogen and hydrogen in a process called the Haber Process. The Haber Process combines nitrogen from the air with hydrogen from natural gas (methane) to create ammonia. The reaction created is reversible and the production of the ammonia is exothermic. The pressure required varies from one plant to another but generally is around 200 atmospheres. As each pass through the reactor only converts about 15% of the nitrogen and hydrogen into ammonia, the blend is continuously recycled until an overall conversation of about 15% is created. As these pressures are very high the design of a plant is quite costly. Pipes, containment vessels, processing equipment all must be built to withstand extreme conditions. These pressures are also associated with excessive maintenance needs and costs.
What is Ammonia used for?
Ammonia is found in foods, fertilizers, pharmaceutical products and commercial clean products. It is estimated that nearly 90% of ammonia is used as fertilizers. When applied to soil, it helps provide increased yields of crops specifically corn and wheat. As a cleaner NH3 is mixed with water to make ammonium hydroxide which makes a general-purpose cleaner for many surfaces. Common surfaces cleaned with ammonia include glass, porcelain, ovens and stainless steel resulting in a relatively streak free shine.
Ammonias food usages are controversial and mainly used in the beef industry to destroy bacteria’s such as E. coli. Lean finely textured beef is made from fatty beef trimmings where E. coli is often created and combatted through treatment with ammonia. While the process has been deemed effective and safe by the US Department of Agriculture, consumer complains remain. From safety concerns about the process and ingestion of ammonia, to complaints about the taste and smell of ammonia treated beef, the usage of ammonia in food production is controversial. Typically, only low quality and low priced beef products are treated with Ammonia.
While Gulf Coast Environmental Systems has systems for ammonia treatment (which we will explore shortly), ammonia is also used in the remediation of other gaseous emissions. Ammonia is used in a technology called SCR (selective catalytic reduction) which is used to scrub SO2 during the burning of fossil fuels. The resulting product is converted to ammonium sulfate for use as a fertilizer. For more examples of revenue production in pollution control read our article on dry scrubber media disposal and pollution control in steel production.
Why is Ammonia a concern?
Ammonia is commonly found in nature and is widely used yet remains a concern as it is both caustic and hazardous when found in a concentrated form. It is classified by the United State Emergency Planning and Community Right-to-Know Act as an extremely hazardous substance. As a result it is subject to strict reporting requirements in regards to its production, storage and use in significant quantities. It has an explosive range in air from 16-25% by volume and is moderately toxic. It has an Immediately Dangerous to Life and Health (IDLH) concentration of 300 parts per million by volume (ppmv) with OSHA Permissible Exposure Limit (PEL) of 50 ppmv. The odor threshold for Ammonia is 5 ppmv, giving ample olfactory warning of potential danger. Although Ammonia is not a Hazardous Air Pollutant (HAP), it is regulated as a precursor to PM2.5 and PM10 Criteria Air Pollutants. This is because it reacts with acid gas pollutants to form respective Ammonium Salts in the atmosphere (such as Ammonium Sulfate or Ammonium Nitrate).
Ammonia is extremely corrosive to animals and humans. Ammonia enters the body through breathing, swallowing or skin contact and damages the body’s cells on contact. Exposure to high concentrations can cause burning of the eyes, nose, throat, respiratory tract and in extreme cases can cause blindness, lung damage and even death. When ammonia is ingested it causes burns to the mouth, throat and stomach.
How do we treat ammonia?
The most effective pollution control technology for the abatement of Ammonia utilizes a Wet Scrubber which is often called an Ammonia Scrubber. Aqueous Ammonia solutions have very high vapor pressure, which prevents plain water from being recycled in a wet, dry or packed scrubber system. The water is discarded after each pass through the air scrubber. In some instances, this may be acceptable or even desirable if the plant has a use for a solution of dilute Ammonium Hydroxide, i.e., Aqua-Ammonia. Due to the alkalinity of NH3, it is very effectively scrubbed using an acid solution. This allows recycling of the water due to the NH3 reacting to form a non-volatile Ammonium Salt.
The most common acid used in air scrubbers is Sulfuric Acid, due to its availability, low cost, and non-volatility. The product formed when Ammonia is scrubbed with Sulfuric Acid is Ammonium Sulfate, which is a common fertilizer ingredient. Thus, depending on the quantity of NH3 being scrubbed, the Ammonium Sulfate by-product may be utilized as an additional revenue stream. Ammonia air scrubbers incorporate a variety of gas-liquid contacting techniques, including packed beds, spray chambers, and water jets. In every application, GCES considers all factors in selecting the optimum design. We offer complete packages for our dry, wet or packed scrubber systems, including instrumentation and controls, skid-mounting of equipment, acid storage tanks, metering pumps, and installation.
For each application, the Ammonia Scrubber is sized and designed to meet specific customer requirements. The tail gas to be cleaned is carefully analyzed to determine the optimum design parameters and to allow for the best operating solution for each installation. After thorough analysis, GCES offers several options of fume or exhaust scrubber equipment packages based on plant equipment, local air regulations, plant locations, and other factors. Our experience in designing scrubbers for many different chemicals shall provide each customer with the assurance that the plant’s air quality will have a minimal impact on the environment.
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Additional articles in the GCES series ‘Abating Hazardous Air Pollutants’ include:
Part 2: Chlorine Abatement
Part 6: SOx, the compounds of sulfur and oxygen molecules including Sulfur Monoxide, Sulfur Dioxide and Sulfur Trioxide