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From oil and gas to fertilizer and air emission reduction

 

September 28, 2024

 

In our modern world, the petroleum industry plays a crucial role in producing compounds that not only fuel our vehicles but also feed our crops and clean our air. Two such versatile compounds are ammonia and urea. Let's explore their journey from natural gas to their various applications, including fertilizers and emission control.

 

From Natural Gas to Ammonia

 

The process begins with natural gas, primarily composed of methane. To produce ammonia, we first extract hydrogen from natural gas through steam reforming. This involves reacting natural gas with high-temperature steam, resulting in hydrogen and carbon monoxide. The carbon monoxide is then further processed to produce additional hydrogen and carbon dioxide.Once we have hydrogen, it's combined with nitrogen from the air using the Haber-Bosch process. This reaction occurs under high pressure and temperature, typically around 752-842°F (400-450°C), with the help of an iron catalyst. The result is ammonia (NH3), a compound that serves as the foundation for various nitrogen-based fertilizers and other applications.

 

Ammonia + CO2 = Urea

 

Urea production cleverly utilizes the carbon dioxide generated during the steam reforming of natural gas. Ammonia and carbon dioxide are combined under high pressure and temperature to form ammonium carbamate, which then decomposes into urea and water:

 

2NH3+CO2→CO(NH2)2+H2O

 

This process not only produces a valuable product but also helps mitigate some of the CO2 emissions from ammonia production.

 

Ammonia and Urea as Fertilizers

 

Both ammonia and urea play crucial roles as nitrogen fertilizers in agriculture worldwide.

 

Anhydrous ammonia, containing 82% nitrogen by weight, is typically injected directly into the soil. It quickly reacts with water to form ammonium (NH4+), which is readily available for plant uptake and is held by soil particles, reducing the risk of leaching.

 

Urea is the most widely used nitrogen fertilizer globally, accounting for more than 50% of nitrogenous fertilizers. It contains 46% nitrogen, making it a highly concentrated and cost-effective option for farmers. When applied to soil, urea undergoes hydrolysis:

 

(NH2)2CO+H2O→urease2NH3+CO2

 

​The resulting ammonia can then be converted to ammonium, which plants can absorb.

 

Emissions Reduction in Power Plants

 

Both ammonia and urea play significant roles in reducing harmful emissions from power plants, particularly nitrogen oxides (NOx).

 

Ammonia is used in Selective Catalytic Reduction (SCR) to reduce NOx emissions. It's injected into the flue gas stream and reacts with NOx over a catalyst, converting it into harmless nitrogen and water vapor:

 

4NO+4NH3+O2→4N2+6H2O

 

This technology can reduce NOx emissions by up to 90%.

 

Urea is used in Selective Non-Catalytic Reduction (SNCR), where a urea solution is injected into the high-temperature region of the boiler. It decomposes to form ammonia, which then reacts with NOx:

 

(NH2)2CO+H2O→2NH3+CO2
2NH3+2NO+12O2→2N2+3H2O

 

SNCR can reduce NOx emissions by 30-50%, providing a cost-effective option for smaller power plants or as a complementary technology to SCR.

 

High-Purity Urea for Diesel Exhaust Fluid

 

Urea also finds application in Diesel Exhaust Fluid (DEF), also known as AdBlue in some regions. DEF is a solution of 32.5% high-purity urea in deionized water. When injected into the exhaust stream of diesel engines, it breaks down into ammonia and CO2. The ammonia then reacts with nitrogen oxides (NOx) in the exhaust, converting them into harmless nitrogen and water vapor.

 

This technology, known as Selective Catalytic Reduction (SCR), significantly reduces NOx emissions from diesel engines, helping meet stringent environmental regulations.

 

Sulfur Removal and Fertilizer Production

 

Refineries face the challenge of removing sulfur from various waste streams to meet environmental standards and protect equipment. The primary method for this is the Claus process, which converts hydrogen sulfide (H2S) into elemental sulfur.

 

The process works as follows:

    1. H2S is partially combusted to form sulfur dioxide (SO2).

    2. The remaining H2S reacts with the SO2 to produce elemental sulfur and water vapor.

    3. This reaction occurs over multiple stages, often using catalysts to improve efficiency.

 

The elemental sulfur produced can then be used in various applications, including fertilizer production. Sulfur is an essential plant nutrient, and sulfur-containing fertilizers help improve crop yields and quality.

 

Closing the Loop
 

It's fascinating to see how the petroleum industry has developed processes to turn potential waste products into valuable resources. By converting natural gas into ammonia and urea, and by recovering sulfur from waste streams, refineries not only reduce their environmental impact but also create products that contribute to food security and cleaner air.The dual role of ammonia and urea in both agriculture and emission control demonstrates a remarkable synergy. These compounds not only help feed the world's growing population by boosting crop yields but also contribute to cleaner air by reducing harmful emissions from power plants and diesel engines.

 

As we continue to seek more true, economically sustainable practices in industry and agriculture, these interconnected processes serve as an example of how waste reduction, product diversification, and environmental protection can go hand in hand and provide true, sustainable operations. The versatility of ammonia and urea will likely play an increasingly important role in balancing our need for food production with environmental stewardship in the years to come.