Urea, with the chemical formula CO(NH₂)₂, is one of the most widely used nitrogen fertilizers. Agricultural urea normally contains 46% nitrogen or more.
In China, about 75%–80% of urea production is coal-based, while the rest mainly comes from natural gas.
There are two different routes for producing urea, but the actual urea reaction is the same:
2NH₃ + CO₂ → CO(NH₂)₂ + H₂O
In both cases, the urea synthesis section uses the same two main feedstocks: liquid ammonia and carbon dioxide (CO₂).
Route 2: Natural Gas-Based Urea
Natural gas-based urea is sometimes simply called gas-based urea.
The main difference from coal-based urea is not in the urea synthesis itself. It is mainly in the front-end process used to prepare hydrogen and CO₂.
Once liquid ammonia and CO₂ are available, the following sections are basically the same as the coal route, including urea synthesis, recovery, evaporation, concentration and granulation.
1. Natural Gas Reforming
Natural gas is mainly methane (CH₄). It is mixed with steam and sent to the steam reforming unit.
At high temperature, methane reacts with steam and produces a gas containing hydrogen and carbon oxides.
The gas then goes through purification and separation. Hydrogen is prepared for ammonia production, while the CO₂ is recovered and sent to the urea section.
Compared with coal gasification, the front-end process is relatively straightforward and there is no large amount of coal ash or solid gasification residue to deal with.
2. Purification and Ammonia Production
After reforming, the gas needs further purification before it can be used for ammonia synthesis.
Nitrogen is separated from air and combined with the hydrogen:
N₂ + 3H₂ → 2NH₃
The ammonia produced is then cooled and compressed into liquid ammonia.
Now the two main feedstocks for urea production are ready:
Liquid ammonia + CO₂
3. Urea Synthesis
Liquid ammonia and CO₂ are fed into the high-pressure urea synthesis system.
From here, the process is essentially the same as for coal-based urea:
Urea Synthesis → Recovery & Recycling → Evaporation → Concentration → Granulation → Screening → Packaging
So, when comparing the two routes, most of the difference is actually found before the ammonia is produced.
Advantages and Limitations of the Gas Route
Natural gas has some practical advantages as a feedstock.
The front-end process is shorter than coal gasification, and there is no coal ash or large quantity of solid coal residue from gasification.
The downside is mainly related to the cost and availability of natural gas.
In China, natural gas is generally more expensive than coal for this type of large-scale chemical production. During the winter heating season, gas supply can also become tight in some regions. When supply is restricted, some fertilizer plants have to lower their operating rate or reduce production.
Does Coal-Based Urea Differ From Gas-Based Urea?
This is a question customers often ask.
The short answer is no, not in terms of the urea itself.
Coal and natural gas are only different feedstocks used at the front end of the plant. Both are ultimately used to prepare the hydrogen and CO₂ needed for ammonia and urea production.
Once the plant has liquid ammonia and CO₂, the urea synthesis and downstream sections are basically the same.
The finished urea is the same chemical:
CO(NH₂)₂
If both products meet the same quality requirements, the fertilizer performance is not determined by whether the urea was made from coal or natural gas.
The real differences are mainly related to feedstock cost, energy consumption, plant design and operating conditions.
Important Quality Control Points in Urea Production
Several factors have a direct effect on the quality of finished urea. Three of them are especially worth watching.
1. Biuret
Biuret is formed when urea is exposed to high temperatures for an extended period.
If the temperature is not well controlled during evaporation, concentration or granulation, the biuret content can increase.
This is particularly important for foliar fertilizer. Too much biuret may cause leaf burn when the fertilizer is applied directly to plant leaves.
For agricultural urea in China, the commonly applied national standard specifies a biuret content of not more than 1.5%.
For this reason, temperature control throughout the high-temperature sections of the plant is important.
2. Moisture
Moisture is another basic but important quality factor.
If the evaporation process does not remove enough water, the finished urea will contain too much moisture. During storage, the granules can become sticky and eventually cake or form lumps.
Proper concentration and moisture control help keep the product dry and free-flowing.
3. Ammonia Loss
The ammonia recovery section is also important for both production cost and product quality.
During urea synthesis, some ammonia does not react in the first pass. It needs to be recovered and returned to the process.
If the recovery system is not working properly, more ammonia will be lost. Raw material consumption goes up, and the production cost goes with it.
In some cases, poor ammonia recovery can also result in a noticeable ammonia smell around the production area or finished product.
Urea Production Flow
The complete production routes can be simplified as follows.
Natural Gas-Based Route
Natural Gas → Steam Reforming → Hydrogen + CO₂ Recovery → Ammonia Synthesis → Liquid Ammonia → High-Pressure Urea Synthesis → Recovery & Recycling → Evaporation & Dehydration → Molten Urea → Granulation → Screening → Finished Urea
The key difference can be summed up very simply:
Coal and natural gas are different ways of preparing the raw materials. Once the process reaches liquid ammonia + CO₂, the urea production process is basically the same.
And regardless of the route, the final urea is CO(NH₂)₂, with the same basic fertilizer function when the product meets the required quality standard.
At Mingwei, we deliver more than equipment. We deliver a complete, workable system that keeps your fertilizer quality consistent, batch after batch.
That's what we mean by:
Beyond Equipment. Total Solutions.