Urea 46% granular vs prilled: specification, biuret, moisture and bagging for tender buyers

Urea 46% granular vs prilled is the first question in almost every fertiliser tender, and it is often answered by habit rather than specification. Both forms are the same compound with the same nitrogen content; they differ in particle size, hardness, dust and handling, and those differences decide whether a cargo is accepted at discharge.

Urea 46% granular vs prilled: the specification lines

A tender specification for urea is short. The lines that matter are nitrogen, biuret, moisture, particle size and the physical form, with the test methods stated:

• Nitrogen: minimum 46.0 % by weight on a dry basis, determined by Kjeldahl or an equivalent standard method such as ISO 5315
• Biuret: maximum 1.0 % by weight in most international tenders, determined spectrophotometrically; lower limits apply for foliar or technical grades
• Moisture: maximum 0.5 % by weight by Karl Fischer, since water drives caking in storage
• Particle size for prilled: typically 1 to 2.4 mm or 1 to 2.8 mm, minimum 90 % within range
• Particle size for granular: typically 2 to 4 mm, minimum 90 % within range, with a maximum on fines below 1 mm
• Colour and form: white, free-flowing, treated with an anti-caking agent, free from harmful substances
• Melting point around 132 °C, usually stated for identification rather than as a limit

Regulatory references vary by destination. The EU fertilising products regulation (EU) 2019/1009 sets a lower minimum nitrogen content and a maximum biuret content for urea placed on the EU market than most commercial tenders, so a cargo can be legally compliant in the EU and still fail a tender written at 46.0 % nitrogen and 1.0 % biuret. Indian and other national tenders publish their own tables; the buyer should attach the applicable one rather than refer to it by name.

Granular and prilled: where they differ in practice

Granular

Granular urea is produced in fluid-bed or drum granulators and gives larger, harder, rounder particles with higher crushing strength and lower dust. It survives multiple handlings, blends evenly with other granular fertilisers such as DAP and potash, and spreads consistently through mechanical equipment. It is the form of choice for bulk blending, mechanised agriculture and long supply chains with several transfers.

Prilled

Prilled urea is made by spraying molten urea down a prilling tower and gives smaller, smoother, slightly softer particles. It dissolves faster, which suits flooded rice and manual application, and it is the dominant form in many Asian and African tenders. It is more prone to dust and breakage under repeated handling, and more sensitive to moisture pickup, so bagging quality and storage conditions matter more.

Rule: specify the form, the particle size range and the biuret and moisture limits in numbers with test methods, and make the independent load-port certificate final. A tender that says only "urea 46 % N, granular or prilled" has left the two most expensive variables to the seller.

Moisture, caking and anti-caking treatment

Urea is hygroscopic. Above its critical relative humidity, which is roughly 70 to 75 % at common warehouse temperatures, it absorbs water from the air and the particles bond into lumps. Producers apply an anti-caking conditioner, often a formaldehyde-based or oil-based coating, to slow this. A tender should state that the product is treated, require the moisture figure at loading, and set storage and shipping terms, such as sealed holds and no loading in rain, that prevent the figure rising before discharge. Caked urea is still 46 % nitrogen, but it cannot be bagged or spread, and the receiving party will claim.

Bagging options and marking

Bag weight should be verified by the inspector at loading, and the tender should state whether weights are net or gross, the tolerance per bag, and whether the cargo is weighed by draft survey, weighbridge or belt scale. Containers of bagged urea should be sealed, with seal numbers on the packing list.

Inspection and documents for a tender

1. Appoint an independent inspector such as SGS, Intertek or Bureau Veritas at the loading port, with sampling from the loading stream and sealed retained samples.
2. Make the inspector's certificate of quality and weight final and binding on both parties, with a documented re-analysis procedure if discharge results differ beyond a stated margin.
3. Require the producer's certificate of analysis, the certificate of origin, the packing list with bag counts or draft survey report, and the bill of lading as documents under a letter of credit governed by UCP 600.
4. Specify delivery under Incoterms 2020, usually CFR or CIF, with loading and discharge ports named and laytime and demurrage terms attached.
5. State the shipment window, the quantity tolerance and who bears the cost of a nitrogen shortfall or a biuret or moisture excess, by rejection or price adjustment.

Written this way, a urea tender leaves the seller nothing to interpret and the buyer nothing to argue about at discharge.