White Paper | Confidential and Proprietary | March 2012

Urea Sourcing Issues

Dry urea is an available commodity on a worldwide basis, with many off-shore urea production facilities being 

located near economical sources of natural gas, which is a key raw material required for urea production. Once 

dry urea is manufactured, it is shipped worldwide to meet the demands of a wide range of markets. 

Solid commercial grade and agricultural grade dry urea is very hygroscopic, and can create a storage and handling 

problems if the dry urea is not manufactured with an anti-caking agent. Dry urea is also very friable and can

break down into a powder during storage and handling. The powder has a high surface area, which is even more 

hygroscopic. Untreated dry urea exposed to moisture or even in humid environments will stick and compact 

during shipment, creating shipping and handling problems.

In order to prevent the problems with handling dry urea, manufacturers will add a small amount of conditioning 

agent to the hot urea liquor. This urea liquor is an intermediate product of the urea production process. The 

conditioning agent is a formaldehyde-based additive, which is consumed in a polymer reaction to form to a 

methylenediurea (MDU) coating. The MDU is what binds the dry urea together and acts as an anti-caking agent 

for the dry urea once it is made into prill or granular form. Most MSDS sheets for dry urea reference MDU, since 

when the hot urea liquor and conditioning agent are added, the formaldehyde is consumed in the reaction. The 

MDU is not a threat to the environment or a personnel hazard.

Some urea manufacturers have marketed a "formaldehyde free” urea product (FF). The 70% urea liquor is 

typically taken right from the urea production process as an intermediate product. 

Whether shipping by truck or rail, the hot 70% liquor will lose about 1.5°F per day in transit. To avoid 

crystallization of the hot liquor, its temperature needs to be maintained above 135°F. Unfortunately, hot urea 

liquor also undergoes an isomer shift to ammonium cyanate that liberates copious amounts of free ammonia, 

which can be potentially hazardous. The shift is irreversible and relentless, and the chemical reaction accelerates 

with increasing temperature. At 135°F, the reaction is rather slow, but at 150°F, it moves at a quicker rate. The 

principle can be identified that urea liquor of increasing concentration takes higher temperatures to keep it in 

solution, and that higher temperatures accelerate the rate of conversion from urea to free ammonia. 

As a result, rail shipments of FF urea have proven to be quite challenging. Due to the uncertainty with rail 

delivery times, shipping the product at higher temperatures in order to avoid crystallization may solve one 

problem, but may create an even larger problem. Truck shipments where the product can be delivered in a day 

or two have been the practical limit of shipping 70% urea liquor. A 60% or 50% urea solution can be created 

from the urea liquor, which can then be delivered via rail. These concentrations would involve dilution prior to 

shipment, and would add to the shipping costs of the product. 

FF urea may be a good economic choice based on the jobsite proximity to the FF source, however, dry urea with 

MDU has more shipping flexibility, and a result, more worldwide sources of the product are available. Dry urea 

can be solutionized at individual plant locations or at regional production facilities to any required concentration. 
White Paper | Confidential and Proprietary | March 2012

Urea Quality Impact on Fuel Tech Processes

Fuel Tech’s NOxOUT SNCR/RRI systems, as well as the NOxOUT ULTRA equipment are both completely 

insensitive to MDU dry urea sources, or for FF urea sources. This includes any urea solutions created by 

solutionizing dry urea, or by the dilution of FF urea. 

The SNCR system typically uses a 50% urea solution as the base feedstock. Prior to injection into the furnace to 

reduce NOx emissions, the urea solution is typically diluted down to levels below 25% concentration prior to 

injection. The final urea concentration is determined during final startup and optimization, where system 

performance is optimized while trying to minimize urea solution consumption. For the RRI systems, the urea 

concentration is usually 30-50% at the point of injection.

Since dilution water from the plant site is used in both systems described above, there is a water quality 

specification associated with the systems to ensure that the dilution water does not cause pluggage of the 

system or loss of NOx reduction performance. In many cases, plants do not have dilution water which is of 

boiler makeup water quality, and the use of some of these water sources may create problems at the plant site. 

When dilution water sources are not of boiler makeup or demineralized water quality, NOxOUT A and NOxOUT 

HP urea solutions are available from independent reagent suppliers. The NOxOUT A and HP help enable the 

systems to function properly when dilution water quality may be questionable or to provide plant flexibility in 

selecting dilution water sources. These NOxOUT end products include small amounts of two different 

concentrates, ACONC or HPCONC accordingly, which are mixed in by the licensed reagent suppliers to create the 

final urea solution products prior to delivery to the jobsite. 

Unstabilized urea solution can be used where there is high quality dilution water available at a plant site. All of 

the urea solutions, whether unstabilized urea solution, NOxOUT A or NOxOUT HP, are not affected by the source 

of the urea, whether the urea came from a dry source which had MDU, or whether it the urea started from a 

“formaldehyde free” product. 

The NOxOUT ULTRA process will generate ammonia on the plant site for use with an SCR system to reduce NOx 

emissions, as an alternative to either anhydrous or aqueous ammonia. There are no issues with the use of the FF 

urea solution or dry urea containing MDU, or any urea solution created using this dry urea. It is our 

understanding based on market reports, that there are other urea conversion technologies to generate ammonia 

on-site for use in SCR applications which require FF urea as the source. The use of urea containing MDU, or any 

solution created from this urea source, seems to cause potential problems within these other systems. The 

NOxOUT Ultra process provides the maximum flexibility in selecting urea sources to be used for on-site 

generation of ammonia.

Summary

Fuel Tech’s complete line of NOxOUT systems are unaffected the source of the urea feedstock, whether a dry 

urea production containing MDU, or a “formaldehyde free” urea source, providing maximum sourcing flexibility 

when meeting the urea specifications. For a list of licensed urea suppliers offering NOxOUT A and NOxOUT HP 

urea solutions for use with the SNCR and RRI systems when plant dilution water quality is a potential issue, go to 

www.ftek.com.