1. WHY IS AMMONIA NEEDED?
Need For Ammonia On Electric Utility Sites
Nitrogen oxides ( NOx) emissions from power plants are heavily regulated because NOx reacts in the atmosphere to form ozone which is harmful to plants, animals and humans. One of the important methods for removing NOx derived from the burning of fossil fuels embodies their conversion to inert nitrogen gas and water vapor by reduction processes such as Selective Catalytic Reduction (SCR) or Selective Non-Catalytic Reduction (SNCR). Two main reductant materials have achieved commercial acceptance for this purpose: ammonia and urea. Ammonia is superior to urea for SNCR in several important aspects, and is required for SCR applications. The disadvantage is that ammonia presents substantial environmental and operating hazards and risks because of its high volatility and noxious nature.
Why Avoid Ammonia?
Numerous accidents that have resulted in deaths have occurred in the transport and handling of ammonia (Noroozi, 1993). Additionally, local authorities have placed restrictions on its use in many locations. Urea, on the other hand, is a stable, non-volatile, environmentally benign material that is safely transported, stored and handled without such risk. This is the material, which is stored and transported for use with the U2A™ system.
- Urea poses less risk in the workplace
- Using urea, the permitting process is easier
- Anhydrous and aqueous ammonia (>20%) are classified as regulated toxic substances by the EPA (40 CFR Parts 9 and 68)
- Anhydrous ammonia is a "highly hazardous chemical" under OSHA 29 CFR Part 1910
- Many local governmental authorities have imposed use restrictions
- Ammonia is a highly volatile and noxious material
- AMMONIA IS THE HAZARDOUS SUBSTANCE THE RELEASE OF WHICH IS MOST OFTEN REPORTED AND IS THE SECOND MOST LIKELY TO RESULT IN INJURY.
Here is why:
| Physiological responses: | ppm in air |
|---|---|
| Least detectable odor | 53 |
| Maximum concentration - prolonged exposure | 100 |
| Maximum concentration - short exposure | 300-500 |
| Least amount causing immediate throat irritation | 408 |
| Least amount causing immediate eye irritation | 698 |
| Least amount causing coughing | 1720 |
| Dangerous for even short exposure | 2500-4500 |
| U2A™ Process | Anhydrous Ammonia | |
|---|---|---|
| NH3 use rate | 1000 lb/hr NH3 use rate | 1000 lb/hr NH3 use rate |
| Storage | 15 days storage of urea | 15 days storage of ammonia |
| NH3 present | NH3 in system < 100 pounds (Under EPA reportable spill threshold) |
NH3 in system> 100 pounds (Most spills will be reportable to EPA) |
| Evacuation Zone | Risk area catastrophic spill ~50 yards radius |
Risk area catastrophic spill ~3 miles radius |
How It Works
In the U2A™ process, dry urea is dissolved to form an aqueous solution, which is fed to an in-line reactor at a rate to produce the required ammonia. Heat is applied to carry out the generation under controlled conditions to maintain a constant ammonia gas supply pressure. The process produces a gaseous mixture of ammonia, carbon dioxide, and water. The process requires no storage of ammonia except for the small amount in the reactor in which it is at an active concentration of less than 2%, significantly less than the 30% concentration of standard commercial aqueous ammonia.
The process is automated, easy to control and far safer than standard ammonia supply systems. The only chemicals required are urea and water.
