Ammonia Vaporization: Have You Checked Your Electric Process Heater Lately?

Submitted by Patrick Bartell || Valin Corporation
on Wed, 03/06/2019
Developing a strong preventative maintenance plan for plant shutdowns and turnarounds is the best way for operators to minimize the risk of equipment failure, which can lead to unnecessary shutdowns and ultimately, higher costs.  Most of the plants we visit have incredibly strong programs outlined for maintenance on pumps, motors and compressors, among other standard equipment. They tend to have a procedure in place for inspecting, testing and easily replacing these during planned shutdowns. This is great to see. However, many plants have an Ammonia Vaporization System designed to eliminate Nitrous Oxide (NOx) emissions into the atmosphere. This system requires an electric process heater to function properly. Far too often, this heater (a crucial piece of equipment necessary to the Ammonia Vaporization System) is not part of the preventative maintenance plans --- a big mistake.

For plants that require an Ammonia Vaporization System due to the NOx being created daily, it is critical that it always be in operation. The EPA have issued regulatory mandates about NOx being released into the air. Furthermore, every gas fired power plant has one of these systems in addition to any plant where there are large boilers or furnaces.

The two types of Ammonia used in this process are Anhydrous and Aqueous. In both instances, the Ammonia is vaporized and injected into an Ammonia Injection Grid (AIG). Once this vaporized ammonia passes through the AIG, it mixes with the NOx which is then neutralized, satisfying the EPA. The key here is “vaporized” Ammonia. Naturally, this means the Ammonia must be heated to a certain temperature for it to be vaporized.  Thus, the electric process heater becomes an essential piece of equipment, although its function changes a bit depending on the type of Ammonia.

Anhydrous Ammonia is typically stored in a large 20,000-gallon tank.  The electric heater is installed beneath the tank and vaporizes the NH3 back into the top of the tank.  This results in 20 percent of the tank being maintained as vapor and 80 percent liquid.  The lines from the tank to the AIG are generally heat traced to maintain the NH3 in a vapor state all the way to the injection site.

Alternatively, because Aqueous Ammonia is only 19-23 percent ammonia (the rest water), super-heated air is created to vaporize both the Ammonia and the water. There are several heating methods used during this process: 1) Duct heaters are superheating the air and injecting it into a stream of Aqueous Ammonia and 2) Flanged immersion heaters are installed vertically into a proprietary vessel, allowing air flow over the heater and into the vessel that has NH4OH injected in it.  The heat, steam and vaporized Ammonia travel to the AIG and meet the NOx. This particular method requires the heater to operate from 650 to 750°F, a very severe duty rate for an electric heater.

Regardless of which ammonia is used, the electric process heaters are absolutely necessary in assuring the process is operational. With such a crucial process happening, one would assume there would be more care given to the essential pieces of equipment that make it run.  However, this is simply not the case. If a heater goes out unexpectedly, most operators don’t know where to turn.  If they call the manufacturer, often lead times can be more than 16 weeks. Those same companies can’t come on site to evaluate issues that could be a simple fix. This lack of preparation can result in significant costs that could have otherwise been avoided.

At Valin, we help plants, especially those with Ammonia Vaporization Processes, develop a plan and proper procedure to assess, maintain and replace their electric process heaters during a planned shutdown or turnaround. 

Valin can do complete, on-site heater audits during an outage.  Our team will come into your plant and evaluate all your heaters’ health. We’ll show you how to perform the necessary tests to determine capacity and make note of which heaters need to be replaced.
 
Part of this service also includes heater storage. A portion of the preventative maintenance plan for heaters should include having available spares.  These spares must be stored in a climate-controlled area where they are kept dry and tested on a regular basis.  If an active heater happens to go out, Valin can also temporarily patch it so it’s operational while a spare is on the way. It is troubling to see how many plants in operation have either no spares on site and/or no direct access to them elsewhere.

The Valin Team takes pride in keeping your plant running. By providing comprehensive electric process heater preventative maintenance, we’re able to meet that goal even more effectively.

Learn more about our Process Heating System Maintenance and Repair services.

Have questions? Contacts us at (866) 351-4328.

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