LEARNING ABOUT AMMONIA VAPORIZERS

Choosing a heat source

Let’s take a closer look at vaporizers designed for ammonia processing.

In practice, there are four heating options available for ammonia vaporizers:

  1. Steam
  2. Thermal oil
  3. Hot air from flue gas
  4. Hot water

Note: Armstrong vaporizers primarily use steam.

There are two main process applications:

  1. Anhydrous ammonia
  2. Aqueous ammonia

Pure, dry liquid or gas is called anhydrous ammonia, while water-based solutions are known as aqueous ammonia, or ammonium hydroxide. The mechanical designs may be horizontal or vertical depending on process specifications.

Armstrong does not recommend water as a heat source for the vaporization of anhydrous ammonia due to the need for higher heat to ensure boiling of any water present in the anhydrous ammonia which is hugely hygroscopic: so much so that only one cubic foot of water can dissolve over 1200 ft3 of ammonia.

Electric vaporizers

For ease of installation, electric vaporizers are favored in power stations. Their added environmental benefits are well publicized. These electric ammonia vaporizers are sometimes called dry electric vaporizers, but that’s a bit of a misnomer. Ammonia must cover all of the elements in order to maintain controlled heat transfer from the heating elements, working at a constant flux, unlike conventional shell-and-tube heat exchangers.

Spray evaporation applications

An aqueous ammonia vaporizer is commonly used for spray evaporation.

Here’s how it works:

  • The process piping incorporates an air atomizing nozzle for the aqueous ammonia. Other vaporizer components can include an electric heater bundle in a pressure vessel, or heated combustion air, using hot flue gas as an energy source to evaporate liquid (water and ammonia).
  • In this system, aqueous ammonia is metered into the atomizing nozzle at a fixed pressure. In the nozzle, the liquid is mixed with atomizing air dispersed into a vaporization chamber as a fine mist.
  • Then, heated air enters the chamber to evaporate the mist of aqueous ammonia.

Now, how does that differ for anhydrous ammonia? Closed-loop anhydrous ammonia vaporization has small quantities of anhydrous ammonia vapor (less than 300-400 pounds per hour). Systems may be used in a closed-loop or as a pressurized tank-type vaporization system. Vaporization in this system is usually facilitated by using a heater placed inside the pressure vessel, adjacent to and beneath the storage tank.

Once-through anhydrous vaporization may require skids which incorporate Control Panels for large installations, like utilities. These produce a continuous stream of ammonia vapor for downstream consumption. Vapor flow in this system is regulated with a flow control valve placed upstream of the inlet and the flow is usually measured by a flow transmitter.

Any questions on industrial vaporizers and their specific applications involving ammonia processing? Don’t hesitate to reach out and ask.