Fig. 1. Typical ammonia-tank installation - 12,000-gallon tank (Photograph courtesy of Airgas Specialty Gases)

My company is looking at using anhydrous ammonia to nitride gears for wind turbines. Do you have information on specifications, tanks and installation details?

First, be sure you find a supplier who is capable of supplying premium-grade (also known as metallurgical-grade) anhydrous ammonia for use in heat treating, industrial applications or refrigeration. This product has little or no water, which could contaminate your process. Look for a specification of 99.995% ammonia.

You have a couple of choices when it comes to ammonia storage. For the lowest product price, you should consider a tank of at least 10,000 gallons (Fig. 1) that holds about 43,000 pounds of ammonia. This allows you to purchase full 38,000-pound tanker trucks of ammonia. Remember, from each pound of ammonia you can get 22.5 cubic feet of vapor or (if you are using an ammonia dissociator, 45 cubic feet of DA, that is, dissociated ammonia (75% H2, 25% N2).

With a 10,000-gallon tank, you need to make sure you comply with OSHA’s Process Safety Management (PSM) and EPA’s Risk Management Plan (RMP). In most states, you must comply with these standards if you have more than 10,000 pounds of anhydrous ammonia on-site.

The second option is to stay below the 10,000-pound threshold by installing a 1,000-gallon (4,400-pound) capacity or a 2,000-gallon (8,800-pound) capacity storage tank. Pricing for ammonia into these tanks runs about 50% higher in the smaller quantities. Even with the lower inventory, you will need to comply with OSHA 1910.111 and any applicable state, city or county laws. It is critical to check with local agencies to make sure you are in full compliance with these regulations.

With regard to the installation, in most cases you need to pour a foundation for the tank, provide electricity to the tank for a side-arm vaporizer (used to maintain pressure in the tank since you will be withdrawing ammonia vapor to the process) and provide piping from the tank to your process. Most suppliers can lease the tank and valves/attachments for a nominal monthly fee depending on your ammonia consumption. You can also add a telemetry unit that allows your supplier to monitor your tank level via Internet site. You will need to install a water shower near the tank and have gas masks close to the tank. It is a good idea to provide a fence around the tank if your company does not have security. Your supplier should provide hazardous-awareness training for ammonia.

Once you are set up with the tank, you can expect relatively trouble-free operation. You should not have any maintenance issues other than an occasional paint job. The tank should be visually inspected yearly, probably by your supplier, and the pressure-relief valves should be changed every five years.