Ammonia Dissociators

Ammonia is comprised of two elements: Nitrogen and Hydrogen. An Ammonia Dissociator or Ammonia Cracker, as it used to be called, is designed to separate or "crack" anhydrous ammonia into its constituent components; to "dissociate" the elements from each other. The resulting gas consists of 25% nitrogen and 75% hydrogen. This gas is used in the bright annealing of high or low carbon steels, chrome tool steels, stainless steels, nickel alloys, copper and copper alloys where a high hydrogen content is necessary in the furnace atmosphere. It's also used to provide an environment in which the sintering of powdered metal is done or to copper braze ferrous metals or to braze stainless steel without having to use special brazing alloys or brazing fluxes.

Two associated characteristics of ammonia dissociation which are of extreme importance are that clean, metallurgical grade, anhydrous ammonia contains virtually no water and no oxygen. When ammonia vapor is dissociated the resulting gas mixture is extremely dry, with a dew point of typically -40 F to -60 F. Gas this dry usually requires no further dehydration prior to use and the absence of oxygen ensures the prevention of scale and discoloration on the finished product.

A Thermal Dynamix ammonia dissociator is a remarkably simple, durable and efficient machine which achieves virtually 100% dissociation of a clean, dry supply of anhydrous ammonia with very few moving parts and only the energy necessary to complete the dissociation process.

Available Sizes

Thermal Dynamix ammonia dissociators are available, either electrically heated or gas fired, in the following nominal sizes (CFH):

500 cfh (Electrically heated only)
1,000 cfh (Electrically heated only)
2,000 cfh (Electrically heated only)
4,000 cfh (Electrically heated only)
6,000 cfh (Electrically heated only)
8,000 cfh (Electrically heated only)
12,000 cfh (Electrically heated or gas fired)
16,000 cfh (Electrically heated or gas fired)

We also have designs for dissociators of up to 32,000 cfh capacity either electrically heated or natural gas fired.

Shown here is our Model AD10E; a 1,000 cfh electrically heated unit.

This is the AD60E;
electrically heated 
6,000 cfh ammonia dissociator

Catalysts

We use 1/2" spherical, nickel catalyst in the Thermal Dynamix ammonia dissociator retort. This enables good packing density within the retort which ensures good performance and exceptionally low residual ammonia levels in a compact configuration.

While the actual residual ammonia levels may vary with specific installation circumstances, it is not uncommon for a standard Thermal Dynamix ammonia dissociators to produce residual ammonia levels below 20 ppm.

Although we recommend 1/2" spherical catalyst for the Thermal Dynamix atmosphere generators we do supply nickel (or iron) catalyst in other configurations such as 3/4" and 1" cube, and 3/4" and 1" spherical.

Configuration

The Thermal Dynamix dissociator uses a vertical retort configuration and is available in either electrically heated or, for units of 6,000 scfh or larger capacity, heated by natural gas.

Thermal Dynamix dissociators are typically air cooled. Supplemental water cooling of the process gas is available if the need exists for lower gas output temperature.

Thermal Dynamix ammonia dissociators are usually configured to run with an internal system pressure of about 5 psi. We can build (and have built) high pressure systems with retorts designed to operate up to 30 psi but discourage high pressure systems unless there is no alternative. The primary reason not to go to a high pressure system is that the dissociation process is slowed under elevated pressure and the residual ammonia levels in a high pressure system are usually greater than those in a low pressure system. Another consequence associated with high pressure systems is the cost attendant to building a retort designed to constrain the high pressure in a high temperature environment.

Left side of an AD10E

Inside the panel enclosure of an AD10E

Two AD80E's; electrically heated 8,000 cfh ammonia dissociators

Front view of an AD10E dissociator

Design Features

Thermal Dynamix dissociators are generally designed for indoor installation but can be configured for outside installation and operation. The design of the Thermal Dynamix dissociator assumes a clean, dry supply of anhydrous ammonia vapor (less than 2ppm water; 2ppm oil and no sulfur) at a pressure not exceeding 35 psig and a temperature of at least 50 degrees F. We also assume the equipment is to be installed on a reasonably smooth, level and non-combustible floor. Side clearance of at least 24" should be provided for servicing and the unit should be accessible by forklift on at least one side.

The Thermal Dynamix dissociator uses a vertical retort configuration with silicon carbide heating elements. We believe this to be the best, simplest and most durable configuration; for several reasons:

1. A vertical retort ensures uniform catalyst packing density. There is no opportunity for the catalyst to settle to the bottom of a horizontal tube leaving a clear channel, free of catalyst, at the top. The absence of such a clear, open channel significantly reduces residual ammonia amounts. We normally expect residual ammonia levels, for our standard low pressure systems, to be below 50 ppm at capacity, it is not uncommon for Thermal Dynamix standard low pressure dissociators to operate with residual ammonia at levels well below 20 ppm.

2. A vertical retort won't "sag" under load. The working temperature in the retort chamber of a dissociator is generally in the 1750F to 1900F range. At this temperature virtually any material may eventually begin to acquire a "load set" or sag between supports. Because a vertical retort is uniformly supported around its entire circumference it isn't subject to this sag. A horizontal retort will begin to exhibit a pronounced sag or "belly" as it ages under the temperatures required for it to function. A vertical retort will simply elongate as it ages and growth clearance is provided at the bottom of the Thermal Dynamix retort chamber to accommodate such growth.

3. Because a vertical retort doesn't sag but remains symmetrical as it ages, the heating of a vertical retort remains uniform over its life. When a horizontal retort begins to sag, invariably one part of the retort surface will approach, and may contact, a heating element while its opposite side will move away from its corresponding element. A vertical retort maintains its heating element clearance even as it ages.

4. We've also given a great deal of thought to accessibility. A vertical retort configuration is very convenient. Even though a Thermal Dynamix dissociator is so durable and simple that it doesn't need much service there will come a time when maintenance is necessary. To accommodate that rare event we have top mounted both the heating elements (of the electrically heated unit) and the retort. When either does need service access is quick and easy. You don't have to remove one to get to the other. A vertical retort configuration allows either a single heating element (or the whole set) to be removed and replaced without disturbing the retort or, conversely, allows the retort to be removed and replaced without disturbing the heating elements.

5. Silicon carbide elements provide greater heat density than available with metallic elements. They are more compact, easier to install and replace, less expensive and generally longer lived than metallic element systems. An added benefit, in most cases, is the elimination of an electrical transformer (although a very large dissociator may still require a transformer).

Thermal Dynamix retort chambers are surrounded by 10 inches of high performance, vacuum formed ceramic insulation. This means heat goes into the chamber and the process, not the room. The uniform density of the ceramic fiber eliminates hot spots. The shell temperature of a Thermal Dynamix dissociator is significantly cooler than others.

Thermal Dynamix dissociators are well instrumented. You don't have to guess about what's going on inside. Pressure gages on the retort(s) and heat exchanger(s) give advance warning of the need to schedule maintenance.

And finally, Thermal Dynamix dissociators are simple. The electrically heated dissociators have no pumps, motors, fans, blowers or other moving parts to wear, make noise or maintain.