Exothermic
generators are inert gas generators. They are combustion type generators
which create the desired protective inert atmosphere based on the controlled
air-gas ratio. These generators are designed is such a way that they produce
cover gases for a several applications. The exothermic generators produce
cover gases from the combustion of hydrocarbon fuels. Although propane and
natural gas are the most commonly used, almost any type of combustible fuel,
like MAP gas or even liquid fuels, like fuel oil or kerosine can be used.
The exothermic generators are a very securely constructed and controlled
combustion chamber into which a accurately measured and controlled
combination of air and fuel are introduced and ignited. The mixture burns at
temperatures from 2,000F to 2,800F.
Types of Exothermic Generators
There are basically two types of exothermic generators:
- Lean exo gas generator: This generator produces lean exo-gas
comprised mainly of nitrogen and carbon dioxide (with very little
hydrogen).
- Rich exo gas generator: This type of generator produces a
rich exo-gas comprising little nitrogen and carbon dioxide and more
hydrogen component.
The lean and the rich generator are very much similar in construction
and operation. The difference between the two is the requirement of a
catalyst bed in the rich exo-gas generator to make sure that there is
complete cracking of the products of combustion. Both the gases are produced
by changing air/fuel ratio. While the first generator is suitable for
non-ferrous metals heat treatment, the second one is used for heat treatment
of steel/brazing/annealing applications. In general, natural gas is the most
common feed gas used in both the generators.
Composition of exo and lean gas
| Gas Composition |
Lean Exo |
Rich Exo |
| CO2 |
11 to 13% |
5 to 6% |
| CO |
0.5 to 1.5% |
11 to 12% |
| H2 |
0.5 to 2% |
12 to 13% |
| N2 |
Balance |
Balance |
The process
The air/fuel mixture in an exothermic generator can be adjusted. This is
done within limits on each type of generator from leaner (which means more
air) to richer (which means more fuel). Under controlled conditions, the
generator burns fuel gas and air to produce an exothermic gas consisting of
hydrogen, carbon monoxide, carbon dioxide, water and nitrogen. When the
combustion process is completed, the gas, now depleted of any oxygen, is
cooled and sent to its intended use. Sometimes the gas is dried to a very
low dew point. At times it is compressed. But most of the time the gas is
used as it is produced without further finishing. The gas thus produced
produce a protective atmosphere used for many processes including annealing,
brazing, and normalizing. In applications where a lower dew point is
required, refrigerant or desiccant dryers can be utilized.
Applications of Exothermic Generators
The gas that is produced from exothermic generators are used in many
applications like as follows:
- Used as a non-oxidizing atmosphere in the heat treating of metals
like aluminum and copper.
- Provides a carburizing atmosphere for some metals.
- Provides an inert and explosion-proof environment to mix chemicals,
prevent combustion or formulate flammable recipes.
- Annealing copper and/or aluminum.
- Used in copper brazing.
Exothermic
Generator
Exothermic
Generator