What is an exothermic gas generator?
An exothermic gas generator produces protective atmospheres by burning a controlled mixture of air and fuel gas in an insulated firing chamber with a top mounted burner firing downward into a water sump to quench the flame. Surface® Combustion named this exothermic gas with the tradename of DX® gas.

How does the DX® generator differ from endothermic generators?
DX® exothermic generators involve an insulated firing chamber with combustion, while endothermic generators react fuel and air over a catalyst with heat input. The materials do not provide detailed technical comparisons between the two types.

What size DX® generator do I need for my operation?
DX® generators range from 4,000 CFH to 25,000 CFH with specific models: DX-4M (4,000 cfh maximum, 2,000 cfh minimum), DX-6M (6,000 cfh maximum, 3,000 cfh minimum), DX-8M (8,000 cfh maximum, 4,000 cfh minimum), DX-10M (10,000 cfh maximum, 5,000 cfh minimum), DX-15M (15,000 cfh maximum, 7,500 cfh minimum), DX-20M (20,000 cfh maximum, 10,000 cfh minimum), and DX-25M (25,000 cfh maximum, 12,500 cfh minimum). All units feature 2:1 turndown capability.

What is the typical composition of DX® gas?
The generator provides a wide range of product gas compositions by varying air/gas ratio. Rich exothermic contains approximately 10% CO and 10% hydrogen, while lean exothermic contains approximately 4% CO and 4% hydrogen.

What fuel types can be used in DX® generators?
Natural gas and many other fuels may be used to make DX gas. Multiple fuels may be used to create DX gas. Air and fuel each have direct reading flowmeter with air-fuel ratio manually set by variable orifice located in fuel gas line.

What heat treating processes can use DX® generated atmospheres?
DX® generators support annealing, blanketing, bluing, brazing, bright annealing, ferritic nitrocarburizing (FNC), normalizing, purging, sintering, stress relieving, and tempering.

Can I produce both rich and lean exothermic atmospheres with the same generator?
Yes, many customers want the flexibility of higher combustibles in the range of 10% CO and Hydrogen (rich exothermic) AND lower combustibles in the range of 4% CO and Hydrogen (lean exothermic). Surface Combustion can offer both capabilities in the same generator with a simple change of the burner air/gas ratio.

Why does the product gas require multiple stages of drying?
The quenched gas is at approximately 100 degree dewpoint at the initial step which is too damp for most applications. First stage drying happens when the DX gas is passed through an integral refrigerant based direct expansion chiller which drives the gas dewpoint down further into the range of 35 to 40 degrees. Several applications in electric motor application require a third stage of drying using desiccant technology to drive the moisture down further to approximately 20 degrees.

How does the cyclone separator improve gas quality?
Product gas spins and cools within cyclone while water condenses out from it. Condensate is transferred to recirculation condensate sump. DX gas leaves cyclone with a dewpoint of approximately 100°F.

How does the annular cooling system work?
The annular cooler is formed by the space between the outside of the combustion barrel and the inside of the generator casing. Cooling water moves counterflow to product gas and is filled with high surface area stainless steel rings to maximize contact between water and gas. This unique cooling system minimizes required floor space and eliminates the need for a hot crossover pipe between the combustion chamber and the heat exchanger.

Can DX® generators be automated for demand-based operation?
Yes, optional automatic turndown systems are available and can be tied to the automatic vent relief regulator to reduce DX gas supply based on demand.

What safety features are included with DX® generators? Standard safety features include integrated pilot and dual flame sensors in the premix tunnel burner system, and safety aids in accordance with NFPA 86 standards.

What is the difference between water-cooled and air-cooled options?
Water- or air-cooled recirculating condensate system and water- or air-cooled DX chiller system are available as optional systems.

How does the recirculating condensate system improve performance?
Water in sump can be cooled by water- or air-cooled heat exchanger, which lowers product gas oxygen concentration to approximately 75 ppm.

What maintenance is required for DX® generators?
The combustion barrel has an integral cover plate that bolts to generator casing to easily remove barrel for maintenance. The stainless steel construction minimizes corrosion.

How does the stainless steel construction benefit long-term operation?
Stainless steel construction of the casing and combustion barrel minimizes corrosion. The combustion barrel is lined with castable refractory to maximize inner barrel temperature.

Can DX® generators operate continuously for extended periods?
DX generators are designed and intended to run and run with minimal downtime. Controls technology at the generator are dewpoint sensor or oxygen probe based.

What technical support is provided with DX® generators?
Surface Combustion provides start-up assistance and operator training. DX generators are shop tested prior to shipment.

What industries typically use DX® exothermic gas generators?
DX® generators are used widely in the pipe, tube, wire and motor industries, as well as many annealing, normalizing and bluing applications.

Can DX® gas be further refined for specialized applications?
Yes, modifications can be made to further refine product gas to create NX® and HNX® gas. Additional refining equipment is available to reduce dewpoint or create NX® or HNX® gas.