Cutting Fuel Chemistry

Hydrogen-based fuel offers new alternative.

By Michael B. Fouse

Acetylene enjoys its popularity in the cutting gas industry partly because it was the first in the market, but also because it is consistently a better performing product in metal cutting. Yet there are many newer fuels that have higher flame temperatures, or a higher BTU value. Most industry professionals will tell you that the cut speeds are not dramatically affected by the various “incremental” fuels. The fact is that all of these fuels are hydrocarbon-based and all of them share a very similar chemistry.

It is the lack of true innovation in the oxy-fuel industry that has been a catalyst for the development of new technologies for metal cutting, such as water jets, laser cutting, plasma cutting, and a hydrogen-based cutting fuel. All of these technologies will play a significant role in the future of metal cutting operations. Water jet cutting and laser technologies provide fantastic results in metal cutting, increasing performance by cutting sharper angles, achieving tighter tolerances, and doing so without creating slag or vapor issues. However, these technologies are capital intensive, which has slowed market acceptance. Plasma cutting technology has enjoyed much of its success, particularly in metal less than 1-1/2 inches thick, as a result of its high cut speeds and low operational costs. Plasma tables typically require more maintenance than traditional oxy-fuel tables, resulting in more down time and higher replacement parts costs. In addition, for cut thickness above 1-1/2 inches, they tend to develop undesirable top edge roll-over.

Hydrogen-Based Fuel
Until recently, hydrogen was used primarily in underwater oxy-hydrogen torches and for welding and brazing. Hydrogen has potential uses in many industries, including metal cutting. A new hydrogen-based fuel was recently created as a by-product from plasma arc technology that destroys hazardous liquid wastes, such as used glycols and oils. This new cutting fuel is suited to cut steel up to 12 inches thick and has many characteristics that could make a significant impact on the future of metal cutting. The chemistry of this fuel is unlike all the other metal cutting gases—it is not a hydrocarbon and produces no hydrocarbons when it is burned.

This new fuel was introduced to a select few end-users in the spring of 2002 in order to develop real-life data to determine whether the “stabilized hydrogen” fuel could compete with, or even outperform, other hydrocarbon-based cutting fuels in a variety of cutting applications. In these real industry applications performed by independent professional burners, the hydrogen-based fuel was proven to cut an average of 40% faster than propylene using the same tips, torches and cutting table, and cutting the same mild steel. At the same time, the finished cuts were of higher quality with little or no finish work required and little or no slag or top-edge rollover.

The reason for the increase in cut speed and quality with the new hydrogen-based fuel lies in its chemistry. It is composed primarily of hydrogen and, for that reason, it has a very high flame speed and thermal conductivity, which gives it some of the same attributes that make acetylene so popular. This allows the heat energy of the gas to be concentrated in the primary cone, resulting in a narrower kerf, less plate warpage, better cut quality, and smaller heat affected zone, with similar preheat times. Although the BTU content of the gas is significantly less than hydrocarbon-based fuels, the BTU's are used more effectively and efficiently, not wasted in the secondary cone.

Safety
From a safety viewpoint, the new hydrogen-based fuel has demonstrated real benefits. As an example, acetylene use is limited to plate material up to about 2 inches because it becomes unstable above 15 psi. However, the stabilized hydrogen fuel can be used safely with pressures exceeding 40 psi, thus making it an effective and efficient cutting fuel for thicker material. This added stability was demonstrated when a leading equipment manufacturer performed flashback testing at its corporate testing facility and found that it would not flashback in a torch that was overheated to the point of destruction. The fuel has a narrower range of flammability in air and oxygen and a higher ignition point (approximately 1100° F).

Unlike any of the other fuel gases, this new cutting fuel does not produce any hydrocarbons when burned, so its emissions are much safer and healthier for employees, and since it is created from the remediation of hazardous wastes and displaces petroleum-based fuels, it is good for the environment. It just may be that this new gas could replace acetylene as the primary fuel in the industry.