Catalytic Gas Infrared: Not Just for Paint Curing
Gas catalytic infrared heaters often are used in the finishing industry to cure and gel paint and powder coatings. While well-suited for finishing, gas catalytic infrared also can be used for many other applications, including in explosive environments.
The oil and gas industry is home to many gas catalytic infrared applications -- especially in the cold climates of northern Canada, where oil and gas are the premiere resources. The heaters are used to maintain the oil or gas flow in production, even in temperatures as low as -60 to -70oF (-51.1 to -56.7oC). Because radiant heat is absorbed much more efficiently than convected heat, infrared equipment is the best choice to heat large production equipment. And, the natural gas available just under the surface provides a local fuel source not dependent upon electrical power or gas storage.
One unusual application where catalytic heaters have been used is pipelines. Transporting oil and gas between provinces and states and between countries has spawned a huge piping network across North America. Catalytic heaters are used at pipeline joints, where sections of pipe are welded together. As the area most susceptible to corrosion and, hence, premature failure, welded joints are a critical part of the pipeline system.
One method used to protect the welded joint is a polyolefin or mastic sleeve that is heat-shrunk into place. The process involves sandblasting the joint, preheating it to approximately 150oF (66oC), coating the area with an epoxy-type paint, and heat shrinking the sleeve in place. Until recently, heating was achieved using a tiger torch. Because it was done manually, the heating results at each joint varied considerably depending on the operator's technique and fatigue level. The amount of heat applied around the joint rarely was uniform, and the results from joint to joint were inconsistent. Using the tiger torch method, a reject rate of one in ten was not unusual. Common problems included an incomplete cure on the epoxy or improper mastic flow inside the polyolefin sleeve, preventing the sleeve from properly adhering to the pipe. Over time, as the pipe expanded, contracted and moved, the sleeve worked loose. Adding catalytic gas infrared radiant heat to this process has made a dramatic improvement.
In this application, the catalytic heaters are spaced evenly around the pipe to provide uniform heat. Once the pipe is heated, the catalytic unit opens up like a clam shell and is rolled down the pipe to the next joint. With a near zero reject rate and improved process times, this sleeve-application method has resulted in significant savings.
Infrared heating also is used to pre- and post-heat welded joints. This application, like many, grew out of need: During the winter of 1996-1997, one of the coldest on record, TransCanada Pipelines decided to try using steel with increased carbon content in some pipeline tie-ins in southern Manitoba, just north of North Dakota. Because of the steel's less ductile nature (due to the higher carbon content), the pipes had to be heated at the areas to be welded. Special units were built and used to keep the joints warm, especially in a post-heat function. As pipelines have such large mass, they act like a large heat sink, quickly draining heat away from the weld. Given the cold weather conditions, without post-heating, weld shrinkage and subsequent cracking would have occurred.
The catalytic heaters were put in place approximately 10 min. prior to the start of welding, left on during welding, and removed about an hour after the weld was complete. The heaters raised the pipeline's temperature to approximately 300oF (149oC) in 20 min., in an ambient environment as cold as -25oF (-31.7oC). By controlling gas flow to the heater with a pressure regulator, it was possible to maintain the required surface temperature throughout the heating period.
As you can see, gas catalytic infrared heaters have many uses in the gas and oil industry. In each example, the heating system improved reliability and extended product life.
Sidebar:A gas catalytic infrared heater is explosionproof by nature of its construction. The stainless steel housing is formed to size and welded gas-tight on the corners. The heater is composed of a series of layers, beginning with the gas dispersion tube, which evenly disperses gas into the heater. Next comes the gas dispersion plate, which allows the gas to disperse uniformly. Above this is a layer of insulation, followed by another layer of insulation with high heat-resistant characteristics to withstand temperatures to 2,300oF (1,260oC). Next is the electrical preheat element, or calrod, which preheats the catalyst bed. Its face is a wire mesh protection screen held in place by a gas-tight bezel. A safety shutoff valve and thermocouple are mounted on back.
The Basics of Gas Catalytic Heaters
How does it operate? First, the preheat element is energized by a power supply from a local utility or, in a remote location, a 12 V truck battery. The element preheats the catalyst bed to approximately 250oF (121oC) -- the temperature at which the catalytic pad will sustain a chemical reaction with the fuel gas to convert it to heat energy. The reaction is self-sustaining, and it is governed by the secondary catalyst to prevent it from running out of control.
If the heater is not electronically controlled -- as in many remote installations -- fuel enters the heater via the safety shutoff valve. The thermocouple senses the pad temperature and sends a millivoltage signal that holds the safety shutoff valve open after it has been depressed.
On electrically controlled systems, the operating principle is similar. Once the minimum reaction temperature is reached, the thermocouple signals the control panel to open a solenoid valve, thereby releasing gas into the heater. The gas enters the heater and is dispersed through the catalyst bed. At the same time, oxygen from the air diffuses through the catalyst pad from the front. Where the gas and air meet, oxidation occurs, and catalytic combustion (which is below the ignition temperature of the gas) occurs. After the reaction is fully established, the preheat element is disconnected and the heater continues to operate at surface temperatures up to 1,100oF (593oC).