Overview

Natural gas-fired catalytic infrared is a safe, flameless heating technology which produces a uniform low intensity, non-glowing heat. This medium to long wavelength energy is readily and evenly absorbed by a wide range of materials. Catalytic heaters have been around for about 35 years, but was first applied to the plastic thermoforming industry in the 1990s by Vulcan Catalytic. Because of its reduced operating costs, it has become the preferred system for larger thermoforming machines.

Operation

When the catalytic heater is turned on it must be preheated with a tubular electric heating element for approximately 15 minutes. Once the catalyst has reached 300F, safety devices are activated and the gas enters the back of the heater. The gas contacts the hot platinum catalyst and reacts with oxygen in the air, raising the catalyst temperature to between 350F and 1000F while emitting infrared energy. Efficiency tests have established that up to 72% of the gas is converted into infrared heat. Since the reaction temperature is well below the auto-ignition temperature for natural gas (1300 F), the reaction is flameless. The catalytic reaction is established five minutes after the gas enters the heater, and the preheater is turned off.

The long wave infrared energy emitted by the catalytic heaters is optimally absorbed by materials such as plastics, and this is what speeds up heating time and reduces cycle length. The catalytic wavelengths are five to ten microns long, coinciding with the six to ten micron maximum absorption range of plastics. Electric heaters, in contrast, produce a shorter wave length of one to three microns that is absorbed less efficiently. Further, the lower temperature of the catalytic heaters produces a more uniform heating with less temperature difference between the surface and the interior. This improves product quality and product consistency, according to Vulcan literature.

The heating system is also available with state-of-the-art controls which incorporate gas pulse technology. Instead of a traditional ball valve system, the Vulcan Gas Pulse System incorporates a recipe-based menu which interfaces with digital output cards. Operators merely call up the recipe on the touch-sensitive screen and the system automatically sets the control using high/low fire cycling solenoid valves.

Catalytic Reaction

The "heat without a flame" concept is not easy to understand. Vulcan's proprietary catalyst composite, chemically oxidizes natural gas or liquid propane producing heater surface temperatures up to 1000F. This process releases energy, water vapor, and carbon dioxide. To initiate the reaction, the platinum catalyst is preheated with a low wattage electrical heating element embedded in the heater. Once the catalyst has reached a 300 - 400 F temperature, and safety devices are activated by the preheat controls, gas is dispersed into the catalyst through the back of the heater. Oxygen for the reaction enters through the front of the heater face. The face screen protects the catalyst from process mishaps while allowing the air to freely reach the reaction sites of the catalytic process. Since the reaction temperature with current catalysts reaches a maximum of 1000 F, which is well below the auto-ignition point for gas (1,300F), the reaction is flameless. Two minutes after the gas enters the heater, the catalytic reaction is sufficiently established that the preheater is turned off.

Catalyst

The platinum impregnation process in Vulcan's catalyst is highly automated ensuring the very best materials within the catalyst composite. The basis for this structure is Saffil, a highly refined alpha alumina ceramic fiber. One gram of Saffil would represent a cube of 2" x 2" x ½". The surface area within this cube measures 100 sq. ft., providing maximum exposed surface area to react the gas.)

Control

The reaction is controlled by varying the gas flow as it enters the heater. The greater the pressure the hotter the heater surface. This adjustment is made either by a simple ball valve/pressure gage combination or with Vulcan's Gas Pulse Technology. The G.P.S. incorporates a recipe-based menu on a touch sensitive screen. The operator-friendly system requires users to merely call up the recipe and the system automatically sets the zone control via high cycling solenoid valves.

Designing the System

Catalytic radiant heating has fast become a recognized alternative to electric infrared process heating. This success has been realized through the precise design of every system in the field. Vulcan's technical and engineering staff have over 500 such systems to their credit in operation today. From initial discussions and the sharing of criteria it can be determined if catalytic heating is suitable for your application. The design process includes detailed quotes, technical drawings, energy audits, payback schedules and arrangements for system leasing where applicable.

Wavelength

As this graph clearly demonstrates, with a surface temperature of 980 deg. F the emission intensity peaks in the main absorption band for plastics (3-4 microns). This Medium Wave emitter, with an energy level of up to 16 watts per square inch, allows for rapid heat up of all organic materials. Precise control of the heat output is via an operator interface that drives multiple zone controls through out gas pulse technology.

More Information

See our Plastics Consortium web site at www.PlasticsSuite.com

Source: Energy TechPro