This organization is seeking insulation for an internally cooled cylindrical component of a gaseous reactor. The end of the cooled cylinder inside the reactor is exposed to high heat fluxes of 1-3 MW/sq meter and an atmosphere consisting primarily of carbon monoxide and hydrogen. The aim is to lower the temperature of the exposed end of the cylinder by 100-200°C. The insulation should be durable, last at least one year and be able to adhere to or blanket a smooth metal surface.
Details of the Technology Call
Conditions inside the gaseous reactor are extreme. Ambient temperature runs about 1500°C at 50–60 atmospheres, with a wind velocity of about 100m/s. The process runs continuously. Projected working lifetime of the reactor between maintenance shutdowns is two years; but because the cylinder component has not been able to be insulated sufficiently, reactor operations require much more frequent shutdowns.
The component is roughly cylindrical with one end placed into the high pressure, high temperature conditions. Only the 0.1–0.2 meter portion of the cylinder that extends into the reactor must be protected. (The entire cylinder is round on one end with a diameter of 0.4 meter, total length of about 3.5 meters and weight of 2,000 kg.) All surfaces are of convex curvature. Currently, the cylinder is cooled internally, and this brings the outer surface to a temperature of about 700°C. This organization needs to insulate the end of the cylinder that enters the reactor (about 0.1–0.2 meter) so as to lower the surface temperature by 100-200°C. Additional internal cooling is not an option.
The failure mode of the cylinder is thermal fatigue, which is failure by cracking causing by alternating stresses caused by alternating temperatures.
Thermal barrier coatings, and underlying bond coatings to increase their adherence to various substrates, are known. However, those known to work at high temperatures have been designed for oxidizing combustion atmospheres; those designed to work with reducing atmospheres are perhaps not well known at similar temperatures. Coatings which work at temperatures of 300-400° C are known to work in reducing (hydrogen-containing) gases with hydrogen sulfide. In petroleum refinery process equipment This application is unique in that it is both high temperature and reducing.
• Must tolerate extreme environment for two or more years: exposure to a gas temperature of 1500°C, carbon monoxide-hydrogen reducing environment at 50–60 atmospheres, modest but high-frequency temperature fluctuations of 2-3 cycles per second and significant pressure fluctuations also of 2-3 per second, continuous operation, and turbulence inside the reactor.
• Must lower the surface temperature of the cooled component by 100-200°C.
• Must survive exposure to humid conditions when exposed to ambient air, as well as shipping and handling by plant personnel.
• Must be chemically inert to reactions with carbon monoxide and hydrogen.
• Thermal conductivity must be no more than one-half of the value of zirconium oxide (2.4 Btu/(hr-ft-oF or 4.1 W/m-oC)
• Coating must stick/adhere to a smooth metal surface made of Inconel (nickel-chromium-iron) and stainless steel (iron-chromium-nickel) alloys. The components contain high pressure cooling water at a temperature of 180oC.
• Failure (loss/spalling) of any insulating coat should not present a problem to the substrate or process. The insulating coating cannot affect the substrate other than by reducing its temperature.
• A “nice to have” feature of the material surface is an emissivity of no more than 0.3, relative to a black body of 1.0. (a good reflector of thermal energy). Lower values will be superior in terms of reflecting more thermal energy away from the component.
POSSIBLE SOLUTION AREAS
Industries of interest might be aerospace propulsion, space craft propulsion, fossil fired combustion facilities, petrochemical plants, chemicals plants, heating, ceramics, insulation, thermal radiation management, pulp and paper processing facilities, nuclear power plants, incinerator facilities, studies/equipment by power generation facilities and organizations and similar organizations.
Field Of Use and Intended Application
High-temperature gaseous reactor.
Ideally, a coating that can be applied to the cylinder component to drop its temperature by 100-200°C.
A substitute material for the Inconel alloy that is more resistant to thermal fatigue (higher fatigue strength, lower coefficient of thermal expansion and/or higher thermal conductivity) might be another avenue.
Previously Attempted Solutions
Plasma spray zirconium oxide, such as that used on aero and land-based turbine engine blades. This coating also requires a bond coat. This coating has failed in previous tests in similar conditions. The suspicion is that it is because the coating is designed for high temperatures in an oxidizing atmosphere (a jet engine), while the chemical process in question is highly reducing with hydrogen and carbon monoxide and the oxidized bond coat may not be stable in contact with hot hydrogen and carbon monoxide.
Refractory bricks have been considered. However, the insulation must be tolerant of mechanical abuse. Refractory bricks tend to break and crack, causing thermal expansion problems.