XThermal Technology & Case Studies
• Revolutionary inorganic superconductive heat transfer medium
• Vacuum sealed into various types of vessels and materials
• Forms a thermal superconducting component known as XThermal
• Uniform temperature distribution
• Passive thermal transfer component
• Long life span only limited to housing material
• Non Radioactive, non toxic (equivalent to the radioactivity of wood)
α= 1.4×10^-1 Bq/g β= 1.7×10^-1 Bq/q
Heat Pipe vs. XThermal
|Heat Transfer Mechanim||Transfers heat via phase change
Pressure build up from thermal runaway
|No phase change
Low internal tube pressure
|Structure||Evaporation/condensation process requires special wick structure||No wick structure|
|Heat Transfer Medium||Liquid medium – water, methanol, etc.
Medium volume up to 1/10 of internal tube volume
|Inorganic compound medium
Medium volume is 1/400,000 of internal tube volume
||Wide operating temperature range
Will not fail as long as housing material stays effective
|Temperature Distribution||Temperature variation along the tube
Heat transfer terminate at cold load – Length limitation
|Uniform temperature distribution along length of tube
XThermal superconductivity has no length limitation
XThermal Air Preheater Comparison
|XThermal Air Preheater||
||Slightly larger in volume when compared to rotary type|
|Rotary Type Air Preheater
|Heat Pipe Air Preheater
Air Preheater Case Study
Air Preheater Case Study – Features
• Exceptional compatibility between heat transfer medium and housing material. (ND Steel and Carbon Steel)
• Long life span. The operating life span of the component is limited to the housing material.
• Each XThermal component operates independently. Defects on one or more of the components will not hinder the operation of the air preheater.
• In each of the cases provided, there is more heat transferred (Btu/hr) in the XThermal Air Preheater than the Ljungstrom.
• In each of the cases provided, the pressure drop (in H2O) is lower in the XThermal Air Preheater. In each of the cases provided, the XThermal Air Preheater is able to maintain the component metal surface temperature above the critical temperature as stated in the Foster Wheeler report.
• Ceramic-fiber cord seals in XThermal Air Preheater guarantees a leakage of 0.5% or less.
• Compared with the 12% leakage in a Ljungstrom, it would result in 24 times less leakage
• Max. surface temperature of the XThermal tube in mass production 350°C (662°F)
• Minimal leakage prevents de-rating of boiler
• Minimal leakage resulting in maximum and consistent boiler efficiency as opposed to the Ljungstrom, which gradually decreases in efficiency due to the increasing leakage rate over time.
• Performance of XThermal Air Preheater is actually greater than that of the Ljungstrom.
• The flue gas outlet temperature appears lower with Ljungstrom due to the mixing of air (air leakage) and gas in the unit and not a result of more heat drawn.
• The leakage also causes the cold spots within the unit and thus, contributes to the corrosion.
• The entire system has no moving parts. Hence the operation is maintenance free. The XThermal component housing is 1.5” diameter carbon steel tubes, and the fin material is 08AL.(ASTM SA 1010) . Flue gas contains an amount of soot which could foul the heating surface and affect the heat transfer capability after a period of operation. To ensure the cleanliness of the heat transfer surface, the components adopt a nearly horizontal position.
• The tilted position of the components is able to accomplish partial cleaning by gravity
• The surface temperature is maintained higher than the critical corrosion temperature
• Therefore, the particles on the surface are mostly dry ash which is easy to clean
• A soot blower is installed on the top and an opening is provided at the bottom for the cleaning.
• Air Preheater is able to expand its capacity through replacing tubes with greater heat transfer area
• This design fully considers the effects of flue gas and air flow rates. Proper flow rates and resistance are used to achieve current fan resistance and high heat transfer efficiency.
• To prevent the surface temperature from dropping below the acid dew point temperature and causing corrosion, fin pitches were adjusted to control the surface temperature.
• Under low load conditions, the flue gas outlet temperature and component surface temperature are below the acid dew point temperature.
• Optimal air bypass was adopted as a solution to maintain component surface temperature above the critical temperature of 260˚F.
See the following temperature profile graphs: