Radiant Tube Technology

Introduction

The Radiant Tube Technology Group set out to find methods of burning natural gas with increased radiant efficiency. Radiating tubes, used as inserts in fire tube systems were suggested as the suitable means for achieving that goal. Also the creation of surface burners of other shapes (eg plate burners) were to be considered.

The results of the research are that systems that use multilayered combustion surfaces can provide sufficient temperatures and hence good radiant performance. Two systems of creating the multilayer effect have been shown to give results. Both should be further investigated to prove reliability of the combustion system and the durability of the materials.

The use of a porous membrane (alumina) to divide a zone of very high temperature from premixed explosive gas has been proved. The effect of transpirational cooling has been demonstrated.

Materials have been selected that withstand the temperatures and provide the correct balance between conduction, emittance, radiance and reflection. By improving the geometry in which these materials are used, even better performances can be expected.

The RTT project has achieved most of its objectives. The one outstanding difficulty has been the reliability and durability of some ceramics. The internal alumina tubes used for gas distribution (sourced from the US) have been of variable quality and have not been readily available. We will look for other sources of this material (preferably in Australia) and improvements in fabrication techniques.

Although we developed techniques for cutting reticulated ceramic foam annular sections (for stress relief), we continued to have a series of structural failures. We have now ascertained a size of reticulated ceramic foam section that is stable with multiple high temperature firings. We however believe that considerable improvement in the performance in such foams could be achieved with further work on geometry and with reduced surface temperatures (and hence reduced surface temperatures) by use of higher emissivity materials. (For tubular sections, spiral cutting will be investigated.)

Their application as facets to plate burners is also being considered.

Silicon Carbide (SiC) proved to be a very interesting material, because of its high radiant emissivity and high thermal conductivity. It is intended to press on with research involving the performance of that material in a second phase of the project.

M.E.T.T.S. and its associates in RTT are looking for partners to assist with the development of candles and plates based on the research already carried out. Specifically we look to:

* Maximise the radiant efficiency of the candles and plate burners, by perfecting the 'geometry' of the second layer of ceramic. The depth and size of voids and windows in the second layer will be studied to achieve optimisation,

* Design structures that make use of ceramic foam sections to produce surfaces of high radiance,

* Improve the alumina base tube or board will be sought to produce more even gas distribution on the interlayer surface, and increased longevity of the underlying material,

* Reduce of thermal stress by the strategic use of higher emissivity materials to reduce temperature gradients, and

* Co-operate with the producers (Japanese) of the SiC material to develop alternative SiC products.

Click here to read the article on Radiant Tube Combustion