Batch carry-over is a major problem that can result in the need for expensive maintenance work on regenerators. An attempt is usually made to limit the problem by using moist batch – 3 % moisture being a typical practical figure.
Interest in batch preheating is currently increasing, fuelled by a potential 10 – 12 % decrease in specific energy consumption. However, the use of preheated batch eliminates all batch moisture and therefore poses a significant risk of increased batch carry-over. This has been confirmed in factories that operate batch preheaters where expensive and even dangerous mechanical cleaning of the regenerator packing is necessary at regular intervals.
The new SORG IRD doghouse is design to change two important operating parameters in the doghouse and thereby to increase the glazing of the batch surface leaving the doghouse – a change that helps to prevent batch carry-over.
An increase in the surface area of the doghouse increases the residence time of the batch, whilst raising the height of the doghouse arch allows more radiation to enter the doghouse area from the much hotter melter. Both of these measures help to ensure that the batch floating on the glass bath surface is well glazed before it leaves the doghouse, and it is thus less likely that fine components will be taken up by the combustion gases.
The first example of the IRD doghouse has now been installed and commissioned, and initial results confirm the predictions of the mathematical modelling carried out at the design stage. Contrary to suggestions from some sources beforehand, the glass temperature at the bottom of the new doghouse is not too low, and it is not necessary to use electrical boost to hold this temperature.
Most importantly, the batch leaving the doghouse is comprehensively glazed over.
This installation is not yet operating with preheated batch, although a SORG batch preheater will be installed on this furnace later this year.
The IRD doghouse is part of the SORG Integrated Concept for batch handling at the furnace, together with the EME-NEND batch charger, which is also being used on this installation.