ENERGY SAVING OPTIONS FOR GLASS FURNACES & RECOVERY OF HEAT FROM THEIR FLUE GASES AND EXPERIENCES WITH BATCH & CULLET PRE-HEATERS APPLIED IN THE GLASS INDUSTRY

Several measures, such as changes in batch composition (less batch humidity), or optimization of operating conditions, and limiting the combustion air excess, can lead to typically 2-8% of energy savings of industrial glass furnaces. Larger energy savings are only possible by new furnace designs, more insulation, increased cutlet ratios or extra recovery of the heat contents of the flue gases. The flue gas heat contents, downstream regenerators or recuperators of air-fired furnaces or downstream the exhaust of oxygen-fired glass melting furnaces, can be exploited to preheat batch and cullet up to 275-350 degrees C for regenerative furnaces and up to more than 500 degrees C for recuperative and oxygen-fired furnaces. Above 550-600 degrees C, the batches may start to show sticking behaviour. Energy savings of 12-20% have been reported for regenerative air-fired glass furnaces after connecting a batch and pellet-preheat system. The highest savings in the consumption of specific energy (energy consumption per metric ton molten glass), can be achieved by combining the application of batch and cullet preheating with an increased pull rate. Increased pull rates of more than 10% have been achieved and this potential of increasing production in the same furnace will improve economics of batch/cutlet pre-heaters. Almost all batch or cullet pre-heater applications are found in the container glass industry. The pay-back of the capital costs of batch & Gullet preheating systems by energy cost savings may take more than 3-4 years, depending on the energy prices and modifications required to the batch and flue gas channel systems. There are 5 or 6 different types of batch and/or cullet preheating systems applied in the glass industry or still in a testing phase. All pre-heaters deliver very dry batch or cullet. This dry batch charged into the furnace may cause batch carry-over (depending on the doghouse design and position of the burners relative to the batch blanket moving from the doghouse into the tank). Especially in end-port fired furnaces, this dust formation in the furnace may lead to fouling of the regenerator checkers. Other problems that have been reported are: odour in case of high levels of externally recycled cullet (with organic contamination) and dust formation and dust deposition in the ambient space surrounding the furnace, especially in the case of long distances between pre-heater and furnace. Direct contact pre-heaters (direct contact between the flue gases and the batch, to be preheated) will show acid gas scrubbing potential. Batch components absorb SOx, HCl, HF and selenium compounds from the flue gas stream.