Forehearths
z Fig 4. Model of a complete PSR Forehearth & Distributor System.
Cooling is normally provided by shutting off the gas supply to the burner and blowing combustion air through the burner. The technologies employed cannot target the heating and cooling where they are required, and therefore no significant glass conditioning can take place before the glass enters the forehearth. PSR views the distributor as an extension of the forehearth, not the furnace, and therefore the forehearth technologies can be installed all the way back to the throat riser, starting the glass conditioning process as soon as the glass leaves the furnace and maximising the energy savings achievable.
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Results The System 500 Forehearth is specifically designed to separate and optimise the heating and cooling functions of the forehearth, and customers have reported that conversions of conventional longitudinal forced air cooled forehearths to System 500 forehearths have produced fuel savings of up to 20%. Similarly, conversions of direct radiation cooled forehearths have produced fuel savings of up to 40%. Savings are not only achieved through reduced fuel consumption, but also through increased glass quality and therefore production output of the forehearth. For example, one customer converted a radiation cooled forehearth to the System 500 by replacing the superstructure refractories, steelwork and cooling mechanisms. They recorded the glass thermal homogeneity figures, the tonnage of glass which could be pulled by the forehearth and the pack rates of the forehearth,
before and after the conversion. The maximum tonnage of the forehearth increased from 137 to 142 tonnes/day, the typical thermal homogeneity value increased from 92% to 97% and the pack rate increased from 92.5% to 93.5%. This 1% increase in pack rate, along with the increased forehearth load, resulted in a 5% increase in the absolute pack rate of the forehearth, providing a payback time for their investment of just a few weeks. One case study carried out recently relates to a client in the Middle East that operates two adjacent furnaces, each manufacturing white flint or emerald green glasses. Furnace ‘A’ has three productions lines with PSR System 500 forehearth and distributor technology, whilst Furnace ‘B’ has two production lines with forehearth and distributors supplied by the furnace supplier. The forehearths installed on Furnace ‘B’ employ conventional direct longitudinal cooling with the cooling air introduced at the front of the cooling zones and exhausted, along with the combustion gases, at the rear of the zones through one common, manually controlled exhaust flue. Over a period of several years the client noticed discrepancies in energy efficiency between the two systems. They decided to carry out a study over a 25 day period during which all five forehearths were producing white flint glass under roughly equivalent operating conditions. The fuel consumption was recorded over this 25 day period and it was found that the three System 500 forehearths and distributor on Furnace ‘A’ were consuming 380.8 normal m³/day and the two forehearths and working end on Furnace
‘B’ were consuming 446.5 normal m³/day, which equates to 17% additional fuel. In order to obtain a direct comparison of the fuel consumption between the two systems, the fuel consumptions relative to the size of the systems, in terms of glass surface area within the forehearths and distributors, were considered. It was found that the System 500 forehearths and distributor on Furnace ‘A’ used 12.63 normal m³ of LPG per m² of glass surface area per day compared to the 19.11 normal m³ of LPG consumed by the forehearths and working end on Furnace ‘B’. This represents a 50% increase in specific fuel consumption over the System 500. This discrepancy in fuel consumption was then put into monetary terms by the provision of an average fuel cost of £0.80 per m³ of LPG. When the energy costs were considered over a typical 10 year furnace campaign it was found that an expected saving of £449,860.00 could be achieved by converting the existing conventional longitudinally cooled forehearths to the System 500 forehearth, and a saving of £588,090.00 achieved by the System 500 forehearths on Furnace ‘A’.
Conclusion The System 500 forehearth and distributor was introduced almost 25 years ago and with more than 600 installations worldwide, continuous development has ensured that it remains at the forefront of glass conditioning technology. What is often overlooked is the superior fuel efficiency that it can achieve as a direct result of the automatic cooling system and close control of the internal forehearth pressure. Sadly, not enough glassmakers are able to make reliable comparisons between our equipment and our competitor’s equipment in the way that our Middle Eastern client did, and as a result investment decisions are often based more upon initial capital cost than longer term energy savings or production efficiencies. The savings demonstrated are not only achieved over the lifetime of the furnace but, through re-using the equipment at subsequent rebuilds, the benefits can be reaped for decades to come. r
*Director, Parkinson-Spencer Refractories, West Yorkshire, UK www.parkinson-spencer.co.uk/
70 Glass International July/August 2016
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