Can the glass industry meet emission reduction targets? Richard Stormont* says the answer to this question is YES, and the technology is already here.

The EU has set specific targets and a timetable for the reduction of greenhouse gas emissions. Many other organisations and governments around the world have set guidelines and adopted policies with the same aim.

In the case of the EU a 20% reduction is called for by this year 2020, 30% by 2030, 40% by 2040, culminating in ‘net zero’ by 2050, all from a reference point of 1990 emissions levels.

In glass melting and conditioning adopting electric heating technologies has long been seen as the way to minimise emissions.

With an insulating layer of batch covering the surface of the glass in a continuous vertical melting process, a well-designed all-electric melter can have a thermal efficiency of 85%, close to twice that of even the most energy efficient fuel fired furnaces.

Caption: The insulating batch blanket of a cold-top electric melter.

Together with the absence of fossil fuel firing and having all the energy applied by means of electrodes immersed in the glass, emissions from the process are typically limited to any carbon dioxide released from raw materials - a small fraction of the emissions from conventional fossil fuel fired melting.

The difference becomes even greater when taking account of variations in the actual output of furnaces in relation to their nominal capacity.

Such variations are almost inevitable due to product mix, market demand, machine maintenance and furnace age and condition.

The thermal efficiency of the cold-top all-electric melter remains high even at reduced pull, in contrast to the fuel-fired furnace, in which thermal efficiency reduces sharply as output is reduced.

Caption: Two Electroflex container glass electric forehearths.

While most glassmakers are well aware of the energy consumption and cost of their furnaces, many take little account of the fuel consumption and cost of conventional gas-fired forehearths and distributor channels.

With small combustion chambers and limited scope for waste heat recovery, the thermal efficiency of gas heating in forehearths, that is the proportion of heat energy transferred to the glass in relation to the total energy input, is typically extremely low.

Electrically heated forehearths and distributors not only eliminate combustion gas emissions entirely, contributing significantly to the total emissions reduction target, but converting from gas to electrically heated can typically reduce operating energy costs by between 60% and 90%.

This is a prime example of both operating cost and environmental benefit going hand in hand.

Electric glass melting and conditioning are established technologies - the author has been involved with both for 50 years.

It remains a fact however that the large majority of electric furnaces have been for so-called ‘special’ glasses, borosilicates, fluoride opal, lead crystal and specialist technical glasses.

Generally, they have also been of modest size, mostly in the range of say 10 to 80 tonnes/day capacity.

In contrast the majority of the world’s container glass, which accounts for some 50% of total glass production, is produced in furnaces with capacities of between 200 tonnes/day and 400 tonnes/day, with some larger still.

Successful designs of small and medium-sized electric melters cannot simply be scaled up, a process that is much easier to achieve with fuel-fired furnaces.

In-depth understanding and great care in concept design are needed to ensure the energy and temperature distribution necessary for successful cold-top vertical melting in larger furnaces.

There is already proven technology and operational experience of all-electric container glass melters of 200 to 250 tonnes/day and more, and Electroglass has well-developed concept designs for 300 to 350 tonnes/day melters.

However scaling up the use of all-electric melting , both in terms of the capacity of individual installations and in rolling it out on a scale needed to match the world’s container glass demands alone will take more time than is available in respect of meeting the EU targets for example.

Caption Control panels for three electric furnaces and their electric forehearths under assembly and test.

Expansion of the use of electric melting in the 200 to 350 tonnes/day range for the container glass industry will continue, with key glassmakers taking the lead.

However to stand a realistic chance of meeting many of the emission reduction targets and plans, a major focus for the next decade or two needs to be based on expanding the use of highly effective and proven technologies we already have - the most efficient electric boosting systems for essentially conventional fuel-fired furnaces.

Electroglass’ CCC (Convection Current Control) boosting systems have, with constant development and refinement, been in use for some years and have an established reputation of delivering the highest energy efficiency combined with marked glass quality improvement.

The average energy consumption is just under 20 kilowatts of continuous power input for each extra tonne/day over and above the unboosted output of the furnace concerned.

Less attention has been focused on the actual percentage of output increase this technology has delivered.

Of course, some of these boost systems have been required to achieve only modest increases in furnace output, but many have increased output by 50% to 65%, and occasionally more, up to 100%.

A 65% increase in output over the unboosted output of a furnace through electric boosting means that 40% of that furnace’s total output is being produced electrically.

Leaving aside the undoubted improvements in the unboosted fuel efficiency and emissions reduction of furnaces from 1990 to now, that translates to a 40% reduction in combustion emissions per tonne of glass produced in that furnace.

The fact that the above output increases have consistently been achieved while maintaining or improving glass quality shows that there is considerable scope for increasing these levels of electric boost, further directly reducing emissions per tonne of glass.

Caption A large all-electric container glass furnace under construction.

The boost design is crucial. Simply installing a high level of boost power is not only unlikely to achieve the desired output, but may well drastically reduce residence time, refining and therefore glass quality, even at substantially higher boost power inputs per tonne of glass.

The zoning, number, size, positions, immersions and electrical connection arrangement of electrodes are critical. The study and understanding of each of these and other design variables, backed by decades of modelling, experience, practical application and proven results, are essential for success.

While we continue with the development and application of larger all-electric melters, multiple-melter installations and other related approaches, existing electric boosting technology (and careful extension of it) and existing electric forehearth technology are already available to meet the immediate requirements for emissions reduction.

Richard Stormont, Managing Director, Electroglass Ltd, Benfleet, UK.