The multiple benefits and multi-faceted success of glass cannot be denied. Endlessly recyclable, its chemically inert properties have offered innovative versatility, helping to change the course of history over many millennia. But glass has a hard future, when you consider the energy intensive melting required to produce it and the mounting pressure for manufacturers to dramatically reduce their carbon footprint.

The Paris Climate Agreement demands a 55% reduction in carbon emissions by 2030 and carbon neutrality by 2050. Compliance will be essential for glass manufacturers to remain competitive and ensure sustainable economic growth. Today’s combustion technology will soon be a thing of the past, as industry moves forward with more renewable sources and environmentally friendly processes.

So, what will the furnace of the future look like? Many different innovations have been considered to provide a sustainable energy supply, including electricity and alternative fuels like hydrogen, oxygen and biodiesel.

All are currently being trialled and tested, but in general these energies, if even available, often do not provide enough power and stability to operate a furnace and keep temperatures constant, to ensure the sustained high quality of the finished products. Let’s weigh up the benefits and limitations of each option, to find out which one offers the most viable solution.

All-electric melting

Electric furnaces, such as the SORG VSM typically operate with a ‘cold-top’ where the batch melts as it passes down through the furnace. This forms an insulating layer which reduces thermal losses from the glass melt. They are more efficient than air/fuel furnaces because they do not produce large volumes of hot waste gases during the combustion process, and also have a higher efficiency because of the direct energy transfer into the melt by the electrodes. The cold-top traps many pollutants produced by the melting process and the batch charging via the closed rotating crown ensures a nearly dust-free environment around the furnace. Although the furnace has a shorter working life compared to gas-powered furnaces, it is significantly cheaper and quicker to build and rebuild.

There are certain limitations, such as in the possible melter size and pull. Requiring an even layer of batch to be spread across the whole surface of the melt, 100% electric furnaces have a size limit of around 200 metric tonnes’ pull per day. Furthermore, the application of 100% electric melting is not suitable for all types of glass and the all-electric melter is more sensitive to raw material and operation variations.

Besides electricity being more expensive than natural gas – up to now – in most parts of the world and therefore uneconomical for standard glasses, significant government investment would be required to make all-electric melting commercially viable. However, as CO2 taxes are being established and will be increased dramatically over coming years, this changes the picture for the producer and will also push governments to start considering electricity infrastructure.

Hybrid furnaces

Many conventional glass melting furnaces are using electricity to complement the fossil firing in the form of electric boosting. This enables the furnace to produce higher output and/or better glass quality. The electric share is typically from 10–15% but can be increased to values around 25%. In the case of green electricity, the CO2 footprint is reduced, with the hybrid furnace able to ‘play’ with the share of electricity. This would offer greater protection against fluctuations in energy prices or availability of electricity, whilst facilitating the transition from natural gas towards new low-carbon fuels. And if hydrogen is to be used instead of gas, the CO2 output can be zero.

SORG’s new concept, the CLEAN Melter, is a logical continuation of the SORG VSM all-electric furnace. The CLEAN Melter can be operated between a range of 20% electric/80% fossil fuels, up to 80% electric/20% fossil fuels, making it extremely flexible when it comes to energy prices and availability. More importantly, the CLEAN Melter can also support higher tonnages (up to 400tpd), is suitable for all glass types and is not as sensitive to raw material and operation variations as the VSM furnace.

Oxy-fuel firing

An oxy-fuel system fires pure oxygen into the furnace along with, for example, the natural gas, making it noticeably more thermally efficient than furnaces using ambient air. Even though the flame is hotter, no actual nitrogen is fed into the furnace by the combustion air, which results in extremely low NOx levels. This type of furnace is mostly used for specific applications, such as the melting of speciality or high temperature glasses like borosilicate, typically in locations where an economic source of oxygen exists, and to aid an old furnace to meet its campaign requirements (oxygen boosting). Similarly, in some areas, oxygen heated furnaces are demanded for all types of furnaces by authorities.

Technically speaking, oxy-fuel firing does bring unique benefits, however the need for either on-site oxygen manufacture or regular deliveries of liquid oxygen can be fairly costly.

Hydrogen

The use of hydrogen instead of gas could be the key for the future. Combined with converting the natural gas network into 100% hydrogen, this would be a great way to decarbonise both industrial and domestic energy applications. The two main routes to produce no or low carbon hydrogen on a large scale are steam methane reformation (SMR), typically known as ‘blue’ hydrogen, and electrolysis of water using renewable electricity. Low or zero carbon hydrogen production offers a potentially lower fuel cost than electricity, however, further research will be required to compare the future costs to those of biofuels.

With hydrogen it is possible to convert existing fossil fired furnaces to green hydrogen fired furnaces, using the same furnace technology.

Hydrogen could be delivered through existing natural gas pipelines, reducing the cost of delivery to site. Plants will need to make significant investment in infrastructure, such as ATEX approved zones and stainless-steel pipework. Yet it should be possible to convert the current design of natural gas furnaces to a pure hydrogen fuel with relatively minimal disruption.

The right time, the right partner

Pull rate, energy consumption and emissions of conventional furnaces have already been improved considerably. Whichever technology is utilised in the future, there are many determining factors, including geographical location, accessibility to fuels and economies of scale.

SORG is always thinking ahead and investing in cleaner technologies to tackle climate change. Introducing the all-electric VSM furnace 50 years ago and providing electric boosters for over 500 fossil-fired furnaces worldwide, we have also just patented the world’s first hybrid furnace to support larger applications. The CLEAN Melter combines our knowledge with proven mathematic modelling carried out by SORG’s in house experts. Suitable for all glass types, it emits significantly less CO2 than conventional furnaces, with up to 80% electric share offering greater flexibility and huge cost savings for furnaces up to 400tpd and even more.

We know that glass manufacturing has to earn the right to continue. We owe it to our industry. We owe it to future generations. And above all, we owe it to the planet. That’s why SORG has the vision to find the most sustainable solutions for its customers. Ones that help to optimise productivity, while reducing emissions and safeguarding the future for everyone to benefit from carbon neutral energy.

SORG VSM and SORG CLEAN Melter are registered trademarks of SORG GmbH & Co. KG