To be honest, I cannot recollect when the discussion around carbon footprint and zero emissions started, even though NOx has been an issue for as long as I can remember. And I have been around for some time! The introduction of oxy-fuel has helped to reduce NOx emissions but I question and doubt if it has had a positive effect on energy efficiency. The technology of controlling the access of air has also had an interesting side effect on energy efficiency improvements.
The GlassTrend 2017 seminar in Haarlem, Netherlands was a mind opener, mostly because an important glass bottle customer presented some harsh statements regarding his company’s desired progression towards the greenest bottle. Since that day, the Paris Agreement on Climate Change has appeared on many presentation slides at countless seminars, several of them coming from me. All-electric, hybrid and hydrogen fired furnace designs have moved back into focus, being perceived as a new technology, which they are not. However, the harsh truth is that only non-fossil fuel fired systems will be able to come close to zero CO2 emissions and in that respect, only electricity and/or hydrogen energised melting technologies are practical.
There is no discussion that electrical furnaces are the most energy efficient and feasible solutions known today. Hydrogen options will not be able to come close in comparison, simply because the combustion process is extremely inefficient. The heat recovery system managing the polluted watery flue gases is likely to be complex and expensive and I assume that hydrogen/air combustion will be out of the question because of the related NOx emissions. In that respect, I urge those who are dreaming about huge solar farms in the desert converting electricity into hydrogen and transporting it to glass manufacturing plants; don’t transport the hydrogen if you cannot supply the oxygen as well! In my opinion, that is why using the existing natural gas infrastructure for hydrogen will not work either. And what about the conversion from 100% natural gas towards 100% hydrogen in a time frame of 30 years, which only represents two furnace life cycles? It is even still questionable if all domestic boilers will be able to manage such a conversion without drastic and complex technical refurbishments.
Several institutes have started tests on hydrogen combustion and they are likely to conclude that hydrogen use is possible but the remaining problems will still be the efficiency and availability of hydrogen and oxygen. Some people in the industry have the opinion that all-electric furnaces are inflexible from a pull rate, glass colour and high cullet percentage point of view and cannot be built large enough to accommodate customers’ requirements. But what about the drawbacks that will come from full hydrogen/oxygen furnace designs that have a close to 100% H2O furnace atmosphere? It is questionable, even though the final designs are still to arrive.
Bio fuels from traditional ethanol feedstocks such as corn and sugar cane are also under discussion but the growth to processing cycle is very energy-intensive, so it is arguable whether the level of environmental benefit is justifiable. Research is being carried out to find more energy-efficient, economically viable feedstocks that will not affect food supplies and the environment. For example, cellulosic ethanol is made from plant-based waste that would not typically be recycled. Grasses, algae, animal waste, cooking grease and wastewater sludge are also possible contenders for bio fuel feedstocks if efficient, cost-effective ways can be found to convert them into viable fuel(1). Perhaps the biggest drawback in the use of bio fuels for glass manufacturing is the fact that other industries such as aerospace, automotive and cement have less potential use cases.
Thermal processes can be used to break down plastic into oils for use as fuels. According to a recent article in The Chemical Engineer, the pyrolysis method involves high temperatures up to approximately 800°C or the use of catalysts.
The newer pressurised thermal depolymerisation method, hydrothermal liquefaction, uses comparatively lower temperatures up to 500°C(2). Perhaps the waste heat of a glass furnace could be utilised as part of a more cost-effective recycling solution for plastic waste but how would the resulting fuels behave during combustion? Would the end result justify the means?
What comes to mind is that we need to look at what energy sources will be sufficiently available and efficient, while being economically acceptable. Think about what will happen to CO2/ton price levels in future?
Today, it seems that a specific design could work in one region but would be completely inappropriate in another. If geothermal power or hydro power is sufficiently available close to your facility, your choice will be clear and you can start work on solving any all-electric melting issues, if there are any. If you are close to a huge solar farm providing kWhs almost for free but only during the day, you will find yourself in a different position. Will you start looking for a combined all-electric and all hydrogen design in one? Perhaps start looking for fuel cells that can provide enough electricity during the night to run a simple all-electric furnace? If you do the maths, you will most likely find such a design to be even more energy-efficient. The use of bio fuels will probably not fly in India but perhaps converting plastic into fuel might become feasible there.
And then there is a cost comparison consideration. Historically, furnaces were built with only one fuel in mind. Energy markets were seen as something vital but out of your control, therefore often relegated to a single line on your OPEX spreadsheet, despite having a much larger €/tonne impact than any CAPEX or efficiency consideration. In the future, there will be choices. What are the risks involved in those choices and how can we help senior managers quantify that risk before investment decisions are made?(3)
So where do you start? Perhaps by first studying the sustainable energy market in depth and how it will evolve as far as possible in the future. Remembering that the situation in one region might be different from what others predict when located somewhere else. It will involve combining different business cases to investigate how the available energy can be used in the most efficient way, finding synergies, working with communities, tying in the supply grid owners and utilities and finding political support.
Why even begin to investigate new technical melting solutions before figuring out which energy carriers will become available and commercially acceptable? There are companies who can help start these conversations and collaborations. The Schneider Electric Energy and Sustainability Services team, as well as Eurotherm by Schneider Electric glass expert team welcome those questions and discussions.
1. Biofuels, explained, Christina Nunez, National Geographic Online, 15 July 2019.
2. A new process for converting plastic waste to fuel, Amanda Doyle, The Chemical Engineer Online, 28 February 2019.
3. The Energy Source of the Future from an Energy Market Perspective, Gary Café, Consultancy Manager – Sustainability, Schneider Electric.