I think it is clear that over the last few months we definitely have [experienced] climate change, and according to the scientists all of this relates directly to the amount of CO2 in the atmosphere. The glass industry is recognising this reality and there are a number of projects around the world looking at various options to reduce our carbon footprint.

Most notably, the Glass Futures Scheme is an embodiment of the commitment by the international glass community to investigate as many of these options as possible with a pilot plant. The initial undertaking is to build a fairly conventional 30tpd pilot furnace that will enable it to undertake some work on alternative fuels as well as the capability to investigate different and new refractories, new raw materials and establish some base information. This furnace will be oxy-fired and have facilities for electric boost. This is a far-reaching project and it is expected that the second phase will investigate some more radical options.

In the meantime, a number of glass plants are planning to conduct their own experiments on alternative fuels such as bio-fuels and hydrogen as well as other projects worldwide, but particularly in Europe, looking at various de-carbonising options including full hydrogen, superboosting and hybrid furnaces. However, it is very important to ‘clear the fog’ that is rapidly accumulating.

Bio-fuels are a non-starter

Since the accumulation of carbon dioxide in the atmosphere increases the absorption of heat and thus represents a major driving force behind climate change, I would suggest that any solution that looks at bio-fuels, which when burnt release CO2, is basically a non-starter. Whilst it is argued that if you take a fuel which is renewable and burn it and just release the same amount of CO2 as you initially consumed, then it is carbon-neutral, I strongly believe this is a false dawn. Why would you cut down a tree, for example, that has taken 30–40 years to grow, to then turn it into a bio-fuel producing heat for three minutes [and] releasing CO2? Similarly, why would you take CO2 to make a synthetic fuel, which then only [produces] the same amount of CO2 that you took to initially make the fuel. Although it is carbon-neutral, it is not helping the planet. I therefore believe that bio-fuels or anything producing carbon dioxide is going to be unacceptable in anything other than the short term.
I don’t believe our customers, or indeed the public at large will accept this as being an option.

Oxy-fuel firing

We therefore need to look at other gases such as hydrogen or ammonia. It is quite clear from existing legislation relating to waste gases that NOx is going to continue to be a major issue and any combustion system should address this problem. It is quite likely, therefore, that there will be a dramatic move in furnace design to oxy-fired furnaces.

The reason for this is that there are efficiency gains to be had by using oxy-fuel firing, provided, of course, that the cost of electricity becomes more economic – more on this later on. It is therefore anticipated by the author that most new firing systems using any kind of fuel will see a likely move to more oxy-fuel firing. This is certainly borne out by the experience of F.I.C., talking to its current customers.

Hydrogen

Let’s look at hydrogen first as an option because ammonia is made from using hydrogen in a Haber-Bosch process where it is combined with nitrogen separated from the air. Hydrogen is often talked about as being an easy option. In simplistic terms: we have natural gas now and a distribution set-up, and all we have to do is to make green hydrogen and reticulate it through the same system. However, it is not as simple as this, as most of us know. The simple fact is that [with] hydrogen being a lighter element, we need three times the volume [that] we currently use for natural gas. This will obviously require a considerable investment in the existing distribution network. As it is a lighter element, and the pressure will need to be increased, this adds to both difficulties in transportation and safety. These issues are not to be dismissed with superficial plausibility.

There are a number of challenges that need to be recognised in going to hydrogen firing, notwithstanding the initial limited trials that have been “successfully” carried out on either mixing hydrogen with natural gas [in] the furnace, or trials of hydrogen on a complete port, as well as flame trials at various institutions such as the Glass Futures flame test rig and the DNV rig in the Netherlands amongst others. Colleagues from our sister company FlammaTec (www.flammatec.com) actually were the first to develop a Hydrogen Oxygen burner, already tested for the first time in 2020. There are a number of trials proposed in Europe for full hydrogen firing supported by various government funds, some of the results of which are to be released in the public domain as they involve subsidies. It will be interesting to see how these go, but broadly speaking the following issues need to be recognised and addressed:-

Foam, refining and effect on refractory

Although the hydrogen flame is invisible, all trials so far show that we can expect satisfactory heat transmission to the glass surface. There are known problems that using hydrogen will affect the refining of the glass as well as the inherent water vapour on the glass surface contributing to increased levels of foam. It is currently not thought that either of these two issues are show-stoppers, however the ability to see the flame and ensure that the flame alignment is satisfactory is slightly more challenging.

One other issue that is yet to be properly recognised, in the opinion of the author, is that we currently do not have refractories that can withstand the effect of super-heated steam in the superstructure. A hydrogen flame is a higher temperature and the product of combustion is water vapour. This super-heated steam in an oxy-fuel fired environment is going to be a major challenge.

Sourcing

It can well be argued that these issues of foam, refining and effect on refractory are relatively easy to overcome, however there is one other elephant in the room and that relates to
a) the availability of green hydrogen and b) the demand from industry and others. Let’s first look at production of hydrogen – one of the biggest problems facing the future is the cost of electricity and this is especially so in the production of hydrogen. Electricity pricing is generally coupled with the price of natural gas as the majority of electricity around the world is produced from fossil fuels in one form or another. However, the move to renewables and in particular solar and wind has brought the cost of generating electricity by these means down considerably but in order to assist the production of renewables, the electricity price has not been reduced to reflect this. Most governments recognise that long-term this has to change in order to encourage the move to CO2 reduction. The cost of electricity generated by wind and solar is typically a third to a half of that generated by fossil fuel but obviously varies enormously from country to country.

Obviously green hydrogen can only be made if we use green electricity made from renewable sources such as photovoltaics, wind-generated or nuclear. The most obvious way to make hydrogen is the electrolysis of water but what is not appreciated generally is that the water needs to be relatively clean. In other words, we just cannot use any water lying around. Most water has to be treated prior to the electrolysis and making oxygen with hydrogen at the same time is obviously a big advantage to the glass industry. This approach has zero carbon emissions. The use of pink, purple, red or yellow hydrogen produced respectively by either nuclear power or grid electricity is obviously an option. Black or grey hydrogen is made from steam methane reforming using natural gas as a feedstock, 95% of current hydrogen is made by this process. It requires a catalyst to produce the hydrogen and carbon monoxide and carbon dioxide.

The steam reforming is endothermic and that heat must be supplied for the reaction to proceed. This process is estimated to be at best 65–75% efficient but as stated earlier there are significant quantities of CO2 produced which needs to be captured. In this case it is often called blue hydrogen. Other forms of hydrogen are so called white hydrogen, which is where hydrogen is produced as a by-product of industrial processes or turquoise, where hydrogen is produced by thermal splitting of methane (methane pyrolysis) and instead of CO2 being produced, solid carbon is the end product. None of these are really significantly produced currently.

Industry demand

Obviously, hydrogen is of significant interest in many industries, particularly those that require a flame such as cement production. If the manufactured cement has to [be]decarbonised, a flame is required and obviously hydrogen is a good option, but this is going to be expensive, not least because it starts in its cheapest form from pure electricity and then if it is to be transported by pipeline or bulk delivery to industry whether glass or cement and then burnt, the overall efficiency is going to be approximately 28% which is less than the overall efficiency currently of about 33% for natural gas firing. This means that it would be a) an expensive option for glass furnaces and b) we would be competing for supply for other reasons. There are other industries as well as cement such as shipping and steel production that have difficulties using electricity so they will be prioritised for supply. It is on this basis that I think hydrogen is part of the journey to decarbonisation, but do not believe it will be a significant requirement going forward. The DNV [Det Norske Veritas engineering group] in the Netherlands predicts hydrogen will only play a role of 0.5% until 2030 and 5% until 2050. Global costs of producing hydrogen until 2050 will be (US) $6.8 trillion with $180 billion on pipelines (source DNV).

Ammonia

If we look at ammonia, which is manufactured from hydrogen and nitrogen captured from the air, under extremely high pressures and moderately high temperatures, its main disadvantages are the high greenhouse gas emissions and high amounts of energy usage due to its operating pressure and temperature. It produces 2.7 tons of carbon dioxide emissions per ton of ammonia produced. Cost of building and operating ammonia terminals is predicted to be $530 billion (source DNV). On this basis I do not believe that ammonia is an option going forward, mainly due to cost and the overall efficiency.

Carbon capture

So, next we need to look at carbon capture utilisation and/or storage (CCUS). Again, Glass Futures did a very comprehensive survey of the various systems currently available. By that it should be recognised that many of these are only at laboratory or pilot plant level and very few are commercially available. Of the more than 30 systems and variations, only one was of any real interest going forward mainly because the other gases formed in the melting process complicate the capture of the CO2. Virtually all the systems investigated would add considerably to the cost of production. I really believe at this stage that CCUS is embryonic and that we have a long wait; however, having said that, with the urgency to remove CO2 from the atmosphere, I am sure there will be considerable research efforts in this regard. Only time will tell, and in any fact we will have to wait a long time because there is nothing really currently available.