The standard thinking is to select raw materials in function of the requested cellular glass. The glass is made by the melting of sand, soda and lime. At a certain point, it became clear that the use of recycled glass was an interesting economic alternative which could be sold as an ecologic improvement. The same approach is used with towels in hotels (please drop your towel only when needed for the sake of the environment) and we all know that reducing cost is the real reason. However, the economy becomes greener which means that an ecologic and economic reasoning gives the same result.
In my opinion, we have to start from the available waste and convert this waste to a product with added value with a minimum ecologic footprint. This is a clear consequence of the future lack of fresh raw materials and energy and also of the climate change. Also transport is becoming an issue.
The best recycling of bottles is still cleaning and refill. But there will be always an important amount of broken bottles, windows and wind screens. And this waste glass is today a better investment than money on the bank thanks to the green economy. But what can we do with this glass waste?
- The most suited glass (colour specification) goes to the bottle and window industry.
- What is left can be converted in cellular glass but is not clear whether it has to be used for thermal insulation with the lowest thermal conductivity possible.
- One possibility is foaming cellular glass gravel. This product is rather easy to produce and can be used as floor thermal insulation but also as landfill for streets or large gardens. Recycled glass powder is mixed with a foaming agent and foamed at 800°C. The foaming is done on a belt and free cooling after foaming generates the gravel.
- Annealing the ribbon allows to produce cellular glass boards. These boards can have a thermal conductivity of 0.048 W/mK and sizes up to 3m.
- Alternatively, foaming can be done in a mold of any shape. However, this method is less interesting and in fact not logic when rectangular boards with larger dimensions are requested.
- The obtained thermal conductivity depends on the glass composition and when a value of 0.040 W/mK is needed, a special composition has to be melted. This involves extra raw materials and an extra heating up to 1400°C together with a large investment. In most cases, this is also not logic because a larger thermal conductivity can be compensated with a larger thickness.
- As foaming agent, we know carbon, which needs a reducing atmospfere. SiC and glycerin, a side product of biodiesel can be used in an efficient neutral atmosphere. Glycerin is clearly the natural choice
- Transport has to be eliminated as much as possible. The logic location of a cellular glass plant is the extension of a glass recycling company. I guess that glass recyclers will extent their companies with a cellular glass production line once the world realizes that cellular glass is not necessarly expensive.
- Mineral wool and glass wool are also produced from recycled glass but both need a melting step at 1400°C. This is also not a logic choice if we compare with cellular glass foamed at 800°C. However the world still buys much more of these wools at comparable prices with cellular glass.
Walter Frank, founder of GLAPOR WERK, in the past a fair competitor and today a friend has chosen the right approach:
- Direct foaming at 800°C of recycled glass WITHOUT remelting at 1400°C.
- Continuous foaming in a neutral atmosphere to large dimensions and later down sizing to pallet dimensions.
- Depending on the quality of the glass powder, thermal conductivities between 0.065 and 0.048 W/mK can be produced.
But between ready to deliver and convincing the world is a big step, called marketing. Windows still owns the PC market while LINUX is a very good free of charge alternative. The same was true for iOS of Apple but ANDROID is growing like shown hereunder.
I expect that the classic cellular glass (0.040 W/mK) will evolute like iOS and the GLAPOR method like ANDROID if enough money is available to take market share from the others (mineral and glass wool). It is the logic evolution but marketing is needed to let faster happen what is logic.