The floor is given to María González Martínez, Assistant Professor at IMT Mines Albi, lecturer in the Master Biomass and Waste for Energy and Materials (BiWEM) and researcher at the RAPSODEE joint research center associated with CNRS. Her research interests are focused on hydrogen and methane production by thermoconversion of bioresources.
Biomass consists of renewable organic material from plants or animals. Its conversion to valuable products, such as energy, chemicals and materials, is well known nowadays. The main valorization routes for biomass consist of thermochemical conversion, using high temperature, and biochemical conversion, using micro-organisms. Some examples of these processes are combustion, pyrolysis, gasification, methanation and anaerobic digestion.
Biomass valorization routes can be expanded to waste valorization, leading to the waste-to-energy route. Waste contains both organic and non-organic materials such as food waste, plastics, metal or glass. As a result, a larger renewable and unutilised resource can be explored and recycled.
At the same time as energy, materials and platform molecules are produced. For example, biochar is a valuable material with diverse applications, such as soil amendment, in electrodes for batteries or in particle boards for construction.
The benefits of waste-to-energy
The main advantage of waste-to-energy is the flexibility of the process, due to the multiple conversion routes and the diversity of the resource. The operating conditions of the process may be adapted as a function of the targeted product and the characteristics of the resource. For example, pyrolysis temperature and heating rate condition the major product obtained, that is, a bio-oil or a biochar. In other words, this flexible process allows to convert an untapped resource such as waste into something that has a high demand in the market, for example, heat or hydrogen.
Another advantage of WtE is that it is possible to obtain a gas, such as biogas, syngas or hydrogen, which acts as an energy carrier. This allows us to store large quantities of energy and to convert intermittent energy sources, such as solar or wind renewable energies, into a permanent source of energy available when needed.
In short, waste is a very diverse resource that enables to obtain a a wide range of products through different conversion routes. Thanks to waste valorization, energy carriers such as hydrogen are produced, which may play a significant role in the energy transition.
The challenges of waste-to-energy
Waste is an heterogenous resource. Consequently, waste-to-energy conversion processes need to be robust so as to be able to adapt to changes in the raw material input. Therefore, it is important to look at the whole chain in the waste-to-energy process. The amount of energy generated as a result of the waste-to-energy conversion process must exceed the energy needed to transform the waste. Furthermore, if it is possible to obtain a high-added value product such as biochar while also generating energy this contributes to the economic balance of the process.
Gasification vs incineration: the advantages
Waste gasification allows to recover not only heat but also syngas, containing hydrogen. The high energy content of the hydrogen molecule makes it a valuable energy carrier. As a result, green hydrogen can be produced from waste through gasification. Then energy stored in the hydrogen molecule can be converted back into energy thanks to fuel cells. Furthermore, gasification syngas can also be transformed into methane to feed the power-to-gas energy system.
Green hydrogen from waste, a valuable resource
Today the most valuable resource from waste is green hydrogen. The societal transition to a hydrogen-based energy system allows to avoid CO2 emissions. However, currently most of the hydrogen used is produced from fossil fuels, so-called brown or grey hydrogen. Hence, the aim is to move to green hydrogen which is produced from renewable resources such as biomass and waste.
Furthermore, the production of platform molecules from waste, in other words high added value chemicals for industry, has attracted more and more interest in recent years, with for example the production of methanol from waste.
Based on an interview with María González, lecturer at IMT Mines Albi and researcher at RAPSODEE joint research laboratory with the CNRS. Her research field includes the production of hydrogen and methane from bioresources thermoconversion.
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