Optimal design of solar assisted hydrothermal gasification plants
Wet biomass represents a very important part of the biomass resources sustainably available in the world. The amount of industrial wastewater and sewage sludge containing high concentration of organic content to be treated is constantly increasing. For instance, the boom of biofuel production generates important volume of wastewater that needs to be treated before being released in the environment. This is also the case of manure and other waste biomass whose disposal creates burden on the environment and therefore requires new innovative techniques for treatment and valorisation.
Hydrothermal gasification (HTG) is a relatively new technology that is able to convert wet biomass or wastewater in supercritical water into gas, clean water and salts. This technology is particularly well suited for the energetic valorisation of wet biomass and sludge. It has also one very important advantage, it allow for recovering the salts contained in the biomass by precipitation. These salts can then be used again as fertilizer. This is particularly important for the phosphorus since its availability is very limited. The peak phosphorus should occur by 2030.
In conventional design this heat is provided by the combustion of a fraction of the produced gas and therefore reduces considerably the biomass to fuel conversion efficiency. With low energetic density wet biomass, this energetic conversion efficiency could even be negative.
This problem could be solved by supplying the heat required by HTG with an external renewable heat source. The heat produced by concentrating solar irradiation is particularly well suited for this application. This project proposes to study the coupling of a solar thermal plant with a HTG plant in order to increase the HTG conversion efficiency and store the solar energy in the fuel produced. This new innovative process has been called “Solar-HTG”.
The optimal design of plants in which a stationary process, such as HTG, is coupled with an intermittent utility such as solar thermal plant, represent a challenge. The mathematical models need to be developed deal with time dependent variables, integer variables, highly non-linear and discontinuous objectives functions.
Keywords:
- Optimal design
- Hydrothermal gasification
- Solar energy
- Waste biomass valorisation
Contact: Alberto Mian
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