Greene's technology recovers all kinds of organic waste in a profitable way, via gasification, regardless of its humidity, composition, calorific value or morphology. This innovative technological development stands out for its versatility and energy efficiency, making it the most flexible gasification technology on the market.
In gasification, unlike incineration, the amount of oxygen present during the process is limited, i.e. just 25-30% of oxygen is needed to complete the combustion of organic matter, which gives rise to many environmental advantages.
Moreover, during gasification the chemical energy stored in organic matter is turned into chemical energy contained in a gas. Said gas can be used as fuel to obtain energy for engines, gas turbines or boilers. Residual ashes may either be treated as waste or used for energy recovery as a building material, fertiliser or for glass manufacturing, among other uses. If the organic matter is a low-ash content waste and its resulting ashes cannot be recycled, after the process it will still have been possible to significantly minimise the waste volume, reducing it to inert ash and taking advantage of its energy content.
Therefore, gasification is an efficient technique for reducing solid waste and recovering energy from such waste, and is thus the most appropriate way to produce electricity and thermal energy as part of sustainable development.
A wide variety of materials containing carbon, such as coal, biomass, organic and carbonaceous waste, can be gasified.
The resulting gas contains carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2), methane (CH4), small amounts of other heavier hydrocarbons, water (H2O), nitrogen (N2) when using air as a gasifying agent, and various pollutants such as fine carbonaceous particles, ashes, tars and oils.
CO, H2 and CH4 contained in the resulting gas give it calorific value as they can react with oxygen in a combustion engine, a boiler or a gas turbine.
Organic matter gasification occurs in a number of sequential steps:
Drying (endothermic process): to evaporate moisture contained in the matter.
Pyrolysis (endothermic process): thermal decomposition occurring in the absence of oxygen. This takes place between 300 and 600 ºC. Volatile elements are released. As the amount of oxygen within the reactor is insufficient, some of these volatiles cannot be thermally destroyed, resulting in unwanted tars.
Partial combustion (exothermic process): oxidation of the carbon (char) which has remained after the pyrolysis. This occurs between 600 and 1100 ºC.
Gasification (endothermic process): this process occurs as the char reacts with CO2, H2 and H2O, producing fuel gases, mainly CO, H2 and CH4.
Partial combustion supplies the energy required to perform the rest of the processes, which are endothermic. It is important to control the fuel/oxidising agent ratio to ensure that the heat generated by the exothermic process is equal to that invested in the endothermic processes, thereby maintaining a thermal balance called autothermal.
Organic matter combusts in the presence of oxygen. As the oxygen concentration in the reactor is insufficient, CO is then produced through incomplete combustion. The excess organic material reacts with the gases present, mainly with CO2 and H2O. The presence of steam favours the production of H2.