The Process
The MSW unloaded from the trash compactor is loaded in AUTOCLAVE in properly weighed quantities (automatic process); then the treatment starts.
Inside the Autoclave, which is placed with an axle of 15° from the ground and which rotates slowly, an adequate quantity of steam is introduced for a period around 45 minutes.
After that, before opening the discharging door, in order to avoid leakage of the steam not absorbed by wastes, the AUTOCLAVE is depressurized and the residual steam– after being filtered – is recycled for the residual heat recovery.
In the meantime, the second AUTOCLAVE has been charged and prepared for the successive treatment.
The length of the process between loading, treatment and unloading, takes 144 minutes. During this period, the plant completely eliminates smells and products putrescence.
During the treatment, the MSW undergoes a transformation. The entire organic mass present as for example food residual, eventual slaughtering refuses, green waste, nappies and its contents, the tetra pack cellulolytic parts, papers and cardboards etc., is transformed in a mash called “FLOC”-
The remaining material (ferrous and not ferrous metals, glasses, plastics, inert materials) at the end of the process result uncontaminated and sterilized and it is automatically sorted. Everything will reach the recycling market, except possible inert materials and textile, which will be digested in the landfill... while plastic, after separation of the PET (this one also recycled), will be treated into the P2P plant, to be transformed into fuel (Synthetic Oil).
After being properly diluted (10% of dry volatile substance and not) it is subjected to mesophilic anaerobic digestion (37° C.)
Within a period of only 15 days the FLOC, which has been pretreated inside of the AUTOCLAVE, produce an absolutely superior quantity of high quality biogas compared to what so far obtained from traditional plants. Indeed, from 1.000kg of dry volatile substance, up to 550 to 700 mc of biogas can be obtained, with a methane percentage between 60 to 70 % and calorific value included between 5.100 and 6.000 Kcal/mc.
A properly treated Biogas is now directed to the cogenerator to produce Electrical and Thermal energy. The Thermic energy is mainly used for the plant’s energy requirement.
In reference to the different plastics parts, after separating them from the PET (it is suitable to recover it), they are directed to P2P to be transformed into Syngas, Coke and Synthetic Oil.
The plastic pass through a shredder and sent to a melter by a screwpump where to a temperature of 380/400° they gasify almost totally. The residual which is about 10% in weight, is the Coke, which is the treatment product.
The gas generated in the reactor is flowed to the catalytic converter, which select the different chains of monomers formed. During their condensation, the catalytic converter allows the production of a very high-quality fuel mixture.
The not condensed at 40° is a Syngas similar to LPG and it is used to the plant energetic self-feeding.
From the total amount of plastic, it can be obtained:
- Coke = ca. 10% with C.P. of ca. 6,000 Kcal/Kg
- Syngas = ca. 10% with C.P. of ca. 10,000 Kcal/mc. (Used for melter and reactor heating)
- Synthetic Oil= ca. 80% with C.P. of 10,000 Kcal/Kg (Sold as it is, refined or sent to cogeneration)
In order to have a general idea on what can be obtained by MWS processing through autoclave and P2P, we may take into consideration a 60,000 tons/year installation, which satisfies the needs of a catchment area of approximately 150,000 inhabitants. As per average European waste composition (i.e.: Organic 85% paper and cardboard included, Plastics 10%, Other 5%), we obtain:
- Sealable electrical energy 2.5 MW/h, equal to 21,000 MW/year
- 5,000,000 lt. abt of synthetic oil (which can be sold as it is to refineries, or refined through a suitable installation integrated in the P2P, or even transformed into electrical and thermal energy: in this case we will have approx. a further 2.66MW/h, equal to 21,120 MW/year)
- about 600 ton of Coke
Furthermore, into our AUTOCLAVE plant, also pure organic matter coming from separate collection can be processed, obtaining different output results.
A higher biogas quantity, but lack of synthetic oil (because of plastics absence).
This treatment is a perfect alternative to the obsolete and evil-smelling composting plants!
