ITMI961754A1 - INTEGRATED PROCEDURE FOR ENERGY RECOVERY FROM MUNICIPAL SOLID WASTE - Google Patents

Description

The present invention relates to an integrated process for energy recovery from urban solid waste,

Currently one of the methods for disposing of municipal solid waste involves collecting them and transferring them to incineration plants with energy recovery or to pre-treat them in order to produce RDF.

In the case of collection over large areas, transfer stations are created where the waste is compacted in order to reduce transport costs.

RDF production plants provide for the shredding of waste, the separation of putrescible components from combustible ones and from inorganic-based ones such as metals and glass.

The separation is very complex and the separated combustible portion, still contaminated by foul-smelling putrescible substances, generally does not exceed 30%.

In RDF plants, the putrescible portion is partly oxidized to compost, a material that has no useful application and is generally disposed of in landfills. Even the inorganic materials recovered in these plants are generally smelly and difficult to reuse.

The insertion plants, on the other hand, have a low energy efficiency as the waste is made up of heterogeneous batches with variable calorie content. For this reason, combustion takes place in grid systems or, with greater difficulty, in fluidized bed systems where the energy efficiency is very low.

Furthermore, in the combustion area there are not indifferent quantities of waste which take long times for complete combustion, making the regulation and shutdown of the plant, in case of emergency, long and complex operations.

A process has now been found by the Applicant for recovering the energy produced by the combustion of municipal solid waste which is not only free from the aforementioned drawbacks but allows an efficiency at least 50% higher than the processes used up to now, since the recovery of thermal energy for combustion is also integrated with a recovery of energy developed during an aerobic fermentation phase.

Therefore, the object of the present invention is an integrated process for energy recovery from urban solid waste which comprises: a) coarsely shredding the waste coming from the collection areas;

b) ferment and dry the organic / biological components of the shredded waste in a closed environment and in the presence of air;

c) filter the air coming from the fermentation through biofilters;

d) recover the energy developed during the fermentation phase from the filtered air;

e) grind, at the same time as stages (c) and (d), the dried waste into pieces with a grain size equal to or less than 3 cm;

f) treat the waste coming from the staff (e) to eliminate the aggregates from the organic residue; g) compacting and / or burning the organic residue thus obtained.

According to the present invention, the first stage of the process provides for the coarse shredding of the waste coming from the collection and contained, therefore, still inside the plastic bags.

The term coarse shredding, as understood in the present description and in the claims, essentially means an operation which avoids the formation of anaerobic fermentation pockets in the mass of waste to be treated. Therefore, this operation essentially consists in a homogenization of the waste mitigated by the demolition of the plastic bags.

In this phase, the rigid components of the waste, such as glass, plastic, inorganic fillers (stones, bricks from the demolition of civil works, metals, etc.), remaining inside the mass to be fermented, guarantee a certain porosity and permeability to the 'air. The latter is passed through the mass of waste, of high thickness (even up to 18-20 meters), by blowing and / or suction from below.

The aerobic fermentation starts spontaneously and causes a temperature increase of the waste up to 60-70 ° C. The increase in temperature favors the drying of the material, the water content of which passes from 35-50% to 15-20% by weight. The fermentation / drying operation ends when the dehydration of the waste reaches a value that is no longer compatible with the microbiological activity.

Generally, the fermentation and drying operation lasts from 15 to 25 days, depending on the quantity of air blown or sucked in, its relative humidity, the humidity of the waste, the external temperature, the organic substance content, etc.

In order to carry out the fermentation operation without environmental impact, the air, after passing through the waste layer, is filtered through biofilters. Biofilters are known in the literature, for example they are described in patent SU 1.337.1S7, and consist of porous layers of peat mixed with wood bark or green compost having a thickness of between 50 and 150 cm.

The air stream that comes out of the biofilters is perfectly deodorized, has a temperature of about 40-45 ° C and carries the fermentation products which are not degraded by the bacterial flora present on the components of the biofilter and which essentially consist of water, in the form moisture, and carbon dioxide. The energy content of the air coming out of the biofilters can be enhanced by recovering the heat with known methods or by integrating the process object of the present invention to a system of greenhouses for horticulture, floriculture where the energy produced during fermentation (heat, CO2 and water) is completely recovered.

The waste, after the fermentation stage, is perfectly odorless, with a good water-repellent index, with a weight loss of around 25-35%. Therefore, they can be transported from the closed fermentation environment and sent to a subsequent grinding stage without the risk of spreading harmful odors in the surrounding areas.

During the second grinding stage, the waste is reduced to a size of less than 3 cm, preferably less than 1 cm, and sent to a separation section to eliminate the inorganic components from the organic ones.

In particular, in a first phase, ferrous and non-ferrous metal materials are separated by means of electromagnets, permanent magnets and magnetic induction and then the inorganic aggregates such as glass, bricks, stones, etc., by screening.

The residue appears as a combustible material (RDF) with a lower calorific value of about 3.00C-3.500 Kcal / Kg which can be burned in a combustion plant integrated with the process object of the present invention or can be compacted in a container arranged on of a vehicle and transported to a remote combustion plant. Alternatively, the residue can be compacted into bales, possibly waterproofed with polyethylene film and buried in landfills

without risk of environmental pollution.

Claims (8)

CLAIMS 1) Integrated process for energy recovery from municipal solid waste which includes: a) coarsely shred waste from collection areas; b) 'ferment and dry the organic / biological components of the shredded waste in a closed environment and in the presence of air; c) filtering the air coming from fermentation through biofilters; d) recover from the filtered air the energy developed during the fermentation phase; e) grind, at the same time as stages (c) and (d), the dried waste into pieces with a grain size equal to or less than 3 cm; f) treating the waste coming from step (e) to eliminate the aggregates from the organic residue; g) compacting and / or burning the organic residue thus retained. 2) Process according to claim 1, in which the coarse grinding of the waste is carried out in such a way as to avoid the formation of anaerobic fermentation pockets. 3) Process according to claim 1 or 2, wherein the fermentation air is passed through the waste mass by blowing and / or suction from below. 4) Process according to any one of the preceding claims, in which the air, after passing through the waste layer, is filtered through biofilters consisting of porous layers of peat mixed with wood bark or green compost having a thickness between 50 and 150 cm. 5) Process according to any one of the preceding claims, in which the energy content of the air coming out of the biofilters is recovered by feeding the air to a greenhouse system for horticulture, floriculture. 6) Process according to any one of the preceding claims, in which the waste, after the fermentation stage, is ground and reduced to a size of less than 1 cm. 7) Process according to any one of the preceding claims, in which the ferrous and non-ferrous aggregates are separated from the organic residue by means of electromagnets, permanent magnets and magnetic induction, while the inorganic aggregates are separated by screening. 8) Process according to any one of the preceding claims, in which the organic residue is burned in a combustion plant integrated with the present process or is compacted in a container arranged on a vehicle and transported to a remote combustion plant.