ITMI20060343A1 - METHOD FOR OBTAINING COMBUSTIBIKES DERIVED FROM PRE-NEUTRALIZED WASTE FUEL SO IT HAS OBTAINED AND ITS USE IN COMBUSTION - Google Patents

Description

Description of the patent for industrial invention entitled:

"METHOD FOR OBTAINING FUEL DERIVED FROM PRE-NEUTRALIZED WASTE, FUEL SO OBTAINED AND ITS USE IN COMBUSTION"

DESCRIPTION STATE OF THE ART

The present invention relates to a non-conventional fuel that is neutralized before being fed to the incinerator.

In particular, it concerns MSW (Urban Solid Waste), RDF (Refuse Derived Fuels) or industrial solid waste.

The waste and among these the MSW contain significant percentages of chlorine, bromine, fluorine and sulfur which are the main cause of the acidity of the fumes and the production of organic micropollutants such as dioxins and / or furans.

To reduce the acidity of the fumes and mainly the hydrochloric, hydrobromic, hydrogen and hydrofluoric acids as well as the sulfuric anhydride present in the fumes, bases such as soda and / or lime and / or bicarbonates injected into various points of the system are used.

Experience shows that it is convenient to use soda at a high temperature and typically in the incineration oven or after the oven itself because in these conditions the soda is in the vapor phase and has a high efficiency.

In the case of feeding in the oven, the drawback is the interaction of the soda with the refractory of the oven. Nebulization after the oven and before the boiler is a little less effective and requires a greater excess of reagent with a consequent increase in the soiling of the boiler tubes.

In the patent EP 744208 of the same applicant it is proposed Γ feeding the soda already vaporized after the boiler in order to have the advantages without the drawbacks of the previous methods but with a somewhat more complex system as an implementation.

All these methods are able to offer an almost complete sulfur abatement and a halogen abatement efficiency of around 70%.

Lime or bicarbonates can be advantageously used at a lower temperature and typically around 160 - 180 ° C in the terminal part of the plants before the bag filters on which they are deposited, continuing the neutralization reactions.

The use factor of lime is not high but it is possible to achieve a good reduction of residual acidity below the legal limits.

For this reason, lime is used in combination with soda in order to benefit from the advantages of both methods.

The problem of the abatement of organic micropollutants such as polychlorinated dibenzo dioxins and polychlorinated dibenzo furans is a bit more complex because in the presence of chlorine these are formed during Γ incineration, if the combustion is not well controlled, but above all they are formed at a lower temperature in the boiler if all the chlorine has not been eliminated before the boiler.

The emission limits imposed by the European Union are very restrictive and equal to 0.1 ng / Nm3, expressed as the toxic equivalent of 2, 3, 7, 8 tetrachloro dibenzo dioxin, equivalent obtained as the sum of specific dioxins and furans normalized with a coefficient proportional to the specific toxicity of each.

Currently the problem of organic micropollutants present in the fumes of incinerators is treated with particular technologies such as:

- the optimization of combustion processes, for example through fuels such as RDF with reduced organic residues

- the minimization of compounds that can act as precursors in the synthesis at low temperature in the boiler, for example chlorine - the use of powdered activated carbon dispersed in the fumes, on fixed beds or in liquid suspension before being released into the environment. he can see the technologies for the abatement of organic micropollutants intersect in part with those for the elimination of acid substances from the fumes.

For example, the patent IT 01306951 of the same applicant uses RDF and soda fed directly into the RDF waste combustor for the purpose of efficient immobilization of chlorine and other halogens. The combustion of the organic is more efficient and the drastic reduction of chlorine avoids the de novo synthesis of dioxins in the boiler around 600 ° C.

This technique, while being very efficient for both the reduction of acidity and micropollutants, has the disadvantage of exposing the refractory walls of the combustion furnace to a potential attack by the soda sprayed in it.

PRESENTATION OF THE INVENTION

Therefore, the subject of the present invention is a new fuel derived from waste neutralized at the origin before being fed to the incineration furnace which does not have the drawbacks of the prior art.

A particular object of the present invention is a method for making said new fuel starting from an ennobled fuel such as an RDF obtained by bio-drying MSW or starting from fuels with a higher calorific value such as RDF refined according to the method disclosed in the EP-A patent. -706839 by the same applicant.

A further object of the present invention relates to the use of this new fuel in incinerators with the aim of reducing acid substances and organic micro-pollutants in the fumes.

Therefore, the aim of the present invention is to provide the neutralizing agent at the time of combustion thus avoiding the production of acid fumes to be neutralized in a subsequent phase.

Another objective is to reduce the direct contact of the soda with the refractory of the furnace, a potential cause of its more rapid wear.

These objects are achieved by the invention, which proposes a method for the production of fuel derived from waste having the characteristics of the attached independent claim 1, and such a fuel derived from waste having the characteristics of the attached independent claim 7.

Preferred embodiments of the invention appear from the dependent claims.

It has in fact been found that bio-dried wastes are greedy for aqueous solutions, being able to absorb up to 60% of their weight and therefore, when said wastes are put in contact with suitably dosed solutions of caustic soda, they adsorb it completely.

Bio-dried waste normally has a water content between 17 and 20% by weight and is made up of plastic, wood, paper, dry food residues and mineral and metal inert materials.

The product obtained from the bio-dried by refining was deprived of the fine undercut and the metals and was ground to a particle size around a few centimeters.

These materials also contain 0.5 - 0.8% by weight of halogens and typically chlorine and 0.2 - 0.4% sulfur.

The amount of stoichiometric soda to be added is therefore very small and around 10 - 20 grams per kilogram of fuel or alternatively 35 - 65 grams of 30% aqueous solution of soda.

The soda, if uniformly dispersed in aqueous solution on the material, diffuses in the cellulosic compounds by hydrolysing them, reacts with the fatty acids originally present in the waste or with the acid substances produced by aerobic fermentation and dehalogenates any halogenated organics possibly present.

The result of this operation is that the soda is bound in the form of organic and inorganic sodium salts and the PH is around the value 10 typical of a solution of a salt of a strong base with a weak acid.

The RDF neutralization operation can be carried out both at the production plant and at the incinerator.

To mix the waste with the soda in solution, it is possible to use various methods such as the nebulization of the solution on the heap of aerated waste and stored at the bio-drying plant or at the incinerator, continuous nebulization on conveyor belts, etc. but it has been seen that it is preferable to spray the solution into the terminal grinding mill of the bio-dried or refined bio-dried product.

This machine is already available on the bio-drying plant, as described in EP-A-706839 and in more detail in IT 01297234 of the applicant, and allows an optimal dispersion of the soda on the waste due to the mixing action that this machine exerts on the waste. during spraying.

The neutralized waste is stored to mature in a pit waiting to be compacted in balances of 20 - 30 tons to be transported to the incinerator.

The reaction of soda with lignin, cellulosic and organic acids and chlorinated present in the waste continues both during transport and in the incinerator's reception pit.

It should also be noted that, although the bio-dried waste is pathogen-free as claimed in EP-A-706839, the treatment with soda offers a further guarantee of sanitation of the waste itself in the case of non-compliant production batches.

The treatment with soda in solution is therefore integrated into the bio-dried production process which includes:

- the coarse grinding of MSW

- the aerobic fermentation in an enclosed space in air flow - the final grinding to medium size (one decimeter) with the addition of soda

- compaction of the waste for transport

It is also integrated into the most complete production process of refined bio-dried products which includes:

- the coarse grinding of MSW

- aerobic fermentation in a closed space in air flow - sieving to separate the fine underscreen

- demetallization

- the final grinding to fine size (a few centimeters) with the addition of soda

- compaction of the waste for transport

It is possible to dose the soda in order to neutralize all the acidity present in the waste, as well as to overdose the soda according to the needs of the incinerator, for example in the case of the co-combustion of the bio-dried product with another non-neutralized waste at the origin. .

In any case, the basicity of the waste is reduced as the amount of soda is completely buffered by the excess of reactive substances present in the waste itself.

In order to better understand the performance of the new fuel object of the present invention and to put it into practice, some non-limiting application examples are given below.

Example 1

The Corteolona (PV) plant has the capacity to process 60,000. t / y of MSW and produces about 30,000 t / y of refined RDF.

MSW are made up on average of paper, cellulosic and wood (33%), plastic (18%), glass, aggregates and metals (8%), organic and undercut (41%) and have a moisture content of around 37% and a lower calorific value (NI) of about 2200 kcal / kg.

After a coarse shredding, the MSW are deposited in heaps and undergo an aerobic fermentation in air flow for about 15 days and lose about 25% of their weight to give a bio-dried product with a moisture content of around 19% and a PCI about 3000 kcal / kg.

The bio-dried product thus produced is screened, deferred and finely ground, losing another 25% of its original weight, to give a refined bio-dried product containing paper, cellulosic and wood (45%), plastic (32%), glass, aggregates and metals (4% ), organic (19%) and having a humidity of around 17% and a PCI of 3800 kcal / kg.

The acidity content of the waste in production without neutralization is around 0.4% by weight expressed as equivalent in HCl and therefore in soda.

The stoichiometric soda is therefore 4.3 kg / t of waste and in a 30% solution 14 kg / t.

For the needs of the incinerator, 30 1 / t of soda were added during fine shredding.

The pre-neutralized material thus had a negligible increase in weight and a decrease in PCI (3%) and pulped in water has a PH around 10 indicating that the added soda has been completely buffered by the weak organic acids present.

In a campaign lasting 15 days, 1300 t of fuel were produced which, compacted in 20 t piles, was sent to the incinerator in Filago (BG).

Example 2

The incinerator located in Filago (BG) has an incineration capacity of up to 100,000. t / y of industrial waste consisting of polluted earth, organic waste with high calorific value, aqueous waste with low calorific value and other various waste.

A certain amount of RDF is also fed to the incinerator as a PCI supplement to the mix of fed waste.

The plant consists of a rotating drum furnace for solids followed by a static chamber for the combustion of liquids and post-combustion.

The combustion fumes pass through a boiler where about 40 t / h of steam are produced, which are expanded in the turbine to give 9 MW of electrical power, pass through an electrofilter, are cooled in an atmospheric unit and filtered in a bag filter before being sent to the fireplace.

The reduction of acidity and organic micro-pollutants is achieved by injecting soda into the combustor and adding lime powder and activated carbon before the bag filter.

The flue gases are subjected to a continuous analysis using the FTIR (Fourier Transform Infra Red) technique to determine the concentration of the acids.

Furthermore, a chimney analysis is periodically carried out according to the EN 1948 standard to determine the concentration of dioxins and furans discharged into the environment.

During the three years that have elapsed since the start-up of the plant, the concentration of HC1 was lower than 5 ppm (compared to 50 ppm by law), that of S03 practically zero and that of micropollutants lower than 0.1 ng / Nm3 prescribed by European Union regulations.

However, during the start-up period, the nebulized soda was fed with low-calorific water also in the rotary kiln and a certain deterioration of the refractory was noted, the duration of which was 30% lower than expected.

It was therefore decided to nebulize the soda as far as possible in the static chamber and in correspondence with the refurbishment of the refractory in the last stop (after 2 years from start-up) to use more acidic and base-resistant refractories and to carry out periodic coatings of the rotating drum. with glassy matrices.

Among the tests carried out, the feeding of activated carbon was suspended for a short time, however, obtaining a peak of 2 ng / Nm3 for micropollutants.

The RDF prepared as described in example 1 was therefore fed into the rotating drum to replace the 3 t / h RDF not neutralized and at the same time gradually reducing from 90 l / h to 10 1 / h of 30% soda fed into the chamber static.

The concentration of HCl was lower than 0.5 ppm and that of organic micropollutants lower than 0.1 ng / Nm3 demonstrating the abatement efficiency of the new fuel object of the present invention.

In the final phase of the test, which lasted about two weeks, the introduction of activated carbon was stopped and the organic micropollutants always remained below the limit of 0.1 ng / Nm3.

It can be deduced that the new fuel shows a higher efficiency in stopping the HCl in the bud compared to the neutralization in the fumes once formed and therefore in not making it available for de novo synthesis in the boiler.

Claims (11)

CLAIMS 1. Method for the production of fuel derived from waste (R. D. F.), in particular from solid urban waste (R. S. U.), comprising the following steps: - coarse grinding of R. S. U., - aerobic fermentation, preferably in a closed space in air flow, - possible screening to separate the fine underscreen, - possible demetallization, - final grinding to medium or fine size, - compaction of waste for transport and possible storage, before incineration, characterized by the fact that during or after any of the aforementioned phases, between said coarse grinding and said incineration, a sufficient amount of soda is added to the waste at least to neutralize the acidity present in the waste. 2. Method according to claim 1, characterized in that the addition of soda is overdosed in case of incineration in co-combustion with non-neutralized waste. 3. Method according to claim 1 or 2, characterized in that said neutralization soda is added in solid form or in aqueous solution. 4. Method according to any one of the preceding claims, characterized in that said neutralization soda is added during said final grinding step to medium or fine size. 5. Method according to claim 4, wherein said soda is sprayed in aqueous solution on the waste in the final grinding step. 6. Method according to claim 1, wherein said soda is added in a stoichiometric quantity of from 10 to 20 grams per kilogram of fuel. 7. Fuel derived from waste, following coarse grinding, aerobic fermentation, possible screening and demetallization, final grinding and compaction, characterized by the fact that it contains soda, added in sufficient quantities at least to neutralize the acidity present in the waste. 8. Fuel according to claim 7, characterized in that said soda is present in a stoichiometric quantity from 10 to 20 grams per kilogram of fuel. 9. Fuel according to claim 7 or 8, wherein said soda is added in an aqueous solution, preferably at 30%. 10. Use of the pre-neutralized fuel according to any one of claims 7 to 9, in incinerators. 11. Use of the fuel according to claim 10, in co-combustion with non-neutralized waste at origin.