ITTO20120760A1 - PROCEDURE AND PLANT FOR THE DISPOSAL OF WASTE OF ALGAL ORIGIN - Google Patents

Description

Description of the Industrial Invention entitled:

"Process and plant for the disposal of waste from aigaie origin",

TEXT OF THE DESCRIPTION

Field of the invention

The present invention relates to the issue of the disposal of waste of aigaia origin, such as residues of aquatic plants and algae which - typically in the event of storm surges - reach the coasts and accumulate in correspondence with beaches and ports.

State of the art

A very common aquatic plant in the Mediterranean Sea is the Posidonia Oceanica, a marine phanerogama that lives on the seabed at a depth ranging from a few centimeters to about 40 meters. Like all plants, Posidonia oceanica loses its leaves (typically in autumn-winter or following strong storms), which are collected in the sea and are then transported by storms near the shore line before, slowing down the wave motion, for then eventually settle on the beaches and / or accumulate in port areas. At the beginning, the accumulations consist essentially of intact dead leaves, but the action of the wind and the mass of water causes them to mix with sand particles and favors their mechanical degradation. After being deposited on the beaches, the loss of moisture in the leaves due to sunstroke and decomposition by the beach fauna promote their degradation. In case of accumulations in water in correspondence of the ports, the dead leaves must in any case be collected and then evacuated, preferably after their natural drying on site.

From an ecological point of view, the accumulations of dead leaves on the beaches can be kept in place, so as not to upset the natural biological cycle of the plant. In this way it is also possible to benefit both from the anti-erosion and stabilization function of the shore line operated by the accumulation of leaves, and from a luxuriant dune vegetation, thanks to the abundance of nutrients coming from the decomposition of the leaves themselves. However, in areas subject to bathing frequentation it is necessary to remove the accumulations of dead leaves and treat them substantially as municipal waste, and therefore to be returned to the landfill, with the consequent costs.

In some cases the plant material, cleaned of waste, is buried under the sand, or moved away from the shoreline, in more secluded areas of the beaches: these compromise solutions, however, prove to be unsatisfactory and do not comply with current legislation.

Summary of the invention

In view of the foregoing, the present invention essentially proposes to indicate a process and a plant that allow to obtain an efficient disposal of beached residues of marine plants and algae, where in particular such residues constitute an energy resource, rather than being treated as a mere urban waste.

This object is achieved, according to the present invention, by a process and a plant having the characteristics indicated in the attached claims. The claims are an integral part of the technical teaching provided herein in relation to the invention.

Brief description of the drawings

Further objects, characteristics and advantages of the invention will become clear from the following detailed description, made with reference to the attached drawings, provided purely by way of non-limiting example, in which:

- Figure 1 is a flow chart aimed at representing the steps of a possible procedure according to the invention; And

- Figure 2 is a block diagram of a possible system for the implementation of the procedure according to the invention.

Description of preferred embodiments of the invention

The reference to "an embodiment" within this description indicates that a particular configuration, structure, or feature described in relation to the embodiment is included in at least one embodiment. Therefore, the terms "an embodiment" and the like, present in different parts within this description, are not necessarily all referring to the same embodiment. Furthermore, the particular configurations, structures or features can be combined in any suitable way in one or more embodiments. The references used below are for convenience only and do not define the scope of protection or the scope of the forms of implementation.

In the context of this description, the generic term "biomass" identifies any substance of organic, plant or animal matrix intended for energy purposes. The more specific term "algae biomass" includes residues of algae and aquatic plants, such as the beached dead leaves of Posidonia Oceanica.

The idea behind the present invention is to use an aigaie biomass for the purpose of generating energy, and particularly for both electricity and thermal energy.

For this purpose, according to the invention, the aigaie biomass is used to feed a pyrogasification process, for the purpose of obtaining a fuel synthesis gas or syngas which, suitably treated, can be used to power one or more endothermic engines. suitable for the production of electricity. An aigaie biomass of the type indicated, however, is not in itself usable in a pyrogasification process, either due to its content of residual moisture, sand and salt, or because it is not suitable for triggering the process of obtaining syngas. For this reason, according to the invention, the aigaie biomass is mixed with at least one complementary biomass. The resulting mixture, preferably after a drying step, is subjected to compaction, in order to obtain briquettes which feed the pyrogasification process.

In a preferred embodiment of the invention, the complementary biomass is a biomass of the "marginal" type, that is, of the residual heterogeneous type from agricultural, agro-industrial or agroforestry production cycles. In this context, the preferred biomasses are ligno-cellulosic biomasses, and in particular wood chips, i.e. wood reduced to flakes, produced through a chipper starting from logs, pruning residues, agricultural and forestry processing residues or wood processing. The preferred use of wood chips is due to the high energy content of this type of biomass (generally higher than 4,000 kCal / kg). However, other biomasses are not excluded from the scope of the invention, such as agricultural residues such as straw and stalks). Preferably, the starting wood comes from non-resinous plants, in order to prevent residues of natural resin in the wood from triggering a combustion process during pyrolysis.

Pyrogasification is a per se known process of biomass gasification, the main final product of which is a synthesis gas, known as syngas. This process, and the means for carrying it out, are known per se and will therefore not be described in detail.

Here it is enough to recall that pyrogasification essentially consists of a double thermochemical splitting reaction, divided into two stages carried out in two successive reactors (pyrolysis reactor and gasification reactor), belonging to the same plant (pyrogasifier).

The first stage is represented by pyrolysis, which consists in a process of physical and chemical decomposition of the biomass, obtained by heating the biomass itself (indicatively from 300 to 600 ° C) in an oxygen-free environment (or with a quantity of oxygen below the stoichiometric ratio). This decomposition splits the material into two states: a gaseous phase, consisting of a mixture of condensable and incondensable gases and liquid compounds, and a solid phase, consisting of coal.

The second stage is gasification. The coal obtained from pyrolysis is partially combusted with oxygen and / or atmospheric air and the pyrolysis gases, added with steam, undergo a reforming process (breaking of higher molecules into simpler molecules inside the pyrolysis gas). The temperature inside the gasification reactor is indicatively maintained at 1,000-1,100 ° C, by regulating the introduction of oxygen. By using oxygen and water, synthesis gas or syngas is obtained. The syngas thus produced is cooled, using water as a cooling medium which is then condensed and put back into circulation, purified and filtered (for example washed through a Scrubber type plant and an activated carbon filter) and then stored and / or used, for example in a cogenerator to produce electrical and thermal energy.

A possible implementation of the invention is described below, with reference to the figures, which schematically represent a possible sequence of the steps of the procedure (Figure 1) and related operating units that carry out these steps (Figure 2).

The aigaie biomass and complementary biomass are temporarily stored in respective dedicated areas, for example consisting of sheds or canopies (blocks 1 and 2 in figure 2). The transport of such biomass to the plant takes place in a manner known per se, for example by means of agricultural machinery (agricultural tractor with trailer, or trucks equipped with articulated / tipping bodies). In the following it is assumed that the complementary biomass is made up of wood chips.

The aigaie biomass is then fed to a recirculating water washing station. Such a station (block 3 of figure 2) can comprise a tank in which the biomass itself is first poured and stirred - for example by means of rotary agitators - to remove salt, sand and any other surface residues. The biomass can then be loaded, in known ways, on a suitable conveyor, along which the biomass itself is rinsed by jets of water.

The water used in the washing station is preferably purified for its re-introduction into the circulation. For this purpose, a filtration system can be operatively associated with the washing station, comprising for example bag filters and / or membrane filters. Any excess water from the washing of the aigaie biomass is also preferably purified, before its discharge from the system (block 4 in figure 2), for example in a surface bed.

The biomass aigaie leaving the washing station is conveyed, by means of a conveyor, to a shredding station (block 5 of figure 2), of known construction. The complementary biomass is preferably also fed to this shredding station, by means of a suitable conveyor, although nothing prohibits in principle that the aigaie biomass and the complementary biomass are shredded in different stations. In the shredding station the two biomasses are then shredded, in order to make the size homogeneous, which is preferably between 30 and 50 mm. This homogeneity of size is advantageous both for the purposes of subsequent loading and handling of the mixed biomass (reduction of the risk of jamming), and for the purpose of subsequent compaction aimed at obtaining briquettes.

Preferably, the two biomasses are shredded together in the same station, with a weight ratio substantially equal to 1: 1, i.e. with a mass subjected to shredding consisting of about 50% of aigaie biomass and 50% of complementary biomass.

The shredded biomass leaving the shredding station (or stations) are then conveyed to a drying station (block 6 of figure 2), also of a per se known concept, in which the biomasses themselves are dried to a content humidity indicatively not higher than 20%, preferably not higher than 15%. The drying takes place preferably using hot air, obtained from the recovery of part of the heat of the gas produced in the gasification process, after having transferred a portion of it to the pyrolysis reactor; for this purpose, heat can also be recovered from the cogeneration plant, described below. If the two biomasses are shredded in different stations, the subsequent dehumidification can take place in different drying stations or in the same station.

The dried biomasses are then conveyed to a mixing station (block 7 in figure 2), also achievable according to a known technique, in which the biomass itself is stirred in order to create a homogeneous mixture. The mass that feeds the mixing station preferably comprises about 30% of aigaie biomass and about 70% of complementary biomass, regardless of whether the two biomasses have been crushed and / or dried jointly or not.

After drying, the mixture of the two biomass feeds a briquetting station (block 8 in figure 2), comprising a briquetting machine or similar press - preferably hydraulic - suitable for the hot production of briquettes, with a round or square section. Preferably, the briquetting phase is carried out without the addition of binders or additives, simply exploiting the strength and heat that develops during the process.

Through the briquetting phase, the mixture of the two biomasses is strongly compressed and compacted, obtaining a significant reduction in the volume of materials (indicatively up to 90%, with a density of less than 1%). The mixture can be fed to the briquetting press through a funnel or hopper, and then transported - for example by means of agitators, augers and pre-compactors - to a real pressing cylinder. From this position, briquettes of the desired lengths are obtained by filling the cylinder volume and subsequent compaction. In the pressing cylinder the mixture, due to friction and compression of the transported air, reaches a high temperature during the extrusion phase (even higher than 130 ° C), thus ensuring further drying and the elimination of germs and bacteria. Subsequently, the briquettes feed the pyrogasifier (block 9 of figure 2).

Given that the pyrolysis process must take place in the substantial absence of oxygen, the briquettes are removed with a transport system, of any known concept, possibly suitable for preheating the briquettes themselves up to a temperature of about 50 ° C. The briquettes transported in this way are unloaded into an accumulation hopper which acts as a feeding lung. From the hopper, by means of a piston thrust system (for example a discontinuous operation hydraulic system), the briquettes are sequentially pushed into the pyrolysis reactor.

Feeding through briquettes has the important advantage of reducing the risk of air entering the reactor; in fact, the briquettes are pushed sequentially into the inlet of the pyrogasifier through the aforementioned piston system, each time constituting a "plug" that opposes the entry of air into the reactor itself. The strong compaction of the briquettes then has the further advantage that, inside the pyrogasifier, the briquettes themselves do not have a tendency to flake or otherwise generate dust that could "suffocate" the pyrolysis process. Furthermore, the briquettes are odorless and sanitized, do not release leachate, eluates and biogas, are stable and non-washable, and with this they can be easily handled and possibly stored even outdoors.

The pyrogasification is carried out in a manner known per se, as previously highlighted. Preferably, however, the pyrolysis step is of the fast type, with heating to temperatures ranging from about 400 ° C to about 500 ° C. As mentioned, in an oxygen-free environment (or with a quantity of oxygen below the stoichiometric ratio), the mixture constituting the briquettes splits into a gaseous phase (essentially condensable and non-condensable gases) and a solid phase (coal / ash ). In the subsequent gasification-reduction phase, the coal / ash - in the presence of oxygen (oxygen in an equivalent stoichiometric ratio) and steam - and the pyrolysis gases undergo a reforming process. During the gasification phase, the temperature is preferably kept below 950 ° C (by adjusting the quantity of injected air).

The waste substances produced by the pyrogasifier are limited to the residual ash from the pyrogasification process, in a quantity equal to approximately Γ8% of the pyrogasified briquettes. These ashes can be collected in a suitable space (block 10 of figure 2) and then be used, for example, as soil improvers in floriculture or in the preparation of cement mixtures.

The syngas obtained from the pyrogasification is then subjected to washing and filtration, in a suitable station (block 11 of figure 2), for example in a Scrubber type plant, with recirculation of the treatment water, and with activated carbon filter. In this way, the syngas is made suitable for the correct operation of the subsequent cogenerator (block 12 of figure 2). After its treatment, the syngas feeds a cogenerator (block 12 of figure 2), for example a cogenerator with an endothermic engine for the production of electrical energy and thermal energy. Part of the electricity produced by the cogenerator can be used to power one or more stations of the plant, and the remaining part sold to a distribution network (block 13 in figure 2).

It is clear that numerous variants are possible for the person skilled in the art to the process and plant described as an example, without thereby departing from the scope of the invention as defined by the attached claims.

As previously explained, in the preferred embodiment of the invention, the biomass that complements the aigaie biomass is made up of wood chips. However, it is clear that, in possible alternative implementations, the complementary biomass or complementary biomasses could be of another nature, selected from those suitable for use in a pyrogasifier, such as agricultural processing residues other than wood chips (straw, stalks, etc). Preferably, the complementary biomass that can be used will be biomass having an energy content of not less than about 2,500 kCal / kg.

Claims (10)

CLAIMS 1. A waste disposal process of aigai origin, comprising the steps of: a) provide an aigaie biomass, consisting of waste from aigaie origin; b) provides a complementary biomass; c) mixing the aigaie biomass and the complementary biomass to obtain a substantially homogeneous mixture; d) compaction the mixture to obtain briquettes; e) feeding a pyrogasifier with the briquettes to obtain a synthesis gas or syngas; And f) subjecting the synthesis gas to purification and / or filtration, before its storage and / or its use. The process according to claim 1, wherein the purified and / or filtered synthesis gas feeds at least one internal combustion engine of an electrical energy and thermal energy generator. 3. The process according to claim 1 or claim 2, in which before step c) the aigaie biomass is subjected to washing, for the elimination of sandy and / or saline residues. 4. The process according to claim 3, in which before step c) the aigaie biomass and the complementary biomass are subjected to at least one of grinding and drying. 5. The process according to any one of the preceding claims, in which the aigaie biomass is based on, or is predominantly constituted by, Posidonia oceanica. The process according to any one of the preceding claims, wherein the complementary biomass is a ligno-cellulosic biomass, preferably a biomass based on, or predominantly consisting of, wood chips. 7. A waste disposal plant of aigai origin, for the implementation of the procedure according to one or more of claims 1 to 6, comprising: - means for mixing the aigaie biomass and the complementary biomass, to form a substantially homogeneous mixture; - means for compacting the mixture and forming briquettes; - a pyrogasifier; - means for feeding the briquettes to the pyrogasifier; - means for purifying and / or filtering the synthesis gas obtained from the pyrogasifier. 8. The plant according to claim 7, further comprising at least one endothermic engine cogenerator fed with purified and / or filtered synthesis gas. 9. The plant according to claim 7 or claim 8, comprising, upstream of the means for compacting the mixture and forming briquettes, at least one of means for shredding the aigaie biomass and the complementary biomass and means for drying the aigaie biomass and the complementary biomass. 10. The plant according to claim 9, comprising means for washing the aigaie biomass upstream of the means for drying the aigaie biomass and complementary biomass.