ITTO20090125A1 - GASIFICATOR EQUIPPED WITH A PERFECT COMBUSTION CHAMBER - Google Patents

Description

Gasifier equipped with an improved combustion chamber

The present invention relates to a gasifier for the gasification of biomass having an improved combustion chamber in order to obtain a final product consisting of lean gas, which, after suitable treatments, can be fed to an internal combustion engine.

From the known literature on the subject it is clear that, by "biomass" we mean everything that has an organic matrix deriving mainly from green plants, such as algae, trees and crops as well as from forest and agricultural residues with the exclusion of plastic materials deriving from the petrochemical industry , as well as traditional fossil fuels (oil, coal) <1>. Biomass is the most sophisticated form of solar energy storage, which allows, through photosynthesis, to transform atmospheric CO2 into organic substance useful for the growth of the plant itself. In it, solar energy, transformed by photosynthesis, is stored in the form of chemical bonds between the carbon, hydrogen and oxygen atoms of the main molecules (essentially carbohydrates). As part of the processes of

1 Peter McKendry, Energy production from biomass (part 1): overview of biomass, Bioresource Technology 83 (2002) 37-46.

conversion of biomass such as digestion, combustion or decomposition, this chemical energy stored in the form of bonds is released making it available to be used directly or indirectly <2>.

The benefits deriving from the use of biomass in energy terms are many and the most important are:> � reduction in the amount of solid waste to be disposed of;

� containment of CO2 emissions, since the CO2 produced during the combustion of biomass is <reabsorbed by new biomass planted in equal quantities;> � it is a form of renewable energy, due to the considerable presence of resources in nature, as well as the speed of regenerating biomass relatively quickly.

As for the biomass-to-energy conversion processes, they include a wide range of conversion types, which can in turn be differentiated by biomass fed, end uses and required infrastructures. The factors that influence the <choice of the most suitable conversion process are:>

<� the type and quantity of biomass fed;>

� the form of energy desired, or the final goal; � environmental parameters;

Economic conditions;

� project specifications 3.

2 Peter McKendry, Energy production from biomass (part 1): overview of biomass, Bioresource Technology 83 (2002) 37-46.

3 Peter McKendry, Energy production from biomass (part 2): conversion technologies, Bioresource Technology 83 (2002) 47-54.

Mainly the processes of converting biomass into energy can be traced back to two broad categories: thermochemical processes and biochemical processes. Among the thermochemical processes there are combustion, pyrolysis and gasification; while among the biochemical ones there is aerobic or anaerobic digestion (with production of biogas) and fermentation (with production of ethanol).

The purpose of the present invention is to propose a biomass gasifier having a combustion chamber with an innovative shape, for which we will focus especially on this specific energy enhancement technology in the context of the aforementioned thermochemical processes.

The simple combustion of biomass is a very common practice to quickly convert the chemical energy of biomass into multiple "outputs" such as heat, mechanical power or electricity. The final output depends on the type of plant used which can be stoves, ovens, boilers, steam turbines, turbogenerators, etc. The hot gases produced by the combustion of biomass have variable temperatures in a range between 800 ° C and 1000 ° C, with the possibility of theoretically burning any type of biomass. However, combustion is only feasible when the moisture content in the biomass is less than 50%; higher humidity values, in fact, make the biomass more suitable for a biochemical treatment. The sizes of biomass combustion plants vary from very small sizes, such as domestic use, to large-scale industrial plants with power from 100 MW to 3000 MW with variable yields between 20% and 40% <4>.

Pyrolysis, on the other hand, is the thermochemical decomposition process of the organic materials contained within the biomasses, by means of the supply of heat at a temperature of about 500 ° C and in severe oxygen deficiency. The products of pyrolysis are gaseous, liquid and solid, in proportions that depend on the pyrolysis methods (fast, slow, conventional) and on the reaction parameters. Pyrolysis is essentially used for the production of bio-oil using fast pyrolysis (or flash pyrolysis) with a conversion efficiency of approximately 80%.

Finally, gasification is a process of converting biomass into a gas mixture through the partial oxidation of the same biomass at high temperatures (800 ° C - 1000 ° C). The lean gas resulting from the gasification process has a composition that depends on the gasifying agent used and the type of reactor used. For the purposes of the application of the present invention, reference will be made to a gasification process with air from which a synthesis gas with a low calorific value (about 4-6 MJ / Nm <3>) is obtained which can be directly burned or constitute fuel for reciprocating gas or turbine engines. In general, the synthesis gas produced can alternatively be used as a raw material for

4 Peter McKendry, Energy production from biomass (part 2): conversion technologies, Bioresource Technology 83 (2002) 47-54.

production of chemical compounds such as methanol which in turn can be used for the production of biodiesel.

The object of the present invention, therefore, is to provide a biomass-fed fixed-bed gasifier with a combustion chamber with an innovative shape, which does not fall within the categories of either an updraft reactor or a downdraft reactor.

In fact, biomass gasification reactors belong to two broad categories: fixed bed reactors and fluidized bed reactors. Among the fixed bed reactors, the different direction of the gasifying agent flow (air) with respect to the bed, mainly gives rise to two different types of reactor: updraft, downdraft.

In the updraft type reactor, the biomass is loaded at the top of the gasifier, while the gasifying agent (air) is introduced from the bottom of the unit through a grid. The biomass, during the descent, is first dried by the hot gases produced that move upwards, producing coal, which continues to descend, and other pyrolysis vapors that join the hot gases produced. Subsequently in the pyrolysis zone all the volatile compounds are separated from the biomass and a considerable quantity of tar is formed, which in part joins the synthesis gas produced at the outlet and in part joins the solid residues. The latter, as they are formed, descend to the bottom to be collected; while in the upper part of the gasifier, where the biomass is dried, the gases produced are cooled to a temperature around 200 ° C - 300 ° C <5>. The downdraft reactor, on the other hand, is characterized by an equicurrent flow between biomass and gasifying agent: the reaction products, before leaving the gasifier, are mixed in a turbulent high temperature region, called diabolo. In this region, the partial cracking of the tar takes place, which limits its excessive production. Due to the high output temperature of the gases produced (about 900 - 1000 ° C), the overall energy efficiency of this reactor is rather low; however the synthesis gas produced is low in dust and tars.

The combustion chamber of the gasifier object of the present invention, on the other hand, proposes a flow of biomass from top to bottom with air supply laterally, thus configuring as a cross flow. The following detailed description will refer to the following tables <attached from 1/5 to 5/5 where:>

� fig. 1 is a 3D view of the upper part of the <gasifier with the combustion chamber inside;>

� fig. 2 is a side view of the upper part of the gasifier highlighting some details of the interior <of the same;>

� fig. 3 is a top view of the upper part of the gasifier;

5 Peter McKendry, Energy production from biomass (part 3): gasification technologies, Bioresource Technology 83 (2002) 55-63.

� fig. 4 shows a longitudinal section of the gasifier, as indicated in fig. 3;>

� fig. 5 is a 3D view of the lower part of the gasifier placed immediately below the upper part of the gasifier shown in fig. 1;>

� fig. 6 is a side view of the lower part of the <gasifier;>

� fig. 7 shows a longitudinal section of the lower part of the gasifier as indicated in fig. 6;>

� fig. 8 shows a cross section of the lower part of the gasifier as indicated in fig. 6.

Overall, the gasifier consists of an "upper" part 1 and a "lower" part 2 mounted respectively one above the other. Descending from top to bottom, in the upper part 1, the combustion process is carried out, which supplies heat to the pyrolysis reactions of the biomass that take place immediately below, up to the height of the adduction holes 11 of the agent gasifier consisting of air. From this point on, the real gasification reactions begin, that is, the reactions that produce the gases useful for the subsequent purposes of the plant. The rotating grid 15 which, suitably sized for the size of the biomass, prevents the same biomass from leaving the still unburned reaction zone, separates the lower zone 2 from the upper one 1. The lower zone 2 is the space in which the reactions are completed gasification; the gas produced is conveyed to the outlet pipe; it allows the fall and collection of the ashes for their removal by means of a special mechanical system (fig. 5).

The upper part 1 of the gasifier consists of an outer casing 3 of an almost cylindrical shape, of an internal section 4 which houses the combustion, pyrolysis and gasification reactions (or reaction chamber 9) and of a series of air spaces 5 between the surface external 3 and internal section 4 of the gasifier. On the external surface there are a plurality of circular openings 6, whose partial opening allows you to regulate the supply of gasifying agent during the production of gas from biomass synthesis. Also on the external side surface of the gasifier there is the gas outlet duct 7 which ends the path of the gases from the reaction chamber, through the cylindrical cavities, to the treatment and supply system of the synthesis gas produced.

As can be seen from the longitudinal section of the "upper" part 1 in fig. 4, inside, starting from the top, follow a truncated cone-shaped inlet area 8 where the biomass is introduced and uniformly distributed by means of suitable mixing devices 12; a reaction chamber 9 characterized by an almost rounded shape, first with an increasing radius then with a decreasing radius; lastly, an outlet section 10, again in a truncated cone shape, partly superimposed on the lower part 2 in correspondence with the grid and the zone of inversion of the motion of the synthesis gas. The lateral supply of the air flow inside the combustion chamber 9 takes place by means of suitable ducts 11 which radially branch off from the combustion chamber 9 towards the outermost interspace 5. The air is regulated by means of a nozzle. air supply, which is surrounded by a perforated ring placed on the side duct in correspondence with the external openings 6.

With a configuration of this type, a "cross" flow is generated inside the reactor 1 and in particular in the reaction chamber 9 between the biomass fed from above moving downwards and the air (gasifying agent) introduced sideways. In this way, a very hot area is formed where the air enters the reaction chamber within which the combustion / pyrolysis and gasification processes take place; the zones of pyrolysis and pre-drying of the biomass are formed, on the other hand, immediately above said combustion / pyrolysis zone. With such a configuration, a type of fixed bed gasifier is obtained which does not fall into either the downdraft or the updraft one.

The "upper" part 1 is kept closed as much as possible by a lid during operation to avoid excess air in the combustion area. Figure 5, on the other hand, shows a three-dimensional representation of the “lower” part 2 of the gasifier, placed immediately below the “upper” part just described. As can be seen from the view in figure 6, said "upper part" 2 consists of a first cylindrical section 13 and a final section 14 with an inverted truncated cone shape, where the ashes are collected as a by-product of the entire process of gasification.

From figures 7 and 8 it can be seen that, inside the cylindrical section 13, there is a rotating circular platform 15 by means of a gear with toothed wheels 16, on which a plurality of perforated grids are placed (due to the biomass size to be treated) 17 for the selective passage of the waste material already consumed by the pyrolysis and gasification reactions.

Fluidized bed gasifiers for biomass, which we have not focused on in this description, are certainly more efficient in terms of overall efficiency, but they involve both initial and maintenance costs higher than fixed bed gasifiers. The latter remain the most convenient option for the production of a synthesis gas with a low calorific value to be used in small-scale power generation plants.

Claims (8)

CLAIMS 1) Fixed bed gasifier fueled by biomass consisting of two parts (upper 1 and lower 2) mounted one on top of the other, where the reaction chamber inside the "upper" part (1) is characterized by an almost rounded shape, with a section at first with an increasing radius and then decreasing in the final section, as well as characterized by the presence of a plurality of ducts (11), which radially radiate from the outside towards the inside and connect the reaction chamber (9) with the external surface (3) by means of the internal interspace (5) to feed the reactions which take place in the same chamber (9) with the gasifying agent coming from the interspace (5) of passage. 2) Fixed bed gasifier fed with biomass according to claim 1, characterized in that the regulation of the gasifying agent to be fed into the reactor takes place by means of one or more supply nozzles located on the side ducts at the external openings (6). 3) Fixed bed gasifier fueled by biomass, according to claim 1 or 2, where the "upper" part (1) consists of an external casing (3) of an almost cylindrical shape, with an internal section (4) comprising the chamber (or zone) of combustion, from a cavity (5) between the external surface (3) and the internal section (4) of the gasifier. 4) Fixed bed gasifier fed with biomass according to claim 2 or 3, characterized by the fact that said external surface (3) is equipped with a plurality of circular openings (6) equipped with valves with various functions including the supply of agent gasifier inside the reactor, as well as a further lateral opening (7) for the outlet of the synthesis gas produced. 5) Fixed bed gasifier fueled by biomass according to claims 1 to 3, characterized by the fact that the internal section of the "upper" part (1), consists of a truncated cone-shaped inlet (8), by mixing elements (12), from the combustion chamber (9) and from an outlet section (10), again in a truncated cone shape, through which the residues of the process pass to the “lower” part (2). 6) Fixed bed gasifier fueled by biomass according to claims 1 and 2, characterized by the fact that the "lower" part (2), placed in series below the upper one (1), consists of a first section shaped cylindrical (13) and a final section (14) with a truncated cone shape with gradually decreasing section, where the ashes are collected as a by-product of the gasification process. 7) Fixed bed gasifier fueled by biomass according to claim 6, characterized by the fact that inside the cylindrical section (13) of the aforementioned gasifier in the "lower" part (2), there is a rotating circular platform (15) by means of of a gear with toothed wheels (16), on which are placed a plurality of perforated grids (17) for the passage of the waste material towards the outlet of the gasifier. 8) System for the production of electrical energy comprising the gasifier (1) and (2) according to one of the preceding claims, aimed in a first stage at the production of a synthesis gas with a low calorific value, subsequently treated for the elimination of impurities unwanted and finally fed to a suitably modified internal combustion engine.