ES2729851T3 - Plastic-based fuel source with improved combustibility - Google Patents

Abstract

Fine particulate material for use as a fuel source or reducing agent derived from waste plastic material comprising: (a) a cellulose component; and (b) a plastic component, in which the dry weight ratio of the cellulose component with respect to the plastic component is greater than 2: 3 and in which the dry weight ratio of the cellulose component with respect to the component of plastic is less than 9: 1, the cellulose / plastic mixture has a particle size distribution so that at least 95% by weight of the particles in the mixture are less than 2.0 mm, based on the Total dry weight of the cellulose / plastic mixture, the mode of particle size distribution is between 0.3 and 1.8 mm, and in which the cellulosic and thermoplastic materials constitute a total of at least 60% by weight of the mixture, based on the total solid components.

Description

DESCRIPTION

Plastic-based fuel source with improved combustibility

This invention relates to a fuel source based on plastic waste for injection into a skull or oven.

In response to environmental, economic and associated regulatory and legislative impulses, there has been a greater tendency to recycle domestic and industrial waste. The life cycle analysis of recycling processes indicates that decontamination and classification of individual waste component flows are often not viable in economic and environmental terms. Therefore, there is a growing emphasis on the use of industrial and household waste as a source of fuel for power generation or other industrial applications.

The combustion of residues of carbonaceous material in boilers is widespread within the industry. The combustion of carbonaceous material in a boiler is achieved through a group of processes. Initially there is pyrolysis or devolatilization of the carbonaceous material as it heats up, which releases volatile gases and produces coal. This process depends on the properties of the carbonaceous material and determines the structure and composition of the carbon, which will then undergo gasification reactions. The combustion process occurs when volatile products and coal react with oxygen to form carbon dioxide and carbon monoxide that provides heat for subsequent gasification reactions.

Modern coal boilers and power plants are operated by combustion of pulverized coal. The coal is milled to a fine powder in a coal mill, which is an integral part of the power plant and then injected directly by blowing with air into the boiler. Due to the small particle size of less than 0.1 or 0.2 mm, the pulverized coal burns rapidly. It is known that secondary fuels, for example, obtained from waste or biomass, can be burned together with coal as primary fuel, if their combustion characteristics are adequate (i.e., under combustion time). Depending on the type and properties of the secondary fuel, it can be combined with the coal before crushing or it can be ground separately and then injected by blowing air into the boiler, either together with the pulverized coal or separately.

The supply of waste material within a boiler has varied depending on the nature of the waste material and the type of boiler to which it is supplied. Conventionally, plastic-based waste is formed in pellets and combined with coal and introduced into a boiler. For example, US 5342418 discloses the use of a thermoplastic and cellulosic fiber in fuel pellets as a resulting mixture with coal for feeding conventional coal boilers, using conventional coal handling equipment, such as feeders below. from the combustion zone. The characteristics of the pellets were such that they should mix well with the coal and burn as long as the coal, having a typical cross-sectional diameter and a length of 12 mm and 38 mm respectively. While this technology provided an alternative fuel source for agglomerating coal, it cannot replace or be combined with finely ground coal that has a shorter burn time. To overcome this limitation, there has been a significant development in the use of ground waste based on plastic.

WO 97/05218 discloses a fuel pellet for a spray boiler comprising densified thermoplastic material and, optionally, carbon and / or cellulosic material, in which the plastic and cellulosic material is approximately 0.074 to 0, 17 mm The pellets expand at the time of their introduction into a spray boiler to release discrete particles, which, due to their size and density, burn faster than larger particles. It's critical

of plastics, which eliminates static electricity and allows a more controlled mixing of the components. US 5772727 discloses the injection of plastic particles having a size substantially between 1 mm and 10 mm directly in a boiler, to make metal from iron ore. Plastic particles are used as a reducing agent, thus saving the coal or coke used for this purpose. The invention overcomes the flow problems and costs associated with the use of finer ground materials.

Patent document DE 19541673 overcomes the poor fluidity of plastics having a 100% distribution of size less than 2-3 mm, and, more particularly, below 1 mm, by premixing the plastic with ground carbon before its feeding pneumatically to a blast furnace.

Patent documents US 6635093 and EP-A-1 083212 address poor fluidity by producing a fuel pellet forcing a stream of plastic and cellulose waste through granulation die holes with a diameter length ratio of at least 5, so that the heat of friction melts the outside of the pellet. The resulting pellet was hard enough to be fed directly into a boiler. If necessary, the pellets can also be ground using an ultra-rotor to achieve a particle size distribution having at least 80% by weight of the pellet group of less than 2 mm. A high plastic content is preferred (for example, it is preferred above 60% by weight, to achieve this results). The freshly ground product is preferably fed directly into a boiler to avoid any transport problem.

Patent document US 6230634 addresses the problem of the relative low combustion capacity of plastic-based waste material in a boiler, by performing injection through nozzles of synthetic resin material, having a combination of specific limitations with respect to the surface area and / or particle size, in a blast furnace for the manufacture of iron. The paper investigates the combustion ratio, which measures the effectiveness of the synthetic resin material blown in the boiler, compared to the performance of coke particles 20 to 30 mm in diameter. It was found that plastic particles with a particle size of about 2 mm (i.e., 1 to 3 mm) had a significantly reduced combustion capacity compared to coke. Although an additional reduction in particle size was considered to obtain an increase in the specific surface area and, therefore, increase combustion rates, this also resulted in a lower degree of combustion due to the increased volatility of the particles outside the combustion zone. In addition, finer particle sizes are also associated with higher crushing costs and lower crushing yields.

While progress has been made in the use of fuel based on plastic waste for increasingly high performance applications, such as a secondary fuel with finely ground coal in power plants and boilers, further improvements are still required. In particular, the trend towards more efficient boilers that use fuel or reducing agents injected through shuttles, is subject to a fuel source with a low combustion time to allow a clean and complete combustion.

An object of the present invention is to provide a plastic waste material suitable for injection into a boiler or oven, having a good combustion capacity, measured by a low combustion time. Summary of the Invention

In an embodiment of the present invention, a fine particulate material is provided for use as a fuel source or reducing agent derived from waste plastic material, comprising:

(a) a cellulose component; and

(b) a plastic component,

in which the dry weight ratio of the cellulose component with respect to the plastic component is greater than 2: 3 and in which the dry weight ratio of the cellulose component with respect to the plastic component is less than 9: 1, having the a cellulose / plastic mixture a particle size distribution such that at least 95% by weight of the particles is less than 2.0 mm, depending on the total dry weight volume of the cellulose / plastic mixture, being the mode of particle size distribution between 0.3 and 1.8 mm, and in which the cellulosic and thermoplastic materials constitute a total of at least 60% by weight of the mixture, based on the total of solid components

It has been unexpectedly found that the combination of the composition and the particle size distribution of the fine particle material improves the combustion efficiency of the material.

The combination of cellulose and plastic particles provides a synergistic effect with respect to combustibility. While it is not intended to be maintained by theory, it is believed that cellulose particles are burned through a rapid initial vaporization of the material into a carbonized component. In contrast, plastic particles require a higher ignition temperature and, therefore, typically require a longer residence time before combustion begins. However, by providing a sufficient amount of cellulose-derived material in relation to the plastic component, there is a sufficient amount of rapid release of energy from the cellulose portion, so that the plastic particles more quickly reach their ignition temperature, which leads to a total reduction of the combustion time of the combined fuel mixture.

It has also been found that, by grinding the mixture more finely below 2.8 mm, the variation in combustion time is significantly reduced. A low and constant burning time is required to allow boilers and furnaces to be optimized to operate efficiently and effectively.

The ratio between the cellulose component and the plastic component required to achieve a sufficient amount of rapid energy release from the cellulose component, to reduce the burning time of the mixture as a whole, depends on the types of plastics and ignition temperatures , which constitute the plastic component. Those skilled in the art can easily determine the required proportion of the cellulose and plastic components by routine experimentation. Preferably, the dry weight ratio of the cellulose component to the plastic component is at least 1: 1 and more preferably at least 3: 2. The upper limit of the proportion of cellulose component is generally limited to the proportions of available waste material and the energy density value requirements of the fuel source. As such, the upper limit of the dry weight ratio of the cellulose component to the plastic component is less than 9: 1 and preferably less than 4: 1.

Brief Description of the Figure

Figure 1 illustrates the particle size distribution of a mixture within the scope of the present invention determined using laser diffraction techniques according to ISO 13320-1: 1999 (Particle size analysis - Laser diffraction methods) using a Malvern Mastersizer 2000

Detailed description of the invention

In a preferred embodiment of the present invention, the cellulose / plastic particle mixture includes a mixture in which a shortage of plastic (and preferably thermoplastic) material is present, preferably comprising from 5 to less than 40% by weight of thermoplastic material (therefore, a mixture rich in cellulose), as well as mixtures in which the content of thermoplastic material is at least 40% by weight and below 60% by weight, each based on the weight in Total dry of cellulosic and thermoplastic materials. Typically, dry cellulose-rich mixtures of the present invention have a lower calorific value, generally from 15 to 25 GJ / t, while conventional low-cellulose mixtures of the prior art have a higher calorific value, preferably 20 at 40 GJ / t. While low cellulose mixtures have the advantage of a higher energy value, this is offset by cellulose rich mixtures, which have a reduced combustion time and are more environmentally sustainable. Therefore, the cellulose-rich mixture of the present invention will be increasingly desired by the industry.

Typically, the cellulose / plastic mixture originates from waste material such as household waste (including municipal and urban waste) and / or industrial waste (for example, "paper waste" obtained after the separation of most paper pulp in the paper recycling process). The cellulosic material may come, for example, from paper, cardboard, beverage cartons, wood, diapers, bandages and textile products such as cotton, viscose and rayon. Typically, the cellulosic material in the cellulose / plastic mixture is mainly based on paper and / or cardboard.

The ignition temperature of cellulosic material, such as paper, is generally below 250 ° C. This contrasts with an ignition temperature for coal typically above 500 ° C. Therefore, the injection of a cellulose component into the boiler results in a faster release of energy, which allows the ignition temperature of the other components of the fuel or the reducing agent to be reached more quickly, thus reducing the times of combustion of the mixture as a whole.

The plastic component is preferably at least 80% by weight more preferably at least 90% by weight and even more preferably at least 95% by weight and most preferably 100% by weight of the thermoplastic material, based on the weight of the total plastic component. The thermoplastic material may come, for example, from packaging material such as sheet material or polymeric film. In principle, all types of thermoplastic polymers may be present in the waste mixture. Examples of thermoplastic polymers that are generally present in waste streams to be treated include polyolefins (substituted); polystyrene; polyesters, such as polyethylene terephthalate (PET); polyamides, and copolymers and mixtures thereof. The thermoplastic material may also comprise halogenated polymers such as polyvinyl chloride (PVC), although this is not preferred. In particular, the thermoplastic material in the cellulose / plastic mixture is preferably based on polyethylene homopolymers and / or copolymers, which have an ignition temperature of about 350 ° C, as compared to up to about 550 ° C for PVC and 420 ° C for polypropylene.

It will be appreciated, therefore, that the burning time of the cellulose / plastic mixture will depend on the types and proportions of plastic in it. To ensure that combustion times are maintained within the desired range of values, the variability of the plastic in the waste stream is monitored and controlled as described below.

Preferably, at least 60% by weight, more preferably at least 70% by weight, even more preferably at least 75% by weight, and most preferably at least 80% by weight of the thermoplastic material are homo- and / or polyethylene copolymers. The high proportion of polyethylene in plastics with higher ignition temperatures further accelerates the burning time of the sample as a whole.

Preferably, the combustion time of the mixture is less than 5.1 seconds and more preferably less than 4.8 seconds and most preferably less than 4.0 seconds, as determined by the method described herein. The burning time preferably has a variation in at least 6 samples of no more than 0.4 seconds, more preferably no more than 0.3 seconds and most preferably no more than 0.2 seconds.

The cellulose / plastic mixture optionally comprises additional materials in smaller quantities, with the cellulosic and thermoplastic materials being the main components of the particle mixture. In general, cellulosic and thermoplastic materials constitute a total of at least 60% by weight of the mixture, preferably at least 70% by weight of the mixture, more preferably at least 80% by weight, even more preferably at least 90% by weight, and most preferably at least 95% by weight, each based on the total solid components. The high proportion of cellulose and plastic ensures regularity in the combustion performance of the mixture.

The other materials that may optionally be included in the cellulose / plastic particle mixture according to the present invention include combustible materials, such as thermosetting polymers, and non-combustible materials, such as metals, stones, ceramics, glass and other inorganic materials used as fillers. and / or pigments in the original paper / cardboard and plastics from which the cellulosic and / or thermoplastic materials originate. Non-combustible materials generally decrease the calorific value of the mixture and increase the ash content and, therefore, are not preferred.

The water (moisture) content of the fine cellulose / plastic particle mixture of the present invention is preferably less than 5% by weight, more preferably less than 3% by weight, even more preferably less than 2% by weight, and most preferably less than 1% by weight, each based on the total dry weight of the cellulose / plastic mixture. The evaporation of moisture from the mixture has a cooling effect and, therefore, extends the time necessary for the components to reach their ignition temperature. Therefore, the lower the humidity level, the lower the combustion times that the cellulose / plastic mixture can reach.

At least 95% and more preferably at least 97.7% by weight, and, even more preferably, at least 99% by weight of the particles, have a particle size of less than 2.0 mm. The higher the proportions of the fuel source below 2.0 mm, the lower the variance of the combustion times. More preferably, at least 99% by weight of the particles have a particle size of less than 1.5 mm, and, even more preferably, at least 99% by weight of the particles have a particle size of less than 1, 4 mm Within this particle size range, the cellulose / plastic mixture is preferably used as a secondary fuel, with fine carbon powder as the primary fuel. More preferably, at least 60% by weight, more preferably at least 70% by weight, even more preferably at least 80% by weight and most preferably at least 85% by weight of the cellulose / plastic mixture has a particle size less than 1 mm.

The average particle size of the mixture is preferably between 0.3 and 1.2 mm and more preferably between 0.5 and 1.0 mm. The average particle size values within this provide a good balance between flow capacity, low combustion times and variations thereof.

The typical lower limit of the particle size range will be governed by the grinding process and its economy. However, the lower particle size limit of the cellulose / plastic mixture is typically between 1 and 5 pm, with generally at least 5% by volume of the mixture below 50 pm, based on the total volume of the cellulose / plastic mixture, with a mode of particle size distribution of at least 0.3 mm, more preferably at least 0.5 mm and most preferably at least 0.8 mm. These fine particles are particularly beneficial when the cellulose / plastic mixture is mixed with finely ground coal of a similar particle size range. [Having a mode below 0.3 mm can cause an increase in volatile particles outside the combustion zone and, therefore, leads to lower levels of combustion. In addition, a too fine particle size leads to an increase in transport problems through the shuttles, since the finer thermoplastic particles are more likely to agglomerate and / or be spread on the internal surfaces of the shuttles as the particles approach the higher temperatures of the boiler injection point.

It has been found that the burning time of the cellulose / plastic mixture has even a smaller variance in these finer particle sizes. A low variance in the combustion time of the fuel source is important to ensure that the combustion conditions of the boiler can be closely controlled to achieve optimum energy efficiency. The particle size distribution is determined by sieving, unless otherwise indicated.

The mixture of fine cellulose / plastic particles according to the present invention can be combined with another carbonaceous material for feeding into a boiler. The additional carbonaceous material preferably has a burn time of a value similar or less than that of the cellulose / plastic mixture. The carbonaceous material may include gaseous material (such as gaseous hydrocarbons) or liquid fuels, especially derivatives of waste streams containing high energy, the resulting mixtures forming a gaseous or liquid slurry. The dry weight ratio of the mixture to the additional carbonaceous material is preferably at least 1:50, more preferably at least 1:20 and even more preferably at least 1: 5.

The mixture of fine cellulose / plastic particles according to the present invention is particularly suitable for use as a secondary fuel in addition to a primary fuel, preferably in coal-fired power plants or lime kilns. The mixture of fine cellulose / plastic particles can be mixed well with the primary fuel, that is, the pulverized coal, before being supplied together to the burner, or it can be supplied to the burner separately from the coal, or it can be supplied directly to the boiler in the burner. Preferably, the mixture of fine particles is dosed to the boiler separately from the pulverized coal; It is supplied directly to the flames of the primary fuel. The mixture of cellulose / plastic particles in which at least 99% by weight of the particles has a particle size of less than 1.4 mm, is also particularly suitable for use as a secondary fuel in power plants that generate gas from synthesis. As the dosing system in these power plants operates at high pressure through shuttles, usually from 30 to 35 bar (3 to 3.5 MPa), the amount of particles having a size of 1.4 is required mm and larger, be minimized to ensure transport problems are avoided. Other uses of the cellulose / plastic particle mixture according to the present invention include, for example, the use as secondary fuel in blast furnaces, lime kilns and cement kilns.

The particle size of the ground coal is preferably, such that at least 80% by weight of the particles is less than 200 ym, more preferably less than 150 ym and most preferably less than 100 ym, based on the total weight of coal. The lower the particle size, the higher the combustion rate, the greater the% of heat emitted by radiation, the lower the deposition of ashes and debris, and the smaller the flame length.

The resulting mixture preferably comprises at least 2.5% by weight, more preferably at least 5% by weight, more preferably at least 10% by weight, even more preferably at least 20% by weight and most preferably at minus 30% by weight of the cellulose / plastic mixture, based on the total weight of the resulting mixture. As the level of the cellulose / plastic mixture increases, so do the economic benefits of using the mixture as a secondary fuel source. The maximum level of the cellulose mixture in the resulting mixture is limited by the segregation problems that may arise, particularly if there is a significant difference in particle size distributions between the components of the mixture.

In embodiments, in which the cellulose / plastic mixture forms a resulting mixture with additional carbonaceous material, such as finely ground coal, the particle size distributions are preferably similar, so that their homogeneous mixture is promoted. Preferably, at least 20% by weight, more preferably at least 25% by weight and most preferably at least 30% by weight of the particles have particle size distributions that overlap with the particles of the finely ground carbonaceous material. . For example, 100% of the ground coal has a particle size distribution of less than 200 ym, and 35% by weight of the cellulose / plastic mixture has a particle size of less than 200 ym, resulting in an overlap of the 35% by weight between the carbon and the cellulose / plastic mixture.

Advantageously, the particle size distribution of the fuel source has a bimodal distribution, or at least is oriented towards finer particle sizes, to improve the homogeneity of the resulting mixture. Normally, one mode is greater than 500 ym and the other less than 500 ym. The formation of a bimodal distribution allows a better mixing of the resulting mixture, while minimizing the cost of grinding the fuel source.

The trend towards finer particle sizes means, for the purposes of the present invention, that the average value is closer to the upper size limit of 95% than the lower size limit of 95%. Preferably, the ratio between the average and upper size limit of 95% and the average and lower size limit of 95% is less than 0.9, more preferably less than 0.7 and most preferably less than 0.5. .

Improved mixing of the particles improves homogeneity, promotes better fluidity and reduces variations in combustibility.

In a special embodiment, the cellulose / plastic mixture of the present invention is combined with a liquid fuel. The high cellulose content of the mixture provides a high absorption property that can be used to convert particularly viscous liquid fuels into a more easily transportable form. For example, the cellulose / plastic mixture can be mixed with a resinous waste material from an oil or plastic processing plant, thus forming a separable solid material that is transported and more easily supplied to the boiler or furnace. Preferably, at least 20% by weight and more preferably at least 30% by weight of the cellulose / plastic mixture is added to the liquid fuel to produce a more transportable fuel source or reducing agent. In this embodiment, the cellulose / plastic mixture functions as a secondary source of fuel / reducing agent and a processing aid.

For obvious reasons, any fuel must be low in components that produce harmful substances in the flue gas or substances that damage the combustion unit. During combustion, chlorine, whether it is contained in organic compounds or inorganic chlorine in combination with organic material, can be converted into highly toxic organic compounds that contain chlorine, such as polychlorinated dibenzodioxins, usually called "dioxins", polychlorinated biphenyls (PCBs) and related compounds. In addition, hydrogen chloride may be formed during the combustion of chlorine-containing materials; The mentioned hydrogen chloride can cause corrosion of the materials that are in contact with the flue gas. Therefore, it would be desirable to provide a fuel that has a low amount of total chlorine.

According to a preferred embodiment of the present invention, the mixture of particles of Cellulose / plastic comprises no more than 1.0% by weight of total chlorine, more preferably no more than 0.6% by weight of total chlorine, even more preferably no more than 0.3% by weight of total chlorine, and more preferably no more than 0.2% by weight of total chlorine, each based on the dry weight of the cellulose / plastic mixture. Total chlorine includes chlorine that comes from inorganic compounds that contain chlorine, that is, primarily in the form of chloride, and organic compounds that contain chlorine. Total chlorine is determined in accordance with ASTM D 4208-97.

In general, considerable efforts are made to reduce the ash content of a fuel because several components of the ashes, for example, alkalis in combination with SiO ² can form a waste that is deposited in various locations of a power plant or unit similar combustion, and it is very difficult to remove. Typically, the cellulose / plastic particle mixture according to the present invention has an ash content of less than 20% by weight, preferably less than 10% by weight, and more preferably less than 7% by weight, each based in the dry weight of the cellulose / plastic mixture.

Another advantageous feature of the cellulose / plastic mixtures of the present invention is that the resulting ash material has a higher flow and hemisphere temperature, compared to mixtures with a higher plastic content.

The hemisphere temperature is the temperature at which the test sample forms approximately one hemisphere, that is, when the height becomes equal to half the diameter of the base. The flow temperature is the temperature at which the ash is spread on a support tile, the height of which is half the height of the test sample at the temperature of the hemisphere.

A higher flow temperature of the ashes of the present invention allows the ash material to resist the formation of waste, thus minimizing the time required for the maintenance of the boiler to eliminate waste. Preferably, the ash flow temperature is greater than 1200 ° C, more preferably greater than 1235 ° C and more preferably greater than 1270 ° C. Preferably, the hemisphere temperature is greater than 1190 ° C, more preferably greater than 1205 ° C and most preferably greater than 1225 ° C.

The mixture of fine cellulose / plastic particles according to the present invention has a superior combustion behavior, that is, it has a high combustion rate and the formation of ashes is reduced due to complete combustion. In addition, small particle sizes of the cellulose / plastic mixture result in better pneumatic transport properties, especially in small pipes. In cases where the cellulose / plastic mixture is mixed with the primary fuel sprayed before combustion, the particles of the cellulose / plastic mixture are characterized by an outstanding compatibility with the particles of the primary fuel, i.e. It produces no or very little segregation.

The cellulose / plastic mixture of the required composition can be formulated through the combination of variations of waste streams or a waste stream.

In another embodiment of the present invention, a method for preparing the fine cellulose / plastic particle mixture of the invention is provided, comprising the steps of:

(a) process a plastic waste material, so that it has a cellulose component and a plastic component and the dry weight ratio of the cellulose component with respect to the plastic component is at least 2: 3;

(b) optionally, forming a pellet from the product of step (a);

(c) grind the product of step (a) or (b), so that 95% by weight of the particles in the mixture is less than 2.0 mm, based on the total dry weight of the mixture of cellulose / plastic

Preferably, the combustion time at 1200 ° C for complete combustion of the mixture is less than 5.5 seconds.

Appropriate variations can be made to the limitations of the above process, based on the previous embodiments describing the cellulose / plastic mixture.

The cellulose and plastic components may come from separate sources and be ground separately before forming the mixture, as described in WO 97/05218.

Alternatively, another method for preparing the mixture of fine cellulose / plastic particles according to the present invention comprises milling cellulose / plastic pellets having a maximum diameter of 10 mm, preferably 8 mm, more preferably 6 mm, even more preferably 5 mm and most preferably 4 mm, and a minimum Kahl hardness of 10 kgf, preferably 15 kgf, and more preferably 20 kgf, in an air turbulence mill.

Kahl hardness is determined using a KAHL pellet hardness meter available from AMANDUS KAHL GmbH & Co. KG, Reinbek, Germany.

Cellulose / plastic pellets can be prepared, for example, in accordance with the teachings of co-pending application PCT / EP2007 / 001951, which provides a method of manufacturing cellulose / plastic pellets in which a cellulose / plastic mixture in particles comprising more than 60 to 95% by weight of cellulosic material, and 5 to less than 40% by weight of thermoplastic material, based on the total dry weight of cellulosic and thermoplastic materials, and 1 to 15% by weight of moisture, based on the total weight of the mixture, is supplied at a Ti temperature of at most 90 ° C to a pelletizing device comprising an annular mold with holes having a diameter D of at most 8 mm and a effective hole length L at a ratio of diameter D of hole R of at least 7, the values of R and Ti being chosen relative to each other so that the temperature T ² of the pellets leaving the annular mold is found between 80 and 125 ° C and the temperature rise of T ² - Ti is at least 10 ° C.

It has been found that the smaller and harder the pellets are, the smaller the particle size of the ground powder. If necessary, an additional detection step may be required to reduce the proportion of particles above the 2.0 mm limit.

An example of the particle size distribution of a cellulose / plastic mixture within the scope of the present invention is provided in Figure 1, which shows the results of a cellulose / plastic mixture having a dry weight ratio of cellulose component with respect to the plastic component of approximately 3: 2. Since the cellulose / plastic mixture is generally homogeneous in the particle size range, the% volume distribution shown would also reflect the% weight distribution.

In an air turbulence mill, the particles are reduced in size mainly by collisions with each other, the collisions being induced by an air jet or any other gas jet. In general, the water content of the particles is reduced during the milling process in the air turbulence mill. If desired, the drying effect can be further enhanced using a heated gas stream. An air turbulence mill, which is particularly suitable for preparing the particulate cellulose / plastic mixture according to the present invention, comprises a rotor bearing individual grinding plates arranged vertically in several grinding sections and a single cylindrical stator common to all the grinding sections, a conveyor gas being used to carry the material through the mill, breaking most of the material by collisions between them induced by the turbulence between the stator and the rotating grinding plates, and only a small part / fraction of the material is broken by interactions of the material with the fixed or rotating elements of the mill. Air turbulence mills of this type are described, for example, in US 5845855. Air turbulence mills that are suitable for the present process are, for example, commercially available from Altenburger Maschinen Jackering GmbH, Germany and Gorgens Engineering GmbH, Germany. As explained above, the mixture of cellulose / plastic particles according to the present invention is preferably low in total chlorine. Most of the total chlorine originates from organic chlorine compounds, mainly chlorine-containing polymers, such as PVC and PVDC. Typical domestic and industrial waste streams always contain considerable amounts of chlorine-containing polymers and, in general, a fuel that is prepared directly from these waste streams will not reach the upper limits of the total chlorine specified above.

Furthermore, since the burning time of the cellulose / plastic mixture is influenced by the composition of the plastic and, in particular, the ignition temperature of the plastic component therein, it is desirable to control the proportion of plastic to have an ignition temperature. above 400 ° C and preferably, at least, above that of polyethylene, that is, approximately 350 ° C. Preferably, the amount of plastic with an ignition temperature above 400 ° C is less than 30% by weight, more preferably less than 20% by weight and most preferably less than 10% by weight, based on weight. Total plastic component.

Thus, in a preferred embodiment of the present invention, the processing step (a) further comprises a step of removing at least part of the particles made of a plastic material containing chlorine or plastic particles having a ignition temperature above 400 ° C from a thick mixture of cellulose / plastic particles.

Preferably, the plastic particles removed in step (a), which have an ignition temperature above 400 ° C, comprise plastic material that does not contain chlorine.

The pelletizing stage (s) can be performed as described in co-pending application PCT / EP2007 / 001951.

Typically, the coarse mixture of cellulose / plastic particles that is subjected to steps (a) and (b) comprises particles having a maximum particle size of 80 mm, preferably 50 mm and most preferably 30 mm.

In a preferred embodiment of the present method, the removal of at least part of the particles made of a chlorine-containing plastic material or having a high ignition temperature is carried out by first identifying at least part of the particles made of a plastic material that contains chlorine or has a high ignition temperature by means of at least one non-contact scanning method and subsequently removing the particles detected. To classify the particles, for example, they are transported on a conveyor belt at a known transport speed, passing through a material recognition system that uses contactless scanning to determine the type of material and emits a signal that identifies the type of material and is used to classify particles according to the type of material. A suitable method of classification is described, for example, in US 5794788.

Preferably, the contactless scanning method is a spectroscopic method, for example, using infrared radiation or x-rays. More preferably it is near infrared reflectance (NIR) spectroscopy. It is known that plastics can be identified by IR spectroscopy in the near-infrared region (NIR). In this region the molecules absorb radiation with overtones and oscillation combinations. Plastics that have a different chemical structure can be identified by characteristic peaks of characteristic bonds within their molecules. NIR reflectance spectroscopy measures the intensity of diffused diffused radiation for a particle. In particular, the intensity is measured at a finite number of wavelengths simultaneously and the measured intensities are compared. A preferred method for identifying and classifying particles transported on a belt is one in which the characteristics of the particle material, that is, the chlorine-containing plastic particles, are determined spectroscopically by means of an appropriate instrument, for example, a NIR measuring instrument or an X-ray detector, and classification takes place based on spectroscopic results by removing the chlorine-containing plastic particles from the conveyor belt. For example, chlorine-containing plastic particles can be removed by means of a line of air blasting nozzles that is located at the end of the conveyor belt, the nozzles being controlled by a computer that processes the signals provided by the instrument measurement, optionally, in combination with other signals that are provided by another contactless scanning method, for example, an image analysis for the purpose of obtaining your situation. The methods for identifying and classifying plastics by means of NIR spectroscopy that are useful in the present invention are taught, for example, in patent documents DE 4312915, CA 2310838 and US 2001/0045518. A method for identifying and classifying plastics using X-ray radiation is taught, for example, in US Pat. No. 5738224.

Despite the method for identifying and removing at least part of the particles made of a chlorine-containing plastic material whose methods include the use of a conveyor belt, other methods for automatically sorting by means of at least one scanning method are preferred. Without contact, preferably NIR reflectance spectroscopy can be used. For example, the coarse mixture of cellulose / plastic particles can be transported in an air flow at a known air flow rate through a three-dimensional detection area of an NIR measuring instrument, the plastic particles being identified that they contain chlorine and then extracted from the air flow. An illustrative method is described in patent document DE 19956624.

In general, any plastic material that contains chlorine or has a high ignition temperature, detectable by a contactless scanning method, preferably NIR reflectance spectroscopy, can be removed from the thick mixture of cellulose / plastic particles. Examples of chlorine-containing plastic materials include polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC). Since PVC typically constitutes the majority of the chlorine-containing plastic materials found in common waste sources, it is often appropriate to remove the PVC by the method described to obtain a final mixture of fine cellulose / plastic particles having the desired low total chlorine content. In one embodiment, prior classification techniques are used to reduce the level of transparent plastic components. Transparent plastics have a lower absorption of radiant heat, which results in a longer burning time. Therefore, the plastic component is preferably concentrated with pigmented plastics that more easily absorb radiant energy.

Prior to the pelletization stage and the optional classification stage, additional optional measures can be taken to reduce the ash content of the final mixture of fine cellulose / plastic particles. Among others, the ash originates from SiO ² impurities contained in the cellulose / plastic mixture, such as stones / sand, ceramics and glass. The aforementioned impurities, as well as other non-combustible impurities, for example, metals, which are heavier than cellulose / plastic materials, can be separated into several stages, depending on the particle size, in the preparation process provided by the mixture. thick cellulose / plastic to be subjected to the pelletization stage or the optional classification stage that precedes the pelletization stage.

Typically, coarse mixtures of cellulose / plastic particles originating from waste sources comprise a considerable amount of moisture that is removed in a drying step. Performing the drying stage in a tubular drying vessel that is slightly inclined downward, large particles, heavier than the cellulosic and thermoplastic material, move downwardly within the tubular container and separate from the plastic cellulose mixture in the tubular container outlet.

Preferably, the dry cellulose / plastic mixture is then passed through a wind sieve where the smallest particles heavier than the cellulosic and thermoplastic particles are separated.

The resulting plastic cellulose particle mixture is preferably collected in a cyclone separator and then optionally placed on a vibrating conveyor belt that has a plurality of holes in the belt. The holes have a diameter of, for example, 5 mm and all fine particles smaller than 5 mm are separated through the holes, the adhesion forces between the particles being overcome by vibrations. The holes may also have a smaller diameter of less than 5 to 3 mm to separate only smaller particles. It has been found that the fine particles that pass through the holes consist mainly of heavier non-combustible ash-forming materials, such as materials containing SiO ² , for example, sand, ceramics and glass. It is believed that adhesion forces between fine particles that are made of cellulosic or thermoplastic material are less impacted by vibration forces, which results in better separation. Therefore, they are only contained in the fraction that passes through the holes of the conveyor belt in smaller amounts. If a sorting stage using a conveyor belt is used, it is preferred that the mixture of cellulose / plastic particles pass directly from the vibrating conveyor belt to the belt that transports the particles to the scanning unit.

Mixtures and mixtures with additives resulting from the present invention are typically used as a source of fuel or reducing agent in boilers. Mixtures and mixtures with resulting additives are typically introduced into the boiler through a pneumatic supply system, such as a shuttle.

Unless otherwise indicated,% by weight is based on the total dry weight of the cellulose / plastic mixture. Examples

Test methods

The particle size distribution was determined by the use of screening sieves as is known in the art, or laser diffraction techniques in accordance with ISO 13320-1: 1999 (Particle size analysis - Laser Diffraction methods) using a Malvern Mastersizer 2000.

The flow temperature was determined according to CEN / TS 15404: 2006 - Solid fuels recovered. Ashes melting behavior was determined using characteristic temperatures.

materials

The composition with low plastic fraction comprises 40% by weight of plastic and 60% by weight of cellulose-based material.

The composition with a high plastic fraction comprises 70% by weight of plastic and 30% by weight of cellulose-based material.

Burning time and sample composition

The agglomerates formed from the fuel particles in large part as a result of the interaction between the fibrous components of the fuel. These agglomerations are mainly created during the injection of fuel into the tubular furnace. The agglomerates can be of different sizes, but the maximum considered was limited to 100 mg, which reflected the maximum agglomerate size for a typical fuel feed or injection system. The samples (100 mg) were injected into a tubular furnace that had a stoichiometric excess of air (approximately 100% in excess) with a surrounding wall temperature of 1200 ° C. The time to complete combustion was taken as the time from when the sample is injected into the oven until the moment when complete combustion is observed. The experiment was repeated six times for the low plastic fraction (example 1) and the high plastic fraction (comparative experiment A).

Table 1. Burning time depending on the composition of the sample

The results indicate that the low plastic fraction containing a higher cellulose fraction achieved a significantly shorter burning time.

Additional tests, using standard screening techniques, revealed that the variation in combustion time was found to decrease with particle size. In particular, particles below 1 mm had a variation (0.1 seconds) of less than half of the particles between 1 - 2.8 mm and almost a fifth of The average variation of the particles above 2.8 mm. In contrast, it was found that said average combustion time was generally independent of particle size. This may reflect that the particles have a relatively constant thickness, despite having varying length ratios with respect to the width from which the particle size is determined. A relatively constant particle thickness would result in a relatively constant surface area to volume ratio, which will likely result in relatively constant burning times.

Hemisphere temperature and ash flow

The hemisphere and flow temperature of a high (comparative experiment B) and low plastic content (example 2) was analyzed according to CEN / TS 15404: 2006, with the result recorded in Table 2.

Table 2. Ash flow and hemisphere temperature

The results show that a fuel source with a high cellulose content contributes to a lower waste formation in the boiler / furnace as evidenced by the higher hemisphere temperature and flow temperature of Example 2, compared to the comparative low cellulose experiment. B.

Claims (13)

i. Fine particulate material for use as a fuel source or reducing agent derived from waste plastic material comprising: (a) a cellulose component; and (b) a plastic component, in which the dry weight ratio of the cellulose component with respect to the plastic component is greater than 2: 3 and in which the dry weight ratio of the cellulose component with respect to the plastic component is less than 9: 1, The cellulose / plastic mixture has a particle size distribution so that at least 95% by weight of the particles in the mixture are less than 2.0 mm, based on the total dry weight of the cellulose mixture / plastic, the mode of particle size distribution is between 0.3 and 1.8 mm, and in which the cellulosic and thermoplastic materials constitute a total of at least 60% by weight of the mixture, based on the total solid components. 2. Material according to claim 1, wherein the particle size distribution is such that at least 60% by weight of the particles in the mixture are less than 1 mm, based on the total dry weight of the mixture of cellulose / plastic. 3. Material according to claim 1, wherein the particle size distribution is such that at least 97.7% by weight of the particles in the mixture are less than 2.0 mm. 4. Material according to any one of the preceding claims, wherein the dry weight ratio of the cellulose component with respect to the plastic component is greater than 1: 1. 5. Material according to any one of the preceding claims, wherein the dry weight ratio of the cellulose component with respect to the plastic component is less than 4: 1. 6. Addition comprising the mixture according to any one of the preceding claims and an additional carbonaceous material. 7. Addition according to claim 6, wherein the additional carbonaceous material is carbon, the carbon having a particle size distribution, such that at least 80% by weight of the carbon particles are less than 200 | im , based on the total weight of the carbon particles. 8. Addition according to claim 6 or 7, wherein the dry weight ratio of the mixture with respect to the additional carbonaceous material is at least 1:50. 9. Addition according to claim 8, wherein the mixture has at least 20% by weight of particles within the particle size distribution range of the additional carbonaceous material, based on the total dry weight of the cellulose / plastic mixture . 10. Method for obtaining a fine particulate material of cellulose / plastic from waste plastic material, comprising the steps of: (a) process a waste plastic material so that it has a cellulose component and a plastic component and the dry weight ratio of the cellulose component with respect to the plastic component is at least 2: 3; (b) optionally forming a granule from the product of step (a); (c) milling the product of step (a) or (b), thereby producing the cellulose / plastic mixture according to claim 1 or 4. 11. The method of claim 10, wherein the processing step comprises removing at least part of the particles composed of a plastic material containing chlorine and / or plastic particles having an ignition temperature above 400 ° C of a mixture of thick particulate material of cellulose / plastic. 12. Method according to claim 11, wherein at least part of the particles are first identified by at least one contactless scanning method and then removed. 13. Use of the addition or mixture according to any one of claims 1-9 to feed an oven.