Field of the invention

The present invention relates to the production of paper, especially cardboard. The present invention further relates to a process for the production of a solid fuel from a starting material comprising a solid recovered fuel, especially from paper rejects, by means of torrefaction. The present invention also relates to a plant for the production of paper. The present invention also relates to a specific arrangement used for the production of a solid fuel from a starting material comprising a solid recovered fuel by means of torrefaction. Furthermore, the present invention relates to the use of a solid fuel obtained by torrefaction of a starting material comprising a solid recovered fuel.

Background of the invention

A process for the production of paper is for instance described in US 5114539. This document describes novel pulp, paper and paperboard manufacturing methods utilizing water-insoluble organic hydrocarbons. These hydrocarbons can be introduced into the pressing operation of the pulp, paper, or paperboard making machine or can be substituted for water at any point prior to the end of the press section. The result is a significant saving in dryer energy which can be translated to greater productivity in dryer-limited processes and systems. Functional chemical additives may be dissolved, dispersed or emulsified in the hydrocarbon and thereby introduced into the web. Much less functional chemical additive is required than with wet end addition.

Over the past two decades, increasing environmental awareness has resulted in a much stricter policy with respect to the handling and processing of household and industrial waste. One of the targets of this European Waste Directive is to decrease the amount of waste that ends up on a landfill. Another result of the increased environmental awareness is the attempt to decrease the burning of fossil fuels with the aim to reduce Cθ2-emission, and, as a consequence, considerable research effort is directed towards the possibilities of converting waste into solid fuels that are suitable for the replacement of fossil fuels. A solid fuel is a solid material that can be used as fuel to produce energy, such as for example wood, coal or peat.

Several methods for the conversion of waste into solid fuels are known in the art and described in for example US 5302254 and WO 2007/145507. In US 5302254 a plant for treating industrial and/or urban waste is described, including a stage for drying of the waste, followed by a stage for effecting thermolysis of the dried waste and a stage for effecting recovery of the solids and gases resulting from the thermolysis. Thermolysis of the waste is effected in a reactor by indirect heat exchange with combustion gases. Drying gases for drying of the waste are subsequently treated to remove vapour materials and then recycled to a gas generator for generating the drying gases. Additionally, the plant includes a stage for effecting dechlorination of the solids resulting from the thermolysis by washing the solids with an aqueous liquid, as well as a stage of separating the washed solids and the resulting wash liquid. WO 2007/145507 describes a method for the preparation, by torrefaction, of a solid fuel wherein a starting composition is heated indirectly, and a solid fuel to be obtained by such method. Furthermore, a method for the removal of one or more metals from, or the reduction of the "total chlorine content", the sulphur content and the trace element content of a solid fuel thus obtained is disclosed. Also, a solid fuel which can be obtained by the carrying out of such a method and the uses of such solid fuels are described.

Summary of the invention

Paper and (card)board are made of fibres. Fibres are made of different types of polymers: cellulose, hemicellulose, lignin and natural resins. The cellulose and hemicellulose form twines. The twines form a layer. The layers are covered with lignin and resins, giving strength and stiffness. Several layers together form the fiber. When twines of (hemi)cellulose are partially freed from the fiber structure they are called fibrils. Fibrils are important to fiber bonding. The characteristics of these fibres have a significant influence on the properties of the final product. The properties of the fibres are determined by the fiber source and pulping process. The most used fiber sources are wood and recycled paper. The first source yields so-called virgin fibres and the second source recycle fibres. The process of releasing fibres from the wood or paper is called pulping. The pulping process depends on the fiber source. When recycling paper, fibres are released by dispersing the paper in water. The pulping process consists of dispersing the collected paper after which the dispersed fibres are purified from ink and dirt using cyclones and screens, and refined to get sufficient active fiber surface. Contrary to fibres in paper, fibres in wood are held together by chemical bonds in a matrix structure. Lignin molecules, i.e. a type of three dimensional polymer and resins, act as glue. Therefore, virgin fibres are not so easily released as secondary fibres. Basically, two approaches exist to pulp wood: mechanical and chemical. These processes differ mainly in the extent to which the lignin and resins are removed and the degree to which the other polymers are affected.

In mechanical pulping the fibres are torn apart from the wood by pressing the wood against a fast rotating grinder. The yield of this pulping process may be high (95- 99%). The pulp obtained by this process may be characterized by damaged fibres, high fines (small fiber parts ) content; high degree of fibrillation (strings of cellulose molecules partly freed from the fiber wall); high percentage of fibres with a thick and stiff fiber wall; and high lignin content. Therefore, paper made using mechanical pulps has a low density combined with a high stiffness, but at a low strength. Additionally, these papers yellow rapidly. In chemical pulping the wood is cooked under high pressure in a very acid or a very alkaline solution. The yield of this process may be about 50 to 60%. The pulp obtained by this process may be characterized by no fiber damage after the alkaline sulphate process. After the acid sulphite process the cellulose chains may be damaged; long flexible fibres with a relatively thin fiber wall; low lignin content and reduced hemicellulose content; low degree of fibrillation. To obtain sufficient fibrils these pulps are often refined after pulping.

Therefore, papers made of chemical pulps have a high surface smoothness, a high strength, and a low bulk. After bleaching they possess a high level of whiteness and a low tendency for yellowing. Paper made of sulphate pulps offers particularly high strength, while sulphite pulps may yield the highest whiteness. The sulphate process may be the most widely applied chemical pulping process. This is an alkaline process, during which a pH of 12 can be reached at temperatures of 160-180 ⁰ C and pressures of 1-6 MPa. Pulp resulting from this process is called kraft pulp (Kraft is German for strength. The German developer Dahl called his invention the kraft process in reference to the high fiber strength). Due to the chemical reactions occurring during kraft pulping, the pulp may darken, so bleaching is necessary for all printing grades. Thermo-mechanical pulp (TMP) currently is the most widely used mechanical pulp. It is called thermo-mechanical pulp since the pulp is heated with steam before being torn apart in a refiner. As a result of the applied heat the fibres are more easily freed from the wood matrix, reducing fiber damage and coarse fiber content. To improve whiteness, mechanical pulp may also be bleached.

Apart from the pulping process, the fiber source also has a significant effect on fiber properties. Wood from deciduous trees, also known as hard wood, generally yields coarser and shorter fibres than those obtained from conifers (soft wood). Additionally, large differences exist between different types of hardwood and softwood, or even between samples of a single type of timber grown under different circumstances. The properties of recycled fibres vary greatly according to the source. The three main categories are: Mill Broke, Post Industrial Waste (PIW) and Post Consumer Waste (PCW). Mill Broke is reused paper that was produced off specification. This may be paper from any stage in the production process, from the wet web directly off the wire to finalized paper that has been incorrectly cut. PIW consists of paper collected from offices or printing shops. This is well-sorted paper, normally made of virgin fibres. Consequently, fibres obtained from PIW will be more similar to virgin fibres. PCW is paper collected from households. PCW normally consists of a mixture of paper and board, with varying percentages of recycled paper.

Each time fibres are reused, the fiber wall degrades a little further, until it is completely worn down. Degradation of the fiber walls of mechanically pulped fibres may change the properties of these fibres to more closely resemble chemically pulped fibres. Further recycling will inevitably results in loss of fiber quality. After fibres have been pulped the pulp is diluted to a highly aqueous mixture of 1-2% fibres by mass. Additives are added, and the pulp is sent to the paper machine. The function of the paper machine is to separate fibres and water in such a way that a sheet with the required properties is formed. This is achieved in three steps. First the forming section, followed by the press section and the dryer section. Depending on the type of paper machine, machine speed varies between 25 and 2000 m/min, i.e. 0.4 and 33 m/s, while paper machine widths vary from 2 to 12 meters. The aqueous solution is spread over a wire, and drained by gravity and suction.

The aim of the formation process is to form a web with an even fiber distribution and to remove 90-95% of the water. After formation the web's dry content is 20-30%. This is enough to give the wet web sufficient strength to support it's own weight. The draw- back of this process is that a density gradient may occur over the thickness of the sheet. Modern machines dewater almost instantly between two wires, allowing for faster dewatering and a more symmetrical sheet structure.

During formation the pulp forms a wet web capable of supporting it's own weight. However, since the wet web is very sensitive to stretching in the machine direction, the web is supported as much as possible while moving through the wet- pressing section. Conventionally, the wet web is forced to dewater by leading it through several nips. A nip is the contact area between two rolls pressed together. In this configuration the aperture of the nip is variable and the load is a setting parameter. The load is applied to the shafts of the rolls, as a result of which the rolls tend to bend slightly in the middle. The crowning of the rolls is adapted to keep the applied pressure profile even over the cross-direction (direction parallel to the machine width).

Together with the web a felt moves through the nip. This felt serves a double function: it supports the web between two consecutive nips, and inside the nip it provides an escape route to the water forced from the web. To prevent slipping between the web and a felt, felts move through the nip(s) at the same speed as the web.

The felt's name derives from the fact that it used to be made of felt (Felt is a material made by pressing together wet layers of wool). Nowadays it is usually made of polymers, mainly nylon, and consists of a combination of non- woven fabrics needled on top of a woven substrate.

In addition to the roll nip described above, extended nip presses (ENP) or shoe nip presses are in use. The advantage of these nips is that they have an extended nip residence time, resulting in improved dewatering without increasing the pressure. This extended nip residence time is realized by replacing one of the rolls by a load shoe, providing a comb-shaped contact surface to the mating roll. Since the load shoe is static, a belt moves over the load shoe at the same speed as the felt to decrease felt attrition.

Pressures applied in the nip vary between 1.0 and 12 MPa. The pressure increases with increasing dry content of the paper. The temperature varies between 25 and 75 ⁰ C. The pressure applied depends on the type of paper being produced, the nip length, and the dry content of the web when entering the nip. The nip length varies between 10 and 25 mm for a roll nip press, and between 100 and 250 mm for an ENP or a shoe nip press. The press roll diameters normally vary between 400 and 900 mm. After wet-pressing the dry content of the wet web varies between 35 and 55%, depending on the type of paper/board being produced. The remaining water has to be removed by means of evaporation. To supply the required heat to the wet web, it is leaded over a sequence of steam-heated drums, commonly referred to as drying cans. To ensure good contact between the cans and the steaming hot web, drying wires tighten the web to the cans. Drying by evaporation is an energy-intensive process.

The procedures described above may form a basis of paper-making. To optimize the web's surface properties for printing purposes, some additional processes may be applied such as sizing, coating, and calendering. These process steps are important to the final appearance and properties of the paper. They improve the surface structure and variations in the base paper may be corrected to some extent. However, the success of these finishing steps depends heavily on the quality of the base paper. Proper process control on formation and wet-pressing therefore remain key to producing top quality paper and board. Therefore, the scope of this paper is limited to the wet-pressing section and it' s effect on paper properties.

Cardboard may especially be prepared from recycled material. Recycled material may be collected and sorted and usually mixed with virgin fibres in order to make new material. This may be necessary as the recycled fibre often loses strength when reused and gets this from the added virgin fibres. Mixed waste paper may not usually be de- inked for paperboard manufacture and hence the pulp may contain traces of inks, adhesives, and other residues which together give it a grey colour. Products made of recycled board usually have a less predictable composition and poorer functional properties than virgin fibre-based boards. Mainly two methods for extracting fibres from its source are used: (1) mechanical pulping may be a two stage process which results in a very high yield of wood fibres, or (2) chemical pulping may use chemical solutions to convert wood into pulp, for instance yielding around 30% less than mechanical pulping. Pulp used in the manufacture of paperboard can be bleached to decrease colour and increase purity. Herein, the terms "paperboard" and "cardboard" are equivalent. The paper making process may use a lot of energy, and there is a desire to reduce consumption of energy. Hence, it is an aspect of the invention to provide an alternative paper making process that preferably has a better energy efficiency. The paper making process can be summarized as a process comprising providing starting materials for making paper, the process of making paper under consumption of energy, and providing paper rejects (as by product) comprising solid recovered fuel

(SRF). Hence, the process of making paper includes the consumption of energy as well as the production of non-desired material (especially paper rejects). In principle, one could burn the paper rejects (for energy recovery). However, it appears that high investments are necessary in order to prevent emission of heavy metals with the flue gas. A better use or reuse of energy may also be possible. The present invention however provides an alternative solution that surprisingly may solve problems of the art and may relatively easily be implemented in present paper making process.

Hence, in a first aspect, the invention provides a process for the production of paper, the process comprising:

- providing starting material (such as pulp, for instance at least partially based on recycled paper); see also above) for making paper; - a process of making paper from the starting material under consumption of energy and production of the (a) paper and (b) paper rejects (by-product) (paper-making stage);

- torrefying a solid recovered fuel comprising starting material, preferably at a temperature selected from the range of 240 - 675 ⁰ C, to provide a torrefied product, wherein during torrefying a gaseous by-product is formed, wherein the solid recovered fuel comprises at least part of the paper rejects produced in the process of making paper, and wherein the paper rejects comprise a mixture comprising paper and plastic (torrefying stage);

- combusting at least part of the gaseous by-product and recovering energy from the combustion (energy recovery stage); wherein at least part of the recovered energy is reused in the process.

Hence, by integrating a torrefaction process in the paper making process, and/or by integrating a torrefying arrangement, for instance as proposed herein, in a paper making plant, the paper making process may be more energy efficient, more especially when one also includes combustion of the torrefied product and reuses the energy from this combustion (the combustion of the torrefied product may be performed elsewhere, such as in a large combustion plant). The energy generated in the combustion process (of the gaseous by-product) can be one or more of thermal energy and electrical energy. At least part of this energy may be reused, but part may also be provided to electricity networks and/or heating of the plant, houses, etc. In an energy recovery unit (for instance including a heat exchanger), energy may be recovered from the combustion of the gaseous by-product. The energy generated in the combustion process can be used in the process of making paper and/or can be used for the torrefaction. For instance, heat may be introduced in an torrefying arrangement, either in the reactor or in a mantle. However, energy may also via a heat exchanger be coupled to the torrefying arrangement, such as to the reactor or to a mantle. The energy generated may also be used in drying processes, see also below.

In the context of the invention, the terms "method" and "process" are considered synonymous.

The paper rejects may, after generation thereof in the paper making process and before being subjected to torrefaction, be subjected to an optional shredding & demetalizing process (shredding & demetalizing stage), to an optional drying process (drying stage), and to an optional particularization process (particularization stage). Energy released in the combustion of the gaseous by-product may be used for one or more of the shredding & demetalizing process, the drying process, and the particularization process, especially the drying process. Hence, in a paper making unit, from the starting material paper, especially cardboard is made, but as by-product, also paper rejects are formed.

The paper rejects may be used as such, or may be used in combination with other fuels. Hence, in the torrefaction, starting material comprising solid recovered fuel is used as is, but the starting material may also include biomass (see also below). The starting material at least comprises paper rejects as SRF. Paper rejects comprise a mixture comprising paper and plastic.

Hence, in a specific embodiment, the process may further comprise a shredding & demetalizing process for shredding and demetalizing paper rejects. In another embodiment, the process may further comprise a drying process for drying (shredded and demetalized) paper rejects. Yet, the process may further comprise a particularization process for providing particulised paper rejects (herein also indicated as particularization stage). Optionally, the process may further comprise a particularization process for providing particulised solid recovered fuel comprising starting material (for instance for particularization of paper rejects and biomass).

Preferably, at least a particularization process is included. Such particularization process thus precedes the torrefaction of the solid recovered fuel comprising starting material. The particularization process is especially used to particulate the paper rejects. If for instance biomass material is added, in an embodiment also the biomass material may be subjected to the particularization process. Further, preferably a drying process is included, which also precedes the torrefaction of the solid recovered fuel comprising starting material, and which preferably precedes the optional particularization process. Yet further, preferably a shredding and demetalizing process is included, which also precedes the torrefaction of the solid recovered fuel comprising starting material, and which preferably precedes the optional particularization process and the optional drying process.

In a specific embodiment, at least part of the recovered energy is reused in one or more of the shredding and demetalizing process, the drying process, and the particularization process (for providing particulated (or particularized) paper rejects), especially the drying process (if any one of those additional processes are applied). In a specific embodiment, the process may further comprise using a heat exchanger, configured to extract thermal energy from the combustion of at least part of the gaseous by-product, and configured to provide at least part of the thermal energy to the process. In a preferred embodiment, the torrefaction of the process is performed with a torrefying arrangement, wherein the torrefying arrangement comprises:

- a torrefying reactor, arranged to torrefy a solid recovered fuel comprising starting material, to produce a torrefied product; - an optional washing unit, arranged downstream of the torrefying reactor and upstream of the particulator, arranged to wash the torrefied product from the torrefying reactor to provide a washed torrefied product; and

- an optional particulator, arranged to particulate the (washed) torrefied product to provide particulated solid fuel. Such arrangement may further comprise a shredder&demetalizer unit, a dryer unit, and a particularization unit, configured to perform the above mentioned shredding & demetalizing process, the drying process, and the particularization process, respectively. Further, such torrefying arrangement may comprise a heat exchanger as mentioned above. The invention also relates to the torrefying arrangement as such, and the torrefying reactor as such.

In a specific embodiment, the process is performed in a plant for the production of paper comprising - a paper making unit arranged to produce paper and paper rejects,

- a torrefying arrangement comprising a torrefying reactor, arranged to torrefy the solid recovered fuel comprising starting material to produce the torrefied product, wherein the solid recovered fuel comprises at least part of the paper rejects produced from the paper making unit, and wherein the paper rejects comprise a mixture comprising paper and plastic;

- a combustion unit configured to combust at least part of a gaseous by-product of torrefaction, and an energy recovery unit, configured to generating energy from the combustion; wherein the energy recovery unit is arranged to provide at least part of the recovered energy to plant, especially one or more of the paper making unit and the torrefying arrangement.

The method further comprises combusting at least part of the torrefied product in a large combustion plant.

Hence, the invention also provides a plant for the production of paper comprising - a paper making unit arranged to produce paper, especially cardboard, and paper rejects (as by-product),

- a torrefying arrangement comprising a torrefying reactor, arranged to torrefy a solid recovered fuel comprising starting material to produce a torrefied product, wherein the solid recovered fuel comprises at least part of the paper rejects produced from the paper making unit, and wherein the paper rejects comprise a mixture comprising paper and plastic;

- a combustion unit configured to combust at least part of a gaseous by-product of torrefaction, and an energy recovery unit, configured to generating energy from the combustion; wherein the energy recovery unit is arranged to provide at least part of the recovered energy to the plant, especially one or more of the paper making unit and the torrefying arrangement. In the paper making unit starting materials for the paper making are separated into usable material and unusable material. Paper rejects belong to the latter.

In a specific embodiment, the plant may comprise a heat exchanger configured to extract thermal energy from the combustion unit, and configured to provide at least part of the thermal energy to the plant, especially one or more of the paper making unit and the torrefying arrangement. The recovered energy (such as thermal energy), may also be provided to other units (if applicable) or stages, such those wherein drying takes place.

With the plant and the process according to the invention, energy consumption can be decreased, whereas also useful products (torrefied product) may be generated.

The process for the production of paper is especially a process for the production of cardboard. The term "cardboard" includes "paperboard" or "pasteboard". The term paper may also especially refer to corrugated paperboards or corrugated fiberboards.

The present process may optimally make use of "undervalued joules". Physical, chemical and logistical properties of (undervalued joules containing) waste streams can be used to produce kWh's in Large Combustion Plants with high yield. The present process may reduce CO ₂ emission relative to coal or other fossil fuels (60-72%). The gaseous by-product is "green" which has been determined by C14-methods. So all the energy produced from that may be green too. The plastics in the paper rejects lift the calorific values of product and transform into binders (after polyolefines are decomposed).

Paper rejects in this process are "upgraded" from a waste stream [P3] (volume or weight) to an energy stream [J2] (Joules). This may be advantageous in view of the energy transition in the paper industry. An aim is to reduce the amount of energy per weight product [J/P2]. Now, paper rejects may be considered as leaving energy stream, which may be subtracted from the energy needed [J] for the paper product [J/P2-P3 --> J-J2/P2], even if the torrefied product would be combusted elsewhere, such as in a large combustion plant or coal plant. If energy generated is introduced back into the process, than the energy consumption is reduced anyhow; if torrefied product is combusted in LCP's etc., than the overall process of paper production and combustion is more energy efficient. Here, Pl relates to the starting material, P2 relates to the final product, and P3 relates to paper rejects. J refers to the energy used in the process for the production of paper and J2 refers to the energy generated in the torrefaction process, preferably including a later energy generation step in for instance a hot combustion plant by combustion of the torrefied product.

Heavy metals are present in the colour pigments of paper and plastics and also flame retardants may contribute to emissions. These can all be removed through cleaning.

In most countries, fossil- fuelled power plants using hard coal are the backbone of the power generation system, such as for example large combustion plants (LCP 's).

Before combustion in a large combustion plant, the coal is pulverized in order to ensure a rapid ignition and complete combustion. State of the art combustion plants generate electricity with an efficiency of about 40 to 48%.

In order to be applicable as an auxiliary solid fuel in a large combustion plant, a solid fuel should preferably be just as easily transportable as coal, have preferably substantially the same storage stability as coal, preferably be easy to handle and be preferably substantially pulverisable like coal and it should preferably substantially burn like coal with substantial similar calorific values and substantial similar chemical specifications.

The solid fuels derived from household or industrial waste described in prior art may have several disadvantages. Generally, these solid fuels cannot be applied in the coal dedicated infrastructure of a large combustion plant without major, and hence costly, modifications.

Industrial and household waste may consist for a large part of biomass. Biomass is defined as organic material from trees and plants, and is a renewable energy source because trees and crops can be grown again. Biomass is considered a "Cθ2-neutral" fuel. Although biomass does release carbon dioxide when burned, a nearly equivalent amount of carbon dioxide was captured through photosynthesis when the biomass was grown. Fossil fuels such as coal and oil have their origin in ancient biomass, nevertheless they are not considered biomass by the generally accepted definition because they contain carbon that has been out of the carbon cycle for a very long time.

The combustion of fossil fuels therefore releases additional carbon dioxide into the carbon cycle and may contribute to global warming.

Raw biomass is generally unsuitable for direct use as a solid fuel, due to a high moisture content, a relatively low energy density and the tendency to rot. Torrefaction (or torrefication), also referred to as thermolysis or mild pyrolysis, is a thermochemical treatment that may improve the properties of biomass. During torrefaction, the biomass may slowly be heated to a temperature typically in the range of about 200 ⁰ C to 300 ⁰ C in an essentially oxygen- free atmosphere, resulting in a partial decomposition of the biomass under the formation of various types of gaseous byproducts. The remaining solid is referred to as torrefied biomass or char. Typically, 70% of the mass of the biomass may be retained as a solid product, containing 90% of the initial energy content. Therefore, a considerable energy densifϊcation and hence an improvement in calorific value of the biomass may be achieved by torrefaction. Also, torrefied biomass has a hydrophobic nature and is not prone to absorb moisture from its environment, resulting in a product that is stable to store without rotting for prolonged periods of time, unlike raw biomass.

A disadvantage of the solid fuels obtained by torrefaction of biomass is that the chemical and physical properties of the torrefied biomass are often not suitable for their large scale application. For example, particulating torrefied biomass, in order to obtain a solid fuel that is easy to transport, to handle and to use in various applications, is problematic.

As mentioned above, the European Waste Directive severely restricts the dumping of waste on a landfill. As a result, an enormous amount of waste becomes available for incineration in waste incineration plants. Since the main purpose of waste incineration is reduction of the waste volume, energy recovery is only of secondary importance and the energy efficiency of the waste incineration process is hardly ever more than 20%. However, waste may contain a considerable calorific value, and potentially an enormous amount of energy can be recovered from waste. Waste is not suitable for direct application as a fuel in a large combustion plant.

A solid recovered fuel (abbreviated SRF) is especially a fuel that may be prepared from non-hazardous combustible waste, for instance to be utilised for energy recovery in combustion plants, or brown coal plants, or in cement production. The properties of the SRF may largely depend on the type of waste it is derived from. Standards and specifications for SRF are being developed by the European Committee for Standardisation (CEN/TC 343). In general, the properties of a solid recovered fuel are not suitable for direct combustion in a large combustion plant. For example, particulating the SRF into particles that are suitable for use in a large combustion plant is not economically feasible, and plasties may melt before reaching the burners of the plant, causing blockages.

Currently, only a small part of the calorific waste stream is converted into solid recovered fuel. This SRF is mainly used as an alternative fuel in calciners and rotary kilns in the lime and cement industry. There is only a limited number of users of this kind in Europe, and this makes entering the market on solid business conditions difficult for SRF producers. SRF prices are kept intentionally low, forcing SRF producers into low profit margins. Also, the heterogeneous nature of the waste feedstock makes it difficult to keep the produced SRF within the right specifications. In addition, the requirements of the cement industry with respect to impurity levels, moisture content and particle size are very strict. The SRF material needs to undergo an energy-consuming drying treatment in order to reduce the moisture content to less than 10%, and the amount of chlorine present in the SRF material has to be low (especially < 0.8%) to prevent the emission of corrosive hydrochloric acid during combustion. Hence, it is an aspect of the invention to provide an alternative process for the production of a solid fuel which preferably further at least partly obviates one or more of the above-described drawbacks. According to a first aspect of the invention, the invention provides a process for the production of a solid fuel from a solid recovered fuel comprising starting material, the process comprising: - torrefying the solid recovered fuel comprising starting material, preferably at a temperature selected from the range of about 240 ⁰ C to about 675 ⁰ C, to provide a torrefied product (torrefying stage); - optionally washing the torrefied product, to provide a washed torrefied product

(washing stage); and - optionally (but preferably) particulating the torrefied (washed) product to provide the solid fuel (particulation stage), wherein the solid recovered fuel comprises paper rejects from the paper industry and wherein the paper rejects comprise a mixture comprising paper and plastic.

The term "solid recovered fuel comprising starting material" relates to a starting material comprising solid recovered fuel.

Thus, in a preferred embodiment of the present invention, the solid recovered fuel comprising starting material comprises paper and plastic. In a further preferred embodiment, the solid recovered fuel containing starting material comprises paper and plastic particles which are inseparable on industrial scale. An example thereof are paper rejects of the paper recycling industry.

A specific type of SRF is derived from the (solid or solids containing) waste stream of the paper industry. Recycled paper is used as one of the feedstocks for the production of for instance paper or paper products, especially cardboard. However, a certain fraction of the recycled paper is unsuitable for further processing in the paper plant. This fraction, also referred to as "paper rejects", may comprise, amongst others, inseparable paper and plastic, and metal parts such as for example staples. The rejects from recovered paper may comprise plastics, lumps of fibres, staples and metals from ring binders, sand, glass and plastics and paper constituents as fillers, sizing agents and other chemicals. Rejects also may have a relatively low moisture content (50 ± 10%), significant heating values, are easily dewatered and are, generally, incinerated or disposed of in landfills. These "paper rejects" may be converted into an SRF material. In a preferred embodiment of the present invention, the solid recovered fuel in the starting material comprises such waste product from the paper industry, especially is a solid recovered fuel derived from "paper rejects". Another term for "solid recovered fuel derived from paper rejects" is "paper rejects fluff.

In a further embodiment, the solid recovered fuel comprises a particulate solid recovered fuel. A particulate solid means a solid that is shaped into particles of (a) certain form(s) or shape(s). Herein, the term "particulating", as known to the person skilled in the art, may refer to the process or process of making particles. By "particulating" especially a process is meant that converts material into a certain shape or form that is desired for further processing of the material. Examples of particulating are briquetting, extruding or pelletizing, but alternative process are equally possible. By providing a particulate solid recovered fuel as (part of the) starting material, the process of the invention may be performed more efficiently. Part of the starting material, or the entire starting material, may be particulated. The present inventors surprisingly found that the use of particulated starting material has several advantages. First of all, heat transfer during torrefaction may be better. Furthermore, the torrefied product may have a more open structure and therefore a larger surface area, with the advantage that the torrefied product may be washed more efficiently. In addition, particulating of the torrefied product (also after washing) may become less energy consuming. The composition of the starting material can be varied by optionally mixing additional plastics and/or biomass with the solid recovered fuel. Alternatively or additionally, the composition of the starting material can also be varied by varying the ratio of the paper and plastic of the solid recovered fuel. The torrefaction of biomass generally leads to a product that is difficult to particulate; this is a disadvantage of torrefaction and may limit the use of this process. Surprisingly, it was found that the solid recovered fuel comprising a mixture comprising paper and plastic is relatively easier to particulate after torrefying, and the plastic material does not necessarily have to be removed from the starting material, if possible at all. Without wishing to be bound to any theory, it may be that decomposition products of polymers, such as of plastics, like polyolefϊns and/or PVC, provide a certain binding property to the torrefied product which enables particulating the torrefied product.

Therefore, in a preferred embodiment, the mixture comprising paper and plastic comprises one or more plastics selected from the group consisting of for example polyethylene (PE), polypropylene (PP) and polyvinylchloride (PVC), but alternatively or additionally, one or more other plastics are also possible.

In a preferred embodiment, the mixture comprising paper and plastic comprises plastic in an amount of about 3-60 wt.%, relative to the total mass of the mixture on dry weight basis. In a more preferred embodiment, the mixture comprising paper and plastic comprises plastic in an amount of about 3 - 40 wt.%, relative to the total mass of the mixture on dry weight basis, and even more preferably the mixture comprising paper and plastic comprises plastic in an amount of about 20 - 35 wt.%, relative to the total mass of the mixture on dry weight basis. Relative to the total mass of the mixture on dry weight basis, the mixture comprising paper and plastic may comprise about 40- 97 % paper, especially about 60-97 wt.%, even more especially 65-80 wt.% paper.

In another embodiment, the solid recovered fuel comprising starting material further comprises biomass, i.e., in addition to the solid recovered fuel, the starting material may also comprise biomass. Especially, the solid recovered fuel comprising starting material may comprise biomass in an amount of about 3-90 wt.% relative to the total mass of the solid recovered fuel comprising starting material, on dry weight basis. Here, the term "biomass" refers to biomass materials other than paper (such as the paper present in the solid recovered fuel derived from paper rejects), that may be added to the solid recovered fuel according to an embodiment of the invention. Examples of biomass that can be added is municipal waste or agricultural waste or agricultural byproducts, such as for example straw.

The process according to the present invention may operate in an autotherm manner when the starting composition comprises up to about 30% moisture. However, such a relatively high moisture content requires more equipment and hence higher costs, and a starting composition containing a lower moisture content is preferred. According to an embodiment of the present invention, the solid recovered fuel comprising starting material may comprise water in an amount of about 1-30 wt.% relative to the total mass of the solid recovered fuel comprising starting material on total weight basis. In a more preferred embodiment, the solid recovered fuel comprising starting material may comprise water in an amount of about 1 - 15 wt.%, and even more preferably in an amount of about 1 - 8 wt.% relative to the total mass of the solid recovered fuel comprising starting material on total weight basis. In a preferred embodiment, the solid recovered fuel comprising starting material is torrefied at a temperature selected from the range of about 240 ⁰ C to about 675°C, more preferably at a temperature selected from the range of about 300 ⁰ C to about 450 ⁰ C, and even more preferably at a temperature selected from the range of 340 - 420 ⁰ C. The phrase "temperature selected from the range of about 240 ⁰ C to about 675°C" may indicate that the temperature in the reactor is at one value, or the temperature in the reactor varies with time or the temperature in the reactor varies within the reactor as function of the position within the reactor. This phrase may also include temperature trajects. However, during performing the process, the solid recovered fuel comprising starting material is subjected to the above temperature in order to be torrefied.

A solid fuel preferably meets certain standards with respect to the presence of impurities and trace elements. Contaminants and trace elements that may be present in the starting material comprise for example ions of Cl, Mg, Ca, Cr, Cu, Mn, Pb, Ba, Cd, Sn and Zn, and so on. It is an aspect of the present invention that the amount of one or more impurities and trace elements may be diminished to a level that makes use of the solid fuel as an auxiliary fuel in for example a coal combustion plant feasible. One way to achieve this is by washing the torrefied product. During torrefaction, the chlorine that may be present in the starting material (for example the chlorine in PVC particles that are difficult to eliminate due to their size) may be converted to free chlorides that in turn form metal salts with the metal ions present in the starting material. These metal salts may be washed out of the torrefied product. The washing liquids that may be used may comprise water and aqueous solutions, and optionally a complexing or chelating agent can be present in the aqueous solutions. Examples of complexing agents include, but are not limited to, sodium tripolyphosphate (STPP). Examples of chelating agents include, but are not limited to, ethylene diamine tetra acetic acid (EDTA) and its derivatives such as the tetrasodium-salt Na ₄ EDTA. Therefore, in a preferred embodiment, the torrefied product is washed to provide the washed torrefied product, wherein washing comprises washing the torrefied product with a washing liquid. In a specific embodiment, the washing liquid comprises a complexing or chelating agent and in yet a further preferred embodiment the washing liquid comprises one or more agents selected from the group consisting of polyphosphates and EDTA and its derivatives. Optionally, the torrefied product is washed more than once, with optionally different washing liquids. Therefore, in another specific embodiment, the torrefied product is first washed with a washing liquid containing polyphosphates, and subsequently the torrefied product is washed with a washing liquid containing EDTA and/or one or more of its derivatives. Washing may for instance be performed by submerging the torrefied product into the washing liquid, and/or spraying the torrefied product with the washing liquid. In a specific embodiment, the warm torrefied product is submerged in a washing liquid, for instance directly upon exiting the torrefying reactor. Heat is transferred from the warm torrefied product to the washing liquid, resulting in cooling of the torrefied product and simultaneously heating of the washing liquid. An additional advantage may be that small metal particles such as for example staples can be separated by gravity during the submerging of the torrefied product into the washing liquid.

The washed torrefied product is separated from the washing liquid, and may in a specific embodiment be provided to a conveyer belt. An optional additional washing comprises spraying the washing liquid to the torrefied product on the conveyer belt. Hence in a preferred embodiment, the torrefied product is submerged in a washing tank comprising a washing liquid, and/or provided to a conveyer belt, wherein washing comprises spraying the washing liquid to the torrefied product on the conveyer belt. A person skilled in the art will appreciate that washing of the torrefied product, either by submerging into a washing liquid and/or by spraying with a washing liquid, may have to be performed several times in order to remove the largest part of the impurities present in the torrefied product. In yet a further embodiment the washed torrefied product is at least partly dried (for instance in a drum dryer) after washing and before particulating. Drying may for instance be performed by using rest heat of the reactor.

As mentioned above, torrefied biomass is difficult to shape into particles that are as easy to handle, and as applicable, as for example coal. It is an aspect of the present invention that the obtained torrefied product can be particulated (into a desired form). Therefore in a preferred embodiment the torrefied (washed) product is particulated. Particulating the torrefied (washed) product may increase the bulk density of the solid fuel. The bulk density of the solid fuel may be increased up to values in the range of 500 - 700 kg/m ³ . An increased bulk density, and thus an increased quantity of energy per m , can create enormous advantages in for example the logistic parameters such as storage, handling and transport of the solid fuel. Also this increased quantity of energy per m ³ may make a more efficient use of the (limited volume of the) coal mills possible. Hence, in a preferred embodiment particulating the torrefied (washed) product to provide the solid fuel comprises particulating the torrefied (washed) product with a particulator arranged to press the torrefied (washed) product into pellets with for instance a flat die pelleting press. In another embodiment, particulating the torrefied (washed) product to provide the solid fuel comprises particulating the torrefied (washed) product into other forms such as for example briquettes or granulates.

In another embodiment of the present invention, the torrefied (washed) product obtained by torrefaction of a solid recovered fuel comprising starting material is optionally mixed with torrefied biomass, after optional washing (of the torrefied product) but before particulating. This way, if necessary, the properties of the solid fuel may be brought within the desired specifications for a certain application of the solid fuel. In a preferred embodiment, the solid fuel comprises torrefied biomass in an amount of 3 - 90 wt.% relative to the total mass of the solid fuel (thus obtained after mixing). In this way, streams of torrefied material (i.e. of torrefied biomass and torrefied SRF) may be combined and subsequently particulated. Hence, in a preferred embodiment, a mixture of torrefied biomass and torrefied (washed) product is particulated to provide the solid fuel. As mentioned above, particulating torrefied biomass is difficult to achieve. However, when torrefied biomass is mixed, before particulating, with the torrefied (washed) product obtained by torrefaction of a solid recovered fuel comprising starting material, particulating of the torrefied biomass (in combination with the torrefied (washed) product) is advantageously facilitated. The torrefied (washed) product obtained by torrefaction of a solid recovered fuel comprising starting material then acts as a kind of binder or particulating improver for torrefied biomass, and improves the properties of the torrefied biomass in such a way that particulating becomes feasible. Therefore, in a preferred embodiment, the torrefied (washed) product obtainable by torrefaction of a solid recovered fuel comprising starting material may be used as binder or particulating improver for facilitating particulating torrefied biomass. An example is the application as a pelleting aid for the production of pellets from torrefied biomass. In order to facilitate particulating torrefied biomass, the amount of torrefied (washed) product obtainable by torrefaction of a solid recovered fuel comprising starting material that may be mixed with torrefied biomass is in the range of 10 to 97%. In a preferred embodiment, the amount of torrefied (washed) product obtainable by torrefaction of a solid recovered fuel comprising starting material that may be mixed with torrefied biomass is in the range of 10 to 50%.

In a preferred embodiment, the invention provides a solid fuel that comprises, preferably substantially cylindrical shaped, particles having a diameter in the range of 4 - 25 mm, preferably in the range of 6 - 8 mm. The length of the particles is in the range of 2 - 8 times the diameter.

The amount of contaminants present in the solid fuel may depend on the composition of the starting material that is torrefied. For example, the total chlorine content of the solid fuel according to the present invention depends on the total chlorine content of the starting material that is torrefied. The total chlorine content of the solid fuel may be reduced with up to 95% with respect to the total chlorine content of the starting material. The heat value of the solid fuel may be increased with up to 30% relative to the heat value of the starting material. In yet a further embodiment, the solid fuel has a chlorine content of 0.5% or less, more preferably 0.2% or less. In yet a further embodiment, the solid fuel has a heat value of at least 22 MJ/kg, more preferably a heat value of at least 24 MJ/kg. In yet a further embodiment, the solid fuel has a moisture content of 15% or less. In yet a further embodiment, the solid fuel has a good grindability (Hardgrove Grindability Index in the range of about 20 - 60, more preferably in the range of about 45 - 60 (such as measured according to ASTM D5003)). In yet a further embodiment the solid fuel has a bulk density of 500 kg/m ³ or more, more preferably of 600 kg/m ³ or more, even more preferably of 650 kg/m ³ or more.

Another disadvantage of prior art is the overall inefficiency of the processes described. For instance the energy efficiency of the overall process may be low due to the type of torrefaction reactor used, or the torrefied product needs to undergo substantial additional treatment in order to be applicable as a solid fuel on a large scale. Also the availability of a large quantity of a suitable starting material at low cost is not always guaranteed since the quality requirements of the end-user often can only be met by selecting a starting material with limited availability, and therefore a higher cost.

Recovered energy may be reused in the torrefying arrangement, for instance in the torrefaction process (i.e. in the torrefying reactor), or in the particulation process (for provide the particulated torrefied product, i.e. particulated solid fuel) or in the washing process, or in two or more of such processes. Hence, it is a further aspect of the invention to provide an alternative reactor and/or arrangement to provide a solid fuel which preferably further at least partly obviates one or more of the above- described drawbacks. According to this aspect of the invention, the invention provides a torrefying arrangement arranged to provide a solid fuel comprising:

- a torrefying reactor, arranged to torrefy a solid recovered fuel comprising starting material to produce a torrefied product;

- an optional washing unit, arranged downstream of the torrefying reactor and upstream of the parti culator, arranged to wash the torrefied product from the torrefying reactor to provide a (washed) torrefied product; and

- a particulator, arranged to particulate the (washed) torrefied product to provide particulated solid fuel.

During the torrefaction of the starting material, various types of gaseous byproducts are formed. Combustion of these volatiles provides energy that may be used for the torrefying process and/or for initial drying of the starting material prior to torrefaction, if necessary, and/or for drying of the torrefied (washed) product. As mentioned above, the solid recovered fuel comprising starting material may comprise water in an amount of up to about 30 wt.% relative to the total mass of the solid recovered fuel comprising starting material on total weight basis. However, if the amount of water is more than about 8 wt.%, initial drying of the starting material may be necessary.

Therefore, in a preferred embodiment, the torrefying arrangement further comprises

- a combustion unit, arranged to combust a gaseous by-product formed in the torrefying reactor and to provide a hot combustion gas wherein the torrefying reactor comprises an inner mantle at least partly enclosed by an outer mantle, thereby defining a volume between the outer mantle and the inner mantle and wherein the combustion unit is external from the inner mantle and is arranged to provide the hot combustion gas to the volume between the inner mantle and the outer mantle of the torrefying reactor. Especially such a reactor may efficiently perform the process of the invention.

In yet a further embodiment, the outer mantle of the torrefying reactor comprises an inlet arranged to receive the hot combustion gas and an exhaust, wherein the volume between the inner mantle and the outer mantle comprises elements arranged to increase the length between the inlet and the exhaust. The function of these elements is to provide a more efficient energy transfer from the hot combustion gas to the inner mantle of the torrefying reactor. These elements can be present in the form of for instance fins, partitions, or other forms that are known to a person skilled in the art. The terms "inlet" and "exhaust" may also refer to a plurality of inlets and a plurality of exhausts, respectively.

In a preferred embodiment the torrefying reactor comprises a transporter, such as for example a (screw) conveyor. Depending on the characteristics of the starting material to be torrefied, the (screw) conveyor may be configured with all possible flight variables as known to a person skilled in the art. Examples are screws with standard, short or variable pitch, double start screws, ribbon flight or notched flight screws, (adjustable) paddle screws, or combinations thereof. In a preferred embodiment, the (screw) conveyor is a variable pitch screw. In a further preferred embodiment, the pitch decreases in the direction of transport of the starting material through the reactor. The decreasing pitch may induce an increase of degree of fill of the reactor in the direction of transport of the starting material. The transporter can be used to move the starting material through the reactor (i.e. through the inner mantle). In this way, torrefied product may be pushed out of the reactor by the transporter, e.g. the (screw) conveyor. In embodiments wherein reactors are used wherein the starting material is moved through the reactor, and wherein the reactor has an inner and an outer mantle and combusted exhaust gasses are led to the outer mantle, preferably the inlet of the outer mantle is upstream of the exhaust, relative to the transport direction of the starting material.

In a further embodiment, the torrefying arrangement comprises a washing unit, wherein the washing unit comprises a washing tank, arranged to comprise a washing liquid, an optional second washing tank, comprising a washing liquid, and wherein a conveyor belt is arranged to transport the torrefied product and wherein the washing unit further comprises a spraying unit arranged to spray a washing liquid to the torrefied product on the conveyer belt.

Another aspect of the invention is to provide an alternative reactor for the process to provide a solid fuel by torrefying a solid recovered fuel comprising starting material which preferably further at least partly obviates one or more of the above-described drawbacks.

According to this aspect of the invention, the invention provides a process wherein the solid recovered fuel comprising starting material is torrefied in the torrefying reactor (as described herein), wherein during torrefying a gaseous by-product is formed, wherein the process further comprises combusting at least part of the gaseous by-product external from the torrefying reactor to provide a hot combustion gas, and wherein the process further comprises heating the torrefying reactor by the hot combustion gas.

Likewise, in a preferred embodiment, the solid recovered fuel comprising starting material is torrefied in the torrefying reactor, wherein the torrefying reactor comprises an inner mantle at least partly enclosed by an outer mantle, thereby defining a volume between the outer mantle and the inner mantle, wherein during torrefying the solid recovered fuel comprising starting material within the inner mantle a gaseous byproduct is formed, wherein the process further comprises combusting at least part of the gaseous by-product in a combustion unit external from the inner mantle, to provide a hot combustion gas, and wherein the process further comprises providing the hot combustion gas to the volume between the inner mantle and the outer mantle. As will be clear to a person skilled in the art, between the reactor outlet and the inlet of the combustion unit, the temperature of the gaseous by-product is preferably kept above the condensation temperature of its components, in order to prevent condensation of the components. In order to facilitate the complete combustion of the gaseous by-product, the combustion temperature is preferably above 850 ⁰ C, more preferably above 900 ⁰ C. In some cases, for example if chlorine is present in the gaseous by-product, a combustion temperature of 1 100° is preferred for complete combustion.

In a further embodiment, the solid recovered fuel comprising starting material is torrefied in a torrefying reactor, wherein the degree of fill of the torrefying reactor during torrefying is in the range of 10 - 40 vol.%. In an embodiment, the degree of fill of the reactor may vary along the direction of transport of the starting material in the reactor. In a further preferred embodiment, the reactor degree of fill increases in the direction of transport of the starting material through the reactor. The optimum degree of fill of the reactor may be dependent on the density of the starting material. In a further embodiment of the present invention, the residence time in the reactor is in the range of 10 - 30, more preferably 15 - 20, minutes.

The solid fuel according to the process of the present invention can be used in various ways for the generation of energy. In a preferred embodiment, the solid fuel obtainable by the process according to the invention is used as auxiliary fuel in a large combustion plant. Therefore a further aspect of the invention is to provide an alternative process for generating energy with a large combustion plant comprising providing the solid fuel obtainable by the process according to the invention and combusting the solid fuel together with coal in the large combustion plant. As will be apparent for a person skilled in the art, the process for the generation of energy with the solid fuel is not limited to large combustion plants, and other applications for the solid fuel are feasible, such as for example shaft or rotary kilns as used in metal or industrial mineral production facilities.

Brief description of the drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: Figure 1 schematically depicts an embodiment of the process for the production of a solid fuel from a starting material comprising a solid recovered fuel, and the use thereof as an auxiliary fuel in a coal fired combustion plant.

Figure 2 schematically depicts an embodiment of the torrefying arrangement, showing the torrefying reactor in more detail.

Figure 3 schematically depicts an embodiment of the torrefying arrangement to provide a solid fuel from a starting material comprising a solid recovered fuel.

Figure 4 schematically depicts an embodiment of the optional washing unit of the torrefying arrangement. Figure 5 schematically depicts a further embodiment of the torrefying reactor.

Figure 6 schematically depicts a further embodiment of the invention; Figure 7 schematically depicts a further embodiment of the invention; and Figure 8 schematically depicts an embodiment of the process for the production of paper making.

Detailed description of the embodiments

Below, several embodiments of the process and arrangement of the invention are described with reference to Figure 1 - Figure 8. However, the process and arrangement of the invention are not confined to the embodiments described below and depicted in Figure 1 - Figure 8.

Figure 1 schematically depicts an embodiment of the process for the production of a solid fuel from a starting material comprising a solid recovered fuel, and the use thereof as an auxiliary fuel in a coal fired combustion plant.

A starting material 100 is subjected to a torrefaction stage 300. The starting material 100 comprises a solid recovered fuel 101 comprising a mixture 102 of paper and plastic. Optionally, the starting material 100 also comprises biomass 103. In a preferred embodiment, the solid recovered fuel 101 is originating from the paper industry waste stream, in particular from inseparable paper and plastic waste. Most preferably, the solid recovered fuel is derived from paper rejects. On average, the paper industry SRF material contains about 50 to 75 % paper, about 25 to 50 % plastics and about 1 % trace impurities such as wood and metal particles, all in weight percentages on dried basis. In addition to the plastics present in the SRF material 101, the starting material 100 may comprise additional plastics, also selected from the group of for example polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC).

Thus, the composition of the starting material 100 can be varied by optionally mixing biomass 103 and/or plastics with the solid recovered fuel 101. As will be apparent to a person skilled in the art, this makes it possible to tune the properties of the solid fuel provided by the process to the desired specifications.

Optionally, the starting material 100 is dried in a drying stage 150 and particulated in a particulating stage 200 before the torrefaction stage 300. As is mentioned above, particulating is accomplished by processes that are well known in the art. Further, optionally before the drying stage, a shredding&demetalization stage 900 may be included. In the particulating stage 200 (or particularization stage), solid recovered fuel, especially paper rejects, may be particularized.

During the torrefaction stage 300, the starting material 100 is heated indirectly, with co-current heating, at a temperature preferably selected from the range of about 240 ⁰ C to about 675°C, more preferably at a temperature selected from the range of about 300 ⁰ C to about 450 ⁰ C, and even more preferably at a temperature selected from the range of 340 - 420 ⁰ C. During the torrefaction stage 300 volatile by-products are formed. These by-products may be combusted to provide a hot combustion gas, and in a heat exchange change stage 350, energy is transferred from the hot combustion gas to the torrefaction stage and/or the drying stage in order to provide (at least part of) the energy consumed during torrefaction of the starting material and/or drying of the starting material or torrefied (washed) product.

Subsequently, the torrefied product may optionally be washed in a washing stage 400, as is described in more detail below. After an optional drying stage 500, and a particulating stage 600, the solid fuel according to the invention may be combusted in a combustion stage 700 in a combustion plant, for instance a large combustion plant, for the generation of energy. In the particulation stage 600, torrefied biomass, indicated with reference 1103 from a biomass torrefier 1000, may be mixed with the torrefied (washed) product. Hence, there may be two particularization stages (or particulation stages): the first may be a particularization (or particulation) of the paper rejects (i.e. before torrefaction), which stage is indicated with reference 200 and there may be a particularization stage 600 (herein often indicated as particulation stage 600 for the sake of understanding) to provide a particulated torrefied product / particulated solid fuel.

Figure 2 schematically depicts an embodiment of the torrefying arrangement, indicated with reference 1, showing an embodiment of the torrefying reactor, indicated with reference 301, in more detail. The torrefying reactor 301 comprises an inner mantle 310 with for instance an inner diameter di in the range of about 100 to 900 mm, more preferably in the range of 100 to 700 mm, and most preferably in the range of 100 to 500 mm, at least partly enclosed by an outer mantle 320 with an outer diameter d ₂ in the range of about 150 to 1050 mm, more preferably in the range of 150 to 850 mm, and most preferably in the range of 150 to 650 mm, thereby defining a volume 315 between the outer mantle 320 and the inner mantle 310. The reactor 301 can be divided into 3 zones: an inlet zone I, a torrefaction zone II, and an outlet zone III.

The starting material 100 is introduced into the inlet zone I of the reactor 301 via the reactor inlet 302. Transport of the starting material 100, the partially torrefied product and the torrefied product 1 10 within the reactor may be accomplished by a screw conveyor 305, and the torrefied product 110 may exit the reactor 301 via a reactor outlet 303 in the outlet zone III.

During torrefaction volatile by-products 131 are formed in the torrefying reactor 301. The gaseous by-products 131 may exit the reactor via an exhaust 304 and enter an optional combustion unit 351 via a combustion unit inlet 352. As will be clear to a person skilled in the art, the exhaust 304 may in an embodiment be the same as the reactor outlet 303. In the combustion unit 351 at least part of the volatile by-products 131 may be combusted to provide a hot combustion gas 360, which may exit the combustion unit 351 via a combustion unit outlet 353. The hot combustion gas 360 may then enter the reactor outer mantle 320 via the outer mantle inlet 322 and enter the volume 315 between the outer mantle 320 and the inner mantle 310 and, after heating the torrefying reactor, exits via the outer mantle and exhaust 323. This means that the hot combustion gas flows in co-current direction with the material in the reactor. The hot combustion gas 360 may in an embodiment also be able to bypass the reactor directly to exhaust 323, and in a preferred embodiment, the hot combustion gas, or part of the hot combustion gas, may go directly from the combustion unit outlet 353 to the reactor exhaust 323. Instead of using the hot combustions gas, also a heat exchanger may be applied. The heat exchanger extracts thermal energy from the combustion unit 351 and may transfer heat to the volume 351. In this way, a closed gas loop may be used, that loops between the volume 351 and the heat exchanger (see also figure 6). In a specific embodiment, the hot combustion gas is lead through a heat exchanger which will take (at least part of) the heat needed for torrefaction reactor. The rest can be used for drying etc. There is a close loop with can be heated via the heat exchanger when necessary.

In Figure 3 an embodiment of the torrefying arrangement 1 to provide a solid fuel 130 from a starting material comprising a solid recovered fuel is depicted schematically. The starting material 100, comprising an SRF material and, optionally, biomass and additional plastics, enters the torrefying reactor 301 and is subjected to the torrefying stage 300. At least part of the volatile by-products that are formed are combusted in the combustion unit 351 and the hot combustion gas is used to heat the torrefying reactor 301. The torrefied product 110 is transported to the washing unit 401, which is located downstream of the torrefying reactor 301 and upstream of the particulating stage 600. The washing stage 400 is described in more detail above and below. The washed product 120 is subjected to a drying stage 500 and at least partly dried in a dryer 501, for instance in a drum dryer. The (partly) dried product is then particulated with a particulator 601 arranged to press the product with for instance a flat die pelleting press to yield the solid fuel 130 according to the invention. In the particulation stage 600, torrefied biomass, indicated with reference 1103 from a biomass torrefϊer 1000, may be mixed with the torrefied (washed) product 110, 120.

In Figure 4 an embodiment of the optional washing unit of the torrefying arrangement is schematically depicted. The washing unit 401 is arranged downstream from the torrefying reactor 301 and comprises a washing tank 440, arranged to comprise a washing liquid 430 (first washing liquid). Optionally, a second washing tank 450, arranged to comprise a washing liquid 430' (second washing liquid) may be present. A conveyor belt 402 is arranged to transport the torrefied product 110. The washing unit 401 further comprises a spraying unit 403. The washing tanks 440, 450 and the spraying unit 403 are arranged in a manner that ensures that contact of the torrefied product 110 with the washing liquid 430, 430' and/or 430" is sufficient for satisfactory washing, as will be clear to a person skilled in the art. As described above, the washing liquids 430, 430' and/or 430" are for instance water or an aqueous solution, optionally comprising chelating or complexing agents. As will be obvious to a person skilled in the art, the washing liquid 430 in the first washing tank 440 may be different from the washing liquid 430' in the optional second washing tank 450, and both these washing liquids 430 en 430' may differ from the washing liquid 430" in the spraying unit. After the washing stage 400, the washed product 120 is transported to the particulator 601, here via optional dryer 501, to yield the solid fuel 130 according to the invention.

Figure 5 schematically depicts a further embodiment of the torrefying reactor. The outer mantle 320 of the torrefying reactor 301 comprises an inlet 322 arranged to receive the hot combustion gas 360 and an exhaust 323, as described above. Furthermore, the outer mantle 320 comprises elements 330 arranged to increase the path length between the inlet 322 and the exhaust 323 in order to improve the heat exchange between the hot combustion gas 360 and the inner mantle 310. It will be apparent for the person skilled in the art that the elements can be present in the form of fins, partitions, or any other process known in the art that improve heat exchange.

Figure 6 is a simplified version of figure 2, but includes another variant. In this variant, a heat exchanger 1 100 is applied, that extracts thermal energy from the combustion unit 351 and leads at least part of this thermal energy to the reactor 301, for instance to the volume 315. In the latter variant, a closed gas loop may be applied, wherein gas escaping from the volume 315 may again be led to the heat exchanger to be heated. In a specific embodiment, the hot combustion gas is lead through a heat exchanger which will take (at least part of) the heat needed for torrefaction reactor. The rest can be used for drying etc. There may be a close loop with can be heated via the heat exchanger when necessary. Figure 7 schematically depicts another embodiment of the process, in part similar to the embodiment and variants schematically depicted in figure 1. A mixture of paper and plastic (especially paper rejects) (and optionally other material, not depicted), is fed to a torrefaction stage 300. Optionally, in the sequence as indicated, one or more stages precede the torrefaction stage 300, visually the (optional) shredding/demetalising stage 900, the (optional) drying stage 150, and the (optional) particulating stage 200. After torrefaction, the (optional) stages as indicate above may be performed, but here an alternative is indicated, wherein in a quench cooling stage 450, the torrefied product is cooled. Thereafter, the product may be particulated in a particularization stage 600. Shredding can be performed with a shredder; demetaliation can be performed with for instance a magnetic separator and/or an eddy current separator. Further, a energy recovery stage 1350 is indicated. The gaseous by-product gasses from the torrefying arrangement (i.e. torrefying reactor) can be combusted. By the combustion, energy can be generated, which can be reused for different stages of the process and/or provided to other sites etc. In an embodiment, a heat exchanger 350 stage is comprised by the energy recovery stage 1350, and the thermal energy can be reused in stages wherein heat is necessary, such as stages 150, 300, and 500 (other variant).

Figure 8 includes the above embodiment in a process for the production of paper. However, the process for the production of paper may also incorporate other variants described herein. Here, starting material Sm for the paper making process is provided to the paper making stage (Pm). This leads to the production of paper (P) and a mixture of paper and plastic, here indicated with reference 102. In the paper making process, the starting materials Sm for the paper making may contain recycled paper (i.e. paper that is returned to the paper making plant). Recycled paper is used as one of the feedstocks for the production of for instance paper or paper products, especially cardboard. However, a certain fraction of the recycled paper is unsuitable for further processing in the paper plant. This fraction, also referred to as "paper rejects", may comprise, amongst others, (especially on an industrial scale) inseparable paper and plastic, and metal parts such as for example staples. The rejects from recovered paper may comprise plastics, lumps of fibres, staples and metals from ring binders, sand, glass and plastics and paper constituents as fillers, sizing agents and other chemicals.

Further, the process may be the same described above; with the exception that energy recovered in the energy recovery stage 1350 may also be reused in the paper making stage PM.

Hence, recovered energy may be provided to one or more of the above mentioned stage, as far as energy is needed in such stage(s). If the recovered energy comprises thermal energy, thermal energy may be provided to one or more of the above mentioned stage, as far as thermal energy is needed in such stage(s). The priority document is herein incorporated by reference. The claims as filed are herein incorporated by reference.

The term "substantially" herein, such as in "substantially all emission" or in "substantially consists", will be understood by the person skilled in the art. The term "substantially" may also include embodiments with "entirely", "completely", "all", etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term "substantially" may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term "comprise" includes also embodiments wherein the term "comprises" means "consists of.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to a process of operation or devices in operation. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Examples Example 1: Torrefaction of SRF derived from paper rejects

A solid recovered fuel derived from paper rejects was torrefied according to the process of the present invention. The torrefied product was washed and dried. Pelletizing the thus obtained product with a flat die pelleting press resulted in a solid fuel with an average pellet size of 6 mm.

Example 2: Tor refaction of biomass Several different types of biomass (straw, grass, yard waste) were torrefied according to the process of the present invention. The torrefied biomass was washed and dried. Pelletizing the torrefied biomass with a flat die pelleting press was unsuccessful in all cases.

Example 3: Mixing torrefied SRF derived from paper rejects with torrefied biomass

Torrefied solid recovered fuel derived from paper rejects (example 1) was mixed with torrefied biomass (example 2). Pelletizing the thus obtained mixture with a flat die pelleting press resulted in a solid fuel with an average pellet size of 6 mm. The relative ease of pelletizing of the various mixtures of torrefied SRF derived from paper rejects with torrefied biomass is summarized in Table 1.

Table 1 : Ease of pelletizing of various mixtures of torrefied SRF derived from paper rejects with torrefied biomass.

- +: Excellent pelletizability; + +: Very good pelletizability; +: Good pelletizability; Pelletizing not possible.