Method for Manufacurmg a Solid Fuel with Waste Materials

FIELD OF THE INVENTION

The invention relates to a method for recovering energy from waste and, more particularly, to a method for manufacturing a solid fuel with waste materials.

BACKGROUND

Many industrial processes, and some stoves in domestic use, use solid fuels. The amount of fuel used in the industrial setting typically translates in significant costs. Many industries have thus been affected by increases in the price of fuels in recent years, and there is an ever lasting desire to obtain fuels at cheaper prices.

The types of fuel which can be used in specific industrial processes are often quite limited. Due to the large volumes of fuel consumed by industries, governmental norms are often present and restrict the amount of emissions allowed by their consumption. Some fuels cannot be used because they would exceed these emission limits. Also, some fuel consuming processes can require a fuel having a calorific value (or heating value) within a specific predetermined range, which eliminate some fuel sources from consideration.

Such restrictions substantially limit the possibility of changing the fuel source of many industrial fuel consumption processes. And it may not be possible to switch to an alternate, less costly fuel, when the price of the original fuel increases.

SUMMARY

Waste materials from agricultural, industrial and domestic sources have to be collected, transported and disposed of. If the waste can be regarded as an energy source and the energy extracted, then not only is the disposal problem solved but energy is both saved and made available for use as a fuel.

It was found that by characterizing two or more waste materials by their individual calorific value and/or their individual emission, and by combining and pelletizing these at least two waste

materials in predetermined proportions, it was made possible to create composite fuels having a calorific value within a predetermined range, and/or having an overall emission factor lower than a predetermined emission limit. Thus, composite fuels can be made and used in applications in which the base waste materials of the composite fuels would be worthless otherwise.

According to a general aspect, there is provided a method for manufacturing a composite fuel material from at least two waste materials. The composite fuel material has at least one of a predetermined calorific value and an emission factor for at least one emission constituent produced below a threshold value. The method comprises: characterizing each of the at least two waste materials by determining at least one of their individual calorific value and their individual emission factor for the at least one emission constituent; determining proportions of the at least two waste materials to obtain the composite fuel material having at least one of the predetermined calorific value and the emission factor for the at least one emission constituent produced below the threshold value; and pelletizing the at least two waste materials in the proportions determined.

According to another general aspect, there is provided a composite fuel material which comprises: at least two waste materials combined together in predetermined proportions, each of the at least two waste materials having a calorific value and producing combustion emissions, the at least two combined waste materials providing the composite fuel material with at least one of a predetermined calorific value and an emission factor for at least one emission constituent produced below a threshold value.

According to another aspect, there is provided a method for obtaining a composite fuel based on a combination of at least two waste materials and having a calorific value within a predetermined range of calorific values, the method comprising the steps of :

a) obtaining a calorific value of each of the at least two waste materials; and

b) determining relative proportions of the at least two waste materials for the combination to yield the composite fuel with the calorific value within the predetermined range, using the calorific values obtained in step a).

In accordance with another aspect, there is provided : a method of manufacturing a composite fuel including at least two waste materials and having a calorific value within a predetermined range of calorific values, the method comprising :

a) preparing at least two waste materials;

b) obtaining a calorific value of the at least two waste materials prepared in step a);

c) determining a relative proportions of the at least two waste materials for obtaining a composite fuel having the calorific value within the predetermined range, based on the calorific values obtained in step b);

d) combining the at least two waste materials in the relative proportions determined; and

e) pelletizing the combined at least two different waste materials to obtain the composite fuel.

In accordance with another aspect, there is provided : a method of pelletizing a solid fuel from solid waste, the method comprising preparing the waste material for pelletizing, and pelletizing the prepared waste, the process being CHARACTERIZED IN THAT the prepared solid waste includes at least two waste materials in relative proportions predetermined for obtaining a pelletized solid fuel having a calorific value within a predetermined range of calorific values.

In accordance with another aspect, there is provided : a composite fuel in pellet form, the composite fuel having a calorific value within a predetermined range of calorific values, and comprising at least two waste materials each having a respective individual calorific value, the at least two waste materials being combined in relative proportions predetermined based on the individual calorific values for yielding the composite fuel calorific value within the predetermined range.

The term "calorific value" (or heating value) refers to the amount of heat released during the combustion of a material. It is measured in units of energy per amount of material. Depending on the context, heating values may be reported as Btu/m ³ , kcal/kg, kJ/kg, J/mol, or a variety of other

combinations of units.

The term "emission" refers to the giving off of a substance, typically an undesired gas or dust, such as chlorine for example, from combustion of a fuel in an industrial process.

The term "emission factor" refers to a measure of the average amount of a specified pollutant or constituent emitted (or released) during the waste material combustion (by weight or volume). The emission factor is usually expressed as the weight of pollutant (or emission constituent) divided by a unit weight or volume of the activity emitting the pollutant (e. g., kilograms of particulate emitted per megagram of coal burned).

DESCRIPTION OF THE FIGURES

In the appended figures, enclosed for the purpose of demonstration :

Fig. 1 is a flow chart of an example of a method for manufacturing a composite fuel;

Fig. 2 is a flow chart of an example of a separating step used in the method shown in Fig. 1 ; and

Fig. 3 is a flow chart of an example of a characterizing step used in the method shown in Fig. 1.

Throughout the appended description and figures, like features are identified by like reference numerals.

DETAILED DESCRIPTION

Figures 1 to 3 show an example of a method for recovering energy from base waste materials 10a, 10b, 1On is described. Base waste materials 10a, 10b, 1On are materials which are typically considered as having no value to their owner, and may even represent a source of costs to dispose of. Large volumes of base waste materials 10a, 10b, 1On come from human industrial activity such as mining, industrial manufacturing, consumer use, etc.

Sources of base waste materials 10a, 10b, 1On are almost infinite. They include agricultural crop residue, food-industry residues, asphalt paving, asphalt roofing, batteries, colored ledgers,

computer paper, concrete, durable plastic items, film plastics, gypsum boards, industrial sludge, magazines, catalogues, major appliances, miscellaneous plastic containers, mixed residue, composite construction and demolition materials, wooden pallets, milk cartons, composite plastics, textiles, elastomers such as tires and rubber, to cite only several examples thereof.

Sources of base waste materials typically vary depending on a particular location. For example, in the tropics, there may be a lot of coconut residue available, whereas in north-american agricultural areas, there may be a lot of corn residue available. In many cases, it will be advantageous to use two or more base waste materials which are readily available, to keep transportation costs at a minimum.

Some of the waste materials 10a, 10b, 1On can be composed of a combination of various constituents, some of them generating an desired exothermic reaction during combustion, and others generating an undesired endothermic reaction, or an insufficient exothermic reaction, during combustion. As well, some of the constituents can have a higher economic value in other recycling processes than as an energy source.

In many instances, it will be advantageous to prepare 12a, 12b, 12n the base waste materials 10a, 10b, 1On to obtain what will be referred to herein as a waste material 14a, 14b, 14n which is better adapted for use in a composite fuel than the base waste materials 10a, 10b, 1On. The preparation 12a, 12b, 12n can include fragmenting 16a, 16b, 16n the base waste material 10a, 10b, 1On, and/or separating 18a, 18b, 18n the base waste material 10a, 10b, 1On, to remove constituents 20a, 20b, 2On thereof which do not satisfactorily contribute to the exothermic reaction upon combustion, and/or which it is desired to remove for other reasons.

Fig. 1 shows that each waste material 14a, 14b, 14n can be prepared individually. Some waste materials 14a, 14b, 14n will benefit by different processing steps than others, or by being processed with the same steps but in a different sequence. Some base waste materials 10a, 10b, 1On can even be obtained in a form which makes them readily useable as waste materials 14a, 14b, 14n, without any particular preparation step. In Fig. 1, all waste materials 14a, 14b, 14c are shown similarly prepared, and only one 14a will be described in greater detail for simplicity.

In the case of some waste materials 14a, it can be advantageous to begin with a fragmentation step 16a to break the base waste material 10a into smaller, more manageable pieces. This can allow, thereafter, to remove undesired constituents 20a from the fragmented base waste material 16a. Particles of smaller size are usually easier to classify, or separate, than a single- piece base waste material 10a having multiple constituents. It will be appreciated that some undesired constituents of the base waste material 10a can be removed prior to the fragmentation step 16a.

Several techniques can be used to fragment the waste material into smaller pieces or particles. Hammer-type shredders and blade-type shredders are the most common examples. Preferably, the fragmenting step 16a and separating step 18a are used to obtain a waste material 14a composed of particles within a desired size range. The size range often depends on the particular type of pelletizing equipment which is to be used in manufacturing the composite fuel.

It can be advantageous to separate 18a, or classify, the base waste material 10a. The base waste material 1 Oa can include several constituents, some of which are preferably removed 20a to obtain the processable waste material 14a. Some of the base waste material 10a constituents can have a higher economic value in other recycling processes than as an energy source. Other constituents of the base waste material 10a can generate an endothermic reaction during combustion. It can thus be desirable to remove constituents 20a having an unsatisfactory calorific value to increase the calorific value of the waste material 14a.

Depending on the constituent content of the base waste material 10a, several separating steps 18a, as shown in Fig. 2, can be carried out consecutively, to obtain the waste material 14a. For example, it is possible to remove magnetic constituents 22a of the base waste material 10a, which have magnetic properties 16. This can be carried out using a magnetic belt. For example, the fragmented waste material can be transported on a conveyor from the fragmentation step 16a, towards the various separation steps 18a. The magnetic belt can be placed above and transverse relatively to the conveyor carrying the fragmented waste material. The magnetic particles of the base waste material are attracted by the magnetic belt and move from the conveyor to a position juxtaposed to the magnetic belt thereby removing the particles containing magnetic material

from the remaining waste material.

Another separation step 18a can include removing the non-ferrous metal constituents 24a, such as aluminum for example, which typically produce an endothermic reaction during combustion. An eddy current mechanism can be used to remove the non-ferrous metal constituents 24a from the fragmented waste material.

In another separation step 18a, inert constituents 26a can also be removed from the base waste material 10a. The term "inert constituents" is used to identify the materials included in the waste material but which will typically not be consumed at the burning temperatures of the composite fuel. One or several sieves or screens, or a mechanism based on particle specific density, can be used to remove the particles containing inert materials from the base waste material 10a.

It will be appreciated that other constituents 28a of the base waste material 10a can also be removed if their economic value is higher in another recycling process than as an energy source or for any other reason. Moreover, any appropriate system, method or mechanism can be used to remove the undesired constituents 20a from the base waste material 10a.

Once the undesired constituents 20a are removed from the base waste material 10a, the waste material 14a typically contains only the constituents which will be used in the composite fuel. It will generally be advantageous to characterize 22a the waste material 14a at this point to determine at least one of its combustion properties.

Fig. 3 shows several properties of waste material 14a can be characterized 22a.

One of the properties which can be characterized 22a is the calorific value 30a. hi fact, the calorific value 30a of the waste material 14a is generally an important factor in determining the relative proportion in which it will be used with the other waste material(s) 14b, 14n in the composite fuel. It is often a goal to obtain a composite fuel having a calorific value within a predetermined range. An appropriate determination of the relative proportions can allow obtaining a composite fuel having a calorific value within the predetermined range, even though the calorific value of some of the waste materials 14a, 14b, 14n are outside the predetermined

range.

Another of the properties which can be relevant to characterize 22a is the emission factor 32a for at least one emission constituent produced by combustion. Many emission constituents can be emitted by a waste material 14a during combustion. Typically, it can be interesting to characterize the emissions of one or more constituents. The emissions can be characterized as an emission factor for each of the one or more emission constituents.

Typically, it is not required to characterize the emission factor of all the emission constituents, because only some are generally relevant to the client's use. Also, it is not necessary to characterize the emission factor of a given emission constituent when it is known that a particular waste material does not emit the emission constituent. For example, it may be relevant to know the amount of chlorine emitted by some waste material, whereas it is known that some other waste materials do not emit a significant amount of chlorine.

It will be appreciated that the waste material can be characterized 22a for other properties 234a than its calorific value 30a and its emission factor 32a in accordance with the customer's needs. Each waste material can thus be characterized 22a using appropriate tests.

Typically, the waste materials 14a, 14b, 14n are sampled for carrying out the characterization step 22a. The remainder of the waste materials 14a, 14b, 14n can be individually stocked 36a, 36b, 36n, awaiting their use.

When a request for a composite fuel is received from a customer, the customer can specify at least one property of the desired composite fuel, and he typically provides a set of specifications. Typically, he can specify a range of calorific values which a specific industrial process requires, and an upper emission limit for one or more emission constituents. The emission limits often stem from governmental rules or norms to which the customer must comply. Emission limits are often given for greenhouse gasses such as carbon dioxide, methane or nitrous oxides, for example, or other undesired substances or fumes such as chlorine.

To satisfy the specifications provided by the customer, two or more waste materials 14a, 14b,

14n can be selected. A relative proportion of two or more of the waste materials is determined 38, for the combination of the two or more waste materials 14a, 14b, 14n in the determined proportions or ratios 38 to yield a composite fuel satisfying the specific needs of the customer. Typically, a mathematical simulation is made to predict the calorific value and/or emission factor which would result from mixing two or more of the waste materials 14a, 14b, 14n in given proportions. The mathematical simulation can be as simple as a rule of three.

Once relative proportions of selected waste materials 14a, 14b, 14n are found which meet the customer's requirements, the waste materials 14a, 14b, 14n are combined 40 in the proportions determined, and are pelletized 42 to obtain the composite fuel material 44. Combining can be carried out using many types of industrial mixers available in the industry.

Several pelletizing technologies can be used in accordance with the customer's needs. Typically, the pelletizing step 42 is carried out using a pellet mill, such as those manufactured by Pioneer and Andritz Sprout in North America, or Kahl in Europe, for example. Such pellet mills can typically generate pellets having between 5mm and 18mm. Other pelletizing techniques can involve an extruder, for example. The size of the pellets produced can be adapted to the customer's specification.

Pelletizing certain combinations of waste materials with a pellet mill can require that the waste materials fed to the pellet mill have between about 50 and 85% of the size of the final pellet, hi the composite fuel obtained 44, individual pellets do not necessarily match the specification. However, when a representative quantity of pellets are characterized, such as 1 pound thereof for example, the representative quantity typically meets the specifications.

To achieve a satisfactory pelletization using a pellet mill, a binder agent should be present in at least one of the waste materials, or added therewith. When using milk cartons, for example, the wax contained therein acts as a binder. Maize gluten also acts as a binder. Plastics such as LDPE (low-density polyethylene) and HDPE (high-density polyethylene) typically act as excellent binders. When only wood-based waste materials are used, vapour can be added after mixing, and the thus treated lignin in the wood fibres can act as a binder. When pelletizing waste materials

which do not have a binder present therein, a binder can be added prior to pelletizing.

Once pelletized, the composite fuel material can then burned and, during burning, generate energy within the predetermined calorific value range, and optionally under specified emission limits.

It is appreciated that other processing steps can be carried out on the composite fuel 44 before burning the latter. For example, it can be stocked, characterized, packaged for shipment, etc. The composite fuel 44 can be used as a fuel source in several industrial processes such as cement plants, pulp and paper industries, biomass cogeneration plants, to list only a few of the many examples. It can even be used in domestic pellet stoves, for example.

EXAMPLES

In the following examples, the identified waste materials prepared using the specified preparation steps were mixed in a 10- ton capacity industrial mixer, and pelletized using a pellet mill in accordance with the manufacturers operating instructions.

Example 1

In this example, a composite material was fabricated using saw dust, milk cartons, and maize cobs in the identified relative proportions. Wax in the milk carton served as a binder. The combination of waste materials in the relative proportions allowed manufacturing a composite fuel comprised of 60% maize cob which has a calorific value of about 8 500 BTU/lb (dry), and a chlorine emission factor below a specified 1000 mg/kg limit. A 1 pound quantity of composite fuel pellets was found representative of the composite fuel characteristics.

Example 2

Example 3

Example 5

The examples given above are intended to be exemplary only. The scope is therefore intended to be determined solely by appreciation of the appended claims.