WO2015181713A1

WO2015181713A1 - Process and apparatus for producing fuel gas obtained by exhausted plastics

Info

Publication number: WO2015181713A1
Application number: PCT/IB2015/053919
Authority: WO
Inventors: Pietro Tolve; Fabio Salvati; Massimo PARAVIDINO; Stefano PETRIGLIERI; Valter FACCIOTTO
Original assignee: Centro Sviluppo Materiali S.P.A.
Priority date: 2014-05-26
Filing date: 2015-05-26
Publication date: 2015-12-03
Also published as: CN106471101A; EP3149115A1

Abstract

The present invention relates to a process for the production of fuel gas obtained from mixtures of end-of-life plastics. The present invention also relates to an apparatus suitable for implementing said process. The figure shows a longitudinal and cross section of an embodiment of the apparatus according to the invention.

Description

PROCESS AND APPARATUS FOR PRODUCING FUEL GAS OBTAINED FROM

EXHAUSTED PLASTICS

The present invention relates to the field of recovery and recycling of plastics treated downstream of the segregated collection of municipal solid waste.

Such plastics are not homogeneous and do not represent a single material, but are rather composed of different materials with their own chemical and physical characteristics. The polymer chosen for each use must in fact meet specific requirements in terms of preservation (protection against air, light) , logistics (efficiency in transport, handling at the points of sale, spaces occupied in homes), and aesthetics (transparency, colours, possibility of applying wording and images) .

For this reason, the plastics originating from segregated waste collection need to undergo processes of selection for polymer (PET, PE, PP) or family of polymers, in order to be afterwards reintroduced into the market for the production of semi-finished or finished products.

The residual left over after such selection processes, consisting of a mixture of plastics, displays a large heterogeneity that makes it substantially impossible to exploit in the recycling market, which demands homogeneous material sorted by polymer or family of polymers.

Said mixture of plastics displays a good calorific value, estimable to be between 20 and 30 MJ/kg, above the limit of 13 MJ/kg, which represents the maximum value for landfillable waste (European Directive 1999/31/EC transposed in Italy by Legislative Decree 13/1/2003 n.36) .

The interest toward this material is therefore due to its high calorific power, which makes it attractive for incineration and energy production.

It is known that gasification, i.e. the thermal treatment of a substance or mixture of substances in the presence of an oxidizing agent in substoichiometric amounts, with the passage from the solid state to a fuel gas, names as synthesis gas or syngas, enables to produce electricity with a greater yield and a lower environmental impact compared to solutions based on combustion alone.

In Italian patent 1352001 a reactor is described having a substantially cylindrical chamber, capable of rotating, for carrying out the gasification process and for the disposal of waste.

Said apparatus and procedure can be optimized in order to implement a gasification process based on the specific characteristics of the mix of plastics.

Thus there is the need, in the specific field of the recovery and recycling of plastics from treatment downstream of the segregated collection of municipal solid waste and end-of-life plastic packaging, to be able to have a process and a simple, economical apparatus for the production of fuel gas.

The present invention contributes to solving the problem of making use of plastics, in particular end-of-life (exhausted) plastic packaging, by providing an alternative solution to landfilling and enabling the production of fuel gas.

Scope of the process and apparatus of the present invention is to obtain, by conducting and performing the thermal treatment in a particular way, without the input of heat from the outside, fuel gases that can be used in a plant for the combined production of electricity and heat energy.

The object of the present invention refers to a process for the production of fuel gases obtained from a mixture of plastics, comprising the following operations:

- loading said mixture of plastics into a rotating cylindrical reactor chamber, preheated to temperatures in the range of 600- 1000°C, and containing a solid mobile bed, chemically inert towards the mixture of plastics, having high values of: thermal capacity, thermal conductivity, density and hardness;

- introducing, contacting and mixing the mixture of plastics in said bed;

- releasing, in the chamber, of volatile substances obtained by the heating activity of said bed on the mixture of plastics and by the mechanical contact activity between the mixture of plastics and said bed;

- inletting and distribution in the chamber of a combustive agent selected from the group comprising: air, oxygen, nitrogen, argon and combinations thereof;

- combusting by means of the inlet combustive agent of at least a part of the volatile substances with the consequent production of gaseous products;

-emitting fuel gas (synthesis gas or syngas), said fuel gas being composed of the mixture of combustion products and volatile substances not combusted at a temperature in the range of 700- 850°C; unloading and collection of solid residual products, such as ashes.

The mixture of plastics treated according to the proposed process includes:

-volatile substances in a percentage in the range between 60 and 90% by weight, preferably 70%;

- an ash content in a percentage in the range between 3 and 30% by weight, preferably 10%; an apparent density in the heap (defined as the ratio between the mass and the apparent volume, which also includes empty spaces) in the range between 80 and 150 kg/m³, preferably 100 kg/m³;

-a lower calorific value (LCV) in the range between 20 and 40 MJ/kg, preferably 30 MJ/kg.

The mixture of plastics, prior to loading in the reactor apparatus, is preferably mechanically pre-treated by grinding with a grinder having a maximum output mesh size in the range between 30 and 60 mm, preferably equal to 50 mm. According to the invention, the solid mobile bed of the gasification apparatus has the following characteristics:

-values of specific heat of the material forming the bed such as to obtain a thermal capacity of the bed in the range between 400 and 2000 kJ/kg, preferably 1000 kJ/kg;

-values of the thermal conductivity of the material forming the bed in the range between 10 and 100 W/ (m^»K) , preferably 30 W/ (m^»K) ;

-values of the absolute density of the material forming the bed in the range between 3800 and 8000 kg/m³, preferably 20 4000 kg/m³;

-values of hardness of the material forming the bed in the range between 160 and 2000 Vickers, preferably 1000 Vickers.

The elementary unit of the material constituting the bed has a roundness (defined as the ratio between the outer surface of a sphere which has the same volume as a particle of the material forming the bed and the outer surface of the particle itself) of 0.6 to 1, preferably 1, with the maximum size in the range between 10 and 40 mm, preferably 25 mm.

The ratio between the mass of the mobile solid bed (kg) and the flow rate of the loaded mixture of plastics (kg/hr) is in the range between 3 and 20, preferably 5, and the flow rate of the combustive agent injected into the combustion chamber has an equivalence ratio (defined as the ratio between the amount of oxygen fed and that necessary for stoichiometric combustion of the loaded mixture of plastics) in the range between 0.16 and 0.30.

The material forming the mobile bed is made with a multiplicity of elements made of metallic or ceramic material.

The choice between a ceramic bed and metal bed is tied to specific configurations connected to the productivity of the plant; in particular, it is based on such parameters as height, weight of the bed, mass of the solid mobile bed (kg) and the flow rate of the loaded mixture of plastics (kg/hour) . When greater productivity is required, the use of bed in ceramic material is preferable.

According to a first variant, the solid mobile bed, when values V of the ratio between the mass of the mobile solid bed (kg) and the flow rate of the loaded mixture of plastics (kg/hour) is in the range between 3 and 8 included (3 < V < 8 ) , is made of ceramic material, preferably in the form of solid elements, the ceramic material being selected from the group comprising: calcinated bauxite, grounded corundum and tabular alumina.

According to a second variant, the solid mobile bed, when values V of the ratio between the mass of the mobile solid bed (kg) and the flow rate of the loaded mixture of plastics (kg/hour) is in the range between 8, excluded, and 20 (8 < V < 20), is made of metallic material, preferably in the form of hollow elements, the metallic material being selected from the group comprising: steel, preferably stainless steel, and cast iron .

The presence of the solid mobile bed brings the following advantages:

- it facilitates the crushing of the solid products generated in the phase of pyrolysis deriving from the contact between the solid residue and the elements forming the hot bed;

- it facilitates the heat exchange between the mixture of plastics and the elements forming the hot bed, thus accelerating the thermal treatment process, with a consequent high production of volatile substances;

- it accumulates the heat generated by the partial combustion of released volatile substances.

One of the advantages of the process according to the invention is that, thanks to the use of a particular solid mobile bed, it is possible to carry out, inside the reactor, a self- sustaining thermal treatment, there being no need for a regime of further heating systems. A further advantage of the present invention is the formation of a syngas mainly consisting of methane and carbon monoxide, with a low percentage of tar.

The present invention also refers to an apparatus suitable for carrying out the process according to the invention.

In fact, a further object of the present invention is an apparatus suitable for the production of fuel gas from a mixture of plastics comprising:

-a substantially cylindrical chamber (1), rotating around its longitudinal axis of symmetry, optionally inclined downwardly from the inlet section to the outlet section relative to the horizontal plane by an angle comprised between 1 and 3%, with a rotation speed in the range between 0.5 and 3.0 rpm, preferably 1.5 rpm, with a ratio between diameter and length ranging between 0.15 and 0.4, and provided with means able to achieve an internal depression of the chamber between -10 and - 40 Pa; the chamber being partially filled with a mobile solid bed (2) chemically inert towards the mixture of plastics;

- preheating means (3), consisting, for example, in at least one burner, preferably supplied with methane;

-supply means (4) for supplying the mixture of plastics, consisting of gravity feeding means, such as, for example, a screw feeder or conveyor belts with a longitudinal distribution over the mobile bed;

-input and distribution means (5) for the combustive agent, consisting preferably in a lance arranged parallel to the axis of longitudinal symmetry of the chamber and having a plurality of nozzles for the emission of the combustive agent toward the mobile bed;

-discharge means (6) for discharging the solid residue, such as, for example, grids with a mesh having dimensions smaller than the grain size of the material constituting the mobile bed.

According to a variant of the apparatus, there are also means for mixing the solid mobile bed and the mixture of plastics, for example consisting of series of blades arranged circumferentially on the inner skirt of the chamber.

Up to now, an overall description of the present invention has been provided. With the support of the figure and examples, a description of the embodiments thereof will now be given in order to provide a better understanding of its embodiments, features, advantages and methods of application, to be understood as non-limiting.

Figure 1 shows a longitudinal section and cross section along the line A-A of one embodiment of the apparatus according to the invention .

The figure of the cross section of the invention shows the position of the system (5) for introducing the combustive agent, positioned higher than the system (4) for introducing the mixture of plastics.

EXAMPLE 1

The mixture of plastics to be treated according to the process of the present invention has the characteristics indicated in the table below (% by weight) .

The mixture of plastics to be treated, ground beforehand with a shredder having an output mesh size of 30 mm, is introduced at a flow rate of 100 kg/h. The density in the heap of the mixture of plastics is equal to 115 kg/m³.

The used cylindrical reaction chamber, also referred to as a drum, has the following dimensional characteristics:

-drum diameter: 0.9 m -drum length: 2.65 m

The diameter/length ratio of the chamber is thus equal to 0.34.

The reaction chamber rotates around its own axis, inclined downwardly from the inlet section to the outlet section relative to the horizontal plane by a 1 degree angle, at a speed of 1.5 rpm.

The screw feeder is positioned inside the reactor so as to ensure a length of the reaction area of 2.65 m.

The average depression inside the chamber is equal to -30

Pa.

The reaction chamber was preheated to a temperature of 900 °C and in such a way the solid mobile bed loaded inside the reactor beforehand was also heated.

In the specific case, use was made of a bed of 500 kg of inert material, consisting in calcinated bauxite having a roundness of 0.6, with a maximum size of the elementary units making up the material in the range between 8 and 15 mm and an average value of said maximum size of 10 mm, an absolute density of 3800 kg/m³, a hardness of 1567 Vickers and a thermal conductivity of 23 W/ (m-K) .

The thermal capacity of the bed is 1055 kJ/kg.

The ratio between the mass of the solid mobile bed (kg) and the flow rate of the loaded mixture of plastics (kg/hour) is equal to 5.

For the input and distribution of the combustive agent in the chamber, a multi-nozzle lance was installed and arranged parallel to the longitudinal axis of symmetry of the drum, so as to inject an overall flow of 83 Nm³/h of the combustive mixture composed of air and oxygen, with a total oxygen content of 43%. The equivalence ratio is equal to 0.22.

The combustive mixture is used for the combustion of part of the volatiles previously produced by the physiochemical interaction between the residue and solid mobile bed. The usual temperature of the mobile bed in the volatilization area is 540°C and in the remaining part of the reactor is 900°C. A fuel gas mixture and a solid residue are obtained as an output from the reactor.

The extracted fuel gas has a flow rate of 165 Nm³/h, at a temperature of 760°C, and a calorific value of 13 MJ/Nm³.

The discharged solid residue has a flow rate of 9.5 kg/h.

EXAMPLE 2

The mixture of plastics to be treated according to the process of the present invention has the characteristics specified in the table below (% by weight) .

The mixture of plastics to be treated, ground beforehand with a shredder having an output mesh size of 30 mm, is introduced at a flow rate of 50 kg/h. The density in the heap of the mixture of plastics is equal to 104 kg/m3.

The reaction chamber, also referred to as a drum, used according to the present invention, has the following dimensional characteristics:

-drum diameter: 0.9 m

-drum length: 2.65 m.

The diameter/length ratio of the chamber is thus equal to 0.34.

The reaction chamber rotates around its own axis, inclined downwardly from the inlet section to the outlet section by 1 degree relative to the horizontal plane, at a speed equal to 1.5 rpm. The screw feeder is positioned inside the reactor in such a way as to ensure a length of the reaction area of 2.2 m.

The average depression inside the chamber is equal to -30

Pa.

The reaction chamber was preheated to a temperature of 900

°C and in such a way the solid mobile bed loaded inside the reactor beforehand was also heated.

In the specific case, use was made of a bed of 815 kg of inert material, consisting in cast iron balls having a roundness of 0,9, with a maximum size of the elementary units making up the material in the range between 9 and 12 mm and with an average value of said maximum size of 10 mm, an absolute density of 7300 kg/m³, a hardness of 200 Vickers and thermal conductivity of 53 W/ (m^»K) .

The thermal capacity of the bed is 490 kJ/kg.

The ratio between the mass of the solid mobile bed (kg) and the flow rate of the loaded mixture of plastics (kg/hour) is equal to 16.

For the input and distribution of the combustive agent into the chamber, a multi-nozzle lance was installed and arranged parallel to the axis of longitudinal symmetry of the drum, so as to inject a flow, at an overall rate of 32 Nm³/h, of a combustive mixture composed of air and oxygen, with a total oxygen content of 50%. The equivalence ratio is equal to 0.24.

The combustive mixture is used for the combustion of part of the volatiles previously produced by the physicochemical interaction between residue and solid mobile bed.

The usual temperature of the mobile bed in the volatilization area is 520°C and in the remaining part of the reactor it is 860°C. A mixture of fuel gas and a solid residue are obtained at the outlet of the reactor.

The extracted fuel gas has a flow rate of 76.7 Nm³/h, at a temperature of 815°C, and a calorific value of 11.3 MJ/Nm³.

The discharged solid residue has a flow rate of 7.5 kg/h.

Claims

CLAIMS 1 - Process for the production of fuel gas obtained from a mixture of plastics, comprising the following steps:

- load with said mixture of plastics a rotating cylindrical reactor chamber, preheated to temperatures in the range 600- 1000°C, and containing a solid mobile bed, chemically inert towards the mixture of plastics, having high values of: thermal capacity, thermal conductivity, density, hardness;

- introduce, contact and mix the mixture of plastics in said bed;

- release of volatile substances in the chamber obtained by the heating activity of said bed on the mixture of plastics and by the mechanical contact activity between the mixture of plastics and said bed;

- inlet and distribution in the chamber of a combustive agent selected from the group comprising: air, oxygen, nitrogen, argon and combinations thereof;

- combustion by means of the inlet combustive agent of at least a portion of volatile substances with consequent production of gaseous products;

- emission of fuel gas (synthesis gas or syngas), said fuel gas being composed by the mixture of combustion products and volatile substances not combusted at a temperature in the range 700-850°C; unload and collection of solid residual products.

2 - Process according to claim 1, wherein the mixture of treated plastics includes:

- volatile substances in a percentage in the range between 60 and 90% by weight, preferably 70%;

- solid residual products, such as ashes, in a percentage in the range between 3 and 30% by weight, preferably 10%;

- an apparent density in the heap in the range between 80 and 150 kg/m3, preferably 100 kg/m3 ;

- a lower calorific value in the range between 20 and 40 MJ / kg, preferably 30 MJ / kg. 3 - Process according to claim 2, wherein said mixture of plastics, prior to loading in the reactor apparatus, is preferably mechanically pre-treated by grinding with a grinder having a maximum size of the mesh of the output in the range between 30 and 60 mm, preferably equal to 50 mm.

4 - Process according to claim 1, wherein said solid mobile bed presents:

- values of specific heat of the material forming the bed such as to obtain a thermal capacity of the bed in the range 400 and 2000 kJ/kg, preferably 1 000 kJ/kg;

- values of the thermal conductivity of the material forming the bed in the range between 10 and 100 W/ (m^»K) , preferably 30 W/ (m^»K) ;

- values of the absolute density of the material forming the bed in the range between 3800 and 8000 kg/m3, preferably 4000 kg/m3 ;

- values of hardness of the material forming the bed in the range between 160 and 2000 Vickers, preferably 1000 Vickers.

5 - Process according to claim 1 or 4, wherein the elementary unit of the material constituting the bed has a roundness of 0.6 to 1, preferably 1, with the maximum size in the range between 10 and 40 mm, preferably 25 mm. 6 - Process according to claim 5, wherein the ratio between the mass of the mobile solid bed (kg) and the flow rate of the loaded mixture of plastics (kg/hr) is in the range between 3 and 20, preferably 5, and wherein the flow rate of the combustive agent injected into the combustion chamber has an equivalence ratio in the range between 0.16 and 0.30.

7 - Process according to any of claims 1 to 6, wherein the material forming the mobile bed is made with a multiplicity of elements made of metallic or ceramic material.

8 - Process according to claim 7, wherein said mobile solid bed

- is made of ceramic material, preferably in the form of solid elements, when values Vof the ratio between the mass of the mobile solid bed (kg) and the flow rate of the loaded mixture of plastics (kg/hour) is in the range 3 < V < 8, being the ceramic material selected from the group comprising: calcinated bauxite, grounded corundum, tabular alumina;

- is made of metallic material, preferably in the form of hollow elements, when values Vof the ratio between the mass of the mobile solid bed (kg) and the flow rate of the loaded mixture of plastics (kg/hour) is in the range 8 < V < 20, being the metallic material selected from the group comprising: steel, preferably stainless steel, or cast iron.

9 - Apparatus suitable for the implementation of the process according to claims 1 to 8, for the production of fuel gas from a mixture of plastics comprising:

- a substantially cylindrical chamber (1), rotating around its longitudinal axis of symmetry, optionally inclined downwardly from the inlet section to the outlet section with respect to the horizontal plane of an angle comprised between 1 and 3%, with a rotation speed of in the range between 0.5 and 3.0 r/min , preferably 1.5 r/min, with a ratio between diameter and length between 0.15 and 0.4, being provided with means able to provide an internal depression of the chamber between -10 and -40 Pa ; said chamber being partially filled with a mobile solid bed (2) chemically inert towards the mixture of plastics; - preheating means (3), consisting preferably in at least one burner, preferably with methane;

- supply means (4) of the mixture of plastics, consisting of gravity feeding means, as preferably a screw feeder or conveyor belts with a longitudinal distribution onto the mobile bed;

- input and distribution means (5) of the combustive agent, consisting preferably in a lance arranged parallel to the axis of longitudinal symmetry of the chamber and having a plurality of nozzles for the emission of the combustive agent toward the mobile bed;

- discharge means (6) of the solid residual products, which preferably grids with a mesh having dimensions smaller than the grain size of the material constituting the mobile bed.

10 - Apparatus as in the previous claim 9, having means for mixing the mobile solid bed and the mixture of plastics, said means consisting of series of blades arranged circumferentially on the inner skirt of the chamber (1) .