WO2013183003A1

WO2013183003A1 - Plant and method of pyrolysis of organic material

Info

Publication number: WO2013183003A1
Application number: PCT/IB2013/054618
Authority: WO
Inventors: Mario CRUCCU
Original assignee: Cruccu Mario
Priority date: 2012-06-08
Filing date: 2013-06-05
Publication date: 2013-12-12
Also published as: BR102013005295A2; ITMI20121000A1

Abstract

The present invention relates to a method for pyrolysis of carbonious or at least partially carbonious material, such as the one originating from biomasses or organic and mixed waste of various origin. In particular, the present invention relates to.

Description

PLANT AND METHOD OF PYROLYSIS OF ORGANIC MATERIAL

The present invention relates to a method for pyrolysis of carbonious or at least partially carbonious material, such as the one originating from biomasses or from organic and mixed waste of various origin.

The pyrolysis is a process of thermal-chemical conversion of organic matrix materials in combustible end product, which takes place in the absence of oxygen, or with so-reduced a presence thereof, such that the oxidation reactions can be neglected, which reactions are responsible for the formation of compounds such as dioxins and furans. Compared to the typically used combustion furnaces for waste incineration, therefore, the pyrolytic reactors are much more safe and do not require complex systems of pulling down toxic oxidation compounds that, in the case of a failure, would eject dioxin and furans into the atmosphere, with a huge risk for the health and environment.

Pyrolysis products are gaseous, liquid, and solid, in proportions depending on the pyrolysis methods, on the reaction parameters, and the material with which the pyrolytic reactor is supplied. Compared to a direct combustion process, the pyrolytic technology allows transferring* the energy content of the starting material to the product, whether they are gaseous, liquid, or solid, in a low-environmental impact process. In the experimental studies that are available both in the literature and the industrial practice, it is noticed that, traditionally, the pyrolysis process was uses in order to maximize the production of char (carbon) or, more often, of pyrolysis oil.

The poor attention devoted to date to the production of a gaseous fuel is to be ascribed to the low gas yield that is intrinsic of the conventional pyrolytic technology, which arrives to a value that is normally less than 40% by weight of the starting material.

There is a huge variability in the processes and the products that can be obtained, which is determined by the wide possibility to act on the parameters ruling the process reactions (temperature, residence time, heating rate, pressure, particle size of the feeding material) . This involves that several classifications of the existent pyrolytic technologies were made, the most common among which being based on process temperature and the reaction speed.

As a function of the temperature at which the pyrolytic processes are carried out, they can be divided into low temperature (400-600 °C) , medium temperature (600-1000 °C) , and high temperature (1000-2000 °C) pyrolysis. The low and medium temperature pyrolysis processes (450-1000 °C) are divided, in turn, based on the type of the reactor into which they are carried out:

1. the vertical oven, in which the organic material is fed from the top, dried, and pyrolized by proceeding from the top downwardly in counter- current with respect to the hot gases. The residues are recovered in the lower section of the reactor, while the gases are evacuated from the top;

2. the rotary oven, similar to the vertical oven, characterized by a more efficient transport of the heat and by a better mixing of the supplied organic material by virtue of' the rotation thereof. On the contrary, the pyrolysis that is carried out in a rotary reactor is a more delicate process, due to the risks related to the possibility of that air enters in the proximity of the rotation joints;

3. the cylindrical vertical fluidized bed oven, in which the organic material to be treated, which requires trituration and sieving pre- treatments, is hold in suspension by an ascending gaseous flow. An inert material is also arranged within the reactor, usually silica sand, which acts to promote the thermal exchanges and to provide the system with a sufficient thermal inertia. Such ovens are very complex and difficult to be managed.

The products generated by the processes carried out in the above-described ovens are generally:

^• Powders, mainly consisting of pulverized coal. They can be more easily treated than those produced during incineration, since they are composed of particles with a larger size, due to the lower service temperature. Furthermore, they are more concentrated, given the lower volume of the gaseous phase that is produced.

• Gas , essentially composed of hydrogen (¾) , carbon monoxide (CO), and inert gases due to infiltrations. It is a gas with a heating power ranging between 12,500 and 20,900 kJ/Nm³. It does not contain nitrogen oxides, by virtue of the moderate temperature and the highly oxidizing atmosphere at which the process is carried out.

• Pyrolytic oil, mainly composed of partially oxidized organic compounds (acids, alcohols, esters) . it is a fuel that must undergo a depurative process due to the corrosive products of chlorine and sulfur contained therein. It can be used to give the endothermic contribution that is necessary to the pyrolysis reactions, or it can be used separately. ^• Solid residue or pyrolysis coke, containing a mineral substrate coming from the inorganic fraction of the waste, and a carbonious organic substrate. Such residue can be used as a solid fuel downstream of depurative treatments, or converted into active carbon.

The high temperature pyrolysis (about 2000 °C) takes place with high reaction speeds ("flash" pyrolysis), and it is characterized by high yields of thermal demolition of wastes in a reducing atmosphere and by a minimization of the formation of the reaction intermediate compounds. The reactors that are used are tubular electric reactors in which the finely triturated organic material is decomposed during its vertical fall due to the action of intense thermal exchanges. The problems related to the chemical-physical compatibility of the materials are minimized by avoiding the contact between waste and wall, keeping the flows to be treated separated ' by the radiating walls. The very low duration of the treatment is sufficient to produce a "clean" gaseous effluent, thus minimizing the need to treat the products.

Based on the reactions speeds, on the contrary, the different technologies that are used for the pyrolysis of organic matrix material on a pilot and industrial scale are divided into: ^• Quick pyrolysis with temperatures not exceeding 650 °C, used to maximize the production of pyrolytic oil. The currently existing processes are: THIDE (potentiality 20,000 - 60,000 t/year) , GARRET, PYROCAL, KEINER, under vacuum pyrolysis;

^• Quick pyrolysis with temperatures exceeding 650 °C. It is used to maximize the production of gaseous products (HTF process, AER process) ;

^• Slow pyrolysis with low temperatures (not exceeding 500 °C) . The maximization of the char production is obtained, through secondary repolymerization and coking reactions;

• Slow pyrolysis with medium temperatures (600 °C) . The maximization of the production of oil and pyrolysis gases is obtained. The NESA FLOWSHEET, ROTOPYR, D.R.P. processes are based on these parameters.

Also a method slow pyrolysis has been implemented, which provides for the addition of an amount in a slight stoichiometric excess of water to promote the reaction with organic carbon to give hydrogen and carbon oxide, but such method has the limitation that, in the case that the organic material to be treated has a water content that is too high, in particular more than 30%, the method is not advantageous. The problem underlying the present invention is to provide a method of pyrolysis of organic matrix material that results in a maximization of the production of gaseous fuel with a high value and that can be applied to any type of material, independently from its initial water content.

Such problem is solved by a pyrolysis method as set forth in the appended claims, the definitions of which are an integral part of the present description.

The pyrolytic technology that is the object of the present invention is based on the combination of three process parameters, i.e., low reaction speed, adjustment of the water content and presence of catalysis, allowing converting the starting organic matrix material, whether it is composed of woody or agricultural wastes or biomasses, into synthesis gases with a very high yield.

Further characteristics and advantages of the present invention will be more clearly apparent from the description of an implementation example, given herein below by way of illustrative, non-limiting example, with reference to the following Figures:

Fig. 1 represents a schematic view of a pyrolysis plant for implementing the method of the invention;

Fig. 2 represents a side sectional view of the reactor according to the invention. The process of the invention allows obtaining a high yield of pyrolytic gases by the combination of three fundamental parameters:

a) reaction speed;

b) humidity;

c) presence of catalysts in the organic matrix material to be pyrolyzed.

The reaction speed ranges between 0.5-1.5 hours, operating at a temperature ranging between 400 °C and 600 °C, more preferably between 400 °C and 500 °C. Therefore, it is classified as a slow pyrolysis process.

The water amount is adjusted as a function of the carbon content of the material to be pyrolyzed, and it is higher than that present in the known pyrolysis processes. Generally, the water amount in the material to be pyrolyzed is of about 30% by weight.

By the term "about 30% by weight" referred to the water content in the material to be pyrolyzed, it is generally meant an aqueous content ranging between 25% and 35% by weight.

the catalysts used for the pyrolysis process of the present invention are catalysts for cracking reactions, preferably selected between iron-, nickel-, or chromium- based catalysts. Since an increase of the catalytic properties is noticed in the order Fe < Ni < Cr, the selection of the most suitable catalyst is made as a function of the reactivity of the starting material, which varies according to the order biomasses > organic wastes with a mainly polymeric matrix (plastic materials) . Therefore, a catalyst less active will be preferably used for a more reactive substrate.

Preferably, such metals will be in the. form of a powder with a particle size not exceeding 1 mm. Preferably, between 100 and 300 mg of catalyst per kg of material to be pyrolyzed are used.

The objects of the present invention are achieved by virtue of a plant and, specifically, a reactor as they are set forth herein below.

With reference to the Figures, a plant according to the invention is generally indicated with the number 1.

The organic matrix material (wastes, biomasses, etc.) to be pyrolyzed is transferred from a tank 10 to a hopper 3 by means of transport means 11, typically screw conveyers. In the hopper 3, the material to be pyrolyzed is added with the selected catalyst through the dispenser 2. The hopper 3 is arranged above a screw conveyer 4. Vacuum means, such as a vacuum pump or a fan provide to evacuate the air absorbed in the material to be pyrolyzed, so as to create, within the pyrolysis reactor 5, a vacuum of about 5-10 mm of water column. The screw conveyer 4 transports the material to be pyrolyzed within the reactor of pyrolysis 5.

The reactor 5 comprises a reaction chamber 5a. The reaction chamber 5a is a rotating horizontal cylindrical chamber. A fixed combustion chamber 6 is arranged coaxially thereto. The combustion chamber 6 is preferably coated with a refractory material.

The reaction chamber 5a comprises a first preheating portion 7, arranged upstream with respect to the advancement direction of the material to be pyrolyzed, and a second pyrolysis portion 8, arranged downstream of the first pre-heating portion 7.

The pre-heating portion 7 comprises a helicoidal tongue 9 on its outer surface.

The pre-heating of the material to be pyrolyzed has also as its object to evaporate all the excess water that may be present, bringing the content thereof below 30% by weight. The dehydration content is adjusted by varying the speed of the screw conveyer 4, thus the residence time in such section 7. However, also an excessive or lower dehydration does not give rise to problems, since in the successive portion of the reactor all the water will be evaporated and will be available for the reactions with the cracking carbon of the organic matrix. The combustion chamber 6 has, in turn, a first preheating portion 12, surrounding the pre-heating portion 7 of the. reaction chamber 5a, and a second heating portion 13, surrounding the pyrolysis portion 8 of the reaction chamber 5a. Burners 14 are located in said second heating portion 13. The burners 14 are arranged longitudinally along the entire heating portion 13 of the combustion chamber 6, typically in the lower part thereof. The fuel for the burners 14 will be able to be either propane, methane, and gasoil, or a part of the pyrolytic gas produced in the reactor 5 itself (line 24) .

The distribution of the burners 14 longitudinally along the entire surface of the pyrolysis portion 8 of the reaction chamber 5a allows achieving surface temperature of the pyrolysis portion 8 of about 800 °C, optimizing the inner heating of the reactor. In this manner, the cracking yield is increased.

Before leaving the combustion chamber 6, the combustion fumes, having a temperature of about 1200 °C, pass through the pre-heating portion 12 by running through a spiral path defined by the helicoidal tongue 9, thus maximizing the contact time with the wall of the pre-heating portion 7 of the reaction chamber 5a. The fumes are then, evacuated through the line 19 suctioned by suction means 20 and, after passing through thermal exchange means 21 and suitable depuration means using an urea solution in a SNCR 21a reactor, they are discharged from a chimney 22.

The air that, through the line 23, is inputted into the burners 14 as an oxidant is pre-heated in the thermal exchange means 21.

Downstream of the reaction chamber 5a, the reactor 5 comprises a vertical axis chamber 15, open on the bottom thereof, from which the coal with the inert materials are discharged through automatized drawer valves. The inert materials and the coal are collected in a tank 16, from which they are then transferred, through a screw conveyer 17, to a water-cooled duct 18 and then to the carts for the removal thereof from the plant. Part of these, again through the screw conveyer 17, can be sent to the hopper 3 for the recirculation and the maximization of the production of pyrolytic gas.

In the reactor 5, kept at a temperature ranging between 400 °C and 500 °C, typically about 450 °C, and in a low oxygen atmosphere, the material undergoes a thermal decomposition process and the thus-produced coal reacts with the water to form the pyrolytic gas (hydrogen and carbon oxide) with a yield of about 80% by weight.

The pyrolytic gases coming out from the reaction chamber 5a of the reactor 5 are sent, through the line 25, to a cyclone 26 for removing the powders. The cyclone allows the separation of the solid or liquid particles present in the gaseous flow by exploiting the centrifuge force created by the whirling motion imparted to the same gaseous flow.

From the cyclone 26, the pyrolytic gases, deprived of most of the powders, undergo a rapid cooling step (quenching) from about 450 °C to about 40-60 °C. In such step the condensation of the acid gases (HC1, S0₂) is further obtained.

The quenching step is implemented by adding cold water to the gases at a controlled temperature. The gases, coming out from the cyclone 26 along the line 27, are passed through a rapid cooling unit 28 preferably provided with a narrowed cross-section duct, where, due to the Venturi effect, the water is injected in a finely dispersed form into the gas.

The thus-cooled gas is sent to a washing unit 29. Such washing unit preferably consists of a washing tower (scrubber) that comprises a vertical tank filled with inert material (small coils) . Basic washing waters are supplied to such tank in counter-current with respect to the gas flow, for the neutralization of the acid substances that are present in the pyrolytic gas. Such basic waters will be able to be advantageously composed of water mixed limewash.

The washing waters, having a temperature of about 40-60 °C, are sent to a settling tank 30 for the separation of the waters clarified from sludges. The sludges, through the line 32a, are sent to the top of the plant in the hopper 3.

The clarified waters are sent again, along the line 32, to the washing unit 29 and the rapid cooling unit 28.

The pyrolytic gas coming out from the washing unit 29 along the line 33, is passed to a condensing unit 31, where the residual liquid particles condensate, and they are then removed, thus obtaining high purity pyrolytic gas that allows high yield in energy conversion.

In an embodiment, the condensing unit 31 is composed of a coiled gas-gas recovery heat exchanger associated to a refrigeration unit 31a, in which the coolant fluid is composed, for example, of an ethylene glycol solution.

The purified pyrolytic gas coming out from the condensing unit 31 along the line 34 is conveyed, by means of suitable pumping means 35 (for example, suction devices with rotating reels), to a build-up buffer tank 36 (pressure-controlled accumulator with double membrane or gasometer) . As stated before, the pyrolytic gas may be partially sent, along the line 24, to the burners 14, while the line 37 conveys it to the co-generation unit 38, typically composed of an internal combustion motor and an alternator fitted to the main shaft of the motor .

In embodiments, the purified pyrolytic gas can be sent, along the line 39, to an emergency torch 40, in which the gas is burned before inputting it into the atmosphere. This measure is useful both when the production exceeds the capacity of the build-up buffer tank 36 (the gas is sent along the line 41 rather than towards the build-up buffer 36) , and when it is necessary to forcedly empty the build-up buffer (line 42) .

By the term "line" in the present description is meant a tubing in which the gas circulates in a natural or forced manner through suitable pumping or suction means .

In an embodiment, the plant is provided with a line 43, 44 for the recirculation of an inert gas through the reactor and the cyclone 26. This line is activated in the plant starting and stopping step. The inert gas, typically nitrogen, is heated within the reactor 5, then it is recirculated along the line 25, the cyclone 26 and the lines 43, 44 so as to heat the pipes along the path of the pyrolytic gases coming out from the reactor. This avoids the condensation of liquid hydrocarbons that could form gain at low temperatures in such pipes, building-up on the walls of both the lines and the cyclone. Once the reactor is started, the temperature itself of the pyrolytic gases keeps the pipe at a temperature sufficiently high to avoid the formation of liquid hydrocarbons .

The pyrolysis plant according to the present invention may advantageously be integrated with a control unit operating by means of an algorithm that, by using as its input the flow rate and the characterization of the organic matrix material supplied to the reactor and the characteristics of all the flows entering and exiting the system, both in general terms and for each single component, allows calculating the matter and energy balance .

The plant is provided with suitable detectors e/or temperature, pressure, ' and composition sensors for chemical-analytic studies on both the pyrolytic gas and on the fumes produced, which create a set of values of parameter that is used as an input for the control unit during all the process steps.

The mathematical algorithm, in particular, provides the following outputs: ^• Flow rate, average composition, and the relevant chemical-physical characteristics of the produced pyrolytic gas, such as temperature, viscosity, density, heating power;

^• Flow rate of the produced pulverized coal and the heating power thereof;

Flow rate and composition of the combustion fumes .

^• Amount of inert materials to be disposed of;

^• produced condensations;

• Flow rate of pyrolytic gas necessary to keep a temperature in the reactor of about 450 °C, necessary for the pyrolysis reactions to occur;

• The air excess necessary for the combustion of the pyrolytic gas and the auxiliary fuels in the burner of the reactor.

Therefore, the pyrolysis process according to the present invention generally comprises the following operative steps:

a) providing a plant as defined above;

b) adding a cracking reaction catalyst, preferably selected from nickel-, iron-, or chrome-based catalysts, to an organic matrix material; c) pre-heating of said organic matrix material and adjustment of the water content to about 30% by weight;

d) slow pyrolysis of said organic matrix material and collection of pyrolytic gases comprising hydrogen and carbon monoxide;

e) rapid cooling step of said pyrolytic gases;

f) washing step of said cooled pyrolytic gases. The step c) of pre-heating and adjustment of the water content typically provides for the evaporation of the excess water until reaching the desired amount, since the organic material typically has a water content exceeding 30% .

However, in the case of an organic material with a lower water content, the adjustment step may provide for the addition of such a water amount as to obtain an overall content equal to the desired value.

In an embodiment, the method of the invention comprises a plant starting or stopping step, in which a pre-heating inert gas is recirculated in the reactor 5, along the line 25 downstream of the reactor 5 and in the cyclone 26.

The process of the invention has a number of advantages, part of which has already been pointed out. The process can be applied to both agricultural or woody biomasses and to wastes of whichever nature, provided that they contain an organic matrix, such as plastic materials, papers, textiles, putrescible organic material , etc ..

Furthermore, the process allows maximizing the production of pyrolytic gas, which is an useful energy source. At the same time, a minimum production of coal and a total absence of liquid fuels is obtained.

The energy consumption of the plant is further ensured by the pyrolytic gas produced.

The helicoidal tongue 9 allows prolonging he contact of the combustion fumes with the wall of the pre-heating portion 7 of the reaction chamber 5a.

The pre-heating of the pipes and the cyclone with the inert gas allows avoiding the condensation of liquid hydrocarbons.

The longitudinal arrangement of the burners 14 increases the heating efficiency of the pyrolysis portion 8 of the reaction chamber 5a.

Therefore, the wet, catalyzed, slow pyrolysis according to the present invention may be considered as an innovation of the pyrolysis processes, since it allows obtaining the conversion of the organic matrix material into synthesis gases with a yield considerably greater than that of the conventional pyrolysis processes. By virtue of its characteristics, the obtained gas can be converted into electric power by means of simple internal combustion motors, the technology of which is to date well established.

It shall be apparent that only a particular embodiment of the present invention has been described, to which those skilled in the art will be able to male all those modifications that are necessary for the adaptation thereof to particular applications, without for this departing from the protection scope of the present invention.

Claims

1. Plant for slow pyrolysis of organic matrix material, comprising:

- a reaction chamber (5a) divided into a pre-heating portion (7) and a pyrolysis portion (8) downstream of said pre-heating portion (7);

- a combustion chamber (6) that is co-axial with and external to said reaction chamber (5a), said combustion chamber (6) being divided into a pre-heating portion (12), surrounding said pre-heating portion (7) of the combustion chamber (5a), and in a heating portion (13) surrounding said pyrolysis portion (8) of the reaction chamber (5a), said heating portion (13) of the combustion chamber (6) housing burners (14),

wherein :

said reaction chamber (5a) rotates along a horizontal axis within said combustion chamber (6), and

- the outer surface of the pre-heating portion (7) of the reaction chamber (5a) comprises a helicoidal tongue (9) creating a spiral path for the combustion gases generated by the burners (14).

2. The plant according to claim 1, wherein said burners (14) are arranged longitudinally throughout the length of the heating portion (13) of the combustion chamber ( 6) .

3. The plant according to claim 1 or 2, comprising thermal exchange means (21) for the combustion fumes that are evacuated from the combustion chamber (6), wherein a line (23) carrying comburent air into the burners (14) passes in said thermal exchange means (21).

4. The plant according to any one of the claims 1 to 3, wherein a cyclone (26) is arranged downstream of the reactor (5) for removing the powders from the pyroiysis gases.

5. The plant according to claim 4, wherein a rapid cooling unit (28) is arranged downstream of the cyclone (26) for cooling the pyroiysis gases to a temperature ranging between 40 °C and 60 °C.

6. The plant according to claim 5, wherein said rapid cooling unit (28) comprises a narrowed cross- section duct for the injection of finely dispersed water.

7. The plant according to claim 5 or -6, wherein a washing unit (29) is arranged downstream of said rapid cooling unit (28) .

8. The plant according to claim 7, wherein said washing unit (29) comprises a vertical tank filled with inert material for washing in counter-current the gas with a water rain.

9. The plant according to claim 7 or 8, wherein a condensing unit (31) for the residual liquids in the pyrolysis gas is arranged downstream of said washing unit (29) .

10. The plant according to claim 9, wherein said condensing unit (31) is a coiled gas-gas recovery heat exchanger associated to a refrigeration unit (31a) , wherein the coolant fluid preferably consists of an ethylene glycol solution.

11. The plant according to any one of the claims 1 to 10, comprising a line (43, 44) for the recirculation of a heated inert gas through the reactor (5) and the cyclone (26) during the plant starting and stopping step.

12. An organic matrix material slow pyrolysis process, comprising the following steps:

a) providing a plant as defined in any one of the previous claims;

b) adding a cracking reaction catalyst, preferably selected from nickel-, iron-, or chrome-based catalysts, to said organic matrix material;

c) pre-heating said organic matrix material and adjusting the water content to about 30% by weight;

d) carrying out a slow pyrolysis of said organic matrix material, and collecting the pyrolytic gases comprising hydrogen and carbon monoxide;

e) quickly cooling said pyrolytic gases;

f) washing said cooled pyrolytic gases.

13. The process according to claim 12, wherein said slow pyrolysis is carried out during a period ranging between 0.5 and 1.5 hours, at a temperature ranging between 400 °C and 500 °C, or about 450 °C.

14. The process according to claim 12 or 13, wherein said cracking reaction catalyst is added in amounts of 100-300 mg per kg of organic matrix material.

15. The process according to any one of the claims 12 to 14, wherein said pyrolytic gases, before being subjected to said rapid cooling step e) , undergo a depulveri zation treatment.

16. The process according to any one of the claims 12 to 15, wherein said rapid cooling step e) takes place by means of a water injection at a controlled temperature into said pyrolytic gases.

17. The process according to any one of the claims 12 to 16, comprising a step of starting and/or stopping of the plant, wherein a pre-heating inert gas is recirculated in the reactor (5) along the line (25) downstream of the reactor (5) and in the cyclone (26), wherein said inert gas is preferably nitrogen.

18. The process according to any one of the claims 12 to 17, wherein said pyrolytic gases are used in an electricity/heat cogeneration plant.