Method for recovering waste material by hydrogen production and system for carrying out method

Abstract

The invention relates to a method for producing hydrogen from waste material using thermochemical treatment.

Description

Technical Field

[0001] The invention relates to a method for obtaining hydrogen from waste materials by thermochemical treatment. Background Art

[0002] There is currently great interest in obtaining hydrogen, not only because of its numerous traditional industrial uses, but also because of its growing use as a fuel that produces no carbon dioxide emissions when used.

[0003] Hydrogen can be obtained in various ways, such as water electrolysis, steam reforming or thermochemical conversion. Thermochemical processes for hydrogen production involve chemical reactions at high temperatures to obtain hydrogen.

[0004] Another area of ​​particular interest today is the development of valorization methods for the increasing amount of waste generated by human activities. For example, patent publication number EP3019274 describes a method for treating wastewater with formaldehyde in the presence of a catalyst to produce hydrogen.

[0005] In the present invention, a method has been developed for producing hydrogen from waste materials, wherein the production is optimized through processes such as pyrolysis and cracking. Summary of the invention

[0006] Hydrogen is an essential compound in industry and is considered an essential energy carrier of the future, since the only product of its combustion is water vapor. For these reasons, it is attractive to develop methods for obtaining hydrogen. Furthermore, in the process of the invention, hydrogen is obtained from waste materials, which means that material valorization is achieved, which has a positive impact on the environment, by avoiding the disposal of waste materials in landfills or incineration.

[0007] The present invention describes a method and system for hydrogen production based on thermochemical treatment of waste materials.

[0008] The method of the invention comprises a pyrolysis reaction, in which the starting waste is decomposed by external heating of a reactor under a reducing atmosphere. From the products obtained in the pyrolysis, the solid phase obtained can optionally be separated. After the pyrolysis, the method comprises a step of cracking the pyrolysis products, in which they react in the presence of oxygen and steam to obtain synthesis gas. At the outlet of the cracking step, the raw synthesis gas obtained is cooled and purified.

[0009] This gas is mixed with steam and reacted in the presence of a catalyst to obtain a hydrogen-rich synthesis gas. In this step, the carbon monoxide in the synthesis gas reacts with water to form hydrogen, which will be purified in the next step to produce the final products: purified hydrogen and tail gas, and the tail gas is used to provide the heat energy required for the different steps of the process. Contrary to what is expected in the process of producing hydrogen, the combination of the process produces a maximum hydrogen production point by mixing steam and purified synthesis gas in a molar ratio of 0.90-1.20, which limits the conversion of carbon monoxide to hydrogen to between 83% and 87%, as Figure 2 shown.

[0010] Therefore, the present invention relates to a method for material valorization of waste materials by obtaining hydrogen, the method comprising the following steps:

[0011] a) pyrolyzing the starting waste material by external heating under a reducing atmosphere to obtain a pyrolysis product;

[0012] b) optionally, separating a solid portion from the pyrolysis product;

[0013] c) cracking the product obtained in pyrolysis step a) or in step b) after separation of the solid fraction in the presence of oxygen and a first steam stream to obtain a crude synthesis gas;

[0014] d) cooling the raw synthesis gas obtained in c);

[0015] e) purifying the crude synthesis gas obtained in d) to obtain purified synthesis gas;

[0016] f) mixing the second steam stream with the preheated gas stream obtained in e) in a molar ratio of 0.90 to 1.20;

[0017] g) converting the mixture obtained in f) in the presence of a catalyst to obtain a hydrogen-rich synthesis gas;

[0018] h) separating the hydrogen-rich synthesis gas to obtain hydrogen and tail gas from the hydrogen separation.

[0019] The term “material valorization” involves the use of waste materials to obtain material products that can be used in socio-economic activities.

[0020] The term "waste" in this specification relates to material discarded from other processes which can be chemically decomposed by heating, producing at least combustible gases. Examples of such waste include: solid municipal waste, waste from industrial activities or biomass waste.

[0021] The term "pyrolysis" relates to thermal decomposition under a reducing atmosphere.

[0022] The term "external heating" relates to indirect heating, ie heat is provided from the outside by electrical heating, external combustion or other means.

[0023] The term "cracking" in the context of the present invention relates to the thermochemical conversion of tar into molecules of lower molecular weight, optionally in the presence of a catalyst.

[0024] The term "tar" in the present invention relates to organic compounds with a molecular weight higher than methane from the pyrolysis reactor.

[0025] The term "synthesis gas" relates to a gas consisting essentially of hydrogen and carbon monoxide and which may contain smaller amounts of carbon dioxide, methane, water, nitrogen and tars.

[0026] The present invention also relates to a system for producing hydrogen, comprising at least:

[0027] Pyrolysis unit,

[0028] Cracking unit,

[0029] Purification unit,

[0030] Synthesis gas conversion unit,

[0031] Hydrogen separation unit.

[0032] The cracking unit comprises a cooling unit for the obtained raw synthesis gas and a cracking reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to supplement the ongoing description and to better understand the characteristics of the invention, a set of drawings is attached as an integral part of said description, according to a preferred example of its practical embodiment, in which the following are represented in an illustrative and non-limiting manner:

[0034] Figure 1 A schematic diagram showing an embodiment of the present invention is shown.

[0035] Figure 2 A diagram is shown which represents: on the horizontal axis the molar ratio between steam and gas in step f); on the left vertical axis the percentage of hydrogen obtained compared to the maximum case; on the right vertical axis the percentage of carbon monoxide conversion obtained under the conditions stated. DETAILED DESCRIPTION

[0036] According to a first aspect of the present invention, a method for material valorization of waste materials by obtaining hydrogen comprises the following steps:

[0037] a) pyrolyzing the starting waste material (1) by external heating under a reducing atmosphere to obtain a pyrolysis product (2);

[0038] b) optionally, separating a solid portion from the pyrolysis product;

[0039] c) cracking the product obtained in the pyrolysis step a) or in step b) after separation of the solid fraction in the presence of oxygen (3) and a first steam stream (15.1) to obtain a crude synthesis gas (4);

[0040] d) cooling the raw synthesis gas (4) obtained in c);

[0041] e) purifying the crude synthesis gas (4) obtained in d) to obtain a purified synthesis gas (5);

[0042] f) mixing the second steam stream (15.2) with the preheated purified synthesis gas (5) obtained in e) in a molar ratio of 0.90 to 1.20;

[0043] g) converting the mixture (6) obtained in f) in the presence of a catalyst to obtain a hydrogen-rich synthesis gas (7);

[0044] h) separating the hydrogen-rich synthesis gas (7) to obtain hydrogen (8) and tail gas (9) from the hydrogen separation.

[0045] Preferably, in step f), the ratio of the second steam flow (15.2) to the synthesis gas (5) obtained in e) is in the range of 0.96 to 1.16.

[0046] The present invention also relates to a method for producing hydrogen, wherein different streams are integrated to maximize hydrogen production. In order to improve the efficiency of hydrogen production, the external heating of step a) is carried out by a step of mixing and burning a portion of the tail gas (9) from step h) with a preheated air stream (11), the flue gas stream (12) produced in this step transfers heat in the external heating of step a), and the flue gas stream after the pyrolysis step (13) transfers heat to at least one stream selected from the following streams: a water stream (14) for generating steam (15) required for steps c) and f) and / or an air stream (10) for obtaining the preheated air stream (11) and / or a purified synthesis gas stream (5) treated in step f), and a heat transfer flue gas stream (23) is generated.

[0047] Therefore, preferably, the method comprises the step of combusting a portion of the tail gas (9) from step h) with a preheated air stream (11) to produce a flue gas stream (12), which flue gas stream (12) transfers heat in the external heating of step a), and the flue gas stream after the pyrolysis step (13) releases heat to at least one stream selected from the following streams: a water stream (14) for producing the steam (15) required for steps c) and f) and / or an air stream (10) for obtaining the preheated air stream (11) and / or the purified synthesis gas (5) in the preheating of step f).

[0048] In another embodiment of the invention, the pyrolyzer has an external heat source which is not generated by a stream coming from the process itself. In this embodiment, preferably, the process comprises the step of burning a fuel stream selected from a portion of the tail gas (9) of step h) with a preheated air stream (11), thereby generating a flue gas stream (12) which releases heat to at least one stream selected from the following streams: a water stream (14) for generating the steam (15) required for steps c) and f) and / or an air stream (10) for obtaining the preheated air stream (11) and / or the purified synthesis gas (5) in the preheating of step f).

[0049] One advantage of the invention is that the separation is carried out in the step of thermochemical treatment of the wastes while optimizing the means of obtaining the temperatures required for the different conversion reactions. In this way, a synthesis gas with a minimum content of impurities and inerts is obtained in a system that minimizes the heat demand at high temperatures, thereby increasing efficiency.

[0050] Preferably, the pyrolysis step a) is carried out at a temperature in the range of 400°C to 650°C and the cracking step c) is carried out at a temperature between 800°C and 1300°C to maximize the content of hydrogen and carbon monoxide in the synthesis gas and minimize the content of tar.

[0051] Preferably, the cooling step d) is performed using the heat of the raw synthesis gas (4) to produce steam. Preferably, the temperature of the cooled raw synthesis gas is between 250°C and 350°C.

[0052] This raw synthesis gas (4) may have various solid and gaseous contaminants and preferably purification requires one or more steps selected from the following steps: solid separation, liquid absorption and / or solid adsorption.

[0053] Another advantage of the process is the recovery and use of the water stream condensed in the process in the same process. Thus, in a preferred embodiment, after the conversion step g), the unreacted steam fraction is condensed from the hydrogen-rich gas (7) and part of the condensed water is recycled together with the feed water (14).

[0054] In another preferred embodiment, after the conversion step g), the hydrogen-rich synthesis gas (7) is cooled by a water stream which is subsequently heated to form steam (15.1) for the cracking step and / or water vapor (15.2) for the conversion step.

[0055] Preferably, the starting waste material (1) is selected from: solid municipal waste, waste from commercial and industrial activities and / or biomass, and possibly other waste materials.

[0056] Preferably, the starting waste material (1) is treated before step a) to adapt it to the needs of the method. More preferably, the starting waste material (1) is size-selected by passing through a sieve and / or crushed and / or pressed and / or dried. In particular, the maximum particle size of the starting waste material should be less than 10 mm.

[0057] Preferably, in step b), a solid fraction is separated from the pyrolysis product. This product can be used as a fuel or for the recovery of metals present in this fraction.

[0058] A second aspect of the present invention relates to a system for carrying out a waste valorization method to produce hydrogen, the system comprising at least the following elements:

[0059] a pyrolysis unit (16),

[0060] Cracking unit (17),

[0061] a purification unit (18),

[0062] Synthesis gas conversion unit (19),

[0063] Hydrogen separation unit (20).

[0064] Preferably, the pyrolysis unit comprises a pyrolyzer (16.1) and at least one burner (16.2) to generate the heat required for pyrolysis.

[0065] Furthermore, preferably, the system for implementing the hydrogen production method comprises a component for recovering waste heat from the flue gas (21). More preferably, the component for recovering waste heat from the flue gas (21) comprises a burner.

[0066] Preferably, the system comprises an oxygen production unit (22), the oxygen being used in the cracking unit (17).

[0067] Example 1. Example of hydrogen production from waste materials

[0068] The shredded municipal solid waste is fed into the pyrolyzer from its feed position through a hopper with a bulk material rejection screen to avoid air from entering the reactor. In the pyrolyzer, the waste is subjected to a temperature of 450°C in a reducing atmosphere to partially decompose it. The pyrolysis products then enter the cracking reactor and are thermally converted into synthesis gas at 1200°C in the presence of steam and oxygen. The raw synthesis gas is cooled to 330°C. The cooled raw synthesis gas is then sent to a purification unit consisting of an absorption unit and an adsorption unit to remove pollutants. The purified synthesis gas is preheated in a unit for recovering waste heat from flue gases and mixed with steam before being sent to the synthesis gas conversion reactor, where CO reacts with steam on a catalytic bed to produce H2 and CO2. The hydrogen-rich synthesis gas is sent to a hydrogen separation unit by pressure swing adsorption (PSA), from which H2 and a tail gas stream for supplying heat to the pyrolyzer are obtained.

[0069] like Figure 2 As shown, different ratios of steam to purified syngas were tested to find the ratio that optimizes the system's hydrogen production. The study found that the best results were achieved when the ratio was between 0.90 and 1.20.

Claims

1. A method for material valorization of waste materials by obtaining hydrogen, comprising the following steps: a) pyrolyzing the starting waste material (1) by external heating under a reducing atmosphere to obtain a pyrolysis product (2); b) optionally, separating a solid portion from the pyrolysis product; c) cracking the product obtained in the pyrolysis step a) or in step b) after separation of the solid fraction in the presence of oxygen (3) and a first steam stream (15.1) to obtain a crude synthesis gas (4); d) cooling the raw synthesis gas (4) obtained in c); e) purifying the crude synthesis gas (4) obtained in d) to obtain a purified synthesis gas (5); f) mixing the second steam stream (15.2) with the preheated purified synthesis gas stream (5) obtained in e) in a molar ratio of 0.90 to 1.20; g) converting the mixture (6) obtained in f) in the presence of a catalyst to obtain a hydrogen-rich synthesis gas (7); h) separating the hydrogen-rich synthesis gas (7) to obtain hydrogen (8) and tail gas (9) from the hydrogen separation.

2. The method according to claim 1, characterized in that The ratio between the second water vapor stream (15.2) and the first gas portion (5.1) in step f) is in the range of 0.96 to 1.

16.

3. The method according to claim 1 or 2, characterized in that: A combustion step of at least part of the tail gas (9) from step h) with a preheated air stream (11), said combustion step producing a flue gas stream (12), said flue gas stream (12) releasing heat to at least one stream selected from the following streams: a water stream (14) for producing the steam (15) required for steps c) and f) and / or an air stream (10) for obtaining a preheated air stream (11) and / or the purified synthesis gas (5) in the preheating of step f).

4. The method according to any one of claims 1 or 2, characterized in that The method comprises: a combustion step of at least a portion of the tail gas (9) from step h) with a preheated air stream (11), the combustion step producing a flue gas stream (12), the flue gas stream (12) releasing heat in the external heating of step a), and after the pyrolysis step, the flue gas stream (13) leaving the pyrolyzer releasing heat to at least one stream selected from the following streams: a water stream (14) for producing the steam (15) required for steps c) and f) and / or an air stream (10) for obtaining the preheated air stream (11) and / or the purified synthesis gas (5) in the preheating of step f).

5. The method according to any one of claims 1 to 4, characterized in that The pyrolysis step a) is carried out at a temperature ranging from 400°C to 650°C, and the cracking step b) is carried out at a temperature ranging from 800°C to 1300°C.

6. The method according to any one of claims 1 to 5, characterized in that After the conversion step g), the hydrogen-rich synthesis gas (7) is cooled by a water stream which is subsequently heated to form steam (15.1) for the cracking step and / or steam (15.2) for step f).

7. The method according to any one of claims 1 to 6, characterized in that After the conversion step g), the unreacted steam portion of the hydrogen-rich synthesis gas (7) is condensed and the condensed water is recycled together with the feed water (14).

8. A system for implementing the method of claims 1 to 7, comprising at least: a pyrolysis unit (16), Cracking unit (17), a purification unit (18), Synthesis gas conversion unit (19), Hydrogen separation unit (20).

9. The system for implementing the method of claims 1 to 7 according to claim 8, characterized in that The system comprises: a component for recovering waste heat from flue gas (21).

10. The system for implementing the method of claims 1 to 7 according to claim 8, characterized in that The system comprises: an oxygen production unit (22).

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