Method for Valorizing Waste Materials by Obtaining Hydrogen and System for Implementing the Same

Abstract

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

Description

Detailed Description of the Invention

[0001] 〔Object of the Invention〕 The present invention relates to a process for obtaining hydrogen from waste by thermochemical treatment.

[0002] 〔Background of the Invention〕 Currently, obtaining hydrogen has attracted great interest both because of its many traditional industrial uses and the expanding use as a fuel that does not emit carbon dioxide during use.

[0003] Hydrogen can be obtained by various methods such as electrolysis of water, steam reforming or thermochemical conversion. The thermochemical hydrogen production process involves chemical reactions at high temperatures to obtain hydrogen.

[0004] Another field that has attracted particular interest today is the development of methods for valorizing the increasing amount of waste generated by human activities. For example, Patent Publication No. EP3019274 describes a method of treating wastewater with formaldehyde to produce hydrogen in the presence of a catalyst.

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

[0006] 〔Description of the Invention〕 Hydrogen is an essential chemical substance for the industry and is expected to be an essential energy vector in the future because its combustion product is only water vapor. For these reasons, it is interesting to develop methods for obtaining hydrogen. Furthermore, in the process of the present invention, hydrogen is obtained from waste, which means the valorization of substances that have a positive impact on the environment by avoiding landfill or incineration of waste.

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

[0008] The method of the present invention includes a pyrolysis reaction for decomposing starting waste under external heating of a reactor and in a reducing atmosphere.

[0009] From the products obtained in the pyrolysis, the obtained solid phase can be optionally separated. After pyrolysis, the method includes a step of cracking the pyrolysis products, in which the pyrolysis products react in the presence of oxygen and steam to obtain a synthesis gas. At the outlet of the cracking step, the obtained raw material synthesis gas is cooled and purified.

[0010] This gas is mixed with steam and reacted in the presence of a catalyst to obtain a hydrogen-enriched synthesis gas. In this step, carbon monoxide in the synthesis gas reacts with water to form hydrogen. The hydrogen is purified in the next step, resulting in purified hydrogen as the final product and tail gas used to supply the thermal energy required in various steps of the method. Contrary to what is expected in a hydrogen production method, by integrating the method, the maximum hydrogen production point is obtained by mixing steam with the purified synthesis gas in a molar ratio in the range of 0.90 to 1.20, and as shown in Figure 2, the conversion rate of carbon monoxide to hydrogen is limited to 83 to 87%.

[0011] Therefore, the present invention relates to a method for valorizing waste materials by obtaining hydrogen, the method including the following steps: a) Subjecting starting waste to pyrolysis under external heating and in a reducing atmosphere to obtain pyrolysis products; b) Optionally separating a solid fraction from the pyrolysis products; c) Cracking the products obtained in step a) of pyrolysis or the products obtained in step b) after separating the solid fraction in the presence of oxygen and a first steam stream to obtain a raw material synthesis gas; d) Cooling the raw material synthesis gas obtained in c); e) Purifying the raw material synthesis gas obtained in d) to obtain a purified synthesis gas; f) Mixing a second steam stream with the preheated gas stream obtained in e) in a molar ratio of 0.90 to 1.20; g) Convert the mixture obtained in f) in the presence of a catalyst to obtain a hydrogen-enriched synthesis gas; h) Separate the hydrogen-enriched synthesis gas to obtain hydrogen and tail gas from the separation of hydrogen.

[0012] The term "material valorization" relates to the utilization of waste to obtain raw material products that can be used in socio-economic activities.

[0013] The term "waste" as used herein relates to substances that are discarded from other processes and can undergo chemical decomposition by heating to produce at least combustible gas. Examples of such waste include solid municipal waste, waste from industrial activities, or biomass waste.

[0014] The term "pyrolysis" relates to pyrolysis under a reducing atmosphere.

[0015] The term "external heating" relates to indirect heating, i.e., supplying heat from the outside by means of electric heating, external combustion, or other means.

[0016] The term "cracking" as used in the present invention relates to the thermochemical conversion of tar into low-molecular-weight molecules, optionally in the presence of a catalyst.

[0017] The term "tar" as used in the present invention relates to organic compounds having a molecular weight greater than that of methane, which exit from the pyrolysis reactor.

[0018] The term "synthesis gas" relates to a gas mainly containing hydrogen and carbon monoxide, which may contain small amounts of carbon dioxide, methane, water, nitrogen, and tar.

[0019] The present invention also relates to a hydrogen production system comprising at least the following: A pyrolysis unit, A cracking unit, A purification unit, A synthesis gas conversion unit, Hydrogen separation unit.

[0020] The cracking unit includes a cracking reactor and a cooling unit for the obtained raw material synthesis gas.

[0021] [Description of the Drawings] To supplement the following description and better understand the features of the present invention, a set of drawings is attached as an essential part of the above description according to a preferred example of its actual embodiment, in which the following drawings are shown, which have an exemplary and non-limiting nature: FIG. 1 is a schematic diagram showing an embodiment of the present invention.

[0022] FIG. 2 is a graph showing on the horizontal axis the molar ratio of steam to gas in step f); on the left vertical axis the percentage of hydrogen obtained compared to the maximum case; and on the right vertical axis the percentage of conversion of carbon monoxide obtained under the above conditions.

[0023] [Preferred Embodiment of the Present Invention] As shown in the first aspect of the present invention, the present invention relates to a method for valorizing waste materials by obtaining hydrogen, the method comprising the following steps: a) Subjecting the starting waste (1) to pyrolysis under external heating and a reducing atmosphere to obtain pyrolysis products (2); b) Optionally separating the solid fraction from the pyrolysis products; c) Cracking the product obtained in the pyrolysis step a) or the product obtained in step b) after separating the solid fraction in the presence of oxygen (3) and a first steam stream (15.1) to obtain a raw material synthesis gas (4); d) Cooling the raw material synthesis gas (4) obtained in c); e) Purifying the raw material synthesis gas (4) obtained in d) to obtain a purified synthesis gas (5); f) Mixing a second steam stream (15.2) with the preheated purified synthesis gas stream (5) obtained in e) at a molar ratio of 0.90 to 1.20; g) Convert the mixture (6) obtained in f) in the presence of a catalyst to obtain a hydrogen-enriched synthesis gas (7); h) Separate the hydrogen-enriched synthesis gas (7) to obtain hydrogen (8) and tail gas (9) from hydrogen separation.

[0024] Preferably, in step f), the ratio of the second steam stream (15.2) to the stream of the synthesis gas (5) obtained in e) ranges from 0.96 to 1.16.

[0025] The present invention also relates to a method for producing hydrogen that integrates different streams to maximize hydrogen production. To improve the hydrogen production efficiency, the external heating in step a) is performed by burning a part of the tail gas (9) from step h) mixed with a preheated air stream (11), thereby generating an exhaust gas stream (12). The exhaust gas stream (12) transfers heat in the external heating of step a), and the exhaust gas stream (13) after the thermal decomposition step transfers heat to at least one stream selected from the water stream (14) for generating the steam (15) required in steps c) and f) and / or the air stream (10) for obtaining the preheated air stream (11) and / or the stream of the purified synthesis gas (5) processed in step f), generating a heat transfer exhaust gas stream (23).

[0026] Therefore, preferably, the method includes a step of burning a part of the tail gas (9) from step h) together with the preheated air stream (11), thereby generating an exhaust gas stream (12). The exhaust gas stream (12) transfers heat in the external heating of step a), and the exhaust gas stream (13) after the thermal decomposition step releases heat to at least one stream selected from the water stream (14) for generating the steam (15) required in steps c) and step f) and / or the air stream (10) for obtaining the preheated air stream (11) and / or the purified synthesis gas (5) in the preheating of step f).

[0027] In another embodiment of the present invention, the pyrolyzer has a source for external heating that is not generated by the flow from the method itself. In this embodiment, preferably, the method includes the step of combusting a fuel stream selected from a part of the tail gas (9) from step h) together with a preheated air stream (11), thereby generating an exhaust gas stream (12), and the exhaust gas stream (12) provides heat to at least one stream selected from a water stream (14) for generating the steam (15) required in 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).

[0028] The advantages of the present invention are to stage the thermochemical treatment of waste and to optimize the means for obtaining the temperatures required for different conversion reactions. In this way, a synthesis gas with a minimum amount of impurities and inert substances is obtained in a system that minimizes the thermal requirements at high temperatures, thereby resulting in high efficiency.

[0029] Preferably, the pyrolysis step a) is carried out in a temperature range between 400 °C and 650 °C, and the temperature of the cracking step c) is carried out at a temperature between 800 °C and 1300 °C in order to maximize the hydrogen and carbon monoxide content in the synthesis gas and minimize the tar content.

[0030] Preferably, the cooling step d) is carried out using the heat of the raw material synthesis gas (4) to generate steam. Preferably, the temperature of the cooled raw material synthesis gas is between 250 °C and 350 °C.

[0031] This raw material synthesis gas (4) can have different contaminants both in solid and gaseous forms. Preferably, the purification requires one or more steps selected from solid separation, absorption into a liquid, and / or adsorption onto a solid.

[0032] Another advantage of this method is to recover the flow of water condensed in this process and use it in the same process. Thus, in a preferred embodiment, after the conversion step g), a part of the unreacted vapor is condensed from the hydrogen-enriched gas (7), and a part of the condensed water is recycled together with the feed water (14).

[0033] In another preferred embodiment, after the conversion step g), the hydrogen-enriched synthesis gas (7) is cooled by a water flow, and the water flow is subsequently heated to form the steam (15.1) for the cracking step and / or the steam (15.2) for the conversion step.

[0034] Preferably, the starting waste (1) is selected from, among other possible wastes, solid municipal waste, waste generated by commercial and industrial activities, and / or biomass.

[0035] Preferably, the starting waste (1) is treated prior to step a) to conform to the requirements of the method. More preferably, the starting waste (1) is selected by size through a sieve and / or pulverized and / or pressed and / or dried. In particular, the particle size of the starting waste must be less than 10 mm in maximum dimension.

[0036] Preferably, in step b), the solid fraction is separated from the pyrolysis product. This product can be used as fuel or can be used to recover the metals present in this fraction.

[0037] The second aspect of the present invention relates to a system for implementing a method for valorizing waste for hydrogen production, the system comprising at least the following elements: A pyrolysis unit (16), A cracking unit (17), A purification unit (18), A synthesis gas conversion unit (19), A hydrogen separation unit (20).

[0038] Preferably, the pyrolysis unit includes a pyrolyzer (16.1) and at least one burner (16.2) for generating heat required for pyrolysis.

[0039] Furthermore, preferably, the system for implementing the hydrogen production method includes a section (21) for recovering residual heat from the exhaust gas. More preferably, the section (21) for recovering residual heat from the exhaust gas includes a burner.

[0040] Preferably, the system includes an oxygen production unit (22), and the oxygen is used in the cracking unit (17).

[0041] (Example 1. Hydrogen production example from waste) The shredded municipal solid waste was supplied through a hopper equipped with a bulky matter removal mesh and charged into the pyrolyzer while avoiding the intrusion of air into the reactor. In the pyrolyzer, the waste was subjected to a temperature of 450 °C in a reducing atmosphere and partially decomposed. Then, the pyrolysis product was put into a cracking reactor and thermally converted into synthesis gas at 1200 °C in the presence of steam and oxygen. The raw material synthesis gas was cooled to 330 °C. The cooled raw material synthesis gas was then sent to a purification unit consisting of an absorption unit and an adsorption unit to remove contaminants. The purified synthesis gas was preheated in a unit for recovering residual heat from the exhaust gas and mixed with steam before being supplied to the synthesis gas conversion reactor. Here, CO reacts with steam to produce H 2 and CO 2 to generate. The hydrogen-enriched synthesis gas was supplied to a hydrogen separation unit by pressure swing adsorption (PSA), from which H 2 and a tail gas stream used to supply heat to the pyrolyzer were obtained.

[0042] Different ratios of steam to the purified synthesis gas were tested, and as shown in Figure 2, the ratio that optimizes the hydrogen yield of the present system was found. As a result, it was found that the best results are obtained at a ratio of 0.90 to 1.20.

Brief Description of the Drawings

[0043]

Figure 1

Figure 2

Claims

1. A method for valorizing waste materials by obtaining hydrogen, comprising the following steps: a) subjecting starting waste (1) to pyrolysis under external heating and a reducing atmosphere to obtain pyrolysis products (2); b) optionally separating a solid fraction from the pyrolysis products; c) cracking the product obtained in pyrolysis step a) or the product obtained in step b) after separating the solid fraction in the presence of oxygen (3) and a first steam stream (15.1) to obtain a raw synthesis gas (4); d) cooling the raw synthesis gas (4) obtained in c); e) purifying the raw synthesis gas (4) obtained in d) to obtain a purified synthesis gas (5); f) mixing a 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-enriched synthesis gas (7); h) separating the hydrogen-enriched synthesis gas (7) to obtain hydrogen (8) and tail gas (9) from hydrogen separation.

2. The method according to claim 1, characterized in that the ratio in step f) between the second flow of steam (15.2) and the first gas fraction (5.1) is in the range from 0.96 to 1.

16.

3. The method according to claim 1 or 2, characterized by a step of burning at least a part of the tail gas (9) from step h) together with a preheated air stream (11), thereby generating an exhaust gas stream (12), which exhaust gas stream (12) releases heat to at least one stream selected from 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).

4. The method according to claim 1 or 2, characterized in that it comprises at least the step of combusting at least a part of the tail gas (9) from step h) together with the preheated air stream (11), thereby generating an exhaust gas stream (12), said exhaust gas stream (12) releasing heat in said external heating of step a), and the exhaust gas stream (13) emerging from the pyrolyzer after said pyrolysis step releases heat to at least one stream selected from the water stream (14) for generating the steam (15) required for steps c) and f) and / or the 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 said pyrolysis step a) is carried out in a temperature range between 400 ° C and 650 ° C, and the temperature of said cracking step b) is in the range between 800 ° C and 1300 ° C.

6. The method according to any one of claims 1 to 5, characterized in that after the conversion step g), said hydrogen-enriched synthesis gas (7) is cooled by a water stream, and said water stream is subsequently heated to form the steam (15.1) for said cracking step and / or the 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 vapor fraction of said hydrogen-enriched synthesis gas (7) is condensed, and the condensed water is recycled together with the feed water (14).

8. A system for implementing the method according to claims 1 to 7, comprising at least the following: A pyrolysis unit (16), A cracking unit (17), A purification unit (18), A synthesis gas conversion unit (19), A hydrogen separation unit (20).

9. The system for implementing the method according to claims 1 to 7 according to claim 8, characterized in that it comprises a section (21) for recovering residual heat from the exhaust gas.

10. The system for implementing the method according to claims 1 to 7 according to claim 8 or 9, characterized in that it comprises an oxygen production unit (22).

Images