Method for preparing hydrogen-rich low-carbon synthesis gas from high-water-content peat residue by chemical looping gasification

Abstract

The application provides a method for preparing hydrogen-rich low-carbon synthesis gas through high-water-content biogas residue chemical looping gasification, and belongs to the technical field of solid waste treatment. The method comprises the following steps: mixing high-water-content biogas residue with an oxygen carrier, and performing a chemical looping gasification reaction to obtain hydrogen-rich low-carbon synthesis gas; the water content of the high-water-content biogas residue is 30-50%; and the oxygen carrier is a transition metal loaded lanthanum oxide. The method uses a metal composite water-carbon oxygen capture oxygen carrier material, i.e., a transition metal loaded lanthanum oxide, to perform chemical looping gasification conversion on high-water-content biogas residue, thereby improving the water content tolerance of biogas residue chemical looping gasification, optimizing the quality of synthesis gas, increasing the hydrogen content in the synthesis gas, and reducing the CO2 content.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste treatment, and in particular to a method for preparing hydrogen-rich, low-carbon synthesis gas by chemical chaining gasification of highly water-containing biogas residue. Background Art

[0002] As global environmental issues become increasingly prominent, climate change caused by the greenhouse effect has had a serious impact on human society and ecosystems. Biomass, as a renewable energy source, plays a vital role in a future zero-carbon energy system. In particular, biomass absorbs CO2 during its growth. If its utilization can be efficiently converted and CO2 emissions are extremely low, or even negative, this will provide a powerful boost to combating climate change. Therefore, biomass has great potential to become a significant alternative to fossil fuels and is of great significance in achieving sustainable development.

[0003] Gasification is an effective way to achieve efficient and rapid biomass conversion. However, raw biomass typically has a high moisture content, and traditional gasification faces limitations when processing high-moisture biomass. During the gasification process, high moisture content reduces energy conversion efficiency, lowers the calorific value of the syngas, and produces more byproducts such as tar. Therefore, traditional gasification requires pre-drying the biomass, and the significant energy consumption of this process is a major factor limiting its application.

[0004] Chemical chaining gasification, as an emerging gasification method, can provide a solution to the challenges posed by the conversion of high-water-content biomass. Chemical chaining gasification uses lattice oxygen in oxygen carriers as an oxygen source to provide the oxygen element required for gasification of the fuel, resulting in a synthesis gas with CO and H2 as the main components. Oxygen carriers play a key regulatory role. They often contain a certain amount of oxygen vacancies, which not only provide active sites for the adsorption and dissociation of water in the biomass itself, but also adsorb and activate CO2. By optimizing the characteristics and composition of oxygen carriers, the composition of the synthesis gas can be effectively controlled, and it is expected to achieve the goals of high hydrogen content and low carbon content, minimize CO2 emissions, and open up new paths for achieving clean and efficient energy conversion.

[0005] As a typical high-water-content biomass, biogas residue treatment has always been a challenge. Traditional treatment methods are often costly, inefficient, and prone to environmental pollution. Therefore, developing an efficient and environmentally friendly chemical-chaining gasification method for producing hydrogen-rich, low-carbon syngas from high-water-content biogas residue is of great practical significance. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing hydrogen-rich, low-carbon synthesis gas by chemical chain gasification of high-water-content biogas residue, improve the moisture content tolerance of biogas residue chemical chain gasification, optimize the synthesis gas quality, increase the hydrogen content in the synthesis gas and reduce the CO2 content.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing hydrogen-rich, low-carbon synthesis gas by chemical-looping gasification of highly water-containing biogas residue, comprising the following steps:

[0009] Mix high-moisture biogas residue with oxygen carriers to carry out chemical chain gasification reaction to obtain hydrogen-rich and low-carbon synthesis gas;

[0010] The moisture content of the high-moisture biogas residue is 30-50%;

[0011] The oxygen carrier is a transition metal-loaded lanthanum oxide; the transition metal element in the transition metal-loaded lanthanum oxide includes Cu and / or Fe;

[0012] The molar ratio of La, Cu and Fe in the oxygen carrier is 1:0 to 1:0 to 1;

[0013] The hydrogen-rich low-carbon synthesis gas has an H2 content of 30-35% and a CO2 content of 25-29%.

[0014] Preferably, the preparation method of the oxygen carrier comprises:

[0015] mixing a lanthanum salt, a copper salt and / or an iron salt to obtain a mixed salt solution;

[0016] The mixed salt solution is mixed with citric acid, and heated in a water bath until the mixture is in a gel state. The obtained gel is sequentially aged, dried and calcined to obtain an oxygen carrier.

[0017] Preferably, the water bath heating temperature is 85-90°C.

[0018] Preferably, the drying temperature is 105-110° C. and the drying time is 24-48 hours.

[0019] Preferably, the calcination temperature is 900-950° C. and the calcination time is 2-4 hours.

[0020] Preferably, the mass ratio of the dry matter of the high-moisture content biogas residue to the oxygen carrier is 0.8 to 1.2:1.

[0021] Preferably, the temperature of the chemical chaining gasification reaction is 850-900° C., and the reaction time is 35-40 minutes.

[0022] This invention provides a method for producing hydrogen-rich, low-carbon syngas from highly water-rich biogas residues through chemical looping gasification. This method utilizes a metal composite water-carbon oxygen capture carrier material—transition metal-loaded lanthanum oxide—to chemically loop gasify the highly water-rich biogas residues. This method not only overcomes the limitations of biogas residue gasification moisture content and effectively alleviates the energy consumption burden of drying and dehydrating highly water-rich biomass, but also achieves the high-value, hydrogen-rich, low-carbon syngas.

[0023] In the transition metal-loaded lanthanum oxide used in the present invention, Cu doping can cause lattice distortion, improve the charge compensation mechanism, promote the formation of oxygen vacancies, and thus enhance oxidation activity. In addition, oxygen vacancies as active sites also create conditions for the adsorption and dissociation of H2O / CO2, strengthening the synergistic effect of oxygen carriers and H2O / CO2; abundant oxygen vacancies not only improve the tolerance of the moisture content of sludge gasification, save energy consumption in the drying and dehydration process of raw materials, and have certain economic benefits, but also catalytically activate CO2, promote the conversion of CO2 to CO, reduce greenhouse gas emissions, and have certain environmental benefits. In addition, the simultaneous compounding of Cu and Fe increases the high-valent metal cations of the oxygen carrier, which provides metal sites for the adsorption and dissociation of H2O / CO2, fully utilizes the moisture in the raw materials to promote the generation of H2 and reduce CO2 emissions. Moreover, the simultaneous compounding of Cu and Fe causes the oxygen carrier to form an Fe-Cu metal interface, providing favorable conditions for the activation and conversion of CO2. Therefore, the method of the present invention can improve the moisture content tolerance of biogas chemical chaining gasification, optimize the quality of synthesis gas, increase the hydrogen content in the synthesis gas and reduce the CO2 content. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 H2O-TPD spectra of oxygen carriers with different Cu doping amounts in Examples 1 to 4;

[0025] Figure 2 CO2-TPSR spectra of oxygen carriers with different Cu doping amounts in Examples 1 to 4;

[0026] Figure 3 HRTEM images of oxygen carriers with different Cu doping amounts in Examples 1 to 4. DETAILED DESCRIPTION

[0027] In the present invention, unless otherwise specified, the required materials or reagents are commercially available products well known to those skilled in the art.

[0028] The present invention provides a method for preparing hydrogen-rich, low-carbon synthesis gas by chemical-looping gasification of highly water-containing biogas residue, comprising the following steps:

[0029] Mix high-moisture biogas residue with oxygen carriers to carry out chemical chain gasification reaction to obtain hydrogen-rich and low-carbon synthesis gas;

[0030] The moisture content of the high-moisture biogas residue is 30-50%;

[0031] The oxygen carrier is a transition metal-loaded lanthanum oxide; the transition metal element in the transition metal-loaded lanthanum oxide includes Cu and / or Fe;

[0032] The molar ratio of La, Cu and Fe in the oxygen carrier is 1:0 to 1:0 to 1;

[0033] The hydrogen-rich low-carbon synthesis gas has an H2 content of 30-35% and a CO2 content of 25-29%.

[0034] The present invention has no special limitation on the source and specific composition of the high-moisture content biogas residue, and the biogas residue well known in the art can be obtained in a manner well known in the art; in the embodiment of the present invention, it specifically comes from the Biomass, Energy and Environment Innovation Laboratory of Tianjin University.

[0035] In the present invention, the moisture content of the high-moisture biogas residue is preferably 30-50%, more preferably 40%.

[0036] In the present invention, the preparation method of the oxygen carrier preferably includes:

[0037] mixing a lanthanum salt, a copper salt and / or an iron salt to obtain a mixed salt solution;

[0038] The mixed salt solution is mixed with citric acid, and heated in a water bath until the mixture is in a gel state. The obtained gel is sequentially aged, dried and calcined to obtain an oxygen carrier.

[0039] In the present invention, the lanthanum salt is preferably lanthanum nitrate; the copper salt is preferably copper nitrate; and the iron salt is preferably iron nitrate.

[0040] In the present invention, the molar ratio of La, Cu and Fe in the lanthanum salt, copper salt and iron salt is preferably 1:0 to 1:0 to 1, more preferably 1:0.8 to 1:0 to 0.3, and more preferably 1:0.75:0.25.

[0041] In the present invention, the citric acid is used as a complexing agent, and the molar ratio of the complexing agent to the total metal cations is preferably 1:1 to 1.1, more preferably 1:1.

[0042] In the present invention, the water bath heating temperature is preferably 85-90° C.; the aging temperature is room temperature, and the time is 3 hours; the drying temperature is preferably 105-110° C., and the time is preferably 24-48 hours.

[0043] In the present invention, the calcination temperature is preferably 900-950° C., the time is preferably 2-4 hours, and the calcination atmosphere is preferably air; the heating rate to the calcination temperature is preferably 3-10° C. / min.

[0044] The oxygen carrier of the present invention is a transition metal-loaded lanthanum oxide, and the Cu and / or Fe elements are uniformly loaded on the surface and in the bulk of the oxygen carrier; the Fe and Cu metals can synergistically exert an active effect, and the La metal regulates the crystal structure stability of the oxygen carrier.

[0045] The present invention can regulate the oxygen vacancy concentration of the oxygen carrier by changing the composite ratio of Fe and Cu in the oxygen carrier, thereby achieving the regulation of the hydrogen-rich, low-carbon and high-value characteristics of the synthesis gas.

[0046] In the present invention, the mass ratio of the dry matter of the high-moisture content biogas residue to the oxygen carrier is preferably 0.8-1.2:1, more preferably 0.9-1.1:1, and further preferably 1:1.

[0047] In the present invention, the dry matter of the high-moisture biogas residue is obtained by placing the high-moisture biogas residue in an oven at 105-110° C. and drying it for more than 48 hours until the mass of the biogas residue is constant, thereby obtaining biogas residue dry matter with a moisture content of 0%.

[0048] In the present invention, the temperature of the chemical chaining gasification reaction is preferably 850-900°C, more preferably 850°C; the reaction time is preferably 35-40 minutes, more preferably 35 minutes; and the reaction equipment used for the chemical chaining gasification reaction is preferably a tubular furnace.

[0049] The present invention preferably collects the synthesis gas generated after the chemical looping gasification reaction through a gas collection bag and detects and analyzes it. The present invention does not specifically limit the specific method and conditions of the detection and analysis, and can be carried out according to processes well known in the art.

[0050] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0051] In the following examples, the high-moisture content biogas residue used is preferably sourced from the Biomass, Energy and Environment Innovation Laboratory of Tianjin University.

[0052] Example 1

[0053] According to the molar ratio of metal cations La:Fe=1:1, 4.33g (0.01mol) La(NO3)3·6H2O and 4.04g (0.01mol) Fe(NO3)3·9H2O were weighed and dissolved in 100mL deionized water and stirred until completely dissolved; 4.03g (0.02mol) citric acid was weighed and added to the mixed solution. After the citric acid formed a homogeneous phase with the solution at room temperature, it was placed in a constant temperature water bath at 85°C and continuously stirred until it became a gel. It was aged at room temperature for 3h and then placed in a 105°C oven to dry for 24h. The solid product was placed in a muffle furnace and calcined at 900°C for 4h to obtain an oxygen carrier recorded as LCF-0.

[0054] First, place the sludge with a moisture content of 40% in an oven at 110°C and dry it for more than 48 hours until the mass of the sludge is constant, obtaining sludge dry matter with a moisture content of 0%. Then, 1g of sludge dry matter is evenly mixed with 1g of LCF-0 oxygen carrier. The reaction temperature is set to 850°C. After reaching the set temperature and stabilizing, the mixed raw materials are pushed into the reaction zone. The reaction time is 35 minutes, and the synthesis gas produced after the reaction is analyzed.

[0055] The analysis results of the obtained synthesis gas are as follows: H2 volume fraction 30.26%, CO2 volume fraction 26.40%, and carbon conversion rate 86.24%.

[0056] Example 2

[0057] An oxygen carrier was prepared according to the method in Example 1, and a chemical looping gasification reaction experiment of aqueous biogas residue was carried out:

[0058] The only difference from Example 1 is that according to the molar ratio of metal cations La:Fe:Cu=1:0.75:0.25, 4.33g La(NO3)3·6H2O, 3.03g Fe(NO3)3·9H2O, and 0.61g Cu(NO3)2·3H2O were weighed and dissolved in 100mL deionized water, and stirred until completely dissolved. The obtained oxygen carrier was recorded as LCF-0.25.

[0059] The analysis results of the obtained synthesis gas are as follows: H2 volume fraction 31.47%, CO2 volume fraction 27.52%, and carbon conversion rate 87.16%.

[0060] Example 3

[0061] An oxygen carrier was prepared according to the method in Example 1, and a chemical chain gasification reaction experiment of aqueous sludge was carried out: the only difference from Example 1 was: 4.33g La(NO3)3·6H2O, 1.02g Fe(NO3)3·9H2O, and 1.82g Cu(NO3)2·3H2O were weighed and dissolved in 100ml of deionized water according to the molar ratio of metal cations La:Fe:Cu=1:0.25:0.75, and stirred until completely dissolved. The obtained oxygen carrier was recorded as LCF-0.75.

[0062] The analysis results of the obtained synthesis gas are as follows: H2 volume fraction 31.58%, CO2 volume fraction 25.98%, and carbon conversion rate 89.19%.

[0063] Example 4

[0064] An oxygen carrier was prepared according to the method in Example 1, and a chemical chain gasification reaction experiment of aqueous sludge was carried out; the only difference from Example 1 was that 4.33 g La(NO3)3·6H2O and 2.42 g Cu(NO3)2·3H2O were weighed and dissolved in 100 mL of deionized water according to the molar ratio of metal cations La:Cu=1:1, and stirred until completely dissolved. The obtained oxygen carrier was recorded as LCF-1.

[0065] The analysis results of the obtained synthesis gas are as follows: H2 volume fraction 31.19%, CO2 volume fraction 28.50%, and carbon conversion rate 90.85%.

[0066] Based on the above experimental data, the oxygen carrier LCF-0.75 has the best performance. That is, through the method provided in Example 3, biogas residue with a moisture content of 40% is subjected to a chemical chain gasification reaction with LCF-0.75. The H2 content in the generated synthesis gas reaches 31.58%, the CO2 content is as low as 25.98%, and the carbon conversion rate is 89.19%.

[0067] Figure 1 The H2O-TPD spectra of oxygen carriers with different Cu doping amounts in Examples 1 to 4. The H2O-TPD curve reflects the strength and characteristics of the interaction between oxygen carriers and H2O molecules. Generally speaking, the higher the H2O signal release temperature, the stronger the sample's adsorption capacity for water, and the higher the peak value, the stronger the sample's desorption capacity for H2O. Figure 1From the information analysis, it can be seen that LCF-0.75 has a stronger binding effect with H2O. This property can not only save the dehydration energy consumption before the raw material reaction, but also help to improve the reaction atmosphere of sludge gasification, release H2O and OH in the high temperature section of the reaction, and provide conditions for further conversion of the reaction products. Oxygen vacancies, as the key sites for H2O adsorption, have a strong interaction with H2O, providing a greater driving force for H2O dissociation. In addition, the substitution of Cu will cause charge imbalance to form oxygen vacancies, which will promote the generation of more high-valent metal cations (Fe 3+ and Cu 2 + ) to maintain electrical neutrality. High-valent metal cations can also serve as active sites for H2O adsorption and dissociation, easily forming coordination bonds (M-OH) with H2O and dissociating to generate OH, creating conditions for the utilization and conversion of water in the biogas residue during the gasification process.

[0068] Figure 2 The CO2-TPSR spectra of oxygen carriers with different Cu doping levels in Examples 1-4 reflect the reaction between the oxygen carriers and CO2 to produce CO. Lower peak temperatures indicate that CO2 molecules are more easily adsorbed by the oxygen carriers and migrate through the active sites, while higher peak intensities indicate stronger interactions between the oxygen carriers and CO2. Figure 2 It shows that LCF-0.75 has a stronger interaction with CO2. Oxygen vacancies serve as active sites for CO2 adsorption and dissociation, which can promote the conversion of CO2 to CO. In addition, metal sites also affect the interaction between oxygen carriers and CO2. Cu provides a place for the decomposition of CO2, thereby producing more active oxygen species. CO2 adsorbs and dissociates on the Cu surface to produce CO* and O*, which then gasify with hydrocarbons to produce CO and H2. However, when the gasification rate is higher than the decomposition rate of CO2, excess CO will inhibit the decomposition of CO2. Therefore, the balance between CO2 decomposition and gasification is crucial to achieving a stable chemical chain gasification process. In the present invention, when the Cu doping amount is 0.75, the highest CO2 conversion rate and good carbon balance are obtained.

[0069] Figure 3 HRTEM images of oxygen carriers with different Cu doping amounts in Examples 1 to 4. The LCF-0 with a lattice spacing of 0.278 nm corresponds to the (121) crystal plane of LaFeO3. As the Cu doping amount increases, the lattice spacing of the oxygen carrier particles decreases. This is because Cu occupies the Fe site, while Cu 2+ (0.073nm) radius is larger than Fe 3+(0.064nm) radius. Notably, when Fe and Cu are co-existing at the B site of the oxygen carrier, i.e., LCF-0.25 and LCF-0.75, their HRTEM images show both distinct lattice fringes and distinct disordered regions with a clear interface, which provides evidence for the establishment of an Fe-Cu metal interface. The Fe-Cu metal interface formed in LCF-0.75 is more pronounced and larger in extent. Therefore, the presence of the Fe-Cu metal interface promotes CO2 activation and produces more active oxygen species suitable for carbon gasification, thereby reducing coke deposition and improving gasification efficiency.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for producing hydrogen-rich, low-carbon synthesis gas by chemical chaining gasification of highly water-containing biogas residues, characterized in that: The following steps are involved: Mix high-moisture biogas residue with oxygen carriers to carry out chemical chain gasification reaction to obtain hydrogen-rich and low-carbon synthesis gas; The moisture content of the high-moisture biogas residue is 30-50%; The oxygen carrier is a transition metal-loaded lanthanum oxide; the transition metal elements in the transition metal-loaded lanthanum oxide include Cu and Fe; The molar ratio of La, Fe and Cu in the oxygen carrier is 1:0.75:0.25 or 1:0.25:0.75; The mass ratio of the dry matter of the high-moisture content biogas residue to the oxygen carrier is 0.8 to 1.2:1; The hydrogen-rich low-carbon synthesis gas has an H2 content of 30-35% and a CO2 content of 25-29%; The preparation method of the oxygen carrier comprises: mixing a lanthanum salt, a copper salt, and an iron salt to obtain a mixed salt solution; The mixed salt solution is mixed with citric acid, heated in a water bath until it is in a gel state, and the obtained gel is aged, dried and calcined in sequence to obtain an oxygen carrier; The water bath heating temperature is 85-90°C; The calcination temperature is 900-950° C., and the calcination time is 2-4 hours.

2. The method according to claim 1, characterized in that The drying temperature is 105-110° C. and the drying time is 24-48 hours.

3. The method according to claim 1, characterized in that The temperature of the chemical chain gasification reaction is 850-900° C., and the reaction time is 35-40 minutes.

Images