Method for preparing hydrogen-rich low-carbon syngas by chemical looping gasification of high-moisture digestate

Abstract

The present invention belongs to the technical field of solid waste treatment and provides a method for preparing hydrogen-rich low-carbon syngas by chemical looping gasification of high-moisture digestate. In the present invention, high-moisture digestate is mixed with an oxygen carrier to carry out a chemical looping gasification reaction to obtain hydrogen-rich low-carbon syngas. The moisture content of the high-moisture digestate is 30-50%. The oxygen carrier is a transition-metal-supported lanthanum oxide. In the present invention, a metal-composite-type water–carbon-capturing oxygen carrier material, i.e., the transition-metal-supported lanthanum oxide, is used to carry out chemical looping gasification conversion of high-moisture digestate, which improves the moisture tolerance of digestate chemical looping gasification, optimizes the quality of syngas, and increases the content of hydrogen and reduces the content of CO2 in the syngas.

Description

Method for preparing hydrogen-rich low-carbon synthesis gas by high-moisture biogas residue chemical looping gasification TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste treatment, and particularly relates to a method for preparing hydrogen-rich low-carbon synthesis gas by high-moisture biogas residue chemical looping gasification. BACKGROUND

[0002] With the increasingly prominent global environmental problems, climate change caused by the greenhouse effect has a serious impact on human society and the ecological system. As a renewable energy source, biomass plays a crucial role in the future zero-carbon energy system. It is particularly worth mentioning that biomass absorbs CO2 during its growth process, and if the utilization process can achieve efficient conversion and extremely low CO2 emission or even negative carbon emission, it will provide a strong boost to address climate change. Therefore, biomass has great potential to become an important substitute for fossil fuels, and is of great significance in achieving sustainable development.

[0003] Gasification is an effective way to achieve efficient and rapid conversion of biomass. However, the original biomass generally has a high water content, and the traditional gasification has limitations in dealing with high-moisture biomass. In the gasification process, high water content will reduce the energy conversion efficiency, reduce the calorific value of synthesis gas, and produce more by-products such as tar. Therefore, the traditional gasification needs to dry the biomass for pretreatment, and the huge energy consumption of this process will be the main factor limiting the application of biomass gasification.

[0004] Chemical looping gasification, as a new gasification method, can provide a solution to the challenges brought by the conversion of high-moisture biomass. Chemical looping gasification uses the lattice oxygen in the oxygen carrier as the oxygen source to provide the oxygen elements required for gasification to the fuel, and obtains synthesis gas mainly composed of CO and H2. The oxygen carrier plays a key regulatory role, and often contains a certain amount of oxygen vacancies, which not only provides active sites for the adsorption and dissociation of biomass water, but also can adsorb and activate CO2. By optimizing the characteristics and composition of the oxygen carrier, the composition of the synthesis gas can be effectively regulated, and the goal of high hydrogen content and low carbon content can be achieved, thereby greatly reducing CO2 emission and opening up a new way for clean and efficient energy conversion.

[0005] Biogas residue is a typical high-moisture biomass, and its treatment has always been a difficult problem. Traditional treatment methods are often high in cost, low in efficiency, and easy to cause environmental pollution. Therefore, it is of great practical significance to develop an efficient and environmentally friendly chemical looping gasification method for preparing hydrogen-rich low-carbon synthesis gas from high-moisture biogas residue.

[0006] SUMMARY

[0007] The application aims to provide a method for preparing hydrogen-rich low-carbon synthesis gas by high-moisture biogas residue chemical looping gasification, improve the moisture content tolerance of biogas residue chemical looping gasification, optimize the synthesis gas quality, increase the hydrogen content in the synthesis gas and reduce the CO2 content.

[0008] To achieve the above-mentioned application purposes, the application provides the following technical solutions.

[0009] The application provides a method for preparing hydrogen-rich low-carbon synthesis gas by high-moisture biogas residue chemical looping gasification, comprising the following steps.

[0010] Mixing high-moisture biogas residue with an oxygen carrier to perform a chemical looping gasification reaction to obtain hydrogen-rich low-carbon synthesis gas;

[0011] The moisture content of the high-moisture biogas residue is 30-50%.

[0012] The oxygen carrier is a transition metal loaded lanthanum oxide; the transition metal elements in the transition metal loaded lanthanum oxide include Cu and / or Fe.

[0013] The molar ratio of La, Cu and Fe in the oxygen carrier is 1:0-1:0-1.

[0014] The H2 content in the hydrogen-rich low-carbon synthesis gas is 30-35%, and the CO2 content is 25-29%.

[0015] Preferably, the preparation method of the oxygen carrier comprises:

[0016] Mixing lanthanum salt, copper salt and / or iron salt to obtain a mixed salt solution;

[0017] Mixing the mixed salt solution with citric acid, heating in a water bath to a gel state, and sequentially performing aging, drying and calcination on the obtained gel to obtain the oxygen carrier.

[0018] Preferably, the temperature of the water bath heating is 85-90 DEG C.

[0019] Preferably, the temperature of the drying is 105-110 DEG C, and the time is 24-48 h.

[0020] Preferably, the temperature of the calcination is 900-950 DEG C, and the time is 2-4 h.

[0021] Preferably, the mass ratio of the dry matter of the high-moisture biogas residue to the oxygen carrier is 0.8-1.2:1.

[0022] Preferably, the temperature of the chemical looping gasification reaction is 850-900 DEG C, and the reaction time is 35-40 min.

[0023] The application provides a method for preparing hydrogen-rich low-carbon synthesis gas by high-moisture biogas residue chemical looping gasification.

[0024] In the transition metal supported lanthanum oxide used in the application, Cu doping can cause lattice distortion, improve the charge compensation mechanism, promote the formation of oxygen vacancies, thereby enhancing the 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 the oxygen carrier and H2O / CO2; abundant oxygen vacancies not only improve the moisture tolerance of biogas residue gasification and save energy consumption in the drying and dehydration process of raw materials, but also have certain economic benefits, and catalyze CO2, promote the conversion of CO2 to CO, and reduce the emission of greenhouse gases, which has certain environmental benefits. In addition, the simultaneous compounding of Cu and Fe increases the high-valence 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 the emission of CO2. Moreover, the simultaneous compounding of Cu and Fe enables the oxygen carrier to form a Fe-Cu metal interface, which provides favorable conditions for the activation and conversion of CO2. Therefore, the method of the application can improve the moisture tolerance of biogas residue chemical looping gasification, optimize the synthesis gas quality, increase the hydrogen content in the synthesis gas and reduce the CO2 content. BRIEF DESCRIPTION OF DRAWINGS

[0025] Fig. 1 is the H2O-TPD spectrum of the oxygen carrier with different Cu doping amounts in Examples 1-4;

[0026] Fig. 2 is the CO2-TPSR spectrum of the oxygen carrier with different Cu doping amounts in Examples 1-4;

[0027] Fig. 3 is the HRTEM diagram of the oxygen carrier with different Cu doping amounts in Examples 1-4. DETAILED DESCRIPTION

[0028] In the application, the required materials or reagents are commercially available goods well known to those skilled in the art unless otherwise specified.

[0029] The application provides a method for preparing hydrogen-rich low-carbon synthesis gas by high-moisture biogas residue chemical looping gasification, which comprises the following steps:

[0030] Mixing high-moisture biogas residue with an oxygen carrier to perform a chemical looping gasification reaction to obtain hydrogen-rich low-carbon synthesis gas;

[0031] The moisture content of the high-moisture biogas residue is 30-50%;

[0032] 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;

[0033] The molar ratio of La, Cu and Fe in the oxygen carrier is 1:0-1:0-1;

[0034] The H2 content in the hydrogen-rich low-carbon synthesis gas is 30-35%, and the CO2 content is 25-29%.

[0035] The source and specific composition of the high-moisture-content biogas residue are not particularly limited in the present application, and the biogas residue known in the art can be obtained in a manner known in the art; in the embodiments of the present application, it is specifically derived from the Tianjin University Biomass Energy Environment Innovation Laboratory.

[0036] In the present application, the moisture content of the high-moisture-content biogas residue is preferably 30-50%, more preferably 40%.

[0037] In the present application, the preparation method of the oxygen carrier preferably comprises:

[0038] Mixing lanthanum salt, copper salt and / or iron salt to obtain a mixed salt solution;

[0039] Mixing the mixed salt solution with citric acid, heating in a water bath to a gel, and sequentially aging, drying and calcining the obtained gel to obtain an oxygen carrier.

[0040] In the present application, the lanthanum salt is preferably lanthanum nitrate; the copper salt is preferably copper nitrate; and the iron salt is preferably iron nitrate.

[0041] In the present application, the molar ratio of La, Cu and Fe in the lanthanum salt, copper salt and iron salt is preferably 1:0-1:0-1, more preferably 1:0.8-1:0-0.3, and more preferably 1:0.75:0.25.

[0042] In the present application, the citric acid is used as a complexing agent, and the molar ratio of the complexing agent to total metal cations is preferably 1:1-1.1, and more preferably 1:1.

[0043] In the present application, the temperature of the water bath heating is preferably 85-90℃; the temperature of the aging is room temperature, and the time is 3h; the temperature of the drying is preferably 105-110℃, and the time is preferably 24-48h.

[0044] In the present application, the temperature of the calcination is preferably 900-950℃, the time is preferably 2-4h, and the calcination atmosphere is preferably air; the temperature rising rate to the temperature of the calcination is preferably 3-10℃ / min.

[0045] The oxygen carrier is a transition metal supported lanthanum oxide, and the Cu and / or Fe elements are uniformly supported on the surface and bulk phase of the oxygen carrier; the Fe and Cu metals can synergistically play an active role, and the La metal adjusts the crystal structure stability of the oxygen carrier.

[0046] The present application can regulate the oxygen vacancy concentration of the oxygen carrier by changing the complex ratio of Fe and Cu in the oxygen carrier, thereby realizing the regulation of the hydrogen-rich low-carbon high-value characteristics of the synthesis gas.

[0047] In the present application, the mass ratio of 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.

[0048] In the present application, the dry matter of the high-moisture-content biogas residue is obtained by drying the high-moisture-content biogas residue in an oven at 105-110℃ for 48h or more until the mass of the biogas residue is constant, and the dry matter of the biogas residue obtained has a water content of 0%.

[0049] In the present application, the temperature of the chemical looping gasification reaction is preferably 850-900℃, more preferably 850℃; the reaction time is preferably 35-40min, more preferably 35min; and the reaction equipment used for the chemical looping gasification reaction is preferably a tubular furnace.

[0050] The synthesis gas generated after the chemical looping gasification reaction is preferably collected by a gas collection bag and detected and analyzed.

[0051] The technical solutions provided by the present application will be described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present application.

[0052] In the following examples, the high-moisture-content biogas residue is preferably obtained from the Biomass Energy Environment Innovation Laboratory of Tianjin University.

[0053] Example 1

[0054] 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 added to the mixed solution, and after the citric acid was uniformly mixed with the solution at room temperature, it was placed in a constant-temperature water bath at 85℃ and continuously stirred until it became a gel. It was aged at room temperature for 3h, and then dried in an oven at 105℃ for 24h. The solid product was placed in a muffle furnace and calcined at 900℃ for 4h to obtain an oxygen carrier, which is denoted as LCF-0.

[0055] The biogas residue with 40% moisture content was first dried in an oven at 110°C for more than 48h until the mass of the biogas residue was constant, obtaining the biogas residue dry matter with 0% moisture content. 1g of the biogas residue dry matter was uniformly mixed with 1g of the LCF-0 oxygen carrier. The reaction temperature was set to 850°C. After the temperature reached the set temperature and was stable, the mixed raw materials were pushed into the reaction zone. The reaction time was 35min. The produced synthesis gas after the reaction was analyzed.

[0056] The analysis results of the obtained synthesis gas were as follows: H2volume fraction 30.26%, CO2volume fraction 26.40%, carbon conversion rate 86.24%.

[0057] Example 2

[0058] The oxygen carrier was prepared according to the method in Example 1, and the water-containing biogas residue chemical looping gasification reaction experiment was carried out:

[0059] The difference from Example 1 was only that 4.33g of La(NO3)3·6H2O, 3.03g of Fe(NO3)3·9H2O and 0.61g of Cu(NO3)2·3H2O were weighed according to the molar ratio of metal cations La:Fe:Cu = 1:0.75:0.25, dissolved in 100ml of deionized water, and stirred until completely dissolved. The obtained oxygen carrier was recorded as LCF-0.25.

[0060] The analysis results of the obtained synthesis gas were as follows: H2volume fraction 31.47%, CO2volume fraction 27.52%, carbon conversion rate 87.16%.

[0061] Example 3

[0062] The oxygen carrier was prepared according to the method in Example 1, and the water-containing biogas residue chemical looping gasification reaction experiment was carried out: The difference from Example 1 was only that 4.33g of La(NO3)3·6H2O, 3.03g of Fe(NO3)3·9H2O and 0.61g of Cu(NO3)2·3H2O were weighed according to the molar ratio of metal cations La:Fe:Cu = 1:0.75:0.25, dissolved in 100ml of deionized water, and stirred until completely dissolved. The obtained oxygen carrier was recorded as LCF-0.25.

[0063] The analysis results of the obtained synthesis gas were as follows: H2volume fraction 31.47%, CO2volume fraction 27.52%, carbon conversion rate 87.16%.

[0064] Example 4

[0065] The oxygen carrier was prepared according to the method in Example 1, and the water-containing biogas residue chemical looping gasification reaction experiment was carried out; the difference from Example 1 is only that 4.33 g of La(NO3)3·6H2O and 2.42 g of Cu(NO3)2·3H2O were weighed, according to the molar ratio of metal cations La:Cu = 1:1, dissolved in 100 mL of deionized water, stirred until completely dissolved, and the obtained oxygen carrier was recorded as LCF-1.

[0066] The analysis results of the obtained synthesis gas are as follows: H2volume fraction 31.19%, CO2volume fraction 28.50%, carbon conversion rate 90.85%.

[0067] Based on the above experimental data, the oxygen carrier LCF-0.75 has the best performance, i.e. through the method provided in Example 3, the water-containing rate of the biogas residue is 40%, and the chemical looping gasification reaction is carried out with LCF-0.75, the H2content in the generated synthesis gas reaches 31.58%, the CO2content is as low as 25.98%, and the carbon conversion rate is 89.19%.

[0068] Fig. 1 is the H2O-TPD spectrum of the oxygen carrier with different Cu doping amounts in Examples 1-4. The H2O-TPD curve reflects the strength and characteristics of the interaction between the oxygen carrier and H2O molecules. Generally, 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. From the information analysis in Fig. 1, it can be known that LCF-0.75 has a stronger combination with H2O. This performance not only saves the dehydration energy consumption before the reaction of raw materials, but also helps to improve the reaction atmosphere of the biogas residue gasification, releases H2O and OH at the high temperature stage of the reaction, and provides conditions for the 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, prompting the formation of more high-valence metal cations (Fe 3+ and Cu 2+ ) to maintain electrical neutrality. High-valence metal cations can also act 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 itself during the gasification process.

[0069] Figure 2 is the CO2-TPSR spectra of oxygen carriers with different Cu doping amounts in Examples 1-4, reflecting the characteristics of oxygen carriers reacting with CO2 to generate CO. Lower peak temperature indicates that CO2 molecules are more easily adsorbed by the oxygen carrier and transferred on the active sites; while higher peak intensity indicates that the interaction between the oxygen carrier and CO2 is stronger. Figure 2 shows that LCF-0.75 has a stronger interaction with CO2. Oxygen vacancies as active sites for CO2 adsorption and dissociation can promote the conversion of CO2 to CO. In addition, metal sites also affect the interaction between the oxygen carrier and CO2. Cu provides a site for the decomposition of CO2, thereby generating more active oxygen species. CO2 adsorbs and dissociates on the Cu surface to generate CO* and O*, which then gasify with hydrocarbon materials to produce CO and H2. However, when the gasification rate is higher than the decomposition rate of CO2, the excess CO will inhibit the decomposition of CO2. Therefore, the balance between CO2 decomposition and gasification is crucial for achieving a stable chemical looping gasification process. In the present application, the highest CO2 conversion rate and good carbon balance are obtained when the doping amount of Cu is 0.75.

[0070] Figure 3 is the HRTEM image of oxygen carriers with different Cu doping amounts in Examples 1-4. The lattice spacing of LCF-0 is 0.278 nm, corresponding to the (121) 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 sites, and the radius of Cu 2+ (0.073 nm) is larger than the radius of Fe 3+ (0.064 nm). It is worth noting that when Fe and Cu coexist in the B sites of the oxygen carrier, i.e. LCF-0.25 and LCF-0.75, their HRTEM images show that there are both clear lattice fringes and clear disordered regions, with a clear interface, which provides evidence for the establishment of Fe-Cu metal interfaces. The Fe-Cu metal interface formed in LCF-0.75 is more obvious and has a larger range. Therefore, the existence of Fe-Cu metal interface promotes the activation of CO2 and generates more active oxygen species suitable for carbon gasification, thereby reducing coke deposition and improving gasification efficiency.

[0071] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, several improvements and refinements can be made, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A method for the production of a hydrogen-rich low-carbon syngas from high-moisture peat sludge by chemical looping gasification, c h a r a c t e r i s e d b y, The method comprises the following steps: mixing high-moisture-content biogas residue with an oxygen carrier to perform a chemical looping gasification reaction, and obtaining a hydrogen-rich low-carbon synthesis gas; the high-moisture-content biogas residue has a moisture content of 30-50%; the oxygen carrier is a transition metal-loaded lanthanum oxide, and the transition metal elements in the transition metal-loaded lanthanum oxide include Cu and / or Fe; the molar ratio of La, Cu and Fe in the oxygen carrier is 1:0-1:0-1; the hydrogen-rich low-carbon synthesis gas has a H2 content of 30-35% and a CO2 content of 25-29%.

2. The method of claim 1, wherein, a preparation method of the oxygen carrier comprises: mixing lanthanum salt, copper salt and / or iron salt to obtain a mixed salt solution; mixing the mixed salt solution with citric acid, heating in a water bath to a gel state, and sequentially performing aging, drying and calcination on the obtained gel to obtain the oxygen carrier.

3. The method of claim 2, wherein, the temperature of the water bath heating is 85-90°C.

4. The method of claim 2, wherein, the temperature of the drying is 105-110°C, and the time is 24-48h.

5. The method of claim 2, wherein, the temperature of the calcination is 900-950°C, and the time is 2-4h.

6. The method of claim 1, wherein, the mass ratio of the dry matter of the high-moisture-content biogas residue to the oxygen carrier is 0.8-1.2:

1.

7. The method according to claim 1 or 6, characterized in that, the temperature of the chemical looping gasification reaction is 850-900°C, and the reaction time is 35-40min.

Images