Selective catalytic reduction denitration system with CO as reducing agent, method and application thereof

Abstract

A selective catalytic reduction, SCR, denitration system using carbon monoxide, CO, as a reducing agent. The denitration system comprises denitration reactor 3 in which reduction-storage double-layer

Description

The present disclosure belongs to the technical field of flue gas purification, and in particular relates to a selective catalytic reduction (SCR) denitration system with CO as a reducing agent, an application thereof and an SCR denitration method. The SCR technology is currently the mainstream solution for industrial flue gas denitration. The introduction of ammonia (NH3), a typical reducing agent, not only increases the cost of denitration technology, but also corrodes the equipment, resulting in secondary pollution caused by the escape of flue gas. Due to incomplete combustion in industrial furnaces and kilns, a large amount of CO is commonly present in the flue gas, which is a reducing gas with a high calorific value and is one of the pollutants of ambient air quality monitoring. Catalytic denitration with CO instead of NH3 may reduce the energy consumption of additional reducing agents, thus preventing the risk of pollution by ammonia escape, and realizing the simultaneous removal of pollutants, which is a promising denitration technology of “treating waste with waste”. However, the high concentration of oxygen in industrial flue gas has a significant inhibitory effect on CO catalytic denitration. On the one hand, the reaction of oxygen with CO consumes the reducing agent; and on the other hand, the reaction of oxygen with NO generates by-products of NO2. The following three reaction processes are mainly involved: 2NO+2CO—>N2+2CO2 (main reaction) 2CO+O2—>2CO2 (main reaction) 2NO+O2—>2NO2 (side reaction) among the processes, the oxidation of CO to produce CO2 is an exothermic process, which may serve to supplement the heat of the flue gas and improve the efficiency of denitration. Thermodynamically, the reduction of NO2 (AG=-1109.74 kilojoules (kJ), 120 degrees Celsius (°C)) by CO is easier than the direct reduction of NO (AG=-668.66 kJ, 120°C). Therefore, NO2 by-products may be captured in time to promote their secondary decomposition. Compared with the catalytic reduction of NOX by CO under Eley-Rideal mechanism (NO adsorption, CO non-adsorption), the adsorption of CO on the material surface is the rate-determining step of CO oxidation reaction. The occurrence of CO oxidation side reactions may be reduced once other gaseous components in the flue gas poison the CO adsorption sites first. Therefore, it is an urgent technical problem for those skilled in the art to provide a method and system for SCR denitration using CO as a reducing agent capable of capturing materials. In order to solve the above technical problems, the present disclosure provides an SCR denitration system with CO as a reducing agent, an application thereof and a SCR denitration method, which solves the problem that CO-SCR technology is difficult to be applied in industrial flue gas with high oxygen concentration. In order to achieve the above objectives, the present disclosure provides following technical schemes: an SCR denitration system with CO as a reducing agent, including an SCR denitration reactor, where the SCR denitration reactor includes reduction-storage double-layer catalysts distributed at intervals in multiple rings. Preferably, the SCR denitration system includes a dust collector, a hot blast stove, the SCR denitration reactor, a desulfurization device and a chimney connected sequentially; Preferably, the SCR denitration reactor is a fixed bed device, an inside of the SCR denitration reactor includes polycyclic catalyst layers, specifically composed of a rectifying layer, polycyclic catalyst layers and an ash hopper assembled from top to bottom; a number of the polycyclic catalyst layers is 2-4; the reduction-storage double-layer catalysts include reduction catalysts filled at intervals in multiple rings in the polycyclic catalyst layers and storage catalysts; the polycyclic catalyst layers include 5-9 rings, preferably 5, 7 and 9 rings; and a mass ratio of the reduction catalysts to the storage catalysts is in a range of 5:1-10:1, preferably 5:1,7:1 and 10:1. The present disclosure employs reduction-storage double-layer catalysts, where NO reacts with CO and O2 on surfaces of the reduction catalysts to produce N2 and NO2, and NO2 subsequently spills over onto surfaces of the storage catalysts and reacts with CO in a secondary reaction to produce N2; a working principle of the SCR denitration reactor provided by the present disclosure includes following steps: (1) NO reacts with CO and O2 on the surfaces of the reduction catalysts to produce N2 and NO2; where the chemical reactions include but are not limited to the following reactions: NO(g) -> NO(ads); NO(ads) + NO(ads) -> ONNO(ads); ONNO(ads) + CO(g) -> ONN(ads) + CO2(g); ONN(ads) + CO(g) -> N2(ads) + CO2(g); N2(ads)^N2(g); NO(ads) + 20* -► NO3'(ads); NO3’(ads) + CO(g) -► NO2(ads) + CO2(g); NO2(ads)^NO2(g); (2) NO2 then overflows onto the surfaces of the storage catalysts and reacts with CO for the secondary reaction to generate N2; the chemical reactions include but are not limited to the following reactions: NO2(g)^NO2(ads); MO + NO2(ads) —► MNO3(ads) (M as metal ions); 2MNO3(ads) + 4CO(g) -> 2MO + N2(ads) + 4CO2(g); N2(ads) -► N2(g). In the above steps (1) and (2), a ratio of CO and NO is in a range of 10-200, preferably 10, 50, 100,150 and 200; an O2 concentration is in a range of 5-16%, preferably 6%, 10% and 16%; and a reaction temperature is 220-320°C, such as 220°C, 240°C, 260°C, 280°C, 300°C and 320°C. Preferably, a catalyst in a reduction catalyst layer includes a carrier, an acidic metal and an active component, where the acidic metal is supported on the carrier and the active component is supported on the acidic metal. Preferably, the active component includes any one or a combination of several components of Ir groups, Pt groups, Ag groups, Au groups, Ru groups, Pd groups and Rh groups; more preferably, the active component includes one or a combination of two of IrO2, IrCh, PtO2, PtCU, Ag2O, AgCl, AU2O3, AuCh, RuO2, RuCh, PdO, PdCh, RhO2, and RI1CI3; the acidic metal includes any one or a combination of W groups, Mo groups and Nb groups acidic metals; more preferably, the acidic metal includes one or a combination of two of WO3, WClg, MoOs, M0CI5, Nb20s, and NbCls; the carrier includes any one or a combination of Al groups, Si groups, Ti groups, Ce groups and Co groups carriers. More preferably, the carrier includes one or a combination of two of AI2O3, SiO2, molecular sieve, TiO2, CeO2 and CO3O4; preferably, a loading amount of the active component is 0.02-1 weight percentage (wt.%); a loading amount of the acidic metal is 3-7 wt.%; the carrier has a particle size of 5-100 nanometers (nm) and a specific surface area of 100-500 square meters per gram (m / g). More preferably, the surfaces of the reduction catalysts include rich hydroxyl groups; the rich hydroxyl groups on the surfaces of the reduction catalysts are caused by the unsaturated coordination of some atoms on the surfaces of the catalysts; the content of the hydroxyl groups is related to the specific surface area and may be controlled by morphology and crystal plane. The hydroxyl groups include any one or a combination of terminal hydroxyl groups, bridged hydroxyl groups and tri-coordinated hydroxyl groups. The hydroxyl groups are mainly terminal hydroxyl groups, preferably with a content of terminal hydroxyl groups accounting for more than 60% of a number of hydroxyl groups. More preferably, the reduction catalysts include one of an Ir-W / TiO2 catalyst, a Pt-W / TiO2 catalyst or an Ir-W / CEO2 catalyst, where a loading amount of Ir or Pt is 0.5 wt.%, a loading amount of W is 5 wt.%, with a rest being the carrier. Preferably, the reduction catalysts are subjected to an activation treatment by activating gas before use; the activating gas includes any one or a combination of H2, CO and NH3; a duration of the activation treatment is 0.5-2 hours (h), preferably 0.5 h, 1 h, 1.5 h and 2 h; a temperature of the activation treatment 200-400°C, preferably 200°C, 300°C and 400°C; and a concentration of the activating gas is 5%-10%, preferably 5%, 8% and 10%. The activation treatment specifically includes following steps: placing a certain amount of catalyst into a tubular furnace, introducing the activating gas at a gas volume of 100 milliliters per minutes (mL / min), heating the tubular furnace to the temperature of the activation treatment at 10 °C / min after 1 h, cooling in a same atmosphere after reaching the duration of the activation treatment, stopping introducing the activating gas after cooling to room temperature, and taking out the catalyst. Preferably, the storage catalyst includes a storage component and a carrier, and the storage component is supported on the carrier; the storage component includes any one or a combination of Ba groups and K groups; more preferably, the storage component includes one or more of BaO, Ba(HCO3)2, BaCOs, KHCO3 and K2CO3; and the carrier includes any one or a combination of Al groups, Si groups, Ti groups, Ce groups and Co groups. More preferably, the carrier includes one or more of AI2O3, SiO2, molecular sieve, TiO2, CeO2 and CO3O4; preferably, a loading amount of the storage component on the carrier is 10-40 wt.%; and the carrier has a particle size of 100 nm-10 micrometer (pm), and a specific surface area of 50-20 m2 / g. More preferably, the storage catalysts include a Ba / Al2O3 catalyst, with a Ba loading of 10 wt.% and a rest being the carrier. The desulfurization device is one or a combination of at least two of a circulating fluidized bed semi-dry desulfurization device, a rotary spray semi-dry desulfurization device and a wet desulfurization device. The system provided by the present disclosure has the advantages that the desulfurization device is placed behind the SCR denitration reactor, and the pollutant SO2 in the flue gas is fully utilized; the design of annular interval arrangement is used to give full play to the synergistic effect between reduction catalysts and storage catalysts. An application of the SCR denitration system with CO as the reducing agent in NOX removal from industrial flue gas with high CO / NO ratio under oxy gen-containing conditions. Preferably, a concentration ratio of CO to NO in the industrial flue gas is 10-200:1, preferably 10:1, 50:1,100:1,150:1 and 200:1. More preferably, an O2 concentration in the industrial flue gas is 5-16%; More preferably, the industrial flue gas with high CO / NO ratio is flue gas from coal-fired power plants, steel sintering flue gas, etc. An SCR denitration method using CO as a reducing agent, whereby the SCR denitration system with CO as the reducing agent as described above is used. Preferably, the SCR denitration method includes following steps: introducing industrial flue gas into the dust collector, then passing through the hot blast stove, SCR denitration reactor and desulfurization device in turn, and finally discharging the treated flue gas through the chimney to complete the flue gas SCR denitration. More preferably, the SCR denitration method specifically includes following steps: (1) the industrial flue gas enters the hot blast stove from an outlet at a top end of the dust collector, a temperature of the industrial flue gas rises after passing through the hot blast stove, then enters the SCR denitration reactor from a lateral outlet of the hot blast stove and passes through a rectifying layer and a catalyst layer from top to bottom, where the industrial flue gas is more uniform after passing through the rectifying layer, and N2 and CO2 are generated after the catalyst layer reacts with the reduction-storage double-layer catalysts for many times; and (2) after the reaction, the industrial flue gas enters the desulfurization device from a bottom outlet of the SCR denitration reactor, and the desulfurized flue gas enters the chimney after reaching an emission standard. More preferably, the hot blast stove heats the flue gas to 200-300°C, preferably 200°C, 220°C, 240°C, 260°C, 280°C and 300°C; a SO2 concentration at an inlet of the SCR denitration reactor is 35-1000 milligrams per cubic □ meter (mg / m ); a working temperature of the multi-layer catalyst layer inside the SCR denitration reactor is 220-320°C; and a space velocity of the multi-layer catalyst layer used for treating the industrial flue gas is 15,000 h4-60,000 h’1, preferably 15,000 h’1, 30,000 h’1,45,000 h'1 and 60,000 h’1. The SCR denitration method provided by the present disclosure uses the heat released during CO oxidation to heat the flue gas, thereby reducing the energy consumption of part of the hot blast stove; the acidic metal is used to promote the adsorption of SO2 on the surfaces of reduction catalysts, thus inhibiting the oxidation side reaction of reducing agent CO; by-products of NO2 may be quickly captured by using storage catalysts, so as to promote its secondary decomposition. The present disclosure provides an SCR denitration system with CO as reducing agent, an application thereof and a SCR denitration method. Firstly, acidic metal is involved in the reduction catalysts in the present disclosure, which promotes SO2 adsorption and oxidation on the surfaces of the reduction catalysts, thus occupying CO adsorption sites and inhibiting the side reaction of CO oxidation, and improving NO conversion efficiency under oxygen-containing conditions. Secondly, the reduction-storage double-layer catalysts are arranged at intervals, and NO2 by-products may be quickly captured by utilizing the overflow effect of gas between the two catalysts, so as to promote the secondary decomposition thereof, and the N2 selectivity may be improved under the oxygen-containing condition. The method and the system provided by the present disclosure may obviously improve the deactivation problem of the CO-SCR denitration catalyst under the oxygen-containing condition, and the NOX removal efficiency of the IrWSiO2 catalyst reaches 85% under the condition of 5% O2, thus having broad application prospects in the field of industrial flue gas purification with high CO / NO ratio. In addition, in the denitration system provided by the present disclosure, the heating temperature of the hot blast stove is lower than that of the conventional NH3-SCR denitration device, so that the denitration system has good economy and is easy for industrial application. The accompanying drawings, which constitute a part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application, and do not constitute an improper limitation of this application. In the attached drawings: Figure 1 is a schematic structural connection diagram of an SCR denitration system with CO as a reducing agent provided in Embodiment 1 of the present disclosure. Among them, 1: dust collector; 2: hot blast stove; 3: SCR denitration reactor; 4: rectifying layer; 5: polycyclic catalyst layer; 6: ash hopper; 7: reduction catalyst; 8: storage catalyst; 9: desulfurization device; 10: chimney. Among them, the solid arrow represents the flow direction of flue gas. In the following, the technical scheme in the embodiments of the present disclosure will be clearly and completely described with reference to the attached drawings. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, but not the whole embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without creative labor belong to the scope of protection of the present disclosure. In order to make the above objects, features and advantages of the present disclosure more obvious and easier to understand, the present disclosure will be further described in detail with the attached drawings and specific embodiments. In the embodiments of the present disclosure, the amount of industrial flue gas treated is 200,000 normal cubic meters per hour (Nm / h), the concentration of NO in industrial flue gas is 400 parts per million (ppm), the concentration of CO is 8,000 ppm, the concentration of O2 is 5%, and the temperature of industrial flue gas is 120°C. Embodiment 1 An SCR denitration system with CO as a reducing agent, as shown in Figure 1, includes a dust collector 1, a hot blast stove 2, an SCR denitration reactor 3, a desulfurization device 9 and a chimney 10 connected in sequence. Specifically, the top outlet of dust collector 1 is communicated with the bottom inlet of the hot blast stove 2, the lateral outlet of the hot blast stove 2 is communicated with the top inlet of SCR denitration reactor 3, the bottom outlet of SCR denitration reactor 3 is connected with the bottom inlet of desulfurization device 9, and the top outlet of desulfurization device 9 is connected with the bottom inlet of the chimney 10. Among them, the SCR denitration reactor 3 is a fixed bed device, which is composed of rectifying layer 4, three polycyclic catalyst layers 5 and an ash hopper 6 connected in turn. The reduction catalysts and storage catalysts on the catalyst layer are distributed at intervals in multiple rings. The reduction catalysts are Ir-W / SiO2 catalyst, with an Ir loading of 0.5 wt.%, a W loading of 5 wt.% and the rest of SiO2 carrier. The storage catalysts are Ba / A^Oa catalyst, with Ba loading of 10 wt.% and the rest as carrier. The mass ratio of reduction catalysts to storage catalysts is 10:1; the reduction catalysts are required to be activated by activating gas before use; the activation treatment specifically includes the following steps: a certain amount of catalyst is placed into a tubular furnace, with 5% 1¾ activation gas introduced at a gas volume of 100 mL / min, after 1 h, the tubular furnace is heated to 400°C at a rate of 10°C / min, and after 0.5 h of activation, the temperature is cooled down under the same atmosphere, and then the introduction of H2 is stopped after reaching the room temperature, and then the catalyst is taken out. The desulfurization device is a circulating fluidized bed semi-dry desulfurization device. An SCR denitration method with CO as a reducing agent, whereby the SCR denitration system with CO as the reducing agent as described above is used, and the SCR denitration method specifically includes the following steps: (1) the industrial flue gas enters a hot blast stove from the top outlet of the dust collector, where the industrial flue gas is heated to 200°C after passing through the hot blast stove, and then the industrial flue gas enters an SCR denitration reactor from the lateral outlet of the hot blast stove, and the temperature of the flue gas at the inlet of the SCR denitration reactor is 250°C, and then the flue gas passes through a rectifying layer and a catalyst layer from top to bottom; among them, the space velocity of denitration reaction is 15,000 h’1; the industrial flue gas is more uniform after passing through the rectifying layer, and N2 and CO2 are generated after the catalyst layer reacts with the reduction-storage double-layer catalysts for many times. (2) after the reaction, the industrial flue gas enters the desulfurization device from the outlet at the bottom of the SCR denitration reactor, and the desulfurized flue gas enters the chimney after reaching the emission standard. The final NOX removal effect is 85%. Embodiment 2 An SCR denitration system with CO as a reducing agent is different from Embodiment 1 only in that the carrier in the reduction catalysts are changed to CeO2, that is, the reduction catalysts are Ir-W / CeOi catalyst. Other conditions are completely the same as those in Embodiment 1, and the NOX removal effect is 75%. Embodiment 3 An SCR denitration system with CO as a reducing agent is different from Embodiment 1 only in that the active component in the reduction catalysts are changed to Pt, that is, the reduction catalysts are Pt-W / CeO2 catalyst, and the inlet flue gas temperature of SCR denitration reactor is 230°C. Other conditions are completely the same as Embodiment 1, and the NOX removal effect is 80%. Comparative embodiment 1 An SCR denitration system with CO as a reducing agent differs from Embodiment 1 only in that the amount of stored catalyst is changed to 0 g, and other conditions are completely the same as those of Embodiment 1. There is no storage reducing agent in this comparative embodiment, and the by-product NO2 is not captured in a timely manner, which leads to a great decrease in the yield of ideal product N2 as compared with Embodiment 1, and the calculated NOX removal effect is only 30%. Comparative embodiment 2 An SCR denitration system with CO as a reducing agent is different from Embodiment 1 only in that the desulfurization device is placed in front of the SCR denitration reactor, that is, the industrial flue gas enters the SCR denitration reactor after passing through the dust collector, the hot blast stove and the desulfurization device. Other conditions are completely the same as those of Embodiment 1. In this comparative embodiment, the SO2 concentration at the inlet of the SCR denitration reactor is low, the side reaction of CO oxidation is obvious, and the denitration reaction lacks sufficient reducing agent, so the NOX removal effect is only 40%. Comparative embodiment 3 An SCR denitration system with CO as a reducing agent differs from Embodiment 1 only in that the loading of acidic metal in the reduction catalysts are changed to 0 wt.%, and other conditions are completely the same as those in Embodiment 1. This comparative embodiment lacks NO adsorption-dissociation sites, so the NOX removal effect is only 16%. By comparing Embodiments 1-3 with Comparative embodiments 1-3, it may be seen that the SCR denitration method and system with CO as reducing agent provided by the present 5 disclosure, through the addition of acidic metal and the synergistic effect between reduction catalysts and storage catalysts, have improved the problems of high cost of additional reducing agent and secondary pollution caused by NH3 escaping in the existing denitration technology, and have broad application prospects in catalytic removal of NOX from industrial flue gas. The above describes only the preferred embodiments of this application, but the protection scope 10 of this application is not limited to this. Any change or replacement that may be easily thought of by a person familiar with this technical field within the technical scope disclosed in this application should be included in the protection scope of this application. Therefore, the protection scope of this application should be based on the protection scope of the claims.

Claims

1. A selective catalytic reduction denitration system with CO as a reducing agent, comprising: a selective catalytic reduction denitration reactor, wherein the selective catalytic reduction denitration reactor comprises reduction-storage double-layer catalysts distributed at intervals in multiple rings.

2. The selective catalytic reduction denitration system with CO as the reducing agent according to claim 1, wherein an inside of the selective catalytic reduction denitration reactor comprises polycyclic catalyst layers;the reduction-storage double-layer catalysts comprise reduction catalysts filled at intervals in multiple rings in the polycyclic catalyst layers and storage catalysts;the polycyclic catalyst layers comprise 5-9 rings; anda mass ratio of the reduction catalysts to the storage catalysts is 5-10: 1.

3. The selective catalytic reduction denitration system with CO as the reducing agent according to claim 2, wherein a catalyst in the reduction catalyst layer comprises a carrier, an acidic metal and an active component, wherein the acidic metal is supported on the carrier and the active component is supported on the acidic metal.

4. The selective catalytic reduction denitration system with CO as the reducing agent according to claim 3, wherein the active components comprise any one or a combination of several of Ir groups, Pt groups, Ag groups, Au groups, Ru groups, Pd groups and Rh groups components;the acidic metal comprises any one or a combination of W groups, Mo groups and Nb groups acidic metals; andthe carrier comprises any one or a combination of Al groups, Si groups, Ti groups, Ce groups and Co groups carriers.

5. The selective catalytic reduction denitration system with CO as the reducing agent according to claim 2, wherein the storage catalysts comprise a storage component and a carrier, and the storage component is loaded on the carrier.

6. The selective catalytic reduction denitration system with CO as the reducing agent according to claim 5, wherein the storage component comprises any one or a combination of Ba groups and K groups; andthe carrier comprises any one or a combination of Al groups, Si groups, Ti groups, Ce groups and Co groups.

7. An application of the selective catalytic reduction denitration system with CO as the reducing agent according to any one of claims 1-6 in removing NOX from industrial flue gas with high CO / NO ratio under oxygen-containing conditions.

8. The application according to claim 8, wherein a concentration ratio of CO to NO is 10-200.

9. A selective catalytic reduction denitration method using CO as a reducing agent, comprising using the selective catalytic reduction denitration system using CO as the reducing agent according to any one of claims 1-6 for denitration.

10. The selective catalytic reduction denitration method with CO as the reducing agent according to claim 9, wherein following steps are comprised:introducing industrial flue gas into a dust collector, then passing through a hot blast stove, a selective catalytic reduction denitration reactor and a desulfurization device in turn, and finally discharging a treated flue gas through a chimney to complete a flue gas selective catalytic reduction denitration.

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