Flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier as well as preparation method and application of flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier

Abstract

The invention relates to the technical field of solid waste resource utilization, in particular to a flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier and a preparation method and application thereof.The modifier is prepared from, by mass, 90% of steel slag, 1%-3% of rare earth tailings and 7%-9% of electric furnace phosphorus slag; the modifier prepared by the invention can realize in-furnace modification of flue gas desulfurization circulating fluidized bed boiler ash, the obtained modified ash is low in water demand, the SO3 content is less than 3.0%, and the strength activity index is increased to 90% or above; the modifier also has combustion-supporting, desulfurization and denitrification functions, and can reduce the combustion temperature, improve the desulfurization and denitrification effect and reduce the load of a flue gas desulfurization system; the raw materials are all bulk solid wastes and do not contain carbonate, the modifier is not decomposed in the using process, CO2 is not discharged, and the modifier is green, low-carbon and environment-friendly, is beneficial to promoting ultra-low emission of a circulating fluidized bed boiler coal-fired power generation technology and is remarkable in economic effect.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste resource utilization, and in particular to a flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier and a preparation method and application thereof. Background Art

[0002] Circulating fluidized bed boiler coal-fired power generation technology is considered to be a clean coal-fired power generation technology. At present, circulating fluidized bed boiler coal-fired power generation mostly adopts a desulfurization process in which limestone desulfurizer is added into the furnace, so that the discharged ash has a higher CaO and SO3 content; CaO and SO3 in the ash generally exist in the form of undecomposed limestone, active CaO and anhydrite (CaSO4), which makes the circulating fluidized bed boiler coal-fired ash generally have water absorption, self-hardening and expansion properties, which is significantly different from traditional coal-fired ash.

[0003] Therefore, if the circulating fluidized bed boiler coal ash is used in cement concrete, it may cause problems such as high water demand, low activity, and poor long-term volume stability. At present, the annual emission of circulating fluidized bed coal ash (solid sulfur ash) is estimated to be more than 200 million tons, and its comprehensive utilization rate is far lower than that of ordinary pulverized coal furnace fly ash and bottom ash, which also makes the circulating fluidized bed boiler coal ash become the third type of bulk industrial solid waste after tailings and fly ash. In order to solve the problem of comprehensive utilization of circulating fluidized bed boiler ash, many power companies have begun to stop using the desulfurization process of adding limestone desulfurizer to the furnace alone, and choose the dual-process combination process of furnace desulfurization and flue gas desulfurization, or directly choose the flue gas desulfurization process, which can overcome the problem of traditional limestone desulfurizer decomposition and absorption of heat in the furnace, so that the combustion temperature is further reduced; at the same time, the active CaO and anhydrite content in the ash are greatly reduced, and it will not cause poor long-term volume stability when used in cement and concrete.

[0004] However, due to the lower combustion temperature, the coal powder burnout rate decreases, the ash water absorption and ignition loss both increase, and the activity decreases; in addition, due to the lack of in-furnace desulfurization, the SO2 content in the flue gas emitted after combustion increases significantly, the desulfurization system load increases, the desulfurization efficiency decreases, and the amount of desulfurization gypsum produced increases significantly; therefore, it is considered to design a flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier, which can increase the coal powder burnout rate and reduce the SO2 content in the flue gas without the need for the desulfurizer to decompose and absorb heat and produce active CaO, without increasing the combustion temperature and under the premise that the SO3 in the ash is controllable, thereby achieving the purpose of reducing the ash water demand and ignition loss and improving the activity; in view of this, we propose a flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier and its preparation method and application. Summary of the invention

[0005] The purpose of the present invention is to solve the deficiencies mentioned in the above background technology and to provide a flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier and a preparation method and application thereof.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The invention discloses an in-furnace modifier for flue gas desulfurization circulating fluidized bed boiler ash. Calculated by dry basis mass percentage, the raw materials of the modifier components include 90% of steel slag, 1%-3% of rare earth tailings and 7%-9% of electric furnace phosphorus slag.

[0008] Preferably, the mass percentage of CaO in the modifier is ≥40%, and the total mass percentage of CaO and MgO is ≥50%.

[0009] Preferably, the sum of the mass percentages of the four oxides CaO, MgO, Fe2O3 and SiO2 in the steel slag is ≥ 90%;

[0010] The mass percentage of SiO2 is less than 12%;

[0011] The mass percentage of CaO is greater than 45%, and the total mass percentage of CaO and MgO is greater than 52%;

[0012] The Fe2O3 mass percentage is greater than 15% and less than 20%.

[0013] Preferably, the rare earth tailings are feldspar rare earth ore grinding tailings, wherein the mass percentage of K2O is 3%-5%, and the mass percentage of F - The mass percentage is 0.2%-0.3%, and the mass percentage of rare earth oxide La2O3 is 0.2%-0.3%.

[0014] Preferably, the total mass percentage of the four oxides CaO, MgO, Al2O3 and SiO2 in the electric furnace phosphorus slag is ≥90%;

[0015] The mass percentage of SiO2 is less than 35%;

[0016] The mass percentage of CaO is greater than 48%, and the total mass percentage of CaO and MgO is greater than 50%;

[0017] The mass percentage of P2O5 is greater than 2.0% and less than 3.0%.

[0018] A method for preparing a flue gas desulfurization circulating fluidized bed boiler ash furnace modifier, the preparation method specifically comprises the following steps:

[0019] Step 1: Weigh various raw materials according to mass percentage;

[0020] Step 2: Mix the weighed raw materials and transport them into a tubular ball mill;

[0021] Step 3: Spray the activation agent and start grinding;

[0022] Step 4: Grind to meet the standard conditions and then store it in the warehouse to obtain the flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier.

[0023] Preferably, the amount of the activation aid accounts for 1% of the total mass of the ground raw material;

[0024] Calculated by mass percentage, the activation aid comprises: 25%-30% phosphoric acid, 15%-20% ethanol, 50% water and 3%-5% triethanolamine.

[0025] Preferably, the compliance conditions in step 4 include: grinding the raw material until the particles pass through a 300 μm sieve.

[0026] Preferably, the modifier is mixed with pulverized coal and then sprayed into a circulating fluidized bed boiler for combustion.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The raw materials used in the modifier of the present invention, steel slag, rare earth tailings and electric furnace phosphorus slag, are all bulk solid wastes, which can overcome the problem of heat absorption caused by decomposition of limestone desulfurizer in the traditional circulating fluidized bed boiler. At the same time, the desulfurization process in the furnace basically does not emit CO2, thus practicing the green and low-carbon concept;

[0029] 2. The modifier contains F, P2O5, rare earth elements, etc. brought by various raw materials, which have combustion catalysis and denitrification catalysis. It can reduce the combustion temperature of coal powder and improve the burnout rate, so that the ash loss is reduced, the unburned carbon particles are reduced, and the water demand of the ash is reduced, which can make SO2 easier to enter the silicate mineral lattice, fix sulfur and improve the activity of ash;

[0030] 3. The pulverized coal of the present invention can maintain a high burnout rate at a relatively low temperature, reduce the SO2 content in the flue gas, reduce the load of the flue gas desulfurization system, reduce the ignition loss and water demand of the ash, but greatly improve the activity, which is conducive to further improving the application value and usage of ash in the field of cement and other building materials.

[0031] 4. The present invention provides a practical in-furnace modification technology and means for circulating fluidized bed boiler ash, which will greatly improve the value and comprehensive utilization rate of ash; the boiler operating temperature is low, and the ash modification can also fix part of SO2 and catalyze nitrogen oxides to convert into nitrogen, so that the modifier has multiple functions such as ash activation, sulfur fixation, and denitrification, and is a green and low-carbon technology suitable for flue gas desulfurization circulating fluidized bed boilers. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0033] The present invention describes the above technical solution in detail through the following embodiments:

[0034] Example 1

[0035] The present embodiment provides a modifier, which is prepared based on a flue gas desulfurization circulating fluidized bed boiler ash slag furnace. The modifier is mixed with a variety of raw materials. The various raw materials, calculated by dry weight percentage, include 90% steel slag, 1% rare earth tailings and 9% electric furnace phosphorus slag; the CaO weight percentage of the modifier prepared by the present invention is ≥40%, and the CaO+MgO weight percentage is ≥50%.

[0036] In this embodiment, steel slag is solid waste generated in the steelmaking process, in which the total mass percentage of the four oxides CaO, MgO, Fe2O3, and SiO2 accounts for ≥90%; the total mass percentage of CaO+MgO is greater than 52%, and the mass percentage of CaO is greater than 45%; it should be explained that the higher the CaO and MgO content in the steel slag, the higher the theoretical absorption and fixation of SO2, the greater the amount of SO2 entering the silicate mineral and iron phase solid solution, and the higher the activity of the slag.

[0037] The total content of CaO and MgO in the steel slag of the present invention is higher than the CaO content of the desulfurizer limestone in the conventional circulating fluidized bed boiler furnace. The steel slag has high CaO and MgO contents and basically exists in the form of silicate, iron phase solid solution and free calcium oxide, and is strongly alkaline and can react quickly with acidic SO2 gas to generate calcium sulfate. Meanwhile, the silicate minerals and iron phase solid solution in the steel slag are cement clinker-like minerals, which can dissolve sulfur in the mineral lattice, thereby achieving desulfurization on the one hand and increasing the clinker mineral lattice defects on the other hand, thereby achieving mineral activation and improving the slag activity. In addition, after desulfurization of steel slag, hard gypsum and solid solution minerals are formed, and the slag basically does not contain active CaO, which reduces the water demand of the slag; the molecular weight of MgO is lower than that of CaO, that is, with the same mass content of CaO and MgO, MgO can absorb more mass of SO2; the mass percentage of SO2 in steel slag is less than 12%; due to the presence of SO2, CaO and MgO in the steel slag will combine with SO2 to form dicalcium silicate, tricalcium silicate and magnesium silicate minerals, which are relatively stable at high temperatures, and the barrier for SO2 to enter the mineral lattice is increased; if the SO2 content is too high, the content of free calcium oxide and iron phase solid solution with higher desulfurization activity will be reduced, the steel slag minerals cannot be activated, and the slag activity will be reduced.

[0038] The mass percentage of Fe2O3 in steel slag is >15% and <20%; if the iron content is too low, the iron phase solid solution content will be reduced, and the reaction product of the modifier and SO2 will be mainly anhydrite with extremely low activity; if the iron content is too high, the amount of SO2 entering the mineral lattice will increase, and the SO3 in the ash will exceed the limit, making it difficult to utilize the ash.

[0039] In this embodiment, the rare earth tailings are feldspar rare earth ore grinding tailings, containing potassium, F and rare earth elements, and phosphorus oxides in the phosphorus slag in the rare earth tailings; rare earth elements generally exist in feldspar, carbonate, and granite minerals in the form of fluorides. Fluorine is a commonly used flux and mineralizer in the high-temperature kiln industry. In cement clinker production, F can reduce the low eutectic point of tricalcium silicate minerals, so that cement clinker can be fired at a lower temperature; at the same time, when F and P coexist, they can also activate clinker minerals and enhance hydration activity; rare earth elements have stronger combustion, catalytic, fluxing and mineralization effects, and can improve the combustion effect within a trace range and promote the formation of target minerals. Therefore, the introduction of rare earth tailings can provide F and trace rare earth elements, on the one hand, to promote combustion; on the other hand, it can promote the absorption of SO2 by free calcium oxide, calcium silicate minerals and iron phase solid solution; third, it can also activate coal ash and steel slag minerals to improve the activity of ash slag.

[0040] In the present embodiment, electric furnace phosphate slag is solid waste discharged from the process of preparing yellow phosphorus by electric furnace method of phosphate ore, wherein the total mass percentage of four oxides of CaO, MgO, Al2O3 and SO2 accounts for ≥90%; the mass percentage of SO2 is <35%; the mass percentage of CaO+MgO is >50%, and the mass percentage of CaO is >48%; the mass percentage of P2O5 is >2.0% and <3.0%; the CaO content of the phosphate slag is high, and it mostly forms glass with SiO2, and mostly exists in the form of calcium silicate glass, has a low softening point, has a desulfurization effect and can absorb SO2, and the phosphate slag is also a more commonly used sintering aid in the cement clinker production industry; generally, when F and P coexist, cement clinker minerals can be formed at low temperature, and the clinker mineral lattice is activated and the activity is enhanced; the present invention mainly utilizes the phosphorus content of electric furnace phosphate slag, and cooperates with F and rare earth in rare earth tailings to achieve the effect of improving coal powder combustion and ash activation.

[0041] Specifically, the method for preparing the flue gas desulfurization circulating fluidized bed boiler ash furnace modifier in this embodiment includes the following steps:

[0042] Firstly, various raw materials are weighed according to the percentage of material mass, and 90% of steel slag, 1% of rare earth tailings and 9% of electric furnace phosphorus slag are weighed for use; the raw materials weighed according to the proportion are mixed and ground, and conveyed to the grinding system for mixed grinding. During the grinding, an activation aid accounting for 1% of the total mass of the ground raw materials is sprayed. After the raw materials are ground to meet the standards, they are discharged from the mill and stored to obtain an in-furnace modifier for flue gas desulfurization circulating fluidized bed boiler ash.

[0043] It should be noted that the activation aid in the present application comprises, by mass percentage, 25% phosphoric acid, 20% ethanol, 50% water and 5% triethanolamine; wherein phosphoric acid is a strong acid, the steel slag and phosphorus slag particles of the present invention are relatively dense, and it is difficult for the solid phase of the calcium-rich mineral CaO inside the particles to melt out, so adding phosphoric acid can corrode the particles and promote the dissolution of CaO, while making the dense particles loose and porous, increasing the contact area between the particles and SO2 and the adsorption of SO2, thereby improving the sulfur fixation efficiency; triethanolamine and ethanol have a grinding aid effect, can improve the grinding efficiency of the modifier and the particle dispersion effect, and both can also burn themselves to provide heat; ethanol and water are both diluents and dispersants, which can buffer the strong acidity of phosphoric acid and reduce the corrosion of phosphoric acid to the grinding equipment.

[0044] In this embodiment, the mixed raw materials are ground until all particles pass through a 300 μm sieve and then discharged from the mill and stored to obtain a flue gas desulfurization circulating fluidized bed boiler ash furnace modifier; the limestone particle size of the circulating fluidized bed boiler furnace desulfurizer is generally required to be 150 μm-500 μm, and the limestone of this particle size level can be suspended in the boiler furnace and has a suitable residence time; the modifier of the present invention is different from the furnace desulfurizer. The modifier has desulfurization ability, but the core purpose is to modify the ash, so the modifier of the present invention only limits the maximum particle size of the particles to no more than 300 μm; in addition, steel slag particles are dense, and its density is much higher than that of limestone. If the particle size is too high, most of the modifier particles are likely to settle to the boiler roadbed, and the fly ash modification effect is poor.

[0045] During the use of the modifier of the present invention, there is no decomposition endothermic reaction, and the main reaction that occurs is a solid phase reaction, which is mostly an exothermic process, and can further improve the combustion efficiency and thermal efficiency of the circulating fluidized bed boiler.

[0046] The application scheme of this embodiment is specifically as follows: testing the sulfur content of coal powder, calculating the amount of modifier according to the Ca / S molar ratio of 0.5:1; weighing coal powder and modifier according to the calculated dosage ratio, mixing and spraying into the circulating fluidized bed boiler for combustion.

[0047] Example 2

[0048] According to the dry basis weight percentage of the materials, 90% of steel slag, 2% of rare earth tailings and 8% of electric furnace phosphorus slag raw materials are weighed; after passing through the iron removal device, they are transported to the grinding system for mixed grinding, and an activation aid accounting for 1% of the weight of the raw materials entering the mill is sprayed during grinding. The materials are ground until all particles pass through a 300μm sieve and then discharged from the mill and stored to obtain a flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier.

[0049] Example 3

[0050] According to the dry basis weight percentage of the materials, 90% of steel slag, 3% of rare earth tailings and 7% of electric furnace phosphorus slag raw materials are weighed; after passing through the iron removal device, they are transported to the grinding system for mixed grinding, and an activation aid accounting for 1% of the weight of the raw materials entering the mill is sprayed during grinding. The materials are ground until all particles pass through a 300μm sieve and then discharged from the mill and stored to obtain a flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier.

[0051] Comparative Example 1

[0052] The comparative example does not incorporate a modifier, and only uses coal powder with a sulfur content of 1.4% as fuel.

[0053] Specifically, the modifiers prepared in Examples 1 to 3 are set aside, pulverized coal with a sulfur content of 1.4% is selected as fuel, and the amount of the modifier is calculated according to a Ca / S molar ratio of 0.5:1; pulverized coal and the flue gas desulfurization circulating fluidized bed boiler ash furnace modifier prepared in Examples 1-3 are weighed according to the calculated dosage ratio, the mixture is sprayed into a circulating fluidized bed boiler equipped with a flue gas desulfurization system, and the combustion temperature is controlled at 750°C-820°C.

[0054] Comparing the SO2 content data of flue gas with and without modifier, the SO2 concentration of flue gas before entering the desulfurization system is shown in Table 1.

[0055] Table 1:

[0056]

[0057] The physical and chemical properties of the circulating fluidized bed boiler ash after using the modifier in Example 1-3 were tested, and the collected circulating fluidized bed boiler fly ash and bottom ash were ground separately, and the fineness (45μm square hole sieve residue) was ≤12%, and then the ash SO3 content, free calcium oxide content, ignition loss, water demand ratio and 28-day activity index were tested with reference to GB / T1596 "Fly ash used in cement and concrete" for analysis. Among them, SO3 content, free calcium oxide content, ignition loss, strength activity index, see Table 2.

[0058] Table 2: Modified circulating fluidized bed boiler ash properties

[0059]

[0060] It can be seen from the data in Table 1 above that the flue gas desulfurization circulating fluidized bed boiler ash furnace modifier prepared by the present invention has a certain desulfurization and sulfur fixation effect. Compared with the control group without the modifier, the flue gas SO2 content is reduced by more than 15%, which will greatly reduce the pressure of the flue gas desulfurization system;

[0061] From the data in Table 2 above, it can be seen that after adding the modifier, the sulfur trioxide content in the fly ash and the bottom ash has increased to a certain extent, which is due to the desulfurization function of the modifier; the free calcium oxide in the ash has always been in a relatively low content range, which is because the modifier does not contain limestone, and the amount of modifier added is lower than the Ca / S molar ratio required for theoretical complete desulfurization, so the free calcium oxide content in the ash is low; the ash loss is greatly reduced compared with the ash without the modifier, which is due to the modifier's combustion-supporting and combustion catalytic effects, and the coal powder burnout rate is high; the water demand ratio of the modified ash is significantly reduced, one is that the ash residual carbon is low, and the other is that no active CaO is produced, so the water demand is reduced. After adding the modifier, the ash strength activity index is greatly improved, one is that SO2 enters the aluminosilicate lattice, the mineral is activated, and the hydration activity is improved; the other is that the coal powder burnout rate is high and the combustion temperature is relatively low, which ensures the full activation and decomposition of the aluminosilicate minerals in the coal powder.

[0062] According to this scheme, after using the modifier, the water demand ratio of the modified ash is ≤105%, the SO3 content is <3.0%, and the strength activity index is >90%.

[0063] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A flue gas desulfurization circulating fluidized bed boiler ash furnace modifier, characterized in that: Calculated by mass percentage, the raw materials of each component of the modifier include 90% of steel slag, 1%-3% of rare earth tailings and 7%-9% of electric furnace phosphorus slag.

2. The flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier according to claim 1, characterized in that: The mass percentage of CaO in the modifier is ≥40%, and the total mass percentage of CaO and MgO is ≥50%.

3. The flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier according to claim 2, characterized in that: The total mass percentage of the four oxides of CaO, MgO, Fe2O3 and SiO2 in the steel slag is ≥ 90%; The mass percentage of SiO2 is less than 12%; The mass percentage of CaO is greater than 45%, and the total mass percentage of CaO and MgO is greater than 52%; The Fe2O3 mass percentage is greater than 15% and less than 20%.

4. The flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier according to claim 2, characterized in that: The rare earth tailings are feldspar rare earth ore grinding tailings, wherein the mass percentage of K2O is 3%-5%, F - The mass percentage is 0.2%-0.3%, and the mass percentage of rare earth oxide La2O3 is 0.2%-0.3%.

5. The flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier according to claim 2, characterized in that: The total mass percentage of the four oxides of CaO, MgO, Al2O3 and SiO2 in the electric furnace phosphorus slag is ≥90%; The SiO2 mass percentage is less than 35%; The mass percentage of CaO is greater than 48%, and the total mass percentage of CaO and MgO is greater than 50%; The mass percentage of P2O5 is greater than 2.0% and less than 3.0%.

6. A method for preparing a flue gas desulfurization circulating fluidized bed boiler ash furnace modifier, applicable to the modifier according to any one of claims 1 to 5, characterized in that: The preparation method specifically comprises the following steps: Step 1: Weigh various raw materials according to mass percentage; Step 2: Mix the weighed raw materials and transport them into a tubular ball mill; Step 3: Spray the activation agent and start grinding; Step 4: Grind to meet the standard conditions and then store it in the warehouse to obtain the flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier.

7. The method for preparing the flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier according to claim 6, characterized in that: The amount of the activation aid is 1% of the total mass of the ground raw materials; Calculated by mass percentage, the activation aid comprises: 25%-30% phosphoric acid, 15%-20% ethanol, 50% water and 3%-5% triethanolamine.

8. The method for preparing the flue gas desulfurization circulating fluidized bed boiler ash in-furnace modifier according to claim 6, characterized in that: The compliance conditions in step 4 include: grinding the raw materials until the particles pass through a 300 μm sieve.

9. An application of a flue gas desulfurization circulating fluidized bed boiler ash furnace modifier, applicable to the modifier according to any one of claims 1 to 8, characterized in that: The modifier is used for mixing with coal powder and then sprayed into a circulating fluidized bed boiler for combustion.

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