Background
Under the background of the era of global warming and ecological environment deterioration, "low carbon economy" based on low energy consumption and low pollution has become the focus of global attention. The steel industry is a basic industry in an industrial system in China, but is also a typical high-energy-consumption and high-pollution industry, and the energy consumption of the steel industry accounts for about 15.25 percent of that of the whole industrial department; the exhaust emission accounts for 16% of the total national industrial emission; the discharged pollution load accounts for about 10% of the total industrial discharge.
The iron-making system of iron and steel enterprises in China mainly adopts a sintering-blast furnace process, wherein the sintering is a process of sintering iron ores, fluxes and fuel ingredients at a high temperature on a sintering machine to form ores after mixing. The sintering process is a main pollution source of the smoke pollutants in the steel industry, the sintering waste gas accounts for 40% of the total waste gas in the steel industry, and the discharged smoke contains various pollutants such as SOx, NOx and the like, so that the treatment difficulty is high.
The emission standard of sintering flue gas pollutants in China is increasingly strict, and from 1 month and 1 day of 2015, China begins to implement a new emission standard of sintering (pelletizing) pollutants in the iron and steel industry, and dust is regulated to be less than or equal to 50mg/Nm3,SO2≤200mg/Nm3,NOx≤300mg/Nm3Dioxin is less than or equal to 0.5ng/Nm3. The national environmental protection department of 6 months in 2017 issues a revised notice of 'emission standards of atmospheric pollutants in the iron and steel sintering and pelletizing industry', and particulate matters and SO are released2NOx emission limit is adjusted to 20mg/Nm3、50mg/Nm3、100mg/Nm3Further stricter the pollutant discharge limit and obviously increased the difficulty of treating the sintering flue gas.
The sintering flue gas treatment in China mainly adopts a single pollutant removal method at present. The flue gas desulfurization mainly adopts limestone-gypsum method, ammonia-ammonium sulfate method, circulating fluidized bed method and the like, and the desulfurization rate can reach more than 90%. The sintering flue gas desulfurization technology is mature in China, and flue gas desulfurization facilities are built in most sintering plants. Therefore, on the basis of desulfurization, how to realize high-efficiency denitration has great significance for treating sintering flue gas pollutants.
The sintering flue gas denitration technology mainly adopts a selective catalytic reduction method (SCR), a non-catalytic reduction method (SNCR), an SCR/SNCR mixed method and the like, and the SCR denitration industrial demonstration of the sintering flue gas is first realized in China. At present, there are two kinds of technical scheme in desulfurization combination SCR denitration, firstly desulfurization afterwards denitration, because desulfurization back sintering flue gas temperature is low, can't reach the required reaction temperature of SCR denitration, need improve sintering flue gas temperature through external heating, lead to that the denitration energy consumption is high, equipment is huge, running costHigh. Secondly, denitration and desulfurization are carried out firstly, and high-concentration SO in the flue gas2Alkali metals, heavy metals and the like have serious poisoning effects on the catalyst, so that the catalyst is easy to lose efficacy, and the catalyst is large in use amount and high in operation cost.
Therefore, although the desulfurization and SCR denitration technologies are mature, the desulfurization and SCR denitration technologies are not organically connected in the sintering flue gas treatment. How to solve the influence of low flue gas temperature and poisoning component on the catalyst, on the basis of guaranteeing desulfurization and denitrification efficiency, the pollutant is economically and efficiently treated, and the method has important practical significance on sintering clean production.
Disclosure of Invention
Aiming at the problems of incompatible desulfurization and denitrification in the prior art of combining desulfurization and denitrification of sintering flue gas with SCR (selective catalytic reduction) denitrification, such as high energy consumption in desulfurization before denitrification, catalyst poisoning in desulfurization before denitrification and the like, the invention aims to provide a method for concentrated and efficient desulfurization and denitrification of sintering flue gas, which is characterized in that SO is used for removing sulfur and denitrification2And NOx are respectively discharged in a specific area of the sintering machine, and are respectively and independently subjected to desulfurization and denitration, so that the compatibility of desulfurization and denitration is realized while the treatment capacity of flue gas is reduced, and therefore, the flue gas is economically and efficiently denitrated on the basis of the existing desulfurization process.
In order to achieve the technical purpose, the invention provides a method for concentrated and efficient desulfurization and denitrification of sintering flue gas, which is characterized in that the flue gas of a sintering machine along the direction from a feeding end to a discharging end is sequentially divided into five parts of flue gas, namely a front section, a front middle section, a middle tail section and a tail section, and the length ratio of the front section, the front middle section, the middle tail section and the tail section is 2-4: 4-6: 8-10: 3-5: 2-4; in the sintering process, the front middle section smoke is circulated to the middle section material surface for cyclic utilization, and meanwhile, the hot waste gas of the circular cooler is added, so that the smoke O circularly entering the middle section material surface2The content is more than 16 percent, and the temperature is higher than 100 ℃; after the heat exchange is carried out between the middle section flue gas and the middle tail section flue gas, the temperature of the middle section flue gas is raised to be higher than 120 ℃, and then the middle section flue gas and the tail section flue gas are converged and enter a denitration device for denitration; and the middle-tail section flue gas enters a desulfurization device for desulfurization after heat exchange.
In the preferred scheme, the middle section flue gas and the tail section flue gas are converged, so that the temperature of the converged flue gas is higher than 250 ℃, and the converged flue gas enters a denitration device for denitration.
In a preferred scheme, the denitration device adopts an SCR reactor for denitration.
In a preferable scheme, the desulfurization device adopts one of a lime-gypsum method, an ammonia method, a magnesium method and a fluidized bed dense-phase dry tower method for desulfurization.
The preferred scheme, desulphurization unit exhaust flue gas, denitrification facility discharge and converge with the anterior segment flue gas, discharge through the chimney.
The key of the method for concentrated and efficient desulfurization and denitration of sintering flue gas is that SOx and NOx are concentrated in flue gas in a specific area section and are subjected to concentrated desulfurization and denitration treatment respectively, so that the defect that in the prior art, desulfurization is performed firstly and then denitration is performed, the energy consumption is high, and the problem that catalyst poisoning is easily caused by desulfurization is also solved. At the same time, adding SO2And NOx are respectively enriched and discharged in a specific area of the sintering machine, so that the treatment capacity of the flue gas is greatly reduced, and the flue gas is economically and efficiently desulfurized and denitrated.
The invention relates to a method for concentrated and efficient desulfurization and denitrification of sintering flue gas, which is mainly characterized in that flue gas generated in each area in a sintering machine in the sintering process is treated by different methods correspondingly, and front-section flue gas SO is treated2And NOx content is low, and the temperature is low, can directly discharge, and preceding middle section NOx content improves relative anterior segment, but directly carry out denitration treatment and can increase flue gas handling capacity, circulate it to sintering machine middle section reutilization, can be with NOxThe smoke gas is enriched in the middle section of the sintering machine and is converted into high NOx content and low SO content2And (4) carrying out denitration treatment on the flue gas with the content in a centralized manner. In the process of denitration by adopting the SCR reactor, the middle section flue gas is difficult to reach more than 250 ℃, and the denitration requirement of the SCR reactor is difficult to meet. While the middle-tail section flue gas is enriched with alkali metal and SO2The catalyst is directly subjected to desulfurization treatment, so that the toxic action of alkali metal on the catalyst of the SCR reactor is avoided.
Sintering according to the inventionIn the flue gas centralized efficient desulfurization and denitrification method, the front and middle section flue gas is circulated to the charge level of the sintering machine for cyclic utilization, the circulating smoke hood covers the middle section of the sintering machine and is added with the hot waste gas of the circular cooler, so that the gas O in the circulating smoke hood2The content is more than 16 percent, and the temperature is higher than 100 ℃. And NOx is intensively discharged into the flue gas of the middle section of the sintering machine through flue gas circulation.
Compared with the prior art, the technical scheme of the invention has the advantages that:
① NOx is intensively discharged into the middle section flue gas of the sintering machine through a flue gas circulation technology, and only the flue gas with high NOx concentration needs to be subjected to denitration treatment, so that the flue gas treatment capacity is greatly reduced.
② the smoke temperature before denitration can reach more than 250 ℃ by the internal heat exchange of the middle section smoke and the middle and tail section smoke and the combination of the tail section high temperature smoke without external heating of the smoke, thereby meeting the temperature requirement of SCR high efficiency denitration.
③ high SO2The flue gas is independently desulfurized, and the treatment capacity of the desulfurized flue gas is reduced to about 1/6 of the traditional process, so that the operating cost of the desulfurization process is greatly reduced.
④ high NOx flue gas and high SO2The flue gas is separately and intensively treated, SO that SO is avoided2The poisoning effect of alkali metals such as K, Na on the denitration catalyst is greatly reduced, and the denitration efficiency can be further improved.
⑤ most sintering plants can use the existing desulfurization facilities, only need to add a relatively small denitration device, and can realize high-efficiency desulfurization and denitration without external heat supply, the desulfurization rate reaches more than 95%, the denitration rate reaches more than 70%, meanwhile, the flue gas treatment capacity is greatly reduced, the desulfurization flue gas treatment capacity is reduced by more than 70%, the denitration flue gas treatment capacity is reduced by 50%, the investment cost of the denitration facilities is reduced by 35-50%, and the desulfurization and denitration operation cost is reduced by 30-40%.
Example 1
Dividing the sintering machine into five parts of a front section, a front middle section and a middle section, a middle tail section and a tail section along the length direction (namely from a material feeding end to a material discharging end), wherein the length ratio is 3:5:9:4:3, and during the sintering process, the particles of the smoke gas at the front section are less than or equal to 20mg/Nm3、SO2≤50mg/Nm3、NOx≤100mg/Nm3The gas can be directly introduced into a chimney for emission, the front middle section circulates the gas to the charge level of the sintering machine for cyclic utilization, the circulating gas hood covers the middle section of the sintering machine and is added with hot waste gas of the circular cooler, so that the gas O in the circulating gas hood2The content is 17 percent and the temperature is 110 ℃; the NOx in the middle section smoke is more than 200mg/Nm3After heat exchange is carried out between the tail section flue gas and the middle section flue gas, the tail section flue gas is heated to 120 ℃, then the tail section flue gas and the tail section flue gas are converged, the temperature is increased to 250 ℃, after dust removal, the tail section flue gas enters a denitration device for denitration by adopting an SCR mode, and finally the tail section flue gas reaches the emission standard and is conveyed to a chimney for emission. The smoke particulate matters in the middle and tail sections are more than 50mg/Nm3、SO2>200mg/Nm3、NOx≤100mg/Nm3Directly enters a desulphurization device after dust removal, and is desulfurized by adopting an ammonia process, and the desulfurized flue gas is conveyed to a chimney for emission. The temperature of the tail section flue gas is more than 300 ℃, the tail section flue gas and the middle section flue gas are converged, and the temperature of the mixed flue gas is increased to 250 ℃ so that the mixed flue gas meets the SCR denitration requirement.
Compared with the series-connection desulfurization and denitrification process flow, the method disclosed by the invention has the advantages that the desulfurization rate reaches 95%, the denitrification rate reaches 70%, the flue gas treatment capacity is greatly reduced, the desulfurization flue gas treatment capacity is reduced by 70%, the denitrification flue gas treatment capacity is reduced by 50%, the investment cost of a denitrification facility is reduced by 40%, and the desulfurization and denitrification operation cost is reduced by 35%.