CN113975956A

CN113975956A - Two-stage sectional desulfurization and denitrification system and method for flue gas

Info

Publication number: CN113975956A
Application number: CN202111365817.5A
Authority: CN
Inventors: 彭振超; 韩默先; 韩硕怀; 李增杰; 王永跃; 张合芹; 王钢; 赵泊然
Original assignee: Xingtai Runtian Environmental Protection Technology Co ltd
Current assignee: Xingtai Runtian Environmental Protection Technology Co ltd
Priority date: 2021-11-05
Filing date: 2021-11-05
Publication date: 2022-01-28

Abstract

A flue gas two-stage sectional desulfurization and denitrification system and a method belong to the technical field of atmospheric pollution treatment. Method for removing NO and SO in flue gas by sodium chlorite₂By oxidation to NO₂And SO₃By reacting NO with magnesium hydroxide₂And SO₃The magnesium nitrate and magnesium sulfate solution is absorbed and converted, and the oxidation absorption process is graded, segmented, ordered and crossed, so that the aims of high-efficiency desulfurization and denitrification are fulfilled. Flue gas waste heat evaporation and purification flue gas desulfurization and denitration liquid escape scrubbing gasThe recycling means realizes a closed loop circulation system without solid waste and waste water discharge and system water balance on the premise of ultra-clean discharge of the flue gas, and is integrated with the desulfurization scientific association on the basis of overcoming the technical problem of low-temperature denitration of the flue gas, so that the desulfurization and the denitration complement each other, and the recycling means has important guiding significance for treating the low-temperature desulfurization and denitration flue gas.

Description

Two-stage sectional desulfurization and denitrification system and method for flue gas

Technical Field

The invention belongs to the technical field of atmospheric pollution treatment, and particularly relates to a two-stage sectional desulfurization and denitrification system and method for flue gas.

Background

The mainstream processes for industrial flue gas denitration at present are a Selective Catalytic Reduction (SCR) method, a selective non-catalytic high-temperature reduction (SNCR) method, an ozone oxidation and absorption method, a sodium hypochlorite and sodium chlorite oxidation and absorption method and the like. The mainstream process of flue gas desulfurization selects a limestone-gypsum method, and additionally comprises desulfurization processes such as a magnesium method, an ammonia method, a double-alkali method, a dry method/semi-dry method and the like. The process methods are mature, the equipment is matched, and the flue gas desulfurization and denitrification basically meet the environment-friendly requirement of ultralow emission. However, there are also many problems, mainly expressed as: most byproducts form solid wastes due to poor quality, the hidden danger of polluting underground water due to a large amount of soluble salt-containing wastewater generated by desulfurization and denitrification, the pollution of escaping ammonia, the hidden pollution caused by Condensable Particulate Matters (CPM) formed by the emission of aerosol generated by flue gas carrying desulfurization liquid, the high operation cost of desulfurization and denitrification, the burden of enterprises and the like are caused. To SO₂And the treatment of low NOx concentration, the flue gas generated by the heat recovery of blast furnace gas, coking gas, biomass, low-calorific-value solid waste fuel and the like in a steel mill, and the conventional method such as a limestone-gypsum method is not suitable, and the conventional method cannot be applied due to the fact that the flue gas temperature is low and cannot support the denitration process technical conditions of SNCR and SCR.

Disclosure of Invention

The invention aims to provide a system and a method for two-stage segmented desulfurization and denitrification of flue gas, wherein the desulfurization and denitrification are synchronously and alternately carried out in order, and sodium chlorite is used for removing sulfur from the flue gasNO and SO₂Efficient oxidation to NO₂And SO₃Magnesium hydroxide rapidly converts NO₂And SO₃Absorbed and converted into MgSO₄And, Mg (NO)₃)₂NO in solution, flue gas_XThe calcium nitrate and the magnesium nitrate are converted into high-quality chemical-grade gypsum, and the system forms a closed-loop balance system, so that zero discharge of waste residues and wastewater is realized on the premise of ensuring ultralow emission of desulfurization and denitrification.

In order to achieve the purpose, the invention provides a two-stage sectional flue gas desulfurization and denitrification system, which comprises equipment and an operation unit which are sequentially matched and connected through components such as pipelines, pipe fittings and the like according to a chemical reaction process, and is characterized in that:

p1: a desulfurization and denitrification subsystem which consists of a primary desulfurization and denitrification tower, a primary circulating desulfurization and denitrification pump, an oxidizing liquid storage tank, an oxidizing liquid supply pump, a secondary desulfurization and denitrification pump, a magnesium hydroxide slurry storage tank, a secondary desulfurization and denitrification transfer pump and a secondary desulfurization and denitrification tower 8 in sequence;

p2: calcium sulfate CaSO sequentially consisting of purification and impurity removal unit, NS separation unit, filtering and washing unit and drying and crushing unit₄·2H₂An O subsystem;

p3: the magnesium hydroxide pulping subsystem consists of a digestion unit, a purification unit, a regenerated magnesium hydroxide unit, a filtering unit and a pulp mixing unit in sequence;

p4: an industrial NaCL subsystem which consists of a first-stage evaporation unit, a first-stage crystallization unit and a first-stage centrifugal separation unit 20 in sequence;

p5: calcium magnesium nitrate CaMgN sequentially consisting of a secondary cooling crystallization unit and a clean water pump₄O₁₂A subsystem;

P6：

the first-stage desulfurization and denitrification tower comprises a flue gas inlet, a first-stage flue gas outlet, a first-stage desulfurization and denitrification liquid outlet, a tower middle atomization sprayer and a tower upper atomization sprayer, wherein the first-stage flue gas outlet is connected with the first-stage flue gas inlet of the second-stage desulfurization and denitrification tower;

the oxidizing liquid storage tank comprises a sodium chlorite solution inlet and an outlet connected with an oxidizing liquid supply pump inlet;

the second-stage desulfurization and denitrification pump comprises an inlet and an outlet, wherein the inlet is connected with the outlet of the magnesium hydroxide slurry storage tank, and the outlet is connected with the inlet of the atomization sprayer of the second-stage desulfurization and denitrification tower;

the magnesium hydroxide slurry storage tank comprises an inlet and an outlet, wherein the inlet is connected with the outlet of the size mixing unit, and the outlet is connected with the inlet of the secondary desulfurization and denitrification pump;

the second-stage desulfurization and denitrification transfer pump also comprises an inlet, and the inlet is connected with a second-stage desulfurization and denitrification liquid outlet at the bottom of the second-stage desulfurization and denitrification tower;

second grade SOx/NOx control tower including one-level flue gas entry, clean flue gas (second grade flue gas) export, second grade SOx/NOx control liquid export and atomizing spray thrower, one-level flue gas entry link to each other with one-level SOx/NOx control tower one-level flue gas export, second grade SOx/NOx control liquid export shift pump import and link to each other with second grade SOx/NOx control, atomizing spray thrower import and second grade SOx/NOx control pump export link to each other.

The purification and impurity removal unit comprises an inlet, an outlet and a filtrate port, wherein the inlet is connected with a first-stage desulfurization and denitrification liquid outlet of the first-stage desulfurization and denitrification tower, and the filtrate port is connected with an inlet of the NS separation unit;

the NS separation unit also comprises a calcium magnesium nitrate solution (calcium nitrate or salt-containing calcium magnesium nitrate) inlet and a slurry outlet, wherein the calcium magnesium nitrate solution inlet is connected with the filtrate outlet of the filtering unit, and the slurry outlet is connected with the inlet of the filtering and washing unit;

the filtering and washing unit also comprises a clear water (condensed water when steam is used) injection port, a filtrate outlet, a washing liquid outlet and a filter material outlet, wherein the filtrate outlet is connected with the filtrate inlet of the regenerated magnesium hydroxide unit, the washing liquid outlet is connected with the washing liquid inlet of the size mixing unit, and the filter material outlet is connected with the inlet of the drying and crushing unit;

the drying and crushing unit also comprises a gypsum outlet;

the digestion unit comprises an ash inlet, a water inlet and a mortar outlet, wherein the water inlet is connected with the outlet of the clean water pump, and the mortar outlet is connected with the inlet of the purification unit;

the purification unit also comprises a discharge hole and a refined pulp outlet, and the refined pulp outlet is connected with a refined pulp inlet of the regenerated magnesium hydroxide unit;

the regenerated magnesium hydroxide unit also comprises a filtrate inlet and a slurry outlet, wherein the filtrate inlet is connected with the filtrate outlet of the filtering and washing unit, and the slurry outlet is connected with the inlet of the filtering unit;

the filter unit also comprises a filtrate outlet and a filter material outlet, the filtrate outlet is respectively connected with the inlet of the first-stage evaporation unit and the inlet of the calcium nitrate solution of the NS separation unit, and the filter material outlet is connected with the inlet of the size mixing unit;

the slurry mixing unit also comprises a washing liquid inlet and a slurry outlet, wherein the washing liquid inlet is connected with the washing liquid outlet of the filtering and washing unit, and the slurry outlet is connected with the inlet of the magnesium hydroxide slurry storage tank;

the first-stage evaporation unit comprises a calcium magnesium nitrate solution inlet, a steam inlet, a condensed water outlet and a concentrated solution outlet, and the concentrated solution outlet is connected with the inlet of the first-stage crystallization unit;

the first-stage crystallization unit also comprises a discharge port, and the discharge port is connected with the inlet of the first-stage centrifugal unit;

the first-stage centrifugal unit also comprises an industrial NaCL outlet and a mother liquid outlet, and the mother liquid outlet is connected with the inlet of the second-stage cooling crystallization unit;

the second-stage cooling crystallization unit also comprises a calcium magnesium nitrate outlet and a clean water outlet, and the clean water outlet is connected with the inlet of the clean water pump.

Optimally, the number of the atomizing sprayers at the upper part of the tower or/and the atomizing sprayers at the middle part of the tower is set to be more than or equal to 1 layer.

According to the technical scheme, the two-stage sectional desulfurization and denitrification system for the flue gas adopts steam as the first-stage evaporation unit, so that other available combustion coal gas, electricity and other heat sources can be selected according to local conditions in practical application.

Preferably, a flue gas waste heat evaporation tower is further connected in series in front of the first-stage desulfurization and denitrification tower, the flue gas waste heat evaporation tower comprises a flue gas inlet, a low-temperature flue gas outlet, a concentrated solution outlet and an atomization sprayer, the low-temperature flue gas outlet is connected with the low-temperature flue gas inlet at the bottom of the first-stage desulfurization and denitrification tower, the concentrated solution outlet is connected with the inlet of the first-stage crystallization unit, and the inlet of the atomization sprayer is connected with the filtrate outlet of the filtration unit;

preferably, the number of layers of the atomizing sprayer is more than or equal to 1.

The technical scheme of the two-stage sectional flue gas desulfurization and denitrification system can remove SO in flue gas₂And NOx can be effectively removed, and the current environment-friendly standard requirement of ultralow emission is met. However, as with all wet desulfurization and denitration processes, the above scheme still remains at a level of PM ≥ 2.5, and for aerosol with PM ≤ 1, the salt-containing droplets are very fine, that is: the high-content soluble salt desulfurization and denitrification liquid is entrained with fuel gas and discharged in an aerosol form (CPM), and the method is also to be perfected.

Therefore, preferably, an escape scrubbing recovery tower is further connected in series behind the second-stage desulfurization and denitrification tower of the two-stage segmented desulfurization and denitrification system for flue gas, and the escape scrubbing recovery tower comprises a second-stage flue gas inlet, an ultra-clean flue gas outlet, a scrubbing liquid outlet and an atomization sprayer; the second-stage flue gas inlet is connected with the clean flue gas outlet of the second-stage desulfurization and denitrification tower, the scrubbing liquid outlet is connected with the clear water inlet of the digestion unit, and the inlet of the atomization sprayer is connected with the outlet of the clear water pump.

In order to achieve better desulfurization and denitrification effects, sodium chlorite and Mg (OH) are improved₂The desulfurization and denitrification are completed in two stages, and the first-stage desulfurization and denitrification is completed in a first-stage desulfurization and denitrification tower. The sodium chlorite denitration liquid is sent to the middle part of the first-stage desulfurization and denitration tower by an oxidizing liquid pump, and is sprayed and absorbed by an atomizing sprayer in the middle part of the tower, so that the sodium chlorite descends in fine fogdrops and goes from the bottomPart of the upward flue gas contacts with SO in the flue gas₂Reacts with NOx to form SO₃、NO₂Wherein unreacted NaCIO₂And NaCIO₂Dissolving NaCL generated by decomposition in the first-stage desulfurization and denitrification liquid. Controlling NaCIO₂The concentration and the spraying amount of the flue gas to ensure the denitration rate of the flue gas.

The desulfurization solution of the first-stage desulfurization and denitrification tower is injected by a second-stage desulfurization and denitrification solution supplied by a second-stage desulfurization and denitrification transfer pump of the second-stage desulfurization and denitrification tower and a first-stage desulfurization and denitrification circulating pump and contains NaCIO₂And a recycled slurry of magnesium hydroxide. The secondary desulfurization and denitrification liquid contains Mg (OH) which is not dissolved and absorbed₂Firstly, fine droplets descend through the atomizing sprayer at the upper part of the tower to contact with ascending flue gas entering from the bottom of the tower and passing through the atomizing sprayer at the middle part of the tower, and NaCIO sprayed by the atomizing sprayer at the middle part of the tower₂By oxidation to SO₃、NO₂Absorbed and converted into MgSO₄And Mg (NO)₃)₂Generation of MgSO₄And Mg (NO)₃)₂The solution continuously goes down along with the secondary desulfurization and denitrification liquid, passes through an atomization sprayer in the middle of the tower to continuously perform desulfurization and denitrification, and falls into and is dissolved in the primary desulfurization and denitrification liquid; secondly, the first-stage desulfurization and denitrification liquid contains incomplete decomposed NaCIO₂And incompletely reacted Mg (OH)₂Repeatedly pumping the smoke into an atomizing sprayer at the upper part of the tower through a first-stage desulfurization and denitrification circulating pump, contacting fine fog drops with upward smoke to implement cross desulfurization and denitrification, and repeatedly carrying out desulfurization and denitrification on NO and SO in the smoke₂By oxidation to NO₂And SO₃And rapidly absorbed by magnesium hydroxide, NO generated by disproportionation reaction is timely absorbed by NaCIO₂By oxidation to NO₂Absorbed by magnesium hydroxide until the desulfurization and denitrification are finished to form a desulfurization and denitrification finished liquid, and the desulfurization and denitrification finished liquid is discharged from a first-stage desulfurization and denitrification finished liquid outlet at the bottom of the tower; the desulfurization liquid and the desulfurization and denitrification liquid are pressed into the upper part of the first-stage desulfurization and denitrification tower under the action of the first-stage desulfurization and denitrification circulating pump, and downward fog drops sprayed by two or more layers of atomizing sprayers are in reverse contact with flue gas ascending from the bottom to oxidize SO in the flue gas₂And NO₂Absorption reaction is carried out to generate MgSO₄And Mg (NO)₃)₂. First-level desulfurization and denitrification controlThe pH value of the circulating desulfurization solution is about 6, and the slightly acidic medium solution is more favorable for absorbing NO₂The disproportionation reaction is carried out, NO is generated in the disproportionation reaction, and the NO can be mixed with NaCLO dissolved in the circulating desulfurization and denitrification liquid₂Continue to react and convert into NO₂Thereby achieving the effect of oxidizing and absorbing NO.

The first-stage desulfurization and denitrification tower uses a second-stage desulfurization and denitrification liquid discharged from the bottom of the second-stage desulfurization and denitrification tower and containing unreacted Mg (OH)₂Can continue to react with SO in the flue gas₃And NO₂And (5) reaction and absorption. The acidic solution of the first-stage desulfurization and denitrification tower with the pH controlled to be about 6 is more beneficial to Mg (OH)₂The dissolution is complete. The first-stage desulfurization and denitrification tower completion liquid is discharged from the bottom of the tower and sent to a purification and impurity removal unit, and finally sulfur (SO 4) in the flue gas is removed^＝) Is removed from the system in the form of gypsum which precipitates into gypsum, and simultaneously removes NOx and Mg (OH) from the flue gas₂The decomposed NaCL is removed from the system in a crystallization mode of calcium nitrate, magnesium nitrate and sodium chloride solution.

For guaranteeing the desulfurization efficiency of flue gas, magnesium hydroxide slurry is adopted in the desulfurization of the second-stage desulfurization and denitrification tower, the pH value of the second-stage desulfurization and denitrification tower is controlled to be 7-8, and the method is favorable for SO₂And NO₂The removal was complete, although higher pH slurries resulted in Mg (OH)₂The dissolution is incomplete, but the solution can be sent into a first-stage desulfurization and denitrification tower to continue desulfurization, denitrification and dissolution.

Two-stage sectional desulfurization and denitrification can better ensure SO in flue gas₂And NOx removal rate, and can also improve Mg (OH)₂Three-phase solution conversion of solid, liquid and gas to increase Mg (OH)₂The utilization rate of the desulfurization solution is reduced, and the discharge amount of the subsequent desulfurization solution purification waste residue is reduced.

In order to reduce the system resistance, the two-stage desulfurization and denitrification tower is completed by adopting hollow tower atomization spraying.

Preferably, the control of one-level SOx/NOx control tower PH is about 6, and second grade SOx/NOx control tower PH value is between 7 ~ 8, and the two-stage SOx/NOx control tower all adopts empty tower atomizing to spray and accomplishes, and its atomizing spray thrower sets up quantity and is 2 layers or multilayer.

For the convenience of understanding the present invention, the calcium nitrate solution according to the present invention contains soluble salt components such as magnesium nitrate and sodium chloride, and thus it is stated that the calcium nitrate solution, the calcium magnesium nitrate solution and the calcium magnesium nitrate solution containing salt according to the present invention are the same component substance.

In order to achieve the above purpose, the invention also provides a two-stage sectional desulfurization and denitrification method for flue gas, which comprises the operating steps matched in sequence according to the chemical reaction process, and is characterized in that:

the method comprises the following steps: purification of desulfurization and denitrification liquid

The first-stage desulfurization and denitrification completion liquid of the first-stage desulfurization and denitrification tower enters a purification and impurity removal unit through a first-stage desulfurization and denitrification liquid outlet, and suspended insoluble magnesium-containing calcium fly ash (coal ash) is filtered to obtain relatively pure MgSO (magnesium sulfate) -containing fly ash₄、Mg(NO₃)₂And soluble salt mixed semen with NaCL as main component;

step two: NS isolation

Pumping the semen obtained in the step one into an NS separation reactor, adding a proper amount of the semen into a filtering unit, wherein the filtrate outlet contains Ca (NO)₃)₂NaCL and small amounts of Mg (OH)₂The filtrate (calcium magnesium nitrate solution) of (4), MgSO in the mixed semen₄With Ca (NO) in the filtrate₃)₂Reaction takes place to precipitate gypsum (CaSO)₄) And obtaining Mg (NO)₃)₂The solution is filtered and washed by a filtering and washing unit, and the filtrate is Mg (NO)₃)₂The solution is sent to a regenerated magnesium hydroxide unit, and the filter material is CaSO₄The wet material is dried and crushed by a drying and crushing unit to obtain high-quality chemical-grade gypsum CaSO₄·2H₂O products;

step three: regenerated magnesium hydroxide

Adding magnesium-containing lime and dolomitic lime into a slaking unit lime slaking reactor according to a certain proportion, slaking the lime with clear water pumped by a clear water pump, and slaking the lime and the dolomitic lime into Ca (OH)₂And Mg (OH)₂The slurry is screened out by a purification unit to remove larger-particle impurities and hydrocyclone to separate out finer-particle impurities to obtain purer magnesium-containing lime slurry, and the lime slurry is pumped into a precipitation reactor of a regenerated magnesium hydroxide unit to react with Mg (NO) obtained in the step two₃)₂Solution reaction, regeneration and precipitation of Mg (OH)₂And regenerating to obtain Ca (NO)₃)₂Filtering the solution by a filter unit, wherein the filter material is Mg (OH)₂The wet material is sent to a size mixing unit, the washing liquid of the filtering and washing unit in the step two is used for mixing size, then the wet material is sent to a magnesium hydroxide size storage tank, and the filtrate is Ca (NO)₃)₂、Mg(NO₃)₂The NaCL solution is mainly sent to the NS separation unit in the second step for precipitation and separation of gypsum, and the rest is sent to the first-stage evaporation unit for concentration;

step four: separation of industrial NaCL

Concentrating the filtrate obtained by the filtering unit in the step three to a saturated state close to NaCL in a first-stage evaporation unit, then sending the filtrate to a first-stage crystallization unit for cooling crystallization, separating out most of NaCL crystals by utilizing the dissolving characteristic of NaCL, separating the crystals by a first-stage centrifugal separation unit to obtain industrial NaCL, and sending the mother liquor to a second-stage cooling crystallization unit;

step five: cooling and crystallizing to obtain calcium magnesium nitrate

The mother liquor obtained from the four-stage centrifugal separation unit of step (IV) contains Mg (NO) as the main component₃)₂And Ca (NO)₃)₂The mother liquor is cooled by indirect heat exchange with cold water to obtain Mg (NO) with crystal water₃)₂·xH₂O and Ca (NO)₃)₂·yH₂Crystal of O, and the calcium magnesium nitrate fertilizer with good water solubility can be obtained by flaking or granulating₄O₁₂(also called as calcium magnesium nitrate) fertilizer, the cold water is changed into clear water which is used for filtering the washing water of the washing unit and digesting the unit to lime respectively;

step six: two-stage desulfurization and denitrification

Pumping the magnesium hydroxide slurry prepared by size mixing of the third size mixing unit into a magnesium hydroxide slurry storage tank, pumping the magnesium hydroxide slurry into an atomization sprayer at the upper part of a second-stage desulfurization and denitrification tower by using a second-stage desulfurization and denitrification pump to move downwards to be contacted with first-stage flue gas entering the upper part of the bottom of the second-stage desulfurization and denitrification tower, controlling the pH value to be 7-8, and enabling the incompletely reacted SO to be completely reacted₂Absorption formed MgSO₄Solution of incompletely reacted NO₂Absorption to form Mg (NO)₃)₂Mixing the solution with the excessive unreacted magnesium hydroxide slurry to obtain a second-stage desulfurization and denitrificationThe liquid is pumped to a primary desulfurization and denitrification tower by a secondary desulfurization and denitrification transfer pump, and the treated flue gas is secondary flue gas or clean flue gas which is discharged from a clean flue gas outlet;

step seven: first-stage desulfurization and denitrification

Oxidizing flue gas: mixing a certain concentration of sodium chlorite (NaCLO)₂) Injecting the solution into an oxidizing solution storage tank, pumping the solution into an atomizing sprayer in the middle of a first-stage desulfurization and denitrification tower through an oxidizing solution pump to form fine downward fog drops to be contacted with upward flue gas from the bottom of the tower, and carrying out NO and SO treatment on the flue gas₂By oxidation to NO₂And SO₃(ii) a Transferring a secondary desulfurization and denitrification solution: pumping the second-stage desulfurization and denitrification liquid into an atomization sprayer at the upper part of the first-stage desulfurization and denitrification tower through a desulfurization and denitrification transfer pump of the second-stage desulfurization and denitrification tower to form fine downward fog drops and newly generated NO₂And SO₃Contacting with Mg (OH) in the secondary desulfurization and denitrification liquid₂Absorption reaction takes place to form MgSO₄And Mg (NO)₃)₂A solution; thirdly, circulating desulfurization and denitrification: incomplete reaction of NaCLO₂And Mg (OH)₂Falling into the tower bottom and being dissolved in the first-stage circulating desulfurization and denitrification liquid; and pumping the primary circulating desulfurization and denitrification liquid into an atomization sprayer at the upper part of the primary desulfurization and denitrification tower through a primary desulfurization and denitrification circulating pump, simultaneously continuing to correspondingly coordinate the steps (i) and (ii), respectively forming descending fine fog drops, continuing to repeat the oxidation reaction and the absorption reaction until the pH value of the primary desulfurization and denitrification liquid is close to or equal to 6, completing the primary desulfurization and denitrification, and delivering the primary desulfurization and denitrification completion liquid to a purification and impurity removal unit to form a closed-loop repeated conversion process according to the flow from the step one to the step seven.

Preferably, the two-stage and sectional desulfurization and denitrification method for flue gas can also use other heat sources to replace the steam heat source of the primary evaporation unit in the fourth step, particularly the waste heat utilization of dry hot flue gas,

the method is characterized in that: before the seventh step, a flue gas waste heat evaporation step in the eighth step is also arranged, hot flue gas enters the tower from the bottom of the flue gas waste heat evaporation tower to move upwards, and Ca (NO) obtained by regeneration in the third step is regenerated₃)₂、Mg(NO₃)₂Pumping with NaCL solution (calcium magnesium nitrate solution)Entering an atomization sprayer at the upper part of a flue gas waste heat evaporation tower to form descending fine fog drops, contacting with ascending hot flue gas, evaporating and concentrating solution moisture until the solution moisture is concentrated to a NaCL saturated state, sending the concentrated solution to a first-stage crystallization unit for crystallization, and separating industrial NaCL through a centrifugal separation unit; the mother liquor crystallized out of NaCL is sent to a secondary cooling crystallization unit to be indirectly cooled by cold water to obtain a magnesium calcium nitrate product; the cold water is changed into clear water with unchanged components, and the clear water is respectively sent to a filtering and washing unit to replace condensed water to wash the filter material and the digestion unit to dissolve ash; the evaporated moisture enters a first-stage desulfurization and denitrification tower along with low-temperature flue gas and is accompanied with desulfurization and denitrification.

Preferably, the two-stage and segmented desulfurization and denitrification method for flue gas can also be used after a two-stage desulfurization and denitrification tower, namely, an escape scrubbing gas recovery step is additionally arranged after the six two-stage desulfurization and denitrification step, and the recovery wet desulfurization and denitrification process is used for obtaining the environmental protection treatment purpose of ultra-clean emission of flue gas by using the aerosol ultrafine particle high-content soluble salt escaping along with the entrainment of desulfurization and denitrification liquid in a clean flue gas or two-stage flue gas mode.

Preferably, the sixth step is followed by a recovery step of escape purge gas of the ninth step, wherein: and D, clean flue gas discharged from the clean flue gas outlet of the second-stage desulfurization and denitrification enters the tower from the bottom of the escape scrubbing gas recovery tower and goes upward, the clean water obtained in the fifth step is used for filtering and washing the unit for washing, other clean water is pumped into an atomizing sprayer at the upper part of the escape scrubbing gas recovery tower through a clean water pump to form descending fine fog drops which are in reverse contact with the upward clean flue gas, soluble salt carried in the clean flue gas is recovered into the scrubbing liquid by utilizing the characteristic that the soluble salt is dissolved in water, the scrubbing liquid returns to the digestion unit for dissolving ash, most of the carried soluble salt in the clean flue gas after scrubbing is washed out, and ultra-clean flue gas is formed and discharged from the ultra-clean flue gas outlet of the escape scrubbing gas recovery tower.

In conclusion, the catalyst has certain temperature and contains NOx and SO₂The flue gas is firstly subjected to waste heat recovery by a flue gas waste heat evaporation tower to evaporate redundant water in the calcium magnesium nitrate solution containing sodium chloride to a saturated state of the sodium chloride, and the sodium chloride is separated for crystallization, so that the sodium chloride is crystallizedThe mother liquid is cooled to crystallize out calcium magnesium nitrate fertilizer, thus creating technological conditions. The capacity of evaporating water by using the waste heat of the flue gas is huge, and the capacity of evaporating and carrying away water is 20-60 g/M in industrial practice³In addition, the general flue gas desulfurization and denitration are mostly in the condition of large flue gas volume, the water in the byproduct can be recovered by adopting the flue gas waste heat evaporation, the higher capital investment of evaporation facilities can be cancelled, the operation cost can be reduced, and the thermal pollution caused by the flue gas emission can be eliminated.

After passing through the flue gas waste heat evaporation tower or the flue gas waste heat evaporation step, the low-temperature flue gas changed from the hot flue gas enters the first-stage desulfurization and denitrification tower and enters the two-stage segmented desulfurization and denitrification system for the flue gas, and the system and the process method adopted by the system have low requirements on the desulfurization and denitrification temperature, which is exactly the essence of the invention which is absorbed after being oxidized. At normal temperature, the sodium chlorite can be used for removing NO and SO in the flue gas₂By oxidation to NO₂And SO₃The method creates good process conditions for magnesium desulphurization, namely magnesium hydroxide desulphurization, so that the magnesium hydroxide is directly absorbed into magnesium nitrate solution and magnesium sulfate solution, and the method is simple.

Through one-level SOx/NOx control tower or one-level SOx/NOx control step, low temperature flue gas purifies into one-level flue gas again and changes and send into second grade SOx/NOx control tower or step into, and in second grade SOx/NOx control stage, the higher pH value than one-level SOx/NOx control environment more is favorable to will be in the remaining NO of one-level SOx/NOx control stage not yet reacted absorbing NO₂And SO₃The rich magnesium hydroxide is used for thorough absorption, so that the primary flue gas is changed into cleaner secondary flue gas or clean flue gas.

Leading one-level SOx/NOx control and rearmounted SOx/NOx control are hierarchical segmentation setting has formed reasonable high-efficient system, and the one-level uses the oxidation earlier, absorb after and the oxidation alternately with the absorption and lift as the key, and the second grade uses remaining purification and links up one-level SOx/NOx control as the key, and its SOx/NOx control material trend has formed reasonable reverse purification trend with the flue gas.

After passing through the second-stage desulfurization and denitrification tower or the second-stage desulfurization and denitrification step, the first-stage flue gas becomes second-stage flue gas and enters an escape scrubbing recovery stage, and the characteristic that soluble salt is dissolved in water is utilized to further scrub the gas by using clear water, so that most soluble salt in the desulfurization and denitrification liquid which normally escapes along with the flue gas enters the scrubbing liquid, and the scrubbing liquid returns to the digestion unit to be dissolved in ash and recovered into the system. From here, the flue gas becomes low temperature flue gas through waste heat evaporation utilization, purifies into the primary flue gas through the one-level SOx/NOx control, continues to purify into the second grade flue gas through the second grade SOx/NOx control, retrieves through escaping gas washing and purifies into ultra-clean flue gas discharge system finally.

The flue gas two-stage sectional desulfurization and denitrification system and the flue gas two-stage sectional desulfurization and denitrification method have the greatest advantages of ultra-clean flue gas emission brought by flue gas resource utilization and no generation of solid waste and wastewater, and the effects are established on the basis that the direct products of desulfurization and denitrification are mixed components of soluble solution. Just because the finished solution obtained by oxidation, absorption, desulfurization and denitrification is a mixed soluble solution of magnesium sulfate, magnesium nitrate and sodium chloride, calcium sulfate is formed by the precipitation reaction of calcium nitrate and magnesium sulfate, and sulfur oxides in the flue gas are discharged out of the system; then, reacting lime and/or dolomite lime milk with a magnesium nitrate solution to regenerate and precipitate magnesium hydroxide and obtain a calcium nitrate solution, wherein the magnesium hydroxide returns to desulfurization and denitrification, and the calcium nitrate returns to precipitate gypsum; finally, by utilizing the characteristic that calcium nitrate, magnesium nitrate and sodium chloride solution can be evaporated, concentrated, crystallized and separated, sodium chloride and calcium magnesium nitrate in the system are separated step by step, so that nitrate salt formed by nitrogen oxides in flue gas is separated from the system, and the aims of desulfurization and denitrification are fulfilled.

The front flue gas waste heat evaporation and rear flue gas escape scrubbing recovery unit or step uses the flue gas resource conditions and the flue gas purification means to the maximum extent, and adds to the improvement of two-stage sectional desulfurization and denitrification of flue gas.

To facilitate an understanding of the structural principles and methods of the system of the present invention, some basic principles and points of the reaction process are provided:

a: magnesium method, sodium chlorite oxidation method desulfur and denitration

2SO₂+NaCLO₂＝2SO₃↑+NaCL

2NO+NaCLO₂＝2NO₂↑+NaCL

SO₃+Mg(OH)₂＝MgSO₄+H₂O

3NO₂+Mg(OH)₂＝Mg(NO₃)₂+NO↑+H₂O

B: the nitrogen (N) and sulfur (S) separation is realized by using a system circulating medium calcium nitrate to precipitate calcium sulfate

NS separation reaction: MgSO (MgSO)₄+Ca(NO₃)₂→Mg(NO₃)₂+CaSO₄↓

C: slaking lime and dolomitic lime to obtain Ca (OH)₂And Mg (OH)₂Slurry

Lime hydrolysis: MgO + H₂O＝Mg(OH)₂

CaO+H₂O＝Ca(OH)₂

Hydrolysis of dolomitic lime: MgO, CaO +2H₂O＝Mg(OH)₂+Ca(OH)₂

D: lime milk and Mg (NO)₃)₂Metathesis to Mg (OH)₂Precipitation of

And (3) regeneration reaction:

2Mg(NO₃)₂+Mg(OH)₂.Ca(OH)₂→Ca(NO₃)₂+3Mg(OH)₂↓

quantitatively charging Mg (NO) into the reaction tank₃)₂Filtrate and lime milk concentrate, due to Ca (OH) in lime milk₂Solubility greater than Mg (OH)₂A metathesis conversion reaction to Mg (OH)₂Precipitation and Ca (NO)₃)₂Solution, lime cream Mg (OH)₂Does not participate in the reaction and remains in Mg (OH)₂And (4) precipitating.

E: NaCL separated by evaporation and crystallization and calcium magnesium nitrate prepared by condensation and crystallization

Separation of Mg (OH)₂The main component of the filtrate is Ca (NO)₃)₂、Mg(NO₃)₂Additionally contains NaCLO₂NaCL produced by decomposition, and NaCL and Na brought in by urban water₂SO₄，Na₂SO₄Can be mixed with chloride (I) inherent in the flue gasCL^-) Conversion to NaCL, SO₄ ^＝Conversion to MgSO₄. By utilizing the dissolving characteristic of NaCL, the saturated state is achieved by evaporating and concentrating the waste heat of flue gas, NaCL crystals are firstly separated out, and the mother liquor mainly contains Mg (NO)₃)₂And Ca (NO)₃)₂Most of NaCL is separated out by utilizing the dissolution characteristic, and the mother liquor is cooled to obtain Mg (NO) with crystal water₃)₂·xH₂O and Ca (NO)₃)₂·yH₂And obtaining calcium magnesium nitrate (also called magnesium calcium nitrate) fertilizer by using the crystal of O.

Compared with the prior art, the two-stage sectional desulfurization and denitrification system and the two-stage sectional desulfurization and denitrification method for the flue gas provided by the invention adopt a normal-temperature desulfurization and denitrification means of sodium chlorite oxidation and magnesium hydroxide absorption, and NO and SO in the flue gas are treated by sodium chlorite₂By oxidation to NO₂And SO₃By reacting NO with magnesium hydroxide₂And SO₃The method also adopts flue gas waste heat evaporation and a flue gas purification desulfurization and denitration liquid escape scrubbing recovery means, realizes a closed loop circulation system without solid waste and waste water discharge and system water balance on the premise of ultra-clean discharge of flue gas, combines with desulfurization science on the basis of overcoming the technical problem of low-temperature denitration of the flue gas, and brings the best in desulfurization and denitration, thereby having important guiding significance for treating the low-temperature desulfurization and denitration flue gas.

Drawings

FIG. 1 is a schematic diagram of a practical implementation of a two-stage staged desulfurization and denitrification system for flue gas according to the present invention

FIG. 2 is an ultra-low implementation schematic diagram of a two-stage staged desulfurization and denitrification system for flue gas provided by the invention

FIG. 3 is an ultra-clean implementation schematic diagram of a two-stage staged desulfurization and denitrification method for flue gas provided by the invention, wherein: 1. a first-stage desulfurization and denitrification tower, a 2 first-stage circulating desulfurization and denitrification pump, a 3 oxidizing solution storage tank,

4. an oxidizing liquid supply pump, a 5 second-stage desulfurization and denitrification pump, a 6 magnesium hydroxide slurry storage tank,

7. a two-stage desulfurization and denitrification transfer pump, 8 two-stage desulfurization and denitrification towers, 9 a purification and impurity removal unit,

10. NS separating unit, 11, filtering and washing unit, 12, drying and crushing unit,

13. digestion unit, 14 purification unit, 15 regeneration magnesium hydroxide unit,

16 filtering units, 17 size mixing units, 18 primary evaporation units,

19. a first-stage crystallization unit, 20, a first-stage centrifugal separation unit, 21, a second-stage cooling crystallization unit,

22 clean water pump, 23 flue gas waste heat evaporation tower, 24 escape scrubbing gas recovery tower

Detailed Description

Example 1: as can be seen from fig. 1, the present invention provides a two-stage staged desulfurization and denitrification system for flue gas, which comprises a device and an operation unit that are sequentially connected in a matching manner according to a chemical reaction process by means of a pipeline, a pipe fitting, etc., and is characterized in that:

p1: a desulfurization and denitrification subsystem which consists of a primary desulfurization and denitrification tower 1, a primary circulating desulfurization and denitrification pump 2, an oxidizing liquid storage tank 3, an oxidizing liquid supply pump 4, a secondary desulfurization and denitrification pump 5, a magnesium hydroxide slurry storage tank 6, a secondary desulfurization and denitrification transfer pump 7 and a secondary desulfurization and denitrification tower 8 in sequence;

p2: calcium sulfate CaSO sequentially composed of a purifying and impurity removing unit 9, an NS separating unit 10, a filtering and washing unit 11 and a drying and crushing unit 12₄·2H₂An O subsystem;

p3: the magnesium hydroxide pulping subsystem consists of a digestion unit 13, a purification unit 14, a regenerated magnesium hydroxide unit 15, a filtering unit 16 and a pulp mixing unit 17 in sequence;

p4: the industrial NaCL subsystem sequentially consists of a first-stage evaporation unit 18, a first-stage crystallization unit 19 and a first-stage centrifugal separation unit 20;

p5: calcium magnesium nitrate CaMgN sequentially consisting of a secondary cooling crystallization unit 21 and a clean water pump 22₄O₁₂A subsystem;

P6：

the first-stage desulfurization and denitrification tower 1 comprises a flue gas inlet, a first-stage flue gas outlet, a first-stage desulfurization and denitrification liquid outlet, a tower middle atomization sprayer and a tower upper atomization sprayer, wherein the first-stage flue gas outlet is connected with the first-stage flue gas inlet of the second-stage desulfurization and denitrification tower 8, the first-stage desulfurization and denitrification liquid outlet is respectively connected with the inlet of the first-stage circulation desulfurization and denitrification pump 2 and the inlet of the purification and impurity removal unit 9, the tower upper atomization sprayer inlet is respectively connected with the outlet of the first-stage circulation desulfurization and denitrification pump 2 and the outlet of the second-stage desulfurization and denitrification transfer pump 7 of the second-stage desulfurization and denitrification tower 8, and the tower middle atomization sprayer inlet is connected with the outlet of the oxidizing liquid supply pump 4;

the oxidizing liquid storage tank 3 comprises a sodium chlorite solution inlet and an outlet connected with an inlet of an oxidizing liquid supply pump 4;

the second-stage desulfurization and denitrification pump 5 comprises an inlet and an outlet, the inlet is connected with the outlet of the magnesium hydroxide slurry storage tank 6, and the outlet is connected with the inlet of the atomization sprayer of the second-stage desulfurization and denitrification tower 8;

the magnesium hydroxide slurry storage tank 6 comprises an inlet and an outlet, the inlet is connected with the outlet of the slurry mixing unit 17, and the outlet is connected with the inlet of the secondary desulfurization and denitrification pump 5;

the second-stage desulfurization and denitrification transfer pump 7 also comprises an inlet, and the inlet is connected with a second-stage desulfurization and denitrification liquid outlet at the bottom of the second-stage desulfurization and denitrification tower 8;

second grade SOx/NOx control tower 8 including one-level flue gas entry, clean flue gas (second grade flue gas) export, second grade SOx/NOx control liquid export and atomizing spray thrower, one-level flue gas entry link to each other with 1 one-level flue gas export of one-level SOx/NOx control tower, second grade SOx/NOx control liquid export and 7 imports of second grade SOx/NOx control transfer pump link to each other, atomizing spray thrower import and 5 exports of second grade SOx/NOx control pump link to each other.

The purification and impurity removal unit 9 comprises an inlet, an outlet and a filtrate port, wherein the inlet is connected with the outlet of the first-stage desulfurization and denitration liquid of the first-stage desulfurization and denitration tower 1, and the filtrate port is connected with the inlet of the NS separation unit 10;

the NS separation unit 10 also comprises a calcium magnesium nitrate solution (calcium nitrate or salt-containing calcium magnesium nitrate) inlet and a slurry outlet, wherein the calcium magnesium nitrate solution inlet is connected with the filtrate outlet of the filtering unit 16, and the slurry outlet is connected with the inlet of the filtering and washing unit 11;

the filtering and washing unit 11 further comprises a clear water (condensed water when steam is used) injection port, a filtrate outlet, a washing liquid outlet and a filter material outlet, wherein the filtrate outlet is connected with a filtrate inlet of the regenerated magnesium hydroxide unit 15, the washing liquid outlet is connected with a washing liquid inlet of the size mixing unit 17, and the filter material outlet is connected with an inlet of the drying and crushing unit 12;

the drying and crushing unit 12 further comprises a gypsum outlet;

the digestion unit 13 comprises an ash inlet, a water inlet and a slurry outlet, wherein the water inlet is connected with the outlet of the clean water pump 22, and the slurry outlet is connected with the inlet of the purification unit 14;

the purification unit 14 also comprises a discharge hole and a refined pulp outlet, and the refined pulp outlet is connected with a refined pulp inlet of the regenerated magnesium hydroxide unit 15;

the regenerated magnesium hydroxide unit 15 also comprises a filtrate inlet and a slurry outlet, wherein the filtrate inlet is connected with the filtrate outlet of the filtering and washing unit 11, and the slurry outlet is connected with the inlet of the filtering unit 16;

the filtering unit 16 also comprises a filtrate outlet and a filter material outlet, the filtrate outlet is respectively connected with an inlet of the first-stage evaporation unit 18 and an inlet of the NS separation unit 10, and the filter material outlet is connected with an inlet of the size mixing unit 17;

the size mixing unit 17 also comprises a washing liquid inlet and a slurry outlet, wherein the washing liquid inlet is connected with the washing liquid outlet of the filtering and washing unit 11, and the slurry outlet is connected with the inlet of the magnesium hydroxide slurry storage tank 6;

the primary evaporation unit 18 comprises a calcium magnesium nitrate solution inlet, a steam inlet, a condensed water outlet and a concentrated solution outlet, and the concentrated solution outlet is connected with an inlet of the primary crystallization unit 19;

the first-stage crystallization unit 19 also comprises a discharge port which is connected with an inlet of the first-stage centrifugal unit 20;

the first-stage centrifugal unit 20 also comprises an industrial NaCL outlet and a mother liquid outlet, and the mother liquid outlet is connected with an inlet of the second-stage cooling crystallization unit 21;

the second-stage cooling crystallization unit 21 further comprises a calcium magnesium nitrate outlet and a clean water outlet, and the clean water outlet is connected with an inlet of the clean water pump 22.

Example 2: as can be seen from FIG. 2, the invention provides a two-stage staged desulfurization and denitrification system for flue gas, which comprises equipment and an operation unit, wherein the equipment and the operation unit are sequentially matched and connected through components such as pipelines and pipe fittings according to a chemical reaction process, and the system is characterized in that:

p1: the system comprises a desulfurization and denitrification subsystem which consists of a flue gas waste heat evaporation tower 23, a primary desulfurization and denitrification tower 1, a primary circulating desulfurization and denitrification pump 2, an oxidizing liquid storage tank 3, an oxidizing liquid supply pump 4, a secondary desulfurization and denitrification pump 5, a magnesium hydroxide slurry storage tank 6, a secondary desulfurization and denitrification transfer pump 7 and a secondary desulfurization and denitrification tower 8 in sequence;

p4: an industrial NaCL subsystem which consists of a first-stage crystallization unit 19 and a first-stage centrifugal separation unit 20 in sequence;

P6：

the flue gas waste heat evaporation tower 23 comprises a flue gas inlet, a low-temperature flue gas outlet, an atomization sprayer and a concentrated solution outlet, the low-temperature flue gas outlet is connected with a low-temperature flue gas inlet at the bottom of the primary desulfurization and denitrification tower 1, the inlet of the atomization sprayer is connected with a filtrate outlet of the filtering unit 16, and the concentrated solution outlet is connected with an inlet of the primary crystallization unit 19;

the first-stage desulfurization and denitrification tower 1 comprises a low-temperature flue gas inlet (flue gas inlet), a first-stage flue gas outlet, a first-stage desulfurization and denitrification liquid outlet, a tower middle atomization sprayer and a tower upper atomization sprayer, wherein the first-stage flue gas outlet is connected with a first-stage flue gas inlet of a second-stage desulfurization and denitrification tower 8, the first-stage desulfurization and denitrification liquid outlet is respectively connected with an inlet of a first-stage circulation desulfurization and denitrification pump 2 and an inlet of a purification and impurity removal unit 9, an inlet of the tower upper atomization sprayer is respectively connected with an outlet of the first-stage circulation desulfurization and denitrification pump 2 and an outlet of a second-stage desulfurization and denitrification transfer pump 7 of the second-stage desulfurization and denitrification tower 8, and an inlet of the tower middle atomization sprayer is connected with an outlet of an oxidizing liquid supply pump 4;

the filtering and washing unit 11 further comprises a clean water filling opening, a filtrate outlet, a washing liquid outlet and a filter material outlet, wherein the filtrate outlet is connected with a filtrate inlet of the regenerated magnesium hydroxide unit 15, the washing liquid outlet is connected with a washing liquid inlet of the size mixing unit 17, and the filter material outlet is connected with an inlet of the drying and crushing unit 12;

the drying and crushing unit 12 further comprises a gypsum outlet;

the size mixing unit 17 also comprises a washing liquid inlet and a slurry outlet, wherein the washing liquid inlet of the magnesium hydroxide slurry storage tank 6 is connected with the washing liquid outlet of the filtering and washing unit 11, and the slurry outlet is connected with the inlet;

the first-stage crystallization unit 19 also comprises a discharge port which is connected with an inlet of the first-stage centrifugal unit;

the first-stage centrifugal unit also comprises an industrial NaCL outlet and a mother liquid outlet, and the mother liquid outlet is connected with the inlet of the second-stage cooling crystallization unit 21;

Example 3: referring to fig. 3, the present invention provides a two-stage staged desulfurization and denitrification method for flue gas, which includes operations matched in sequence according to a chemical reaction process, and is characterized in that:

The first-stage desulfurization and denitrification completion liquid of the first-stage desulfurization and denitrification tower 1 enters the purification and impurity removal unit 9 through a first-stage desulfurization and denitrification liquid outlet, and suspended insoluble magnesium-containing calcium fly ash (coal ash) is filtered to obtain relatively pure MgSO-containing (MgSO) fly ash₄、Mg(NO₃)₂And soluble salt mixed semen with NaCL as main component;

step two: NS isolation

Pumping the semen obtained in the step one into an NS separation reactor, adding proper amount of the semen into a filtering unit 16, wherein the filtrate outlet contains Ca (NO)₃)₂NaCL and small amounts of Mg (OH)₂The filtrate (calcium magnesium nitrate solution) of (4), MgSO in the mixed semen₄With Ca (NO) in the filtrate₃)₂Reaction takes place to precipitate gypsum (CaSO)₄) And obtaining Mg (NO)₃)₂The solution is filtered and washed by a filtering and washing unit 11, and the filtrate is Mg (NO)₃)₂The solution is sent to a regenerated magnesium hydroxide unit 15, and the filter material is CaSO₄The wet material is dried and crushed by a drying and crushing unit 12 to obtain high-quality chemical-grade gypsum CaSO₄·2H₂And (4) products O:

step three: regenerated magnesium hydroxide

Adding magnesium-containing lime and dolomitic lime into a slaking unit 13 lime slaking reactor according to a certain proportion, slaking the lime with clear water pumped by a clear water pump 22, and slaking the lime and the dolomitic lime into Ca (OH)₂And Mg (OH)₂The slurry is screened by a purification unit 14 to remove larger-particle impurities and hydrocyclone to separate out finer-particle impurities to obtain purer magnesium-containing lime slurry, and the lime slurry is pumped into a precipitation reactor of a regenerated magnesium hydroxide unit 15 to react with Mg (NO) obtained in the step two₃)₂Solution reaction, regeneration and precipitation of Mg (OH)₂And regenerating to obtain Ca (NO)₃)₂The solution is filtered by a filter unit 16, and the filter material is Mg (OH)₂The wet material is sent to a size mixing unit 17, the washing liquid of the second filtering and washing unit 11 is used for size mixing, then the wet material is sent to a magnesium hydroxide size storage tank 6, and the filtrate is Ca (NO)₃)₂、Mg(NO₃)₂And NaCl, the rest of the solution is sent to the step eight except that part of the solution is sent to the step two NS separation unit 10 to precipitate and separate gypsumThe atomization sprayer in the step of evaporating the waste heat of the flue gas is used for evaporation and concentration;

step four: separation of industrial NaCL

Evaporating and concentrating the concentrated solution which is evaporated and concentrated by a flue gas waste heat evaporation tower 23 in the step eight to be close to the saturated state of NaCL, sending the concentrated solution to a primary crystallization unit 19 for cooling and crystallizing, firstly separating out most of NaCL crystals by utilizing the dissolving characteristic of NaCL, separating by a primary centrifugal separation unit 20 to obtain industrial NaCL, and sending the mother solution to a secondary cooling and crystallization unit 21;

step five: cooling and crystallizing to obtain calcium magnesium nitrate

The mother liquor obtained from the step four-stage centrifugal separation unit 20, whose main component is Mg (NO)₃)₂And Ca (NO)₃)₂The mother liquor is cooled by indirect heat exchange with cold water to obtain Mg (NO) with crystal water₃)₂·xH₂O and Ca (NO)₃)₂·yH₂Crystal of O, and the calcium magnesium nitrate fertilizer with good water solubility can be obtained by flaking or granulating₄O₁₂(also called as calcium magnesium nitrate) fertilizer, the cold water is changed into clear water to be respectively used for washing by the filtering and washing unit 11 and washing by the atomizing sprayer in the escape washing gas recovery step in the ninth step by the clear water pump 22, and the washing gas completion liquid (washing gas liquid) returns to the digestion unit 13 to be ashed;

step six: two-stage desulfurization and denitrification

Pumping the magnesium hydroxide slurry prepared by size mixing in the third size mixing unit 17 into a magnesium hydroxide slurry storage tank 6, pumping the magnesium hydroxide slurry into an atomization sprayer at the upper part of a second-stage desulfurization and denitrification tower 8 by using a second-stage desulfurization and denitrification pump 5 to move downwards to make the magnesium hydroxide slurry contact with first-stage flue gas entering the upward direction from the bottom of the second-stage desulfurization and denitrification tower 8, controlling the pH value to be within the range of 7-8, and enabling SO which is not completely reacted₂Absorption formed MgSO₄Solution of incompletely reacted NO₂Absorption to form Mg (NO)₃)₂The solution is mixed with the excessive unreacted magnesium hydroxide slurry to form a secondary desulfurization and denitrification solution, the secondary desulfurization and denitrification solution is sent to a primary desulfurization and denitrification tower 1 by a secondary desulfurization and denitrification transfer pump 7, and the treated flue gas is secondary flue gas or clean flue gas and is discharged from a clean flue gas outlet;

step nine: recovery step of escape purge gas

Clean flue gas discharged from the clean flue gas outlet of the second-stage desulfurization and denitrification enters the escape scrubbing recovery tower 24 from the bottom thereof and ascends, clear water obtained in the fifth step is used for filtering the washing unit 11 and is used for washing water, and other clear water is pumped into an atomizing sprayer at the upper part of the escape scrubbing recovery tower 24 through a clear water pump 22 to form descending fine fog drops which are in reverse contact with the ascending clean flue gas, soluble salt carried in the clean flue gas is recovered into the scrubbing liquid by utilizing the characteristic that the soluble salt is dissolved in water, the scrubbing liquid returns to the digestion unit 13 to be dissolved into ash, most of the soluble salt carried in the clean flue gas after scrubbing is washed out, and the ultra-clean flue gas is discharged from the ultra-clean flue gas outlet of the escape scrubbing recovery tower 24.

Step eight: flue gas waste heat evaporation step

The hot flue gas enters the tower from the bottom of the flue gas waste heat evaporation tower 23 to move upwards, and Ca (NO3) obtained by regeneration in the step three is regenerated₂、Mg(NO₃)₂Pumping a NaCL solution (calcium magnesium nitrate solution) into an atomization sprayer at the upper part of the flue gas waste heat evaporation tower 23 by a pump to form descending fine fog drops, contacting with ascending hot flue gas, evaporating and concentrating the water content of the solution until the solution is concentrated to a NaCL saturated state, sending the concentrated solution to a primary crystallization unit 19 for crystallization, and separating industrial NaCL by a centrifugal separation unit; the mother liquor crystallized out of NaCL is sent to a secondary cooling crystallization unit 21 to be indirectly cooled by cold water to obtain a magnesium calcium nitrate product; the cold water is changed into clean water with unchanged components, and the clean water is respectively sent to the filtering and washing unit 11 to replace condensed water to wash the filter material and the digestion unit 13 for ash dissolution through the clean water pump 22; the evaporated moisture enters the primary desulfurization and denitrification tower 1 along with the low-temperature flue gas and is accompanied with desulfurization and denitrification.

Step seven: first-stage desulfurization and denitrification

Oxidizing flue gas: mixing a certain concentration of sodium chlorite (NaCLO)₂) Injecting the solution into an oxidizing solution storage tank 3, pumping the solution into an atomizing sprayer in the middle of a first-stage desulfurization and denitrification tower 1 through an oxidizing solution pump to form fine downward fog drops to be contacted with upward flue gas from the bottom of the tower, and carrying out NO and SO treatment on the flue gas₂By oxidation to NO₂And SO₃(ii) a Transferring a secondary desulfurization and denitrification solution: pumping the second-stage desulfurization and denitrification liquid into a first pump through a desulfurization and denitrification transfer pump of the second-stage desulfurization and denitrification tower 8The upper part of the stage desulfurization and denitrification tower 1 is provided with an atomizing sprayer to form fine downward fog drops and newly generated NO₂And SO₃Contacting with Mg (OH) in the secondary desulfurization and denitrification liquid₂Absorption reaction takes place to form MgSO₄And Mg (NO)₃)₂A solution; thirdly, circulating desulfurization and denitrification: incomplete reaction of NaCLO₂And Mg (OH)₂Falling into the tower bottom and being dissolved in the first-stage circulating desulfurization and denitrification liquid; and (3) pumping the primary circulating desulfurization and denitrification liquid into an atomization sprayer at the upper part of the primary desulfurization and denitrification tower 1 through a primary desulfurization and denitrification circulating pump, simultaneously continuing to correspondingly coordinate the steps (i) and (ii), respectively forming descending fine fog drops, continuing to repeat the oxidation reaction and the absorption reaction until the pH value of the primary desulfurization and denitrification liquid is close to or equal to 6, completing the primary desulfurization and denitrification, and delivering the primary desulfurization and denitrification completion liquid to a purification and impurity removal unit 9 to form a closed-loop repeated conversion process according to the flow from the step one to the step seven.

Claims

1. The utility model provides a flue gas two-stage segmentation SOx/NOx control's system, includes equipment and the operating unit that matches and connects according to the chemical reaction process in proper order through parts such as pipeline, pipe fitting, its characterized in that:

p1: the system comprises a desulfurization and denitrification subsystem which consists of a primary desulfurization and denitrification tower (1), a primary circulating desulfurization and denitrification pump (2), an oxidizing liquid storage tank (3), an oxidizing liquid supply pump (4), a secondary desulfurization and denitrification pump (5), a magnesium hydroxide slurry storage tank (6), a secondary desulfurization and denitrification transfer pump (7) and a secondary desulfurization and denitrification tower (8) in sequence;

p2: calcium sulfate CaSO sequentially consisting of a purification and impurity removal unit (9), an NS separation unit (10), a filtering and washing unit (11) and a drying and crushing unit (12)₄·2H₂An O subsystem;

p3: a magnesium hydroxide pulping subsystem which consists of a digestion unit (13), a purification unit (14), a regenerated magnesium hydroxide unit (15), a filtering unit (16) and a pulp mixing unit (17) in sequence;

p4: an industrial NaCL subsystem which consists of a primary evaporation unit (18), a primary crystallization unit (19) and a primary centrifugal separation unit (20) in sequence;

p5: sequentially comprises a secondary cooling crystallization unit (21) and a clean water pump(22) Calcium magnesium nitrate of composition CaMgN₄O₁₂A subsystem;

P6：

the first-stage desulfurization and denitrification tower (1) comprises a flue gas inlet, a first-stage flue gas outlet, a first-stage desulfurization and denitrification liquid outlet, a tower middle atomization sprayer and a tower upper atomization sprayer, wherein the first-stage flue gas outlet is connected with the first-stage flue gas inlet of the second-stage desulfurization and denitrification tower (8), the first-stage desulfurization and denitrification liquid outlet is respectively connected with the inlet of the first-stage circulation desulfurization and denitrification pump (2) and the inlet of the purification and impurity removal unit (9), the tower upper atomization sprayer inlet is respectively connected with the outlet of the first-stage circulation desulfurization and denitrification pump (2) and the outlet of the second-stage desulfurization and denitrification transfer pump (7) of the second-stage desulfurization and denitrification tower (8), and the tower middle atomization sprayer inlet is connected with the outlet of the oxidizing liquid supply pump (4); the number of layers of the atomizing sprayers in the middle of the tower is more than or equal to 1, and the number of layers of the atomizing sprayers in the upper part of the tower is more than or equal to 1;

the oxidizing liquid storage tank (3) comprises a sodium chlorite solution inlet and an outlet connected with an inlet of an oxidizing liquid supply pump (4);

the second-stage desulfurization and denitrification pump (5) comprises an inlet and an outlet, the inlet is connected with the outlet of the magnesium hydroxide slurry storage tank (6), and the outlet is connected with the inlet of the atomization sprayer of the second-stage desulfurization and denitrification tower (8);

the magnesium hydroxide slurry storage tank (6) comprises an inlet and an outlet, the inlet is connected with the outlet of the slurry mixing unit (17), and the outlet is connected with the inlet of the secondary desulfurization and denitrification pump (5);

the second-stage desulfurization and denitrification transfer pump (7) also comprises an inlet, and the inlet is connected with a second-stage desulfurization and denitrification liquid outlet at the bottom of the second-stage desulfurization and denitrification tower (8);

the second-stage desulfurization and denitrification tower (8) comprises a first-stage flue gas inlet, a clean flue gas outlet, a second-stage desulfurization and denitrification liquid outlet and an atomization sprayer, wherein the first-stage flue gas inlet is connected with the first-stage flue gas outlet of the first-stage desulfurization and denitrification tower (1), the second-stage desulfurization and denitrification liquid outlet is connected with the inlet of a second-stage desulfurization and denitrification transfer pump (7), the inlet of the atomization sprayer is connected with the outlet of a second-stage desulfurization and denitrification pump (5), and the number of layers of the atomization sprayer is more than or equal to 1;

the purification and impurity removal unit (9) comprises an inlet, an outlet and a filtrate port, wherein the inlet is connected with the outlet of the first-stage desulfurization and denitration liquid of the first-stage desulfurization and denitration tower (1), and the filtrate port is connected with the inlet of the NS separation unit (10);

the NS separation unit (10) also comprises a calcium magnesium nitrate solution inlet and a slurry outlet, wherein the calcium magnesium nitrate solution inlet is connected with a filtrate outlet of the filtering unit (16), and the slurry outlet is connected with an inlet of the filtering and washing unit (11);

the filtering and washing unit (11) also comprises a clean water filling opening, a filtrate outlet, a washing liquid outlet and a filter material outlet, wherein the filtrate outlet is connected with a filtrate inlet of the regenerated magnesium hydroxide unit (15), the washing liquid outlet is connected with a washing liquid inlet of the size mixing unit (17), and the filter material outlet is connected with an inlet of the drying and crushing unit (12);

the drying and crushing unit (12) also comprises a gypsum outlet;

the digestion unit (13) comprises an ash inlet, a water inlet and a mortar outlet, wherein the water inlet is connected with the outlet of the clean water pump (22), and the mortar outlet is connected with the inlet of the purification unit (14);

the purification unit (14) also comprises a discharge hole and a refined pulp outlet, and the refined pulp outlet is connected with a refined pulp inlet of the regenerated magnesium hydroxide unit (15);

the regenerated magnesium hydroxide unit (15) also comprises a filtrate inlet and a slurry outlet, wherein the filtrate inlet is connected with the filtrate outlet of the filtering and washing unit (11), and the slurry outlet is connected with the inlet of the filtering unit (16);

the filter unit (16) also comprises a filtrate outlet and a filter material outlet, the filtrate outlet is respectively connected with an inlet of the first-stage evaporation unit (18) and an inlet of the calcium nitrate solution of the NS separation unit (10), and the filter material outlet is connected with an inlet of the size mixing unit (17);

the size mixing unit (17) also comprises a washing liquid inlet and a slurry outlet, wherein the washing liquid inlet is connected with the washing liquid outlet of the filtering and washing unit (11), and the slurry outlet is connected with the inlet of the magnesium hydroxide slurry storage tank (6);

the primary evaporation unit (18) comprises a calcium magnesium nitrate solution inlet, a steam inlet, a condensed water outlet and a concentrated solution outlet, and the concentrated solution outlet is connected with the inlet of the primary crystallization unit (19);

the first-stage crystallization unit (19) also comprises a discharge port, and the discharge port is connected with an inlet of the first-stage centrifugal unit 20;

the first-stage centrifugal unit 20 also comprises an industrial NaCL outlet and a mother liquid outlet, and the mother liquid outlet is connected with an inlet of the second-stage cooling crystallization unit (21);

the secondary cooling crystallization unit (21) also comprises a calcium magnesium nitrate outlet and a clean water outlet, and the clean water outlet is connected with an inlet of a clean water pump (22).

2. The system for two-stage and sectional desulfurization and denitrification of flue gas according to claim 1, characterized in that:

the device is characterized in that a flue gas waste heat evaporation tower (23) is also connected in series in front of the first-stage desulfurization and denitrification tower (1), the flue gas waste heat evaporation tower (23) comprises a flue gas inlet, a low-temperature flue gas outlet, a concentrated solution outlet and an atomization sprayer, the low-temperature flue gas outlet is connected with a low-temperature flue gas inlet at the bottom of the first-stage desulfurization and denitrification tower (1), the concentrated solution outlet is connected with an inlet of a first-stage crystallization unit (19), and an inlet of the atomization sprayer is connected with a filtrate outlet of a filtering unit (16); the number of layers of the atomization sprayer is more than or equal to 1.

3. The two-stage sectional flue gas desulfurization and denitrification system according to claim 1 or/and 2, characterized in that:

an escape scrubbing recovery tower (24) is also connected in series behind the second-stage desulfurization and denitrification tower (8), and the escape scrubbing recovery tower (24) comprises a second-stage flue gas inlet, an ultra-clean flue gas outlet, a scrubbing liquid outlet and an atomization sprayer; the second-stage flue gas inlet is connected with a clean flue gas outlet of the second-stage desulfurization and denitrification tower (8), the scrubbing liquid outlet is connected with a clear water inlet of the digestion unit, and the inlet of the atomization sprayer is connected with the outlet of a clear water pump (22); the number of layers of the atomization sprayer is more than or equal to 1.

4. The two-stage sectional desulfurization and denitrification method for the flue gas comprises the following operations which are matched in sequence according to the chemical reaction process, and is characterized in that:

The first-stage desulfurization and denitrification completion liquid of the first-stage desulfurization and denitrification tower (1) enters a purification and impurity removal unit (9) through a first-stage desulfurization and denitrification liquid outlet, and suspended insoluble magnesium-containing calcium fly ash is filtered to obtain relatively pure MgSO-containing (MgSO)₄、Mg(NO₃)₂And soluble salt mixed semen with NaCL as main component;

step two: NS isolation

The semen obtained in the step one is injected into an NS separation reactor, and a proper amount of the semen is added into a filtering unit (16) and the filtrate outlet contains Ca (NO)₃)₂NaCL and small amounts of Mg (OH)₂The filtrate of (4), MgSO in the mixed semen₄With Ca (NO) in the filtrate₃)₂Reaction takes place to precipitate gypsum (CaSO)₄) And obtaining Mg (NO)₃)₂The solution is filtered and washed by a filtering and washing unit (11), and the filtrate is Mg (NO)₃)₂The solution is sent to a regenerated magnesium hydroxide unit (15), and the filter material is CaSO₄The wet material is dried and crushed by a drying and crushing unit (12) to obtain high-quality chemical-grade gypsum CaSO₄·2H₂O products;

step three: regenerated magnesium hydroxide

The lime containing magnesium and the dolomitic lime are put into a slaking unit (13) lime slaking reactor according to a certain proportion, clear water pumped by a clear water pump (22) is used for slaking lime, lime and dolomitic lime are slaked into Ca (OH)₂And Mg (OH)₂The slurry is screened out by a purification unit (14) to remove larger-particle impurities and hydrocyclone to separate out finer-particle impurities to obtain purer magnesium-containing lime slurry, and the lime slurry is pumped into a precipitation reactor of a regenerated magnesium hydroxide unit (15) to react with Mg (NO) obtained in the step two₃)₂Solution reaction, regeneration and precipitation of Mg (OH)₂And regenerating to obtain Ca (NO)₃)₂The solution is filtered by a filtering unit (16), and the filtering material is Mg (OH)₂The wet material is sent to a size mixing unit (17), the washing liquid of the step two filtering and washing unit (11) is used for mixing size, then the wet material is sent to a magnesium hydroxide size storage tank (6), and the filtrate is Ca (NO)₃)₂、Mg(NO₃)₂And NaCL, and the rest of the solution is sent to the flue gas waste heat evaporation step of the step eight except that part of the solution is sent to the NS separation unit (10) of the step two for precipitation and separation of gypsumEvaporating and concentrating the mixture by using an atomization sprayer;

step four: separation of industrial NaCL

Evaporating and concentrating the concentrated solution which is evaporated and concentrated by a flue gas waste heat evaporation tower (23) in the step eight to be close to the saturated state of NaCL, sending the concentrated solution to a primary crystallization unit (19) for cooling and crystallizing, separating out most of NaCL crystals by utilizing the dissolving characteristic of NaCL, separating the NaCL crystals by a primary centrifugal separation unit (20) to obtain industrial NaCL, and sending the mother solution to a secondary cooling and crystallizing unit (21);

step five: cooling and crystallizing to obtain calcium magnesium nitrate

Mother liquor obtained from the step four first-stage centrifugal separation unit (20) and mainly containing Mg (NO)₃)₂And Ca (NO)₃)₂The mother liquor is cooled by indirect heat exchange with cold water to obtain Mg (NO) with crystal water₃)₂·xH₂O and Ca (NO)₃)₂·yH₂Crystal of O, and the calcium magnesium nitrate fertilizer with good water solubility can be obtained by flaking or granulating₄O₁₂Chemical fertilizer, cold water is changed into clear water which is used for washing by the filtering and washing unit (11) and washing by the atomizing sprayer in the escape washing gas recovery step in the ninth step through the clear water pump (22), and the washing gas completion liquid returns to the digestion unit (13) for ash dissolution;

step six: two-stage desulfurization and denitrification

Pumping the magnesium hydroxide slurry prepared by size mixing in the third size mixing unit (17) into a magnesium hydroxide slurry storage tank (6), pumping the magnesium hydroxide slurry into an atomization sprayer at the upper part of a second-stage desulfurization and denitrification tower (8) by using a second-stage desulfurization and denitrification pump (5) to move downwards to enable the magnesium hydroxide slurry to be contacted with first-stage flue gas entering the upward bottom of the second-stage desulfurization and denitrification tower (8), controlling the pH value to be within the range of 7-8, and enabling the incompletely reacted SO to be in contact with the first-stage flue gas₂Absorption formed MgSO₄Solution of incompletely reacted NO₂Absorption to form Mg (NO)₃)₂The solution is mixed with the excessive unreacted magnesium hydroxide slurry to form a secondary desulfurization and denitrification solution, the secondary desulfurization and denitrification solution is sent to a primary desulfurization and denitrification tower (1) by a secondary desulfurization and denitrification transfer pump (7), and the treated flue gas is secondary flue gas or clean flue gas and is discharged from a clean flue gas outlet;

step nine: recovery step of escape purge gas

Clean flue gas discharged from the second-stage desulfurization and denitrification clean flue gas outlet enters the escape scrubbing gas recovery tower (24) from the bottom and ascends, clear water obtained in the fifth step is used for filtering the washing unit (11) and is used for washing water, other clear water is pumped into an atomizing sprayer at the upper part of the escape scrubbing gas recovery tower (24) through a clear water pump (22) to form descending fine fog drops which are in reverse contact with the ascending clean flue gas, soluble salt carried in the clean flue gas is recovered into the scrubbing liquid by utilizing the characteristic that the soluble salt is dissolved in water, the scrubbing liquid returns to the digestion unit (13) to be dissolved into ash, most of the soluble salt carried in the clean flue gas after scrubbing is washed out, and ultra-clean flue gas is discharged from the ultra-clean flue gas outlet of the escape scrubbing gas recovery tower (24).

Step eight: flue gas waste heat evaporation step

Hot flue gas enters the tower from the bottom of the flue gas waste heat evaporation tower (23) to move upwards, and Ca (NO3) obtained by regeneration in the step three is regenerated₂、Mg(NO₃)₂Pumping the NaCL solution into an atomization sprayer at the upper part of a flue gas waste heat evaporation tower (23) by a pump to form descending fine fog drops, contacting with ascending hot flue gas, evaporating and concentrating the water content of the solution until the solution is concentrated to a NaCL saturated state, sending the concentrated solution to a primary crystallization unit (19) for crystallization, and separating industrial NaCL through a centrifugal separation unit; mother liquor crystallized to obtain NaCL is sent to a secondary cooling crystallization unit (21) to be indirectly cooled by cold water to obtain a magnesium calcium nitrate product; the cold water is changed into clean water with unchanged components, and the clean water is respectively sent to a filtering and washing unit (11) to replace condensed water to wash a filter material and a digestion unit (13) for ash dissolution through a clean water pump (22); the evaporated moisture enters a primary desulfurization and denitrification tower (1) along with low-temperature flue gas and is accompanied with desulfurization and denitrification;

step seven: first-stage desulfurization and denitrification

Oxidizing flue gas: sodium chlorite solution with certain concentration is injected into an oxidizing solution storage tank (3) and is pumped into the middle part of a first-stage desulfurization and denitrification tower (1) through an oxidizing solution pump to form fine downward fog drops to be contacted with upward flue gas from the bottom of the tower, and NO and SO in the flue gas are treated₂By oxidation to NO₂And SO₃(ii) a Transferring a secondary desulfurization and denitrification solution: the second-level desulfurization and denitrification liquid is pumped into the upper atomization sprayer of the first-level desulfurization and denitrification tower (1) by the desulfurization and denitrification transfer pump of the second-level desulfurization and denitrification tower (8) to form fine particlesDroplet and newly generated NO₂And SO₃Contacting with Mg (OH) in the secondary desulfurization and denitrification liquid₂Absorption reaction takes place to form MgSO₄And Mg (NO)₃)₂A solution; thirdly, circulating desulfurization and denitrification: incomplete reaction of NaCLO₂And Mg (OH)₂Falling into the tower bottom and being dissolved in the first-stage circulating desulfurization and denitrification liquid; and (2) pumping the primary circulating desulfurization and denitrification liquid into an atomization sprayer at the upper part of the primary desulfurization and denitrification tower (1) through a primary desulfurization and denitrification circulating pump, simultaneously continuing to correspondingly coordinate the steps (i) and (ii), respectively forming descending fine fog drops, continuing to repeat the oxidation reaction and the absorption reaction until the pH value of the primary desulfurization and denitrification liquid is close to or equal to 6, completing the primary desulfurization and denitrification, and delivering the primary desulfurization and denitrification completion liquid to a purification and impurity removal unit (9) to form a closed-loop repeated conversion process according to the flow from the step one to the step seven.