Desulfurization method and device with regenerable desulfurizer
The invention relates to a desulfurization method and a desulfurization device for removing sulfur dioxide in waste gas, in particular to a desulfurization method and a desulfurization device with a reproducible desulfurizing agent.
In boilers and kilns commonly used in the industries of electric power, chemical industry, metallurgy and the like, exhaust gas contains a large amount of sulfur dioxide, which causes serious pollution to the atmosphere and is a main pollution source formed by acid rain. At present, the research of flue gas desulfurization is actively developed at home and abroad, certain progress is made, and some desulfurization technologies and processes are applied and popularized in practical engineering. For example, the most commonly used lime/limestone-gypsum method utilizes the characteristic that lime or limestone can react with sulfur dioxide to perform wet desulfurization and washing on flue gas, thereby achieving the purpose of purifying the flue gas; there are other methods such as spray drying, electron beam, ammonia, and the like. However, the methods have the disadvantages that the final desulfurization by-product of the lime/limestone-gypsum method is gypsum which is restricted by the process and the market, cannot be commercialized and only occupies land to discard and stack, thus forming secondary pollution; in the method for regenerating the desulfurizer by electrolyzing sodium sulfate mentioned in some foreign documents, a large amount of by-product dilute sulfuric acid is difficult to treat, and the cost for purifying to commercial concentrated sulfuric acid is high. In other desulfurization process methods, some methods have high initial investment, some methods have high operation cost, some methods form secondary pollution, and some methods have low desulfurization efficiency. These disadvantages have largely restricted the development of the desulfurization environmental protection industry.
The invention aims to provide a desulfurizing method with regenerable desulfurizing agent, which has low investment, low operating cost, high desulfurizing efficiency and no secondary pollution, and is particularly suitable for low electricity price (such as
In order to achieve the purpose, the technical scheme of the invention is as follows:
the desulfurization method with the regenerable desulfurizer comprises the following steps:
(A) with NaOH and Na2SO3The mixed solution as the main component is used as a desulfurizer to wash and desulfurize the waste gas;
(B) mixing the desulfurized waste water with gaseous HCl, SO2Is replaced out;
(C) and (3) electrolyzing the concentrated wastewater to regenerate NaOH, wherein the generated NaOH is used as a desulfurizer and is led back to the step (A) for recycling, hydrogen and chlorine generated in the electrolysis process are led into an HCl synthesis chamber to synthesize HCl gas, and gaseous HCl is led back to the step (B) for recycling.
In a preferred embodiment of the present invention, after the step (a) is completed, the desulfurized wastewater is precipitated or filtered, and then the step (B) is performed.
And (C) after the step (B) is finished, evaporating and concentrating the wastewater containing NaCl as a main component after replacement to improve the concentration of NaCl in the wastewater, and then performing the step (C).
The device for implementing the method of the invention comprises:
at least one desulfurization scrubber 1;
at least one SO2Replacement chamber 2, the SO2The displacement chamber 2 is connected to the desulfurization scrubber 1 by a first conduit 4 equipped with a shut-off valve 3;
at least one concentrating compartment 5, the concentrating compartment 5 being in communication with the SO via a second conduit 62The replacement chambers 2 are connected;
at least one cationic membrane electrolyzer 7 comprising an anode compartment and a cathode compartment, the anode compartment of the electrolyzer 7 being connected to the concentrating compartment 5 by a third conduit 8, the cathode compartment of the electrolyzer 7 returning the solution to the desulfurization scrubber 1 by a fourth conduit 9;
at least one HCL synthesis chamber 10 for feeding the electrolytic cells 7 through a fifth conduit 11, respectivelyHydrogen in the cathode chamber of the electrolysis cell 7 is introduced into the HCL synthesis chamber 10 through a sixth conduit 12, and HCL in the HCL synthesis chamber 10 is introduced into SO through an eighth conduit 132The chamber 2 is replaced.
In a preferred embodiment of the present invention, the apparatus further comprises:
at least one wastewater collection tank 14 connected to the bottom end of the desulfurization scrubber 1 through an eighth conduit 15;
at least one filter 16, the waste water in the waste water collecting tank 14 being introduced into the filter 16 through a ninth conduit 18 provided with a pump 17, the filter 16 being openThrough a first conduit 4 provided with a shut-off valve 3 and SO2The replacement chambers 2 are connected;
at least one intermediate tank 30 for introducing the solution in the cathode compartment of the electrolytic cell 7 to the intermediate tank 30 through a fourth conduit 9, the intermediate tank 30 being connected to the desulfurization washing column 1 through a tenth conduit 20 equipped with a pump 19;
at least one condenser 21 to which the water vapor in the evaporation chamber 5 is introduced through an eleventh conduit 22;
at least one transition tank 23 for introducing the water in the condenser 21 through a twelfth conduit 24 and the solution in the intermediate storage tank 17 through a thirteenth conduit 25 into the transition tank 23, the transition tank 23 being connected to the cathode chamber of the electrolytic bath 7 through a fourteenth conduit 26;
the top end of the desulfurization washing tower is provided with at least one gas outlet pipe 27, and the bottom of the desulfurization washing tower is provided with at least one gas pipeline 28 to be treated;
the intermediate storage tank 30 is provided with a supplement pipeline 29 for supplementing NaOH and water;
the SO2The replacement chamber 2 is provided with a gas SO2A discharge pipe 31 for discharging the gas SO2。
Said electrolytic cell 7 is further provided with a fifteenth conduit 33 equipped with a valve 32 for introducing the solution in the anode compartment of the electrolytic cell 7 to the concentrating compartment 5.
By adopting the method and the device, the whole desulfurization and desulfurizing agent electrolysis regeneration process does not generate solid waste and secondary pollution, and the byproduct is high-purity SO2The gas can be processed into various downstream products, so that the market demand is large and the commercial value is high; in addition, the high-concentration NaOH solution is adopted as a desulfurizer to carry out desulfurization, and the desulfurization efficiency is far higher than that of other common desulfurizers; the initial investment of the whole desulfurization and desulfurizer electrolysis regeneration system is relatively low; in the occasions with low electricity price, such as power station desulfurization occasions, the desulfurization operation cost is greatly lower than that of the prior common desulfurization process and method after the sales income of byproducts is deducted; in addition, it avoids the production of large amounts of dilute sulfuric acid which is difficult to handle in conventional sodium sulfate electrolytic regeneration processesAnd (4) the defect.
FIG. 1 is a flow chart of the apparatus of the present invention.
The invention is explained in more detail below with reference to the figures and examples:
the desulfurization method with the regenerable desulfurizing agent comprises the following steps:
using sodium hydroxide (NaOH) and sodium sulfite (Na)2SO3) The mixed solution is used as a desulfurizer to perform wet scrubbing desulfurization on the flue gas to be treated, and the purified flue gas is discharged to the atmosphere. The desulfurization washing equipment can be any desulfurization tower which can use NaOH desulfurizing agent. The sulfur dioxide in the flue gas and the desulfurizer react as follows:
when CO is present in the flue gas2Then, the following reaction takes place:
when the NaOH is completely consumed, Na2SO3Can be mixed with SO2Further reaction takes place:
it can be seen that Na is contained in the desulfurized wastewater2SO3And NaHSO3Is a solution of main components, and of course, depending on the components in the flue gas, there may be some suspended solids and small amounts of other impurity ions such as SO in the desulfurization waste water4 2-And the like.
In order to ensure better efficiency of electrolytic regeneration of the desulfurizer and reduce electrolytic energy consumption, the concentration of the desulfurizer NaOH is as high as possible, preferably more than 20%, and the provided high-concentration NaOH can be used in a desulfurization washing tower for multiple self-circulation or multi-stage washing to ensure thatThe total consumption of NaOH is changed into Na2SO3And NaHSO3(ii) a However, NaOH is preferably not diluted, which may cause Na in the desulfurization waste water2SO3And NaHSO3Is lower, thereby increasing the energy consumption of electrolysis.
In order to prolong the service life of the ionic membrane, the solid suspended substances in the desulfurization wastewater are separated as far as possible by adopting methods such as filtration and the like before the desulfurization wastewater enters the electrolytic bath. The filtered desulfurization waste water is introduced into a displacement chamber, HCl is introduced into the displacement chamber, and Na is added to the filtered desulfurization waste water2SO3And NaHSO3Reaction is carried out:
the displacer HCl comes from the HCl synthesis chamber. Replacement of chamber generated SO2The gas needs to be led out. To reduce SO2Dissolving in solution, heating the solution to a temperature suitable for avoiding heating to boiling, or SO2The gas contains a large amount of water, which increases the difficulty of post-treatment.
By-product of high concentration of SO2Introduction of SO2The post-treatment process can prepare liquid sulfur dioxide or high-purity oleum. SO (SO)2The post-treatment process is not within the scope of the present invention.
Is replaced by SO2The desulfurized waste water is mainly diluted sodium chloride (NaCl) and is mixed with the diluted NaCl solution led out from the anode chamber in a concentration chamber, and the mixed solution is evaporated and concentrated into concentrated NaCl solution.
The concentrated NaCl solution is led into an anode chamber of an ion membrane electrolytic cell to carry out electrolysis to regenerate a desulfurizer. Whether the wastewater needs to be refined before introduction and to what extent depends on the conditions such as the selection of the ionic membrane, the planned membrane replacement period, the extent to which the user is subjected to increased operating expenses, etc., which affect the economic indicators of the operation of the desulfurization system, but have no substantial effect on the principle of the present invention. Generally, the higher the degree of purification, the longer the service life of the ionic membrane, but the higher the running cost of the purified part. The ion membrane electrolytic cell is a common ion membrane electrolytic cell in the chlor-alkali industry.
Introducing desulfurization wastewater into an anode chamber solution inlet of the electrolytic cell, introducing most of an outlet solution into a concentration chamber for thickening, and sending a small part of the outlet solution to a sulfate radical removing process so as to remove more and more sulfate radical ions accumulated in the system; the inlet lead-in of the cathode compartment was partially filtered but not SO2The outlet of the replaced solution is used for leading out concentrated NaOH and Na2SO3The mixed solution of (1). The following electrolytic reactions take place in the electrolytic cell:
concentrated NaOH and Na produced by electrolysis2SO3The mixed solution is used as a desulfurizer and is led into a desulfurization washing tower to complete the cycle process.
Chlorine and hydrogen generated by the anode chamber and the cathode chamber of the electrolytic cell are led into the HCl synthesis chamber to synthesize HCl. The chemical reaction is as follows:
the HCl produced is introduced into the displacement chamber as displaced SO2And (4) using the method to complete the circulation process.
Since the solution is lost during the processes of desulfurization washing, filtration and the like, sodium ions and water are reduced, so that NaOH and water need to be supplemented in the whole desulfurization and desulfurizer regeneration system.
As shown in fig. 1, the desulfurization apparatus of the present invention comprises:
the flue gas to be treated is led into the gas desulfurization washing tower 1 through the flue gas pipeline 28 to be treated,with NaOH and Na2SO3The desulfurizer taking the mixed solution as the main component is introduced into the desulfurization washing tower 1 through a tenth conduit 20 provided with a pump 19, and the desulfurizer reacts with sulfur dioxide in the flue gas, thereby achieving the purpose of desulfurization washing. The gas after washing and purification is led out through a gas outlet pipe 28;
the desulfurized product contains Na2SO3And NaHSO3The wastewater flows into a wastewater collection tank 14, is collected, is passed to a filter 16,the filtered waste water is led to SO2In the displacement chamber 2.
In SO2In the displacement chamber 2, the desulfurized waste water from the filter 16 is mixed with the HCl solution from the HCl synthesis chamber 5, SO2Is displaced to form a gas from SO2And the output of the delivery pipe 31.
The desulfurized wastewater containing dilute NaCl after replacement is sent to the concentration chamber 5 together with the anode chamber effluent of the electrolytic cell 7, the dilute NaCl solution is heated and concentrated into a concentrated NaCl solution in the concentration chamber 5, the evaporated water vapor is output by a pipeline 22, and is diluted and mixed with part of the concentrated NaOH solution generated from the cathode chamber of the electrolytic cell 7 in a transition tank 23 after being condensed by a condenser 21, and then is led back to the cathode chamber of the electrolytic cell 7.
The concentrated NaCl solution from the concentrating compartment 3 is directed to the anode compartment of the electrolytic cell 7 and the dilute NaOH solution from the transition tank 23 is directed to the cathode compartment of the electrolytic cell 7. Under the action of current, an electrolytic reaction is carried out, chlorine is generated in the anode chamber, and meanwhile, NaCl is partially consumed to form a dilute NaCl solution which is led out; hydrogen gas is generated in the cathode chamber, and NaOH and Na are simultaneously generated2SO3The mixed solution of (1). Hydrogen and chlorine are led into the HCl synthesis chamber 5, and the effluent of the cathode chamber is used as a desulfurizer and sent into an intermediate storage tank 17, and then is pressurized by a pump 19 and sent to the desulfurization washing tower 1 for recycling.
A small part of anode chamber effluent is led out by a pipeline and sent to a sulfate radical separation process.
Concentrated HCl, which is synthesized in the HCl synthesis chamber 5, is conducted to SO2Replacement chamber 2 for replacing SO2The application is recycling.
The supplementary water and NaOH are supplied from the pipe 29 to the intermediate tank 30 to supplement the decrease of the water and NaOH due to the loss of the solution.