CN1339332A

CN1339332A - Sulphur dioxide removing electrolysis process

Info

Publication number: CN1339332A
Application number: CN 00117344
Authority: CN
Inventors: 张春红
Original assignee: KELEIEN ENVIRONMENT SCIENCE AND TECHNOLOGY CO LTD SHENZHEN CITY
Current assignee: Shenzhen Kelein Lantian Technology Co., Ltd.
Priority date: 2000-08-21
Filing date: 2000-08-21
Publication date: 2002-03-13

Abstract

The wet gas desulfurizing and desulfurizing agent regenerating process of the present invention belongs to the field of gas purifying and electrolysis technology. Inside a gas washer, the desulfurizing mixture solution containing sodium sulfate and sodium hydroxide as main components is used to wash and desulfurize SO2 containing gas, the effluent after desulfurization is aerated before electrolyzed in an ionic film electrolyzer, and the mixed solution after electrolysis and containing sodium sulfate and sodium hydroxide as main components in returned to gas washer for reuses as desulfurizing agent. The by products of the system includes H2, O2 and H2SO4. The process has the advantages of high desulfurizing efficiency, no solid slag produced and high value of by product.

Description

Removal of sulfur dioxide by electrolysis

The invention discloses a wet gas desulfurization and desulfurizer regeneration method, and relates to the technical field of gas purification and electrolysis.

With the rapid development of economy, the emission of sulfur dioxide in China is increased sharply. Areas that occupy around 40% of the national area are subject to acid rain pollution due to sulfur dioxide emissions. The pollution of acid rain and sulfur dioxide becomes an important factor for restricting the economic and social development of China, and the control of the acid rain and the sulfur dioxide is imperative. The sulfur dioxide in the atmosphere mainly comes from coal-fired boilers, particularly power station boilers, and the most commonly adopted method for controlling the emission of the sulfur dioxide from the boilers at present is a limestone-gypsum method. The method has high primary investment, the pollution of the matched powder mill is large, the byproduct gypsum can not be sold outside and can only be discarded, and secondary pollution is formed. Other desulfurization methods such as in-furnace calcium addition, spray drying, coal washing and the like have the defects of low desulfurization efficiency, large one-time investment, high operation cost, solid waste residue and the like respectively.

The invention aims to provide a method for gas desulfurization and desulfurizer regeneration, which has high desulfurization efficiency, no solid waste residue and high commercial utilization value of byproducts.

The purpose of the invention is realized as follows: using Na-containing gas in gas scrubber₂SO₄And the mixed solution with NaOH as the main component is used as a desulfurizer to remove SO₂The gas is washed and desulfurized, the desulfurized wastewater is aerated and then is led into an ion membrane electrolytic cell for electrolysis, and Na-containing gas generated by the cathode of the electrolytic cell after electrolysis₂SO₄And the mixed solution with NaOH as the main component is used as a desulfurizer and returned to the gas scrubber for recycling. And pumping the washed and purified gas to the atmosphere by a draught fan.

The gas scrubber can be any scrubbing equipment capable of using NaOH solution as a desulfurizing agent, such as a spray, a venturi, a cyclone water film, and the like.

NaOH and SO in a gas scrubber₂The following chemical reactions occur:

when the NaOH is completely consumed, Na₂SO₃Can be mixed with SO₂Further chemical reactions take place:

the desulfurized waste water from the gas scrubber contains mainly Na⁺、H⁺、SO₃ ^2-、HSO₃ ^2-、OH^-、SO₄ ^2-、HSO₄ ^-Ions, etc., the proportions of the various components vary depending on the operating parameters of the various gas scrubbers.

Introducing the desulfurization waste water into aeration equipment such as an aeration tank or an aeration tower for aeration treatment, wherein oxygen in the air and SO in the desulfurization waste water₃ ^2-、HSO₃ ^-The following oxidation reactions occur:

aerating fully, and aerating SO₃ ^2-、HSO₃ ^-The smaller the residual content, the better.

However, if the content of suspended solid in the desulfurization wastewater is high due to the high content of impurities in the gas to be treated, the desulfurization wastewater before electrolysis needs to be precipitated or filtered so as to reduce ionic membrane blockage, electrode deposition and the like, and ensure that the electrolytic cell can normally operate for a long time under a better working condition. The precipitation or filtration device may be placed before or after the aeration device.

The aerated desulfurization waste water is introduced into an electrolytic bath for electrolytic treatment. The aerated desulfurization waste water is led to the inlet of the cathode chamber of the electrolytic cell, and water or dilute sulfuric acid is led to the inlet of the anode chamber of the electrolytic cell. Under the action of the electric field in the electrolytic bath, cations in the solution tend to the cathode, anions tend to the anode, and electrolytic reaction occurs at the anode and the cathode.

Cathode:

anode:

the cathode of the cell produces NaOH and hydrogen and the anode of the cell produces sulfuric acid and oxygen.

The electrolytic cell has anode chamber and cathode chamber, the anode chamber and cathode chamber have liquid inlet, liquid outlet and gas outlet, and the anode chamber and cathode chamber are separated by anion exchange membrane.

The cathode lead-out liquid mainly comprises NaOH generated by electrolysis and non-electrolyzed Na₂SO₄The alkaline mixed solution is used as a desulfurizing agent and returned to the gas scrubber for recycling. The byproducts of hydrogen, oxygen and sulfuric acid generated by electrolysis can be exported and treated for self use or export sale.

In the gas desulfurization and desulfurizer regeneration system, the desulfurized gas carries water, the water is consumed by electrolysis, the filtered ash carries water, and the anode sulfuric acid solution carries Na away⁺And the like, resulting in water and Na in the desulfurizer circulating system⁺The ions are continuously reduced, so that the water or NaOH or Na is required to be supplemented to the desulfurizer circulating solution system₂SO₄。

The concentration parameters of the inlet and outlet solutions of the gas scrubber should be matched with the optimal concentration parameters of the inlet and outlet solutions of the electrolytic cell as much as possible, so that concentration or dilution procedures performed due to parameter matching are reduced, and the whole system runs economically and efficiently. For example, the following fit is adopted: the gas scrubber is a Venturi-cyclone water film tower, the solution of the desulfurizer at the inlet is a mixed solution with 3% -5% of NaOH and 10% -20% of sodium sulfate as main components, and the PH value of the desulfurization wastewater at the outlet is 5-9; the electrolytic cell is designed to have a cathode inlet solution containing 15-25% sodium sulfate as a main component and a cathode outlet solution containing 3-5% NaOH and 10-20% sodium sulfate as a mixed solution.

The temperature of the desulfurization wastewater entering the electrolytic cell is preferably adjusted to be between 50 and 70 ℃. The temperature is reduced and the current efficiency is reduced although the system can operate. The electrolysis process is a heat release process, and when the temperature of the solution at the cathode outlet of the electrolytic cell is higher, the solution can be guided into the gas scrubber after heat dissipation and temperature reduction so as to meet the requirement of the gas scrubber on the design temperature of the inlet washing solution. The heat exchange process can be realized by any heat exchange equipment and method.

Compared with the prior art, the method has the advantages that ① has high desulfurization efficiency due to the fact that strong alkaline solution containing NaOH is used as a desulfurizer, ② of desulfurization system byproducts such as hydrogen, oxygen and sulfuric acid has high commercial utilization value, ③ does not produce solid waste residue, ④ is applied to occasions with low electricity price cost such as power station boilerdesulfurization and the like, and operation cost is low.

An example of the present invention is a smoke volume of 150,000Nm³H, dust content less than 40mg/Nm³The smoke temperature is 25 ℃, and SO in the smoke gas₂At a concentration of 10,000mg/Nm³The method for treating gas desulfurization and desulfurizing agent regeneration.

FIG. 1 is a process flow diagram of this example.

The serial number 1 is a conveying pipe of the treated flue gas;

serial number 2 is draught fan, air quantity 200,000m³H, wind pressure 3000Pa, with an air damper;

number 3 is qiA body washer, a spray desulfurizing tower is selected, and the designed flue gas treatment capacity is 150,000m³Designing a mixed solution containing 3% of NaOH and 15% of sodium sulfate in an inlet solution, and designing the pH value of a desulfurization wastewater outlet to be 7-9;

no. 4 is a frequency conversion solution pump, which requires acid and alkali corrosion resistance and has a maximum flow rate of 80m³/H；

The serial number 5 is a flue gas conveying pipe to be treated;

serial number 6 is a valve;

number 7 is a dilute sulfuric acid delivery pipe;

the serial number 8 is an anode gas conveying pipe;

number 9 is a hydrogen transport pipe;

no. 10 is a steam type heat exchanger, the heat exchange amount is 3,000,000 Kcal/H;

filter number 11, filtration flow 80m³H, the filtration precision is more than 400 meshes;

serial number 12 is a variable frequency solution pump, which requires acid and alkali corrosion resistance and a maximum flow of 80m³/H；

The serial number 13 is an aeration tank, and the flow of the treatment liquid is required to be designed to be 100m³H, SO in aerated solution₃ ^2-、HSO₃ ^-The residual concentration is less than 0.5 percent;

the serial number 14 is a desulfurized wastewater conveying pipe;

number 15 is supplementary conveying pipe of NaOH solution;

serial number 16 is a make-up water delivery pipe;

the serial number 17 is electrolytic equipment, an ion membrane electrolytic cell is selected, the NaOH output (100% NaOH) is 2T/H, the electrolytic cell is provided with an anode chamber and a cathode chamber, the anode chamber and the cathode chamber are separated by an anion exchange membrane, and the cathode chamber and the anode chamber are respectively provided with a solution inlet pipe orifice, a solution outlet pipe orifice and a gas outlet pipe orifice;

serial number 18 is a valve;

number 19 is sulfuric acid solution delivery pipe;

serial number 20 is a valve;

number 21 is a desulfurizer solution delivery pipe;

number 22 is a compressed air delivery pipe;

serial number 23 is a valve;

number 24 of the desulfurizing agent solution intermediate storage tank, 80m³；

Serial number 25 is a valve;

the flue gas to be treated enters agas washing device 3 through a flue pipe 5, a desulfurizer solution containing NaOH enters the gas washing device 3 through a pump 4, and in the gas washing device 3, the desulfurizer and SO in the flue gas₂And (4) reacting, and performing flue gas desulfurization and washing. The washed and purified flue gas is pumped and exhausted to the atmosphere through a flue pipe 1 and an induced draft fan 2.

The desulfurized wastewater after completion of desulfurization is introduced into the aeration tank 13 through the pipe 14, the compressed air is introduced into the aeration tank 14 through the pipe 22, and in the aeration tank 14, oxygen in the air reacts with sulfite and bisulfite in the desulfurized wastewater to generate sulfate and bisulfate. The aerated desulfurization wastewater is conveyed to a filter 11 through a pump 12 for filtering, then is heated through a heat exchanger 10, the temperature of the solution is adjusted to 50-60 ℃, and finally is led into a cathode chamber of an electrolytic cell 17 for electrolysis. 1% dilute sulphuric acid is introduced into the anode chamber of the electrolysis cell via line 7. NaOH and Na contained in the electrolyte discharged from the cathode chamber of the electrolytic cell₂SO₄The liquid is led into a desulfurizing agent solution intermediate storage tank 24 through a pipeline 21 and then led into a gas scrubber 3 through a pump 4 for recycling; the sulfuric acid solution generated in the anode chamber is led out through a pipeline 19 to the sulfuric acid treatment process; hydrogen gas generated in the cathode chamber is led out through a pipe 9 and sent to a hydrogen gas treatment process; oxygen generated in the anode chamber is led out through a pipe 8 to an oxygen treatment process.

A35% NaOH solution for make-up is introduced into intermediate tank 24 via line 15 and make-up water is introduced into intermediate tank 24 via line 16. The amount of the make-upwater and the make-up NaOH is adjusted to ensure that the NaOH concentration of the intermediate storage tank 24 is kept at about 3 percent and the sodium sulfate concentration is kept at about 15 percent.

Claims

1. A wet method for desulfurizing gas and regenerating desulfurizing agent features that the gas is treated by wet methodThe scrubber contains Na₂SO₄And the mixed solution with NaOH as the main component is used as a desulfurizer to remove SO₂The desulfurized wastewater is introduced into an aeration device, and SO contained in the desulfurized wastewater is treated by air₃ ^2-、HSO₃ ^-Carrying out aeration oxidation, wherein the Na is contained after aeration₂SO₄Introducing the wastewater as main component into an electrolytic tank for electrolysis, and discharging Na-containing wastewater from cathode chamber of the electrolytic tank₂SO₄And the mixed solution with NaOH as the main component is used as a desulfurizer and returned to the gas desulfurization scrubber for recycling.

2. A process as claimed in claim 1, wherein the electrolytic cell has an anode chamber and a cathode chamber, the anode chamber and the cathode chamber are separated by an anion exchange membrane, the anode chamber and the cathode chamber have a liquid inlet, a liquid outlet and a gas outlet, respectively, the desulfurized wastewater after aeration is introduced into the cathode chamber inlet of the electrolytic cell, water or dilute sulfuric acid is introduced into the anode chamber inlet of the electrolytic cell, the alkaline mixed solution discharged from the cathode chamber is recycled as a desulfurizing agent, and the sulfuric acid solution produced in the anode chamber, the oxygen produced in the anode chamber and the hydrogen produced in the cathode chamber are separately discharged.