CN102172470B - Method and device for removing sulfur and carbon oxides from power plant flue gas in combination mode - Google Patents

Abstract

A method and device for jointly removing sulfur and carbon oxides in power plant flue gas are used for removing sulfur and carbon oxides in power plant flue gas with high efficiency and low consumption. The method is carried out according to the following steps: the high-temperature flue gas after electrostatic dust removal is introduced into a heat exchanger, and the decarburized solution in the removal process is heated by the waste heat of the flue gas; the heated decarburized solution enters the desorption tower, and ammonia water is decomposed and sent back to the ammonia water storage tank; the low-temperature flue gas after heat exchange enters the removal process to combine desulfurization and decarbonization. The present invention also provides the device used for realizing the above method. The invention uses ammonia water as the absorbent to realize the chemical cycle of ammonia and reduce the cost of the absorbent; effectively utilize the waste heat of the flue gas to heat the solution after decarburization, realize the cascade utilization of power plant energy, and greatly reduce the energy consumption of carbon capture . The invention has the characteristics of high efficiency, cleanness, low energy consumption, highly integrated desulfurization and decarbonization system, etc., and has good application prospects for desulfurization and decarbonization of coal-fired power plants.

Description

A method and device for combined removal of sulfur and carbon oxides in power plant flue gas

technical field

The invention relates to a flue gas purification method, in particular to a method and a device for jointly removing sulfur and carbon oxides in power plant flue gas with high efficiency and low energy consumption, and belongs to the technical field of flue gas purification.

Background technique

There is no doubt that global warming is mainly caused by greenhouse gases such as CO2 emitted by humans burning coal and other fuels. The abnormal increase in global temperature caused by the excessive emission of greenhouse gases will bring many immeasurable adverse effects on natural ecosystems and human social life. According to data from the Organization for Economic Cooperation and Development and the International Energy Agency, the annual CO2 emissions of existing power plants are about 10.6 billion tons, accounting for 40.6% of the world's total emissions, of which coal-fired power plants are 7.6 billion tons, accounting for 72% of the emissions from the power generation industry . Therefore, CO2 emission reduction in thermal power plants is the key to achieving greenhouse gas emission reduction. For the vast majority of existing power plants, the separation and capture of CO2 from post-combustion flue gas is a development trend. A comprehensive evaluation study of various post-combustion CO2 capture technologies shows that chemical solvent-based CO2 absorption is currently the preferred technology for CO2 capture. Absorption CO2 removal has been widely used in chemical industries such as synthetic ammonia and urea, but it is rarely used in CO2 capture in power plant flue gas. The reason is that the flue gas of the power plant has a high flow rate (about 1.2 million m3/h for the mainstream 300MW unit), high flow rate, high smoke temperature (about 120 ℃ after ESP), relatively low CO2 volume fraction (12~15%), The characteristics of complex flue gas coexistence components (including PM, SO2, NOX and HCl), which make the use of conventional absorption processes have problems such as large system volume, high investment and operating costs. At present, the typical wet limestone gypsum method is widely used in the field of flue gas desulfurization. This technology is mature and reliable, but there are also problems that cannot be ignored. Among them, the utilization rate of gypsum by-product of desulfurization is limited, which leads to the fact that the desulfurization gypsum in various power plants cannot be effectively utilized and piled up. In the ash yard, it not only wastes the limited ash yard resources, but also increases the desulfurization operation cost because there is no income from selling gypsum. Another outstanding problem is water consumption. The existing wet limestone gypsum method has a high flue gas temperature at the entrance of the absorption tower, which is generally around 100-150°C, resulting in serious evaporation water consumption in the absorption tower. The flue gas desulfurization system is 70- 80% of water consumption comes from this.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method and device for combined removal of sulfur and carbon oxides in power plant flue gas with high efficiency, cleanliness, low energy consumption and highly integrated desulfurization and decarbonization system.

The said problem of the present invention is solved by following technical scheme:

A method for combined removal of sulfur and carbon oxides in power plant flue gas, which is special in that it uses ammonia water as an absorbent to integrally remove sulfur and carbon oxides in power plant flue gas, and the method is carried out as follows :

a. The high-temperature flue gas after electrostatic dust removal is introduced into the heat exchanger, and the decarburized solution in the removal process is heated by the waste heat of the flue gas;

b. The heated decarburized solution enters the desorption tower, decomposes ammonia water and returns it to the ammonia water storage tank;

c. After heat exchange, the low-temperature flue gas at 40°C-50°C enters the desulfurization tower in the removal process, where sulfur dioxide in the flue gas is removed by spraying ammonia water;

d. After desulfurization, the flue gas enters the decarbonization tower in the removal process, and the carbon dioxide in the flue gas is absorbed by spraying ammonia water. After decarburization, the solution is sent to the heat exchanger, and the purified flue gas is condensed by the flue gas condenser to remove carbon dioxide in the flue gas. Ammonia, the small water droplets carried in the flue gas collide with the condenser and are removed.

In the above method for combined removal of sulfur and carbon oxides in power plant flue gas, in step a, the high-temperature flue gas heats the decarburized solution to 70-80°C, and the heated decarburized solution enters the desorption tower and is then heated by steam Analysis; a small part of the volatile and escaped ammonia enters the condenser together with the desorbed CO2 to remove the escaped ammonia, and the separated CO2 is to be stored or transformed for utilization.

In the above method for combined removal of sulfur and carbon oxides in power plant flue gas, in step c, desulfurization is sprayed with ammonia water in the desulfurization tower, the pH of the ammonia water in the desulfurization holding tank is adjusted to 4-6, and ammonium sulfite is oxidized in the desulfurization holding tank The forced oxidation air provided by the fan is oxidized to produce ammonium sulfate. When the solid content of ammonium sulfate reaches 5-15% (wt%), it is discharged by the pump and sent to the solid-liquid separation system for dehydration to obtain ammonium sulfate fertilizer.

In the above method for combined removal of sulfur and carbon oxides in power plant flue gas, the step d is decarburized by spraying ammonia water in the decarbonization tower, and adjusting the pH of the decarburization ammonia water in the decarburization liquid holding tank to 8-10.

A device for combined removal of sulfur and carbon oxides in flue gas of a power plant, in particular: it includes a high-temperature flue, a desulfurization tower, a decarbonization tower, an analysis tower, an ammonia water storage tank, a solution extraction pump after decarburization, and an ammonia water return pump, desulfurization ammonia supply pump, and decarbonization ammonia supply pump, wherein the high-temperature flue, desulfurization tower, and decarbonization tower are connected in sequence. The decarburization holding tank of the carbon tower and the inlet of the heat exchanger, the outlet of the heat exchanger are connected to the inlet of the desorption tower, the ammonia water return pump is respectively connected to the ammonia water outlet of the desorption tower and the ammonia water storage tank, and the desulfurization ammonia supply pump is respectively connected to the ammonia water storage tank and the desulfurization liquid holding tank of the desulfurization tower, and the decarburization ammonia supply pump are respectively connected to the ammonia water storage tank and the decarbonization liquid holding tank of the decarbonization tower.

The above-mentioned device for combined removal of sulfur and carbon oxides in power plant flue gas, the upper part of the decarbonization tower is provided with a decarburization nozzle, and the decarbonization circulating pump is connected to the decarbonization nozzle and the decarbonization liquid holding tank at the lower part of the decarbonization tower. A shell and tube flue gas condenser is installed at the flue gas outlet of the carbon tower, and the flue gas condenser outlet is connected to the cooling tower.

The above-mentioned device for combined removal of sulfur and carbon oxides in the flue gas of a power plant, the upper part of the desulfurization tower is provided with a desulfurization nozzle, and the desulfurization circulating pump is connected to the desulfurization nozzle and the desulfurization holding tank at the lower part of the desulfurization area, and the desulfurization tower is also provided with an oxidation fan. The outlet of the oxidation fan leads to the desulfurization liquid holding tank, and the desulfurization tower is also equipped with a discharge pump and a solid-liquid separation device, and the discharge pump connects the desulfurization liquid holding tank and the solid-liquid separation device. the

In the above-mentioned combined device for removing sulfur and carbon oxides in flue gas of a power plant, the gas outlet of the desorption tower is connected to a condenser.

Aiming at the problems existing in the desulfurization and decarburization of flue gas in current power plants, the present invention provides a method for combined removal of sulfur and carbon oxides in power plant flue gas by using residual heat of flue gas to analyze the solution after decarburization. The method uses ammonia water as an absorbent, And realize the recycling of ammonia, reduce the cost of absorbent, and solve many disadvantages brought by ammonia for denitrification, limestone for desulfurization, and MEA for decarbonization in the current treatment process of atmospheric gaseous pollutants; the invention effectively utilizes the waste heat of flue gas, Heating the solution after decarburization changes the traditional analytical single steam heating method, realizes the cascade utilization of power plant energy, greatly reduces the energy consumption of carbon capture, and its energy consumption is only about 1/3 of the traditional MEA method; the present invention Ammonia absorbent is used to realize the integration of desulfurization and decarbonization, and a new coal-fired flue gas pollution control mode has been constructed. The by-products of desulfurization have a large utilization market, and the process is characterized by high efficiency, cleanness and low energy consumption; and the desulfurization and decarbonization system is highly integrated. , has a good application prospect in the desulfurization and decarbonization of flue gas in coal-fired power plants.

Description of drawings

Fig. 1 is a schematic diagram of device embodiment 1 of the present invention;

Fig. 2 is a schematic diagram of Embodiment 2 of the device of the present invention.

The meanings of the symbols in the drawings are as follows: 1. Electrostatic precipitator; 2. Induced fan; 3. Heat exchanger; 4. Desulfurization tower; 5. Oxidation fan; 6. Solid-liquid separation device; 7. Horizontal flue; Carbon tower; 9. Flue gas condenser; 10. Cooling tower; 11. Ammonia water storage tank; 12. Analytical tower; 13. Condenser; 14. Ammonia water return pump; 15. Desulfurization ammonia supply pump; 16. Extraction pump; 17 1. Decarbonization ammonia supply pump; 18. Solution extraction pump after decarbonization; 19. Decarbonization circulation pump; 20. Desulfurization circulation pump; 21. Desulfurization tower nozzle; 22. Decarbonization tower nozzle; 23. High temperature steam; 24. High temperature flue.

Detailed ways

The method of the present invention uses ammonia water as an absorbent to integrally remove sulfur and carbon oxides in the flue gas of a power plant. After carbonization, the inlet temperature of the flue gas is 100-180°C, and the inlet temperature of the solution after decarburization is 20-30°C. After decarburization, the solution is preheated to 70-80°C and then enters the desorption tower for steam heating and analysis. After decarburization, the solution (the main component is ammonium bicarbonate) decomposes, ammonia and CO2 are separated, and a small part of the volatile and escaped ammonia gas and The analyzed CO2 enters the condenser together to remove escaped ammonia, and the separated CO2 is to be stored or converted for utilization. The ammonia water condensed by the condenser and the ammonia water resolved by the desorption tower are returned to the ammonia water storage tank in the removal process for recycling. The low-temperature flue gas cooled by heat exchange enters the desulfurization tower, where the ammonia solution is sprayed to remove sulfur dioxide in the flue gas. The ammonia water forms a separate circulation loop, the NH3/SO2 is about 2, and the pH of the slurry is 4-6. Ammonium sulfate is obtained after forced oxidation of ammonia water. After the solid content of ammonia water reaches 5-15% (wt%), it is extracted for solid-liquid separation, and the separated ammonium sulfate is used as fertilizer. After desulfurization, the flue gas enters the decarbonization tower, the decarbonization absorption liquid is ammonia water, the NH3/CO2 is 1.4-2.0, the pH of the circulating slurry is 8-10, and most of the carbon dioxide is absorbed here, reaching 5-10% (wt %) concentration after the decarburized solution was extracted and analyzed. After purification, the flue gas is condensed by the flue gas condenser to remove the escaping ammonia gas, and the small water droplets carried in the flue gas can be removed due to the impact effect, and a part of the heavy metal mercury carried in the flue gas will also be dissolved in the condensed water and removed ( Mainly elemental mercury), after desulfurization and decarbonization, the flue gas can be discharged from the cooling tower or the existing chimney.

The inventive method realizes the chemical cycle of ammonia, and the reaction formula involved in ammonia decarburization is as follows:

CO2 + NH3 + H2O → NH4HCO3

The actual reaction is more complicated, which can be regarded as a step-by-step reaction, and NH2COONH4 is first generated:

CO2 + NH3 → NH2COONH4

NH2COONH4 + H2O → NH4HCO3 + NH3

NH3 + H2O → NH4OH

NH4HCO3 +NH4OH → (NH4)2CO3 +H2O

(NH4)2CO3 +CO2 +H2O → 2NH4HCO3

The principle of ammonia desulfurization process is as follows:

(1) SO2＋H2O = H2SO3     (2) H2SO3＋(NH4)2SO4= NH4HSO4＋NH4HSO3     (3) H2SO3＋(NH4)2SO3 = 2NH4HSO3   (4) H2SO3＋NH3 = NH4HSO3     (5) NH4HSO3＋NH3 = (NH4)2SO3     (6) NH4HSO4＋NH3 = (NH4)2SO4

(7) (NH4)2SO3＋1/2O2 = (NH4)2SO4

Referring to Fig. 1, the device realizing the method of the present invention comprises high-temperature flue 24, desulfurization tower 4, decarburization tower 8, analysis tower 12, ammonia water storage tank 11, solution pump out 18 after decarburization, ammonia water return pump 14, desulfurization ammonia supply Pump 15, decarbonization ammonia supply pump 17, wherein the high-temperature flue, desulfurization tower, and decarburization tower are connected in sequence. The high-temperature flue gas dedusted by the electrostatic precipitator 1 is introduced by the induced draft fan 2 into the heat exchanger 3 installed at the high-temperature flue 24, and the decarburized solution is drawn out by the pump to send the decarburized solution into the heat exchanger for heating. The outlet of the heat exchanger is connected to the inlet of the analysis tower, and the preheated decarburized solution enters the analysis tower to be decomposed by high-temperature steam 23 . The separated ammonia water is returned to the ammonia water storage tank by the ammonia water return pump. The desulfurization ammonia supply pump is respectively connected to the ammonia water storage tank and the desulfurization holding tank of the desulfurization tower, and the decarbonization ammonia supply pump is respectively connected to the ammonia water storage tank and the decarbonization holding tank of the decarbonization tower. The ammonia water required in the whole desulfurization and decarbonization process Both are provided by the ammonia storage tank. After the decarburized solution is pumped out of the pump 18, a branch directly connected to the desorption tower is set. When the temperature fluctuation of the high-temperature flue gas does not meet the heating requirements or when a heat exchanger failure occurs, the decarburized solution can be directly connected to the decarburized solution by this branch. Send it to the desorption tower to keep the device running.

Still referring to Fig. 1, one or two layers of desulfurization nozzles 21 are provided on the upper part of the desulfurization tower 4, and the desulfurization circulating pump 20 is connected to the desulfurization holding tank and desulfurization nozzles 21 at the lower part of the desulfurization tower, and the cooled flue gas (temperature 50°C- 70°C) enters the desulfurization tower and is washed and desulfurized by the ammonia water sprayed by the desulfurization nozzle, and then enters the horizontal flue 7 for secondary washing. The desulfurization tower is also equipped with an oxidation fan 5, the outlet of the oxidation fan leads to the desulfurization liquid holding tank, the ammonium sulfite in the desulfurization liquid holding tank is oxidized by the forced oxidation air provided by the oxidation fan, and the generated ammonium sulfate is sent to the solid-liquid by the pump 16. Separation device 6 dehydrates to obtain ammonium sulfate fertilizer.

Still referring to Fig. 1, the upper part of the decarbonization tower 8 is provided with two layers of decarburization nozzles 22, and the decarbonization circulating pump 19 is connected to the decarburization liquid holding tank and the decarburization nozzles at the lower part of the decarbonization tower, and the flue gas after desulfurization is discharged in the decarburization tower. The ammonia water sprayed by the decarbonization nozzle is decarbonized by countercurrent washing and decarburization. A shell and tube flue gas condenser 9 is installed at the flue gas outlet of the decarbonization tower. This structure omits the conventional demister, and the escaped ammonia carried in the flue gas is dissolved The condensed water on the tube wall of the flue gas condenser is removed, and the small water droplets carried by the flue gas are also dehydrated due to collision with the tube wall of the condenser. The clean flue gas is discharged from the cooling tower 10 connected with the condenser. Existing chimneys can also be used to exhaust smoke.

Still referring to Fig. 1, the gas outlet of the desorption tower 12 is connected to the condenser 13, and the CO2 after desorption and a small part of volatile and escaped ammonia enter the condenser 13 together, and the ammonia is separated from the CO2 after condensation, and the separated CO2 is to be sealed up or converted and utilized . The ammonia water condensed by the condenser 13 is returned to the ammonia water storage tank 11 for recycling through the ammonia water return pump 14 together with the ammonia water resolved by the desorption tower.

Fig. 2 shows another embodiment of the device of the present invention, it is applicable to the combined desulfurization and decarburization device that has built the unit of desulfurization device, in this embodiment heat exchanger 3 is positioned at the inclined section of high-temperature flue 24, and horizontal flue 7 Connect the desulfurization tower 4 and the top of the decarburization tower 8 to each other. The working principle and working process of the device are the same as those in Embodiment 1, and will not be repeated here.

Claims (8)

1. A method for combined removal of sulfur and carbon oxides in power plant flue gas, which introduces power plant flue gas into the desulfurization tower and decarbonization tower of removal process to remove carbon and sulfur oxides therein, it is characterized in that: it uses Ammonia liquor is absorbent, removes the sulfur carbon oxide in the flue gas of power plant together, and described method is carried out as follows: a. The high-temperature flue gas after electrostatic dust removal is introduced into the heat exchanger, and the decarburized solution in the removal process is heated by the waste heat of the flue gas; b. The heated decarburized solution enters the desorption tower, decomposes ammonia water and returns it to the ammonia water storage tank; c. After heat exchange, the low-temperature flue gas at 40°C-50°C enters the desulfurization tower in the removal process, where sulfur dioxide in the flue gas is removed by spraying ammonia water; d. After desulfurization, the flue gas enters the decarbonization tower in the removal process, and the carbon dioxide in the flue gas is absorbed by spraying ammonia water. After decarburization, the solution is sent to the heat exchanger, and the purified flue gas is condensed by the flue gas condenser to remove carbon dioxide in the flue gas. Ammonia, the small water droplets carried in the flue gas collide with the condenser and are removed. 2. The method for combined removal of sulfur and carbon oxides in power plant flue gas according to claim 1, characterized in that: in the step a, the high-temperature flue gas will heat the decarburized solution to 70-80 ° C, after heating The decarburized solution enters the desorption tower and is then heated and decomposed by steam. A small part of the volatile and escaped ammonia gas enters the condenser together with the desorbed CO ₂ to remove the escaped ammonia gas. The separated CO ₂ is to be stored or converted for utilization. 3. the method for combined removal of sulfur and carbon oxides in power plant flue gas according to claim 2, is characterized in that: desulfurization tower ammonia spray desulfurization in the described c step, ammoniacal water in the desulfurization holding tank adjusts pH 4-6 , ammonium sulfite is oxidized by the forced oxidation air provided by the oxidation fan in the desulfurization holding liquid tank to generate ammonium sulfate. When the solid content of ammonium sulfate reaches 5-15% (wt%), it is discharged by the extraction pump and sent to the solid-liquid After dehydration in the separation system, ammonium sulfate fertilizer is obtained. 4. the method for combined removal of sulfur and carbon oxides in power plant flue gas according to claim 3, is characterized in that: said d step uses ammonia water to spray decarburization in the decarburization tower, and adjusts the decarburization in the liquid holding tank Decarburized ammonia pH 8-10. 5. A device for the combined removal of sulfur and carbon oxides in power plant flue gas for the method described in claim 1, 2, 3 or 4, characterized in that: it comprises a high-temperature flue (24), a desulfurization tower (4 ), decarburization tower (8), desorption tower (12), ammonia water storage tank (11), solution extraction pump after decarburization (18), ammonia water return pump (14), desulfurization ammonia supply pump (15), decarbonization supply Ammonia pump (17), wherein the high-temperature flue, the desulfurization tower, and the decarbonization tower are connected in sequence, the high-temperature flue is provided with a heat exchanger (3), and the decarburized solution extraction pump is respectively connected to the decarburization tower. The carbon liquid holding tank and the heat exchanger inlet, the heat exchanger outlet are connected to the analytical tower inlet, the ammonia water return pump is respectively connected to the analytical tower ammonia water outlet and the ammonia water storage tank, and the desulfurization ammonia supply pump is connected to the ammonia water storage tank and the desulfurization tower respectively. The desulfurization holding tank and the decarburization ammonia supply pump are respectively connected to the ammonia water storage tank and the decarbonization liquid holding tank of the decarbonization tower. 6. The device for combined removal of sulfur and carbon oxides in power plant flue gas according to claim 5, characterized in that: the upper part of the decarbonization tower (8) is provided with a decarburization nozzle (22), and the decarbonization circulating pump (19) Connect the decarburization nozzle and the decarburization liquid holding tank at the lower part of the decarbonization tower, and install a tube-type flue gas condenser (9) at the outlet of the decarbonization tower flue gas, and the outlet of the flue gas condenser is connected to the cooling tower (10 ). 7. The device for combined removal of sulfur and carbon oxides in power plant flue gas according to claim 6, characterized in that: the upper part of the desulfurization tower is provided with a desulfurization nozzle (21), which is connected to the desulfurization nozzle by a desulfurization circulating pump (20) and the desulfurization liquid holding tank at the lower part of the desulfurization tower. The desulfurization tower is also equipped with an oxidation fan (5), and the outlet of the oxidation fan leads to the desulfurization liquid holding tank. The desulfurization tower is also equipped with a discharge pump (16) and a solid-liquid separation device (6). The discharge pump connects the desulfurization holding tank with the solid-liquid separation device. the 8. The device for combined removal of sulfur and carbon oxides in power plant flue gas according to claim 7, characterized in that: the gas outlet of the desorption tower (12) is connected to the condenser (13).

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