CN102343201A - Process for removing acid gas from flue gas by using residual heat of flue gas - Google Patents

Abstract

A process for removing acidic gases by using the waste heat of flue gas. It is to pass the flue gas into the heat exchanger Ⅰ, the temperature of the flue gas is lowered, and it enters the desulfurization absorption tower, and the heat exchanger in the tube side The water is heated and vaporized into the phase separator, the heat exchanger and the phase separator are combined to form a waste heat boiler, and the steam pressure generated is 3-6 atmospheres, and the water steam is divided into three streams and enters the low-pressure steam turbine Ⅰ and low-pressure steam turbine Ⅱ and the heater respectively. The steam drives the low-pressure steam turbine I, which is used as the power source of the refrigerator to obtain chilled water, and the chilled water is used as the refrigerant for the desulfurization absorption tower, denitration absorption tower and _CO2 absorption tower respectively, so that their temperatures are kept at their respective required temperatures. The second stream of water steam is used to drive the low-pressure steam turbine II, compress the desulfurized flue gas, and enter the denitrification absorption tower to remove NOx and produce dilute nitric acid at the same time, and the third steam is provided for the _CO2 regeneration tower through the heater H1 The heat source is used to regenerate the CO ₂ absorbing liquid for recycling while generating and collecting CO ₂ .

Description

A process for removing acidic gas by using waste heat of flue gas

technical field

The invention relates to a technology for removing acid gas from flue gas by using its waste heat.

Background technique

my country is one of the few countries in the world where coal is the main energy source, and it is the largest producer and consumer of coal in the world. Coal still accounts for a large proportion of my country's energy structure, and my country's coal-based energy consumption structure is the most important reason for my country's increasingly serious air pollution. According to statistics, 90% of sulfur dioxide, 67% of nitrogen oxides, and 70% of soot emissions in my country come from coal combustion. Among them, coal-fired power stations, coal-fired industrial boilers, coal-fired furnaces and other flue gas pollution problems are the most prominent. Taking the 10-year period from 2001 to 2010 as a sample, coal power accounts for about 75% of China's annual power generation. With the accelerated pace of industrialization in our country, the power consumption is also increasing, and more and more coal is needed for power generation. The resulting flue gas emissions are also increasing the pollution of the atmosphere. Taking a 1 million-kilowatt coal-fired power plant as an example, its sulfur dioxide emissions are 26,000 tons per year, nitrogen oxide emissions are 14,000 tons per year, and carbon dioxide emissions are 6 million tons per year. Carbon dioxide in the flue gas emitted by coal-fired power plants is the main substance that causes the greenhouse effect, and SO ₂ and NOx are the main sources of air pollution such as acid rain and photochemical smog. How to eliminate these pollutions is an urgent problem to be solved. However, the flue gas discharged from coal-fired power plants contains a certain amount of waste heat, and the direct discharge wastes a huge amount of latent heat, which does not meet the requirements of energy saving. In view of the above situation, the present invention proposes a new process for removing the acid gas contained in the waste heat of the flue gas. This process can not only make full use of the waste heat in the flue gas, but also remove the sulfur oxidation in the flue gas. pollutants, nitrogen oxides and CO ₂ , so that the flue gas meets the emission standards and meets the requirements of energy saving and emission reduction. At the same time, part of the acidic substances are recycled to obtain nitric acid products and CO ₂ . It is used as a raw material in various fields such as chemical industry and modern agriculture, thereby creating value.

Contents of the invention

The purpose of the present invention is to provide a new process for removing the acid gas contained in the flue gas by using the residual heat of the flue gas, mainly removing sulfur oxides, nitrogen oxides and carbon dioxide, so that the flue gas emission can reach the corresponding national standards, And recover useful chemical resources therein.

In order to achieve the above object, the technical scheme of the present invention is as follows:

A process for removing acidic gas by using waste heat of flue gas, which is composed of desulfurization system, denitrification system and decarbonization system. Its process is shown in Figure 1, and it includes the following steps:

(1) The flue gas first passes through the electrostatic precipitator to remove most of the dust in the flue gas, and then the flue gas is passed into the heat exchanger ⅠE1 through the pipe 2, the water goes through the tube side, and the flue gas goes through the shell side , after heat exchange, the temperature of the flue gas decreases and enters the desulfurization absorption tower T1, while the water in the tube side is heated and vaporized and then enters the phase separator V1, and the phase-separated water returns to the heat exchanger IE1 for exchange. The combination of heater E1 and phase separator V1 is equivalent to a waste heat boiler, and the steam pressure generated is 3~6 atmospheres, and the water vapor is divided into three streams through the flow divider IS1 and enters the low-pressure steam turbine ITU1, low-pressure steam turbine IITU2 and heater H1 respectively. The water vapor drives the low-pressure steam turbine ITU1, and the steam turbine TU1 is used as the power source of the refrigerator C1 to cool the refrigerator C1, thereby obtaining chilled water (ice brine, etc.), and the ice brine is sent to the cooler IC2, cooling The cooler ⅡC3 and cooler ⅢC4 are used as the refrigerant for the desulfurization absorption tower T1, denitration absorption tower T2 and _CO2 absorption tower T3, so that the temperatures of the desulfurization absorption tower T1, denitration absorption tower T2 and _CO2 absorption tower T3 are kept at their respective required temperatures , the second stream of steam is used to drive the low-pressure steam turbine IITU2, which is used as the power source of the compressor CO1 to make the compressor CO1 do work and compress the flue gas discharged from the top of the desulfurization absorption tower T1 to make its pressure change from micro The positive pressure is increased to above 0.25MPa, and enters the denitrification absorption tower T2 to remove NOx and produce dilute nitric acid at the same time, and the third steam passes through the heater H1 to provide heat source for the _CO2 regeneration tower T4 to regenerate the _CO2 absorption liquid, and circulate use;

(2) The flue gas exchanged by heat exchanger IE1 enters the bottom of desulfurization absorption tower T1, and the sulfur absorption liquid (usually a mixed solution of calcium hydroxide and sodium hydroxide) fed from pipeline 3 at the top of desulfurization absorption tower T1 Fully contacted, the desulfurized flue gas is discharged from the top of the desulfurization absorption tower T1, mixed with the air entering from the pipeline 12 (the amount of mixed air is determined by stoichiometric calculation according to the amount of NO contained in the flue gas) and enters the steam turbine IITU2 In the driven compressor CO1, the pressure of the gas increases to above 0.25MPa and then enters the denitrification absorption tower T2 from the bottom, while the sulfur absorption liquid descends to the bottom of the tower along the desulfurization tower, and the solid phase is removed through solid-liquid separation, and the liquid phase can be Return to the desulfurization liquid distribution tank for recycling;

(3) After the mixture of pressurized flue gas and air enters the denitrification absorption tower T2, it contacts with the NOx absorption liquid (usually water) that enters through the pipeline 5 at the top of the denitrification absorption tower T2. discharge from the top, and then enter the _CO2 absorption tower T3, while the absorption liquid (dilute nitric acid) descending from top to bottom along the denitrification tower enters the bottom of the denitrification tower, and is transported to the nitric acid product storage tank through pipeline 6;

(4) The flue gas after denitrification enters the CO ₂ absorption tower T3 from the bottom. The CO ₂ absorption liquid generally adopts hot potassium alkali solution or organic amine. After the CO ₂ in the flue gas is absorbed in the decarbonization tower T3, The top of the tower is discharged through pipeline 7, at this time, the acidic components in the flue gas are basically removed, among which, SOx and NOx can be controlled below 50ml/ ^m3 and 30ml/ ^m3 respectively, and _CO2 can be lower than Below 5000ml/m ³ , the CO ₂ absorption liquid that descends from the CO ₂ absorption tower T3 from top to bottom is pumped to the heat exchanger IIE2 through the bottom of the tower to exchange heat and enter the upper part of the CO ₂ regeneration tower T4;

(5) CO ₂ is re-desorbed in the CO ₂ regeneration tower T4, enters the filling system from the top of the tower through the pipeline 11, and pressurizes filling to obtain CO ₂ products, which are sold or used to manufacture other products. The regenerated CO ₂ The absorption liquid passes through the bottom of the T4 tower and returns to the heat exchanger IIE2 through the pump ⅢP3. After heat exchange, it enters the decarbonization absorption tower T3 through the mixer M2 for recycling. The heat required by the CO ₂ regeneration tower T4 is provided by the steam provided by the phase separator V1 through the heater. H1 is obtained, and the condensed liquid is returned to the mixer M1 through the pump IP1 for recycling, and the refrigerant at the outlet of the cooler IC2, cooler IIC3 and cooler IIIC4 is pumped back to the refrigerant refrigerator C1 through the pump P2 to be refrigerated again and recycled.

Through the above five steps, the heat source in the flue gas can be continuously used to provide the required energy (including heat energy, pressure energy and cold energy) for the removal of sulfur oxides, nitrogen oxides and _CO2 , and make The flue gas meets the emission standard. It should be pointed out that the above steps are carried out continuously. Under steady conditions, the five steps are carried out simultaneously and organically combined, not intermittently. The present invention is only divided into five steps for the convenience of description.

According to the energy balance calculation of the whole process, for the flue gas above 300°C, the energy contained in the flue gas is much higher than the total energy required for the removal of acidic substances in this process (about 2 times more). Therefore, considering the loss of the energy conversion process and the impact of heat utilization efficiency, as long as the design and selection of the process and equipment are appropriate, the energy for removing acidic substances in this process can be fully self-sufficient.

The above-mentioned process for removing its acidic gas, the removal method of the sulfur oxide is a mixed solution of calcium hydroxide and sodium hydroxide (the mass fraction of calcium hydroxide and sodium hydroxide in the solution is 10-40%, hydrogen The mass ratio of calcium oxide and sodium hydroxide is 4:1) as the absorption liquid, the temperature of the flue gas entering the absorption tower is above 120°C, and the removal rate of sulfur oxides is above 90%.

In the process for removing the acid gas mentioned above, the nitrogen oxide removal method uses air and water as the absorbing liquid, and the temperature is kept at 5-30°C. The ratio of NOx-containing flue gas to air is determined as follows: 1 volume of NO consumes 0.75 volume of O ₂ , 1 volume of NO ₂ consumes 0.25 volume of O ₂ , and 1 volume of air contains 0.2 volume of O ₂ . According to the content, ratio and flow of NO and _NO2 in the flue gas, the theoretical air flow is calculated, and the ratio of the actual air flow to the theoretical air flow is 1.5~2:1, so as to obtain the required actual air volume.

For the above-mentioned process of removing its acid gas, the CO ₂ removal method generally adopts a hot potassium alkali (the composition is K ₂ CO ₃ , and the absorption effect is the best when the mass fraction is 30%) solution, or an organic amine can be used (Industrial application of mature monoethanolamine (MEA). Diethanolamine (DEA), triethanolamine (TEA) or N-methyldiethanolamine (MDEA)) as the absorption liquid, the absorption reaction is a reversible reaction, and the temperature needs to be kept at the respective For the required temperature, the temperature of the organic amine as the absorption liquid should be kept at 20~40°C, while the temperature of the hot potash solution should be kept at 95~105°C.

For the above-mentioned process of removing its acid gas, the CO ₂ regeneration method is selected to use steam heating, so that the temperature can be kept at about 110°C. The principle is that when the temperature of the solution rises or the pressure is low, the substance formed by the absorption solution that absorbs CO ₂ reacts in reverse, and CO ₂ can be released, and the solution can be regenerated.

In the above-mentioned process for removing its acidic gas, it is determined whether the denitrification step of the denitrification absorption tower T2 is required in the process according to whether the flue gas contains nitrogen oxides.

The new process of utilizing the waste heat of flue gas to remove its acid gas of the present invention has the following advantages:

(1) The present invention aims at current coal-fired power projects where the flue gas contains a large amount of pollutants such as sulfur oxides, nitrogen oxides, and CO ₂ . If discharged directly, it will cause serious pollution to the environment. At present, desulfurization, denitrification and decarbonization And CO ₂ regeneration is very mature in technology, but because the desulfurization, denitrification and decarbonization systems need to be carried out under low temperature and high pressure, especially the high pressure system requires additional energy consumption, and the desulfurization, denitrification and decarbonization devices use absorption Liquid absorption method, since the absorption process is a strong exothermic process, if the heat released in each absorption section is not transferred in time, the absorption effect will be unsatisfactory. Compressor CO1, coolers C1, C2, C3, C4, heater H1 all require additional energy input. The flue gas itself contains a certain amount of waste heat, and direct discharge does not meet the requirements of energy saving. The present invention aims at this situation, obtains the heated steam through the heat exchanger E1 and the phase separator V1, and provides energy sources for the compressor CO1, the coolers C1, C2, C3, C4, and the heater H1. The new process not only makes full use of the waste heat in the flue gas, but also removes sulfur oxides, nitrogen oxides and CO ₂ in the flue gas and collects the CO ₂ , so that the flue gas can meet the emission standards without additional The energy input meets the requirements of energy saving and emission reduction.

(2) In the literature, there are many studies on desulfurization, denitrification, decarbonization and _CO2 regeneration alone, but few studies on integrated technologies. The invention organically couples the desulfurization system-denitration system- _CO2 absorption system- _CO2 regeneration system together, so that the desulfurization, denitrification, decarbonization and _CO2 regeneration of flue gas are integrated. In actual use, one or more of desulfurization, denitrification, decarbonization and _CO regeneration devices can be determined according to the content of nitrogen oxides, sulfur oxides and _CO2 in the flue gas.

(3) This patent does not simply remove the acidic substances in the flue gas, but recycles the removed acidic substances, and partially recycles the acidic substances to obtain nitric acid products and CO ₂ . It is used as a raw material in various fields such as chemical industry and modern agriculture, thereby creating value.

Description of drawings

Fig. 1 is a kind of technical flow schematic diagram of the production technology and the device of utilizing flue gas residual heat to remove its acid gas of the present invention, wherein: T1 is desulfurization absorption tower; T2 is denitrification absorption tower; _T3 is CO Absorption tower; T4 _E1 is heat exchanger Ⅰ; E2 is heat exchanger Ⅱ; C1 is refrigerator; C2 is cooler Ⅰ; C3 is cooler Ⅱ; C4 is cooler Ⅲ; TU1 is low-pressure steam turbine Ⅰ; TU2 CO1 is the compressor; P1 is the pump I; P2 is the pump II; P3 is the pump III; M1, M2, M3, M4 are the mixers; Supplement fresh water feed pipe, 2 is the flue gas feed pipe, 3 is the desulfurization absorption liquid feed pipe, 4 is the sulfuric acid discharge pipe, 5 is the denitrification absorption liquid feed pipe, 6 is the nitric acid discharge pipe, 7 is the The flue gas discharge pipe after desulfurization, denitrification and decarburization, 8 is the liquid water feed pipe, 9 and 10 are respectively the added denitrification absorption liquid and the absorption liquid feed pipe returned by the desorption tower, 11 is the _CO2 collection pipe, 12 for the air duct.

Detailed ways

The present invention is described in detail by the following examples, but it should not be understood as a limitation to the scope of patent protection of the present invention.

Example 1:

The flue gas being treated now contains 13.98% CO ₂ , 3.49% O ₂ , 72.87% N ₂ , 0.21% SO ₂ , 9.45% H ₂ O in terms of volume fraction, and the flue gas volume is 1,124,980 m ³ /h, the flue gas temperature is 300°C. It can be seen from the above content that since it does not contain nitrogen oxides and contains SO ₂ and CO ₂ acid gases, desulfurization absorption tower T1, CO ₂ absorption tower T3 and CO ₂ regeneration tower T4 are required, and denitrification absorption tower T2 is not required. The flue gas enters the heat exchanger E1 through the pipeline 2, so that the temperature of the flue gas is reduced from 300°C to 120°C, and the water is heated at the same time, and the mixture of water vapor and liquid water obtained enters the phase separator V1, and the water returns after phase separation Heat exchanger E1 recirculates. The steam is divided into two streams through the splitter S1, and one stream is used as a heating source, which is heated by the heater H1 for the _CO2 regeneration tower T4, so that the temperature of the desorption tower T4 is 110°C. The other stream enters the low-pressure steam turbine ITU1, which converts heat energy into mechanical energy, making the refrigerator C1 refrigerate, thereby obtaining ice brine, and the ice brine passes through the cooler C2 to keep the desulfurization tower T1 at a constant temperature of 120°C, and passes through the cooler C4 to make the _CO2 absorption tower Keep a constant temperature of 25°C to prevent the temperature from rising, which is not conducive to the absorption of sulfur oxides and carbon oxides. The flue gas cooled by the heat exchanger ⅠE1 enters the desulfurization absorption tower T1. The desulfurization absorption tower T1 adopts a packed tower with a diameter of 9.9 meters and a tower height of 59.5 meters. Calcium hydroxide and sodium hydroxide with a solute mass fraction of 20% are used. The mixed solution of sulfur is used as the absorption liquid, which is fed from the top of the tower through pipeline 3, and its flow rate is 18585. After absorption, the sulfur absorption liquid descends to the bottom of the tower along the desulfurization absorption tower T1, and the solid phase is removed through solid-liquid separation, and the liquid phase can return to The desulfurization liquid dosing tank is recycled. The desulfurized flue gas enters the _CO2 absorption tower T3. The _CO2 absorption tower T3 adopts a packed tower with a diameter of 9.8 meters and a tower height of 49 meters. Monoethanolamine (MEA) is used as the absorption liquid and enters the _CO2 absorption tower T3 through a pipeline 9. The flow rate of the absorbed flue gas is from Pipeline 7 is discharged into the atmosphere after entering the chimney, because the acidic components in the flue gas are basically all removed at this time, which meets the emission standard. The CO ₂ absorption liquid that descends from the CO ₂ absorption tower T3 from top to bottom is pumped from the bottom of the tower to E2 for heat exchange and then enters the upper part of the CO ₂ regeneration tower T4. Using part of the steam in the phase separator V1 to provide heat source for heating, the desorption tower T4 has a diameter of 4.3 meters and a tower height of 21.5 meters, and the temperature inside the tower is maintained at about 110°C. CO ₂ is re-desorbed in the CO ₂ regeneration tower T4 with a flow rate of 286235kg·h ^-1 , enters the filling system from the top of the tower through pipeline 11, and is pressurized and filled to obtain CO ₂ products, which are sold or used to manufacture other products. The monoethanolamine (MEA) at the bottom of the tower is returned to the _CO2 absorption tower T3 for recycling through the pump P3.

Example 2:

The flue gas being treated now contains 7.6% CO ₂ , 10% O ₂ , 54% N ₂ , 28% H ₂ O and 1500 mg SO ₃ per cubic meter in terms of volume fraction. NO _X is mainly NO, which is 1200 mg, the flue gas volume is 12000 m ³ /h, and the flue gas temperature is 300°C. It can be seen from the above content that since it contains nitrogen oxides, _SO2 and _CO2 acid gases, desulfurization absorption tower T1, denitrification tower absorption T2, _CO2 absorption tower T3 and _CO2 regeneration tower T4 are required. First pass the flue gas through the heat exchanger E1, so that the temperature of the flue gas is reduced from 300°C to 120°C, and at the same time, the water from the pipeline 1 through the mixer M1 is heated after passing through the heat exchanger E1, and the heated water and steam The mixture enters the phase separator V1, and the liquid water after phase separation returns to the heat exchanger E1 through the mixer M1 for recycling. The water vapor after phase separation is divided into three streams through the splitter S1, one stream is used as a heating source, and the _CO2 regeneration tower T4 is heated by the heater H1, and the second stream enters the low-pressure steam turbine ITU1, which serves as the power source of the refrigerator C1 , so that the refrigerator C1 is refrigerated, thereby obtaining frozen water (ice brine, etc.). The ice brine is sent to the cooler IC2, cooler II C3 and cooler III C4 through the splitter S2 respectively as the refrigerant for the desulfurization absorption tower T1, denitration absorption tower T2 and _CO2 absorption tower T3, so that the desulfurization absorption tower T1, denitration absorption tower T1 The temperatures of T2 and _CO2 absorption tower T3 are kept at 120°C, 20°C and 25°C respectively to prevent the temperature rise from being unfavorable to the absorption of sulfur oxides, nitrogen oxides and _CO2 . The third stream of water vapor passes through the low-pressure steam turbine IITU2, which serves as the power source of the compressor CO1 to make the compressor CO1 do work and compress the flue gas discharged from the top of the desulfurization absorption tower T1 to increase its pressure from a slight positive pressure to above 0.25MPa, and enter the denitrification absorption tower T2.

The flue gas cooled by the heat exchanger E1 enters the desulfurization absorption tower T1, which uses a packed tower with a diameter of 1 meter and a tower height of 7 meters, using calcium hydroxide and sodium hydroxide with a solute mass fraction of 10%. The mixed solution is used as the absorption liquid, which is fed from the top of the tower through the pipeline 3, and its flow rate is 85. After absorption, the sulfur absorption liquid descends to the bottom of the tower along the desulfurization absorption tower T1, and the solid phase is removed through solid-liquid separation, and the liquid phase can return to the desulfurization The liquid distribution tank is recycled. The flue gas after desulfurization is mixed with the air with a flow rate of 66° from the pipeline 12, enters the compressor CO1 for pressurization, and then enters the denitrification absorption tower T2. The denitrification absorption tower T2 is a packed tower with a diameter of 0.9 meters and a height of 5 meters. The NOx absorbing liquid water is passed through the pipeline 5 at the top of the tower. The absorption liquid (dilute nitric acid) descending from top to bottom along the denitrification tower enters the bottom of the denitrification absorption tower T2, and is transported to the nitric acid product storage tank through pipeline 6. The de-stocked flue gas comes out from the top of the denitrification absorption tower T2 and enters the _CO2 absorption tower T3. The _CO2 absorption tower T3 is a packed tower with a diameter of 1.1 meters and a height of 5.5 meters. Diethanolamine (DEA) enters the _CO2 absorption tower T3 from the pipe 9 through the mixer M2 as the absorption liquid, and the flow rate is . The fully contacted flue gas passes through the pipe 7 from the top of the tower and is discharged from the chimney. Since the acid components in the flue gas are basically removed at this time, it meets the emission standard. The organic amine absorption liquid that absorbs _CO2 is heated from the _CO2 absorption tower T3 through the heat exchanger IIE2 and then enters the _CO2 regeneration tower T4. It is heated by part of the steam from the phase separator V1 to keep the temperature at about 115°C. After desorption, it is discharged from the tower The top pipeline 11 enters the filling system according to the flow rate, and pressurizes filling to obtain CO ₂ products, which are sold or used to manufacture other products. The diethanolamine (DEA) at the bottom of the tower passes through the pump P3 and passes through the heat exchanger IIE2 for heat exchange, and then flows back to the _CO2 absorption tower T3 through the mixer M2 for recycling.

Example 3:

Now the flue gas is treated, in terms of volume fraction, it contains 12.06% CO ₂ , 10.1% O ₂ , 60.54% N ₂ , 0.12% SO ₂ , 0.1% NOx, 17.08% H ₂ O, smoke The gas volume is 1,442,650 m ³ /h, and the flue gas temperature is 415°C. It can be seen from the above content that since it contains nitrogen oxides, _SO2 and _CO2 acid gases, desulfurization absorption tower T1, denitrification absorption tower T2, _CO2 absorption tower T3 and _CO2 regeneration tower T4 are required. First pass the flue gas through the heat exchanger IE1, so that the temperature of the flue gas is reduced from 415°C to 120°C, and at the same time, the water from the pipeline 1 through the mixer M1 is heated after passing through the heat exchanger E1, and the heated water and steam The mixture enters the phase separator V1, and the liquid water after phase separation returns to the heat exchanger IE1 for recycling through the mixer M1. The water vapor after phase separation is divided into three streams through the splitter S1, one stream is used as a heating source, and the _CO2 regeneration tower T4 is heated by the heater H1, and the second stream enters the low-pressure steam turbine ITU1, which serves as the power source of the refrigerator C1 , so that the refrigerator C1 is refrigerated, thereby obtaining frozen water (ice brine, etc.). The ice brine is sent to the cooler IC2, cooler II C3 and cooler III C4 through the splitter S2 respectively as the refrigerant for the desulfurization absorption tower T1, denitration absorption tower T2 and _CO2 absorption tower T3, so that the desulfurization absorption tower T1, denitration absorption tower T1 The temperature of T2 and _CO2 absorption tower T3 is maintained at 130°C, 30°C and 40°C respectively to prevent the temperature rise from being unfavorable to the absorption of sulfur oxides, nitrogen oxides and _CO2 . The third stream of steam passes through the low-pressure steam turbine IITU2, which serves as the power source of the compressor CO1 to make the compressor CO1 do work and compress the flue gas discharged from the top of the desulfurization absorption tower T1 to increase its pressure from a slight positive pressure to above 0.25MPa, and enter the denitrification absorption tower T2.

The flue gas cooled by the heat exchanger ⅠE1 enters the desulfurization absorption tower T1. The desulfurization absorption tower T1 adopts a packed tower with a diameter of 11.29 meters and a tower height of 60 meters. Calcium hydroxide and sodium hydroxide with a solute mass fraction of 40% are used. The mixed solution of sulfur is used as the absorption liquid, which is fed from the top of the tower through pipeline 3, and its flow rate is 13618. After absorption, the sulfur absorption liquid descends to the bottom of the tower along the desulfurization absorption tower T1, and the solid phase is removed through solid-liquid separation, and the liquid phase can return to The desulfurization liquid dosing tank is recycled. The desulfurized flue gas is mixed with the air with a flow rate of 5500 from the pipeline 12, enters the compressor CO1 for pressurization, and then enters the denitrification absorption tower T2. The denitrification tower T2 is a packed tower with a diameter of 10.97 meters and a height of 48 meters. The NOx absorbing liquid water is passed through the pipeline 5 at the top of the tower. The absorption liquid (dilute nitric acid) that descends from top to bottom along the denitration absorption tower T2 enters the bottom of the denitration absorption tower T2, and is transported to the nitric acid product storage tank through pipeline 6. The de-stocked flue gas comes out from the top of the denitrification absorption tower T2 and enters the _CO2 absorption tower T3.

The flue gas after denitrification enters the _CO2 absorption tower T3. The _CO2 absorption tower T3 adopts a packed tower with a diameter of 9 meters and a tower height of 38 meters. Triethanolamine (TEA) is used as the absorption liquid and enters the _CO2 absorption tower T3 through the pipeline 9. Pipeline 7 is discharged into the atmosphere after entering the chimney, because the acidic components in the flue gas are basically all removed at this time, which meets the emission standard. The CO ₂ absorption liquid that descends from the CO ₂ absorption tower T3 from top to bottom is pumped to the heat exchanger IIE2 through the bottom of the tower to exchange heat and enter the upper part of the CO ₂ regeneration tower T4. Using part of the steam in the phase separator to provide heat source heating, the desorption tower T4 has a diameter of 4 meters and a height of 19 meters, and the temperature inside the tower is maintained at about 115°C. In the CO ₂ regeneration tower T4, CO ₂ is desorbed again, and the flow rate is , enters the filling system from the top of the tower through the pipeline 11, and pressurizes filling to obtain CO ₂ products, which are sold or used to manufacture other products. The triethanolamine (TEA) at the bottom of the tower is returned to the _CO2 absorption tower T3 through the pump P3 for recycling.

Example 4:

Now the flue gas is treated, in terms of volume fraction, it contains 12.06% CO ₂ , 10.1% O ₂ , 60.54% N ₂ , 0.12% SO ₂ , 0.1% NOx, 17.08% H ₂ O, smoke The gas volume is 1,442,650 m ³ /h, and the flue gas temperature is 360°C. It can be seen from the above content that since it contains nitrogen oxides, _SO2 and _CO2 acid gases, desulfurization absorption tower T1, denitrification absorption tower T2, _CO2 absorption tower T3 and _CO2 regeneration tower T4 are required. First pass the flue gas through the heat exchanger IE1, so that the temperature of the flue gas is reduced from 360°C to 120°C, and at the same time, the water from the pipeline 1 through the mixer M1 is heated after passing through the heat exchanger IE1, and the heated water and steam The mixture enters the phase separator V1, and the liquid water after phase separation returns to the heat exchanger E1 through the mixer M1 for recycling. The water vapor after phase separation is divided into three streams through the splitter S1, one stream is used as a heating source, and the _CO2 regeneration tower T4 is heated by the heater H1, and the second stream enters the low-pressure steam turbine ITU1, which serves as the power source of the refrigerator C1 , so that the refrigerator C1 is refrigerated, thereby obtaining frozen water (ice brine, etc.). The ice brine is sent to the cooler IC2, cooler II C3 and cooler III C4 through the splitter S2 respectively as the refrigerant for the desulfurization absorption tower T1, denitration absorption tower T2 and _CO2 absorption tower T3, so that the desulfurization absorption tower T1, denitration absorption tower T1 The temperature of T2 and _CO2 absorption tower T3 is maintained at 120°C, 25°C and 95°C respectively to prevent the temperature rise from being unfavorable to the absorption of sulfur oxides, nitrogen oxides and _CO2 . The third stream of water vapor passes through the low-pressure steam turbine IITU2, which serves as the power source of the compressor CO1 to make the compressor CO1 do work and compress the flue gas discharged from the top of the desulfurization absorption tower T1 to increase its pressure from a slight positive pressure to above 0.25MPa, and enter the denitrification absorption tower T2.

The flue gas cooled by the heat exchanger ⅠE1 enters the desulfurization absorption tower T1. The desulfurization absorption tower T1 adopts a packed tower with a diameter of 11.29 meters and a tower height of 60 meters. Calcium hydroxide and sodium hydroxide with a solute mass fraction of 30% are used. The mixed solution of sulfur is used as the absorption liquid, which is fed from the top of the tower through pipeline 3, and its flow rate is 13618. After absorption, the sulfur absorption liquid descends to the bottom of the tower along the desulfurization absorption tower T1, and the solid phase is removed through solid-liquid separation, and the liquid phase can return to The desulfurization liquid dosing tank is recycled. The desulfurized flue gas is mixed with the air with a flow rate of 5500 from the pipeline 12, enters the compressor CO1 for pressurization, and then enters the denitrification absorption tower T2. The denitrification absorption tower T2 is a packed tower with a diameter of 10.97 meters and a height of 48 meters. The NOx absorbing liquid water is passed through the pipeline 5 at the top of the tower. The absorption liquid (dilute nitric acid) descending from top to bottom along the denitrification absorption tower enters the bottom of the denitrification tower, and is transported to the nitric acid product storage tank through pipeline 6. The de-stocked flue gas comes out from the top of the denitrification absorption tower T2 and enters the _CO2 absorption tower T3.

The flue gas after denitrification enters the _CO2 absorption tower T3. The _CO2 absorption tower T3 adopts a packed tower with a diameter of 10 meters and a tower height of 48 meters. The hot potash is used as the absorption liquid, and enters the _CO2 absorption tower T3 through the pipeline 9. After entering the chimney, it is discharged into the atmosphere. Since the acidic components in the flue gas are basically removed at this time, it meets the emission standards. The CO ₂ absorption liquid that descends from the CO ₂ absorption tower T3 from top to bottom is pumped to the heat exchanger IIE2 through the bottom of the tower to exchange heat and enter the upper part of the CO ₂ regeneration tower T4. Using part of the steam in the phase separator to provide heat source heating, the desorption tower T4 has a diameter of 4 meters and a tower height of 19 meters, and the temperature inside the tower is maintained at about 120°C. In the CO ₂ regeneration tower T4, CO ₂ is desorbed again, and the flow rate is , enters the filling system from the top of the tower through the pipeline 11, and pressurizes filling to obtain CO ₂ products, which are sold or used to manufacture other products. The hot potash solution at the bottom of the tower is refluxed to the _CO2 absorption tower T3 through the pump P3 for recycling.

Example 5:

The flue gas being treated now contains 7.6% CO ₂ , 10% O ₂ , 54% N ₂ , 28% H ₂ O and 1500 mg SO ₃ per cubic meter in terms of volume fraction. NO _X is mainly NO, which is 1200 mg, the flue gas volume is 12000 m ³ /h, and the flue gas temperature is 415°C. It can be seen from the above content that since it contains nitrogen oxides, _SO2 and _CO2 acid gases, desulfurization absorption tower T1, denitrification absorption tower T2, _CO2 absorption tower T3 and _CO2 regeneration tower T4 are required. First pass the flue gas through the heat exchanger IE1, so that the temperature of the flue gas is reduced from 415°C to 120°C. At the same time, the water from the pipeline 1 through the mixer M1 is heated after passing through the heat exchanger IE1. The heated water and steam The mixture enters the phase separator V1, and the liquid water after phase separation returns to the heat exchanger IE1 for recycling through the mixer M1. The water vapor after phase separation is divided into three streams through the splitter S1, one stream is used as a heating source, and the _CO2 regeneration tower T4 is heated by the heater H1, and the second stream enters the low-pressure steam turbine ITU1, which serves as the power source of the refrigerator C1 , so that the refrigerator C1 is refrigerated, thereby obtaining frozen water (ice brine, etc.). The ice brine is sent to the cooler IC2, cooler II C3 and cooler III C4 through the splitter S2 respectively as the refrigerant for the desulfurization absorption tower T1, denitration absorption tower T2 and _CO2 absorption tower T3, so that the desulfurization absorption tower T1, denitration absorption tower T1 The temperature of T2 and _CO2 absorption tower T3 is maintained at 130°C, 30°C and 105°C respectively to prevent the temperature rise from being unfavorable to the absorption of sulfur oxides, nitrogen oxides and _CO2 . The third stream of water vapor passes through the low-pressure steam turbine IITU2, which serves as the power source of the compressor CO1 to make the compressor CO1 do work and compress the flue gas discharged from the top of the desulfurization absorption tower T1 to increase its pressure from a slight positive pressure to above 0.25MPa, and enter the denitrification absorption tower T2.

The flue gas cooled by the heat exchanger IE1 enters the desulfurization absorption tower T1, which uses a packed tower with a diameter of 1 meter and a tower height of 7 meters, using calcium hydroxide and sodium hydroxide with a solute mass fraction of 20%. The mixed solution is used as the absorption liquid, which is fed from the top of the tower through pipeline 3, and its flow rate is 85. After absorption, the sulfur absorption liquid descends to the bottom of the tower along the desulfurization absorption tower T1, and the solid phase is removed through solid-liquid separation, and the liquid phase can return to the desulfurization The liquid distribution tank is recycled. The flue gas after desulfurization is mixed with the air with a flow rate of 66° from the pipeline 12, enters the compressor CO1 for pressurization, and then enters the denitrification absorption tower T2. The denitrification absorption tower T2 is a packed tower with a diameter of 0.9 meters and a height of 5 meters. The NOx absorbing liquid water is passed through the pipeline 5 at the top of the tower. The absorption liquid (dilute nitric acid) that descends from top to bottom along the denitrification tower enters the bottom of the denitrification tower, and is transported to the nitric acid product storage tank through pipeline 6. The de-stocked flue gas comes out from the top of the denitrification absorption tower T2 and enters the _CO2 absorption tower T3. The _CO2 absorption tower T3 is a packed tower with a diameter of 1.1 meters and a height of 5.5 meters. The hot potassium alkali solution enters the _CO2 absorption tower T3 from the pipeline 9 through the mixer M2 as the absorption liquid, and the flow rate is . The fully contacted flue gas passes through the pipe 7 from the top of the tower and is discharged from the chimney. Since the acid components in the flue gas are basically removed at this time, it meets the emission standard. The hot potash absorption liquid that absorbs _CO2 is heated from the _CO2 absorption tower T3 through the heat exchanger IIE2, and then enters the _CO2 regeneration tower T4, and is heated by part of the steam from the phase separator V1, so that the temperature is kept at about 120°C, and the _{CO2 is} desorbed Afterwards, the pipeline 11 at the top of the tower enters the filling system according to the flow rate, and the _CO2 product is obtained by pressurized filling, which is sold or used to manufacture other products. The hot potassium alkali solution at the bottom of the tower passes through the pump IIIP3, passes through the heat exchanger IIE2 for heat exchange, and then flows back to the _CO2 absorption tower T3 through the mixer M2 for recycling.

Claims (7)

1. A technique for utilizing waste heat of flue gas to remove its acid gas, it is made up of desulfurization system, denitrification system and decarburization system, and is characterized in that it comprises the following steps: (1) The flue gas first passes through the electrostatic precipitator to remove most of the dust in the flue gas, and then the flue gas is passed into the heat exchanger Ⅰ (E1) through the pipe (2), the water goes through the tube, and the flue gas The flue gas goes through the shell side. After heat exchange, the temperature of the flue gas decreases and enters the desulfurization absorption tower (T1). The water in the tube side is heated and vaporized and then enters the phase separator (V1). The water after phase separation Returning to the heat exchanger Ⅰ (E1), the combination of the heat exchanger Ⅰ (E1) and the phase separator (V1) is equivalent to a waste heat boiler, and the steam pressure generated is 3 to 6 atmospheres, and the steam passes through the splitter (S1) is divided into three strands, which respectively enter the low-pressure steam turbine I (TU1) and low-pressure steam turbine II (TU2) and the heater (H1). The power source makes the refrigerator (C1) refrigerate to obtain chilled water, and the chilled water is sent to cooler I (C2), cooler II (C3) and cooler III (C4) through the splitter (S2) as The refrigerants in the desulfurization absorption tower (T1), denitration absorption tower (T2) and _CO2 absorption tower (T3) keep the temperatures of the desulfurization absorption tower (T1), denitration absorption tower (T2) and _CO2 absorption tower (T3) at The temperature required by each, the second steam is used to drive the low-pressure steam turbine II (TU2), and the steam turbine II (TU2) is used as the power source of the compressor (CO1), so that the compressor (CO1) does work, and the compression is absorbed from the desulfurization The flue gas discharged from the top of the tower (T1) raises its pressure from a slight positive pressure to above 0.25MPa, and enters the denitrification absorption tower (T2) to remove NOx and produce dilute nitric acid at the same time, and the third steam passes through the heating The device (H1) provides a heat source for the CO ₂ regeneration tower (T4) to regenerate the CO ₂ absorption liquid for recycling; (2) The flue gas exchanged by heat exchanger Ⅰ (E1) enters the bottom of the desulfurization absorption tower (T1), and the sulfur absorption liquid (usually hydrogen oxidation The mixed solution of calcium and sodium hydroxide) is fully contacted, and the desulfurized flue gas is discharged from the top of the desulfurization absorption tower (T1), mixed with the air entering from the pipeline 12, and enters the compressor driven by the steam turbine II (TU2) ( CO1), the pressure of the gas is increased to above 0.25MPa and enters the denitrification absorption tower (T2) from the bottom, while the sulfur absorption liquid descends to the bottom of the tower along the desulfurization tower, and the solid phase is removed through solid-liquid separation, and the liquid phase can be recycled Return to the desulfurization liquid distribution tank for recycling; (3) After the mixture of pressurized flue gas and air enters the denitrification absorption tower (T2), it contacts with the NOx absorption liquid entering through the pipe (5) at the top of the denitrification absorption tower (T2) countercurrently, and from the denitration absorption tower (T2) T2) is discharged from the top of the tower, and then enters the CO ₂ absorption tower (T3), while the absorption liquid (dilute nitric acid) that descends from top to bottom along the denitrification tower enters the bottom of the denitrification tower, and is transported to the nitric acid product storage tank through the pipeline (6) ; (4) The flue gas after denitrification enters the CO ₂ absorption tower (T3) from the bottom. The CO ₂ absorption liquid generally adopts hot potassium alkali solution or organic amine, and the CO ₂ in the flue gas is absorbed in the decarbonization tower (T3). After absorption, it is discharged from the top of the tower through the pipeline (7). At this time, the acidic components in the flue gas are basically removed, and among them, SOx and NOx can be controlled below 50ml/ ^m3 and 30ml/ ^m3 respectively. _CO2 can be lower than 5000ml/ ^m3 , and the _CO2 absorption liquid that descends from the _CO2 absorption tower (T3) from top to bottom is pumped to the heat exchanger II (E2) through the bottom of the tower to exchange heat and enter the CO2 ₂ The upper part of the regeneration tower (T4); (5) CO ₂ is re-desorbed in the CO ₂ regeneration tower (T4), and enters the filling system from the top of the tower through the pipeline (11), pressurized filling to obtain CO ₂ products, sold or used to manufacture other products, and regenerated The final _CO2 absorption liquid passes through the bottom of the _CO2 regeneration tower (T4) and returns to the heat exchanger II (E2) for heat exchange through the pump III (P3), and then enters the decarbonization absorption tower (T3) through the mixer (M2) for recycling ;The heat required by the CO ₂ regeneration tower (T4) is obtained by the steam provided by the phase separator (V1) through the heater (H1), and the condensed liquid is returned to the mixer (M1) for recycling through the pump I (P1) and cooled The refrigerant at the outlet of cooler I (C2), cooler II (C3) and cooler III (C4) is pumped back to the refrigerant refrigerator C1 through pump II (P2) to be refrigerated again and recycled. 2. The process for removing its acidic gas according to claim 1, characterized in that: the removal method of the sulfur oxides is a mixed solution of calcium hydroxide and sodium hydroxide, calcium hydroxide and hydrogen in the solution The mass fraction of sodium oxide is 10-40%, the mass ratio of calcium hydroxide and sodium hydroxide is 4:1, as the absorption liquid, the temperature of the flue gas entering the absorption tower is above 120°C, and the sulfur oxide removal rate is 90% above. 3. The process for removing acidic gases according to claim 1, characterized in that: the nitrogen oxide removal method uses air and water as the absorbing liquid, the temperature is kept at 5~30°C, and the NOx The method for determining the ratio of flue gas and air is as follows: 1 volume of NO consumes 0.75 volume of O ₂ , 1 volume of NO ₂ consumes 0.25 volume of O ₂ , and 1 volume of air contains 0.2 volume of O ₂ ; The content, ratio and flow of NO and NO ₂ are used to calculate the theoretical air flow. The ratio of the actual air flow to the theoretical air flow is 1.5~2:1, so as to obtain the actual amount of air required. 4. The technology for removing its acidic gas according to claim ₁ is characterized in that: described CO The removal method generally adopts hot potassium alkali solution or organic amine as the absorption liquid, and the absorption reaction is a reversible reaction, and the temperature It needs to be kept at the required temperature. The temperature of the organic amine as the absorption liquid should be kept at 20~40°C, while the temperature of the hot potash solution should be kept at 95~105°C. 5. The process for removing acid gas according to claim 4, characterized in that: said organic amine is monoethanolamine, diethanolamine, triethanolamine or N-methyldiethanolamine. 6. The process for removing acid gas according to claim 1, characterized in that: the CO ₂ regeneration method is to use steam heating, so that the temperature can be kept at 110°C. 7. The process for removing acidic gases according to claim 1, characterized in that: according to whether the flue gas contains nitrogen oxides, it is determined whether the denitrification step of the denitrification absorption tower T2 is required in the process.