FLUE GAS LOW-TEMPERATURE ADSORPTION DENITRIFICATION METHOD

Abstract

The present invention discloses a flue gas low-temperature adsorption denitrification method, including: pressurizing a flue gas that has been subjected to dust removal and desulfurization, precooling the pressurized flue gas, cooling the precooled flue gas to a temperature lower than room temperature by a flue gas cooling system, flowing the flue gas at the temperature lower than room temperature into a low-temperature denitrification system, performing physical adsorption denitrification in the low-temperature denitrification system, precooling the flue gas that has been subjected to dust removal and desulfurization with the denitrificated flue gas, and flowing the heat-absorbed clean flue gas into a chimney to be discharged.

Claims

1. A flue gas low-temperature adsorption denitration method, comprising: pressurizing a flue gas that has been subjected to dust removal and desulfurization, precooling the pressurized flue gas, cooling the precooled flue gas to a temperature lower than room temperature by a flue gas cooling system (1), flowing the flue gas at the temperature lower than room temperature into a low-temperature denitrification system (2), performing physical adsorption denitrification in the low-temperature denitrification system (2), precooling the flue gas that has been subjected to dust removal and desulfurization with the denitrificated flue gas, and flowing the heat-absorbed clean flue gas into a chimney to be discharged.

2. The flue gas low-temperature adsorption denitrification method according to claim 1, wherein the precooled flue gas is indirectly cooled with a heat exchanger, or cooled by direct spray cooling, or cooled by a combination of indirect cooling with a heat exchanger and direct spray cooling.

3. The flue gas low-temperature adsorption denitrification method according to claim 2, wherein the precooled flue gas is subjected to staged cooling, the flue gas is subjected to a first stage cooling by heat exchange or spraying.

4. The flue gas low-temperature adsorption denitrification method according to claim 3, wherein the flue gas is subjected to a second stage cooling by absorption refrigeration or compression refrigeration.

5. The flue gas low-temperature adsorption denitrification method according to claim 1, wherein condensate water generated after flue gas cooling is recovered to a reclaimed water treatment system.

6. The flue gas low-temperature adsorption denitrification method according to claim 1, wherein a denitrification adsorption tower is filled with activated carbon or molecular sieves to adsorb NOx.

7. The flue gas low-temperature adsorption denitrification method according to claim 1, wherein adsorbed NO.sub.2 is desorbed and then recycled.

8. The flue gas low-temperature adsorption denitrification method according to claim 1, wherein a denitrification adsorption tower is thermally insulated at the same time when physical adsorption denitrification is performed in the denitrification adsorption tower.

9. The flue gas low-temperature adsorption denitrification method according to claim 1, wherein a temperature of the flue gas obtained after the flue gas is cooled is −30° C.-0° C.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0016] FIG. 1 is a schematic diagram of a denitrification method according to the present invention.

[0017] FIG. 2 is a graph of the NOx adsorption effect of activated carbon at room temperature.

[0018] FIG. 3 is a graph of the NOx adsorption effect of activated carbon when the flue gas drops to 0° C.

[0019] FIG. 4 is a graph of the NOx adsorption effect of activated carbon when the flue gas drops to −30° C.

[0020] 1—flue gas cooling system, 2—low temperature adsorption denitrification system.

[0021] The drawings are used to provide a further understanding of the present invention and constitute a part of the present invention. The illustrative embodiments of the present invention and the descriptions thereof are used to explain the present invention, and are not intended constitute an improper limitation on the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0022] In order to clearly explain the present invention, the present invention will be further described in detail with reference to examples and drawings. It is understood by those skilled in the art that the following contents do not limit the protection scope of the present invention, and any improvements and changes made on the basis of the present invention are within the protection scope of the present invention.

[0023] A flue gas denitrification method by low-temperature adsorption includes: pressurizing a flue gas that has been subjected to dust removal and desulfurization, precooling the pressurized flue gas, cooling the precooled flue gas to a temperature lower than room temperature by a flue gas cooling system, flowing the flue gas at the temperature lower than room temperature into a low-temperature denitrification system, performing physical adsorption denitrification in the low-temperature denitrification system, precooling the flue gas that has been subjected to dust removal and desulfurization with the denitrificated flue gas, and flowing the heat-absorbed clean flue gas into a chimney to be discharged.

[0024] The precooled flue gas is indirectly cooled with a heat exchanger, or cooled by direct spray cooling, or cooled by a combination of indirect cooling with a heat exchanger and direct spray cooling.

[0025] The precooled flue gas is subjected to staged cooling, the flue gas is subjected to a first stage cooling by heat exchange or spraying, and the flue gas is subjected to a second stage cooling by absorption refrigeration or compression refrigeration.

[0026] Condensate water generated after flue gas cooling is recycled to a reclaimed water treatment system, and the adsorbed NO.sub.2 is desorbed and recycled.

[0027] The denitrification adsorption tower is filled with activated carbon or molecular sieves to adsorb NOx.

[0028] The denitrification adsorption tower is thermally insulated at the same time when physical adsorption denitrification is performed in the denitrification adsorption tower, i.e., the outer wall of the fixed bed adsorption tower adopts a cold box structure, which reduces the heat dissipation loss of low-temperature flue gas and keeps adsorption denitrification of the flue gas at a low temperature.

[0029] The temperature of the flue gas obtained after the flue gas is cooled is −30° C.-0° C.

[0030] The adsorption denitrification mechanism of the method is as follows:

[0031] 1. Adsorption removal of NO.sub.2 in NOx: NO.sub.2 is an easily adsorbed gas, and is directly adsorbed and removed when the flue gas flows through the surfaces of activated carbon, molecular sieves or other porous adsorption materials.

[0032] 2. Adsorption removal of NO in NOx: NO is a gas that is extremely difficult to adsorb, and cannot be directly adsorbed and removed when the flue gas flows through the surfaces of activated carbon, molecular sieves or other porous adsorption materials; the removal is realized by the following steps:

[0033] (1) the temperature of the flue gas is reduced to below room temperature through multistage cooling;

[0034] (2) NO and O.sub.2 in the flue gas below room temperature are enriched on the surface of a porous adsorption material when flowing through the surface of the porous adsorption material, which greatly increases the concentration of NO and O.sub.2, thus rapidly oxidizing NO into NO.sub.2;

[0035] (3) oxidized NO.sub.2 is adsorbed on the surface of the porous material.

[0036] Steps (2) and (3) are carried out at the same time, and finally, the low-temperature adsorption and removal of NO is realized; the flue gas temperature reduction in step (1) is a necessary condition to realize enrichment and oxidation of NO and O.sub.2, and refractory gases such as NO and O.sub.2 can be easily adsorbed and enriched on the adsorbent surface only at a low temperature.

[0037] The denitrification method of the present invention is shown in FIG. 1; the denitrification method is realized by two main systems, namely a flue gas cooling system 1 and a low-temperature adsorption denitrification system 2.

[0038] The flue gas temperature is reduced to a temperature below room temperature by circulating cooling water and multistage cooling equipment of low-temperature water chillers, and the flue gas condensate water is separated; the flue gas cooling system 1 is provided with cold recovery heat-exchange equipment for low-temperature clean flue gas; in the physical adsorption denitrification process, a fixed bed adsorption tower is adopted, which is filled with activated carbon, molecular sieves or other porous adsorption materials, and the outer wall of the fixed bed adsorption tower adopts a cold box structure to reduce the heat dissipation loss of low-temperature flue gas and maintain the flue gas adsorption denitrification at a low temperature.

[0039] The process of the denitrification method of the present invention is described as follows:

[0040] The boiler flue gas without denitrification is subjected to dust removal and desulfurization, then heat recovery by an air preheater, and then introduced into a denitrification system by a fan; the flue gas first passes through the flue gas cooling system 1, and is cooled to a temperature below room temperature after multistage cooling, and the condensate water in the flue gas is separated from the flue gas; the flue gas after cooling flows through the low-temperature adsorption denitrification system 2, where NOx (NO.sub.2 and NO) is adsorbed and removed by the adsorption layer; the adsorption layer is activated carbon or molecular sieves filled, and the denitrificated low-temperature clean flue gas is discharged into the chimney after cold recovery.

[0041] Example 1: the flue gas with a NO content of 500 mg/Nm.sup.3 was cooled to 0° C. and flowed through 5 g activated carbon at a flow rate of 1 L/min (space velocity=6000 h.sup.−1), and the NOx content of the flue gas after passing through the activated carbon bed over time is shown in FIG. 3. The penetration time through the activated carbon bed and the effective NOx adsorption capacity are shown in Table 1.

[0042] Example 2: the same method as in example 1 was adopted, except that the flue gas temperature was reduced to −30° C.; and the NOx content of flue gas after passing through activated carbon bed over time is shown in FIG. 4. The penetration time through activated carbon bed and the effective NOx adsorption capacity are shown in Table 1.

[0043] Comparative example: the same method as in example 1 was adopted, except that the flue gas temperature was maintained at room temperature; the NOx content of the flue gas after passing through activated carbon bed over time is shown in FIG. 2. The penetration time through the activated carbon bed and the effective NOx adsorption capacity are shown in Table 1.

TABLE-US-00001 TABLE 1 Comparison of bed penetration time and NOx effective adsorption capacity of examples Effective NOx adsorption Penetration time (min) capacity NOx NO NO.sub.2 (mg/g) Examples penetration penetration penetration A0 A50 Comparative 0 0 240 0 0 example (room temperature) Example 1 230 230 720 27.6 86.4 (0° C.) Example 2 1500 1500 2600 180 312 (−30° C.) Note: A0 is the effective adsorption capacity corresponding to zero discharge of NOx at the outlet of the bed; A50 is the effective adsorption capacity corresponding to ultra-low discharge of NOx at the outlet of the bed.

[0044] The analysis results show that NO penetrates prior to NO.sub.2 at any temperature, so the penetration time of NOx is consistent with the penetration time of NO; at room temperature (comparative example), NOx penetrates instantaneously, so the effective adsorption capacity of NOx is 0; when the flue gas temperature drops to 0° C. (Example 1) and −30° C. (Example 2), the penetration time and effective adsorption capacity increase rapidly with the decrease of temperature. Therefore, the low-temperature adsorption method of the present invention can effectively adsorb and remove NOx at a low temperature to meet the requirements of zero or ultra-low discharge.