SYSTEM AND METHOD FOR INTEGRATED REMOVAL OF MULTIPLE POLLUTANTS IN FLUE GAS WITH NEAR-ZERO EMISSION

Abstract

A system for integrated removal of multiple pollutants includes an economizer, an air preheater, an electrostatic precipitator, a flue gas cooler and a low-temperature adsorber; the economizer has a shell side inlet for feeding boiler flue gas, a tube side inlet for feeding boiler feedwater, and a shell side outlet connected to a tube side inlet of the air preheater; the air preheater has a shell side inlet for introducing boiler intake air, and a tube side outlet connected to the electrostatic precipitator; the electrostatic precipitator has a dust discharge port at a bottom thereof and a flue gas outlet connected to the flue gas cooler; the flue gas cooler has a condensate outlet at a bottom thereof and a cold flue gas outlet at a top thereof and connected to the low-temperature adsorber; and the low-temperature adsorber has a purified flue gas outlet at a tail thereof.

Claims

1. A system for integrated removal of multiple pollutants in a flue gas with a near-zero emission, comprising an economizer (1), an air preheater (2), an electrostatic precipitator (3), a flue gas cooler (4) and a low-temperature adsorber (5); wherein the economizer (1) has a shell side inlet for feeding boiler flue gas, a tube side inlet for feeding boiler feedwater, and a shell side outlet connected to a tube side inlet of the air preheater (2); the air preheater (2) has a shell side inlet for introducing boiler intake air, and a tube side outlet connected to the electrostatic precipitator (3); a dust discharge port is provided at a bottom of the electrostatic precipitator (3), and a flue gas outlet of the electrostatic precipitator (3) is connected to the flue gas cooler (4); a condensate outlet is provided at a bottom of the flue gas cooler (4), and a cold flue gas outlet is provided at a top of the flue gas cooler (4) and connected to the low-temperature adsorber (5); and a purified flue gas outlet is provided at a tail of the low-temperature adsorber (5).

2. The system for integrated removal of the multiple pollutants in the flue gas with the near-zero emission according to claim 1, wherein the flue gas cooler (4) is connected with a direct spraying and cooling device or an indirect heat exchange cooling device.

3. The system for integrated removal of the multiple pollutants in the flue gas with the near-zero emission according to claim 1, wherein the low-temperature adsorber (5) is a fixed bed adsorber or a moving bed adsorber.

4. The system for integrated removal of the multiple pollutants in the flue gas with the near-zero emission according to claim 1, comprising two low-temperature adsorbers (5).

5. A method for integrated removal of multiple pollutants in a flue gas with a near-zero emission, using the system for integrated removal of the multiple pollutants in the flue gas with the near-zero emission according to claim 1, comprising: feeding boiler flue gas into an economizer (1) in which boiler feedwater is heated by the boiler flue gas; transferring the boiler flue gas to an air preheater (2) in which boiler intake air is heated by the boiler flue gas; transferring the flue gas after heat recovery in the economizer (1) and the air preheater (2) to an electrostatic precipitator (3) to remove dust in the flue gas; transferring the dedusted flue gas to a flue gas cooler (4) to be cooled to room temperature or lower; discharging condensate water with some or all of pollutants dissolved therein out of the flue gas cooler (4); and transferring the cooled flue gas to a low-temperature adsorber (5) to adsorb the pollutants and discharging a purified flue gas.

6. The method for integrated removal of the multiple pollutants in the flue gas with the near-zero emission according to claim 5, wherein the flue gas cooler (4) is operated in a direct spraying and cooling manner or an indirect heat exchange cooling manner, wherein in the direct spraying and cooling manner, a small amount of dust not removed by the electrostatic precipitator (3) is washed down and discharged along with the condensate water.

7. The method for integrated removal of the multiple pollutants in the flue gas with the near-zero emission according to claim 5, wherein the low-temperature adsorber (5) includes a first low-temperature adsorber (5) and a second low-temperature adsorber (5), and when the first low-temperature adsorber (5) reaches saturation such that SO.sub.2 or NO begins to permeate, the cooled flue gas is switched to the second low-temperature adsorber (5), and the first low-temperature adsorber (5) is regenerated by heating or vacuum sucking.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings are used to provide a further understanding of the present disclosure and constitute a part of this specification, and embodiments of the present disclosure and the related descriptions are used to explain the present disclosure, and cannot be improperly construed to limit the present disclosure.

[0023] FIG. 1 is a schematic diagram showing a method for integrated removal of multiple pollutants in a flue gas with a near-zero emission according to the present disclosure;

[0024] FIG. 2 shows a removal efficiency of flue gas pollutants by dissolved in condensate water at different condensing temperatures.

REFERENCE NUMERALS

[0025] 1: economizer; 2: air preheater; 3: electrostatic precipitator; 4: flue gas cooler; 5: low-temperature adsorber.

DETAILED DESCRIPTION

[0026] Detailed description of the present disclosure is given below.

[0027] As shown in FIG. 1, a system for integrated removal of multiple pollutants in a flue gas with a near-zero emission provided in the present disclosure includes an economizer 1, an air preheater 2, an electrostatic precipitator 3, a flue gas cooler 4 and a low-temperature adsorber 5.

[0028] The economizer 1 has a shell side inlet for feeding boiler flue gas, a tube side inlet for feeding boiler feedwater, and a shell side outlet connected to a tube side inlet of the air preheater 2. The air preheater 2 has a shell side inlet for introducing boiler intake air, and a tube side outlet connected to the electrostatic precipitator 3. A dust discharge port is provided at a bottom of the electrostatic precipitator 3, and a flue gas outlet of the electrostatic precipitator 3 is connected to the flue gas cooler 4. The flue gas cooler 4 is connected with a direct spraying and cooling device or an indirect heat exchange cooling device. A condensate outlet is provided at a bottom of the flue gas cooler 4, and a cold flue gas outlet is provided at a top of the flue gas cooler 4 and connected to the low-temperature adsorber 5. A purified flue gas outlet is provided at a tail of the low-temperature adsorber 5. The low-temperature adsorber 5 is a fixed bed adsorber or a moving bed adsorber. Two low-temperature adsorbers 5 are provided.

[0029] The boiler flue gas passes through the economizer 1 to heat the boiler feedwater, and then passes through the air preheater 2 to heat the boiler intake air. The flue gas after heat recovery in the economizer 1 and the air preheater 2 is transferred to the electrostatic precipitator 3 to remove dust in the flue gas. The dedusted flue gas is transferred to the flue gas cooler 4 to be cooled to room temperature or lower. The flue gas cooler 4 is operated in a direct spraying and cooling manner or an indirect heat exchange cooling manner. Moisture in the flue gas is condensed and discharged out of the system.

[0030] In the flue gas cooler 4, a part or all of the pollutants in the flue gas are dissolved in the condensate water, and discharged along with the condensate water. As shown in FIG. 2, HCl and HF have strong solubility and are almost completely dissolved in the condensate water. NO.sub.2 and SO.sub.3 are partially dissolved in the condensate water, SO.sub.2 is slightly dissolved in the condensate water, elemental mercury (Hg.sup.0) is insoluble in the condensate water, and divalent mercury (Hg.sup.2+) is partially dissolved in the condensate water. If the spraying and cooling manner is used, a small amount of dust not removed by the precipitator 3 is washed down and discharged along with the condensate water.

[0031] The cooled flue gas is transferred to the low-temperature adsorber 5, in which SO.sub.2, NO, elemental mercury (Hg.sup.0) and the remaining NO.sub.2, SO.sub.3, divalent mercury (Hg.sup.2+), VOCs and other pollutants are adsorbed and removed integrally. Among them, SO.sub.2, NO.sub.2, SO.sub.3, Hg and VOCs are directly adsorbed and removed. NO cannot be directly adsorbed and removed, but it can be oxidized by O.sub.2 in the flue gas, and then be adsorbed and removed by adsorbents at the low temperature through a low-temperature oxidation and adsorption mechanism. That is, NO and O.sub.2 in the flue gas are enriched on a surface of the adsorbent at the low temperature to form a local high concentration, such that NO is quickly oxidized to NO.sub.2, and adsorbed on the surface of the adsorbent. The oxidation and adsorption mechanism is the key to realize low-temperature adsorption denitration.

[0032] After passing through the flue gas cooler 4 and the low-temperature adsorber 5, SO.sub.2, SO.sub.3, NO, NO.sub.2, HCl, HF, Hg.sup.0, Hg.sup.2+, VOCs, dust and other pollutants in the flue gas are almost completely removed to achieve the near-zero emission.

[0033] The adsorbent in the low-temperature adsorber 5 is regenerated by heating or vacuum sucking to be recycled. The low-temperature adsorber 5 may be a fixed bed adsorption tower or a moving bed adsorption tower. The desorbed gas is rich in SO.sub.2 and NO.sub.x, and may be reused for preparing sulfuric acid, sulfur, nitric acid, sulfate or nitrate.

[0034] In order to clearly explain the present disclosure, detailed descriptions are made below in connection with examples and drawings. It would be appreciated by those skilled in the art that the following examples cannot be construed to limit the present disclosure, and any changes and modifications made on the basis of the present disclosure shall fall within the scope of the present disclosure.

[0035] Examples: as shown in FIG. 1, the boiler flue gas is cooled to 400° C. after the heat recovery in the economizer 1, and is further cooled to 120° C. after passing through the air preheater 2. The dust in the flue gas is reduced to 20 mg/Nm.sup.3 by the electrostatic precipitator 3. The flue gas is transferred to the flue gas cooler 4, and indirectly exchanged heat with a low-temperature refrigerating liquid to be cooled to 5° C. HCl, HF and a part of SO.sub.2, SO.sub.3, NO.sub.2 and divalent mercury Hg.sup.2+ in the flue gas are dissolved in the condensate water and discharged out of the flue gas cooler 4 together with the condensate water. The low-temperature flue gas is transferred to the fixed-bed adsorber 5, and pollutants such as SO.sub.2, NO, NO.sub.2, SO.sub.3, Hg and VOCs are adsorbed and removed by the filled activated carbon, such that a near-zero emission is achieved.

[0036] The low-temperature adsorber 5 includes two adsorbers, i.e., adsorber A and adsorber B, to perform adsorption-regeneration operations alternately. When the adsorber A reaches saturation such that SO.sub.2 or NO begins to permeate, the low-temperature flue gas is switched to the adsorber B, and the adsorber A is regenerated by heating or vacuum sucking.