Sludge oxygen-enriched combustion system and method based on oxygen concentration zoning regulation

Abstract

The application discloses a sludge oxygen-enriched combustion system and method based on oxygen concentration partition regulation, and sets oxygen concentration of combustion partition for different sludge, establishes a differential oxygen supply mechanism, constructs two different oxygen concentration combustion zones in the furnace of the combustion boiler, which are a low-oxygen combustion zone and a high-oxygen combustion zone, and the oxygen concentrations of the combustion gas flowing into the two zones are 28-32% and 35-42% respectively; the sludge is pre-dried, the C and H element contents of the dried sludge are detected in real time based on a near-infrared spectrometer, and the sludge with high and low C / H molar ratios is recorded as S1 sludge and S2 sludge respectively; the S1 sludge after drying treatment is conveyed into the low-oxygen combustion zone for combustion, and the S2 sludge after drying treatment is conveyed into the high-oxygen combustion zone for combustion.The application adopts relatively low concentration to reduce oxygen production energy consumption for the S1 sludge, and maintains high thermal efficiency; and relatively high concentration is adopted to solve the burnout problem for the S2 sludge.

Description

Technical Field

[0001] This invention belongs to the field of carbon reduction technology in thermal power plants, specifically relating to a sludge oxygen-enriched combustion system and method based on oxygen concentration zone control. Background Technology

[0002] Sludge is a substance composed of organic debris, bacteria, inorganic particles, and colloids, which is difficult to completely separate into solid and liquid phases through sedimentation. Although the volume of sludge is much smaller than that of wastewater, the investment in sludge treatment facilities accounts for 30%-40% of the total investment, or even more than 50%. From the perspective of harmless treatment of sludge, sludge treatment occupies a very important position.

[0003] Oxygen-enriched combustion technology uses high-purity oxygen to replace traditional air and reconstruct the combustion atmosphere in the furnace, which can enrich high concentrations of CO2, greatly reducing the energy consumption and cost of carbon capture systems. It is a potential pathway to reduce carbon emissions in thermal power units. Currently, there are few patents related to sludge oxygen-enriched combustion systems.

[0004] In existing technologies, sludge incineration produces fly ash, slag, and flue gas. In particular, fly ash contains a large amount of Cd, Pb, and other heavy metals, which are classified as hazardous waste. If not properly handled, it can easily leak and pollute groundwater, nearby surface water, and soil, thereby endangering human health. The emitted flue gas contains highly toxic substances such as dioxins, which can cause secondary pollution if not properly controlled. Summary of the Invention

[0005] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a sludge oxygen-enriched combustion system and method based on oxygen concentration zone control.

[0006] The technical solution adopted in this invention is as follows: A sludge oxygen-enriched combustion method based on oxygen concentration zone control establishes a differentiated oxygen supply mechanism by setting the oxygen concentration for combustion zones for sludge with different characteristics. The method includes the following steps: Step 1: Construct two combustion zones with different oxygen concentrations within the furnace of the combustion boiler: a low-oxygen combustion zone 1 and a high-oxygen combustion zone 2. The oxygen concentration of the combustion gas introduced into the low-oxygen combustion zone 1 is 28-32%, while the oxygen concentration of the combustion gas introduced into the high-oxygen combustion zone 2 is 35-42%. Step 2: Sludge pre-drying treatment. The C and H element content of the dried sludge is detected in real time using a near-infrared spectrometer. The C / H element molar ratio of the dried sludge is calculated. The sludge is classified according to the size of the C / H molar ratio. Sludge with high and low C / H molar ratios are designated as S1 sludge and S2 sludge, respectively. The dried S1 sludge is transported to the low-oxygen combustion zone 1 for combustion, and the dried S2 sludge is transported to the high-oxygen combustion zone 2 for combustion.

[0007] Furthermore, S1 type sludge is dyeing and printing sludge, and its detected C / H molar ratio is 6.0-7.0; S2 type sludge is municipal sludge, and its detected C / H molar ratio is less than 6, preferably 5.5-5.8.

[0008] Furthermore, in step 2, the combustion temperature is 900-1000℃.

[0009] Furthermore, in step 2, the sludge is dried until the moisture content is below 5%.

[0010] Furthermore, the combustion exhaust gases discharged from both the low-oxygen combustion zone one and the high-oxygen combustion zone two are divided into two paths. One path is discharged to the post-treatment system, and the other path dilutes the input pure oxygen to form combustion gas, which is then returned to the corresponding combustion zone in the boiler furnace for combustion treatment.

[0011] Furthermore, Ca(OH)2 micro powder with a particle size ≤10μm is injected into the high-oxygen combustion zone. The Ca(OH)2 micro powder reacts with SO2 in the combustion gas to generate CaSO4 in a high-oxygen environment. After the combustion exhaust gas carries the CaSO4 dust out, it is first collected by gas-solid separation. The separated gas is divided into two paths. One path is discharged to the post-treatment system, and the other path is used to dilute the input pure oxygen to form combustion gas, which is then returned to the high-oxygen combustion zone for combustion treatment.

[0012] A sludge oxygen-enriched combustion system based on oxygen concentration zone control, the system includes a near-infrared spectrometer, a sludge conveying device, a combustion boiler and an air separation unit (ASU), the combustion boiler furnace is divided into a low-oxygen combustion zone I and a high-oxygen combustion zone II. The near-infrared spectrometer is connected to the sludge conveying device via a PLC control system. The PLC control system uses the near-infrared spectrometer to detect the C and H content of the sludge in real time, calculates the C / H molar ratio of the sludge, classifies the sludge, and controls the conveying path of the sludge conveying device to be either low-oxygen combustion zone one or high-oxygen combustion zone two based on the sludge classification results. The air separation unit (ASU) is used to provide pure oxygen for combustion in the combustion boiler. The pure oxygen is diluted with the combustion exhaust gas discharged from the combustion boiler to form combustion gas, and then returned to the corresponding combustion zone in the boiler furnace for combustion treatment.

[0013] Furthermore, the low-oxygen combustion zone one and the high-oxygen combustion zone two can be arranged vertically within the furnace of the combustion boiler.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. A differentiated oxygen supply mechanism is established by setting oxygen concentrations in combustion zones based on the different characteristics of sludge. Combustion zones with different oxygen concentrations (Zone 1 and Zone 2) are constructed within the boiler furnace. Pure oxygen discharged from the air separation unit (ASU) can be output in two streams, mixing and diluting it with the combustion exhaust gas from the boiler to adjust the oxygen concentration. In Zone 1 (corresponding to S1 type sludge), the oxygen concentration of the combustion gas is 28-32%, while in Zone 2 (corresponding to S2 type sludge), the oxygen concentration is 35-42%. For S1 type sludge, a relatively low concentration is used to reduce oxygen production energy consumption and maintain high thermal efficiency; for S2 type sludge, a relatively high concentration is used to solve the burnout problem.

[0015] 2. Integrating a near-infrared spectrometer to detect the C / H element ratio of sludge in real time and to achieve precise sludge classification and transportation, automatically distributing sludge to the corresponding area.

[0016] 3. In the second zone, Ca(OH)2 micro powder (particle size ≤10μm) is injected to enhance the desulfurization reaction by utilizing the high oxygen environment, and to further control the SO2 concentration under oxygen-rich conditions.

[0017] 4. During the sludge combustion process, Pb, Zn, and Cu will form gaseous species that volatilize. This invention reduces the volatilization of heavy metals by adjusting the oxygen concentration during combustion. Attached Figure Description

[0018] Figure 1 The results show the effect of different oxygen concentrations on the sludge combustion characteristics; Figure 2 The trends of CO2 generation with combustion temperature for S1 and S2 sludge under different oxygen concentrations are shown. Figure 3 The trends of SO2 generation with combustion temperature for S1 and S2 sludge at different oxygen concentrations are shown. Figure 4 The effects of different oxygen concentrations on NOx generation of S1 and S2 type sludge, respectively. Figure 5 This is a schematic diagram of the structure of a sludge oxygen-enriched combustion system based on oxygen concentration zone control according to the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0020] A schematic diagram of a sludge oxygen-enriched combustion system based on zoned oxygen concentration regulation according to the present invention is shown below. Figure 5 The system includes a near-infrared spectrometer, a sludge conveying device, a combustion boiler, and an air separation unit (ASU). The combustion boiler's furnace is divided into a low-oxygen combustion zone I and a high-oxygen combustion zone II, which can be arranged vertically within the combustion boiler's furnace.

[0021] The exhaust gas from the low-oxygen combustion zone 1 is divided into two paths: one path goes to the aftertreatment system, and the other path goes out through return pipe 1. The exhaust gas from the high-oxygen combustion zone 2 is also divided into two paths: one path goes to the aftertreatment system, and the other path goes out through return pipe 2.

[0022] The near-infrared spectrometer is connected to the sludge conveying device via a PLC control system. The PLC control system uses the near-infrared spectrometer to detect the C and H element content of the sludge in real time, calculates the C / H element molar ratio of the sludge, classifies the sludge, and controls the conveying path of the sludge conveying device to be either low-oxygen combustion zone one or high-oxygen combustion zone two based on the sludge classification results.

[0023] The air separation unit (ASU) is used to provide pure oxygen for combustion in the combustion boiler. The oxygen supply pipeline of the air separation unit (ASU) is divided into two lines. The first oxygen supply pipeline is connected to the low-oxygen combustion zone 1, and the aforementioned return pipe 1 is connected to the first oxygen supply pipeline. The second oxygen supply pipeline is connected to the high-oxygen combustion zone 2, and the aforementioned return pipe 2 is connected to the second oxygen supply pipeline.

[0024] Example 1: Detailed Experimental Evaluation S1 type sludge is dyeing sludge from a factory. It is dried to a moisture content of less than 5%. The C and H element content of the dried sludge is detected in real time using a near-infrared spectrometer, and the C / H element molar ratio of the dried sludge is calculated. The detected C / H molar ratio is 6.5.

[0025] S2 type sludge is municipal sludge, dried to a moisture content of less than 5%. The C and H element content of the dried sludge was detected in real time using a near-infrared spectrometer, and the C / H element molar ratio of the dried sludge was calculated. The detected C / H molar ratio was 5.7.

[0026] Thermogravimetric analysis (TGA) experiments were conducted on two types of dried sludge (S1 and S2) under oxygen-enriched conditions. Simultaneously, online monitoring of pollutants during the combustion process was achieved using a flue gas analyzer. After drying, both types of sludge were ground and passed through a 100-mesh sieve. Samples of 10-20 mg were used for each TGA test. To ensure the repeatability of measurement data under different operating conditions, each experiment was repeated three times at each oxygen concentration. During the experiment, a set ratio of O2 / N2 mixed gas (flow rate 50 mL / min) was introduced, and the temperature was increased to 950℃ at a rate of 10℃ / min. TG (total TG) and DTG (differential thermogravimetric) curves were recorded. The changes in the content of various substances in the exhaust gas were monitored in real time using a gas analyzer. The exhaust gas mainly contained CO2, CO, SO2, CH4, and nitrogen oxides (NO, NO2, and N2O). The heavy metal content in the waste residue after combustion of the two types of sludge under different oxygen concentrations was studied. The molten salt of the digested waste residue was detected and analyzed by ICP. The specific experimental conditions included in this thermogravimetric experiment are shown in Table 1.

[0027] Table 1 .

[0028] 1. The influence of different oxygen concentrations on sludge combustion characteristics: Following the experimental procedure described above, for both S1 and S2 type sludge, under conditions where different O2 concentrations of O2 / N2 mixed gas (flow rate 50 mL / min) were used, and the temperature was increased from room temperature to 950℃ at a rate of 10℃ / min as the evaluation endpoint, the results of the effect of different oxygen concentrations on the sludge combustion characteristics are shown below. Figure 1 .

[0029] from Figure 1 As can be seen, the ignition performance index (Di) of both types of sludge increased significantly with increasing oxygen concentration. The Di of S1 sludge increased from 0.00511 to 0.00728, while the Di of S2 sludge increased from 0.00280 to 0.00364. This increase in Di value indicates that increasing oxygen concentration significantly improves the ignition performance of the sludge, not only by potentially lowering the ignition temperature but also by significantly increasing the combustion intensity in the initial ignition stage. Furthermore, the trend of sludge weight loss rate under different oxygen concentrations also shows that the burnout rate of both types of sludge increased with increasing oxygen concentration. Therefore, increasing oxygen concentration has a significant improving effect on the sludge combustion process.

[0030] 2. Variation patterns of exhaust gas components in oxygen-enriched combustion Following the experimental procedure described above, for both S1 and S2 type sludge, under conditions of different O2 concentrations and O2 / N2 mixed gas (flow rate 50 mL / min), with the temperature increased from room temperature to 950℃ at a rate of 10℃ / min as the evaluation endpoint, the trend of CO2 generation with combustion temperature under different oxygen concentrations is shown in the figure. Figure 2 The trend of SO2 generation with combustion temperature under different oxygen concentrations is shown in the figure. Figure 3 The effect of different oxygen concentrations on NOx formation is shown in [reference needed]. Figure 4 . Figures 2-4 In the diagram, the top image corresponds to S1 type sludge, and the bottom image corresponds to S2 type sludge.

[0031] against Figures 2-4Experimental results show that for S1 dyeing and printing sludge and S2 municipal sludge, within an oxygen concentration range of 21%-70%, the formation rate of various gaseous products increases with increasing oxygen concentration, and the initial formation time is advanced. The formation rate of gaseous products increases significantly within an oxygen concentration range of 21%-30%, but the rate of increase weakens significantly when the oxygen concentration exceeds 30%. Therefore, in summary, for both types of sludge, an oxygen concentration above 30% is a suitable combustion oxygen concentration, but an oxygen concentration exceeding 50% will lead to a rapid increase in pollutant concentration.

[0032] 3. Migration patterns of heavy metal elements during oxygen-enriched combustion Following the experimental procedure described above, the migration results of heavy metal elements after combustion of S1 dyeing and printing sludge and S2 municipal sludge were shown in Tables 2 and 3, respectively, under the conditions of different N2 concentrations of O2 / N2 mixed gas (flow rate 50 mL / min), with the temperature increasing from room temperature to 950℃ at a rate of 10℃ / min as the evaluation time endpoint.

[0033] Table 2. Heavy metal content (mg / L) in raw sludge and sludge after drying and combustion under different conditions. .

[0034] Table 3. Heavy metal content (mg / L) in raw sludge and sludge after drying and combustion under different conditions. .

[0035] In Tables 2 and 3, the heavy metal content refers to the heavy metal content remaining in the waste residue after sludge combustion. A decrease in heavy metal content indicates that more heavy metals in the sludge volatilize into the gaseous state and migrate into the gas phase during the combustion process, which can easily lead to excessive heavy metal emissions.

[0036] Tables 2 and 3 show that increasing the oxygen concentration effectively inhibits the volatilization of moderately volatile heavy metals such as Pb, Zn, and Cu during combustion by promoting the formation of high-boiling-point oxides. As shown in the table, the concentrations of various elements in the waste residue after the combustion of S1 and S2 sludge show a clear and stable upward trend with increasing oxygen concentration, indicating that high oxygen levels promote the fixation of these elements.

[0037] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A sludge oxygen-enriched combustion method based on zoned oxygen concentration control, characterized in that, A differentiated oxygen supply mechanism is established by setting the oxygen concentration in combustion zones for sludge with different characteristics. This includes the following steps: Step 1: Construct two combustion zones with different oxygen concentrations within the furnace of the combustion boiler: a low-oxygen combustion zone 1 and a high-oxygen combustion zone 2. The oxygen concentration of the combustion gas introduced into the low-oxygen combustion zone 1 is 28-32%, while the oxygen concentration of the combustion gas introduced into the high-oxygen combustion zone 2 is 35-42%. Step 2: Sludge pre-drying treatment. The C and H element content of the dried sludge is detected in real time using a near-infrared spectrometer. The C / H element molar ratio of the dried sludge is calculated. The sludge is classified according to the size of the C / H molar ratio. Sludge with high and low C / H molar ratios are designated as S1 sludge and S2 sludge, respectively. The dried S1 sludge is transported to the low-oxygen combustion zone 1 for combustion, and the dried S2 sludge is transported to the high-oxygen combustion zone 2 for combustion. The high-oxygen combustion zone II is sprayed with Ca(OH)2 micro powder with a particle size ≤10μm.

2. The sludge oxygen-enriched combustion method based on oxygen concentration zone control as described in claim 1, characterized in that, S1 type sludge is dyeing and printing sludge, and its tested C / H molar ratio is 6.0-7.0; S2 type sludge is municipal sludge, and its tested C / H molar ratio is less than 6.

3. The sludge oxygen-enriched combustion method based on oxygen concentration zone control as described in claim 2, characterized in that, The C / H molar ratio for S2 type sludge is 5.5-5.

8.

4. The sludge oxygen-enriched combustion method based on oxygen concentration zone control as described in claim 1, characterized in that, In step 2, the combustion temperature is 900-1000℃.

5. The sludge oxygen-enriched combustion method based on oxygen concentration zone control as described in claim 1, characterized in that, In step 2, the sludge is dried until the moisture content is below 5%.

6. The sludge oxygen-enriched combustion method based on oxygen concentration zone control as described in claim 1, characterized in that, The combustion exhaust gas discharged from the top outlet of the combustion boiler is first separated into gas and solid by a gas-solid separator. The exhaust gas discharged from the outlet of the gas-solid separator is divided into two paths. One path is discharged to the post-treatment system, and the other path is diluted with the input pure oxygen to form combustion gas, which is then returned to the corresponding combustion zone in the boiler furnace for combustion treatment.

7. The sludge oxygen-enriched combustion method based on oxygen concentration zone control as described in claim 6, characterized in that, Ca(OH)2 powder reacts with SO2 in the combustion gas in a high-oxygen environment to generate CaSO4. After the combustion exhaust gas carries CaSO4 dust out, it is first collected by gas-solid separation. The separated gas is divided into two paths: one path is discharged to the post-treatment system, and the other path is diluted with the input pure oxygen to form combustion gas, which is then returned to the high-oxygen combustion zone for combustion treatment.

8. The system of the sludge oxygen-enriched combustion method based on oxygen concentration zone control as described in claim 1, characterized in that, The system includes a near-infrared spectrometer, a sludge conveying device, a combustion boiler, and an air separation unit (ASU). The combustion boiler's furnace is divided into a low-oxygen combustion zone I and a high-oxygen combustion zone II. The near-infrared spectrometer is connected to the sludge conveying device via a PLC control system. The PLC control system uses the near-infrared spectrometer to detect the C and H content of the sludge in real time, calculates the C / H molar ratio of the sludge, classifies the sludge, and controls the conveying path of the sludge conveying device to be either low-oxygen combustion zone one or high-oxygen combustion zone two based on the sludge classification results. The air separation unit (ASU) is used to provide pure oxygen for combustion in the combustion boiler. The pure oxygen is diluted with the combustion exhaust gas discharged from the combustion boiler to form combustion gas, and then returned to the corresponding combustion zone in the boiler furnace for combustion treatment.

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