A combustion method for a circulating fluidized bed boiler

Abstract

The present invention discloses a combustion method for a circulating fluidized bed boiler. Biomass generated during the wood chipping process is transported to a storage yard for stacking and fermentation to obtain fermented biomass. Sludge and fermented biomass are mixed at a mass ratio of 1:3 to 5 to obtain biomass sludge, or sludge and biomass generated during the wood chipping process are mixed at a mass ratio of 1:3 to 5 and then stacked and fermented to obtain biomass sludge. Then, the biomass sludge and raw coal are respectively fed into the furnace for combustion, the proportion of biomass sludge in the total fuel is ≤ 40%, and the addition amount of biomass sludge is ≤ 20 tons per hour. The moisture content of the fermented biomass is 50% - 60%, and the moisture content of the sludge is 60% - 68%. This method realizes the co-combustion of biomass and sludge with a relatively high moisture content, can ensure its good combustion performance, reduce the impact on the environment, and improve the economy.

Description

Technical Field

[0001] The present invention relates to the technical field of boiler combustion, and relates to a combustion method for a circulating fluidized bed boiler, specifically to a method for co-firing sludge and biomass in a circulating fluidized bed boiler. Background Art

[0002] Sewage treatment sludge is transported to a sludge drying shed after being pressed and dewatered (with a moisture content of 65% - 68%) and then transported to a circulating fluidized bed boiler for co-firing after drying. Single sludge co-firing will generate a large amount of flue gas, and the flue gas has a high humidity, which is easy to adhere to the tail heating surface and cause blockage of the air preheater tube bundle.

[0003] CN116354578A discloses a method for co-disposing biomass and sludge in a coal-fired unit. Biomass and sludge are mixed in a mass ratio of (1.5 - 5):1 to obtain a combustion material, which enters the circulating fluidized bed boiler of the coal-fired unit for combustion and heat release, realizing sludge reduction. By mixing biomass with a lower moisture content with sludge, the flue gas volume can be reduced, and after reducing the flue gas humidity, the adhesion of dust to the tail heating surface can be slowed down to avoid blockage of the air preheater tube bundle. However, in this method, the moisture content of the biomass ≤ 35%, and the biomass has a low moisture content, which requires additional drying or an extended drying time.

[0004] The combustion of biomass sludge generally goes through a heating stage, a volatile combustion stage, a carbonization stage, and an ash formation stage. The combustible components in the biomass sludge fuel are relatively few, and its energy density is relatively low. The higher the moisture content of the biomass sludge fuel, the lower its calorific value and the relatively lower its combustion temperature. High-moisture-content biomass sludge needs to absorb more heat after entering the boiler, which is likely to cause a sharp drop in the boiler bed temperature and flameout. Based on this, a method suitable for co-firing high-moisture-content biomass is needed. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides a combustion method for a circulating fluidized bed boiler, which realizes the co-firing of high-moisture-content biomass sludge and can ensure good combustion effects.

[0006] The present invention provides a combustion method for a circulating fluidized bed boiler, including:

[0007] Transporting the biomass generated during the wood chipping process to a yard for stacking and fermentation to obtain fermented biomass;

[0008] Mixing sludge and fermented biomass in a mass ratio of 1:3 - 5 to obtain biomass sludge, and then separately feeding the biomass sludge and raw coal into the furnace for combustion. The proportion of biomass sludge in the total fuel ≤ 40%, and the addition amount of biomass sludge ≤ 20 tons per hour;

[0009] The moisture content of the fermented biomass is 50%-60%, and the moisture content of the sludge is 60%-68%.

[0010] Furthermore, the boiler bed temperature is 740°C to 880°C.

[0011] Furthermore, the boiler furnace outlet temperature is 710°C to 850°C.

[0012] Furthermore, the negative pressure at the furnace outlet is -50 Pa to -200 Pa, and the oxygen content in the furnace is 4% to 6%.

[0013] Furthermore, for the flue gas emissions of the circulating fluidized bed boiler, SO 2 ≤200 mg / m 3 、NOx ≤ 200 mg / m 3 、dust ≤ 30 mg / m 3 .

[0014] Furthermore, the biomass is the biomass generated during the wood chipping process, with a sulfur content ≤ 1%, an ash content ≤ 13.6%, and a lower calorific value ≥ 1300 kcal / kg.

[0015] Furthermore, the sludge is the sludge generated from pulp and paper making, with a sulfur content ≤ 1.26%, an ash content ≤ 29.86%, and a lower calorific value ≥ 450 kcal / kg.

[0016] The present invention also provides a combustion method for a circulating fluidized bed boiler, replacing the preparation process of the above biomass sludge with: mixing the sludge and the biomass generated during the wood chipping process in a mass ratio of 1:3 to 5, and carrying out stacking and fermentation to obtain biomass sludge, with the moisture content of the biomass sludge ≤ 65%.

[0017] The method of mixing first and then fermenting effectively reduces the heat loss during the mixing process compared to the method of fermenting first and then mixing, so that the temperature of the biomass sludge is relatively higher when fed into the furnace, reducing the heat absorbed by the biomass after entering the furnace, thereby improving its combustion efficiency.

[0018] In addition, due to the presence of microbial communities (such as Chloroflexi, Bacteroidetes, Proteobacteria, etc.) in the papermaking sludge, these microorganisms can decompose complex and diverse organic substances such as cellulose, hemicellulose, and lignin in the papermaking plant sludge, and can also play a positive role in the fermentation of biomass, making the biomass sludge after mixed fermentation more conducive to combustion.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] The combustion method for the circulating fluidized bed boiler provided by the present invention realizes the mixed combustion of biomass with a relatively high moisture content and sludge, avoiding the secondary pollution caused by sludge landfill, and having good environmental benefits. Specific Embodiments

[0021] The present invention will be further described in detail below through specific embodiments.

[0022] Example 1

[0023] This example provides a combustion method for a circulating fluidized bed boiler, including:

[0024] Using a plate - width filter press to dewater the sludge, and then using a vehicle to transport it to a sludge drying shed for drying for about 10 days, so that the moisture content drops to 60% - 68%, the sulfur content of the sludge ≤ 1.26%, the ash content ≤ 29.86%, and the low - calorific value ≥ 450 kcal / kg.

[0025] The biomass generated during the wood - chipping process is transported to a biomass storage yard by vehicle for stacking and fermentation. Specifically: The biomass generated during the wood - chipping process is transported to the biomass storage yard by vehicle and stacked and stored outdoors by a loader (3 - 4 meters high), and the internal temperature of the stacked biomass is increased by using the natural environment temperature and stacked for 20 to 30 days for fermentation. After partial water evaporation (to make the biomass reach a moisture content of 50% - 60%), it is transported to the biomass house by vehicle. The sulfur content of the biomass ≤ 1%, the ash content ≤ 13.6%, and the low - calorific value ≥ 1300 kcal / kg. Stacking and fermentation can not only reduce the moisture content but also increase the internal temperature of the biomass (which can be increased to 38°C - 45°C), thereby reducing the heat absorbed by the biomass after entering the furnace, and thus improving its combustion efficiency.

[0026] In addition, the biomass ferments under anaerobic conditions through the action of microorganisms. The fermentation products usually contain a high content of organic matter and volatile fatty acids. As combustible substances, volatile fatty acids can release more energy during the combustion process. At the same time, they can also improve the combustion characteristics of the sludge, reduce the ignition temperature of the sludge, make the sludge easier to ignite, and burn more fully, thereby further improving the combustion efficiency.

[0027] The sludge is transported from the sludge drying shed to the biomass house and mixed with the fermented biomass at a mass ratio of 1:3 - 5 to obtain biomass sludge. The biomass sludge is transported to the circulating fluidized bed boiler for co - firing by a screw feeder and a conveyor belt. At the same time, raw coal is fed into the boiler furnace from the coal bunker, and the proportion of biomass sludge in the total fuel ≤ 40%.

[0028] During the combustion process, the boiler operators shall perform monitoring and operation adjustment. During operation, the boiler load shall be kept stable (the boiler load (steam production) is controlled between 105 t / h and 120 t / h according to the steam and power balance of production), the boiler bed temperature is controlled between 740 °C and 880 °C, the boiler furnace outlet temperature is controlled between 710 °C and 850 °C, the furnace outlet negative pressure is controlled between -50 Pa and -200 Pa, the furnace oxygen content is controlled between 4% and 6%, and the SO in the flue gas emission 2 ≤ 200 mg / m 3 、NOx ≤ 200 mg / m 3 、the dust ≤ 30 mg / m 3 .

[0029] Example 2

[0030] Biomass with a moisture content of 50% and sludge with a moisture content of 60% are mixed and co-fired at a mass ratio of 1:4. During operation, the boiler load is kept stable, the boiler bed temperature is controlled between 740 °C and 880 °C, the boiler furnace outlet temperature is controlled between 710 °C and 850 °C, the boiler thermal efficiency can reach over 84%, the ash and slag generated by combustion are reduced by 1%, the furnace outlet negative pressure can be controlled between -50 Pa and -200 Pa, the furnace oxygen content is controlled between 4% and 6%, and the SO in the flue gas emission 2 is below 150 mg / m 3 , NOx is below 130 mg / m 3 , the dust is below 23 mg / m 3 , and the flue gas emission is lower than the standard. The cost of the biomass and sludge mixture is 150 yuan per ton, the raw coal procurement cost is 500 yuan per ton. Each ton of biomass and sludge mixture added can replace 0.4 tons of raw coal. Adding 1 ton of biomass and sludge can save 50 yuan in cost. 100,000 tons of biomass are added annually, and 5 million yuan in cost can be saved annually.

[0031] Example 3

[0032] Biomass with a moisture content of 50% and sludge with a moisture content of 65% are mixed and co-fired at a mass ratio of 1:4. During operation, the boiler load is kept stable, the boiler bed temperature is controlled between 740 °C and 860 °C, the boiler furnace outlet temperature is controlled between 710 °C and 830 °C, the boiler thermal efficiency can reach over 82.6%, the ash and slag generated by combustion are reduced by 1%, the furnace outlet negative pressure can be controlled between -80 Pa and -150 Pa, the furnace oxygen content is controlled between 4% and 6%, and the SO in the flue gas emission 2 is below 120 mg / m 3 , NOx is below 120 mg / m 3 , the dust is below 21 mg / m 3The following is that the flue gas emissions are below the standard. After mixing biomass and sludge, the cost is 150 yuan per ton, the procurement cost of raw coal is 500 yuan per ton. Each ton of added biomass sludge can replace 0.38 tons of raw coal. Adding 1 ton of biomass sludge can save 40 yuan in cost. 100,000 tons of biomass are added annually, and 4 million yuan in cost can be saved annually.

[0033] Example 4

[0034] Biomass with a moisture content of 55% and sludge with a moisture content of 65% are mixed and co-fired at a mass ratio of 1:5. During the operation, the boiler load remains stable. The boiler bed temperature is between 740°C and 850°C, and the boiler furnace outlet temperature is between 710°C and 810°C. The boiler thermal efficiency can reach over 82.3%. The ash and slag generated by combustion are reduced by 1%. The negative pressure at the furnace outlet can be controlled between -80 Pa and -130 Pa, and the oxygen content in the furnace is controlled between 4% and 5%. The flue gas emissions of SO 2 are controlled below 110 mg / m 3 , NOx is below 110 mg / m 3 , and soot is below 19 mg / m 3 . The flue gas emissions are below the standard. After mixing biomass and sludge, the cost is 150 yuan per ton, the procurement cost of raw coal is 500 yuan per ton. Each ton of added biomass sludge can replace 0.36 tons of raw coal. Adding 1 ton of biomass sludge can save 30 yuan in cost. 100,000 tons of biomass are added annually, and 3 million yuan in cost can be saved annually.

[0035] Example 5

[0036] Biomass with a moisture content of 60% and sludge with a moisture content of 68% are mixed and co-fired at a mass ratio of 1:5. During the operation, the boiler load remains stable. The boiler bed temperature is between 740°C and 810°C, and the boiler furnace outlet temperature is between 710°C and 780°C. The boiler thermal efficiency can reach over 82%. The ash and slag generated by combustion are reduced by 1%. The negative pressure at the furnace outlet can be controlled between -80 Pa and -110 Pa, and the oxygen content in the furnace is controlled between 4% and 5%. The flue gas emissions of SO 2 are controlled below 100 mg / m 3 , NOx is below 100 mg / m 3 , and soot is below 17 mg / m 3 . The flue gas emissions are below the standard. After mixing biomass and sludge, the cost is 150 yuan per ton, the procurement cost of raw coal is 500 yuan per ton. Each ton of added biomass sludge can replace 0.34 tons of raw coal. Adding 1 ton of biomass sludge can save 20 yuan in cost. 100,000 tons of biomass are added annually, and 2 million yuan in cost can be saved annually.

[0037] Example 6

[0038] Add biomass sludge that is fermented first and then mixed (hereinafter referred to as biomass sludge A) and biomass sludge that is mixed first and then fermented (hereinafter referred to as biomass sludge B) in different time periods. The total addition of biomass and sludge is 200 tons, about 60 tons of sludge, and the sludge accounts for 30%. The moisture content of the fermented biomass in biomass sludge A is 52% - 58%, and the moisture content of the sludge is 62% - 66%.

[0039] The biomass generated during the wood chipping process and the sludge generated from sewage treatment are dewatered using a plate width filter press. The sludge is transported to the biomass yard by truck and evenly mixed at a ratio of 1:3 - 5 using a loader and then piled up (3 - 4 meters) for open storage. The internal temperature of the piled biomass is increased using the natural environment temperature, and it is piled for 20 to 30 days for fermentation. Biomass sludge B is obtained after 23 days of mixed fermentation and piling of biomass and sludge, and its moisture content is 62.98%.

[0040] Test implementation plan:

[0041] (1) Before the test, the air pressure of the 4# boiler should be controlled at about 8.5 kPa, and all operating parameters of the boiler should be controlled within the optimal range to ensure the stable and efficient operation of the boiler before the test.

[0042] (2) Add biomass sludge A and biomass sludge B normally for 8 hours at different time periods. The boiler bed temperature is controlled to operate between 750 - 900 °C; the oxygen content in the flue gas is controlled at 5 - 6%; the exhaust gas temperature is controlled below 150 °C. The boiler load is controlled to operate at 120 - 130 t / h.

[0043] Test record form

[0044]

[0045]

[0046] As can be seen from the above table, the parameters such as boiler load, air volume, air pressure, and oxygen content when adding biomass sludge B changed little. When adding biomass without mixed sludge (pure biomass with a moisture content of 57.38%, sulfur content of 0.98%, ash content of 13.49%, and low calorific value of 1345 kcal / kg), the average rotational speed of the No. 1 coal feeder during that period was 30.3 r / h, and the average coal feeding amount was 11.5 t / h. The average rotational speed of the No. 2 coal feeder was 30.25 r / h, and the average coal feeding amount was 10.19 t / h (displayed value in the DCS room). During the period of adding biomass sludge A, the average rotational speed of the No. 1 coal feeder was 35.5 r / h, and the average coal feeding amount was 13.55 t / h. The average rotational speed of the No. 2 coal feeder was 33.4 r / h, and the average coal feeding amount was 11.13 t / h (displayed value in the DCS room). During the period of adding biomass sludge B, the average rotational speed of the No. 1 coal feeder decreased by 5.2 r / h, and the average coal feeding amount decreased by 2.05 t / h. The average rotational speed of the No. 2 coal feeder decreased by 3.15 r / h, and the average coal feeding amount decreased by 1.0 t / h (displayed value in the DCS room); the average rotational speed of the two coal feeders adding biomass sludge B was 68.83 r / h (the average value of the sum of the rotational speeds of the No. 1 and No. 2 coal feeders), and the coal consumption was 211.35 tons. It was concluded that each rotation of the coal feeder corresponded to 0.384 tons of coal, and the average rotational speed of the two coal feeders decreased by 8.35 r / h.

[0047] As can be seen from the data in the above table, the average bed temperature of the boiler during the period of adding biomass sludge A was 794 °C, and the average bed temperature of the boiler during the period of adding the biomass after fermentation of biomass and sludge was 779 °C, and the average bed temperature of the boiler decreased by 15 °C.

[0048] Under the condition that the load of the No. 4 boiler was not much different, when adding biomass sludge B, the average rotational speed of each coal feeder decreased by 4.17 r / h per hour; if calculated according to 0.384 tons of coal fed per rotation of the coal feeder, when adding the biomass after fermentation of biomass and sludge, the coal consumption per hour decreased by about 3.17 tons of coal, and the coal consumption decreased by about 76.08 tons of coal per day. Calculated according to the original coal price of the mixed coal type at 470 yuan / ton, adding the biomass after fermentation of biomass and sludge could reduce the cost by about 35,800 yuan per day.

[0049] The conclusion is:

[0050] When adding the biomass after fermentation of biomass and sludge to the No. 4 boiler, the rotational speed of each coal feeder decreased by 4.17 r / h. The biomass after fermentation of biomass and sludge (i.e., biomass sludge B) with a moisture content below 65% could be added normally. Under the same boiler load, the rotational speed of the coal feeder decreased by 4.12 r / unit, which could effectively reduce the addition amount of raw coal.

[0051] The above uses specific examples to elaborate on the present invention, which is only used to help understand the present invention and is not intended to limit the present invention. For those skilled in the art to which the present invention pertains, based on the idea of the present invention, several simple deductions, deformations or substitutions can also be made.

Claims

1. A circulating fluidized bed boiler combustion method, characterized in that: include: The biomass generated in the wood chipping process is transported to a storage yard for open-air storage and fermentation, and is stored for 20 to 30 days for fermentation to obtain fermented biomass; The sludge and the fermented biomass are mixed in a mass ratio of 1:3-5 to obtain biomass sludge; The biomass sludge is transported to the circulating fluidized bed boiler for blending by a screw feeder and a conveyor belt. At the same time, the raw coal is fed from the coal bunker into the boiler furnace. The proportion of biomass sludge in the total fuel is ≤40%, and the amount of biomass sludge added is ≤20 tons / hour. The moisture content of the fermented biomass is 50%-60%, and the moisture content of the sludge is 60%-68%; The sludge is sludge produced by pulping and papermaking, with a sulfur content of ≤1.26%, an ash content of ≤29.86%, and a low calorific value of ≥450kcal / kg.

2. The method according to claim 1, characterized in that The boiler bed temperature is 740℃~880℃.

3. The method according to claim 1, characterized in that The boiler furnace outlet temperature is 710℃~850℃.

4. The method according to claim 1, characterized in that The negative pressure at the furnace outlet is -50Pa~-200Pa, and the oxygen content in the furnace is 4%~6%.

5. The method according to claim 1, characterized in that Circulating fluidized bed boiler flue gas emission SO2≤200mg / m 3 、NOx≤200mg / m 3 、Smoke ≤30mg / m 3 .

6. The method according to claim 1, characterized in that The biomass is biomass produced in the process of wood chipping, with a sulfur content of ≤1%, an ash content of ≤13.6%, and a low calorific value of ≥1300 kcal / kg.

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