CN105727731A - Desulfurization system and desulfurization method for improving boiler efficiency - Google Patents

Abstract

The invention provides a desulfurization system and method for improving boiler efficiency. Two kinds of limestone powders with an average particle size close to 500 μm and close to 100 μm respectively enter the furnace through a coal conveyor and a powder delivery pipe. The molar ratio of calcium to sulfur is greater than 0.5, the two kinds of limestone powder absorb heat in the furnace, calcined and decomposed into calcium oxide for desulfurization, the circulating ash collected by the cyclone separator and part of the fly ash collected by the dust collector return to the furnace, and the calcium oxide participates in Desulfurization reaction, the desulfurization efficiency in the furnace is greater than 20%. During the desulfurization process in the furnace, the total heat absorption of the calcined decomposition of the two limestone powders is less than the heat release of SO2 converted into calcium sulfate. The desulfurization process in the furnace increases the efficiency of the boiler; outside the furnace Set up a desulfurization tower to further complete flue gas desulfurization, so that SO2 can be discharged up to the standard. The invention solves the problems that the traditional furnace desulfurization process has a large calcium-sulfur molar ratio and excessive heat absorption of limestone calcination, which leads to the reduction of boiler efficiency, and has remarkable energy-saving and emission-reduction effects.

Description

Desulfurization system and method for improving boiler efficiency

technical field

The invention relates to the field of desulfurization, in particular to a desulfurization system and method for improving boiler efficiency.

Background technique

The SO2 emission status of coal-fired boilers: coal contains a certain amount of sulfur, most of which are converted into SO2 during the coal-fired combustion process, if not controlled, it will be discharged into the atmosphere with flue gas to cause acid rain, SO2 is the main One of the air pollutants, causing harm to the ecology. my country is a country that uses coal as the main energy source. Coal combustion accounts for more than 60% of my country's energy structure. SO2 emitted from coal combustion has caused serious air pollution problems in my country, especially in the southeast coastal areas and southwest regions. SO2 Acid rain caused by emissions is a serious problem. In order to solve the serious problem of air pollution in our country, the Ministry of Environmental Protection of the People's Republic of my country has formulated the "Emission Control Standard of Air Pollutants from Thermal Power Plants", the standard number is GB13223-2011, which greatly increases the requirements for the SO2 emission concentration of coal-fired boilers in thermal power plants. According to the current situation of sulfur content in coal, coal-fired power plants that did not install desulfurization facilities need to install desulfurization facilities, and most coal-fired power plants that have installed desulfurization facilities need to upgrade their original desulfurization facilities. High desulfurization efficiency can meet the emission requirements of SO2.

Current status of circulating fluidized bed boiler desulfurization technology: the rise of coal prices stimulates boiler users, especially boiler users in thermal power plants, to use low-priced coal with low calorific value and high sulfur content. As a clean combustion equipment, circulating fluidized bed boilers , is especially suitable for burning the above-mentioned fuels, and has been widely used in my country, according to incomplete statistics. There are more than 3,000 circulating fluidized bed boilers of various capacities in service in my country.

The traditional circulating fluidized bed boiler desulfurization process is to transport limestone powder to the furnace, and the limestone powder is calcined to form calcium oxide, which reacts with SO2 released from coal combustion to form calcium sulfate to achieve the purpose of desulfurization. If the SO2 emission requirements are not high, the amount of limestone powder is not too large. Generally, under the condition that the calcium-sulfur molar ratio is not greater than 2.5, the desulfurization efficiency can reach 80%, and the SO2 emission concentration can meet the emission requirements. However, with the increasingly stringent SO2 emission requirements, it is generally required that the SO2 emission concentration of power plant boilers should be below 200mg/Nm3, and the desulfurization efficiency should be over 95%. If high-sulfur coal is used, the desulfurization efficiency can even be as high as 98%. With such a high desulfurization efficiency, if you still use limestone powder in the furnace for desulfurization, you must greatly increase the amount of limestone powder, and the molar ratio of calcium to sulfur can even be as high as 4-5. Calcination in the furnace requires the absorption of a large amount of heat, resulting in reduced boiler efficiency. Taking the coal fired in the Furong Coal Mine in Sichuan Province as an example, the received base sulfur content of the fired coal is 4.05%, and the low calorific value is 4739Kcal/kg. Without desulfurization measures, the SO2 emission concentration is 11240mg/Nm3. To meet the environmental emission requirements of SO2 emission concentration of 200mg/Nm3, the desulfurization efficiency needs to be as high as 98.3%. If only limestone powder is sprayed in the furnace for desulfurization, and the calcium-sulfur molar ratio is calculated as 4, for a coal-fired boiler equipped with a 300,000-kilowatt generating set, the coal consumption per hour is 149 tons, and the limestone powder consumption per hour The calcined heat of limestone powder is 75.6 tons. Under the condition of desulfurization efficiency of 98.3%, the calcined heat of limestone powder is much greater than the heat released by desulfurization reaction. 1.6%, that is, adding a large amount of limestone powder to the boiler causes the boiler efficiency to decrease by 1.6%. Putting up to 75.6 tons of limestone into the boiler per hour caused serious consequences: the heating surface of the boiler was severely worn, the operating load of the limestone powder conveying system, ash discharge facilities and dust collectors increased significantly, and the failure rate and operation and maintenance costs of these facilities were high. increase in magnitude.

If in order to avoid the above problems, instead of adding limestone powder to the furnace for desulfurization, only using the desulfurization tower outside the furnace for desulfurization will cause low-temperature corrosion on the heating surface of the boiler tail. Coal-fired flue gas contains a large amount of water vapor, and the flue gas containing high concentration of SO2 flows through the low-temperature heating surface of the boiler tail flue. When the surface temperature of the heating surface is lower than the acid dew point, SO2 combines with water vapor to form acid dew condensation On the surface of the low-temperature heating surface, the low-temperature corrosion leakage will quickly occur on the low-temperature heating surface, which will cause harm to the safe and stable operation of the boiler.

Contents of the invention

The technical problem to be solved by the present invention is to provide a desulfurization system and method for improving boiler efficiency, which overcomes the problems of large calcium-sulfur molar ratio and excessive heat absorption of limestone calcination in the traditional furnace desulfurization process, which lead to the reduction of boiler efficiency. Limestone powder and fine limestone powder are calcined in the furnace to absorb heat and decompose into calcium oxide for desulfurization. The circulating ash collected by the cyclone separator and part of the fly ash collected by the dust collector return to the furnace. Calcium sulfate is released during the desulfurization process in the furnace. The heat is greater than the heat absorbed by the calcination and decomposition of coarse limestone powder and fine limestone powder, so that the desulfurization process in the furnace improves the boiler efficiency, and the flue gas desulfurization is further completed through the desulfurization tower installed outside the furnace, so that SO2 emissions meet the requirements.

The technical scheme that the present invention adopts is as follows:

A desulfurization system for improving boiler efficiency, comprising a furnace, a cyclone separator, and a desulfurization tower, characterized in that: the feed port of the furnace communicates with a coal hopper and a coarse limestone powder bin through a coal conveyor, and the feed port of the furnace The powder feeding pipe is connected with the fine limestone powder bin, the feed port of the furnace is connected with the dust collector through the return pipe, the feed port of the furnace is connected with the cyclone separator through the feeder, and the outlet of the furnace is connected with the cyclone separator. The inlet of the cyclone separator is connected with the inlet of the tail flue, the outlet of the tail flue is connected with the inlet of the dust collector, the outlet of the dust collector is connected with the inlet of the desulfurization tower, and the outlet of the desulfurization tower is connected with the chimney connected.

Preferably, the desulfurization system for improving boiler efficiency is characterized in that: the ash outlet of the dust collector is connected to the distributor, and the distributor is connected to the furnace and the ash store respectively.

Preferably, the desulfurization system for improving boiler efficiency is characterized in that: the inlet of the desulfurization tower is also connected to the desulfurizer tank.

Preferably, the desulfurization system for improving boiler efficiency is characterized in that: a feeder is provided at the lower part of the fine limestone powder bin, and the inlet of the feeder is connected to the blower.

A desulfurization method based on the system of claim 1, characterized in that it comprises the following steps: coal-fired coal containing a certain amount of sulfur enters the furnace for combustion through a coal feeder to generate flue gas, and most of the sulfur element is oxidized into SO2 and enters the flue gas; The coarse limestone powder in the limestone powder silo enters the furnace through the coal conveyor, and the compressed air from the blower carries the fine limestone powder provided by the fine limestone powder silo into the furnace through the powder delivery pipe, and the coarse limestone powder and fine limestone powder undergo calcination reaction in the furnace , decomposes into CaO and CO2, and absorbs heat; the flue gas in the furnace leaves the furnace with coal ash, unburned carbon and calcium oxide particles and enters the cyclone separator, which captures more than 99.5% of the particles in the flue gas As recycled ash, it is returned to the furnace through the feeder; the flue gas leaving the cyclone separator and the rest of the fly ash carried by it enter the tail flue, and release heat to the heat exchanger, the temperature is lowered, and then enter the dust collector, which is greater than 99.5 % of the fly ash is collected by the dust collector, and the collected fly ash contains a certain concentration of calcium oxide. Part of the fly ash is returned to the furnace through the return pipe, and the other part is sent to the ash store. The distribution ratio of the two is controlled by the distributor; The flue gas leaving the dust collector enters the desulfurization tower for further desulfurization, and the desulfurization agent tank provides desulfurization agent to the desulfurization tower. After desulfurization, the flue gas that meets the environmental protection emission requirements leaves the desulfurization tower and is discharged through the chimney; coarse limestone powder and fine limestone powder are in the furnace Decomposition produces calcium oxide, which is collected by the cyclone separator and sent to the furnace to contain calcium oxide. The fly ash collected by the dust collector and returned to the furnace by the distributor contains calcium oxide. These calcium oxides participate in desulfurization in the furnace. The reaction generates calcium sulfate and releases a certain amount of heat.

Preferably, the desulfurization method is characterized in that: the average particle size of the coarse limestone powder is close to 500 μm, the average particle size of the fine limestone powder is close to 100 μm, and the residence time of the coarse limestone powder and its decomposition products in the furnace is shorter than that of the fine limestone powder. The residence time of limestone powder and its decomposition products in the furnace is more than 10 times. The flow rate of coarse limestone powder and coal combustion is controlled at a calcium-sulfur molar ratio above 0.3. As the basic desulfurization control method, the flow rate of fine limestone powder and coal combustion flow is controlled When the calcium-sulfur molar ratio is below 0.2, as a fine desulfurization control method, the circulating ash captured by the cyclone separator is returned to the furnace. The circulating ash contains calcium oxide, which is a necessary means for desulfurization control, but it cannot be actively used in boiler operation. Control, the fly ash collected by the dust collector and returned to the furnace contains calcium oxide, and the calcium oxide escaped from the cyclone separator is returned to the furnace again, and the proportion of this part of fly ash returned to the furnace can be controlled to make up for the cyclone separator. Insufficient active control; after the recycled ash collected by the cyclone separator and the fly ash collected by the dust collector enter the furnace, the calcium oxide in these recycled ash and fly ash can directly participate in the desulfurization reaction without the heat required for limestone calcination.

Preferably, the desulfurization method is characterized in that: the calcium-sulfur molar ratio of the total flow of the coarse limestone powder and fine limestone powder to the coal flow is greater than 0.5, and the calcium oxide of the coarse limestone powder, fine limestone powder, and recycled ash Calcium oxide and fly ash returned to the furnace together to achieve desulfurization in the furnace. The coarse limestone powder and fine limestone powder need to absorb heat during the calcination and decomposition process. The calcining heat absorption per mole of calcium carbonate is 184kJ. During the desulfurization process, The release heat of calcium sulfate per mole of SO2 is 486kJ, and the desulfurization efficiency in the furnace is greater than 20%, ensuring that the heat released by the desulfurization reaction of these desulfurizers in the furnace is greater than the heat absorbed by the calcining and decomposition of coarse limestone powder and fine limestone powder, ensuring that The desulfurization process increases boiler efficiency.

Preferably, the desulfurization method is characterized in that: the flue gas leaving the deduster enters the desulfurization tower, and performs desulfurization again to remove SO2 in the flue gas, so that the concentration of SO2 in the flue gas leaving the desulfurization tower Below a certain concentration, the emission requirements of SO2 are met.

Compared with the prior art, the beneficial effects of the present invention are as follows:

1) Compared with the traditional furnace desulfurization process, the beneficial effects of the present invention are: the calcium-sulfur molar ratio of furnace desulfurization is greatly reduced, and the heat release of calcium oxide desulfurization reaction in the furnace desulfurization process is greater than that of limestone powder calcination reaction The desulfurization process not only achieves the purpose of desulfurization, but also effectively improves the boiler efficiency.

(2) Compared with the traditional desulfurization process using fine limestone powder alone, the furnace desulfurization process of the present invention adopts an in-furnace desulfurization process in which coarse limestone powder and fine limestone powder are combined. Limestone powder is used for precise desulfurization control, reducing the amount of fine limestone powder that adopts the pneumatic conveying method, saving the amount of compressed air and the power consumption of the air compressor; the transportation of coarse limestone powder by coal conveyor is more reliable, the failure rate is low, and the limestone powder is reduced. The failure rate of the powder conveying system improves the reliability of the desulfurization system and reduces the risk of excessive SO2 emissions.

(3) Compared with the traditional desulfurization process using fine limestone powder alone, the furnace desulfurization process of the present invention uses a furnace desulfurization process in which coarse limestone powder and fine limestone powder are combined, and the time for coarse limestone powder to participate in the desulfurization reaction in the furnace is much longer Compared with fine limestone powder, under the same desulfurization efficiency conditions, the calcium-sulfur molar ratio required for desulfurization in the furnace of the present invention is greatly reduced, reducing the consumption of limestone powder, effectively reducing the calcined heat absorption of limestone powder, and helping to improve boiler efficiency .

(4) Furthermore, most of the current desulfurization processes in the furnace use a dust collector to collect and discharge the calcium oxide that escapes the cyclone separator. The present invention uses a part of the dust collector to collect the fly ash containing a certain concentration of calcium oxide and returns it to the furnace. Utilize this part of calcium oxide in the fly ash for desulfurization, improve the utilization rate and desulfurization efficiency of limestone, use this part of calcium oxide for desulfurization, save the calcined heat absorption of limestone, and further improve the boiler efficiency.

(5) Furthermore, the present invention utilizes a desulfurization process combining in-furnace desulfurization and out-of-furnace desulfurization, which not only improves boiler efficiency, but also effectively reduces the SO2 concentration in the flue gas flowing through the low-temperature heating surface in the tail flue, Effectively avoid low-temperature corrosion on the low-temperature heating surface, reduce the failure rate of the boiler, and improve the safe operation period of the boiler.

(6) Further, the present invention realizes desulfurization and at the same time improves boiler efficiency, and has remarkable energy-saving and emission-reducing effects.

Description of drawings

Fig. 1 is a schematic diagram of the workflow of the present invention.

1-blower, 2-feeder, 3-powder delivery pipe, 4-furnace, 5-feeder, 6-return pipe, 7-distributor, 8-ash storage, 9-desulfurizer tank, 10- Chimney, 11-desulfurization tower, 12-dust collector, 13-tail flue, 14-heat exchanger, 15-cyclone separator, 16-coal hopper, 17-coarse limestone powder bin, 18-feeder, 19- Coal conveyor, 20-fine limestone powder bin.

detailed description

The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings to describe the technical solution of the present invention in detail.

As shown in the accompanying drawings, the desulfurization system and method for improving boiler efficiency, the feed port of the furnace (4) is connected with the coal hopper (16) and the coarse limestone powder bin (17) through the coal conveyor (19), and the furnace (4) ) is connected to the fine limestone powder bin (20) through the powder delivery pipe (3), the feed port of the furnace (4) is connected to the dust collector (12) through the return pipe (6), and the furnace (4) ) is connected to the cyclone separator (15) through the feeder (5), the outlet of the furnace (4) is connected to the inlet of the cyclone separator (15), and the outlet of the cyclone separator (15) is connected to the tail The inlet of the flue (13) is connected, the outlet of the tail flue (13) is connected with the inlet of the dust collector (12), the outlet of the dust collector (12) is connected with the inlet of the desulfurization tower (11), and the desulfurization tower ( 11) the outlet communicates with the chimney (10). The ash outlet of the dust collector (12) is communicated with the distributor (7), and the distributor (7) is respectively communicated with the furnace (4) and the ash storehouse (8). The inlet of the desulfurization tower (11) is also connected with the desulfurizer tank (9). A feeder (2) is arranged at the lower part of the fine limestone powder bin (20), and the inlet of the feeder (2) is connected with the air blower (1).

The working steps of the present invention are as follows: coal-fired coal containing a certain amount of sulfur enters the furnace (4) through the coal feeder (19) to burn to generate flue gas, most of the sulfur element is oxidized into SO2 and enters into the flue gas; the coarse limestone powder bin (17 ) into the furnace (4) through the coal conveyor (19), and the compressed air from the blower (1) carries the fine limestone powder provided by the fine limestone powder bin (20) into the furnace through the powder delivery pipe (3). Coarse limestone powder and fine limestone powder undergo a calcination reaction in the furnace (4), decompose into CaO and CO2, and absorb heat; the flue gas in the furnace (4) leaves the furnace with coal ash, unburned carbon and calcium oxide particles (4) Enter the cyclone separator (15), the cyclone separator (15) captures more than 99.5% of the particles in the flue gas and send them back to the furnace (4) through the feeder (5) as circulating ash; leave the cyclone separator The flue gas of (15) and the rest of the fly ash carried by it enter the tail flue (13), release heat to the heat exchanger (14), lower the temperature, and then enter the dust collector (12). More than 99.5% of the fly ash Collected by the dust collector (12), the collected fly ash containing a certain concentration of calcium oxide, part of the fly ash is returned to the furnace (4) through the return pipe (6), and the other part is sent to the ash storage (8). The distribution ratio of the latter is controlled by the distributor (7); the flue gas leaving the dust collector (12) enters the desulfurization tower (11) for further desulfurization, and the desulfurization agent tank (9) supplies the desulfurization agent to the desulfurization tower (11). After desulfurization, it meets the environmental protection requirements. The flue gas required for emission leaves the desulfurization tower (11) and is discharged through the chimney (10); coarse limestone powder and fine limestone powder are decomposed in the furnace (4) to produce calcium oxide, which is captured by the cyclone separator (15) and sent to the The circulating ash in the furnace (4) contains calcium oxide, and the fly ash collected by the dust collector (12) and sent back to the furnace (4) through the distributor (7) contains calcium oxide. These calcium oxides participate in the desulfurization reaction in the furnace. Calcium sulfate is generated and a certain amount of heat is released.

Furthermore, the average particle size of coarse limestone powder is close to 500 μm, and the average particle size of fine limestone powder is close to 100 μm. The residence time of coarse limestone powder and its decomposition products in the furnace (4) is longer than that of fine limestone powder and its decomposition products in the furnace ( 4) The residence time within is greater than 10 times, and the flow rate of coarse limestone powder and coal combustion is controlled at a calcium-sulfur molar ratio above 0.3. As a basic desulfurization control method, the flow rate of fine limestone powder and coal combustion is controlled at a calcium-sulfur molar ratio of Below 0.2, as a fine desulfurization control method, the circulating ash captured by the cyclone separator (15) is returned to the furnace (4). The circulating ash contains calcium oxide, which is a necessary means for desulfurization control, but it cannot be realized actively during boiler operation. Control, the fly ash collected by the dust collector (12) and returned to the furnace (4) contains calcium oxide, and the calcium oxide escaped from the cyclone separator (15) is returned to the furnace (4) again, and this part of the fly ash can be realized. The proportion of ash returned to the furnace makes up for the deficiency that the cyclone separator (15) cannot be actively controlled; after the circulating ash collected by the cyclone separator (15) and the fly ash collected by the dust collector (12) enter the furnace (4), The calcium oxide in these recycled ash and fly ash can directly participate in the desulfurization reaction without the heat required for limestone calcination.

Furthermore, the flue gas leaving the deduster (12) enters the desulfurization tower (11) for desulfurization again to remove SO2 in the flue gas, so that the concentration of SO2 in the flue gas leaving the desulfurization tower (11) is lower than a certain A specific concentration, to meet the emission requirements of SO2.

Claims (8)

1. the desulphurization system improving boiler efficiency, including burner hearth, cyclone separator, desulfurizing tower, it is characterized in that: the charging aperture of described burner hearth is connected with coal bunker and thick limestone powder bin by coal conveyor, the charging aperture of burner hearth is connected with thin limestone powder bin by duff pipe, the charging aperture of burner hearth is connected with cleaner unit by feed back pipe, the charging aperture of burner hearth is connected with cyclone separator by material returning device, the outlet of burner hearth is connected with the import of cyclone separator, the outlet of cyclone separator is connected with the import of back-end ductwork, the outlet of back-end ductwork is connected with the import of cleaner unit, the outlet of cleaner unit is connected with the import of desulfurizing tower, the outlet of desulfurizing tower is connected with chimney.

2. the desulphurization system of raising boiler efficiency according to claim 1, it is characterised in that: the ash discharging hole of described cleaner unit is connected with allotter, and allotter is connected with burner hearth and Hui Ku respectively.

3. the desulphurization system of raising boiler efficiency according to claim 1, it is characterised in that: the import of described desulfurizing tower is also connected with desulfurizing agent tank.

4. the desulphurization system of raising boiler efficiency according to claim 1, it is characterised in that: described thin limestone powder bin bottom arranges batcher, and batcher import is connected with pressure fan.

5. the sulfur method based on claim 1 system, it is characterised in that comprise the following steps: the fire coal containing certain sulphur content enters hearth combustion by coal conveyor and produces flue gas, and major part element sulphur is oxidized to SO2 and enters in flue gas；Rubble limestone flour in thick limestone powder bin enters burner hearth by coal conveyor, the microlith limestone flour that compression air from pressure fan carries thin limestone powder bin and provides enters burner hearth by duff pipe, calcination reaction is there is in rubble limestone flour and microlith limestone flour in burner hearth, resolve into CaO and CO2, and absorb heat；Flue gas in burner hearth carries coal ash, uncompleted burned carbon and calcium oxide particle and together leaves burner hearth entrance cyclone separator, and cyclone separator is recycled to burner hearth by being used as circulating ash under the granule capturing of more than 99.5% in flue gas by material returning device；The flue gas leaving cyclone separator and the remainder flying dust carried thereof enter back-end ductwork, and reduce to heat exchanger heat release, temperature, enter cleaner unit afterwards, the flying dust more than 99.5% that flue gas carries is collected by cleaner unit, it is collected the flying dust containing certain calcia concentration got off, a part returns to burner hearth through feed back pipe, and another part delivers to ash storehouse, and the two allocation proportion is by allotter control；The flue gas leaving cleaner unit enters the further desulfurization of desulfurizing tower, desulfurizing agent tank provide desulfurizing agent to desulfurizing tower, and the flue gas meeting environment protection emission requirement after desulfurization leaves desulfurizing tower, through smoke stack emission；Rubble limestone flour and microlith limestone flour decompose generation calcium oxide in burner hearth and participate in desulphurization reaction, part has neither part nor lot in the calcium oxide of desulphurization reaction and is trapped by cyclone separator and cleaner unit respectively, and along with circulating ash and flying dust return to burner hearth, this partial oxidation calcium again participates in desulphurization reaction in burner hearth and generates calcium sulfate, and discharges certain heat.

null6. sulfur method according to claim 5，It is characterized in that: the mean diameter of described rubble limestone flour is close to 500 μm，The mean diameter of microlith limestone flour is close to 100 μm，Rubble limestone flour and catabolite thereof the time of staying in burner hearth than microlith limestone flour and catabolite thereof the time of staying in burner hearth more than more than 10 times，Rubble limestone flour flow and coal-fired flow-control at calcium to sulphur mole ratio more than 0.3，Based on desulphurization control mode，Microlith limestone flour flow and coal-fired flow-control at calcium to sulphur mole ratio below 0.2，As fine desulphurization control mode，The circulating ash that cyclone collection gets off returns to burner hearth，Containing calcium oxide in circulating ash，It it is the necessary means of desulphurization control，But actively control cannot be realized in boiler operatiopn，What cleaner unit was collected is recycled in the flying dust of burner hearth containing calcium oxide，The calcium oxide fleeing from cyclone separator is recycled to burner hearth again，And the ratio controlling this part cinder reinjection to burner hearth can be realized，Make up the deficiency that cyclone separator can not actively control；After the flying dust entrance burner hearth that circulating ash and the removing dust device of cyclone separator trapping are collected, the calcium oxide in these circulating ash and flying dust can directly participate in desulphurization reaction, it is not necessary to limestone calcination institute calorific requirement.

7. sulfur method according to claim 5, it is characterized in that: the calcium to sulphur mole ratio of the total flow of described rubble limestone flour and microlith limestone flour and coal-fired flow is more than 0.5, rubble limestone flour, microlith limestone flour, the calcium oxide of circulating ash and cinder reinjection realize desulfurization in burner hearth jointly to the calcium oxide of burner hearth, wherein rubble limestone flour and microlith limestone flour need heat absorption in calcining and decomposing process, the calcining caloric receptivity of every mole of calcium carbonate is 184kJ, in sweetening process, the release heat being generated calcium sulfate by every mole of SO2 is 486kJ, desulfuration efficiency in burner hearth is more than 20%, guarantee that desulphurization reaction the discharged heat caloric receptivity more than rubble limestone flour and microlith limestone flour calcining and decomposing occurs these desulfurizing agents in sweetening process, guarantee that sweetening process makes boiler efficiency increase.

8. sulfur method according to claim 5, it is characterized in that: described in leave the flue gas of cleaner unit and enter into desulfurizing tower, carry out desulfurization, the SO2 in elimination flue gas again, make the SO2 concentration leaving in the flue gas of desulfurizing tower lower than a certain certain concentration, meet the emission request of SO2.