Analysis on smoke dust control and emission sources of iron and steel enterprises

0 Preface

Since the reform and opening up, China's steel industry has developed rapidly and has become an important pillar industry of the national economy. According to the statistics of China Steel Association, China's crude steel output reached 820 million tons in 2014, a year-on-year increase of 0.9%, accounting for 49.3% of global crude steel production. As the output continues to rise, the problem of smoke and dust pollution in steel companies is becoming more and more serious. According to the Ministry of Environmental Protection statistical analysis, ferrous metals 2013 smoke dust emissions smelting and rolling processing industry was 1.935 million t, an increase of 6.7 percent over the previous year, accounting for 15.1% of total national tobacco dust emissions, improving by 0.4 over the previous year Percentage points. At the same time, the steel industry has become the third largest source of industrial smoke dust in China. At present, the dust removal technology and equipment of China's iron and steel enterprises have been widely used, and the construction of emission monitoring system is still not perfect, and the coverage rate is low, especially the monitoring of key emission sources is not in place [3, 4]. The reason is because the process of steel production in China is complicated, the process is long, and there are many processes. The corresponding sources of smoke dust pollution are numerous, the emissions are large and the distribution is wide. According to statistics, in an iron and steel enterprise with an annual output of 10 million tons, the number of organized emission sources equipped with dust removal facilities can reach dozens or even hundreds. If the key emission sources cannot be distinguished, it will not only affect the effectiveness and rationality of the emission monitoring data, but also reduce the pertinence of the enterprise smoke dust prevention and control. Therefore, it is necessary to sort out the organized dust removal system of steel enterprises according to the process, and analyze the smoke dust emissions of each dust removal system in order to screen out the key emission sources. Through this analysis, it can provide scientific evidence for scientific monitoring of iron and steel dust emission levels, implementation of emission reduction targets, and verification of total emissions. It can also provide a strong basis for the company's smoke dust prevention and control technology upgrade and plant atmosphere control.

1 research object and method

1.1 Company Profile

The research object of this paper is a typical steel joint enterprise with an annual output of 10 million tons of steel in the north. The steel plant covers the main processes of sintering, pelletizing, coking, blast furnace ironmaking, converter steelmaking, hot rolling and cold rolling, as well as supporting processes such as self-supplied power stations and limestone rotary kiln. The main production equipment includes: 2 500m2 sintering machines, 1 504m2 belt roasting pelletizing machine, 4 60-hole coke ovens, 4 125t/h dry quenching furnaces, 2 5500m3 blast furnaces, 4 300t converters, 1 set. 2250mm hot rolling mill, 1 1780mm hot rolling mill, 1 2230mm cold rolling mill, 1 1700mm cold rolling mill and 1 1550mm cold rolling mill, and 3 sets of 1200t/d limestone rotary kiln, 2 300MW boiler generator sets And two 150MW gas-steam combined cycle (CCPP) generator sets.

1.2 Production process and its dust removal system

The steel company uses long process production, and its process flow is shown in Figure 1. According to the characteristics of the production and discharge of smoke dust, each process has set up perfect control measures and designed corresponding dust removal system. Among them, the dust removal system of the sinter plant includes: a flue gas dedusting system for the machine head, a dust removal system for the finished product and a dust removal system for the raw material; the dust removal system of the pellet plant includes: a roasting flue gas dedusting system, a dust removal system, a batch dust removal system, and finished dust removal system; coking plant flue gas and dust removal system comprising: dust removal system pulverized coal, coke dust ground station, the ground station for dust removal CDQ, blast furnace coke dust library ground station, the ground station for dust removal and screening coke oven flue The dust removal system and flue gas of the ironmaking plant include: the dedusting system of the iron yard, the dedusting system of the silo, the dust removal system of the cast iron machine, the dust removal system of the coal powder preparation and the flue gas of the hot blast stove; the dust removal system of the steelmaking plant includes: the hot metal pouring tank And pre-treatment dust removal system, loading dust removal system, underground silo dust removal system, converter primary flue gas dedusting system and converter secondary flue gas dedusting system; hot rolling mill dust removal system and flue gas include: finishing mill dust removal system and heating furnace Flue gas; the dust removal system and flue gas of the cold rolling mill include: welding machine dust removal system and waste acid regeneration flue gas. In the supporting process, the dust removal flue gas of the self-supplied power station includes: dust removal flue gas of the boiler generator set and flue gas of the CCPP generator set; the dust removal system of the lime kiln includes: a raw material batch dust removal system, a kiln top dust removal system and a finished product dust removal system.

1.3 Calculation method of smoke dust emission

The calculation method of the smoke dust emission of each dust removal system of the steel plant is to calculate the hourly smoke (waste) gas volume LN in the standard state according to the design air volume Li, m3/h and the smoke (waste) gas temperature Ti, °C of the dust removal system. , i, m3 (standard state) / h. The lower corner i represents each dust removal system, the same below.

Then, according to the smoke dust emission concentration ρi, mg/m3 (standard state) and the annual operation hours ti, h/a of the dust removal system, the annual smoke emission amount Mi, t/a of each dust removal system is calculated, as follows

Among them, the smoke dust emission concentration is based on the air pollutant emission standards of each process, and refers to the actual emission data. For the convenience of accounting, the flue gas dedusting of the sintering machine head, the flue gas dedusting of the pellets and the dust removal flue gas of the generator set of the self-provided power station boiler are 30mg/m3 (standard state), and the value of the coke oven flue gas is 10mg/m3 (standard state). The ironmaking hot blast stove flue gas value is 5mg/m3 (standard state), the hot rolling furnace flue gas value is 3mg/m3 (standard state) and the CCPP generator set flue gas value is 2mg/m3 (standard state), and the rest of the dust removal The system exhaust gas is worth 20mg/m3 (standard state).

2 smoke dust emission accounting

Table 1 summarizes the annual emissions of smoke dust from the dust removal system of the steel company in sintering, pelletizing, coking, iron making, steel making, hot rolling, cold rolling, and self-supplied power stations and lime kiln, as well as the total emissions of the plant. proportion.

3 results analysis

3.1 Analysis of smoke emission from the whole plant

According to Table 1, the annual emissions of smoke dust from the whole plant, the emission of smoke dust from the main processes of sintering, pelletizing, coking, iron making, steel making, cold and hot rolling accounted for 91.10% of the whole plant; The dust emission of the supporting technology such as lime kiln accounts for 8.90% of the whole plant. In the main process, the smoke emission of the four units of sintering, pellets, coking and iron making before iron accounted for 73.13%, which was 3.1 times that of steelmaking. China's steel industry is dominated by long processes. The pre-iron process is mainly for the initial processing of raw fuels such as iron fines and coal powder. Not only the raw fuel is used in large quantities, but also the smelting intensity is high, and the smoke (waste) gas emissions are large. At the same time, the mineral materials used and produced in these processes contain a large amount of ash and impurities, and a large amount of dust is generated in the production processes such as transportation, cooling, screening, loading and unloading [6]. Based on the above factors, the smoke dust emission of the pre-iron process is the most, which is also a feature of China's long-flow steel production.

3.2 Analysis of smoke dust emissions in each process

In terms of the proportion of smoke dust emission in each process, the sintering plant, converter steelmaking plant and blast furnace ironmaking plant are the three major sources of smoke dust emissions of iron and steel enterprises, and their emissions account for 32.80% and 21.42% of the total plant, respectively. 16.47%, a total of 70.68%. For each major process, study the dust removal system or smoke that has the highest proportion of smoke dust emissions. In the sintering plant, pellet plant, coking plant, ironmaking plant, steel mill, rolling mill (co-cold rolling joint consideration), the highest smoke dust emission is: the head flue gas dedusting system, roasting flue gas dust removal System, pre-burning coke dedusting station, tapping yard dust removal system, converter secondary flue gas dedusting system and finishing mill dust removal system. The proportion of each dust removal system in the process smoke dust emissions is: 75.53%, 88.11%, 26.37%, 52.12%, 54.14% and 62.81%. Accelerate the transformation and upgrading of these dust removal systems and improve the efficiency of dust removal, which can have an immediate effect on the control of smoke dust in the process unit.

3.3 Analysis of key smoke emission sources

According to Table 1, the dust emission of each dust removal system accounts for the proportion of the whole plant, and combined with the actual smoke dust treatment and emission monitoring needs, the following 10 major smoke dust emission sources are selected: 1) Sintering machine head flue gas dedusting system, 24.77%; 2) Steelmaking converter secondary flue gas dedusting system, accounting for 11.60%; 3) Ironworks de-dusting system, accounting for 8.58%; 4) Iron and steel plant silo dust removal system, accounting for Ratio 6.73%; 5) pelletizing plant roasting flue gas dedusting system, accounting for 6.57%; 6) boiler generator set flue gas, accounting for 6.21%; 7) sintering plant tail finished dust removal system, accounting for 5.85%; 8) Steelmaking pretreatment dedusting system of steelmaking plant, accounting for 4.82%; 9) steelmaking plant dust removal system, accounting for 2.71%; 10) coking plant front coke dedusting station, accounting for 2.61%. The above ten key smoke dust sources accounted for a total of 80.44% of the whole plant. In order to improve the atmospheric environment of iron and steel enterprises, and to improve the construction of monitoring points and monitoring systems, we can consider taking the lead in the implementation of dust removal system renovation and emission data monitoring of the above key smoke dust sources.

4 Summary and recommendations

(1) This paper analyzes the main processes of smoke dust emission in the factory through the accounting of the annual emissions of typical full-process steel enterprises, and selects 10 key sources. Among them, the smoke dust removal system of the sintering machine head, the secondary flue gas dedusting system of the converter and the blast furnace dedusting system have the highest smoke dust emission, accounting for 44.95% of the whole plant.

(2) The smoke dust emitted by iron and steel enterprises mainly comes from industrial kiln smoke (waste) gas of sintering, pelletizing, coking, iron making and steel making, with large discharge, high smoke temperature, strong paroxysity, and emission. The characteristics of relative concentration. In the treatment of smoke dust, the dust removal equipment renovation and system optimization can be carried out for the key emission sources in these processes, including the electrostatic precipitator, the bag dust removal or the electric bag integrated dust removal, the anti-blowing cloth bag dust removal and the long bag pulse bag. Measures such as wind speed design such as dust removal, dust removal equipment and low resistance of the system [7-9]. Only effectively improve the dust removal efficiency of the system such as the dedusting of the sintered machine head and the finished tail, the dust removal of the pellet roasting, the dust removal of the coke oven, the de-dusting of the blast furnace and the silo of the silo, the secondary flue gas of the converter and the pretreatment of the hot metal. Reducing the emission concentration will ensure the realization of the total emission reduction target of the steel plant.

(3) At the same time as the control of smoke dust, effective monitoring of end emissions cannot be ignored. Because the whole process of steel enterprises has many emission points and wide distribution, it is difficult to comprehensively monitor in a short time, and the monitoring data is complex, which is not convenient for later analysis and management. Therefore, it is possible to consider setting up a smoke dust monitoring (control) system in priority sources to ensure that emissions at these points are up to standard, and it is also possible to monitor 80% of the emissions of the entire plant. It not only reduces the human and material consumption of environmental supervision, but also saves the initial investment of the enterprise's environmental monitoring facilities. At the same time, it can improve the scientific and rationality of the monitoring data, and curb the possibility that some steel companies want to set up the target at the monitoring point.

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