Blast furnace coal-fired flue gas treatment equipment

1、 Flue gas dust removal - dry bag dust removal for blast furnace gas

Blast furnace gas purification can be divided into two types: wet dust removal and dry dust removal. Currently, in China, gas purification for blast furnaces with a capacity of 500m3 or below is mainly carried out using dry bag dust removal technology, while gas purification for blast furnaces with a capacity of 1000m3 or above is relatively rare using dry bag dust removal technology.

The dry bag dust removal technology for blast furnace gas is one of the important comprehensive energy-saving and environmental protection technologies in the steel industry. With its advantages of high gas purification quality, water and electricity conservation, low investment, low operating costs, and low environmental pollution, it is superior to traditional wet washing and dust removal processes and belongs to the environmental protection and energy saving project. It is currently at the forefront of the "three dry and one electric" (blast furnace gas dry dust removal, converter gas dry dust removal, dry quenching, and blast furnace gas residual pressure power generation) promoted in the national steel industry. It is a clean production technology vigorously promoted by the country.

1. Process flow and equipment

1.1 System composition

1. Dry dust removal consists of a bag filter, an ash unloading and conveying device (including a large ash silo), a waste gas pipeline, valves and maintenance facilities, a comprehensive pipeline, an automated detection and control system, and auxiliary parts.

Blast furnaces with long-term high furnace top temperatures should install cooling devices before bag dust removal, including heat pipe heat exchangers and tube heat exchangers. Heat pipe heat exchangers should be preferred.

1.2 Filtration area

Calculate the filtration area based on the gas volume (including gas moisture content, the same below) and the determined filtration rate

Calculation formula:

Among them, F - effective filtration area m2

Q - Gas flow rate m3/h (operating condition)

V - working condition filtration speed m/min

Flow rate under two operating conditions.

The actual gas flow rate at a certain temperature and pressure is called the operating flow rate. The standard state flow rate multiplied by the operating condition coefficient is the operating condition flow rate.

3 working condition coefficients

The ratio of operating condition volume (or flow rate) to standard condition volume (or flow rate) is called the operating condition coefficient, expressed as η.

Calculation formula:

Among them, η - operating condition coefficient

Q0- Standard state gas flow rate m3/h

Q - Gas flow rate under working conditions m3/h

T0- Absolute temperature at standard state 0 ℃ 273K

T - Gas temperature of bag filter (℃)

P - Gas pressure (gauge pressure) MPa

P0- Standard state of one engineering atmospheric pressure, 0.1 MPa

When the t-value is calculated based on the average gas temperature of 165 ℃, the above formula is simplified as:

H=1.6

At this time, the relationship between the operating condition coefficient η and pressure is shown in Table 3-2. The temperature values vary slightly.

Table 3-2 Relationship between operating condition coefficient η and pressure

1.3 Gas Release

1. The dust collector box, pre heat exchanger, waste gas main pipe, and sealed glasses valve should be equipped with gas release pipes.

At the end of the main gas pipeline, a vent pipe for gas introduction should be installed. The setting of the discharge pipe should comply with the gas safety regulations, and the pipe mouth should be equipped with an ignition device.

3. Reliable partition devices must be installed for the exhaust pipes used for air intake.

1.4 Pre corrosion protection

Part 1 of the dry dust removal coal gas condensate has strong corrosiveness. The material of the corrugated expander should preferably be corrosion-resistant stainless steel, with the pipe wall appropriately thickened. The inner wall of the pipeline should be coated with anti-corrosion paint, and the weld seam should be carefully polished before painting.

2. Alkali spray or water spray device can be set up.

All gas pipelines should be insulated.

2、 Gas desulfurization - dry desulfurization

For a specific project, the determination of desulfurization scheme should consider both feasibility and economy. For users with small gas consumption (such as less than five or six thousand cubic meters per hour) and low sulfur content in the gas, single-stage dry desulfurization can be considered.

Dry desulfurization

The most commonly used dry desulfurizers at present are iron oxide and activated carbon. Usually, the desulfurization process of dry desulfurization is relatively simple, but considering environmental protection and economy, it is generally necessary to use desulfurizer regeneration, while the regeneration of iron oxide and activated carbon varies greatly from process to cost.

1.1 Iron oxide desulfurizer

The usage conditions of iron oxide desulfurizer are generally limited to the following points:

1) The normal operating temperature is 20-30 ℃. Excessive temperature will accelerate the oxidation rate, relatively reduce the sulfurization rate, and decrease the desulfurization efficiency. At the same time, excessive temperature will cause the hydrate of iron sulfide (Fe2S3 • H2O) to lose moisture, thereby affecting the humidity and acidity of the desulfurizer and the desulfurization effect. If the temperature is too low, it will greatly reduce the sulfurization rate, decrease the desulfurization efficiency, and also condense the moisture in the gas, causing the desulfurizer to become too wet.

2) The moisture desulfurizer should maintain a moisture content of 25% -35%. If the moisture content is less than 10%, it will affect the desulfurization operation. Moisture can maintain sufficient contact time between hydrogen sulfide and iron oxide, reduce the agglomeration of desulfurizer, and dissolve some salts to prevent them from coating the surface of iron oxide and affecting the progress of desulfurization reaction.

3) Gas with oxygen content contains a certain amount of oxygen, which can enable the regeneration of iron oxide during desulfurization. Generally, an oxygen content of 1.0-1.1% is recommended. Excessive oxygen content can accelerate the corrosion of iron and form coal gas gel.

4) The impurity content of coal gas, such as tar and other impurities, should be removed completely, otherwise it is easy to cause the surface of the desulfurizer to be covered by tar and become ineffective.

5) Acidic and alkaline iron oxide desulfurization generally requires a weakly alkaline environment (pH 8-9), and high or low pH values can affect desulfurization efficiency.

1.2 Activated carbon desulfurization

The main process conditions for activated carbon desulfurization production are:

1) The normal operating temperature can be between 27-82 ℃, but the optimal operating temperature is 32-52 ℃. Therefore, when used in cold regions, the desulfurization tower should be insulated.

2) The ratio of sulfide to oxygen content should be above 1:2, and air can be supplemented when the oxygen content is insufficient.

3) The relative humidity of gas should be between 70-100%. When the humidity is insufficient, water vapor can be added, but liquid water should not be brought into the activated carbon bed.

4) The acidity and alkalinity requirements in gas require an alkaline environment for activated carbon desulfurization. If the gas does not contain alkaline gas components, alkaline impregnated activated carbon can be used.

5) The impurity content of coal gas, such as tar and other impurities, should be removed completely, otherwise it is easy to cause the micropores on the surface of activated carbon to be covered by tar and become ineffective.

6) The pressure operation pressure should be less than 5Mpa, and currently most gas production processes do not exceed this pressure. In addition, the design of the desulfurization tower should take into account requirements such as airspeed and linear velocity.

1. Flue gas dust removal - dry process of blast furnace gas

Blast furnace gas purification can be divided into two types: wet dust removal and dry dust removal. Currently, in China, gas purification for blast furnaces with a capacity of 500m3 or below is mainly carried out using dry bag dust removal technology, while gas purification for blast furnaces with a capacity of 1000m3 or above is relatively rare using dry bag dust removal technology.

Compared with wet dust removal, dry bag dust removal has the following advantages:

1) Water saving, dry dust removal basically does not require water, while wet dust removal requires a large amount of cooling water.

2) It can increase TRT power generation. Due to the use of dry dust removal, the temperature of the gas is higher and the pressure loss of the gas is less, resulting in an increase in TRT power generation, generally by 30% to 50%.

3) Reduce the coke ratio. Due to the high temperature of the gas after dry dust removal, supplying it to the hot blast stove can increase the air temperature by more than 50 ℃, which can reduce the coke ratio.

4) Energy saving: After using dry dust removal, there is no cooling water, so there is no need for a sewage treatment system, which can reduce electricity consumption.

5) Environmental protection, as it does not require a sewage treatment system, can reduce pollution.

2. Flue gas desulfurization - dry desulfurization

Dry desulfurization - the production cost is relatively low. This homemade iron oxide desulfurizer generally has high desulfurization efficiency and good desulfurization effect, but its sulfur capacity is low and the number of regenerations is limited. After a period of use, the desulfurizer needs to be regenerated, and this homemade iron oxide desulfurizer is generally regenerated outside the tower. Remove the desulfurizer and place it on the sun field for thorough oxidation and regeneration.

However, although this homemade iron oxide desulfurizer has a low cost, it requires a large site, a lot of labor for production and regeneration, and is also quite troublesome. Therefore, many units now purchase molded iron oxide desulfurizers, and many units also develop and sell molded iron oxide desulfurizers. These formed iron oxide desulfurizers have uniform particles, high porosity, high strength, high iron oxide content, high desulfurization efficiency, large sulfur capacity, and multiple regenerations. Their regeneration can be carried out inside the tower.

At present, the ecological damage and environmental pollution caused by coal development and utilization in China are still very serious. How to improve the utilization rate of coal and other resources and reduce environmental pollution under economic conditions is an urgent problem that we need to solve

The implementation of clean coal technology is a strategic choice for China's energy sector, which will address three issues: (1) control of pollutant and greenhouse gas emissions; (2) Reduce dependence on imported oil; (3) Improve utilization efficiency.

2. Implementing China's clean coal strategy (i.e. coal processing and conversion) can most economically and effectively solve the problems of low efficiency, high pollution, and substitution of oil in coal utilization. In order to adapt the coal industry to the needs of the national economy, the country should actively devote itself to the research and development of clean coal in China, and promote the rapid development of coal processing and conversion;

3. Further improving the efficiency of coal utilization, reducing environmental pollution, and promoting sustainable development of the national economy and society are fundamental national policies of China. It is suggested that relevant government departments provide corresponding policy support for large-scale pithead cogeneration and high-efficiency dry coal preparation technology projects, and conduct industrial demonstrations to achieve clean, efficient, economical, and stable supply of coal energy in China.