Engineering design of flue gas purification system for lime vertical kiln
Lime vertical kiln produces a large amount of flue gas during the production process, which contains pollutants such as dust, sulfur dioxide, nitrogen oxides, etc. If these flue gases are directly discharged into the atmosphere without treatment, they will cause serious pollution to the environment and do not comply with environmental regulations. Therefore, designing an efficient flue gas purification system is crucial for the normal operation and environmental protection of lime vertical kilns. This article will elaborate on the engineering design of the flue gas purification system for lime vertical kilns.
1、 Analysis of Smoke Characteristics
The flue gas from lime vertical kiln has the following characteristics:
High temperature: generally between 100 ℃ and 300 ℃, which requires high temperature resistance of purification equipment. High dust content: Smoke carries a large amount of particulate matter such as lime dust, and the dust concentration may reach thousands of milligrams per cubic meter.
Containing a certain amount of sulfur dioxide and nitrogen oxides: These pollutants mainly come from the combustion of fuel and the decomposition process of limestone.
2、 Overall design concept of purification system
The design of this flue gas purification system adopts a multi-stage purification method to sequentially remove dust, sulfur dioxide, and nitrogen oxides from the flue gas. The specific process is as follows: first, most of the dust is removed by dust removal equipment, then sulfur dioxide is removed by desulfurization device, and finally the nitrogen oxide content is reduced by denitrification equipment, so that the purified flue gas can meet the emission standards.
3、 Dust removal equipment design
（1） Equipment selection
Considering the high dust content and temperature of flue gas, a bag filter is selected. Bag filters have the advantages of high dust removal efficiency and the ability to adapt to a certain temperature range.
（2） Structural Design
The bag filter is mainly composed of a box, filter bags, and a dust cleaning device. The box is made of steel structure and has flower plates inside for fixing the filter bag. The filter bag is made of high temperature resistant and corrosion-resistant materials, which can effectively filter dust in the flue gas. The dust cleaning device adopts pulse blowing method to regularly clean the filter bag to ensure the normal operation and dust removal efficiency of the dust collector.
（3） Parameter design
Determine the filtration area and filtration wind speed of the dust collector based on parameters such as the flue gas flow rate and dust concentration of the lime vertical kiln. For example, for a flue gas flow rate of 100000m ³/h and a dust concentration of 3000mg/m ³, the filtration area can be designed to be around 2000m ², and the filtration wind speed can be controlled at around 1m/min.
4、 Design of desulfurization device
（1） Process selection
The wet desulfurization process is commonly used, including the lime gypsum method. This method has high desulfurization efficiency and mature technology.
（2） Equipment composition
Mainly including absorption tower, slurry circulation pump, oxidation fan, etc. The absorption tower is the core equipment for desulfurization. The flue gas enters from the bottom of the absorption tower and comes into contact with the desulfurization slurry sprayed down from the top of the tower in reverse flow, absorbing sulfur dioxide. The slurry circulation pump is used to continuously circulate and spray the desulfurization slurry to improve the desulfurization effect. The oxidation fan oxidizes the slurry after absorbing sulfur dioxide into gypsum.
（3） Parameter determination
Determine the concentration and circulation of desulfurization slurry based on the sulfur dioxide content and emission standards in the flue gas. For example, when the initial concentration of sulfur dioxide is 1000mg/m ³ and the required emission concentration is below 50mg/m ³, the concentration of desulfurization slurry can be selected as around 10%, and the slurry circulation amount is calculated and determined based on factors such as the size of the absorption tower and the flue gas flow rate.
5、 Design of denitrification equipment
（1） Process selection
Adopting selective catalytic reduction (SCR) denitrification process. This process generates nitrogen gas and water by reacting nitrogen oxides with ammonia gas under the action of a catalyst.
（2） Equipment composition
Mainly including denitrification reactor, catalyst, ammonia injection system, etc. The denitrification reactor is a place where denitrification reactions are carried out. The catalyst is installed inside the reactor, and the ammonia injection system uniformly sprays ammonia into the reactor. After mixing with nitrogen oxides in the flue gas, the reaction occurs under the action of the catalyst.
（3） Parameter design
Determine the amount of ammonia, catalyst type, and dosage based on the content and emission standards of nitrogen oxides in the flue gas. For example, when the initial concentration of nitrogen oxides is 300mg/m ³ and the required emission concentration is below 100mg/m ³, the molar ratio of ammonia to nitrogen oxides can be controlled at around 1:1. The type of catalyst can be selected as honeycomb catalyst, and the dosage is determined based on factors such as reactor size and flue gas flow rate.
6、 Design of Smoke Emission Monitoring System
To ensure that the purified flue gas meets the emission standards, design a comprehensive flue gas emission monitoring system. The system includes online monitoring devices such as smoke and dust concentration detectors, sulfur dioxide detectors, nitrogen oxide detectors, etc., which monitor the real-time content of various pollutants in the flue gas. At the same time, the monitoring data will be transmitted to the central control room so that operators can timely understand the operation of the purification system. Once pollutants are found to exceed the standard, measures can be taken in a timely manner for adjustment.
7、 Auxiliary system design
（1） Fan system
Set up induced draft fans and supply fans. The induced draft fan is used to extract flue gas from the lime vertical kiln and send it into the purification system, while the supply fan is used to provide air for the denitrification system. The selection of fans should be based on parameters such as flue gas flow rate and pressure to ensure the normal operation of the system.
（2） Pipeline system
A well-designed flue gas pipeline should have good sealing and corrosion resistance, while considering insulation and thermal expansion issues to reduce heat loss and prevent pipeline deformation.
（3） Control system
Adopting an automated control system to centrally control the entire flue gas purification system. By using PLC and other controllers to control the start stop and operation parameter adjustment of various devices, the stability and reliability of the system can be improved.
8、 Engineering implementation and maintenance
During the implementation of the project, equipment installation and debugging must be strictly carried out in accordance with the design requirements. After installation, a system trial run should be conducted to optimize and adjust various equipment and parameters. In daily maintenance, it is necessary to regularly inspect, repair, and maintain purification equipment, such as replacing filter bags, cleaning absorption towers, checking catalyst activity, etc., to ensure the long-term stable operation of the purification system. At the same time, it is necessary to regularly test and evaluate the purification effect in accordance with environmental regulations to ensure that the flue gas emissions meet the standards.
The engineering design of lime vertical kiln flue gas purification system is a complex and important task. Through reasonable design and selection, advanced purification technology and equipment can be used to effectively remove pollutants from flue gas, achieve standard emissions, and protect the environment. Meanwhile, good engineering implementation and maintenance measures can ensure the long-term stable operation of the purification system, providing guarantees for the sustainable development of lime vertical kilns.
