Flue gas desulfurization technology in petroleum refining and chemical enterprises

[ Filter element of FGD system: Wedge wire screen filter ]

At present, people’s requirements in environmental protection and other aspects have been significantly improved, and the technical requirements for flue gas desulfurization in petroleum refining and chemical enterprises are more stringent.

This paper gives some suggestions and opinions on the current flue gas desulfurization technology in petroleum refining and chemical enterprises, hoping to have a clear and comprehensive understanding of the flue gas desulfurization technology in petroleum refining and chemical enterprises, to clarify the advantages and application scope of each technology, to better meet the needs of flue gas desulfurization, and to improve the effectiveness of flue gas desulfurization.

A large amount of sulfur dioxide needs to be discharged in the production process of petroleum refining and chemical enterprises, which involves various processing technologies. There are obvious differences in emission characteristics and emission reduction projects among enterprises.

At present, sulfur dioxide produced in the production process of petroleum refining and chemical enterprises mainly comes from boiler flue gas, flue gas of desulfurization device and catalytic regeneration flue gas, etc., so it is necessary to select targeted emission reduction technology in combination with specific emission path.

Therefore, it is necessary to do a good job in the research of sulfur dioxide emission reduction technology in mature industries such as power plants and make clear the advantages and disadvantages of each construction process in practical application. At the same time, combined with the characteristics of flue gas emissions, the best flue gas desulfurization process is selected. This paper studies and analyzes this.

Wet flue gas desulfurization technology

The wet flue gas desulfurization technology is mainly the reaction between liquid absorbent and SO2, and the product is also liquid. Wet flue gas desulfurization technology not only has a very high desulfurization efficiency but also the operation of the whole system is relatively stable. However, the specific application requires high operating costs and investment costs. At the same time, the treatment of the products after desulfurization is difficult and prone to secondary pollution Problems arise.
Common wet flue gas desulfurization technologies include lime gypsum wet process, magnesium oxide process, double alkali process, ammonia process, seawater process, etc.

• Lime gypsum wet process.
  Lime is selected as desulfurized, which is cheap. It is broken into powder and mixed with water to make absorption slurry. The flue gas is fully mixed in the absorption tower. The calcium carbonate component in the absorption slurry can react with sulfur dioxide and oxygen in the flue gas to survive the gypsum product.
  The flue gas after desulfurization is discharged after being treated by a heat exchanger, the gypsum can be recovered after dehydration, and the utilization rate of desulfurization absorbent is high. This flue gas desulfurization technology is the most widely used desulfurization technology in the world. The technology is mature. The lime gypsum wet method is also widely used in the desulfurization of coal-fired power plants in China. However, this technology needs to do a good job in the actual application of anti-corrosion work. At the same time, the pipeline is prone to plug, there will be a lot of CO2 production, resulting in its development and application limited.

• Magnesia process.
  The principle of magnesium oxide method is basically the same as that of the lime gypsum wet method. Magnesium oxide is used instead of lime. Magnesium oxide reacts with sulfur dioxide in the reaction tower to generate magnesium sulfite and water. Magnesium sulfite reacts with oxygen to generate magnesium sulfate. Magnesium sulfate is soluble in water, does not block the pipeline, and can be reused. However, the preparation of MgO is relatively complex and requires high commitment, which limits its practical application.

• Double alkali method.
  

  The double alkali method refers to the use of sodium and alkali to absorb sulfur dioxide in the flue gas. After the reaction, the liquid is treated with lime. The whole process can be divided into absorption, regeneration and solid separation.
  Generally, materials such as sodium hydroxide and sodium carbonate will be used in the absorption process, and lime will be selected in the regeneration process, in which sodium hydroxide can be reused.
  In practical application, the reaction between the absorbent and sulfur dioxide is carried out outside the reaction tower, which can reduce the loss of the reaction tower to the maximum extent, avoid blocking and other situations. The operation cost is low and has a very high desulfurization effect. However, due to the increase in the working procedures, the whole investment cost will increase significantly.

Dry flue gas desulfurization technology

Dry flue gas desulfurization technology refers to desulfurization and product treatment in a dry state. The whole desulfurization process will not produce sewage, equipment corrosion is small, desulfurization cost is low, but desulfurization efficiency is not very ideal. The common dry flue gas desulfurization technologies include electron beam irradiation, lime drying, activated carbon adsorption, etc.
The electron beam irradiation method is mainly to mix a certain amount of ammonia in the flue gas, promote the reaction of oxygen and water vapor to produce free radicals with very strong oxidation ability, accelerate the oxidation of sulfur dioxide in the flue gas, and also react with ammonia to generate ammonium sulfate.
The whole work is easy to operate and control, but it needs high power electron gun and radiation shielding.

Semi-dry flue gas desulfurization technology

Semi-dry flue gas desulfurization technology combines the advantages of dry and wet methods. The desulfurization is completed in the wet state and the products are removed in a dry state.

The semi-dry flue gas desulfurization technology has the advantages of fast desulfurization speed, high efficiency, no wastewater and acid, and simple product treatment.

The common semi-dry flue gas desulphurization technologies include spray drying, circulating fluidized bed and NID desulphurization technology.

In the medium spray drying method, the calcium hydroxide is selected as the absorbent. The lime is made into a slurry and sent to the atomizer of the absorption tower. After atomization, it is mixed with the flue gas to react with the flue gas to remove sulfur dioxide from the flue gas.

In the circulating fluidized bed process, most of the absorbents are hydrated lime powder. The flue gas is put into the bottom of the absorption tower and mixed with the absorbent powder. The water mist is injected to control the flue gas temperature. The sulfur dioxide in the oxygen reacts with the absorbent to generate calcium sulfate. The flue gas is discharged from the top of the absorption tower after desulfurization, with high absorption efficiency.

Different flue gas desulfurization technologies have their own advantages and disadvantages in practical application. Although wet desulfurization technology has fast reaction speed and high desulfurization efficiency, there are problems such as complex systems, high energy consumption, and large equipment. At the same time, the product treatment is difficult and requires a high operating cost.

There are some problems in the dry reaction, such as slow speed, serious wear, and scaling. The reliability and stability of the equipment can not be guaranteed.

The semi-dry process can integrate the advantages of dry process and wet process, with high desulfurization efficiency, simple process, and broad development prospects. The selection of desulfurization technology in petroleum refining and chemical enterprises can give priority to this process.