Titanium Clad Plates For Thermal Power

1.Background

 

With the increasing attention of the country to environmental protection work, for the main atmospheric pollutant S0₂ and the key industry of emissions - thermal power plants, according to environmental regulations, it is necessary to install flue gas desulfurization devices. In recent years, a large number of desulfurization devices have been put into operation, and the vast majority of desulfurization processes use limestone gypsum wet desulfurization technology. For many coastal power plants, compared with limestone wet desulfurization technology, seawater desulfurization process has obvious advantages such as high desulfurization efficiency, low operating costs, low investment, simple and reliable system, no additives, and no by-products. Adopting seawater desulfurization will be a good choice for coastal power plants. Therefore, there is a widespread demand for seawater desulfurization technology in coastal power plants in China. However, at present, seawater desulfurization technology is completely monopolized by foreign companies, and the high cost of technology introduction and post service fees have formed a great obstacle for domestic desulfurization companies to adopt seawater desulfurization technology, making this desulfurization process with obvious cost advantages unable to be widely applied in coastal power plants, greatly increasing the cost of desulfurization and emission reduction in thermal power plants. At the same time, the seawater desulfurization projects that have been put into operation generally have low technical indicators, with desulfurization rates around 90% and drainage pH values generally below 6.5, which cannot meet the requirements of China's regulations for desulfurization emissions. Therefore, it is imperative to develop independent seawater desulfurization processes. titanium clad plates for thermal power are widely used in seawater flue gas desulfurization technology.

 

2.The necessity of flue gas desulfurization in power plants

According to the "Emission Standards for Air Pollutants from Thermal Power Plants" (GB13223-1996), different control requirements are proposed for sulfur dioxide in thermal power plants at different time periods. For new, expanded, and renovated thermal power plants (third period) whose environmental impact reports are pending review and approval since January 1, 1997, on the basis of implementing total emissions control for the entire plant, restrictions on chimney sulfur dioxide emissions concentration have been added and linked to the "two control zones" and the sulfur content of coal. For coal with a sulfur content greater than 10%, the maximum allowable emission concentration is 1200mg/Nm, and for coal with a sulfur content less than or equal to 1%, it is 2100mg/Nm. Power plants located in the "two control zones" are required to desulfurize coal with a sulfur content greater than 1%, otherwise they cannot meet emission standards. For power plants with coal sulfur content below 1%, desulfurization should be determined through environmental impact assessment based on the total allowable emissions and regional control limits of the power plant, as well as local environmental quality requirements.
The emission control of SO from coal-fired power plants is currently the most urgent task in the field of air pollution control in China. The construction of flue gas desulfurization facilities in coal-fired power plants will be a key focus of air pollution prevention and control, and an important measure to build a resource-saving and environmentally friendly society. Actively developing and applying advanced flue gas desulfurization technology will be an important guarantee to ensure SO and emission reduction. The topic proposed in this master's thesis - pure seawater desulfurization technology is a new technology and engineering practice for flue gas desulfurization in coal-fired power plants.
 

3.Research and application status of flue gas desulfurization technology in coal-fired power plants

The earliest coal-fired power plant desulfurization technology, FLUE GASDESULPHRIZATION (FGD), originated in the United Kingdom. In 1927, the country first adopted limestone desulfurization technology at the Butterworth and Banziside power plants (totaling 120MW) on the banks of the River Thames.

 

4. Research status of seawater flue gas desulfurization technology

Seawater flue gas desulfurization technology is a type of wet flue gas desulfurization technology, suitable for power plants built on the coast and cooled by seawater. Due to the use of power plant cooling water as a desulfurizer in seawater desulfurization process, no waste is generated, and the system operation is reliable. Compared with other wet flue gas desulfurization processes, it has very low operating costs, due to the use of titanium clad plates for thermal power. Currently, about 30% of coal-fired power plants in the world are built on the coast, which greatly promotes the development of seawater desulfurization technology.
Today, seawater flue gas desulfurization has a history of more than 40 years. As early as the 1960s, the University of California, Berkeley in the United States conducted research on the process mechanism of seawater flue gas desulfurization. Seawater flue gas desulfurization devices were first widely used as supporting facilities for non coal-fired industries such as aluminum refineries and oil refineries. Dozens of seawater flue gas desulfurization devices have been put into operation in Norway, the United Kingdom, the Netherlands, Spain, Cyprus and other countries in Europe. However, the application of seawater flue gas desulfurization technology in coastal power plants is still relatively limited, and it is still in its infancy in China. The seawater flue gas desulfurization units put into operation in China.

 

5. Theoretical Analysis of S02 Absorption Purification Process

Double membrane theory

The process of seawater desulfurization is a physical and chemical process, and its mass transfer is based on the absorption purification theory - the "double membrane theory". Its basic argument is that gas absorption is the process of absorbing substances in the gas phase being transferred between phases to the liquid phase. When gas and liquid come into contact with each other, even if there is turbulence in the body of the fluid, there are still stable gas stagnation layers (gas film) and liquid stagnation layers (liquid film) on both sides of the gas-liquid phase. The absorption process is that the absorbing molecules move from the gas phase body to the gas film surface, and then diffuse through the gas film to reach the gas-liquid phase interface. At the interface, the absorbing molecules dissolve into the liquid phase, and then diffuse into the liquid phase body through the liquid film in a molecular diffusion manner from the liquid phase interface.

Physical absorption equilibrium

When a mixed gas comes into contact with an absorbent, the mass transfer of the absorbable components in the gas phase to the liquid phase is called the absorption process. During the absorption process, there is also a mass transfer process where the absorbed components in the liquid phase escape into the gas phase, known as the desorption process. At a certain temperature and pressure, the absorption process rate and desorption process rate will eventually be equal, and the mass transfer between gas and liquid phases will reach dynamic equilibrium. At this point, the solute content of the gas in the liquid phase is the solubility of the gas. The solubility of gases is related to the properties of gases and solvents. An increase in solvent solubility, pressure, or temperature will all increase the solubility of solutes. The solubility of gas is the number of kilograms of dissolved gas per 100kg of water. When using water as an absorbent, SO is a moderately dissolved gas.

Gas liquid equilibrium with chemical reactions

Both physical absorption and chemical absorption are affected by the gas phase diffusion velocity (or gas film resistance) and liquid phase diffusion velocity or liquid film resistance. In engineering, it is commonly used to enhance the disturbance of gas-liquid phases to eliminate the resistance between gas film and liquid film. In flue gas desulfurization, a large amount of flue gas containing low concentration S0 needs to be continuously purified in an instant. If physical absorption is used alone, its purification efficiency is very low and it is difficult to meet the emission standards of SO. Therefore, chemical absorption method is widely used in flue gas desulfurization technology. The use of chemical absorption method for flue gas desulfurization is technically mature, with rich operational experience and strong practicality, and has become the most widely used and widespread flue gas desulfurization technology. The seawater desulfurization process is also based on chemical absorption.
Chemical absorption is composed of two processes: physical absorption and chemical reaction. In the process of physical absorption, the absorbed gas dissolves in the liquid phase. When the gas-liquid reaches phase equilibrium, the equilibrium concentration of the absorbed gas is the limit of the physical absorption process. The active components in the absorbed gas undergo chemical reactions, and when the chemical reaction reaches equilibrium, the consumption of the absorbed gas is the limit of the chemical absorption process. In practical engineering applications, such as seawater desulfurization technology, the purification process of gaseous pollutants usually adopts chemical absorption method. At this time, the total dissolved amount of gaseous pollutants is composed of liquid phase physical absorption and chemical consumption.

 

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