Specification of limestone for desulphurization in coal power plants

How is limestone used in coal power plants?

In coal power plants, limestone is used as a desulphurization agent to remove sulphur dioxide from flue gas emissions. When the flue gas passes through the limestone, the sulphur dioxide reacts with the calcium carbonate to form calcium sulphate. The calcium sulphate is then captured by the plant's scrubber system and removed from the emissions before they are released into the atmosphere.

Limestone is an effective desulphurization agent because it is inexpensive and readily available. It also has a high reaction rate with sulphur dioxide, making it an efficient way to remove this pollutant from coal power plant emissions.

The benefits of using limestone for desulphurization

The use of limestone for desulphurization in coal power plants has a number of benefits. First, limestone is highly effective at removing sulphur from coal. This results in cleaner burning coal, which reduces emissions of sulphur dioxide (SO2). Additionally, the use of limestone can help to improve the efficiency of coal-fired power plants. Finally, limestone is a relatively inexpensive material, making it an attractive option for power plant operators.

The challenges of using limestone for desulphurization

The challenges of using limestone for desulphurization are:

-The high cost of limestone

-The need for a large quantity of limestone

-The difficulty in grinding the limestone

-The potential for impurities in the limestone

How to overcome the challenges of using limestone for desulphurization

The challenges of using limestone for desulphurization are twofold. Firstly, the calcium carbonate in limestone is less reactive than other materials that can be used for desulphurization, such as magnesium oxide. This means that it takes longer for the limestone to break down the sulphur dioxide molecules into calcium sulphite and carbon dioxide. Secondly, when limestone is used for desulphurization, a significant amount of calcium sulphite is produced. This calcium sulphite can then go on to form gypsum, which can clog up the coal power plant's equipment. To overcome these challenges, it is necessary to use a high quality limestone with a high surface area to increase its reactivity, and to ensure that the calcium sulphite formed is removed from the system before it has a chance to turn into gypsum.

The role of limestone in desulphurization

The role of limestone in desulphurization is to remove sulphur from coal before it is burned. This is done by passing the coal through a bed of limestone, which absorbs the sulphur. The limestone can then be removed and used again, meaning that there is no need to store or dispose of hazardous waste products.

Limestone desulphurization is an important process in coal-fired power plants, as it helps to reduce emissions of sulphur dioxide (SO2), a harmful pollutant that can cause acid rain and respiratory problems. By removing sulphur from coal before it is burned, power plants are able to significantly reduce their emissions of SO2.

There are a number of different ways to desulphurize coal, but limestone desulphurization is one of the most common and effective methods. It is also relatively inexpensive and does not require any major changes to existing power plants.

The different types of limestone

1) sedimentary limestone: This type of limestone is formed from the accumulation of small calcite particles that are precipitated from seawater. The major advantage of using this type of limestone for desulphurization is that it is relatively cheap and easy to obtain.

2) metamorphic limestone: This type of limestone is formed when sedimentary limestone is subjected to high temperatures and pressures. It is typically more expensive than sedimentary limestone, but its higher purity makes it ideal for use in coal power plants.

3) igneous limestone: This type of limestone is formed when molten rock cools and solidifies. It is typically the most expensive type of limestone, but its high purity means that it can be used effectively for desulphurization in coal power plants.

How to select the right type of limestone for your power plant

There are many types of limestone available for use in coal power plants, and the right type must be selected for the specific application. The most common type is high-calcium limestone, which is widely used in flue gas desulfurization (FGD) systems. Other types include dolomitic limestone, magnesium-rich limestone, and phosphoric acid-treated limestone.

High-calcium limestone is the most effective at reducing sulfur dioxide emissions from coal-fired power plants. It is also the most commonly used type of limestone in FGD systems. Dolomitic limestone is less effective than high-calcium limestone, but it can be used in some applications where high-calcium limestone is not available. Magnesium-rich limestone is not as effective as high-calcium or dolomitic limestone, but it can be used in some situations where those types of limestone are not suitable. Phosphoric acid-treated limestone is not as effective as other types of limestone, but it has the advantage of being able to be injected into the boiler directly, without the need for a separate FGD system.

The Need for Desulphurization

The desulphurization of coal is an important process in the operation of a coal-fired power plant. The removal of sulphur from coal prior to combustion reduces the emission of sulphur dioxide (SO2) into the atmosphere. SO2 is a major contributor to acid rain and air pollution.

There are two main methods of desulphurization: physical removal and chemical removal. Physical removal involves separating the sulphur-containing minerals from the rest of the coal. This can be done through flotation or gravity separation. Chemical removal involves treating the coal with chemicals that react with and remove the sulphur.

The most common chemical used for desulphurization is limestone (calcium carbonate). When limestone is injected into the flue gas, it reacts with the SO2 to form calcium sulphite (CaSO3). The calcium sulphite can then be removed from the flue gas through a variety of methods, including scrubbing, electrostatic precipitation, and wetting agents.

The role of limestone in desulphurization

In coal-fired power plants, the exhaust gases from the boiler are passed through a desulphurization unit in order to remove the sulphur dioxide (SO2) emissions. The most common technology for this is the wet scrubber, which uses a slurry of limestone (CaCO3) and water to remove the SO2 from the flue gas.

The advantage of using limestone for desulphurization is that it is a relatively cheap and readily available material. In addition, limestone is very effective at removing SO2 from flue gas, with up to 99% removal efficiency achievable.

The main disadvantages of using limestone for desulphurization are that it can lead to build-up of scale in the boiler and on other equipment in the power plant, and also that it can produce sludge that needs to be disposed of.

Specifications of limestone

The main component of limestone is calcium carbonate (CaCO3), which is widely used as desulphurization agent in coal-fired power plants. The CaCO3 content of limestone varies from over 90% to below 40%. Other components present in small quantities include silica, alumina, iron oxide, magnesium oxide and sulphate.

The size distribution of the limestone is an important parameter for its use as desulphurization agent. The particle size distribution is usually expressed as a percentage retained on a given mesh screen. For example, a common specification for power plant limestone is that 80% of the particles should be smaller than 0.5 mm and 95% smaller than 2 mm.

The chemical purity of limestone is another important parameter. It should be low in impurities such as sulphur, silicon, aluminium and iron. These impurities can have a negative effect on the efficiency of the desulphurization process.

How to ensure the quality of limestone?

In order to ensure the quality of limestone used for desulphurization in coal power plants, it is important to follow these steps:

1. source limestone from a reputable supplier that has extensive experience in supplying limestone for this specific purpose

2. have the limestone tested by an independent lab to confirm its purity and suitability for use in desulphurization

3. work with the supplier to develop a comprehensive quality control plan that includes regular testing of the limestone throughout the manufacturing process

4. ensure that the limestone is properly stored and handled prior to use to prevent contamination or degradation of its quality

Conclusion

The specification of limestone for desulphurization in coal power plants is a process that needs to be carefully considered. There are a number of different factors that need to be taken into account, including the type of limestone, the size of the particles, and the sulfur content. All of these factors will have an impact on the efficiency of the desulphurization process and the final product.