Injectors or Jets in Flue Gas Treatment Systems

1. Flue Gas Treatment System

Combustion of solid, liquid or gaseous fuels all produces flue gas. The flue gas produced by combustion is mainly composed of high-temperature dust and various gases. Therefore, flue gas treatment usually consists of cooling, dust removal and degassing, followed by discharge. As environmental protection standards become increasingly stringent and flue gas must meet the standards before discharge, a large amount of flue gas must undergo relevant treatment measures before emission.

Among the flue gas treatment processes, dust removal and degassing are the most important. Dust removal mainly relies on wet dust removal (including Venturi wet dust removal), bag dust removal, electrostatic dust removal and other equipment. The degassing process varies depending on the fuel type and the components in the flue gas that need to be treated, but it is generally evolved from the coal-fired desulfurization process, with the combustion of coal-containing fuels being the most typical. Therefore, it is often simply referred to as the desulfurization process.

The desulfurization process is divided into dry, semi-dry, wet, electron beam, seawater and other methods, with the wet method being dominant. For example, about 85% of coal-fired power plants use wet desulfurization, followed by dry and semi-dry methods. The key and difficult points of flue gas treatment are desulfurization and the removal of heavy metal vapors. The three processes are briefly described as follows:

1) Dry desulfurization uses powdered absorbents to remove SO₂ from flue gas. A typical method is in-furnace calcium injection (lime/limestone). In-furnace calcium injection has the advantages of no wastewater generation and no secondary pollution, but it has low desulfurization efficiency, large equipment and high operating requirements, so it is less used in large industrial applications.

2) Wet flue gas desulfurization is currently the most widely used desulfurization process, accounting for more than 80% of total desulfurization. Depending on the choice of desulfurizing agent, wet desulfurization can be further divided into the limestone/lime process, ammonia process, sodium-calcium double alkali process, magnesium oxide process, basic aluminum sulfate process, etc. Among them, the limestone/lime process, ammonia process, sodium-calcium double alkali process and magnesium oxide process are more commonly used.

3) Semi-dry desulfurization is an emerging desulfurization technology. The rotary calcium injection method is currently used more often: lime is made into lime slurry and absorbs SO₂ in the tower, but the reaction efficiency is low and the calcium-sulfur ratio is relatively large, generally above 2.5 according to relevant data. It is mainly adopted by thermal power plants with large boilers.

In the above processes, jet equipment and devices such as Venturi flue gas scrubbers/towers, liquid-gas jet aerators or activated carbon injectors are required. The following introduces these jet/injection devices respectively.

2. Venturi Flue Gas Scrubber/Tower

Flue gas washing usually includes physical washing of dust, as well as chemical washing and adsorption.

Physical washing of flue gas usually uses a clean water jet to entrain the flue gas for jet-mixing washing. After washing, the dust content in the flue gas can meet the emission standard requirements. Some special-shaped jet devices are also used for spray washing and dust reduction of flue gas.

Chemical washing uses an adsorbent solution as the jet medium. Through jet suction (or atomized spraying), it strengthens the contact with the medium to be adsorbed (or reacted) in the flue gas, produces chemical reactions, and generates media that are easy to remove, so as to achieve the purpose of purifying the flue gas.

The gas-liquid ratio in Venturi scrubbers or scrubber towers is usually large.

3. Liquid-Gas Jet Aeration System

In wet desulfurization, the jet aeration oxidation device is powered by a slurry circulation pump. Through the negative pressure generated by the jet, air (or oxygen) is drawn into the mixing chamber. During the turbulent mixing process, the gas and liquid are in close contact, and the oxidation efficiency is much higher than that of conventional oxidation devices. Moreover, no oxidation blower is required, there are no rotating parts, and no other mechanical stirring device is needed (with a built-in secondary enhancement device).

Because the jet aerator has no dense aeration pipe network, no mechanical rotating parts, and a larger pipe diameter, it has very good operational reliability, stable performance and is not easy to clog. Moreover, due to the unique mass transfer advantages of the jet aerator system, its aeration process produces the finest bubbles, long retention and contact time, high mixing intensity, and high aeration efficiency with low air volume, and no oxidation blower is needed. Therefore, it is increasingly popular with users.

The desulfurization slurry aeration system consists of a slurry tank, circulation pump, jet aerator, secondary enhancement device and related piping.

4. Activated Carbon Injection System

In the dry and semi-dry desulfurization processes, injectors for adsorbents such as activated carbon are required. The activated carbon injector is a jet device powered by air. The air can come from a Roots blower or the compressed air system of the plant. Since the operating pressure of the flue gas system is very low, the back pressure of the injector mainly depends on the distance between the activated carbon silo and the flue gas system.

The activated carbon injection system mainly consists of a Roots blower, air ejector, feeder and related piping.

5. Summary

As a company specializing in the development and manufacture of various injectors and ejectors, Chengdu GreenWater Technology Co., Ltd. can provide both standard injector or ejector products and optimized design and manufacture according to the specific needs of users.

In some cases, such as aeration contact oxidation, or applications involving two-phase or multi-phase flows, more accurate design and calculation are required to ensure better results. Our company will provide the design and construction drawings of the relevant system, the performance parameters and selection of the main components, and the installation requirements. The injectors (or ejectors) and related jet enhancement devices in the system are all developed, designed, manufactured and supplied by our company.