Ejectors or Injectors in Flue Gas Treatment Systems

Flue Gas Treatment System

Whether solid, liquid or gaseous fuel is burned, flue gas is produced. The flue gas generated by combustion is mainly composed of high-temperature smoke dust and various gases. Flue gas treatment usually includes cooling, dust removal, degassing and discharge. As environmental standards become increasingly strict, flue gas must meet the required limits before discharge, so appropriate treatment measures are required before emission.

The most important processes in flue gas treatment are dust removal and degassing. Dust removal mainly relies on wet dust collection, including Venturi wet scrubbing, bag filters, electrostatic precipitators and other equipment. Degassing processes vary according to fuel type and the components that need to be treated in the flue gas, but most evolved from coal-fired desulfurization processes. Since coal-containing fuel combustion is the most typical case, these processes are often still referred to as desulfurization processes.

Desulfurization processes include dry, semi-dry, wet, electron beam and seawater methods, with wet processes being dominant. For example, about 85% of coal-fired power plants use wet desulfurization, followed by dry and semi-dry methods. The focus and difficulty of flue gas treatment lie in desulfurization and the removal of heavy metal vapors.

1. Dry desulfurization uses powdered absorbents to remove SO₂ from flue gas. Typical methods include in-furnace calcium injection using lime or limestone. This method produces no wastewater and avoids secondary pollution, but its desulfurization efficiency is low, equipment is bulky and operating requirements are high, so it is less common 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 capacity. Depending on the desulfurizer, wet desulfurization can include limestone/lime, ammonia, sodium-calcium dual alkali, magnesium oxide and alkaline aluminum sulfate methods. Limestone/lime, ammonia, sodium-calcium dual alkali and magnesium oxide methods are commonly used.
3. The semi-dry method is an emerging desulfurization technology. Rotary calcium injection is widely used: lime is prepared as slurry and absorbs SO₂ in the tower. However, the reaction efficiency is low and the calcium-sulfur ratio is relatively high, generally above 2.5 according to relevant data. It is mainly used in some large boiler thermal power plants.
4. In the above processes, jet equipment and devices such as Venturi flue gas scrubbers/towers, liquid-gas jet aerators and activated carbon injectors are used.

Venturi Flue Gas Scrubber/Tower

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

Physical washing of flue gas usually uses a clean water jet to entrain flue gas and perform jet mixing and washing, so that the dust content in the washed flue gas meets emission standards. Special-shaped jet devices can also be used to spray and wash flue gas for dust reduction.

Chemical washing uses an adsorbent solution as the jet medium. Through jet suction or atomized spraying, it strengthens contact with the substances in the flue gas that need to be adsorbed or reacted, producing chemical reactions and generating media that are easier to remove, thereby purifying the flue gas.

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

Liquid-Gas Jet Aeration System

In wet desulfurization, the jet aeration oxidation device is powered by a slurry circulation pump. Negative pressure generated by the jet draws air or oxygen into the mixing chamber. During turbulent mixing, gas and liquid are in close contact, and oxidation efficiency is much higher than that of conventional oxidation devices. No oxidation blower, rotating parts or additional mechanical agitator is required, and the system includes a secondary efficiency-enhancing device.

Because the jet aerator has no dense aeration pipe network, no mechanical moving parts and a relatively large pipe diameter, it offers excellent operating reliability, stable performance and strong resistance to blockage. Thanks to its unique mass transfer advantages, the ejector system produces finer bubbles, longer residence and contact time, stronger mixing, higher aeration efficiency, lower air demand and no need for an oxidation blower, making it increasingly popular with users.

The desulfurization slurry aeration system consists of a slurry tank, circulation pump, ejector, secondary efficiency-enhancing device and related pipelines.

Activated Carbon Injection System

In dry and semi-dry desulfurization processes, injectors are required for adsorbents such as activated carbon. The activated carbon injector is an air-powered jet device. Air can be supplied by a Roots blower or a plant compressed air system. Since the operating pressure of the flue gas system is very low, injector back pressure 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 injector, feeder and related pipelines.

Overview

Chengdu GreenWater Technology Co., Ltd. specializes in the development and manufacture of various ejectors and injectors. The company can provide selected standard ejector or injector products, and can also optimize design and manufacturing according to specific user requirements.

In some applications, such as aeration contact oxidation or two-phase and multiphase flow, accurate design and calculation are required to ensure better performance. GreenWater provides design and construction drawings, performance parameters and selection guidance for main components, and installation requirements. The ejectors or injectors used in the system, along with related jet efficiency-enhancing devices, are independently developed, designed, manufactured and supplied by the company.