What Is Gas Scrubbing?

Gas scrubbing refers to the process of scrubbing gas with liquid in specialized equipment (usually forming gas in close contact with liquid in an upright cylinder) in industrial practice. ^{[1] The} most common gas washing method in the industry: the gas is a continuous phase, and the washing liquid is a dispersed phase, and the gas is washed. ^[2]

The most commonly used gas washing and absorption method in the industry: the gas is a continuous phase, and the washing liquid is a dispersed phase, and the gas is washed. Spray liquid washing gas in a uniform air flow, mainly using the liquid dispersion function of the nozzle and different gas-liquid speeds to achieve contact mixing. Venturi tube gas washing mainly uses pressurization in front of the throat, severe turbulence in the throat and jet turbulence behind the throat to achieve gas-liquid mixed contact and mass and heat transfer. Impinging stream scrubbing mainly uses liquid impact, capture, turbulence, etc. to complete the gas-liquid mixed contact, thereby completing the mass-to-liquid heat and gas transfer.

The boiler flue gas purification process is first to change the gas-solid heterogeneous system into a gas, liquid, and solid system, such as the spray washing process and the Venturi process, as much as possible to mix the three states of gas, liquid, and solid. The main principle of boiler flue gas spray washing is inertial collision and interception. The droplets of spraying airflow mainly capture dust particles when they are sprayed, rather than staying in the airflow, waiting for the dust in the airflow. Particles inertial collision occurs only when the air flows around it; there are also collisions between droplets and dust particles due to turbulence, diffusion, electrostatic forces and other interactions. After the capacity of the system is determined, the volume of the flue gas is determined within a certain range, and the time for the flue gas to pass through the purification equipment is determined. Therefore, when designing the structure, it is necessary to consider how to make the gas, liquid, and gas in the shortest possible time. A solid heterogeneous phase system was formed as quickly as possible.

If SO ₂ or other harmful gases in the air stream such as NOx, HCl, H2S, NH ₃ are gaseous substances, separating the gaseous substances from the gaseous system is different from the purification principle of solid and liquid substances. The method used is also different and requires The slow air flow rate is good for sufficient contact time with the washing liquid. The absorbed gas component chemically reacts with the washing liquid. The temperature and pressure in the system, the liquid-gas ratio of the washing liquid to the flue gas, the flue gas flow rate, and the residence time in the equipment all affect the mixing and absorption efficiency. In order to accelerate the chemical reaction, the movement of the air flow must be in a turbulent state, because the diffusive effect of turbulence is greater than that of laminar flow, which can transfer mass and energy more efficiently, and the dissipating function speed is much faster than laminar flow.

The main process of washing and absorbing gas in Venturi: The velocity of dust-containing gas gradually increases after entering the constriction tube from the intake pipe, and the maximum flow velocity of the throat gas is reached, and the relative flow rate of the gas-liquid phase in the contraction tube and the throat tube reaches The maximum value. The water droplets sprayed from the nozzle are atomized under the impact of high-speed airflow, and reach a turbulent state violently. The gas and the washing liquid are fully contacted and mixed at the throat. In the diffusion tube, the air velocity decreases and the pressure rises, and the dust particles or droplets are used to form the condensation effect of condensed nodules, which are aggregated into dust-containing water droplets with a larger particle diameter, which is easier to be captured, thereby achieving the dust removal and scrubbing gas. purpose.

In summary, in the design of the equipment, it is necessary to make full use of spray interception, collision, turbulent mixing, gas-liquid vortex mixing, and Venturi effect to complete the full contact and mixing of washing liquid and gas, and to ensure the mixing contact time and reduce the equipment Volume, reducing equipment resistance. Structural design and parameter determination focus on theoretically studying the fluid dynamics laws that must be followed for the relative motion and interaction of gas, liquid, and solid three-state materials. Make full use of these laws, and refer to existing successful design experience to improve the design and make The device achieves the expected results. ^[2]

Gas scrubbing

Gas scrubber (or scrubber). Industrially, this equipment is used for scrubbing gas for various purposes, such as absorbing certain components of a gas mixture with a liquid, removing dust from the gas, humidifying the gas or Dry etc. But its most widely used is cooling gas, and most of the liquid used for cooling is water. The spray room widely used in air-conditioning engineering can be considered a special form of it. The spraying chamber can not only cool the air like a gas washing tower, but also heat it. However, it also has disadvantages such as high water quality requirements, large floor area, and high energy consumption of pumps: so, at present, in general buildings, the spray room is not often used or is only used as a humidifying device. However, it is still widely used in textile mills and cigarette mills whose main purpose is to regulate humidity.