What Is a Wet Scrubber? How Do You Make It the Most Efficient?
If you look outside when it rains, all the pollution we generate and fine particles in the air, get washed out by water droplets. A physical contact is present between the particles and water droplets. In comparison, a wet scrubber is a liquid and particle contactor that absorbs harmful airborne pollutants and odors with water, or a water-based solvent. Typically, these pollutants are being removed from exhaust gas from furnaces or other devices.
Wet scrubbers are commonly used in the following applications (just to name a few):
The use of Wet Scrubbers come with many advantages as they will allow the user to safely handle combustible, sticky, or abrasive dust, as well as remove fine particulate, mists, and unwanted soluble gases from industrial processes. Continue reading below to learn more about particle collection and design data.
Scrubbers work by the impaction, interception, and diffusion theory.
Imagine a piece of pipe: you have air, water droplets, and solids running through it. If particles are big enough and flow in the same direction with the water droplets, air and solids, then the solid particle, because of its own weight, will hit the water droplet and get collected (interception). Wet Scrubber's generally have various throat designs with the main purpose of creating contact between the gas, water droplets, and solid particles, as this is what creates pressure drop.
In diffusion, the particles are so fine that they behave like air molecules. Consider this: we all are standing, or sitting, and air molecules are constantly moving around us. However, we don't feel it because air molecules are so light that they change their path and go around us. In scrubbers, when particles are fine, they create a random zig zag motion. Due to this motion and the constraint of the throat, the particles do not have a large area to move around in. This is how the particles collide with the water droplets and get collected by the scrubber.
Finer particles will need more pressure drop to have impaction, interception, and diffusion; whereas heavier, larger particles require less pressure drop.
Lets look at an example. The figure above shows how the Venturi Wet Scrubber works in order to provide the most efficient results.
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Particle collection depends on the particle size, distribution and the particle's specific gravity, among many other factors.
Pressure drops, liquid rate (liquid to gas ratio), and percentage of solid in the recycled loop, are very important for efficiency as well. To obtain impaction, interception, and diffusion, you can create more pressure drop to bring them together, use more liquid rate, or you can use a lower percentage of solids in the recycled loop.
These three variables can be adjusted to achieve the efficiency goal you want. You can change these three parameters so that you have either a lower or higher pressure drop; lower or higher liquid rate; or lower, or differing, percentage of solids in the recycled loop. It should be noted that there are two types of solids - dissolved solid and undissolved solid. When particulates are soluble in the water, you can design for higher percentages in the recycled loop.
Design Data
There are many different ways to design a Wet Scrubber, as long as you know the design data and the overall goal. Design data is a key component when considering wet scrubbers. This data has to be very precise. Incorrect data will cause your scrubber to either use more horsepower, more liquid, or a combination of both, ultimately costing you more money in the long run. Gathering the most accurate information will be considerably more cost-effective throughout the life of the equipment.
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