What are Smokestack Scrubbers? 

Once we believe in the environment and remember the pollution-producing facets of it, we will consider the smoke-stacks scrubber to be a number of the worst offenders. Although this is often legally correct, smoke-stack scrubbers often have a big function in terms of keeping ground-level air pollutants- safe to breathe and assisting within the management of emissions. 

"Smoke coming out from chimneys"

When we remember the non-developing -industrial revolution era, we will romanticize the period. We will picture rolling hillsides, a shortage of coal plants, coal burning, coal-based fired power stations, forestry, farmland, carbon dioxide, and a down-to-earthiness that we long for today. While any of these may be accurate, we must note that this was still a time before proper waste control or pollution controls. 

During the non-developing -industrial era, if people burnt something, the smoke lingered near the bottom. All the toxins like coal-fired, exhaust gases, nitrogen oxide, synthetic gypsum, smokestack emission, scrubber system, dry scrubber that folks were completely unaware of will remain right where people breathed. And what we consider natural pollutants, like particulates emitted while burning wood for heating or cooking, are often very hazardous to the human system. 

Types of Scrubbers 

Wet Scrubber 

In wet scrubbers, there is a direct contact of the harmful gases and particulate matter with the scrubbing solution. Different scrubbing solutions are used for various nuisance-creating materials that have to be neutralized or removed from the effluents. For example, to remove dust particles, only clear water solution is needed while to remove certain targeted compounds, specific solutions have to be chosen. 

The contaminated gases are forced to travel through wet limestone slurry, which traps sulphur particles. Scrubbers of this sort may manage particulate particles smaller than 10 micrometres in addition to inorganic gases such as: 

  • Sulfur dioxide 
  • Hydrogen sulfide 
  • Chromic acid 
  • Ammonia 
  • Fluorides 
  • Chlorides. 

Wet scrubbers can also be accustomed to manage volatile organic pollutants on occasion (VOCs). After that, the wasted solvent is disposed of in an ecologically friendly manner. Venturi scrubbers are wet scrubbers that atomize the scrubbing liquid and wash away pollutants more efficiently by accelerating the passage of exhaust gases through a liquid solution. 

"Working of a wet scrubber"

Pollutants condense during condensation cleaning, making them easier to remove. Water running down the sides of impingement-plate scrubbers traps sulphur particles by pushing pollutants up a vertical chamber.  Most coal-fired power plants with scrubbers employ wet scrubbers. 

In removing harmful effluents, the efficiency of scrubber solution can be increased by: 

  • Increasing the contact time between solution and effluents. 
  • Increasing the surface area of the scrubber 
Dry Scrubbers 

The dry scrubbing method doesn’t result in a dense stack steam plume as in wet scrubbing method. With or without limited use of moisture, this method scrubs off the effluents. The dry scrubbing is either completely dry or it leaves very limited moisture content that it will evaporate along with gases without creating condensed steam plume. By using various adsorber materials from the effluent gas stream of exhaust systems of power plants, many harmful chemicals can be removed. 

Dry scrubbers can remove over 90% of sulfur dioxide under ideal conditions, but they are limited to small- to medium-sized power plants with a capacity of less than 200 MW. Dry scrubber technology accounts for just 16,200 megawatts of the 120,000 megawatts of power generated by coal-fired power plants using scrubbers. Using this technique has several advantages, including lower waste disposal costs and less water use. Other pollutants treated by dry scrubbers include polycyclic aromatic hydrocarbons (PAHs), hydrofluoric acid (HF), hydrochloric acid (HCL), and heavy metals. 

"Working of a dry scrubber"

Scrubbers in SmokeStacks: What Do They Do? 

Sulphur and other Particulate Reduction 

Given the recognized health risks associated with manufacturing smokestack emissions, particularly those from coal-burning electric power plants, reducing emissions at the source is extremely desirable. Scrubbers in the emission system are one established method of accomplishing this. Scrubber technology, which can remove a significant amount of sulfur dioxide from chimney emissions, is continually improving. While scrubbers are often put immediately within a chimney, they can also be added at various places within or around it. Some scrubber systems necessitate the construction of a whole building or complex adjacent to a coal plant. 

Even with scrubbers, environmental concerns abound 

While the concept of recycling scrubber waste into reusable synthetic gypsum is intriguing, it has not yet been widely implemented. Scrubbers discharge a lot of the trash they remove from flue gas back into the coal mines where it came from. If the highly toxic sludge gets into touch with groundwater, it can cause significant environmental harm. The highly concentrated pollutants dissolve quickly in water, including drinking water wells and aquifers. 

Calculating Smokestack Pollution 

We will enter the technicalities of how engineers decide how big a smokestack has got to be and what impact it will have on the ambient air now that we've addressed the risks of pollution and the way engineers could conduct risk assessments for every pollutant. 

The action of smoke or air when it leaves a smokestack is decided by a spread of things. The temperature of the smoke about the air, wind conditions, volume, scale, flow rate, height, and other factors also can be considered. As a result, how smoke reacts in real-world situations varies significantly, but engineers have classified smoke-stack scrubber plumes or the smoke that exits the stack, into many various plume forms for models and calculations. Examples are coning, looping, fanning, fumigations, and lofting 

Smoke plumes from smoke-stacks scrubber usually scatter in a Gaussian fashion, implying that the smoke concentration would take the form of a bell curve in cross-section. When smoke leaves a stack of a certain height, h, it eventually transforms into a plume, which may be a gas emission remove trail, the plume origination height, H, are often greater than the smoke-stack height, h. This means that the smoke will rise slightly before becoming a plume. 

Although the plume's cross-section can battle several types at any given stage, the normal plume cross-section is Gaussian in shape, which is why engineers would generally assume this. 

Engineers would be more concerned with the plume's ground-level concentration at a fixed distance generally. Assume there was a town 30 miles far away from the plume. The concentration of the plume at A level between the world and a given height, at a worth of x = 30 miles, is going to be calculated by environmental engineers. Pollutants from the smoke-stack scrubber are diluted at higher speeds during strong winds, assuming an equivalent flow from the stack. High winds can help dilute contaminants quicker during this situation, but they will also create turbulence, which changes the plume form and throws the equations off. 


The method for calculating the concentration of a plume at the ground level at a given point could look like this;  

C ground (x,y)= S πu σ y σ z exp Y 2 2 σ 2 y H 2 2 σ z 2
  • Cground –concentration, 
  • S -  emission rate, 
  • u  - wind speed at height  H, 
  • σy  - horizontal dispersion coefficient, 
  • σz  - vertical dispersion coefficient, 
  • y- being cross-wind distance, 
  • H - effective stack height.  

Context and Application 

This topic is significant in the professional exams for undergraduate and postgraduate courses, especially for Chemistry. 

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