For a high-efficiency wet scrubber to perform as anticipated, it must have the correct setup and maintenance. However, having the proper structure is not the only aspect that affects performance. Issues can still appear after a time of efficient operation. Eight common factors can influence the efficiency and performance of a wet scrubber. Through troubleshooting these problems and conducting preventive maintenance, you can restore the scrubber’s operational capabilities.
8 Factors That Affect Wet Scrubber Performance
Often the causes of a performance drop in wet scrubbers originate in design flaws or improper maintenance. There are eight common factors that reduce the operation of high-efficiency wet scrubbers. These factors are as follows:
1. Inadequate Sump Fluid Replacement
Freshwater makeup needs to meet the scrubber system’s fluid needs. If the sump fluid uses overflow or blowdown to replenish it, problems could arise when it does not have enough liquid. With overflow, the sump overflow mixes with freshwater into the drain of the scrubber. Blowdown gets to the drain through force with a recirculation pump.
An improper balance of sump fluid and fresh makeup water can prevent the concentration gradient from maintaining its necessary balance between gas and liquid states. A breakdown of the state of the concentration could compromise the performance of the wet scrubber.
Inadequate sump fluid replacement could occur from a problem with the recirculation pump when using blowdown liquid or failing to add enough makeup water. Re-entrainment of pollutants may occur when the scrubbing liquid is not enough to treat the gas coming in. Keeping an eye on the liquid balance of the wet scrubber is essential for its performance.
Correct measurements for the liquid-to-gas ratio rely on calculations based on the concentration of the contaminants, the temperature of the inlet gas and the method of liquid distribution. With values varying from 2 to 40 gallons of scrubbing liquid per 1,000 feet of inlet gas, you cannot guess the amount of liquid.
You must have an engineer calculate the exact volume of liquid needed to remove pollutants from the treated gas. Be aware that the amount of freshwater added to the system can change over time. Evaporation requires changes in the amount of freshwater added to the system to reach and maintain proper liquid levels.
2. Improper Pump Size
The pump must work to properly move liquid through the wet scrubber. This movement must also overcome gravity, strainers and any other components that can slow its flow. Improperly sized pumps will not allow for adequate fluid flow. Have a professional engineer design the pump and size it correctly for the wet scrubber’s needs.
3. Improper Addition of Scrubbing Liquid
The scrubbing liquid acts as a solvent to absorb the pollutants from the gas. Therefore, you must use the correct type and amount of liquid for the wet scrubber’s operation. Having an incompatible solvent will decrease efficiency and increase the costs of the scrubber. Additionally, an improper liquid to gas ratio prevents the absorption of pollutants. Use appropriate neutralizing scrubbing liquids based on the type of products removed from the gas that passes through the wet scrubber.
4. Packing and Gas-To-Liquid Ratio
The type of packing also makes a difference in the performance of a wet scrubber. Ideal packing will achieve the most efficient mass transfer rates. For instance, the effectiveness of a wet scrubber depends on the gas contact with the solvent. By optimizing this liquid-to-gas ratio, you can improve the efficiency of the scrubber. After the liquid solvent absorbs the maximum amount of contaminants it can, it requires replacement through flooding. The ideal flooding percent can optimize the function of the scrubber.
Working with the liquid and gas in the scrubber is the packing. Various types of packing are available to optimize mass transfer. Packing optimizes the surface area improves contact between the solvent and particles for absorption. Ideal surface areas based on the particle size of the pollutants optimize the wet scrubber’s function. Poorly chosen packing can compromise efficiency by reducing the surface contact between particles and the solvent.
5. Excessive Velocity Profile
When properly scrubbing particulates from gas, the velocity of the gas compared to the liquid makes a difference. Balancing these velocities ensures the proper removal of particulates from the gas. If a mismatch between the unit’s velocity ability and the fan flow rate occurs, the pressure may drop, reducing absorption, increasing evaporation, flooding parts of the bed and lowering the overall efficiency of the system. Premature flooding of the system with solvent changes the liquid-to-gas ratio, reducing the efficiency of the system.
6. Channeling Caused by Plugged Spray Nozzles
Plugged spray nozzles create areas of packing directly below them that do not have fluid flow. This results in no absorption from the gas that flows through that portion of the packing medium. Consequently, efficiency drops.
Spray nozzle clogging regularly happens. Checking the nozzles frequently and clearing them as needed will prevent this cause of channeling and efficiency drop.
7. Channeling Caused by Poor Air Distribution and Rectangular Housings
Poor air distribution or rectangular vertical housings can contribute to channeling and reduced performance from the wet scrubber. Air distribution is not even when a vertical scrubber does not have a design to account for perpendicular air entry. The unequal air movement creates channels of airflow that move through the packing material. Thus, poor air distribution results in a loss of function by not allowing even movement and treatment of the air through the system.
Rectangular housings in vertical scrubbers also do not allow for even air distribution. As with poor airflow, the design of the scrubber should accommodate the housings and air distribution system to ensure even air movement and distribution.
8. Buildups of Biological Growth
The buildup of biological growth can thwart the function of a wet scrubber. Anything that can impede the flow of the gas contributes to channeling. Biological growth is among the factors in channeling. In systems that have high pH values, biological growth can readily happen, especially in the warm, wet environment inside the wet scrubber’s beds. Pressure drops in the system could indicate channeling that may come from biological growth or another cause.
To prevent the growth of algae and bacteria inside the scrubber, consider regularly washing the interior of the unit with acid. Systems that include chlorination or bromination can also reduce bacteria and algae growth. Use UV rays to your advantage by blocking light from entering viewing ports to prevent algae. Plus, use UV treatment of recirculating and supply liquids to kill microbes.
Wet Scrubber Troubleshooting
When your wet scrubber encounters problems, troubleshooting the unit reduces the time required for repairs. Some signs indicate problems with specific scrubber components. Using appropriate scrubber monitoring and conducting regular inspections can make the troubleshooting and repair process much faster and easier. Watch for the following issues and how to fix them:
1. Pressure Drop in Scrubber or Mist Eliminator
There can be low or high pressure drops in the scrubber or mist eliminator:
- Low drops: For low drops in the scrubber section or mist eliminator, check for reduced airflow or liquid flow. Low pressure drops can also happen from plugged meters or eroded cleaning areas. When the mist eliminator has a low pressure drop, the media may have dislocated.
- High drops: High pressure drops can also occur in the mist eliminator and scrubber sections. For either section, high airflow rates or clogging can contribute to the issue. When the problem occurs only in the mist eliminator section, it could also happen from flooding. Check the mist eliminator and drain it of excess liquid to correct the flooding issue.
2. High Temperature
Use thermometers to track the inlet and outlet temperatures of the treated gas. When the exiting temperature gets too high, your scrubber may be using too little wash liquid to cool the system. Another possibility that could lead to high exiting temperatures could be the wash liquid itself is too hot. Look for clogs in the pump or nozzles for inadequate wash liquid.
Monitoring the temperature of the liquid is another aspect of troubleshooting. When the temperature of the liquid is too high, look at the sump temperature and make corrections to the cooling equipment if needed.
3. Pump Problems
The pump may produce too much noise, have excessive pressure or too little pressure. For noisy pumps, check the bearings and alignment. Cavitation may also contribute to noisy pumps.
For pumps with high pressure, check for plugged nozzles, closed valves or worn packing. Make replacements or repairs to nozzles, valves and packing to fix this issue.
When the pump doesn’t produce enough pressure, it could have too low of a motor speed. Check and increase the speed if needed. Other aspects of the system that could cause low pressure include worn impellers, worn packing or blocked piping. Examine these attributes and fix them as needed or replace worn parts.
4. Corrosion, Erosion or Buildup
For scale buildup or pipe plugging, check the chemical balance of the scrubber and examine pipes for tight bends that could cause clogs. Make changes in these areas to fix plugging or scale.
Corrosion and erosion may stem from inappropriate pH levels, improper materials or an inappropriately operating wastewater system. Check these components for faults to correct corrosion or erosion problems.
Considerations for Optimal Wet Scrubber Performance
To optimize wet scrubber performance, pay special attention to the following components and attributes of the unit:
The pumps need to have enough capacity to handle the volume for the wet scrubber. To avoid performance problems, monitor the discharge with flow meters and pressure gauges. Include a backup pump to automatically engage if the main pump reduces flow or pressure. These systems can prevent pump failure from causing a complete loss of operation from the wet scrubber.
Wet scrubber packing needs to optimize the contact between the gas and solvent. The material and shapes of the packing make significant differences in their performance. Look at the type of packing material to ensure it meets the requirements of the scrubber.
Check for corrosion of the packing materials, which will impede their function. Corrosion indicates damage from the gas or solvent and requires an alternative packing material. For instance, stainless steel materials work well in high-temperature environments but not in the presence of hydrochloric acid. Ensure the packing materials used work with the chemicals they will be exposed to in the wet scrubber environment.
Additionally, packing must not cause an excessive drop in pressure or deform in shape in the tower beds. Towers with large, deeper beds may need packing material to resist crushing or pressure drops, such as Interpack®. If pressure drops too much, consider the type of packing as a cause. Improperly used packing can cause a reduction in pressure throughout the column. Upgrading to better packing to reduce this problem can help improve performance.
Optimizing the wet scrubber function starts with collecting data about the unit’s operation. Use instruments to monitor the:
- Pump pressure and flow rate
- Sump temperatures and levels
- Freshwater makeup
- Airflow before the scrubber
- Pressure drop in both the mist eliminator and scrubber
Monitoring these areas will provide information about the operation of the scrubber, helping you make corrections before performance problems arise.
The design of the wet scrubber must include means to access the various components of the system that would need monitoring or maintenance. For instance, access to the nozzles allows for easier checking to see if they have corrosion or plugging. Sump access or view windows should be above the water level to reduce the chance of leaks.
Working with a qualified engineer to design the wet scrubber can ensure the design will function well and allow for regular maintenance and monitoring.
The Importance of Preventive Maintenance for Wet Scrubber Efficiency
Quality design of a wet scrubber is essential to avoid some causes of efficiency drop. For instance, a well-designed scrubber will have properly designed air distribution and pump size. You cannot rely completely on the design of the wet scrubber to ensure performance. Maintaining the scrubber plays a major role in keeping it performing at its best.
Preventive maintenance can stop many of the most common problems of reduced performance. Maintenance chores include those conducted daily, weekly, quarterly and semiannually. Workers should check various aspects of the scrubber before starting it up. These checkups should not take much time, and they provide valuable information about the state of the components of the wet scrubber. Note that some types of scrubbers are more sensitive to changes in pressure or temperature, making monitoring and adjustments of these factors vital.
During wet scrubber operation each day, check the pressure drop, pH and signs of re-entrainment. Checking these aspects of the scrubber and making corrections to restore the unit to ideal operation reduces damage to components. For instance, unchecked pH can lead to crystal formation inside the scrubber, and re-entrainment leads to discoloration of the scrubber.
Once a week, examine the headers and nozzles for signs of plugs or erosion. Plugged or eroded spray nozzles can lead to channeling, which ranks among the common factors in the inferior performance of a wet scrubber. Empty the sump and clean it before refilling it with an appropriate liquid. Replacing the sump fluid weekly can prevent one of the top causes of reduced efficiency, which is inadequate fluid.
Quarterly, examine the entire wet scrubber for signs of leaks, and repair them immediately. At least twice a year, conduct an internal inspection of the components of the wet scrubber. Correct causes of solid accumulations in mist eliminators or tray orifices, clogged nozzles or eroded nozzles.
Get reliable scrubber design services, replacement parts and on-site troubleshooting from MACH Engineering. We have a quarter of a century of experience in the field of mass transfer and offer affordable prices, expert engineering, quality materials and custom design. Contact us today for more information on how we can help you restore efficiency to your wet scrubbers.