Taylor Morgan | Camfil APC
Dust collection systems help protect workers and equipment from nuisance and dangerous airborne particles. While these systems are costly, you can achieve a return on investment (ROI) by understanding the true costs of operating a dust collection system and taking informed action to reduce these expenses. This article presents the three main cost contributors that impact a budget required to operate a cartridge-style dust collector and how to mitigate those costs to get the most cost-effective ROI for your process.
Controlling the dust generated by bulk solids processing and handling is critical for employee safety, product quality, and maintaining regulatory compliance, which is why powder and bulk solids manufacturers use dust collection systems. Purchasing and operating a high-efficiency dust collection system designed specifically for your operation is a necessary expenditure because the system will filter hazardous and nuisance dust to make the indoor environment safer.
Not only does a dust collection system ensure a safer workplace but investing in the right system means a return on investment (ROI) for years to come. An ROI measures the amount of money that’s spent on maintaining a major financial investment in relation to the investment’s original implementation costs. This information is used as a performance measure to determine the efficiency of a particular investment — in this case, a dust collection system. You can also compare one dust collection system’s ROI to another’s ROI to determine which system is more efficient. You can achieve a better ROI over the long-term by evaluating the major contributing factors to the cost of operating a dust collection system and then taking the necessary steps to reduce these expenses.
Three major cost contributors
If you’re processing a dust-producing material, you’re going to need a dust collection system. While there are many different dust collector types, for the purpose of this article, we’ll be focusing on achieving an ROI with a cartridge-style dust collector, which is widely used across the powder and bulk solids industry. There are three major cost contributors to operating a cartridge-style dust collector. There’s the energy required to run the collector, the purchase price of cartridge filters and other consumables (items that will be used relatively quickly), and the maintenance labor, production downtime, and waste disposal costs that come with servicing the equipment, as shown in Figure 1. With these three major costs in mind, the greatest cost savings can be achieved over time by consuming less electricity and compressed air, using fewer cartridge filters, and performing less-frequent filter changeouts.
A dust collector consumes electrical energy the entire time the collector is running, but the electrical load’s largest portion goes to the fan motor that moves the air through the system. In addition, a lot of energy is used to heat or cool the air that replaces the air that the dust collection system constantly draws out of the plant or facility it’s cleaning.
Reducing fan motor energy use. The fan motor’s electricity consumption is directly proportional to the volume of air, expressed as cubic feet per minute (cfm), that the motor is moving through the system. However, dust collectors are variable systems in that the collector’s resistance to airflow, referred to as pressure drop or static pressure, changes over time according to how loaded the cartridge filters are with dust. This relationship is seen in Figure 2. As you can see in Figure 2, the new filters are able to easily pass through more airflow while keeping a lower static pressure when compared to aged filters, which have difficulty passing more air through due to the dust buildup on the cartridge filters.
Without any intervention, the fan will move more air than needed in the filters’ early stages of life when the static pressure across the filters is low. This consumes unnecessary energy and also causes high-velocity air to hit the filters, which reduces filter life.
In the late stages of the filters’ life when the filter media is loaded with dust particles, the airflow through the media becomes restricted, and the fan motor has to work harder to keep the airflow high enough to capture the dust particles in the filter. This increases the static pressure, which is measured in inches water gauge. When the static pressure increases, the airflow needs to be adjusted to avoid excessive energy usage. This can be accomplished manually or by installing a variable-frequency drive (VFD).
Manual airflow adjustment. Dust collectors typically use a damper at the fan’s outlet to mechanically vary the system’s static pressure and airflow. A damper is a valve or plate that regulates airflow inside a duct or other air-handling equipment by opening and closing. A dust collection system has one damper per fan, and in some cases, more than one fan is used. One option to alter the airflow is to manually adjust the damper. When the filters are new, the damper can be closed more to achieve the desired airflow. As the filters become dirty, the damper can be opened more to increase airflow.
Figure 3 illustrates the typical relationship between a constant-speed fan and the energy consumed when using an outlet damper to mechanically control a system’s static pressure. As shown in Figure 3a., the more the damper is opened, the more airflow is let through, which allows for the proper system filtration. At the same time, the pressure drop decreases, and the fan’s horsepower remains the same throughout, as shown in Figure 3b.
VFD energy control device. A better option than manually adjusting the airflow is to use a VFD to electrically control the fan speed, which helps to reduce the energy used. A VFD is an electrical device that automatically manipulates the frequency and power supplied to the fan motor. Routine human interaction is no longer required when a VFD is implemented. The VFD will automatically sense changes in airflow and pressure drop within the dust collector and will adjust the fan speed to return the system to optimal airflow. Operators achieve significant long-term electrical savings using a VFD because the amount of energy needed to operate the fan motor varies with speed.
For example, when the filters are new, not as much airflow is needed to push air through the filters, so the VFD decreases the fan speed to obtain the desired airflow. When the filters become loaded with dust, the airflow needs more energy behind it to push through the filters, so the VFD speeds up the fan to keep the airflow consistent. The automated electrical control is much more efficient than manual human intervention in maintaining a desired airflow and minimizing the electrical energy consumed.
Adjusting the incoming power’s frequency is an effective way to change the fan motor speed since the power frequency and fan motor speed’s relationship is directly proportional. For example, a VFD can change a motor that runs at 3,600 rpm at 60 hertz to run at 1,800 rpm at 30 hertz. The fan draws only the amount of power required for the specific fan speed. For another example, a fan that runs 25 percent slower than 100 percent would use 42 percent of the power that would be required for full speed, as shown in Figure 4a. and Figure 4b. The same fan running 50 percent slower would use 12 percent of the full speed power.
The bottom line is that a VFD enables users to save an average of 30 percent on their energy costs to operate the dust collector. Also, because fan speed adjustments don’t require human intervention, maintenance and operation costs are reduced.
There are multiple relationships taking place that define the amount of energy being used at different speeds, as shown in the graphs in Figure 4. VFDs have been proven to save a lot of energy over the life of the filters. The additional capital cost savings made possible by installing a VFD on a dust collection system will vary with different applications. However, the ROI is typically achieved within less than a year.
Consider the following example: Assume you have a dust collector with a 50-horsepower motor running at 460 volts with 58 amps of current at full load. Operating 24 hours a day, 7 days a week, the fan motor would use 46.2 kilowatts power at full load. (Actually, the fan motor would use 37.3 kilowatts if power losses didn’t occur, but because losses do happen, we added a cushion of 8.9 kilowatts for any losses.) If the electricity rate is $0.10 per kilowatt-hour, operating the fan motor would cost $40,481 per year. However, by installing a VFD at an estimated cost of $11,000 for installation, the same motor would cost $28,337 per year to operate, resulting in a savings of $12,144 per year. The VFD would pay for itself in less than 11 months.
Reducing compressed-air usage. Pulse cleaning is a critical technology to help dust collectors maintain a steady airflow and run at peak efficiency. When the pressure drop reaches a certain level, a pulse-cleaning system in a dust collector sends quick bursts of compressed air back through the filters. If the filters are designed properly, the compressed-air bursts blast the accumulated dust on the filters off the filter media and into the dust collector’s hopper, helping to maintain a lower average pressure drop and increasing filter life.
However, producing compressed air is extremely expensive, resulting in pulse cleaning being one of the highest operating costs associated with dust collection. For that same reason, pulse cleaning is also one of the operating costs with the most potential savings.
Advanced dust collectors. Today’s most advanced dust collectors can reduce compressed-air consumption by as much as 50 percent versus older, less technically advanced dust collectors. The advanced dust collectors use less compressed air because they’re able to pulse clean far less often. This is because the advanced dust collectors require high-efficiency filters that are made with better media and a better design. And while these filters are more expensive, they are better than lower cost, lower efficiency filters.
When designed properly, the dust collector’s cleaning system will remove the built-up material from the cartridge filters, which then leads to a reduced pressure drop across the filters, reduced fan energy consumption, and reduced associated energy costs. Dust collection systems that take these variables into consideration will provide more airflow while maintaining a low pressure drop.
When using high-efficiency cartridge filters, the dust collection system can handle higher airflows while maintaining a high level of filtration efficiency. This is because pleating technology enables advanced cartridge filters to contain more usable media than standard cartridge filters, so the cartridges can accept more air and process more dust. So when cartridges are fabricated with downward-facing pleated media, they can evenly distribute the pulsed air through the filter. With each pulse, more dust is ejected from the filters straight into the hopper.
The result is a more thorough cleaning with each pulse, so the airflow remains unrestricted and the pressure drop remains low for a longer period of time. The cleaning system doesn’t have to pulse as often, providing a large savings on compressed air over the collector’s life.
Recirculating heat and air conditioning. To do their job effectively, dust collection systems move a lot of air from the facility they’re cleaning. Dust collectors generally send the inside dust-laden air through the filters to remove the dust, and then expel it outside via fan discharge or ducting. When the inside air is heated or air conditioned, the facility’s HVAC system has to work hard to continually replace the heated or cooled air that was removed.
Secondary filtration. Facilities can reduce their energy use by safely recirculating the cleaned air back into the workspace. However, this cannot be done safely without secondary filtration on the return ducting. A secondary filtration system, as shown in Figure 5 and Figure 6, prevents any potential dust from re-entering the workspace should there be a leak in the primary filter system. This secondary monitoring system is an added measure of safety and, depending on the vendor, can be integrated into an existing dust collection system.
Considering cartridge filter quality. When it comes to purchasing filters for your cartridge-style dust collector, there are two options to choose from: low-efficiency, low-cost cartridge filters and high-efficiency, high-cost cartridge filters.
Low-efficiency filters. These filter types, known as standard filters, are less expensive upfront, which makes for instant savings. Also, standard filters, while low efficiency, can be useful for filtering depending on the application.
High-efficiency filters. These filter types are more expensive than standard filters due to their advanced design and media use, but these high-efficiency filters generally last 50 percent longer because they pulse clean more effectively, as shown in Figure 7. This is because high-efficiency filters are able to maintain a consistent airflow and low pressure drop longer than standard filters. The vertical lines in the graph in Figure 7 represent the times that cartridge filters are changed out.
High-efficiency filters also produce other cost savings, which add up significantly over their lifecycle. Since quality high-efficiency filters allow more air to flow through the system, they use less compressed air. The filters use less compressed air because they don’t need to be cleaned as often and are changed out less frequently, which also reduces maintenance, transportation, downtime, and disposal costs. Disposal costs can be significant, particularly if a hazardous material is being collected and the filters require incineration.
Estimating filter replacement costs. When replacing filters, their initial purchase price is only part of the cost. Purchase price is usually evaluated per cartridge, but some collectors operate using fewer cartridges to move air. For example, one dust collector could use 24 filter cartridges to move 36,000 cfm of air, while another dust collector might require 32 cartridges to move the same volume of air. Properly designed high-efficiency cartridges can also filter more air at a lower pressure while using less energy and compressed air. In addition, they can maintain that airflow and efficiency for a longer period of time.
As a hypothetical example, consider a side-by-side comparison of two identical dust collection systems — one outfitted with standard cartridge filters and the other with high-efficiency cartridge filters. Here is what would likely play out during the course of a year with the two cartridge types:
Four months in. The standard cartridge filter dust collector would be using twice as much compressed air as the high-efficiency cartridge filter collector. The standard cartridge filters wouldn’t clean off as well as their high-efficiency counterparts, which is the reason for more compressed-air use.
Six months in. The standard cartridges would need to be changed out because they’d be too clogged with dust for the pulse-cleaning system to maintain a low pressure drop. The clogged filters also increase the probability of dust bypassing the filters through the fan’s outlet. If not changed at this point, the filters will put undue stress on the fan motor and use unnecessary energy. However, the high-efficiency filters would still be working effectively at this time because they have more usable media, and the media is pleated in a way that releases more dust with each pulse.
Twelve months in. The standard filters would need to be changed again as 6 months have passed since their initial changeout, and if the standard cartridge filters weren’t changed out at this point, the same problems that could occur at 6 months could occur now. The high-efficiency filters would need to be changed out for the first time because they would be fully loaded and unable to maintain a low pressure drop and prevent excess energy from being consumed.
After 12 months. In this hypothetical situation, the standard cartridge filter dust collector would have used 5,037 cubic feet of compressed air and $14,600 of energy, as shown in Figure 8. The high-efficiency cartridge filter dust collector would have used 2,518 cubic feet of compressed air and $7,300 of energy. The standard cartridge filter dust collector’s additional $7,300 of energy used and 6 additional standard cartridge filters far exceed the cost of a year’s worth of high-efficiency cartridge filters.
Reducing labor. It takes maintenance personnel time to change out the cartridge filters, so labor costs can be reduced by using a collector that uses fewer filters and filters that last longer and perform better between changeouts. As discussed, high-efficiency filters can last twice as long and can handle more cubic feet per minute per filter while maintaining a lower average pressure drop.
Reducing downtime. In addition, some dust collector suppliers monitor their dust collectors remotely, receiving alerts when high differential pressure setpoints are reached. The vendors can then alert the customer whose system is experiencing problems and troubleshoot issues that the operator likely wouldn’t have yet noticed, such as underperforming or overloaded filters. When offered, these monitoring systems are good preventive maintenance tools that reduce the overall downtime costs.
Reducing waste disposal. There are costs associated with properly disposing filters that are laden with process dust, and costs are based on the type of material being filtered. Also, depending on which state you live in and the local requirements for dust, filter and dust disposal costs and regulations for properly disposing of these materials vary. However, despite where you live, reducing waste disposal costs can be achieved with high-efficiency filters because they last longer and need to be replaced less frequently.
Also, while the carbon dioxide emissions from the operation of high-efficiency dust collection systems are significantly less, the emissions should be considered and stated as a cost impact on the environment.
- American Conference of Governmental Industrial Hygienists, Industrial Ventilation: A Manual of Recommended Practice for Design, 26th ed., ACGIH Signature Publication Series, 1951.
For further reading
Taylor Morgan (800-479-6801) is a regional manager for Camfil APC, with responsibility for territory development, product implementation, and problem solving industrial ventilation applications within Texas, New Mexico, Oklahoma, and Louisiana. He has worked for the company since 2012 with extensive experience in thermal spray, metalworking, and abrasive blasting applications and a strong focus on NFPA and Industrial Ventilation guidelines.
Camfil APC • Jonesboro, AR
800-479-6801 • www.camfilapc.com
Copyright CSC Publishing Inc.