By John Constance, Professional Engineer (P.E.)
The Engineers Collaborative
Dust control exhaust systems for industrial settings are engineered and designed to help protect plant personnel from exposure to nuisance and hazardous airborne particulates. The usual components of an industrial dust control exhaust system includes dust capture hoods, ductwork, dust collectors, exhaust fans, and a safety monitoring HEPA (High Efficiency Particulate Air) filter for redundant protection of the industrial environment. A good operating industrial ventilation system will have all these components working together to give you the protection you need.
The various State departments of environmental protection, require that dust control exhaust systems perform as filed for in the application for operating permits. Some state agencies require that a formal preventive maintenance program be filed with the operating permit application. Most states require that preventive maintenance program records be kept on file for the state agency inspector's review.
Everyone knows how to turn on a dust control exhaust system - you just flip the switch! But just flipping a switch day in and day out does not guarantee that the system will operate the way it was intended to. What kind of system checks should be made? When should you start asking questions about system checks and maintenance? These are just a few of the many questions that need to be answered in order to assure peak performance of an industrial dust control exhaust system for maximum protection.
The Engineering and Design Phase
During the engineering and design phase of the dust control exhaust system, thought must be given to operation and maintenance as well as to system performance and the project's budget. Objectives need to be established in order to simplify the future operation and maintenance of the system. The time to establish these objectives is during the engineering and design phase. Here are some guidelines to follow:
Detailed Engineering Documents
Provide extra detail in the preparation of the engineering specifications and industrial dust control exhaust system design drawings. Don't leave anything up to the imagination of the contractor. It is not the contractor's job to be a dust control system expert. The contractor is a fabrication and installation specialist. Give the contractor complete information so that the system is built right.
Detailed documents will also minimize the possibility of receiving a very low price during the construction bid phase. If an unusually low bidder is awarded the project, poorly detailed engineering and design documents will generate many construction extras and a poorly installed system.
Selection of Construction Materials
Specify the right materials for construction for dust hoods and exhaust ductwork. The correct metal gauge will lengthen the life of these components. If corrosive dusts are expected to be involved, stainless steel may be better than galvanized steel.
Position the exhaust system's components in the plant for ease of inspection and repair. This simple but important matter is often overlooked. Components cannot be maintained without proper access. The component manufacturer has information to help you determine proper access.
Original Equipment Manufacturer (OEM) Component Specifications
Specify dust collectors, exhaust fans and other OEM components based on your needs rather than on the supplier's product line. Don't purchase unique items unless there is an absolute need. You may be locked in to buying expensive spare parts in the future.
Service and Support For Your Ventilation Equipment
The ventilation equipment supplier should have a local representative to give you personal and immediate attention in future operation and maintenance emergencies. The fabrication and installation contractor should be local to your plant operation for efficient and effective service. Working with a qualified local contractor will give you opportunities to interview his present customers for an evaluation of the contractor's past performance.
The Construction Phase
If the project's engineering and design documents are sufficiently detailed, it will not be difficult to follow the project during the construction phase to assure compliance with the design intent. This will give you a leg-up on minimizing future operating and maintenance problems. Here are a few guidelines to follow during the construction phase:
Visit the contractor's fabrication shop to inspect ventilation system components as they are being made - not only just before shipment. Check the materials for proper construction and gauge. Check to see that items to be bolted (for ease of disassembly) are bolted and not welded.
Ventilation and Exhaust System Installation Checks
Check to see that ventilation system components are not installed in such a way as to block access to each other or to other plant services and equipment.
Inspect the system for components that are damaged during shipping or installation. Check to see that these items are properly repaired or replaced in order to meet the standards set by the engineering and design documents.
Note how dust collector and HEPA filters are stored on site. They must be carefully protected from weather and construction activities. Apparently insignificant damage to filters will cause major operational problems. Small holes burned through by welding sparks or punched through by poor handling and storage will allow dust to bleed through the filters. This will contaminate whatever is downstream of the filters.
Perform a thorough inspection just prior start-up to assure that the installed ventilation or exhaust system meets the requirements stated in the engineering and design documents.
The Start-Up Phase
The effectiveness of dust capture hoods is measured by how well they reduce the airborne dust concentration at the dust sources in the work place. The system's ductwork needs to convey the captured dust to the dust collector with the proper transport velocity. This is important to minimize particles settling within the ductwork. The efficiency of the dust collector is measured by the cleanliness of its discharge air. The safety monitoring filter (HEPA) needs to provide an effective barrier in case of dust collector filter media failure. All these system components need to be validated at start-up:
System Air Balancing
The installing contractor is called upon to balance the air flow in the duct system so that the dust capture hoods exhaust the designed air quantities. The procedures for air balancing, as described in the Industrial Ventilation Manual published by the American Conference of Governmental Industrial Hygienists, are the standards to be followed. Pitot tube readings of duct velocity pressure in each duct connected to a dust capture hood provide the most accurate readings of exhaust air quantities. Air system balancing must be done with all dust capture hoods installed and connected to the dust control exhaust system ductwork.
All the data taken during the system air balancing should be recorded and filed for future reference as it is the baseline against which future system performance will be measured.
Industrial Ventilation System Safety Components
If collected dust is flammable or explosive, the dust collector will have been installed with fire and explosion protection components. These may include a sprinkler system, mechanical vents or chemical suppression systems. These systems should be thoroughly checked out to assure they will operate as intended.
System pressure gauges, low flow, and overpressure alarm systems should be checked out to assure compliance with the engineering and design documents. Any system which does not read-out or operate as designed should be investigated to determine the cause and must be corrected.
Component Base Line Documentation
In addition to the system air balancing data recorded during the start-up phase, additional baseline information should be recorded concerning all the system components.
- Dust capture hood static pressures should be measured and recorded for future reference. If a hood's static pressure changes later on, there will be no doubt that the hood exhaust air quantity has changed. If the exhaust air quantity has dropped, then the effectiveness of the hood has decreased. Knowing what the start-up static pressure was after air balancing will help you correct the problem.
- Operating static pressures of the dust collector and safety monitoring filter system (HEPA) should be recorded to signify their "clean" static pressure baselines. Static pressure drops across the filters will increase over time. However, any deviation from an expected pressure drop at start-up indicates a problem that may prematurely shorten the life of that component.
- A velocity pressure measurement in the main duct just before or after the dust collector or exhaust fan can be converted to the total system exhaust air quantity. This check should be carefully taken so that the resultant total exhaust air quantity can be compared to the air quantity submitted to the state department for environmental protection. If the measured exhaust air quantity exceeds that recorded on your state permit application forms by even a small amount, you are in violation of your dust control exhaust system operating permit.
Industrial Hygiene Particulate Air Sampling
Effective dust capture hoods can reduce the dust concentration in the air at the dust source by an average of 90%. To assure that this goal is satisfied by the dust control system, air monitoring for particulates should be done at system start-up at each dust source served by a dust capture hood. Industrial hygienists should perform this function to assure that the air monitoring is properly performed.
If it is found that certain dust sources are not controlled to the level desired, modifications will need to be made to the dust control system components:
- Certain dust capture hood exhaust air quantities may need to be increased.
- Certain dust capture hoods may need to be modified.
- Production material handling methods may need to be modernized to reduce the amount of dust generation at the source. This approach to dust control should normally be investigated by the dust control engineer during the engineering and design phase of the project. However, there is usually resistance to this type of change in the early stages of the project.
Once the desired level of dust control is achieved at the modified portions of the system, Component Baseline Documentation should be updated for accurate future reference. See THE START-UP PHASE and PREVENTIVE MAINTENANCE ACTIVITIES.
Plant supervisory, production and maintenance personnel should be trained in the operation of the new dust control ventilation system. The training topics should include:
- Dust control system safety features and components.
- System air meter read-outs and alarms.
- Component baseline documentation.
- Dust control equipment manufacturer's operating, maintenance instructions, and recommendations.
- Operation and use of dust capture hoods and dampers.
- Preventive maintenance program.
Preventative Maintenance Activities
Greasing fan bearings and emptying dust collector hoppers on schedule are important maintenance activities. Replacing obsolete dust capture hoods and ductwork are absolutely necessary to promote continued safe operating conditions. Repairing damaged dust control system components keeps the ventilation system running at peak efficiency. But these and other component repair activities are by no means sufficient to maintain top notch operating conditions. Here are four critical activities that should be performed on a regular basis:
1. System Operating Characteristics
Periodic visual inspection of system components permits early detection of potential system failure. As important as the visual inspection is, so is the scheduled checking of dust control system component operating characteristics. Component static and velocity pressures should be regularly measured and recorded. This data should then be compared to the data in the Component Baseline Documentation recorded during the start-up phase. Deviations from Baseline data should then be analyzed and corrected as necessary.
2. Explosion Protection Components
If the collected dust is organic or metallic in nature, an explosion relief or suppression system most likely was installed on the dust collector. Inspection and maintenance of these components should be done in accordance with the manufacturer's recommendations and applicable safety guidelines. An important activity often neglected is the periodic sampling of the collected dust for an explosivity determination. If the process has changed so that the particle size or shape of the collected dust has changed, dust explosivity may be affected. If the chemistry of the processed product has changed, dust explosivity may again be affected. If the collected dust shows an increase in explosivity above the level for which the installed explosion venting or suppression system was designed, immediate action must be taken to correct the deviation from the design condition.
3. Processed Product Changes
Changes in the nature and quantity of the processed product can also affect the performance of the dust control exhaust system. Raw material changes can dramatically change a well performing dust control system into a maintenance nightmare. New hygroscopic ingredients can plug filter media and drastically reduce air flow through the system. Finer powder can promote even finer collected dust that may bleed through filter media and cause an air pollution or return air system problem. Maintenance personnel must be included in the new product information loop so that they do not waste time looking for the solution to a system component problem that does not exist.
4. Industrial Hygiene Particulate Air Sampling
In order to help maintain a healthy atmosphere in the plant, periodic air sampling should be performed by qualified industrial hygiene personnel. It is an overall way of checking to see that the dust control system is in good working order. If air sampling shows that the operation is not running up to the standards recorded during the Start-up Phase, an investigation by production and maintenance personnel should be performed to determine the causes.
The Engineers Collaborative is the dust control and industrial ventilation expert that you need on your project!
Contact us today at (215) 300-9563, to find out more about how we can help you with your industrial ventilation or dust control review, analysis, or design.