Baghouse Control - Google+

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Pneumatic Conveying

Pneumatic Conveying

BCE pneumatic conveying provides material transport systems where a powder or granular material is moved from one place to another down a pipeline by means of a pressure differential. BCE pneumatic conveying systems are generally categorized as either dilute-phase or dense-phase. Dilute phase is normally under 12 lb material per lb of air and assumes that the material is suspended in the air stream. Dense phase operates at an air velocity below the material's saltation velocity and typically includes a high-pressure blow tank to force the slug of material into a line and booster air at regular intervals to keep it moving until it reaches a receiving vessel. Dense phase conveying can have material ratios up to 100-to-1 and can convey material very long distances. This discussion will be limited to dilute-phase pneumatic conveying systems, which are commonly used with dust collectors.

Dilute-phase pneumatic conveying systems can transport material by either positive pressure or vacuum. Both systems will have the following four basic components:

• The pressure blower or mechanical exhauster, to move the gas-solid mixture.
• The material intake valve
• The pipeline
• The dust collector

In a positive-pressure system, a pressure blower is upstream of the pipeline, designed to pressurize the pipeline so that the material is conveyed to a receiving vessel. The receiving vessel is typically a silo on top of which a bin vent filter is located. The pressure at the end of the line is low enough for a standard low-pressure dust collector to be used. In order to feed material into the line, a pressurized material feeder is often used at each pick-up point. The flow rate in the line is significantly higher at the "no-load" (air only) condition; therefore, the dust collector needs to be sized accordingly. The upstream line pressure can be 50-70 psig and therefore can convey for much longer distances than a vacuum system.

In vacuum conveying, a mechanical exhauster is located downstream of the dust collector to pull material through the system. Since the dust collector is at the end of the line, it will see the maximum vacuum, which could be greater than 15" Hg. Therefore, this dust collector (also called a filter-receiver) must be a special design to handle the high vacuum as well as a very high inlet dust loading perhaps on the order of 2000-5000 gr/ft³. If the material is abrasive (such as fly ash), a rotary valve may not be suitable to feed the material across a high pressure differential. In that case either a double dump valve or vented transfer hopper with isolation valves may be indicated to discharge the material and allow continuous operation.

BCE has extensive experience in designing pneumatic conveying systems and we look forward to assisting you with selecting the right equipment for your system.

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Explosion Protection

Explosion Protection

BCE explosion protection is engineered to meet and exceed your requirements in order to provide the best protection for your staff.  In order for a dust explosion to occur, the following factors must be present:
• A concentration of dust in suspension above its flammable limit.
• A sufficient concentration of oxygen to ignite the fuel.
• A source of energy (e.g. a spark) to ignite the fuel.
• Confinement of the dust/oxygen mixture.

Particle size has a major influence on combustibility. Any oxygen concentration above 13% will support combustion. Additionally, the smaller the particle size, the greater the specific surface and the higher is the likelihood of spontaneous combustion.

Ignition can be initiated from a number of possible sources. For example, there could be friction on collector surfaces from hard impurities in the coal, such as pyrites, metals or rock, or sparks coming off of defective fan blades or dampers. Reaction rate increases with temperature, therefore an explosion is more likely with a high operating temperature.

Standards for Explosion Protection

The National Fire Protection Association (NFPA) issues a wide variety of safety standards pertaining to securing buildings and equipment against damage from fire. The accepted standard in the United States for dust collector explosion venting is NFPA-68, called the "Standard on Explosion Protection by Deflagration Venting." A deflagration is defined as the propagation of combustion at less than the speed of sound in the unreacted medium, as opposed to a detonation, which exceeds the speed of sound. Dust collector explosions are deflagrations by nature.

This publication was first introduced as a guide in 1954, compiling the best available test data on the fundamentals of explosions, using vent types current at the time. Panels and doors were sized according to "vent ratios," or the vented volume of the enclosure divided by the panel area. Dust types were categorized as Type 1, Type 2 or Type 3, corresponding to ratios of 50:1, 30:1 and 15:1, respectively. These rule-of-thumb ratios were very conservative in some cases, untested in others, and were used to size dust collector explosion vents for many years.

The deficiencies of using such an approach became apparent as issues of insurance and liability came to the fore. Besides the limited accuracy of the rules of thumb, other parameters needed to be better quantified, such as the effects of vent panel inertia (or weight per square foot), enclosure geometry, locations of vents, pressure effects, vent aspect ratios and ducting the vent to an external location. As more testing was done in the US, UK and West Germany, and better methodology was created, NFPA-68 went through a number of major revisions dating from 1974. The earlier revisions incorporated the researches of the German VDI and the Factory Mutual Research Corporation with the object of improving the accuracy of the vent ratio calculation. Subsequently, the vent ratios were abandoned altogether for the much more rigorous approach used today, whose accuracy was improved with each succeeding edition. The latest edition (2007) is a "standard" rather than a "guide" for the first time. As a standard, more power is given to the Authority Having Jurisdiction (e.g. OSHA or an authorized company official). ATEX is the European equivalent with the additional requirement that its use in the EU is legally mandatory.

The following parameters used fir explosion vent sizing are fundamental and deserve discussion:

Kst: The value K is known as the deflagration index, and is the maximum rate of pressure rise attained by combustion of a particular dust in a spherical test vessel of at least 20 liter capacity. This is a specific property of the dust, which can be found in the literature, if known, or by test. Dust Hazard Class 1 has a Kst ≤ 200. Class 2 dusts have 200 < Kst ≤ 300 and Class 3 dusts have Kst > 300. These classes replace the types associated with the vent ratio method.

Pmax: This is defined as the maximum pressure developed for an optimal mixture of a particular dust in a contained deflagration and is a property of the dust. The Pmax for most dusts fall into a range between about 7-10 bar, but this can be much higher for highly reactive metal dusts such as aluminum or magnesium.

Pstat: The static activation pressure of the vent closure, or the pressure at which the closure opens with rising pressure.

Pred: The "reduced pressure" or the maximum pressure developed in a vented enclosure after an explosion.

The relative importance of these factors is seen in the following basic equation for determining the minimum required vent area.

A = 10-4 (1+1.54 Pstat4/3) Kst V3/4 ((Pmax / Pred) -1)1/2

Types of Explosion Vents

At the time when vent ratios was the predominant method of sizing explosion vents, most vent closures on dust collectors were hinged steel doors, usually spring-loaded but sometimes using refrigerator-style latches. Because the high inertia of these doors increased their resistance to opening, a relatively large number of doors were needed in most cases to keep the backpressure (Pred) from exceeding the design pressure of the unit. Many older dust collectors can be seen with these types of explosion doors lining almost the entire perimeter of the dusty air plenum. The 2002 edition of NFPA-68 specifically stated that the movable part of a vent closure should not exceed 2.5 lb/ft², essentially making these older hinged steel doors noncompliant. A new method to account for higher-inertia doors was introduced in the 2007 edition, but the use of these type doors will be at the cost of a significantly higher overall vent area for the same Pred. We recommend one of the following vent closures, which are under 2.5 lb/ft², and have been proven in thousands of installations:

• Rupture Membranes

A rupture membrane is a composite diaphragm, either round or rectangular, which is installed on a flanged duct and secured with a mating frame. The membrane is scored and tears away at the scoring lines when the design burst pressure is reached. For high-vacuum applications, round membranes are bulged and are available up to a full vacuum rating. Flat panels are usually fitted with support bar frames to withstand the normal dust collector negative pressure rating. Rupture membranes come in standard sizes and are stocked at specific burst pressures (Pstat). If none of the standards are suitable, custom burst pressures can be specified at higher cost. Spares should be kept on hand for immediate replacement of burst membranes.

• Doors

Specialty hinged doors are available which are under 2.5 lb/ft² inertia and specifically designed to meet NFPA-68 explosion venting requirements. The major advantage of the door is that no panels need replacement after an explosion; it's ready for service again after being reclosed. The disadvantage is the cost, as it is several times as expensive as the same size rupture panel.

• Flame-arresting Vents

This is a cylindrical device which combines a rupture membrane with a flame-arresting element. This was designed specifically for an indoor dust collector for which it is impractical or impossible to duct an explosion vent to the exterior. In this device, the deflagration is vented through the rupture membrane, after which combustion gases are cooled in the element, with only steam emerging with no flames, while all burned and unburned dust is retained inside the element. This is by far the most expensive option, but is the only one which allows operation of a vented indoor collector without an external duct. It is also useful in minimizing the collector Pred since a long external duct adds significantly to the backpressure, requiring a stronger collector design at higher cost.

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RISK MANAGEMENT

BCE risk management identifies and performs analyses of risks, and follows that by acting to minimize the chances of negative events and maximize the probability of success. Risk management should be an integral part of any project, recognizing that not everything will go as planned. It is of such a critical character that several standards have recently been written, such as ISO 31000 and the Project Management Institute's Practice Standard for Project Risk Management.

BCE risk management is a complex undertaking and needs to be tailored to each specific application. In an industrial setting, the following is generally applicable:

• Planning
  Determine the risk management plan, to include the various activities, methodology, budget and schedule.
   
• Risk Identification
  Using the risk management plan, determine which risks could affect the project. Risks can be classified as either business risks, involving both gains and losses or insurable risks, involving only losses.
   
• Risk Analysis
  Risks are rated for the likelihood that such events will occur, how they would affect the project objectives, and impact cost, schedule or quality. Moderate-to-high risks are analyzed further to create a quantified list of the probability of occurrence and consequences of each risk.
   
• Response Planning
  Develop a risk response plan and contingency plans for the risks on the quantified list.
   
• Monitoring and Control
  Develop plans for corrective action, etc.

Contact BCE for a Consultation:

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Structural Analysis

Structural Analysis

 

BCE has a full staff of registered Structural Engineers. We design and supply structural supports and access packages for all BCE equipment. In addition, we provide a separate service to perform structural engineering analyses for other equipment. We offer the following structural engineering services:

• Support columns and bracing
• Lifting analysis, including sizing lugs and lifting frames
• Saddle supports and girth channels
• Access packages, including platforms and stair towers
• Wall thickness and stiffener analysis for flat-walled and cylindrical units.

You will receive a complete set of calculations and drawings with any of the aforementioned structural services.

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Remote Monitoring

Remote Monitoring

Thanks to BCE remote monitoring, you no longer need to be physically present at the equipment or the local control panel to monitor the functions, adjust the settings or be alerted to problems. A remote monitoring system uses high-speed transmitters connected to a modem having its own static IP address. Data is transferred to a web-based application and transmitted between computer locations by means of a gateway. BCE remote monitoring system is a particularly attractive option for installations containing multiple units or a large amount of auxiliary equipment.

The following are some of the key benefits you can experience with a BCE remote monitoring system:

• Monitor dozens of baghouses or other pollution control equipment simultaneously.
• Records critical data in real time, such as pressure drop, compressed air pressure, unit temperature, unit pressure (or vacuum), dust emissions, air flow, and pulse on-and-off times. Also records operations of auxiliaries such as dampers, fans and material discharge equipment.
• Data is synchronized with the plant and all remote operators.
• Data is stored as hourly or daily averages and is completely downloadable for a comprehensive operating history.
• Receive alarm e-mail for any malfunction or operation outside of preset parameters.
• Receive service alerts for items requiring regular maintenance.
• Change set points from a remote location.
• If a problem should occur, automatic diagnostics locates the precise unit and item causing the fault.
• Automatically optimizes pulse cleaning, resulting in lower compressed air consumption, long bag life and lower emissions.

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EXPLOSION VENTING

Explosion Venting

 

BCE engineers custom explosion vents to go along with custom systems in order to provide clients with the best protection for their employees and their investments.

Explosion vents are used as a safety device to protect equipment against excessive pressures by means of pressure relief, of which the design and application range are based on NFPA 68 rules.

Explosion vents are typically available in re-usable and non-re-usable models depending on the design constraints.  

Contact BCE to find out how we can design, install or repair your explosion vents and explosion protection systems.

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China invests $56 billion for air pollution control

China announces that they will spend nearly $56 billion by 2015 in order to fight air pollution in major cities throughout China.

"Chinese officials have acknowledged that the thick cocktail of smokestack emissions, vehicle exhaust, dust and aerosols that often fills the air in many cities is a growing concern to increasingly prosperous urban residents"

The air we breathe is just as important as the water we drink, and BCE is here to help you ensure that the air is as clean and safe as possible.


Read the full article

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Environmental Assessment

BCE staff is fully trained and capable of providing you with the appropriate environmental assessments in order to ensure that your project meets local standards and regulations.  BCE believes in offering you the best service possible and can design and engineer a solution to meet or exceed the requirements set forth in the environmental assessment.

An industrial site will inevitably come under the jurisdiction of one or more government agencies charged with ensuring compliance with various environmental regulations. An environmental assessment can be a long-term and complex process. For example, in Nova Scotia, an assessment for a new paper mill or cement plant typically takes 275 days, including 110 days for public hearings. Needless to say, dealing with government regulators and community leaders can be difficult and exasperating.

BCE wants to help. As specialists in air pollution control, we have the expertise to assist you in the environmental assessment process. We offer the following services:

• Stack and ambient emissions testing and sampling
• Dispersion modeling
• Assistance with regulatory applications and obtaining licenses
• Consultation with community leaders
• Environmental audits
• Equipment maintenance and calibration

Also, remember that BCE will custom design pollution control equipment to meet whatever standards exist in your area and according to your job specifications.

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BCE Manufactured Equipment

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BCE designs, manufactures and fabricates dust collection and pollution control system equipment, including spare parts for any installation. Our team of engineers is ready to take on whatever task is set before them in order to keep your air clean and safe.

Please take a look at some of the examples and image galleries here on the website to familiarize yourself with our capabilities and feel free to contact us to for more information.

Dust Collectors

BCE offers full service design, support and supply of dust collectors for most industries. Our expertise has come from years of working with the full spectrum of units from ASME code vessels, to bin vents and cyclones.Discover how we can extend our years of experience of meeting and exceeding the challenges of the pollution control industry to you. Contact us to discuss your needs.

Learn More

We have extensive experience with:

ASME Code Vessels  Pulse-jet  Cartridge Filters  Reverse-air Collectors Shaker Type Dust Collectors

Cyclones High Temperature Collectors Explosive Environment Collectors Pleated Filter Multiclones

BCE Dust Collector Manufacturing

BCE has a wide range of pollution control equipment manufacturing experience.

Our engineers have designed, engineered and manufactured dust collectors, thermal oxidizers, and baghouses for a variety of industries and applications.

Check out our galleries to learn more.

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