Air pollution control systems and components, including fabric filters, fans, heat exchangers and scrubber for cooling, cleaning and moving industrial process exhausts.
| Location: | Fort Lauderdale, Florida - United States  |
| Desc: | BoldEco Environment - Air pollution control solutions Designing and Upgrading Air Pollution Control Equipment Using Modern Analytical Tools Joseph Riley, Managing Director Maurizio Archetti, Technical Director BoldEco Environment, NJ, USA Introduction To those in the market for process equipment, a performance guarantee is probably as important as price. In the case of standardized equipment, it is usually enough to rely on the supplier's experience in order to be satisfied with his ability to achieve a particular level of performance. In the case of a custom engineered system, and especially in more demanding applications, not only must the supplier have had previous experience in a similar application, but he must be able to evaluate the critical design conditions of the particular application in order to properly modify his basic design. In the case of air pollution control systems, it is imperative that not only the company responsible for executing the order have the experience, but that the it also have the experienced staff who can make distinctions about the very important and often overlooked differences between the reference projects and the one at hand. Only with this knowledge can he properly modify his design to achieve the guaranteed level of performance. As pollution regulations become more stringent, the ability to modify a particular base design to meet the stricter levels of emissions becomes harder and harder to do with experience and traditional methods of calculation alone. It is therefore advantageous to implement the latest prediction and calculation tools available in order to achieve a higher degree of certainty of meeting the desired emissions levels and operational requirements. Fabric Filter EGC Evaporative Gas Cooling Baghouse Air Pollution Control BoldEco Eco Group Cement Dedusting Spray Cooling evaporative gas conditioning gas cooling baghouse inlet design pulse jet pulse-jet pulsejet dedusting desox so2 removal wet scrubbing denox sncr ammonia water denox systems www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion Application of modern analytical tools The use of modern analytical tools such as Computation Fluid Dynamics (CFD) or physical modeling for the design of gas collection equipment is not new. Air pollution control companies have used physical modeling for large electrostatic precipitator dust collectors, especially when the pollution control apparatus has to be integrated into the network of ducting as specified by the engineer. The state-of-the-art of flow modeling is such that most gas flow analysis companies that once only offered physical modeling, now offer CFD as an option. This came about as a result of many years of CFD implementation, not only in the high tech industries, such as aerospace and biomedical, but also in the basic industries, such as cement, steel, power, etc. This general acceptance by even the harshest critics means that CFD has become the de-facto standard for modeling gas flows, as well as chemical reactions, capture efficiency, droplet evaporation, gas mixing and other modeling tasks due to its lower cost, speed of results, and ease of model modification. The implementation of CFD technology in many of the components used in air pollution control systems has traditionally been relegated to the simpler modeling tasks, such as spray tower and EP flow distribution, cyclone collection efficiency, gas-gas interaction (such as reactions, and cooling) and fan design. These exercises have traditionally been applied after the installation of the systems when problems have arisen that are at least potentially attributable to problems with a particular flow field. It is rare, with the exception of research and development efforts or the design of standard series equipment, that CFD be used habitually in the design of new, custom engineered electrostatic precipitators, fabric filters, spray towers, scrubbers, and other gas flow treatment apparatus used in air pollution control systems. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion BoldEco philosophy BoldEco made the decision that it would acquire in-house CFD capabilities in order to aid in the design of its own equipment, as well as to improve the operation of competing or related systems, and as part of the consulting services offered to its customer base. BoldEco has invested in the tools required to apply CFD technology to the study of its custom engineered and standard air pollution control equipment. We believe that this capability will provide BoldEco with a decided advantage over its competition, as well as advance the state-of-the-art of various air pollution control technologies. By bringing these advanced tools in-house, we can provide our designers and engineers with the latest technological advancements, thereby ensuring the highest probability of a job well done while maintaining our competitive edge. Equipment design BoldEco uses CFD to optimize the design of various standard and custom equipment designs: - Scrubbers - Fabric filters - EPs - Spray towers - Heat Exchangers The principle of operation of each component is analyzed in depth by our fluid mechanics, and each finding is used to refine the base design. For each project or to solve a particular problem with an existing system, CFD is employed to determine what the flow might look like and is any flow-based corrections are warranted. These solutions are then; either incorporated into the design of the new equipment, or are presented to the client for implementation. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion Examples Some of the more recent cases of implementation of CFD to determine a solution to poor flow field distribution are listed below. Case 1 - Spray Tower This example shows a spray tower before and after modifications. The flow field before modifications is shown to hug one side of the tower, with the other side experiencing a large amount of recirculation. This recirculation is the cause of impingement of water on walls of the spray tower, resulting in incomplete or inconsistent cooling of the gases. Case 2 - Fabric Filter This example shows a fabric filter hopper before and after modifications. The flow field before modifications is biased toward the side opposite the inlet. The installation of ladder vanes shows an optimized flow field, resulting in much better wear and pressure drop characteristics. Case 3 - Duct Cooling This example shows a model of an emergency in-duct cooling system in front of a fabric filter. The model was run to determine the droplet size distribution that would be able to be carried by the gas stream long enough to cause a given temperature drop at the inlet of the collector. Case 4 - Heat Exchanger This example shows a heat exchanger tube where a modification was made to the basic design in order to improve heat exchanger characteristics. Though not shown here, the model shows not only heat transfer, but also pressure drop. Case 5 - Wet Scrubber This example shows a wet scrubber that was modeled in order to determine whether the flow was well distributed throughout. Conclusion Implementation of modern analytical tools, such as CFD technology, not only in research and development or the design of standard equipment, but as an integral part of a system's design, will result in the optimal operation and efficiency of custom engineered air pollution control systems. Not only will the resultant system be better designed, it will be better understood by both the customer and the engineer, and will make any future modifications easier and more efficacious. Retrofitting an Existing Electrostatic Precipitator with Modern Fabric Filter Technology Joseph Riley, Managing Director, BoldEco Environment, NJ, USA www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion Introduction Dedusting systems are installed on cement kilns and clinker coolers for the recovery of process material and to reduce or eliminate dust emissions. The cement and lime industries in general have made valuable contributions to improve ambient air quality in recent years. Electrostatic Precipitators (ESPs), historically regarded as acceptable emission control technology can be found on numerous cement and lime kilns around the world. Many of these systems, however, can experience high dust emissions caused by transitory process conditions, mainly due to the precipitator's inability to respond to the changing conditions of the process or of the gas conditioning system to properly control them. In many cases, it is possible to greatly improve the operation of the ESP by upgrading the evaporative gas conditioning system upstream of the ESP. However, when the existing emission control system is no longer able to achieve the required dust emission levels because of design limitations or increased plant capacity, it is necessary to upgrade or replace it. The most common way to improve the outlet dust emissions is to replace or retrofit the ESP with a properly designed modern fabric filter. However, the importance of proven experience and process knowledge in the application of fabric filters cannot be underestimated. When considering an upgrade or replacement, not only must the ultimate plant efficiency be taken into account, but also the time required for conversion and integration with existing equipment due to short kiln shutdown requirements. Upgrade Design and Project Execution Choosing the right equipment design for the particular application is a critical step in the process of retrofitting a fabric filtration system within the confines of an existing ESP casing. In many cases, the geometry of the system with respect to gas flow distribution, emission efficiency and system maintainability requires sophisticated methods of analysis. For this reason, it is preferable for the supplier to possess in-house experience to carry out the complete execution of the project, from its analysis and design, to its fabrication and erection. It is also important to choose a supplier that has demonstrated success in carefully balancing its proven designs with leading-edge technological advancements in order to achieve maximum efficiency and superior reliability. In the case of a custom engineered system, and especially in the critical application of process gas filtration, where just a few day's down time results in many times the price difference between one supplier and another, not only must the supplier have a proven experience base, but he must also be able to properly evaluate critical design conditions in order to adapt his basic design and product arsenal to the specific project conditions. Let us not forget, however, that it is just as much the personnel, as it is the company, that carries with it the experience of past installations. Therefore, not only is it important to evaluate the company's technology, executive ability and experience list, but also, and this is becoming of increasingly critical importance, the experience of the staff that is charged with the project design and execution. It is the human experience coupled with modern analytical tools, not the company experience alone, that enables efficient modification of a particular base design to meet the stricter levels of emissions. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion Application of modern analytical tools The substantial cost savings from a retrofit make it attractive to re-use the existing equipment as much as possible. However, the physical geometry of the existing equipment also limits the design options and make it difficult to achieve satisfactory performance and reliability using experience and traditional methods of calculation alone. It is therefore advantageous to implement the latest prediction and calculation tools available in order to achieve the lowest possible emissions while satisfying the highest standards of operation. Air pollution control equipment designers have used physical gas flow modeling for many years for the design of complex pollution control systems. The time and expense required to carry out these models, however, have made its implementation in the fast-paced, competitive field of ESP to fabric filter conversions impractical. Numerical simulation methods, such as Computational Fluid Dynamics (CFD), have traditionally been applied only after a system has exhibited operational problems after commissioning. Due to its relatively low-cost and speed of implementation on fast, inexpensive PC platforms, however, the implementation of CFD technology has been adopted as the only practical means of predicting the performance of a particular retrofit design. It is thus advantageous to invest modern CFD technology as it gives designs based on its successful result a decided advantage over competitive designs based on more traditional approaches. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion Example Project BoldEco recently completed a project for Ciments Vicat that implemented CFD analysis in the design of an ESP to fabric filter conversion. First, however, as in all retrofit projects it was important to determine what equipment was reusable, and what portion of the ESP casing needed replacement. It is necessary at the beginning of these projects to analyze the condition of the metallic parts of the ESP in order to determine the cut lines on the casing upon which the newly designed fabric filter will sit. Most often, the choice is between placing a new fabric filter plenum on the existing casing, or to install an entirely new casing and plenum on top of the existing hoppers. This is often decided by the level of corrosion on the casing, though many times the determining factor is the desired operational flexibility, which is more easily achieved by the installation of a new casing. Another factor in the determination of reutilizing the old versus replacing it with a new one is the configuration of the hoppers. Normally, if the casing is in good shape, an ESP with a trough hopper configuration will more easily accept field fitted design modifications than one with pyramidal hoppers. This is a crucial step. If not carefully analyzed and executed, this modification can spell disaster for the operation of the new filter. Once the approach is properly identified, the proposed design is put through a complete and thorough geometric analysis, taking into account desired characteristics for the specific process conditions. Points to be analyzed are the bag cross-sectional area and the height of the casing, which, together with the desired can velocity determine the volume available for the filtration media, and thus the filtration velocity. Once it is determined that the geometric constraints do not effectively limit the performance of the filter, the filtration elements are arranged in the optimum configuration and the filter is analyzed for performance by way of CFD. The performance of the design is analyzed in depth by competent fluid mechanics, and each finding is used to refine the base design. For each project or to solve a particular problem with an existing system, CFD is employed to determine what the flow might look like and if any correction is warranted.. After the design analysis and all of the subsequent variations and revisions have been studied, the final potential candidate designs are rigorously scrutinized for potential construction and installation difficulties. Finally, an optimized approach is chosen, and the design is ready for physical execution. The final solution is then presented to the client for approval. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion Conclusion Implementation of modern analytical tools, such as CFD technology, not only in research and development or the design of standard equipment, but as an integral step in the execution of a retrofit project will result in optimal operation and efficiency. Not only will the resultant system be better designed, it will be better understood by both the customer and the engineer, and will make any future modifications easier and more efficacious. Evaporative Gas Conditioning Systems State-of-the-Art Technology to the Rescue Joseph Riley Maurizio Archetti BoldEco Environment / Eco SprayTech Hillsborough, NJ, USA A competent consideration of the essential Evaporative Gas Conditioning system operational factors is required to achieve optimum performance under all operating conditions and process variations, not merely at the specified process conditions, and will avoid the necessity of revisiting the legalese of the contract documentation. Computational Fluid Dynamics is the tool that, when used properly at the hands of a competent technician, can cost-effectively analyze all the scenarios that are likely to cause problems and provide reliable performance. Introduction The cement industry is not unlike any other modern industrial sector, where the pressures to maintain a competitive position demand a careful analysis of all capital improvement purchases, and where those that are most likely to affect production receive the closest scrutiny. It is also precisely at this stage that an analysis emphasizing initial equipment price can at once defeat internal production goals and exceed operational costs, thus transforming this seemingly "smart-buy" into a "penny-wise and pound-foolish" loser. In order to avoid this scenario, two things are normally generated prior to the purchase of a capital improvement project: - Detailed specifications - Total cost of ownership analysis Unfortunately, during the budgeting stage of many fast-track projects (and most today seem to be blessed with this characteristic), many of the costs and schedules are under-estimated, only to be discovered during the execution stage that the project is over budget and behind schedule. It is here where desperate attempts will be made at rescuing it from these afflictions - and exactly why the lowest equipment price Kool-aid is so eagerly swallowed. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion Standard vs. custom-engineered In the case of standard equipment, it normally suffices to rely on the appropriate specification and good sense to ensure a satisfactory level of performance. In the case of custom-engineered equipment, however, the result in not that easily achieved. This is because most equipment suppliers modify a "standard" design, "customizing" it for the specified engineered application according to accepted traditional design practices. Due to the complexity of the process variations, however, a traditional approach is only capable of taking into account a few possible variations, limiting the operational flexibility of the equipment to the "normal" or "design" conditions rather to what is required by the full spectrum of the process, resulting in operation that is less than satisfactory at the plant level. Evaporative gas conditioning This is certainly the case with Evaporative Gas Conditioning (EGC) technology, a field that utilizes highly specialized equipment subjected to operational ranges that are difficult to thoroughly quantify and where individual companies with a complete spectrum of process experience are a rarity. EGC is a gas cooling technique wherein the heat present in a gas is itself used to evaporate finely atomized water injected into its flow field. Through the process of evaporation, heat energy in the gases is used up when the water droplets are converted to steam, resulting in a gas that is lower in temperature, but also higher in humidity. It is a cost-effective method of lowering the temperature of a hot gas that, for a defined period of time at least, recovery of its heat content is of little value, such as when the gases normally utilized for drying and fluidizing the limestone are not needed as the raw mill is down for weekly maintenance. During this period, the gases are bypassed around the raw mill, and cooled in a Gas Conditioning Tower (GCT) where the atomized water is injected. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion New or used, it's all the same It may appear a simple task to spray a few drops of water in a GCT, but in reality, if it were so easy, there wouldn't be so many poorly functioning GCTs. Designing a modern EGC system, as simple as it may seem, is a sophisticated process that must result in a system that is: - Responsive to changing process conditions - Maintenance friendly - Energy efficient - Cost-effective and, most importantly, - That works! To make matters all the more difficult, poorly functioning GCTs that serve as evaporation chambers for existing high-pressure water EGC systems, although blessed with long theoretical gas residence times, end up working just as poorly after being retrofitted with new dual-fluid sprays and controls due to their poor gas distribution characteristics. Which leads us to the most important of all aspects of an EGC system - the gas flow distribution. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion The role of modern analytical tools The reality is that stringent emissions requirements of today, coupled with the need for energy-efficient and cost-effective designs, make it an increasingly complex task to meet performance requirements through experience and traditional methods of calculation alone. This is especially true for equipment that has a fixed geometry, but must provide a predictable level of performance under varying process conditions. In a cement environment, examples of such equipment are preheater cyclones, alkali bypass mixing chambers, main dust collectors, and GCTs. If not properly designed to handle the full range of operating conditions, operating too far beyond the specified design boundaries can have disastrous consequences. Computational Fluid Dynamics (CFD) is exactly the tool that has provided the means for surpassing the traditional methods of predicting performance in these cases. CFD is a modern analytical modeling technique that utilizes advanced algorithms to predict the flow field in a given static or dynamic condition. The calculation process iterative, made up of millions of floating point calculations. In the past, technology was such that an expensive computing workstation capable of millions of floating point calculations per second was required in order to create a useful 3-dimensional model and to execute a run, thus generating a useful 3-D report. Thus, the implementation of CFD technology in many of the components used in air pollution control systems has traditionally been relegated to the simpler modeling tasks, such as spray tower or ESP flow distribution and cyclone collection efficiency. These exercises have traditionally been applied after installation when it is suspected that certain flow field conditions may be causing performance problems after the initial equipment design and installation. It is rare, with the exception of research and development efforts or the design of standard series equipment, that CFD be used habitually in the design of new, custom engineered electrostatic precipitators, fabric filters, spray towers, scrubbers, and other gas flow treatment apparatus used in air pollution control systems. Fortunately, advances in modern analytical tools have made it possible to achieve the desired high degree of operational performance without a major impact to the competitiveness of relatively low-cost and low-tech equipment, such as cyclones, ductwork and spray chambers. With the advent of more modern CFD programs now capable of running on a standard PC platform, models can be generated that are just as detailed and realistic as those that just a few years ago required the use of super-computers. In the past, small-scale models have been used by fluid mechanics to optimize gas handling and separation equipment during the design stage, but this method is costly and time-consuming. Its great cost and time requirement can be justified when considering one single application unless the cost of the equipment is great, the design and production time allows it, and the consequences of a design flaw are great. Thus, air pollution control companies have used physical modeling for large electrostatic precipitator dust collectors, for example, especially when the pollution control apparatus has to be integrated into the network of ducting as specified by the engineer, and where the potential of liquidated damages is great, such as in a power plant application. It is difficult, however to justify it in those cases where the equipment cost is relatively low and the industry has already acquiesced as a whole and accepted the consequences of basic design flaws as problems that need to be lived with. Nowhere is this truer than in the case of a spray tower in a cement application. The universal acceptance of CFD as a technically valid prediction model however, has brought a much needed analytical tool within the reach of budget-conscious designers, and has begun to impact the expectation levels of the technically savvy cement manufacturer. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion As a result of the many successful outcomes, not only in such high tech industries as aerospace and biomedical, but also in the basic industrial sectors of cement and steel, gas flow modeling houses that once only offered physical modeling, now offer CFD as an option. This general acceptance of CFD has made it the de-facto standard for modeling gas flows, and provides additional modeling parameters that are not available in simple mechanical models. These parameters include chemical reactions, capture efficiencies, temperature profiles, droplet evaporation and gas mixing, among others. Coupled with the ability to rapidly make changes to a model's input process conditions, CFD has become an essential design tool, thus providing a much more accurate predictive model that are easily modifiable, and at a lower cost and in a shorter time frame. A unique philosophy A few years ago, when it became clear that the technology was mature enough to be reliable and affordable, BoldEco Environment made the decision that it would acquire in-house CFD capabilities of its own. This decision was reached as a result of one particular customer's request for an in-depth study of several ESP to Fabric Filter conversions it was planning on carrying out. CFD was found to be such an invaluable tool in those projects and we discovered fallacies in many of the accepted fabric filter inlet design practices that we decided to apply it to all of our projects, including all of our Evaporative Gas Conditioning (EGC) systems. Prior to this, we were utilizing traditionally accepted design practices, an approach that was effective the majority of the time and was generally effective. CFD, however, in the hands of a team of skilled technicians, has been vital in convincing the end user exactly where the problems lie, thus resulting in a savings in both time and money. This capability as allowed us to advance the state-of-the-art of various air pollution control technologies, including EGC. Already, it has resulted in the development of new and innovative technologies, such as the OptiVap nozzle, which is 30% more efficient than the best-known designs on the market and which is immune to over-driving (condition when water pressure supercedes the air pressure at the nozzle), a known cause of unevaporated water conditions in a GCT. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion CFD-aided equipment design BoldEco utilizes CFD to optimize the design of the main standard components for each custom-designed system at the initial stages of the engineering phase of a project. The systems that have been already designed utilizing CFD include Wet and Dry Scrubbers (particulate and SO2), Pulse Jet Fabric Filters (low-pressure, medium-pressure and traditional high-pressure), ESP-to-FF Conversions, Gas Conditioning Towers and Air-to-Air Heat Exchangers. Various scenario models are generated and the flow fields analyzed in depth by our fluid mechanics. Each new finding is used to refine the base design of the system component. For each new project or to solve a particular problem with an existing system, CFD is employed to determine what the flow fields might look like at various operating conditions and if any flow or process-based correction is warranted. Case Histories BoldEco has carried out several CFDs for various end users and OEMs, spanning several industrial sectors. In all of these cases, an improperly functioning EGC system was analyzed and a solution presented. Some of the more recent cases of implementation of CFD to determine a solution to poor flow field distribution are listed below. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion Case History 1 - New GCT Against the recommendations of the supplier, a brand new GCT was designed with a slanted inlet duct and close-coupled to the GCT inlet. This inlet duct design resulted in a skewed flow field at the inlet cross section of the tower that was too poorly distributed for the standard inlet straight section design to accommodate. This resulted in wet material falling from the walls of the tower down into the hopper below, or in water running out from the hopper screw conveyor airlock. It thus became imperative to define the flow field in the GCT. Without knowledge of the gas distribution, it would be very difficult to devise an effective way of correcting any existing gas distribution problem upstream of the water injection location. The CFD identified the cause of the difficulties. Analysis of the flow field in the GCT inlet showed the high-velocity gases to remain on one side of the tower instead of being distributed evenly across the entire cross-section of the GCT. This caused a region of gas recirculation in the inlet cone of the GCT, which caused the water injected in those locations to impinge on the walls of the GCT. The region that became wet with water also became a point of impact for the dust penetrating the top cyclones of the preheater tower, causing it to become a sort of mud that broke off intermittently and fell into the hopper below. Although this is a common occurrence in the operation of numerous GCTs around the world, this particular problem was not a usual case as it occurred under virtually all operating conditions rather than just during transitory periods of switching from bypass operation to direct operation (mill on to mill off) and vice versa just during mill off operation. In this case, the flow field exhibited the recirculation phenomenon under most operating conditions, resulting in incomplete or inconsistent cooling of the gases. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion The preferred solution was to have a pipe grid that could be removed for cleaning, should the need arise. Several attempts were made to place the pipe grid in the CFD model directly above the spray elevation, but the energy of the gases was so high that the flow field was very unstable at various gas flow rates. The CFD models showed that, despite the pipe diameter, the pipe spacing or the pipe grid location, at different gas velocity conditions, the flow field either maintained its original impetus, or it was completely blocked by the pipe grid, thus rendering that solution impracticable. After various attempts, BoldEco devised a novel solution, placing a diagonal pipe grid in the high velocity section of the inlet duct that acted as a set of straightening vanes. A second set of pipes was installed directly beneath the diagonal pipe grid, this time in a horizontal arrangement, which acted as a secondary flow distribution device, thus providing a stable and predictable flow field at the inlet of the GCT. This solution was implemented and the GCT was found to perform according to design. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion Case History 2 - Old Design Cement GCT A cement plant OEM wanted to utilize an old GCT design from the 1970's, originally designed to be used with high pressure water sprays, except fitted with a more modern air atomized spray system. The idea was to save on the engineering required for a new GCT design by simply installing the new system, but, despite its large dimensions and correspondingly long gas residence time, this particular design had notoriously poor gas distribution characteristics. Similarly designed GCTs had been retrofitted with air atomized systems before, and, although the installation of the replacement spray system provided much improved reliability over the original high-pressure design, the GCT was still plagued with unreliable operating service due to the poor inlet distribution. It thus was decided to install a gas distribution device at the inlet that would provide a high degree of re-distribution of the inlet flow field in order to make the operation of the GCT more dependable. Without the correct distribution characteristics, the resultant poor gas distribution would prevent the injected water to only partially evaporate, a condition that leads to problems with the hopper material transport system. A series of CFD models were run and the unmodified flow field defined. Analysis of the flow characteristics at the GCT inlet showed the classic pattern of gas recirculation in the inlet cone of the GCT, and the resultant impingement on the walls of the GCT. Another set of CFD models was created utilizing the original GCT design, this time with distribution devices with different open areas, one with 40% open area, one with 50% open area and another with 60% open area. The models generated showed that there was no distribution device that provided a perfect gas flow distribution at all flow rates, but it did allow us to find the open area that provided the best possible distribution characteristics at all flow conditions. This solution presented to the customer for approval. The GCT has been functioning as planned, showing no signs of gas-related operational difficulties. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion Conclusion Implementation of modern analytical tools, such as CFD technology, not just in research and development or the design of production-run components, but as an integral part of the design phase at the beginning of a custom-engineered project, will result in the optimal operation and efficiency of custom engineered systems. Not only will the design of the system be much improved over previous, traditional methods, but its performance and limitations will be better understood by all involved with the project, thus allowing process designers and operators alike greater flexibility in defining production-oriented process parameters and operational limits for the entire plant. www.boldeco.com fabric filters dust collector ESP pulsejet conversion baghouse spray evaporative cooling gas conditioning spraying system dual-fluid air atomized nozzle gas flow CFD process analysis heat exchanger air-to-air gas cleaning filtration so2 so3 h2so4 caco3 ca(oh)2 gaseous dry scrubber wet venturi turnkey smokestack nuisance pjff pulse jet pulsejet pulse-jet self-cleaning non-fouling industrial utility centrifugal custom fan axial materials handling pulse timer pulse controller sequencer vento automatic voltage controller AVC rigid discharge electrode bha elex reverse air sub-micron submicron sub micron small particle size aerosol BoldEco Environment Eco Spray Tech Eco Environment Ecology low-energy nozzle dual-fluid air-atomized LEC limestone scrubber emission control CFB circulating fluid bed TFB turbulent fluid bed desox scrubbing denox SNCR selective non-catalytic reduction NOx removal particulate ammonia catalyst bed poor combustion |
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| Tags: | Advanced - Fabric Filters - Esp - Pulsejet Conversions - Baghouse - Spray Cooling - Evaporative Cooling - Gas Conditioning - Gas Cooling - Spraying Systems - Nozzles - Cfd - Computational Fluid Dynamics - Gas Cleaning - Air Filtration - Dry Scrubbers - Wet Scrubbers - Venturi Scrubbers - Pjff - Pulsejet Pulse Jet - Industrial Fans - Materials Handling - Fabric Filter Controllers - Vento - Bha |
