Design and Upgrade - Air Pollution Control

8/7/2019 Design and Upgrade - Air Pollution Control

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Designing and Upgrading Air Pollution Control Equipment Using

Modern Analytical Tools

Joseph Riley, Managing Director

Maurizio Archetti, Technical Director

BoldEco Environment, Skillman 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 suppliers 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 airpollution 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.

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 aresult 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.


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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 theexception 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.

BoldEco Environment philosophy

BoldEco Environment 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 Environment has invested in the tools required to apply CFDtechnology to the study of its custom engineered and standard air pollution control

equipment. We believe that this capability will provide BoldEco Environment 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 Environment 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 tosolve 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.


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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.

Figure 1a Side view of gas conditioning tower before modification


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Figure 1b - Velocity through modified design showing stabilized flow


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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.

Figure 2a - Velocity through existinghopper design showing uneven flow

Figure 2b - Velocity through modifiedhopper design showing stabilized flow


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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.

Figure 3a Velocity profile enabled us to calculate droplet transport velocity

Figure 3b Emergency sprays are modeled to show cooling effect


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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.

Figure 4a - Velocity contour through the HE tube

Figure 4b The new temperature profile is much improved due to modification


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Case 5 Wet Scrubber

This example shows a wet scrubber that was modeled in order to determine whether the

flow was well distributed throughout.

Figure 5 a/b Scrubber element layout and velocity through collection elements

Figure 5 c/d Flow through scrubber elements and into separator tank


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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

systems 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.

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Design and Upgrade - Air Pollution Control