Gas Flow Systems

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The Littoral Combat Ship (LCS) concept boat was studied for the U.S. Navy.  The LCS is intended to operate in coastal areas of the globe, and the ship will be fast, highly maneuverable, and geared to support mine detection/elimination, anti-submarine warfare, and surface warfare, particularly against small surface craft.

Alden performed a 1:5 scale physical model study for the air intake and the uptake for one of the 2 gas turbine enclosures.  The main objectives of the model study were to provide velocity distributions and pressure loss data within the intake, uptake, and enclosure as well as the mixing of the enclosure cooling air with the turbine exhaust gas and the exhaust plume flow characteristics.

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{id=18271797071, createdAt=1571226251837, path='train-station-ventilation-system-design', name='Train Station Ventilation System Design | Alden Lab Projects', 32='{type=number, value=40}', 1='{type=string, value=Train Station Ventilation System Design}', 2='{type=list, value=[{id=12, name='Municipal', order=9}]}', 34='{type=number, value=0}', 3='{type=list, value=[{id=16, name='Gas Flow', order=18}, {id=19, name='Ventilation', order=21}]}', 4='{type=list, value=[{id=4, name='Numerical Modeling', order=1}]}', 5='{type=string, value=

Background

The South Station Transportation Center (SSTC), located in Boston, Massachusetts, consists of a train terminal, regional bus terminal, and a public parking garage. Currently the bus terminal and parking garage are located above the south portion of the train platforms. The section of the tracks and platforms between the north end of the SSTC and the head house, which ranges in length from about 365 to 525 feet, is currently uncovered and open to the atmosphere.

The Boston South Station Project proposed to build high rise structures and to expand the bus terminal over the existing platform areas of South Station. In effect, the development will fully enclose the station tracks and platforms with the exception of the south “portal” area and the east edge of the development along Track 13.

Work Performed

Three locomotive/track arrangements were modeled to provide a representation of the “worst case” conditions with respect to the collection of the main and HEP engine diesel exhausts and cooling fan flows.

The efficacy of multiple exhaust hoods were evaluated to meet target health and safety standards while trains were parked at idle at the head end of the tracks. Specifically, the analyses were performed to ensure that the proposed track exhaust and general ventilation systems were able to maintain safe levels of train engine emissions concentrations and ambient air temperature while the trains were parked and idling in the station.

Project Evolution

• 1990 Alden initially provided the design for track exhaust hoods to remove diesel products from the ventilation systems to achieve safe levels. Design work was proved out through the use of physical scale modeling, chosen for its cost effectiveness
• 2005-2008 Alden provided the initial ventilation design for the high rise overbuild construction project
• 2017-2018 Following the reboot of the projct, Alden evaluated multiple scenarios to develop and finalize a robust ventilation system that could handle a variety of station situations.

Visualization of the Computational Model [below] shows the transient locomotive through station to show thermal and pollutant capture.

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Discover More

South Station Air Rights Project

What to know about the big South Station tower project — and how it will affect your commute [boston.com]

}', 30='{type=string, value=Read how CFD modeling was used to show compliance with specifications and code requirements for a major New England rail station.}'}

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An existing roof vent arrangement was allowing rainwater to enter the Pot Room. Alden supported efforts to develop a roof vent geometry to eliminate the intrusion of rain water. The purpose of the CFD study was to ensure that the roof vent modification did not increase pot room temperature levels beyond specified limits for workers in the plant.

To evaluate the existing and proposed Pot Room arrangements, thermal and fluid flow profiles in the immediate vicinity of the pots were determined based on air flows through the plant floor and wall mounted vents. The detailed CFD model was developed from plant drawings to include all major basement, pot room and roof venting geometries. The surrounding ambient environment was included with quiescent atmospheric conditions and average ambient temperature. Thermal losses form the pots to the pot room air and from the pot room to the environment were included in the analysis. The results of the CFD modeling showed that the proposed modification to the roof venting arrangement was acceptable and would not increase the temperature in the worker-occupied spaces by more than 2 degrees F.

}', 9='{type=image, value=Image{width=null, height=null, url='https://www.aldenlab.com/hubfs/Projects/Smelter-Pot-Room/Smelter-Pot-Room-Diagram.jpg'}}', 10='{type=string, value=Thermal and fluid flow profiles were evaluated for both existing and proposed venting arrangements}', 11='{type=image, value=Image{width=null, height=null, url='https://www.aldenlab.com/hubfs/Projects/Smelter-Pot-Room/Smelter-Pot-Room-Temperature-CFD.jpg'}}', 12='{type=string, value=Heat transfer from the pots to the air passing through the pot room were evaluated}', 13='{type=image, value=Image{width=null, height=null, url='https://www.aldenlab.com/hubfs/Projects/Smelter-Pot-Room/Smelter-Pot-Room-Ventilation-CFD.jpg'}}', 14='{type=string, value=CFD confirmed the efficacy of the modified roof vent system to maintain safe temperatures.}', 26='{type=number, value=0}', 30='{type=string, value=Read how a CFD study ensured that a roof vent modification did not increase pot room temperature levels beyond safe levels}'}

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A streamlined modeling approach reduced both cost and time to achieve an optimized design solution.

Williams Station Unit 1 is a 610 MW coal fired station owned by South Carolina Electric & Gas (SCE&G). The plant installed a new wet flue gas desulphurization (WFGD) system, which removes SO2 entrained in the flue gas stream. The approach of the physical flow model study was to minimize the potential for liquid pullback into the absorber inlet ducts by improving the gas flow distributions into the absorber. A parallel CFD model study was performed to optimize the spray nozzle locations and spray types to reduce high gas velocity zones and create a uniform even spray coverage across the absorber vessel to optimize SO2 removal.

Computational fluid dynamic (CFD) and scaled physical models of the planned WFGD system used velocity inlet profiles based on field data to provide better accuracy of the simulations. Modifications to the inlet ductwork and within the WFGD were made to improve the gas flow and SO2 removal efficiency. The CFD model was also used to design and optimize the spray nozzle grid and wall rings while the physical model minimized the potential for liquid pullback into the inlet ducting with designs to the inlet awning. The results of the study provided flow controls and a spray nozzle injection grid design to minimize liquid pullback while providing uniform spray coverage, which is necessary to optimize SO2 removal.

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When an SDA unit that was showing signs of improper droplet evaporation, CFD modeling was used to predict spray and deposition patterns in an SDA reactor in order to develop a solution to improve droplet evaporation.

Background

Spray Dryer Absorbers (SDAs) are designed to remove acid gases, mainly sulfur dioxide (SO2), from flue gas streams. Atomizers are used to inject droplets of lime slurry into the SDA reaction chamber, which then evaporate and react with the sulfur dioxide in the flue gas to form calcium sulfate, a solid powder that is typically captured in a fabric filter (or baghouse). Proper evaporation of the injected slurry is critical to the performance of SDA units. When the droplets do not evaporate, the system can have decreased removal performance, exhibit deposition on the walls, and cause droplet carryover into the outlet ductwork, which can then create issues with fabric filter operation.

Work Performed

A Computational Fluid Dynamic (CFD) model of the SDA reactor was used to simulate the gas and droplet flow patterns, droplet evaporation, and wall wetting due to droplet deposition. The model was validated using temperature and moisture content field data, as well as by the comparison of the predicted wall wetting to field photographs of deposition. The model predictions were incredibly accurate and provided a unique insight into the spray patterns within the reactor. Using this information, modifications to the reactor swirl vanes and outlet hood design were made to improve evaporation and mitigate wall wetting.

Results

The new reactor modifications were implemented in the field. The client has happily reported improved SDA removal performance, the elimination of deposits on the walls, no fabric filter bag wetting, and reduced operating pressure loss—all of which result in reduced SDA operating costs.

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Clay Boswell Energy Center Unit 4 is a coal fired station owned by Minnesota Power. The plant had a need to reduce flue gas temperatures upstream of their NID emissions control system for removing SO2 from the flue gas stream—while the plant remained online. This created a design limitation for the injection system since the nozzles would have to fit through the duct ports, and the lances would only be supported by the duct penetration, not internally.

Our engineers calculated the quench water requirements to achieve the desired gas temperature cooling and then selected candidate spray nozzles for the system. The sulfuric acid dewpoint temperature was also calculated for design considerations. Remaining above the acid dewpoint is important to avoid corrosion of the ductwork. Then a computational fluid dynamic (CFD) model of the scope of ductwork was created, and prepared using inlet boundary conditions representative of the plant flue gas profiles. Based on the desired gas flow pattern for optimal spray injection, required residence time for evaporation, and access in the field to the ductwork for lance installation and quench system piping, a location for the quench system was selected. The candidate spray nozzle injection characteristics, such as droplet size distribution, spray pattern, and droplet velocity, were input into the model and used to evaluate various nozzle arrangements. The final arrangement provided the target gas temperature reduction, within the desired uniformity, and minimized wetting of surfaces.

ALDEN worked closely with plant personnel to design a quench system that could be installed while the plant remained online · ALDEN used CFD modeling to simulate numerous quench spray nozzles types and arrangements to determine the best option · ALDEN designed a cost-effective functional design for the quench system

}', 26='{type=number, value=0}', 30='{type=string, value=Read how Alden used prior experience with spray header system design, as well as CFD simulations to evaluate various quench system designs for a coal fired power station.}'}

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Shiller Station, a 150 MW coal and oil fired station owned by Public Service Company of New Hampshire, was experiencing high bag wear in their fabric filter (FF) unit that was causing unscheduled outages for repair. Using computational fluid dynamic (CFD) modeling to simulate the ash laden gas flow through the fabric filter system, causes of the bag wear were identified, and modifications were developed to stop the issue. The plant has installed the recommended flow controls, and have reported that not only is the bag wear issue resolved, they also gained over 1-inwg of pressure savings from the modifications.

Work Performed

Using a CFD model of the complete fabric filter system, including connecting ductwork, inlet and outlet manifolds, and each FF compartment with bags, the cause of the high bag wear rate was identified—poor gas flow distributions in the inlet manifold and entering each compartment. Modifications were developed to create more uniform gas velocities through the inlet ductwork and entering each compartment, and to reduce the gas velocity magnitude impacting the bags. The final design created smooth flow throughout the connecting ductwork and manifolds. The design also eliminated the high velocity jets that were impinging on the bags.

Results

The plant has reported that they are no longer experiencing premature bag wear and ash deposition in the ductwork has been minimized. As a result of this modification, the plant also reported a gain of over 1-inwg due to the pressure loss savings.

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Our team and Air Consulting Associates (ACA) were was contracted by Southern Environmental Inc. (SEI) for the planned Electrostatic Precipitator (ESP) upgrades for a large US utility. Our team performed the upfront physical flow model studies while ACA proivded technical support throughout the entire project.

An ESP operates by electrically charging ash particles in the fluegas and then attracting the charged particles onto collecting plates which are then rapped to send the ash to the hoppers where it can safely be removed from the system. For optimum system operation, the distribution of the gas velocity must be very uniform entering the ESP to maximize the collection efficiency of the ESP and to minimized particulate emissions. Upstream duct fallout of ash particles and the flue gas distribution into the ID fans are also important components of ESP operation that must be considered to inhibit premature outages.

Work Performed

Physical flow modeling techniques were used to develop and optimize duct and ESP flow controls and ash handling devices to achieve best performance targets for ash removal. The connecting ductwork from the existing air preheaters to the rebuilt ESPs were also included in the studies to provide flow controls designs to optimize air preheater performance. The model simulated the field gas velocities, pressure losses, and ash particulate transport and removal.

Results

Not only did we design a cost-effective design for the flow controls and perforated plates to provide optimal ash removal, our recommended design achieved the ICAC EP-7 targets for uniformity of flue gas velocities at the inlets to the first collecting fields and at the outlets of the last collecting fields to maximize particulate removal efficiency

Each of the three units passed their respective performance test guarantees after the recommendations from the physical flow model had been implemented.

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Alden simulated the planned Kansas City Power and Light Iatan Unit 2 (POWER Magazine’s 2011 plant of the year) Selective Catalytic Reduction Systems (SCR) to maximize the NOx removal efficiency. An SCR operates by injecting a reagent, typically ammonia (NH3), into the flue gas stream, and then catalyzing a reaction to convert the NO2 and NO3 into nitrogen and water. For optimum system operation, the distribution of the NOx, reactant, gas velocity, and temperature must be very uniform entering the catalyst to maximize the reaction and prolong catalyst life. Upstream collection of large particle ash (LPA), and the distribution of fine ash at the inlet face of the first catalyst are also important components of SCR operation that must be considered to inhibit premature outages caused by pluggage.

Work Performed

Physical and computational flow modeling techniques were used to develop and optimize duct and SCR flow controls, ammonia injection grid, mixing devices, and ash handling devices to achieve best performance targets for NOx removal. The new connecting ductwork from the retrofit SCR to the existing air preheaters was also included in the study to provide flow controls designs to optimize air preheater performance. The models simulated the field gas velocities, temperatures, pressure losses, NOx concentrations, NH3 injections, and ash particulate transport and removal.

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Marsulex Environmental Technologies (MET) contracted Alden to re-engineer a heat recovery system for flue gas reheat at Great River Energy Coal Creek Generating Station. The goal of the system was to ensure that no condensation would be present in the flue gas system as it enters the stack and vents to ambient conditions. The reheat was provided through the use of multiple available heat sources within the existing facility. A Computational Fluid Dynamics (CFD) Model Study was also peformed to simulate the operation of the system.

With the available heat from various locations in the plant analyzed, our flow experts designed the final system to remove ambient air from the boiler house and to heat that air through contact with the economizer ductwork prior to the re-heat fans. Two separate CFD models—that included convective and radiative heat transfer—were then used for final evaluation of the design. The first model included the Reheat Air System and Wet Flue Gas Desulfurization inlet ductwork. The second model was for the reheat ducting and mixing chamber, in which the reheated air mixed with the flue gas.

CFD results showed that the project goals for pressure drop, temperature rise, and mixing of ambient air with flue gas were all met.

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Clay Boswell Station Unit 4, a 535 MW coal fired station owned by Minnesota Power, planned to retrofit a new SO2 removal system, and needed design through flow modeling to ensure successful operation of the system. Alden used a scaled physical flow model to simulate coal ash deposition in the connecting ductwork and distribution manifold of the planned emissions control system. A modification to the manifold ductwork and new internal flow controls were developed to mitigate areas of ash piling. The plant installed the recommended flow controls and has experienced no major ash piling.

Work Performed

Alden developed a scaled physical model of the planned emissions control system and associated ductwork. The model used velocity inlet profiles based on field data to improve the accuracy of simulations. Initial tests identified one area in particular where high levels of ash deposition were observed in the distribution manifold. Duct modifications and flow control designs were investigated to mitigate the deposition. The final design eliminated the ash deposition.

Results

After several months of operation with the recommendations implemented, plant personnel conducted a walkdown of the system and confirmed that the ductwork and distribution manifold were free of ash piling.

Project Highlights

• The testing simulated ash transport and deposition in a scaled cold flow model
• A cost-effective design for the DFGD inlet ducting system was provided
• Plant feedback after operation confirmed the recommendations were effective

}', 9='{type=image, value=Image{width=1200, height=348, url='https://www.aldenlab.com/hubfs/Projects/Duct-Dust-Elimination/Duct%20Dust%20Elimination-1.jpg'}}', 10='{type=string, value=A streamlined approach to the modeling process reduced both cost and time to achieve an optimized design solution}', 11='{type=image, value=Image{width=953, height=714, url='https://www.aldenlab.com/hubfs/Projects/Duct%20Dust%20Elimination/Model-Prediction-Ash-Piling.jpg'}}', 12='{type=string, value=Model prediction of ash piling}', 13='{type=image, value=Image{width=1369, height=766, url='https://www.aldenlab.com/hubfs/Projects/Duct%20Dust%20Elimination/Field-inspection-no-ash.jpg'}}', 14='{type=string, value=Field inspection observes no ash piling in system}', 26='{type=number, value=0}', 30='{type=string, value=Read how scaled physical flow modeling helped eliminate coal ash deposition at a power plant in Minnesota}'}

{id=52046388785, createdAt=1627930130486, updatedAt=1627931745911, path='hrsg-flow-control-design', name='Heat Recovery Steam Generator Flow Control Design', 32='{type=number, value=16}', 1='{type=string, value=Heat Recovery Steam Generator (HRSG) Flow Control Design}', 2='{type=list, value=[{id=18, name='Oil & Gas', order=12}]}', 34='{type=number, value=0}', 3='{type=list, value=[{id=16, name='Gas Flow', order=18}, {id=23, name='Process Engineering', order=25}]}', 4='{type=list, value=[{id=4, name='Numerical Modeling', order=1}]}', 5='{type=string, value=

A Heat Recovery Steam Generator (HRSG) had suspected flow deficiencies which was causing suboptimal performance of the unit. Alden was contacted to use CFD to conduct an evaluation of the unit and design flow controls to improve its steam generation.

To complete this evaluation, Alden developed a baseline CFD model of the HRSG from the turbine outlet to the tube bank inlet to understand how the flow develops in this section. An area of recirculation and the reasons it developed were identified. A set of flow controls was designed to address the recirculating gas. Alden worked with the client to ensure that the flow controls were both effective and practical to construct and install into the existing system.

Results

Using the drawings provided, the oil & gas plant constructed and implemented the flow controls designed by Alden. Subsequently, the plant saw a 17% improvement in steam generation when the unit was tested with the new flow controls

Project Highlights

• CFD model identified flow inefficiency
• Flow controls were iteratively designed with input from the clients
• Steam generation increased 17% after implementation of the flow controls

 

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