Computational Fluid Dynamics (CFD)

The operation of industrial combustion equipment has always constituted the proverbial “black box” for engineers because of the difficulties associated with observing and measuring high temperature combustion phenomena. CFD is the key to unlocking this “black box”. CFD simulations constitute a virtual test bench on which design problems can be diagnosed, current designs can be optimized, and new designs can be developed.

A CFD analysis involves the following steps: building a 3D CAD model of the equipment, selecting the pertinent physical models and boundary conditions, and discretizing (meshing) of the geometry. The CFD solution would typically include a detailed 3D map of the flow velocity, pressure, temperature, chemical concentrations and other relevant parameters at any position inside the model. Once the solution is obtained via an iterative calculation procedure, its analysis and interpretation allows the user to gain very useful insight into the problem being investigated. CFD can be used to simulate equipment under various operating conditions in order to predict and understand its behaviour.

With BMA's combustion expertise, CFD simulations are enhanced with customized in-house combustion models for simulating the combustion of many different types of fuels. This type of specialized CFD analysis provides additional information on flame contours, CO and NOx concentrations, and heat flux patterns in the client’s boiler or furnace.

CFD can help eliminate a lot of the uncertainty related to the development of new combustion equipment designs. It can be used to:

• Virtually test new concepts and make effective design decisions before building a prototype or commercial unit. CFD is the perfect tool to complement engineering design.
• Debug equipment operation by testing its performance before implementation. No need to rely on empirical equations since CFD reproduces the real equipment’s behaviour. For example, instead of relying on pressure drop correlations to determine your equipment’s pressure drop, CFD can be used to determine actual pressure drop curves for the entire range of operation of your equipment.
• Eliminate scale-up problems by simulating actual-sized, virtual equipment instead of building and testing scaled-down models.

For existing equipment and processes, CFD is a powerful troubleshooting and optimization tool. It can be used to:

• Eliminate on-site trial and error through virtual field-testing. This is ideal when the equipment is not available to be run at test conditions for troubleshooting purposes.
• Gain insight into equipment or processes that are difficult to measure because of limitations on which types of probes can be used, and where they can be placed. This is ideal for optimizing the performance and productivity of your equipment or process by identifying underlying bottlenecks.

CFD can reproduce:

• Fluid flow (liquid or gaseous)
• Heat transfer
• Combustion
• Pollutant formation (CO, NOx, etc.)
• Turbulence and mixing
• Particle tracking
• Acoustics
• And more…

To date, we have used CFD techniques on:

• Natural gas, oil, coal, bark and biomass-fired industrial boilers
• Incinerators
• Heaters
• Furnaces
• Rotary kilns
• Low NOx burners
• Combustion air and flue gas ducting
• Burner windboxes
• Heat exchangers
• HVAC systems
• Desulfurization tanks
• Spray cooling equipment
• Turbines
• Pumps
• Attemperators
• Wind engineering

The possibilities are "virtually" endless!

Examples of how clients have benefited from our CFD expertise:

BMA carried out a CFD analysis to evaluate the performance of a newly designed combustion air duct supplying the 48-burner furnace of a refinery, which could operate with either forced draft preheated air or with ambient air drawn in by the natural draft of the unit. The CFD study revealed that the proposed ducting configuration would not be able to provide an equal air distribution to all 48 burners. Recommendations were therefore provided for modifications of the ducting based on information obtained from additional CFD runs, in order to obtain the proper air distribution for both of the air input methods stated above.

BMA carried out a CFD analysis on a residential biomass water heater in order to provide fundamental operational information which aided in the design and optimization of a scaled-up version of the water heater. The report issued contained recommendations to avoid hot spots on the interior front plate of the combustion chamber.

BMA carried out several CFD studies as part of the modernization of a municipal incinerator with a capacity of 1000 metric tons per day. The preliminary simulation served as a base case simulation of the existing installation in order to determine the system's weak points and pinpoint where improvements could be made. Recommendations were given for the modification of the operating conditions in order to improve the distribution between primary and secondary air. Subsequent simulations were carried out in parallel with tests on the incinerator in order to validate the simulation results as well as understand how the different operating parameters such as excess air, air distribution, and air temperature affected the incinerator's performance.

Boiler Circulation Analysis

BMA has its own in-house developed software for analyzing water tube boiler circulation (natural or assisted).

Similar to CFD, the process involves building a model of the boiler tube geometry, discretization of the model and applying the heat flux on the tube walls in the various regions of the boiler. The software reproduces the boiling and two-phase flow that occurs in the tubes in order to predict the flow conditions such as flow rate, velocity, quality, void fraction, heat transfer characteristics, flow pattern information, as well as the critical heat flux and anisothermality limits inside the tubes of the boiler.

Ultimately, a boiler circulation analysis will determine if there is any potential boiler tube overheating problem, which could lead to tube failure (leakage or rupture). In addition, a waterside circulation analysis can be used in conjunction with a detailed CFD simulation of the combustion side of a boiler in order to provide a powerful tool for boiler designers to test and refine new designs quickly and economically.

Whether you are a boiler manufacturer or operator, an analysis of the waterside circulation can help you to:

• Detect in advance any potential flow problems in the boiler, which would allow you to take corrective measures before a tube failure problem arises.
• Determine if you can increase the steam output of your boiler without compromising the natural circulation of your boiler. If changes are necessary in order to increase the boiler steam output, the circulation analysis will also aid in determining what changes are required.

Examples of how clients have benefited from our boiler circulation expertise:

BMA conducted a study to determine the potential to increase the capacity of two existing 20 ton/hr package boilers for a ferroalloy plant. In addition to carrying out a verification of the capacities of all the boiler auxiliary equipments, the study included a boiler circulation analysis to determine the maximum possible steam output of the boiler without compromising its natural circulation. The study determined that the circulation of the boiler allowed 135% of the original steam output, which was not the limiting factor for increasing the boiler capacity.

BMA conducted a boiler circulation study to analyze the effect of a new design feature on the waterside circulation for a 200,000 PPH, D-type package boiler for a boiler manufacturer. While the new design feature had advantages for improving boiler efficiency, the study revealed that certain areas of the boiler had reduced waterside circulation. Several design recommendations were provided to improve the circulation of the boiler while keeping the desired improvement on efficiency.