Analyzing Coal-to-Gas Conversions, An Engineering Study
Many utilities are considering burning natural gas in a boiler constructed for coal-firing. TRAX has assisted customers by performing studies on full and partial gas-firing conversions to predict the effects of natural gas combustion on draft system pressures.
With natural gas, units will see more severe furnace pressure excursions during an MFT. The figure below compares a unit MFT from a full load while burning 100% coal vs. 100% gas. The more severe pressure excursion is due to the kinetics of gas combustion, and to a control system that was designed for coal only.
TRAX looks at gas shut-off timing as well as control system response to design the most favorable setup for gas burning. Along with control changes, we examine stroke times for gas shut-off valves and ID fan IGVs. The ID fan IGV stroke time is critical in making sure the ID fan can react quickly for the faster fireball collapse seen with gas burning.
Testing various fuel trip scenarios enabled TRAX to make recommendations for gas valve stroke times and ID fan IGV stroke times to minimize negative pressure excursions that will be seen in the furnace on a loss of fuel. TRAX also made controls recommendations that will both assist with the minimum negative pressure in the furnace and prevent any positive furnace pressure during recovery from the fuel trip.
TRAX can conduct similar studies based on other plant changes such as fan upgrades, FGD modifications, or other process changes. These studies can also be combined with TRAX CFD analysis in areas of special interest.
TRAX has delivered a carbon capture simulator for a 150 MW coal-fired unit that models the capture of the full flue gas stream. The system provides both CO2 and SO2 capture, delivering the captured CO2 to a pipeline for industrial use and underground storage.
—CO2 and SO2 capture
—Sulfuric acid plant
—CO2 and SO2 amines filtration and purification
—CO2 compression
—CO2 pipeline and cavern
As shown below, TRAX built a modular simulation replicating the plant layout using our software, ProTRAX. ProTRAX contains a full suite of modules specific to carbon capture functions and can model a wide variety of processes. TRAX also virtually replicated the user interface that appears in the plant.
Upon initial delivery, the TRAX simulator was used to debug control logic and processes prior to site installation and to provide operations training prior to plant startup. There was a clear need to begin training operators as early as possible since they had multiple unfamiliar systems to learn.
Thanks to the ProTRAX simulator, our customer gained considerable insight into control functionality and system interactions, resulting in modification to some control logic and correction of simple errors. TRAX was able to assist with controls tuning, and helped in development of initial plant Operating Procedures.
The latest upgrade brings the model into alignment with the as-built plant condition by updating and tuning the simulator models to match the current plant dynamics. In addition, TRAX has updated the simulator controls and HMI graphics to the as-built state. Keeping the simulator aligned with the current plant condition is critical to maintaining a positive training value, and is of paramount importance to the customer.
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