Scheduled maintenance outages are critical windows of opportunity for any power generation plant to upgrade or retrofit sections of a system to meet today’s standards and regulations for efficiency and emissions. Fundamental assessments of and adjustments to fuel delivery and draft systems can pay big dividends, without the huge capital replacement costs of upgrading to a new boiler system.
Fuel Delivery and Overfire Air Systems
A common cause of emissions issues is inconsistent fuel flow. With stoker coal-fired boilers, this will show up as uneven mounds on the boiler grate. It results in excessive levels of unburned carbon (UBC) being blown by the combustion air into the exhaust gas draft system, raising NOx and CO2 levels, and increasing particulate matter and greenhouse gases.
One upgrade that often can be carried out during a maintenance outage is installation of proper fuel-feed equipment to deliver a consistent fuel flow. Another is a properly sized overfire air system, which recaptures and burns much of the UBC before it can reach the fly ash, releasing additional BTUs and while minimizing particulate carryover. Using computational fluid dynamic modeling can help pinpoint airflow and combustion problems for determining the exactly amount and location of overfire air system needed to maximize the effect on combustion.
One facility, the Baltimore Gas and Electric Company, realized reductions in NOx emissions of 30 to 44 percent, depending on production levels, from a retrofit for an overfire air system and an enhanced burner mixer, the combination designed by using computational fluid dynamics modeling.
Fans and Draft Systems
Many plants today have draft systems that are 30-50 years old, and retrofitting components such as ineffective impeller blade designs with more modern and efficient blades can result in major reductions in carbon emissions and fan horsepower demands
One utility plant had an oversized primary fan, creating problems with vibration and flow control. Installing an optimized primary fan along with new dampers helped bring carbon emissions down by 2,443 metric tons per year, generated $48,500 in energy savings, and allowed the plant to sell megawatts back to the grid, reaping another $161,700 annually.
Make the most of your scheduled down time. ProcessBarron has over 20 years of experience in the field of fuel systems, and can handle every stage of retrofits and upgrades, from design and engineering—including computational fluid dynamic modeling—to installation, maintenance and repair. Visit our Preventive Maintenance page on the web at https://processbarron.com/field-technical-services/preventative-maintenance.