Combustion Control- totalizing metering


Thread Starter

B Darling

Does anyone know where to find or have available information regarding totalizing metering combustion controls. I would like to maximize use of one fuel and have the second fuel provide the balance of the required Btu's automatically. Thanks [email protected] is my email address

William T. Dolan, P.E.

The Control of Boilers by Sam Dukelow is a good resource. I believe you're looking for a metered cross-limited combustion control system. Since you have two fuels of likely different BTU/lb values, the control scheme will need to normalize the two fuels on a BTU basis as it relates to airflow. Therefore, as an example; a 50% firing rate from the boiler master equates to the same BTU input to the boiler regardless of fuel fired. An O2 trim controller may be considered to characterize excess air as a function of boiler load.
You will find several brands of high reliability flow totalisers, just consulting the ISA Buyer's Guide. Canadian Meter (also Aerican Meter) were like the most prefered. Now, trying to understand your project sounds not easy. Is there a constant ratio between the fuels so that the thermal output is constant if they don't have the same heat capacity ? Can you just ratio one fuel in relation to the plant load and trim the remaining demand with the second fuel ? The oxydising agent (probably air) may need be calculated ? I doubt any DCS or PLC (worse) can output the appropriate thermal algorithm. Back to flow totalising, above: If your flow measurement is " true ", you could totalise without introducing error, using a very reliable Numerical Integration maths module. This is not available, unless by deep search and luck. For that, I have adapted the Romberg Integration to suit data acquisition. Ignore error, the accuracy of the method reaches 10 decimals. Good luck.