(60e) Optimized Combustion of Hydrocarbon and Hydrogen Fuel Mixtures Using Coriolis-Based Measurements

Process-derived hydrogen gas is often utilized by powerhouse boilers and fired heaters for steam production and process heating.  The extremely high heating value of hydrogen gas coupled with its water vapor combustion product makes it a desirable primary or supplemental fuel.  In addition, process hydrogen can easily help to offset natural gas or other fossil fuel consumption, thus lowering operating costs.  Hydrogen is often mixed together with natural gas and sent to the burners as a single fuel source.  Efficient combustion of this mixture over a wide range of hydrogen concentrations can prove problematic for conventional combustion controls.  This is due chiefly to the very different stoichiometric air-to-fuel ratio requirements of hydrogen versus the alkane series.  The typical method used to ensure safe combustion is to fire the boiler or heater with excessive air.  The consequence of this practice is reduced thermal efficiency which translates to increase purchased fuel use.  Using a cost-effective method to measure and determine the hydrogen concentration in real time can allow precise calculation of the required stoichiometric and excess combustion air by the control system.  The result is optimized combustion over a very wide range of hydrogen concentration.

This paper will discuss a technique for determining the hydrogen concentration in a hydrocarbon fuel (namely natural gas) using coriolis-based devices.  The principles of measurement will be explained as well as how the process data obtained is translated into a specific fuel-to-air ratio that can be employed by an advanced combustion control system.  The principles of fuel and air cross-limiting and the calculation of excess combustion air using this method will also be examined.  It will be illustrated how real-time knowledge of a varying fuel-to-air ratio allows a boiler or fired heater combustion process to be safety controlled and thermally optimized across all loads.