This is part two of our continuing discussion on Pulse Firing and the issues it addresses in these three key areas:
- Poor temperature uniformity in the furnace which results in sub-standard product uniformity
- Inadequate turndown of the system in total
- Excessive Fuel Consumption
Neither of these issues exists solely by itself. They are all interrelated. Until the introduction of Pulse Firing technology, it was not possible to address these three issues at once. One still had to give up something to gain something else.
For instance, if the temperature was at set point and the system needed to go to a lesser output but uniformity of temperature in the furnace was critical, the solution to this was to reduce the fuel flow but maintain the high velocity burners at a constant rated high fire combustion air flow. The reason for the combustion air remaining at high fire was in an effort to maintain the stirring action of the furnace atmosphere to keep the load uniform. As a result, uniformity could be maintained, to a degree, but the efficiency was compromised by the volume of excess air being introduced into the furnace. Air absorbs heat so in addition to maintaining the proper temperature, not only did the load need to be heated, but so did the volume of air being circulated.
As indicated previously, something has to give. Two issues were addressed but at the expense of fuel efficiency. Pulse Firing allows for the control of the entire process without sacrificing one desired outcome for another.
A very key component in the Pulse Fire system is the high velocity burner itself. In general terms, High Velocity burners achieve an exit velocity somewhere in the realm of 25,000 to 26,000 ft/min. This exit velocity of the hot exhaust gasses allows for high degree of entrainment of the furnace atmosphere. This results in a large volume of hot gases moving throughout the furnace chamber and the load. As these gases travel throughout the furnace and, especially, the load, they “scrub” against the load. It is this scrubbing action, referred to as forced convection. To reiterate, forced convection is the transfer of heat between solids (The Load) and Fluids (Hot Exhaust Gases) by a mechanical means (High Velocity Burner) It should be noted that the convective heat transfer for both the Pulse Fire System and a Cross-Connected Modulated/Fuel Only Control system is equal as long as the heat input requirements demand a firing rate of 90% or higher. It is when the input requirements are reduced that Pulse Firing proves its superiority.
In Part Three of our discussion on Pulse Firing, we will discuss three types of combustion controls applied to High Velocity Burners. Those being:
- Cross Connected Modulated (On Ratio)
- Cross Connected Modulated/Fuel Only
- Pulse Firing
We will discuss the operation of each and compare their functions.
Until next time, work safe and be safe.