When reviewing a facility or plant’s overall cost of operation, fuel is a significant contributor. The boiler plays a major role in this cost many times burning in excess of 4 times its initial cost in fuel annually. When looking at ways to greatly mitigate this cost, there are a number of boiler retrofit opportunities one can look to save energy.
The Pressure Vessel
Begin with closely evaluating the boiler’s pressure vessel regardless of age, to determine if it still has years of life in it. Closely look at metal and weldment integrity, any large deposits of scale, signs of leaking or metal corrosion. This close inspection can all be done during the boiler’s annual shutdown and draining. If all things are positive, and the vessel is in good shape, proceed to the burner.
The Burner
A burner evaluation starts with a qualified technician inspecting and testing the burner. The technician will make sure it properly tracks through its modulating range and combusts without excessive O2, and CO, shutting down and purging both pre and post-firing. If it does not, and it can’t be confidently adjusted, replace the burner. A burner must be properly sized, meet the application needs, and match the furnace in which it is firing. This is most important because it’s the furnace that provides the time for combustion to complete.
Boiler retrofit options to consider for both a new or existing burner; reducing the fuel spend:
Parallel Positioning
Include parallel positioning actuators for fuel and air regulation, replacing single point positioning linkages. An efficient burner provides the proper air-to-fuel mixture throughout the full range of firing, without constant adjustment. Many burners with complex linkage designs do not hold their air-to-fuel settings over time. Often, they are adjusted to provide high levels of excess air to compensate for inconsistencies in the burner’s modulation. This high excess air costs extra fuel dollars.
Instead, install servomotors with parallel positioning to independently control the quantities of fuel and air delivered to the burner head. This control system allows for easy tune-ups and minor adjustments, while eliminating hysteresis, or lack of repeatability. This will deliver accurate point-to-point control and save significant fuel dollars annually.
High Turndown Burner
Boiler “short cycling” occurs when a boiler quickly satisfies the process and/or space heating demand, and then shuts down until heat is again required. This results in numerous pre and post air purges of the furnace for safety reasons, literally blowing countless Btu’s out the stack; driving up needless fuel costs. Energy losses of 15% are not at all uncommon when cycles exceed ten (10) per hour.
The solution to this problem is retrofitting or specifying in the case of a new burner, a High Turndown Burner with 10:1 turndown capability. In addition to this option, the boiler may also be oversized for the load. Especially during certain months of the year, like summer, when specific loads such as comfort heating are shed. In this case, you could consider an additional Smaller Boiler (new or used). This would mitigate cycling losses and allow the boiler to operate and fire at its most efficient point. For most boilers, that is above 85% of its rating.
Oxygen Trim System
Another retrofit consideration making cent$ is the use of a good Oxygen Trim system. As you know, a burner needs fuel and air to combust, and the combustion air fan is delivering air at a specific rate regardless of the changing conditions in the boiler room.
This means when the boiler room gets colder the air gets denser. As the room heats up, it gets less dense. This means if the fan discharge is not regulated to account these density changes, the burner can go from excessively high excess air (loss of energy) to excessively short of air; forming dangerously high CO levels and possibly explosive unburned carbon.
The O2 Trim system accounts for these changes, automatically adjusting the air damper or fuel valve to account for the irregularities. This retrofit saves energy dollars and greatly improves safety.
Alternate Waste Fuel
Is there an Alternate Waste Fuel in your facility which could be burned or are you close to a landfill or digester gas facility? These fuels can be burned in a properly designed and controlled burner. Many times your local Utility will offer discounts for going “off peak” while also assisting in the retrofit cost. Worth checking out…
Operating Controls
The next thing to look at is the Operating Controls on the boiler (operating, modulating, and high limit controls). Are they old? If they are, it would be wise to check their settings against the actual pressure or temperature in the boiler to see if they are actually shutting the boiler’s burner off and turning it on at the proper point.
Many times they may be causing the boiler to overshoot the desired pressure/temperature point or undershoot it causing a needless loss of energy and/or process/comfort heating problems. If this is the case, retrofit new operating controls on the boiler; saving energy while improving the desired outcome in the facility.
Automatic Stack Damper
The last priority for saving fuel dollars is the Automatic Stack Damper. When discussing pre and post purge losses, it is the air blowing through the boiler when the burner is not firing which causes needless boiler cooldown and energy loss. The same is true for excessive stack draft occurring when a “live” boiler is offline awaiting the firing command from its burner management system.
An automatic draft control can save this loss, closing the damper during the boiler’s off cycle then automatically opening it again when the boiler is called to come on line. Many energy dollars are saved with this feature, and it’s imperative it be considered when draft exceeds approximately 2” WC. Also in this case, the auto damper control will regulate the pressure at the vent stub during firing, assisting in keeping the burner’s air/fuel ratio in the proper range at all firing rates.
It all makes good economic cents!
Contact Frank I. Rounds Company for a boiler room evaluation to identify cost-saving opportunities you can benefit from year after year.
Learn more about our boiler upgrade and conversions.
Helpful tools: Energy Cost Savings Calculator for Boilers