Achieving site energy savings does not necessarily always require intensive capital investments. Often, simply returning a process that has drifted away from its previously demonstrated performance ensures a "quick win" in providing an energy efficient operation. Such was the case in a recent Emerson engagement with a Midwestern specialty chemical producer.
Emerson was called in to survey four boilers in an effort to look for possible reasons for declining thermal efficiency over the years. No obvious physical changes were observed on the boilers but upon analyzing the historical data, it was immediately clear that the excess oxygen levels in the flue gas for all four boilers were excessively high and not being controlled. High excess oxygen indicates that too much combustion is being provided to the burner and has the affect of reducing thermal efficiency by essentially over-cooling the furnace. Seeing this trend across all four boilers was somewhat novel. Further investigation revealed that the site had experienced a notable shift in natural gas composition that was not accounted for in the combustion control system.
The boiler survey resulted in a two week combustion tuning engagement in which Emerson (namely myself) was commissioned to solve the problem and get the boiler emissions back in control. It should be noted that this was a non-Emerson DCS using relatively out-dated combustion control strategies. The fact that the customer came to us rather than the original DCS supplier (and combustion code developer) is a very telling example of how our Industrial Energy team's reputation for combustion expertise puts us in demand.
During the tuning engagement, the fuel/air ratios, excess air curves, and other logic were updated. Additionally, there were numerous mistakes found relating to pressure-temperature flow compensation and we even found that there were non-linearities in some recently supplied air flow elements. The result is that all four boilers are now controlling excess oxygen according to the originally demonstrated burner set points. Thermal efficiency was increased an average of 1% equating to approximately $30k USD in natural gas savings. Energy savings through a thorough understanding of combustion fundamentals and modern control strategies can be a powerful combination.
Andrew J. Verdouw, P.E. | Professional Services Organization