Emerson’s Andrew Smith and Jesse Sumstad presented “Tune into Savings by Maximizing Your Combustion Efficiency” at the 2019 Emerson Exchange conference. Here is the abstract of their session:
There are two major, competing theories to fired equipment control: maximizing fuel savings and efficiency or prioritizing consistent operation at a high level of excess oxygen and lower efficiency. In order to achieve safe operation, while maximizing cost savings, users can undertake a process called boiler trim. There are several strategies users can employ to trim their boilers, process heaters and kilns including, adding CO measurement and redundant measurements. This session seeks to educate users on ways to improve efficiency without compromising safety using products and options for the Rosemount Combustion Portfolio.
Andrew opened with an overview of combustion. Excess oxygen is one of the most effective measurement for combustion. 1% reduction in excess oxygen can provide large savings. A dangerous condition is when there is excess fuel. The optimum point of the combustion curve is in the area of 2-5% excess oxygen before the efficiency curve falls off with more oxygen.
Too much oxygen increases NOx emissions. Andrew highlighted 3 oxygen transmitters CX1100, 6888 OXT, OCX8800. The CX1100 is good for package boiler O2 measurement. The 6888 OXT is for traditional O2 measurements and the OCX8800 is for traditional multi-gas applications. These probes are used in process control to adjust the ratios of fuel to air to attain the right levels of oxygen.
Some common application solutions for the combustion analyzers include high-temperature bypass, isolation valving system, probe mounting jackets, abrasive shield, variable insertion mounting and pressure balancing systems.
Carbon monoxide (CO) measurement types of technologies include calorimetric, mixed potential, and tunable diode laser (TDL). Mix potential is more for lab environments and less so for industrial application. TDL sends an infrared wave which can find the amount of CO in the sample. TDL provides a cross-stack average and is suitable for high temperatures and particulates. The cost of TDL technology vs. Calorimetric is much greater. Calorimetric probes are easy to retrofit and low cost. They are not well suited for high particulates and don’t provide true CO measurements.
Jesse shared an energy efficiency calculator tool to input boiler process conditions to calculate improved efficiency and ROI to optimize combustion performance.
He shared some customer success stories. The first was a non-alcoholic beverage manufacturer. Manual O2 measurements were taken. For the project they added oxygen probes to improve combustion efficiency and payout the project in less than half a year. The second case was a food & beverage manufacturer with 6 air dryers that use hot air to process the food. For the 6 boilers they improved combustion efficiency and payed back the project in under a year and reduce their CO2 emissions.
The third case was paper mill lime kiln with a fired end to create the lime. They were running in a negative O2 condition which is a dangerous condition with too much fuel for the amount of oxygen. Probes were added to measure this ratio, and safely return the combustion to an excess oxygen condition in the optimum range. Additional wireless probes were added to the spinning kiln to optimize kiln efficiency.
Energy is the largest controllable cost in many production processes. Optimizing the fuel to oxygen ratio will improve combustion efficiency, avoid dangerous fuel-rich operating regions and reduce emissions.
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