Revamps 2022 Issue

Safer and efficient combustion for fired heaters and boilers A technological approach to achieving efficiency improvements, CO2 emissions reduction, and parallel effects in NOx emissions control in a crude oil-fired heater Francisco Rodríguez, Enrique Tova, Miguel A. Portilla, Miguel A. Delgado, Sixto López and Alfonso García-Marcos Suanzes INERCO

C ombustion optimisation offers the greatest potential for economic savings in industrial-fired heaters and boilers. This article presents the fundamentals and results of applying ABACO (Advanced Boiler Automation for Combustion Optimisation) technology in a 480 MMBtu/h fired heater. The improved controls provided by this tech - nology resulted in increased efficiency, minimum pollutant emissions (CO₂, CO, NO X , SO X , particles), and safer operation. This technology relies on the closed-loop control of com- bustion based on monitoring in-furnace conditions and enhanced regulation capabilities. The sampling and direct measurement of actual gas composition at each burner result in a balanced firing pattern and overall optimisation of the combustion process. While preserving the unit from det- rimental combustion conditions, maximum safety, reliability and process profitability are achieved. These optimised sce - narios are durable, and the process is continuously surveyed to maintain sustainable operating conditions. The effectiveness of this approach has been demon- strated in more than 150 testing programmes developed in over 75 industrial facilities worldwide, including 20 combus - tion units firing gaseous fuels and/or liquid fuels. The main results in refinery-fired heaters and boilers are: • Improved unit combustion efficiency, resulting in fuel consumption savings of up to 7%. Equivalent CO₂ and SO X emission reductions • Simultaneous reduction in NO X emissions (t/h) up to 50% (by excess O₂ decrease and burner tuning) • Increased heater capacity • Controlled combustion performance leading to higher unit safety, capacity, and availability • Control of unburnt fuel and CO emissions • Reduced preventive maintenance and corrective costs • Increased fuel flexibility • Efficient operation for variable duty or load scenarios. The reduction in fuel consumption typically leads to com- bined fuel and CO₂ savings of over 1 million USD/yr for unit duties around 400 MMBtu/h. These savings give rise to extremely short payback periods that can even be below one year. Combustion tuning Combustion is a relatively opaque process offering great

potential for economic savings in industrial boilers and fired heaters. Despite the economic and environmental importance of the combustion process, there is usually a low level of monitoring and control. The process is typi- cally governed by a few global variables, such as excess oxygen or process stream results, with no direct control of the combustion conditions. Fired heater or boiler operation is typically supported by standard procedures rather than effective online informa- tion and optimised flame control. In most multi-burner appli - cations, the standard monitoring used for controlling global excess oxygen in the combustion unit does not represent the real average in-furnace excess O 2 , which introduces a critical restriction for combustion tuning. In recent years, a considerable amount of attention has been given to the application of combustion tuning for efficiency optimisation, operational safety, and reduction of pollutant emissions. However, the cost-effectiveness of these tunings is greatly limited by the referred restrictions on combustion monitoring and control. This situation is even more relevant in scenarios of high variability in fuel prop- erties, load profiles, and/or burner arrangement for multi- burner systems. In these cases, uncontrolled combustion conditions might force operators to apply ‘too conservative’ operating settings, which are far from the optimum tuning. To solve these limitations, a methodology and technical approach known as ABACO has been developed for com - bustion process optimisation in fired heaters and boilers with different designs and fuels (oil, gas, coal, pet-coke, and biomass). Technical approach Efficiency and emissions in industrial fired-heaters and boil - ers depend largely on the correct distribution of fuel and air supplied to the combustion process. Improper fuel/air ratios at critical locations are severely detrimental to these impor- tant parameters and the operational safety of the unit (see Figure 1 ). The ABACO approach relies on closed-loop control of combustion based on in-furnace monitoring. This combus- tion optimisation technology makes possible the individual optimisation of any single burner, which results in an overall optimisation of the combustion process.

Revamps 2022