Since the advent of industrialization, industries have heavily relied on fossil fuels like coal and oil for heat, steam, and power generation, forming the backbone of their processes. Many medium and large-scale industries have established their heat and power generation units to meet their process needs and reduce dependency on external resources.
However, the COVID-19 pandemic and its aftermath have put numerous industries in financial crises, making it challenging to sustain their operations. Adding to the struggle, fossil fuels are depleting over time, leading to rising costs and disrupting industry budgets.
The combustion process, a chemical reaction between fuel and oxygen, has been a pivotal force in industrial development for centuries. During combustion, various flue gases such as Carbon Monoxide (CO), Carbon Dioxide (CO2), Sulfur (SO2), Nitrogen Dioxide (NOx), Nitric Oxide (NO), Volatile organic compounds (VOCs), and Hydrocarbons (HCs) are generated.
While progress has been made in understanding combustion science, regulatory and competitive pressures have driven the need for combustion equipment that offers better performance, lower environmental impact, and increased flexibility—all at a reasonable cost.
BASIC COMBUSTION REACTION:
Carbon and hydrogen are principal constituent of any petroleum fuel.
In any combustion process, the reaction between fuel and oxygen in the air releases heat energy.
The combustion products are primarily carbon di-oxide (CO2), water vapour (H2O), which pass through the chimney along with nitrogen (N2).
After surrendering useful heat in the heat absorption area of a furnace, the combustion products or flue gases leave the system through the chimney, carrying away significant.
Quantity of heat with them.
From the chart, we can find out that as the excess air increases the %CO2 decreases. Which reduces the combustion efficiency.
The key to enhanced efficiency: boiler's combustion efficiency.
Optimizing combustion efficiency is crucial for minimizing heat loss and achieving effective heat transfer from the fuel to usable heat. The stack temperature and flue gas oxygen (or carbon dioxide) concentrations serve as primary indicators of combustion efficiency.
Achieving complete mixing between fuel and air is ideal, requiring a precise or stoichiometric amount of air to react fully with the given fuel quantity. However, combustion conditions are seldom perfect, necessitating additional or “excess” air to ensure complete fuel burn.
Finding the correct amount of excess air is determined by analysing flue gas oxygen or carbon dioxide concentrations. Inadequate excess air leads to unburned combustibles, while excessive air results in unnecessary heat loss, reducing boiler fuel-to-steam efficiency.
The optimal balance: managing excess air.
Optimum excess air input results in the most desirable combustion, where CO2 peaks, CO is minimized to safe levels, and fuel burns efficiently. The amount of CO, unburned fuel, and harmful emissions depends on how well the burner mixes fuel and air, with high-performance burners exhibiting peak combustion efficiency at 1-2% excess oxygen.
Achieving optimal excess oxygen levels in the field requires multi-gas analyzers to measure exhaust components and make adjustments to fuel and air control devices. Controlling combustion ratios to minimize excess air reduces fuel consumption, maximizes heat transfer, and lowers toxic CO emissions.
A case study – fuel-saving operations & payback-time.
When does fuel get wasted ?
- When too little oxygen us supplied, part of the fuel will be unburned and lost with the flue gases.
- When too much oxygen is supplied, the extra air is heated and it carries away the heat via the chimney, as wasted heat. Extra fuel would be bedded to make up the heat required, thus increasing the fuel consumption.
What is the Usual Operating approach regarding excess oxygen for maximum combustion efficiency ?
- Both safety & maxi. Efficiency exists in the relatively narrow range of 2% to 3% oxygen.
- The recommended levels of oxygen in flue gases are as follows:
Computations involved in establishing Cost benefit & pay- back time.
- Stack gas temperature
- O2 & CO reading
- Refer % Efficiency, before initial adjustment.
- Adjust excess air to decrease O2 % with traces of CO
- Allow few minutes after adjustment and take another reading.
Refer improved % Efficiency related to new stack temperature and O2 reading.
Compute the fuel saving per month Using following equation:
Compute payback time using Following equation:
Fuel Combustion Efficiency Monitor (FEM): A Solution for Efficiency
To ensure high combustion efficiency and comply with emission limits, PRIMA offers a solution with the Portable Flue Gas Monitor. The Flue Gas Combustion Efficiency Monitor (FEM) measures the total combustion efficiency of flue gas, aiding fuel combustion analysis and indirectly saving fuel.
FEM instruments are used to check combustion parameters emitted through stacks of boilers, furnaces, heaters, and kilns. These microprocessor-based flue gas analyzers store average values of sampled data, using technologies like electrochemical, non-dispersive infrared, and/or palliators sensors to enhance combustion efficiency, save fuel, and reduce pollutant gas emissions.
By incorporating flue gas measurement and combustion optimization, industries can improve efficiency, reduce operational costs, and contribute to a more sustainable future.
For more information, visit: www.primaequipment.com
