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Co-firing refers to the simultaneous combustion of two different fuels—typically coal and natural gas or biomass—in the same boiler or turbine system. It enables existing thermal plants to reduce carbon emissions while maintaining grid reliability. By blending fuels, operators can diversify energy sources, optimise fuel costs, and support a smoother transition toward low-carbon energy generation.

Performance optimisation ensures that co-firing systems achieve maximum thermal efficiency, stable combustion, and minimal emissions. Because dual-fuel operations involve complex interactions between fuels, air supply, and temperature control, ongoing optimisation helps maintain a low heat rate, enhance fuel flexibility, and reduce operating costs while ensuring compliance with ASME and ISO performance standards.

Heat rate measures the efficiency of converting fuel energy into electricity, expressed as energy input per unit of electrical output (e.g., kJ/kWh). A lower heat rate indicates higher efficiency. Engineers use it as a key performance indicator to identify losses in boilers, turbines, and auxiliary systems. Optimising heat rate directly translates into fuel savings and lower greenhouse gas emissions.

Two primary methods are applied: the Input-Output (Direct) Method, which compares total fuel energy input with net electrical output, and the Heat Loss (Indirect) Method, which calculates efficiency by quantifying all measurable energy losses. The latter provides greater diagnostic detail and is guided by ASME PTC 4 standards, making it ideal for troubleshooting and optimisation.

Challenges include maintaining flame stability, preventing slagging and fouling in boilers, controlling excess air, and ensuring accurate fuel flow measurement. Differences in fuel moisture, calorific value, and ash composition can affect combustion quality. Effective performance monitoring and frequent calibration of instrumentation are critical to sustaining efficiency and reliability.

Fuel blending alters combustion characteristics and heat release patterns. Properly balanced blending ratios of coal and gas can improve boiler performance and reduce unburnt carbon losses. However, improper mixing or inadequate air distribution may cause efficiency drops or increased maintenance. Advanced fuel analysis and monitoring tools help achieve the optimal balance.

Key standards include ASME PTC 4 (Boilers), ASME PTC 6 (Steam Turbines), ASME PTC 22 (Gas Turbines), and ISO 2314 (Gas Turbine Performance). These codes ensure accurate, repeatable measurements of efficiency, heat rate, and output under defined conditions, providing a common framework for benchmarking and improvement across the industry.

Data analysis enables engineers to detect inefficiencies, quantify performance penalties, and predict maintenance needs. By using regression analysis, correction curves, and real-time monitoring software, operators can normalise performance data to reference conditions and identify trends. This analytical approach supports proactive decision-making and long-term operational planning.

Co-firing offers a transitional pathway toward decarbonisation by enabling existing thermal plants to reduce CO₂ emissions by up to 15%. It allows operators to incorporate cleaner fuels without major infrastructure changes. Combined with heat rate improvements and performance monitoring, co-firing supports national energy transition goals while maintaining grid stability.

Future trends include increased integration of digital twins, AI-based performance monitoring, and the use of alternative fuels like hydrogen and ammonia. Advances in sensor technology and combustion modelling will further improve accuracy and reliability. As carbon-intensity targets tighten, co-firing plants are expected to play a vital role in flexible, low-emission power generation.