November 2022 Volume 4

EQUIPMENT & TECHNOLOGY

Decarbonization through Heat Recovery and Hydrogen Fuels From a decarbonization perspective, heat recovery provides a significant benefit in that it simultaneously decreases CO2 emissions and fuel cost by improving process efficiency. Furnace efficiency can be expressed in terms of percent available heat, which represents the best possible furnace efficiency. %Available Heat = available heat ⁄gross heat input

The Sankey Diagram in Figure 3 shows that available heat is equal to the gross heat input minus all flue gas losses. It represents the sum of the heat to the load and all other losses. By extracting energy from the exhaust gases and using it to preheat the combustion air or furnace load, heat recovery minimizes the amount of gross heat input required, and, therefore, increases the percent available heat of the process.

Figure 3: Sankey Diagram showing the heat balance in a furnace.

Regenerative burners use heat recovery to provide up to a 45% decrease in fuel consumption and CO2 emissions compared to a cold air, natural gas system. Achieving the same reduction in CO2 emissions without heat recovery would require 72% hydrogen by volume blended with natural gas. Regenerative burners can be retrofitted to an existing furnace. However, if the goal is to eliminate all CO2 emissions from the combustion system, hydrogen will eventually need to be introduced. The most significant benefit of regenerative burners is the reduction in fuel consumption, which results in lower CO2 emissions as well

as improved fuel costs. Figure 4 compares the cost range of CO2 reduction with hydrogen fuels on a cold air system (purple) and the cost range of CO2 reduction with hydrogen fuels on a regenerative system (grey). With relatively minimal hydrogen blending, regenerative burners can provide a significant decrease in CO2 emissions. For example, a hydrogen blend having a median fuel cost of $30 per MMBtu (million BTU) available to the process would improve CO2 emissions by about 10% for a cold air system but 65% for a regenerative system. Furthermore, as the level of hydrogen in the fuel increases, high efficiency regenerative burners mitigate the progressively high fuel cost.

Figure 4: Comparison of fuel operating expense with cold air and North American TwinBed® II regenerative hydrogen-fired combustion systems.

FIA MAGAZINE | NOVEMBER 2022 20