The climate targets set for 2030 and 2050 will progressively compel to use sustainable fuels in combustion facilities for the generation of steam, electricity or other uses. Solid biomass, gases from gasification, biogas, liquid biofuels or hydrogen are examples of sustainable fuels. Even, in the short term, the substitution of fuel oil / coal for natural gas can be a transitory step towards sustainable fuels.

At this point, questions and uncertainties may arise regarding how the fuel switch will affect the current installation. For example: Can I completely replace the current fuel? What percentage of the current fuel can I replace without the need for investments? Do I have to modify the operating conditions (air distribution) to operate with the new fuel? Can the installation be damaged if I use another fuel?

Substituting a fossil fuel for a sustainable fuel (fully or partially) will, of course, have an effect on the installation. The length and intensity of the flame can change, affecting the burners or areas attached to them. On the other hand, the radiant properties of flue gases can change (for example, H2 will only produce water vapor, not CO2), and this can affect heat exchange in the radiant zone. Also, by changing the composition of the gases, the convective heat transfer coefficient will be affected, modifying the heat exchange in the heat recovery zone. Thus, the replacement of a fuel has an impact on the flame and the distribution of heat in the boiler. Depending on the case (proportion of fuel replaced, burner and boiler characteristics), these impacts can be mitigated without the need to carry out any investment, by adapting the operating conditions (for example, air distribution). In other cases, certain investments will be necessary.

The following image shows the temperature contours in a boiler operating with fuel-oil and natural gas with the same configuration. With natural gas, the flame is shorter, increasing the probability of overheating (and damage) to the burner. Furthermore, by changing the radiation properties of the combustion gases, the heat transfer in the water walls decreases considerably, forcing an increase in the tempering flow rate to maintain steam production. Finally, the heat transfer in the heat recovery zone also decreases. For this reason, the substitution of fuel-oil for natural gas, in this case, would make it necessary to change the current operation of the boiler.

Temperature contours in the boiler

At nablaDot we have the necessary tools to evaluate the effects of fuel changes (any fuel, any scale) in your facility and we can recommend the appropriate strategies to introduce these new fuels optimally and safely. Consult us without obligation.