Pulp mills are making increasing efforts to reduce fossil fuel use and carbon dioxide emissions. Lime kilns, which are typically fired with fuel oil or natural gas, use the most fossil fuel in modern pulp mills. A modern kraft pulp mill can be fossil fuel-free during normal operation if fossil-based lime kiln fuels are substituted with renewable alternatives. This study compared the production and use of various renewable fuels, namely, hydrogen, producer gas, torrefied biomass, lignin, and pulverized biomass, in lime kiln operations in a 1.5 Mt/a kraft pulp mill in South America to define the techno-economic optimum for the fossil fuel-free operation of the pulp mill. The attractiveness of each of the concepts was dependent on local conditions and especially the prices of fossil fuels and electricity. The results showed, however, that feasible options exist for the replacement of fossil fuels in lime kiln operations.