The thermochemical conversion of pulverized solids is essential during combustion in dust-firing systems or injecting pulverized reducing agents in the blast furnace process. When injecting the particles, harsh conditions, e.g., high heating rates, high temperatures, and elevated pressures, can cause substantial intra-particle temperature gradients. Such processes are typically modeled using Euler-Lagrange frameworks assuming isothermal particles. However, resolved particle models are essential to fully understanding the conversion process under these harsh conditions. A 1D and a novel 3D resolved particle model implemented to OpenFOAM are employed to investigate thermochemical conversion processes under high heating rate conditions. Temperature and species concentration gradients are employed to identify potential conversion bottlenecks and the conversion mode. Intra-particle temperature gradients of O(10⁶) K/m exist within O(10) µm sized particles under high heating rate conditions. The shrinking particle conversion mode prevails under these conditions. However, a shrinking core mode is superimposed on the shrinking particle one due to the build-up of an ash layer. Detailed investigations of the thermochemical conversion of pulverized particles is essential to identify potential bottlenecks and improve processes to ensure efficient, total particle burnout. Furthermore, more accurate simplified models can be derived from the detailed particle models, which can be applied in large-scale simulations of industrial processes.