  The acceleration of charged particles is relevant to the solar corona over a
broad range of scales and energies. High-energy particles are usually detected
in concomitance with large energy release events like solar eruptions and
flares, nevertheless acceleration can occur at smaller scales, characterized by
dynamical activity near current sheets. To gain insight into the complex
scenario of coronal charged particle acceleration, we investigate the
properties of acceleration with a test-particle approach using
three-dimensional magnetohydrodynamic (MHD) models. These are obtained from
direct solutions of the reduced MHD equations, well suited for a plasma
embedded in a strong axial magnetic field, relevant to the inner heliosphere. A
multi-box, multi-scale technique is used to solve the equations of motion for
protons. This method allows us to resolve an extended range of scales present
in the system, namely from the ion inertial scale of the order of a meter up to
macroscopic scales of the order of $10\,$km ($1/100$th of the outer scale of
the system). This new technique is useful to identify the mechanisms that,
acting at different scales, are responsible for acceleration to high energies
of a small fraction of the particles in the coronal plasma. We report results
that describe acceleration at different stages over a broad range of time,
length and energy scales.
