  The observation of primordial B-modes in the Cosmic Microwave Background
(CMB) represents the main scientific goal of most of the future CMB
experiments. This signal is predicted to be much lower than polarised Galactic
emission (foregrounds) in any region of the sky pointing to the need for
effective components separation methods, such as the Needlet-ILC (NILC). In
this work, we explore the possibility of employing NILC for B-mode maps
reconstructed from partial-sky data of sub-orbital experiments, addressing the
complications that such an application yields: E-B leakage, needlet filtering
and beam convolution. We consider two complementary simulated datasets from
future experiments: the balloon-borne SWIPE telescope of the Large Scale
Polarization Explorer, which targets the observation of both reionisation and
recombination peaks of the primordial B-mode angular power spectrum, and the
ground-based Small Aperture Telescope of Simons Observatory, which is designed
to observe only the recombination bump. We assess the performance of two
alternative techniques to correct for the CMB E-B leakage: the recycling
technique (Liu et al. 2019) and the ZB method (Zhao & Baskaran 2010). We find
that they both reduce the E-B leakage residuals at a negligible level given the
sensitivity of the considered experiments, except for the recycling method in
the SWIPE patch at $\ell < 20$. Thus, we implement two extensions of the
pipeline, the iterative B-decomposition and the diffusive inpainting, which
enable us to recover the input CMB B-mode power for $\ell \geq 5$. We
demonstrate that needlet filtering and beam convolution do not affect the
B-mode reconstruction. Finally, with an appropriate masking strategy, we find
that NILC foregrounds subtraction allows to achieve sensitivities for the
tensor-to-scalar ratio compatible to the targets of the considered CMB
experiments.
