One approach to this question is to try to give a description of the centralizer. This can be done using the [Nielsen-Thurston classification][1] of elements in mapping class groups. 

To describe this in this case, first note that the braid group $B_n$ is the [mapping class group][2] of the $n$-punctured disk. Then $B_n/\Delta_n$ is a subgroup of the mapping class group of an $n+1$-punctured sphere, where $\Delta_n$ is a full twist, generating the center of the braid group (and corresponding to a Dehn twist about the boundary of the disk). 


Hence if one can describe the centralizer of the image of an element in the mapping class group of an $n+1$-punctured sphere, then one can describe the centralizer in $B_n$ by taking the preimage. 

The Nielsen- Thurston classification then says that every element is either reducible, finite-order, or pseudo-Anosov. The normalizers of pseudo-Anosovs are virtually cyclic groups, generated by minimal pseudo-Anosov and its symmetries, and the centralizer is finite index in the normalizer.

If a mapping class is finite order, then it is realized by a finite-order homeomorphism, and the centralizer is related to the mapping class group of the quotient surface (punctured at the fixed points). This can be described then by induction. 

If a mapping class is reducible, then there is a minimal set of curves which are preserved by the element up to isotopy (corresponding to the JSJ decomposition of the mapping torus), and the action on the mapping class groups of the complementary components are either finite order or pseudo-Anosov (taking into account the permutation action on components). The centralizer here then can be described inductively by considering the centralizer of the action on the complement of the reducing curve and the Dehn twists about these curves. 

Applying this to the braid group, this means that we can conjugate any element so that it looks like braids on sub collection of strands, which in turn are braided together, etc. The centralizers then have a description (up to finite index) as products of centralizers of the subbraids (which are either virtually cyclic or virtually braid groups),  product with Dehn twists about the multi curves. All this is complicated by how the reducing curves are permuted, which must be taken into account in the final description. I wouldn’t be surprised if this can be found in the literature; I would consult Farb-Margalit’s [primer][3].


  [1]: https://en.wikipedia.org/wiki/Nielsen%E2%80%93Thurston_classification?wprov=sfti1
  [2]: https://en.m.wikipedia.org/wiki/Mapping_class_group_of_a_surface
  [3]: https://www.jstor.org/stable/j.ctt7rkjw