The three arches seem to be over latrines.
This is behind the Great Hall, where a "huge hall stretches for 120 m. taking one whole side of the inner fortifications and looping around to the north to join the chapel. This hall probably served multiple purposes: kitchens (there is also a well and a bread oven at the south end) [...]. This structure is within the immediately post-1170 Crusader construction forming the basic shape of the central fortress." (Ross Burns' The Monuments of Syria).