An air filtration bank which includes: at least two adjacent cyclonic air classifiers, each cyclonic air classifier including a hollow classifier body which includes: a vortex-inducing inlet duct at an upstream inlet, the hollow classifier body defining a longitudinal axis; a tubular extraction pipe, arranged downstream of the inlet, the extraction pipe defining a discharge outlet which is axially aligned with the inlet; and an at least partially conical diffuser which extends from the inlet duct toward the extraction pipe such that a downstream end of the at least partially conical diffuser and the extraction pipe together define a waste outlet in a plane transverse to the longitudinal axis of the hollow classifier body; and a frame to which the cyclonic air classifiers are mounted, characterized in that the vortex-inducing inlet ducts of the adjacent cyclonic air classifiers are configured to induce oppositely orientated vortices in the respective hollow classifier bodies of the adjacent cyclonic air classifiers and wherein the at least partially conical diffusers of the adjacent cyclonic air classifiers are of different lengths such that their respective waste outlets are not coplanar and are longitudinally spaced apart along the air filtration bank which serves to limit waste outlet flow interference and results in less pressure drop across the air filtration bank, which in turn leads to more efficient particle removal, further characterized in that a cyclonic air classifier having a shorter conical diffuser (15.1), when compared to a length of the other conical diffuser (15.2), includes a deflector which is connected to an outer surface of the extraction pipe, downstream of the waste outlet, and wherein the deflector extends radially outwardly away from the extraction pipe thus serving further to limit waste outlet flow interference between the adjacent cyclonic air classifiers. at least two adjacent cyclonic air classifiers, each cyclonic air classifier including a hollow classifier body which includes: a vortex-inducing inlet duct at an upstream inlet, the hollow classifier body defining a longitudinal axis; a tubular extraction pipe, arranged downstream of the inlet, the extraction pipe defining a discharge outlet which is axially aligned with the inlet; and an at least partially conical diffuser which extends from the inlet duct toward the extraction pipe such that a downstream end of the at least partially conical diffuser and the extraction pipe together define a waste outlet in a plane transverse to the longitudinal axis of the hollow classifier body; and a vortex-inducing inlet duct at an upstream inlet, the hollow classifier body defining a longitudinal axis; a tubular extraction pipe, arranged downstream of the inlet, the extraction pipe defining a discharge outlet which is axially aligned with the inlet; and an at least partially conical diffuser which extends from the inlet duct toward the extraction pipe such that a downstream end of the at least partially conical diffuser and the extraction pipe together define a waste outlet in a plane transverse to the longitudinal axis of the hollow classifier body; and a frame to which the cyclonic air classifiers are mounted, characterized in that the vortex-inducing inlet ducts of the adjacent cyclonic air classifiers are configured to induce oppositely orientated vortices in the respective hollow classifier bodies of the adjacent cyclonic air classifiers and wherein the at least partially conical diffusers of the adjacent cyclonic air classifiers are of different lengths such that their respective waste outlets are not coplanar and are longitudinally spaced apart along the air filtration bank which serves to limit waste outlet flow interference and results in less pressure drop across the air filtration bank, which in turn leads to more efficient particle removal, further characterized in that a cyclonic air classifier having a shorter conical diffuser (15.1), when compared to a length of the other conical diffuser (15.2), includes a deflector which is connected to an outer surface of the extraction pipe, downstream of the waste outlet, and wherein the deflector extends radially outwardly away from the extraction pipe thus serving further to limit waste outlet flow interference between the adjacent cyclonic air classifiers.