Classifier, pulverizing and classifying device, and pulverized coal burning boiler

1. A classifier, comprising:

a housing configured to take in an air flow from below into a radially outer region of an inside space;

a flow deflection portion disposed on an inner wall surface of the housing and configured to deflect the air flow toward a center axis of the housing; and

an annular rotational portion disposed rotatably in a radially inner region positioned on a radially inner side of the radially outer region, of the inside space of the housing, and configured to classify particles which accompany the air flow,

wherein the annular rotational portion includes a plurality of rotational blades arranged at intervals around a rotational axis of the annular rotational portion, and

wherein the plurality of rotational blades form an outer shape of the annular rotational portion which forms an angle θ of not greater than 75° with a segment extended in a horizontal direction from the annular rotational portion outward in a radial direction, in a side view of the annular rotational portion, and

wherein the classifier further comprises a material feed pipe extending downward into the housing of the classifier from an upper part of the housing of the classifier,

wherein the plurality of rotational blades of the annular rotational portion are disposed around the material feed pipe, and

wherein, provided that H is a total height of the annular rotational portion, a vertical distance between a lower end of the material feed pipe and a lower end of the plurality of rotational blades is not greater than 0.1H.

2. The classifier according to claim 1 , wherein each of the rotational blades is arranged obliquely with respect to a vertical direction such that an upper end of the rotational blade is positioned on an upstream side of a lower end of the rotational blade, with respect to a rotational direction of the annular rotational portion.