An alkali gas separator comprises a cylinder (1), a tangent inlet (2), an inner cylinder (3), an outlet (4), and a cleaning opening (5), wherein the bottom of the cylinder (1) is in cone structure which upper portion is provided with the tangent inlet (2), and the cone is provided with the outlet (4) and the cleaning opening (5). The cylinder (1) is provided with the inner cylinder (3) inside, which bottom is a receive opening, lower than the tangent inlet (2).