A combustion device in the form of an elevated fixed-grate that includes arcuately shaped solid refractory brick with ribs placed thereunder so as to allow horizontal air flow for fuel combustion. The brick are arranged atop one another in a stacked concentric configuration that forms a central fuel passageway and allows cascading of a fuel pile throughout the combustion stages. The device provides the benefit of proper de-ashing online while distributing the underfire air radially around the fuel pile. The elevated design of the bricks allows the air to be evenly distributed throughout the fuel pile and further allows the isolation of overfire and underfire air. Segregating overfire and underfire air in an evenly distributed manner allows the burner to combust a wide range of fuel moisture contents without modifying the mechanical components of the burner.