A kiln having a plurality of reaction zones (A, B, C, D) therein that thermally convert non-radioactive combustible waste to a substantially non-hazardous, non-leachable, sintered particulate carbon-less ash by-product, the kiln comprising: first and second ends (104, 106); a body provided between the first and second ends (104, 106) that defines a cavity having a refractory lining that provides resistance to heat conduction, the body having a length-to-diameter ratio and a longitudinal axis oriented substantially horizontal or tilted such that a portion of a lower surface that is adjacent to the second end is lower relative to a portion of the lower surface located adjacent to the first end, wherein the length-to-diameter ratio and the resistance to heat conduction provide a temperature gradient within the cavity that forms separate reaction zones (A, B, C, D) during operation; a first inlet port provided at the first end to receive waste and a first outlet port provided at the second end to expel ash by-product; a second inlet port provided at the second end to receive oxidant gas and a second outlet port provided at the first end to expel fuel gas; flow rate controllers (206, 212) provided at the first inlet port and the second inlet port to control a flow rate therethrough; a thermal sensor that measures a temperature value of the waste within the separate reaction zones (A, B, C, D); and a processor that is electrically coupled to the flow rate controllers (206, 212) and the thermal sensor, the processor having instructions executable to: receive signals from the thermal sensor indicating the temperature value of the waste within the separate reaction zones (A, B, C, D); and control the corresponding flow rate controllers (206, 212), based on the signals received from the thermal sensor, to adjust the flow rates therethrough to maintain the separate reaction zones (A, B, C, D) at preselected conditions. first and second ends (104, 106); a body provided between the first and second ends (104, 106) that defines a cavity having a refractory lining that provides resistance to heat conduction, the body having a length-to-diameter ratio and a longitudinal axis oriented substantially horizontal or tilted such that a portion of a lower surface that is adjacent to the second end is lower relative to a portion of the lower surface located adjacent to the first end, wherein the length-to-diameter ratio and the resistance to heat conduction provide a temperature gradient within the cavity that forms separate reaction zones (A, B, C, D) during operation; a first inlet port provided at the first end to receive waste and a first outlet port provided at the second end to expel ash by-product; a second inlet port provided at the second end to receive oxidant gas and a second outlet port provided at the first end to expel fuel gas; flow rate controllers (206, 212) provided at the first inlet port and the second inlet port to control a flow rate therethrough; a thermal sensor that measures a temperature value of the waste within the separate reaction zones (A, B, C, D); and a processor that is electrically coupled to the flow rate controllers (206, 212) and the thermal sensor, the processor having instructions executable to: receive signals from the thermal sensor indicating the temperature value of the waste within the separate reaction zones (A, B, C, D); and control the corresponding flow rate controllers (206, 212), based on the signals received from the thermal sensor, to adjust the flow rates therethrough to maintain the separate reaction zones (A, B, C, D) at preselected conditions. receive signals from the thermal sensor indicating the temperature value of the waste within the separate reaction zones (A, B, C, D); and control the corresponding flow rate controllers (206, 212), based on the signals received from the thermal sensor, to adjust the flow rates therethrough to maintain the separate reaction zones (A, B, C, D) at preselected conditions.