Powder-gas heat exchanger and applications thereof

A reactor for exchanging heat between a powder stream and a gas stream in counter-current flow, the reactor being configured such that a mass flow rate associated with the powder stream is substantially equal to a mass flow rate associated with the gas stream in a vertical shaft heat exchanger, wherein the reactor comprises:

• a first powder-gas heat exchanger configured to cool a hot powder from a reactor stage of one or more reactor stages included in the reactor as a part of a reaction with a cool gas stream implemented in the reactor;
• and
• a second powder-gas heat exchanger, configured to inject an output hot gas stream from the first powder-gas heat exchanger, to preheat a cool powder for injection into the one or more reactor stages as a preheated powder stream, wherein each of the first and second powder-gas heat exchanger comprises:
• a powder injection stage wherein a powder is injected at a top of a vertical shaft so as to produce a falling stream of powder in the heat exchanger;
• a gas injection stage wherein a gas is injected near a base of the vertical shaft in a diffuser tube so as to create a rising gas stream;
• a powder disperse stage comprising a first length of the vertical shaft in which the powder from the powder injection stage disperses across the vertical shaft;
• a mixing stage wherein powder from the powder disperse stage and gas from the gas injection stage flow in contact to exchange heat;
• a powder hopper stage at a base of the heat exchanger wherein powder falling past the gas injection stage accumulates as a powder waste product, wherein the powder waste product is exhausted from the heat exchanger by a valve;
• and
• a separation stage at a top of the diffuser tube configured to substantially separate the gas injected at the base of the vertical shaft from any entrained solids, wherein the solids are reinjected in a vertically-downward direction into the diffuser tube, wherein the gas exhausts from the reactor in a manner which does not substantially impact the dispersal of the powder below, wherein
• an entrance velocity of the powder from the powder injection stage, and a velocity of the rising gas from the gas injection stage are selected to minimise recirculation of powder particles in the mixing stage, such that the falling powder stream and the rising gas stream are substantially in contacting counterflow in the mixing stage;
• wherein
• the reactor is configured to process the powder;
• the reactor is configured to recover heat from an exhaust stream from one or more reactor stages, and use the heat to preheat an input powder stream to optimise a thermal energy efficiency of the one or more reactor stages;
• and
• the reaction does not generate a process gas stream, and combustion gas is not injected into either a first reactor stage or a second reactor stage of the one or more reactor stages.