A pyrolysis method comprising: (a) combining biomass particles and a solid heat carrier in a mixing zone at the bottom of an upflow entrained bed pyrolysis reactor to provide a pyrolysis reaction mixture, wherein the solid heat carrier is recycled from step (d) and upon being combined with the solid biomass particles rapidly heats the solid biomass particles therefore forming a hot pyrolysis reaction mixture having a temperature from 300 °C to 1100 °C, and wherein the weight ratio of solid heat carrier to biomass particles is from 10:1 to 500:1; (b) subjecting the pyrolysis reaction mixture to pyrolysis conditions to provide a pyrolysis effluent comprising solid char, the solid heat carrier, and pyrolysis products, wherein an oxygen depleted transport gas lifts the pyrolysis reaction mixture through the mixing zone and the reaction zone of the upflow entrained bed pyrolysis reactor, wherein the superficial velocity of the transport gas is sufficient to obtain a residence time of less than 2 seconds of the pyrolysis reaction mixture in the reaction zone, wherein the transport gas enters a lower section of the upflow entrained bed pyrolysis reactor, and wherein the temperature of the pyrolysis reaction mixture is maintained over its duration in the reaction zone; (c) separating, from the pyrolysis effluent, a solids-enriched fraction comprising solid char and a portion of the solid heat carrier, the solid char and the portion of the solid heat carrier having a combined weight of greater than 90% of the weight of the solids-enriched fraction, and a solids-depleted fraction comprising gaseous and liquid pyrolysis products, wherein the separating is carried out in a cyclone; (d) contacting the solids-enriched fraction with an oxygen-containing combustion medium to combust at least a portion of the solid char and reheat the portion of the solid heat carrier to form heated solid heat carrier, and a cooling quench medium to limit the temperature of the recycled portion of the solid heat carrier, and, wherein the contacting is carried out in the reheater containing a fluidized bed comprising a dense phase bed of the solid heat carrier below a dilute phase of the solid heat carrier, wherein the quench medium is introduced to the reheater in the dilute phase of the solid heat carrier and/or within the dense phase bed of the solid heat carrier, wherein the introduction of the quench medium into the dense phase bed is carried out with sufficient control, and at a quench medium flow rate, that avoids significant disruptions of the dense phase bed. (a) combining biomass particles and a solid heat carrier in a mixing zone at the bottom of an upflow entrained bed pyrolysis reactor to provide a pyrolysis reaction mixture, wherein the solid heat carrier is recycled from step (d) and upon being combined with the solid biomass particles rapidly heats the solid biomass particles therefore forming a hot pyrolysis reaction mixture having a temperature from 300 °C to 1100 °C, and wherein the weight ratio of solid heat carrier to biomass particles is from 10:1 to 500:1; (b) subjecting the pyrolysis reaction mixture to pyrolysis conditions to provide a pyrolysis effluent comprising solid char, the solid heat carrier, and pyrolysis products, wherein an oxygen depleted transport gas lifts the pyrolysis reaction mixture through the mixing zone and the reaction zone of the upflow entrained bed pyrolysis reactor, wherein the superficial velocity of the transport gas is sufficient to obtain a residence time of less than 2 seconds of the pyrolysis reaction mixture in the reaction zone, wherein the transport gas enters a lower section of the upflow entrained bed pyrolysis reactor, and wherein the temperature of the pyrolysis reaction mixture is maintained over its duration in the reaction zone; (c) separating, from the pyrolysis effluent, a solids-enriched fraction comprising solid char and a portion of the solid heat carrier, the solid char and the portion of the solid heat carrier having a combined weight of greater than 90% of the weight of the solids-enriched fraction, and a solids-depleted fraction comprising gaseous and liquid pyrolysis products, wherein the separating is carried out in a cyclone; (d) contacting the solids-enriched fraction with an oxygen-containing combustion medium to combust at least a portion of the solid char and reheat the portion of the solid heat carrier to form heated solid heat carrier, and a cooling quench medium to limit the temperature of the recycled portion of the solid heat carrier, and,