A vertical dryer, comprising: - a first permeable wall and a second permeable wall configured so as to confine a material to be dried in between the two walls (1, 2) and to allow a stream of air to pass through crosswise to the two walls (1, 2) to dry the confined material, both permeable walls (1, 2) comprising both lengthwise ends corresponding to the inlet and outlet for the material to be dried, - a holding and discharge system adapted to retain the material being dried in the space between the two permeable walls (1, 2) and to discharge the material being dried by gravity, the holding and discharge system being located at the lengthwise end of the permeable walls (1, 2) at the outlet for the dried product, - a forced air system configured to move a stream of air through the permeable walls (1, 2) and the material to be dried, the forced air system comprising: - a first section that extends lengthwise along the permeable walls (1, 2) from the lengthwise end conforming the material inlet, the forced air system being configured to move the air stream in a direction crosswise to the permeable walls (1, 2), and - a second section that extends that extends lengthwise along the permeable walls (1, 2) from the first section to the lengthwise end conforming the material outlet, the forced air system being configured to move the air stream in a direction crosswise to the permeable walls (1, 2) opposite to that of the first section, such that both sections (21, 22) define crosswise air flows, - a suction and impeller means next to the second permeable wall configured to draw the air stream from the first permeable wall towards the second permeable wall in the second section and to blow the air stream towards the first section of the forced air system from the second permeable wall towards the first permeable wall, - a first heat transfer member configured to heat the air stream before it flows crosswise through the permeable walls (1, 2), - the first heat transfer member located in the first section of the forced air system, characterised in that it comprises a second heat transfer member located in the second section of the forced air system, the first and the second heat transfer member (5, 6) being configured to heat the air stream before it flows crosswise through the permeable walls (1, 2) and the forced air system being configured to move the stream of air such that the air is heated by the first heat transfer member for an initial drying stage of the material located in the first section after which the air is reconditioned by the second heat transfer member for a second drying stage of the material located in the second section. - a first permeable wall and a second permeable wall configured so as to confine a material to be dried in between the two walls (1, 2) and to allow a stream of air to pass through crosswise to the two walls (1, 2) to dry the confined material, both permeable walls (1, 2) comprising both lengthwise ends corresponding to the inlet and outlet for the material to be dried, - a holding and discharge system adapted to retain the material being dried in the space between the two permeable walls (1, 2) and to discharge the material being dried by gravity, the holding and discharge system being located at the lengthwise end of the permeable walls (1, 2) at the outlet for the dried product, - a forced air system configured to move a stream of air through the permeable walls (1, 2) and the material to be dried, the forced air system comprising: - a first section that extends lengthwise along the permeable walls (1, 2) from the lengthwise end conforming the material inlet, the forced air system being configured to move the air stream in a direction crosswise to the permeable walls (1, 2), and - a second section that extends that extends lengthwise along the permeable walls (1, 2) from the first section to the lengthwise end conforming the material outlet, the forced air system being configured to move the air stream in a direction crosswise to the permeable walls (1, 2) opposite to that of the first section, such that both sections (21, 22) define crosswise air flows, - a first section that extends lengthwise along the permeable walls (1, 2) from the lengthwise end conforming the material inlet, the forced air system being configured to move the air stream in a direction crosswise to the permeable walls (1, 2), and - a second section that extends that extends lengthwise along the permeable walls (1, 2) from the first section to the lengthwise end conforming the material outlet, the forced air system being configured to move the air stream in a direction crosswise to the permeable walls (1, 2) opposite to that of the first section, such that both sections (21, 22) define crosswise air flows, - a suction and impeller means next to the second permeable wall configured to draw the air stream from the first permeable wall towards the second permeable wall in the second section and to blow the air stream towards the first section of the forced air system from the second permeable wall towards the first permeable wall, - a first heat transfer member configured to heat the air stream before it flows crosswise through the permeable walls (1, 2), - the first heat transfer member located in the first section of the forced air system,