A method and facility for the hydrothermal carbonization of pasty products or waste, or sewage sludge, in a pressurized reactor heated to carbonization temperature T0. Before entering the reactor, the products undergo: pressurization, and preheating in an exchanger, by a thermal fluid flowing in a closed loop, and receiving heat from products exiting the reactor; the thermal fluid is heated in the loop by an external heat source, downstream from the exchange with the products exiting the reactor, and upstream from the preheating of the products entering the reactor, and the temperature of the product to be treated, preheated by the thermal fluid, when it enters the reactor, is between the carbonization temperature T0 and T0-100° C. The product to be treated flows in at least one tube, where in at least one location therein, liquid is injected to create a liquid ring against the inner wall, and reduce pressure drops.