A hydrothermal reaction system comprising: a plurality of hydrothermal reactors, wherein an individual hydrothermal reactor is configured to pressurize and heat a reaction solution to reach a target pressure and a target temperature so as to form a superheated reaction solution, the superheated reaction solution being used for reacting with a batch of raw materials deposited in the individual hydrothermal reactor to yield a plurality of solid reaction products; a filtering subsystem comprising one or more filters for separating the plurality of solid reaction products from the superheated reaction solution, whereby the superheated reaction solution is recovered; a fluid subsystem comprising one or more pipes, one or more valves and one or more pumps for carrying a liquid to and from the filtering subsystem and to and from the individual hydrothermal reactor, the liquid being the superheated reaction solution or a mixture of the superheated reaction solution and the plurality of solid reaction products; a computer control subsystem comprising one or more computers for controlling the plurality of hydrothermal reactors and the fluid subsystem, the one or more computers being arranged and programmed: to configure the fluid subsystem to transfer the recovered superheated reaction solution previously used for reacting with a first batch of raw materials deposited in a first hydrothermal reactor to a second hydrothermal reactor different from the first hydrothermal reactor for recycling the superheated reaction solution in reacting with a second batch of raw materials, wherein the first and second hydrothermal reactors are selected from the plurality of hydrothermal reactors; and to configure the second hydrothermal reactor to receive the second batch of raw materials under atmospheric pressure before the superheated reaction solution used in reacting with the first batch of raw materials is recovered by the filtering subsystem. a plurality of hydrothermal reactors, wherein an individual hydrothermal reactor is configured to pressurize and heat a reaction solution to reach a target pressure and a target temperature so as to form a superheated reaction solution, the superheated reaction solution being used for reacting with a batch of raw materials deposited in the individual hydrothermal reactor to yield a plurality of solid reaction products; a filtering subsystem comprising one or more filters for separating the plurality of solid reaction products from the superheated reaction solution, whereby the superheated reaction solution is recovered; a fluid subsystem comprising one or more pipes, one or more valves and one or more pumps for carrying a liquid to and from the filtering subsystem and to and from the individual hydrothermal reactor, the liquid being the superheated reaction solution or a mixture of the superheated reaction solution and the plurality of solid reaction products; a computer control subsystem comprising one or more computers for controlling the plurality of hydrothermal reactors and the fluid subsystem, the one or more computers being arranged and programmed: to configure the fluid subsystem to transfer the recovered superheated reaction solution previously used for reacting with a first batch of raw materials deposited in a first hydrothermal reactor to a second hydrothermal reactor different from the first hydrothermal reactor for recycling the superheated reaction solution in reacting with a second batch of raw materials, wherein the first and second hydrothermal reactors are selected from the plurality of hydrothermal reactors; and to configure the second hydrothermal reactor to receive the second batch of raw materials under atmospheric pressure before the superheated reaction solution used in reacting with the first batch of raw materials is recovered by the filtering subsystem. to configure the fluid subsystem to transfer the recovered superheated reaction solution previously used for reacting with a first batch of raw materials deposited in a first hydrothermal reactor to a second hydrothermal reactor different from the first hydrothermal reactor for recycling the superheated reaction solution in reacting with a second batch of raw materials, wherein the first and second hydrothermal reactors are selected from the plurality of hydrothermal reactors; and to configure the second hydrothermal reactor to receive the second batch of raw materials under atmospheric pressure before the superheated reaction solution used in reacting with the first batch of raw materials is recovered by the filtering subsystem.