This invention is a novel process for recovering heat from the high temperature reactor effluent without the use of heat exchangers. The reactor product is approximately 650 degF and >2,600 psig. Flash steam will be formed if the pressure is suddenly reduced adiabatically. A simple pressure letdown valve can be used to reduce the pressure, followed by a separation drum to separate the steam from the remaining liquid product. The flash steam can be routed to an earlier stage of the process to heat the reactor feed stream. The flash steam can be mixed with the cold feed through an inline mixer or a mixing drum, as shown in Figure 4. To maximize heat recovery, the pressure letdown can be performed in multiple stages to provide heating at multiple temperatures and pressures. Through a staged pressure letdown process, higher steam temperatures can be achieved, while still recovering the maximum amount of lower temperature heat. Multiple stage letdown is also less erosive to the pressure letdown equipment, so longer life and better reliability can be expected. The flash steam will leave the oil 'biocrude" product behind, limiting recycle of the oil stream. The majority of the organics from the aqueous stream will not flash, however, a substantial portion of the CO2, H2S, ammonia, and other light products will be stripped from the reactor effluent. Some of the major advantages of this novel process configuration may include reduced capital costs, reduced maintenance of equipment and equipment cleaning frequency (due to fouling), and improved operability. Figure 1 of the attachment file shows a traditional HTL processing scheme, where heat recovery is conducted at one pressure level. An adaptation of the traditional HTL process, where heat is recovered at two pressure stages is shown in Figure 2. This process scheme is described by a separate patent application (23-108720-01). Figure 3 illustrates the present invention, where the heat recovery of the low-pressure heat exchangers are replaced by flash steam heating. Note that the flash steam heating in this example is performed in two stages, which could be more (3-stage, 4-stage, etc) or just a single stage in application.