Hot recycling

Hot recycling is the most common method used worldwide for the rehabilitation of asphalt layers. As the name implies, heating is required during mixing and repaving of the reclaimed or the recycled asphalt. 

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PETROSIX. The PETROSIX technology is operated in the IH mode using hot recycle gas as the heat-transport medium. The PETROSIX retort has only one level of heat input, uses countercurrent flows, and uses a circular grate to control the flow of soflds (Eig. 3). The PETROSIX has been operated by Petrobras (Brazil) since the 1950s and is one of the few retorting processes producing shale oil in 1995. 

UNISHALE B. The UNISHALE process, like the Paraho process, uses lump feed and countercurrent flows, and can be operated ia either the DH or IH mode. The UNISHALE B process is an IH process that uses hot recycled gas as the heat-transport medium (Fig. 6). The unique feature of the UNISHALE processes is the rock pump. The soflds move upward through the retort as the vapors are moving downward. The rock pump was used ia the UNISHALE technology at Parachute, Colorado to produce more than 0.64 x 10 m (four million battels) of cmde shale oil. Operations were shut down in 1991. 

Another factor that may account for the relatively higher rate of deactivation with the HGR reactor system is the entrainment in the catalyst bed of oil vapors from the hot recycle gas compressor. This occurrence was evidenced by traces of heavy oil collected downstream of the HGR reactor. Such oil vapors would tend to decompose thermally... 

Dr. Moeller I think to answer this question now is a bit difficult. It s just a mechanical problem of the maximum temperature the recycle compressor can handle. So, in the end, we will go to the inlet temperature to the compressor in the range of the inlet temperature to the reactor. So what we are endeavoring to attain is a simple reaction system consisting of an adiabatic reactor in series with waste heat boilers and nothing more than one recycle compressor. These compressors are used in the chemical industry with no problem in operation. So, in the end, you can go to hot recycle with an inlet compressor temperature the same as the inlet reactor temperature. All the heat from... 

H. Roberts (South African Coal, Oil, and Gas Corp.) May I say that for the pilot plant we used a reciprocating compressor which would operate only at near ambient temperature. So we simulated the operation of the hot recycle compressor by adding high pressure steam on the delivery side of the reciprocating compressor. We did not use a hot recycle compressor in the pilot plant. 

The THF soluble conversion figures may be high however, since hot recycle solvent is probably a better solvent for coal liquids than THF and may have dissolved some material during the hot filtration which would be insouble in THF. 

Figure 4.2 presents a simplified flow diagram of the ENCOAL Liquid from Coal (LFC) process. The process upgrades low-rank coals to two fuels, Process-Derived Coal (PDF ) and Coal-Derived Liquid (CDL ). Coal is first crushed and screened to about 50 mm by 3 mm and conveyed to a rotary grate dryer, where it is heated and dried by a hot gas stream under controlled conditions. The gas temperature and solids residence time are controlled so that the moisture content of the coal is reduced but pyrolysis reactions are not initiated. Under the drier operating conditions most of the coal moisture content is released however, releases of methane, carbon dioxide, and monoxide are minimal. The dried coal is then transferred to a pyrolysis reactor, where hot recycled gas heats the coal to about 540°C. The solids residence time... 

Borax decahydrate is produced from borate ores, primarily colemanite and also from dry lake brines. When produced from its ore, the ore is crushed and then blended with B2O3. The blend is mixed with hot recycle liquor in a dissolving plant. Rock and clay particles from the liquor are removed over vibrating screens. The hquor is then fed to thickeners for settling of insolubles after which the underflow mud is washed with water. The strong liquor of borax hydrates is then pumped into continuous vacuum crystallizers for the separation of the pentahydrate first and then the decahydrate. The products are dried in rotary or fluid bed driers. 

T0474 Lawrence Livermore National Laboratory, Hot-Recycled-Sohd (HRS)... 

The hydrodesulfurization process is essentially the reaction of hydrogen with a predominantly hydrocarbon feedstock to produce a desulfurized hydrocarbon product and hydrogen sulfide. In a very simplified process (Figure 5-1), the feedstock is first pressurized to a pressure which is a little higher than that of the reactor section, mixed with hot recycle gas and preheated to the temperature of the reactor inlet. The hot feedstock (and the recycle gas) is then introduced to the catalyst in the reactor where temperatures on the order of 290 to 455°C (550 to 850°F) and pressures in the range 150 to 3000 psi prevail. 

Crude and refined hydrated sodium borates and hydrous boric acid are produced from kernite and tincal. The ore is fed to the dissolving plant and mixed with hot recycle liquor. Liquor and fine insolubles are fed to a primary thickener. The strong liquors are crystallized in a continuous vacuum crystallizer. 

Description The flowsheet shown is only one of several possible schemes. The raw materials to a free-standing glycol plant are refined ethylene oxide and pure water. These are mixed with recycle waters and pumped from a feed tank (1) to the hydration reactor after being preheated with hot recycle water and steam. When the glycol unit is part of a combined oxide/glycol plant, it is economically desirable to feed it bleed streams from the ethylene oxide... 

Almost all feedstocks of interest have such properties that they do not flow readily through cither pipes or shell of a conventional heat exchanger without distribution problems. Afler a number of alternatives had been considered it was concluded that the most adequate way of preheating is direct injection of hot water. In Fig. 3 this is done in vessel V where a stream of hot recycle water is mixed with the feed. A special way of contacting achieves efficient heat and mass transfer. It has been verified in our experiments that at 200-250°C biomass feedstocks of different origin, including wood chips, arc softened and form a pastc-like substance [7,8]. The... 

Disodium tetraborate, or borax, containing 5 to 10 molecules of water is produced mainly from sodium-containing borate ores (International Programme on Chemical Safety 1998). Crushed and ground ore is mixed with hot recycled water containing some borax. Insoluble gangue (clay particles) is separated from the hot slurry to leave a clear concentrated borax solution. Evaporative cooling of the solution produces crystals of borax that are separated from the residual liquor and dried. 

Smith RW (1980) State-of-the-art hot recycling (Transportation Research Board, Record No. 780), Proc National Seminar on Asphalt Pavement Recycling, Washington, DC,p 534... 

The Exxon donor solvent, direct liquefaction process also used hot oil drying. In this process, LRC is dried by a high-pressure hydrogenation reactor contact with hot recycle hydrogen donor solvent prior to entering. Unfortunately, no data were developed for solvent recovery after drying becanse the dried coal and vehicle solvent were reacted immediately with hydrogen in the Uqnefaction reactor. 

Pavement recycling methods differ from the flexible to the rigid type of pavement. In flexible pavements, two basic methods are distinguished hot recycling (HR) and cold recycling (CR). Each one is further distinguished into in situ (or in-place) and in-plant (central plant) recycling. 

Hot recycling in flexible pavements consists of removing the existing asphalt layer to a determined depth and replacing it with hot asphalt resulting from the same reclaimed material, with the possible addition of new material, that is, mixed in situ or new/recycled asphalt mixed in a central plant. 

Hot recycling may be carried out in situ or in a central mixing plant (in-plant). Hot in situ recycling is distinguished into repave, remix and reshape procedures. The basic steps followed in all versions of hot recycling are shown in Figure 18.4. 

The repave process offers perhaps the ultimate rehabilitation/hot recycling results compared to the other two hot recycling in situ processes. In particular, its advantages over the other two in situ processes are as follows (a) complete restoration of surface skid resistance since new asphalt material is used, (b) strengthening of the pavement to a certain extent and (c) minimisation of smoke emission. 

Various mix design methods for hot recycled mix have been developed by various organisations worldwide. The main principles in all mix design procedure are the same, and the following are the general design steps followed ... 

The other difference with hot recycling mix design is the pre-mix moisture content and final moisture content of the recycled mixture. Moisture content determination is important in cold recycling mix design because it affects the workability of the material and can control the degree of compaction achieved. 

ASTM D 4887/D 4887M. 2011. Standard practice for preparation of viscosity blends for hot recycled asphalt materials. West Conshohocken, PA ASTM International. 

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