Retorting temperature

Properties of the tar oil products are given in Table 14. The oils change only slightly with change in the retorting temperature sulfur levels are low. The fraction boiling up to 230°C contains 65 wt % of phenols, cresols, and cresyUc acids. 

Temperature and Product Yields. Most oil shale retorting processes are carried out at ca 480°C to maximize liquid product yield. The effect of increasing retort temperature on product type from 480 to 870°C has been studied using an entrained bed retort (17). The oil yield decreased and the retort gas increased with increased retorting temperature the oil became more aromatic as temperature increased, and maximum yields of olefinic gases occurred at about 760°C. Effects of retorting temperatures on a distillate fraction (to 300°C) are given in Table 6. 

Table 6. Effect of Retorting Temperature on Product Type ...

Retorting temperature of distillate (reduced to 300°C) Saturates, vol % Olefins, vol % Aromatics, vol %... 

G. U. Diaeen, "Effect of Retorting Temperature on the Composition of Shale Oil," A.lChE Meeting, Denver, Colo., Aug. 1962. 

Retort temperatures are about 200° less than oven Combination of liquids and paraffin waxes from solids collection dmm... 

It is emphasized that rheological data described by Equations 8.41 and 8.42 of a STD cannot be predicted a priori and must be obtained experimentally. Because viscosities at > 95°C were severely affected by water evaporation in the rheometer (Yang and Rao, 1998a), for temperatures fi om 95 to 121°C (retort temperature) (C-D), the decrease in magnitudes of the rf with increase in temperature was assumed to follow an Arrhenius equation (Equation 8.43). 

Figure 8-16 Broken Heating Curve From Simulation of Heat Transfer to a Canned Starch Dispersion at a Retort Temperature (/ 7) 101 °C. The og RT — T) versus time at the assumed slowest heating point and the corresponding fliud apparent viscosity (ija) versus time profiles are shown (Yang, 1997).

The oil yield results of the Fischer assay obtained by the modified TOSCO procedure have been discussed previously (16) and are summarized in Table I. The relative standard deviation in this set of assays was 2.5% on nine oil-yield assays. TOSCO has obtained precision limits of 0.6%. Further examination of the weight fractions in 46 retort runs showed that the major source of this scatter was in the weight of liquid product obtained. This probably can be attributed to the inadequate control of the retort temperature program. The above summary indicates... 

TABLE 17.10 Effect of Retorting Temperature of Colorado Oil Shale on Product Distribution"... 

Chen, C. R. and Ramaswamy, FI. S. (2002). Modeling and optimization of variable retort temperature (VRT) thermal processing using coupled neural networks and genetic algorithms, J.Food Eng., 53, pp. 209-220. 

RETORT CALCULATION During the retort process we assume that no oxygen is present so that only water transport is considered. At retort temperatures the diffusion coefficient of water in materials of interest is sufficiently high so that a pseudo-steady-state model, in which linear profiles are assumed across all structural layers, can be used. The EvOH layer is assumed to be at a uniform water activity at a given time which is good assumption based on water permeability measurements in EvOH at humidities found in package applications (13 ). 

The temperature profile during retort can be specified as any general function of time however, we have used only constant rise and fall rates and fixed retort temperature. By so doing we assume that heat transfer through the package and rate of heating the contents is very rapid. This assumption is reasonable to relax it would serve only to complicate the calculation. 

An important part of the retort simulation for LEP and PEP structures is the temperature dependence of the polypropylene and polycarbonate water permeabilities. Measurements of polypropylene and polycarbonate water permeabilities were made using a MOCON Permatran-W and it was found that polycarbonate has a water permeability which decreases slightly with temperature whereas polypropylene increases with temperature. Near retort temperature the water permeabilities of both materials are similar at storage polycarbonate has a water permeability about ten times greater than polypropylene. Measurements shown in Figure 4 are in good agreement with previously reported results for polycarbonate (2,14-18) and polypropylene (5,19-11). ... 

Higher oil yields and lower coke yields are obtained for smaller particles. Retorting temperature in the range 800-1000°F does not affect coke yield but has an effect on the relative yield of oil and gas. The experimental data are correlated by a simple empirical pyrolysis model where kerogen decomposes by a first-order reaction into a light hydrocarbon product and a heavy intermediate product, "bitumen." Subsequently, the bitumen is subject to two competing processes ... 

In a dense-bed fluidized bed the preheated shale is further heated to and held at the retorting temperature for sufficient time to complete the pyrolysis reactions (Figure 3). The total inventory of shale in the retorting vessel is determined by the required residence time for complete kerogen conversion and the shale throughput. The retort heat requirements are supplied by ceramic balls which circulate in the inner loop. They are reheated in a separate vessel which may operate as a moving bed, raining pellet bed, or entrained flow heater. 

With food materials in which a free liquid fills the interspaces the rate of change of pressure and of temperature is very rapid but while the maximum temperature is reached promptly, the maximum pressure, on the other hand, is never reached during the ordinary processing periods, the pressure continuing to rise slowly as long as the high retort temperatures are maintained. 

In cans filled with material of heavy consistency, the rate of change of temperature at the center of the can is very slow. In contrast with this, the rate of change of pressure is very rapid at first and then becomes slower after the first few minutes. An equilibrium of pressure apparently is never reached, since in experiments where proceseing was continued for several hours the pressure continued to rise as the retort temperature was maintained. 

---