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Table 2: Rate coefficient of model reactions. (Sundaram and Froment 1977). With considering mentioned reactions, rate of them will be declared as following: — Table 2 Rate coefficient of model reactions. (Sundaram and Froment 1977). With considering mentioned reactions, rate of them will be declared as following:

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“ Figure 2 shown the furnace zones and coil arrangement. Also for better view about type of segment, Figure 3 illustrates Az segment. Hydrocarbons pyrolysis usually is accompanied with coke formation as a negative component which settle down on the internal side of coil’s wall that it leads to pressure and heat transfer drop as well as hot spots that will eventuate to furnace run-time and selectivity decrease. Due to descent any undesired progress; pyrolysis outlet shall be cooled-down immediately. Therefore trans- fer line exchangers (TLE) have been set in the furnace outlet (Technip Process Description). Figure 1 illustrates the furnace and TLEs flow diagram and arragement.

Table 1: Actual operation & selected model conditions. According to actual data and analysis 8 basic reactions have been presented which are dominant in thé reactor among more than 1000 reactions (Norinaga and Deutschmann 2007; Norinaga et al. 2009; Norinaga, Ja nardhanan, and Deutschmann 2007; Rahimpour et al. 2013). The rate coefficient of model reactions are includec in table 2. After a wide and accurate research, it is understood that Sundaram & Forment model (Froment 1992; Sundaram and Froment 1977; Sundaram and Froment) shall be opted because of akin operation condition with ASPC’s furnaces such as dilution factor and Coil Outlet Temperature (COT). Actual operation & selected model condi- tions are included in Table 1.

Where, T is temperature in K, R is constant of gas, P is pressure in Pa, and F is molar flow rate of in mole s7l, Due to gaseous feed and spacious rang of produced component in the length of coil, Ethylene (C,H) propylene (C3H,) and 1,2butadine (C,H) are in majority so they have been selected as infrastructure of coke formation (Rahimpour et al. 2013; Zarinabadi et al. 2010; Zou et al. 1993). The rate coefficient of coke forming reaction is mentioned in Table 3.

Where, v is stoichiometric coefficient, ris rate of reaction in mole m~2 s—!, Cy is heat capacity in J mole-1 K-1, C is heat flux in W m~?, d is coil diameter in m, AH is heat of reaction in J kmol-!, M is average molecular weigh kg mole~!, Fr is friction factor and finally G is total mass flow rate in Kg m~? s71. For simulation and parameter analysis, Az is provided as following figure, then all for this control volume. Afterward, to the mass and momentum h of the eight materials contained in the model. Thus, and coke formation equa equations shall be expanded as well as simplified for eac in simultaneous solving in different length s ion can be written can be obtained and an adequate analysis of which is caused by the co _ unsatisfactory products by changing each of the change in feed is large ly unavailable, but t ke formation or passing throug eps, the amount of production or consump he changes in the amount of material with these materials in the feed and simulating t ransfer phenomena ion of each material he pressure changes h the knees. It is also possible to reduce the amount of he process. However, he impact of auxiliary feeds, suchas the addi ion of some propane, can be considered. In this way, the optimal amount of propane in the feed can be obtained in such a way that the increase in the production of the admixture C;* does not cause a loss in the amount of ethylene production.

Table 3: Rate coefficient of coke forming reaction (Nabavi et al. 2011).

_ In order to calculate the viscosity of hydrocarbons at low pressures, Bromley & Wilke provided an equation as follows (Perry and Green 1997): F, is different and varies in the knees, depending on the movement of the fluid in the straight area of the coil. Where eq. (25) is for straight parts and eq. (26) is for knees:

Table 4: gas analysis. Table 5: COT and wall temperature. In this section all hydrocracking reactor’s simulation outputs will be presented and discussed. The results of gas analysis and COT and wall temperatures are specified in Tables 4 and 5, respectively.

The temperature of cracked gas is always fixed about 840°C, however by increasing in the coke formation; the fuel gas flow will increase to reach the proper temperature.In the third column of Table 10 actual coils’ wall temperature has been measured and noted. Technip® has considered 1100°C as maximum coil temperature according to its material and has called it End of Run (EOR) temperature that will be reached in the case of coke accumulation. The wall temperatures of the coil will change between 1030 to 1090°C so decoking operation shall be started before this point. The figure 4 illustrates coke and coil radial sketch. Algorithm for numerical solution of equations is described in Figure 5. — 7 7 oe + + 7 7 + _ a

Figure 6: (a) Temperature profile; (b) Pressure profile vs. reactor length for first day of furnace run. Figure 5: Algorithm for numerical solution of equations

Figure 8 shows the thickness of cock at the end of run that would be very useful to predict thickness of cok according to pressure drop in various days. Figure 7: Flow rates of components vs. reactor length for first day of furnace run.

Table 6: The error of model results with actual data. The comparison between experimental and predicted values of model for various parameters are summarizec in Table 6. According to data from this table, there is a good agreement between the values of prediction anc experimental parameters in most cases. After modeling and obtaining results and comparing them with actua conditions, it is possible to have accurate study by changing the conditions on the furnace to achieve highe: efficiency, either in terms of purity of products or in terms of the amount of energy needed to perform the entire cracking operation. And also, all responses indicate tolerable coordination between experiments and estimatec data.

Nomenclature Albright, L.F, and J.C. Marek. 1988. “Coke formation during pyrolysis: roles of residence time, reactor geometry, and time of operation.” In- dustrial Engineering Chemical Researcher 27 (5): 743-51.