A coupled furnace/reactor simulation was conducted to determine product yields and coking rates for an industrial SL-II naphtha cracking furnace fired by both floor and wall burners. The process gas side, as well as the fire side, is simulated using the computational fluid dynamics (CFD) approach. The molecular kinetic model of Kumar and co-workers was used to simulate the naphtha cracking reactions in the reactor. The results show that the asymmetrical design of the furnace results in asymmetrical profiles of flue gas velocity, temperature, and concentration, and leads to poor heat supply of the wall burners on the front wall as well as a high-temperature zone in the crossover section. The recirculation of flue gas caused by the positioning of burners makes the temperature more uniform in the middle of the furnace. Good agreement between simulation and industrial product yields has been obtained without any tuning of the kinetics, indicating that the proposed approach can be used as a guide for further optimization of geometries and operating parameters of naphtha cracking furnaces with burners located both in the floor and in the wall. The coking rate profile reveals that the maximum coking rate is not located at the coil outlet or near the last reactor bend, but rather at a height of 7 m in the second reactor pass.
The
density, viscosity, and surface tension of aqueous solutions
containing three imidazolium bromine ionic liquids (ILs) [C
n
MIM]Br with different alkyl chain lengths (n = 2, 3, 4) are determined within the temperature ranging
from 283.15 to 343.15 K and at ambient pressure, respectively. The
effect of the alkyl chain length of the imidazolium cation on the
properties of the solutions is investigated. The experimental density
and viscosity are satisfactorily described with the linear model and
the Vogel–Tammann–Fulcher type equation, respectively.
On the basis of the experimental data, the energy barrier and the
surface entropy/enthalpy are calculated. The results show that the
density and surface tension of aqueous ILs solution decrease and the
viscosity increases with the increase of carbon atom number in imidazole
ring carbon chain under the same conditions. The surface ordering
in each aqueous solution follows [C2MIM]Br > [C3MIM]Br > [C4MIM]Br. The calculation of the molecular/ionic
cluster interaction energy shows that there is a strong interaction
between IL and water molecules, and the strong interaction between
water and bromine ions is the main factor determining the properties
of the solution. The data and results can provide a reliable support
for the design and process calculation of chemical absorption cycle
with water/IL working pairs.
The 1-octanol/water partition coefficients (log P) at 298.15 K and the vapor–liquid and liquid–liquid
equilibria (VLE and LLE) of biofuel-related mixtures have been predicted
with four different thermodynamic models: conduct-like screening models
for real solvent (COSMO-RS), conduct-like screening models for segment
activity coefficient (COSMO-SAC) (2002 version), modified COSMO-SAC
(2006 version), and universal functional activity coefficient (UNIFAC).
The 2002 version of COSMO-SAC gives more reasonable predictions for
log P for most investigated mixtures than the other
two approaches when appropriate molecular geometries are chosen for
the computation of the σ profiles. However, the COSMO-RS model
gives better predictions for VLE pressures and vapor-phase compositions
for biofuel-related mixtures, as well as for the LLE of the 1-octanol
+ water and furfural + water mixtures. The accuracy of the models
for the predictions of the partition coefficients and VLE may be improved
by changing the molecular conformations used to generate the σ
profiles. Generally, the three COSMO-based models give better predictions
than UNIFAC for log P and VLE of the investigated
systems and can be applied to predict the thermodynamic properties
of the biofuel-related mixtures especially when no experimental data
are available.
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