Commercial risers

Comparison of the mini-commercial riser-downer unit with the industrial riser... 

The effect of time averaging on yields in transient tests can be minimized by shortening the duration of the test. Also, a fixed bed test is superior to an FFB activity test in that backmixing is minimized. Furthermore, an isothermal fixed bed test would be easier to interpret than the adiabatic MAT test. This work shows that from the point of view of a catalyst characterization test, a small steady state riser will give the most direct information for catalyst performance in a commercial riser. 

A number of different types of laboratory scale units have been developed to simulate commercial catalytic crackers. These include fixed bed (MAT), fluidized bed, and riser units.(1,2,3) In particular, for simulating commercial riser FCC units which process residue, a riser pilot plant is the preferred choice. 

Johnson et al. suggest that poor feed injection into a FCC riser results in poor reactor performance FCC profitability and product selectivity are largely determined by feedstock-catalyst contacting at the point at which they meet in the riser [119]. Optimum oil feed distribution minimizes regions of high and low catalyst-to-oil ratios and reduces catalyst backmixing. The atomizer they developed produces superior atomization at modest pressure drop and improved both gasoline selectivity and overall conversion in two different commercial risers. 

In the riser model, detailed hydraulics and heat effects are eaptured by linking flow equations to kineties. The riser model can be eonfigured vertieally, horizontally, or at any angle of inclination. Multiple risers ean be used. The individual risers can process different feeds or the same feed. In essenee, any commercial riser/reactor configuration can be simulated with the modular components of AFCC. 

The ten-lump model has shown success in adequately describing selectivity and conversion behaviour in pilot plant and commercial risers for a wide variety of feeds without modification of the rate constants. However, the simplicity of kinetic representations such as the ones for the three-lump model are partially lost. In using higher lumping models where the number of parameters is significantly increased means that greater amounts of experimental data are also required. 

Inability to closely simulate commercial riser with high temperature regeneration... 

By the late 1980s six principal commercial CEBC technologies were available (42). In 1993 the largest CEBC ia operation is expected to be the Pyropower Corporation s 165 MWe reheat coal-fired unit, under constmction siace 1991 at the Poiat Aconi Station of Nova Scotia Power Corp. (43). Combustion and SO2 control ia this unit is to be carried out ia the water-cooled riser. The unit is expected to operate at 870°C to optimize sulfur capture. The cyclone separators are refractory-lined and are supported approximately 30 m above grade. 

In most of today s FCC operations, the desired reactions take place in the riser. In recent years, a number of refiners have modified the FCC unit to eliminate, or severely reduce, post-riser cracking. Quick separation of catalyst from the hydrocarbon vapors at the end of the riser is extremely important in increasing the yield of the desired product. The post-riser reactions produce more gas and coke versus less gasoline and distillate. Presently, there are a number of commercially proven riser disengaging systems offered by the FCC licenser designed to minimize the post-riser cracking of the hydrocarbon vapors. 

For the sake of developing commercial reactors with high performance for direct synthesis of DME process, a novel circulating slurry bed reactor was developed. The reactor consists of a riser, down-comer, gas-liquid separator, gas distributor and specially designed internals for mass transfer and heat removal intensification [3], Due to density difference between the riser and down-comer, the slurry phase is eirculated in the reactor. A fairly good flow structure can be obtained and the heat and mass transfer can be intensified even at a relatively low superficial gas velocity. 

To construct a model which will give behavior similar to another bed, for example, a commercial bed, all of the dimensionless parameters listed in Eqs. (37) or (39) must have the same value for the two beds. The requirements of similar bed geometry is met by use of geometrically similar beds the ratio of all linear bed dimensions to a reference dimension such as the bed diameter must be the same for the model and the commercial bed. This includes the dimensions of the bed internals. The dimensions of elements external to the bed such as the particle return loop do not have to be matched as long as the return loop is designed to provide the proper external solids flow rate and size distribution and solid or gas flow fluctuations in the return loop do not influence the riser behavior (Rhodes and Laussman, 1992). 

When a chemical reaction occurs in the system, each of these types of behavior gives rise to a corresponding type of reactor. These range from a fixed-bed reactor (Chapter 21-not a moving-particle reactor), to a fluidized-bed reactor without significant carryover of solid particles, to a fast-fluidized-bed reactor with significant carryover of particles, and ultimately a pneumatic-transport or transport-riser reactor in which solid particles are completely entrained in the rising fluid. The reactors are usually operated commercially with continuous flow of both fluid and solid phases. Kunii and Levenspiel (1991, Chapter 2) illustrate many industrial applications of fluidized beds. 

An even larger one-quarter barrel per day circulating unit came very close to simulating both the 200 B/D demonstration unit and later commercial operations. It also possessed a two-stage regenerator and vented riser (both hallmarks of the RCC process). This allowed simulation and evaluation of additional RCC operating parameters. 

In an exploratory experiment, 13 different powder materials were tested in a FFB ACE unit. Most of the results were unremarkable except for three catalysts a low Z/M commercial maximum distillate catalyst (the same LZM catalyst used in the pilot riser experiment), a spray dried low surface area silica (inert) and the minimum aromatics breakthrough (MAB) catalyst. The inert material was included in the study to represent thermal cracking. The catalysts were steam deactivated in the fixed bed steamer prior to testing. Catalysts and the VGO-B feed properties are displayed in Tables 2.3 and 2.1, respectively. LCO aromatics were measured with 2D GC. Figures 2.7 through 2.9 illustrate the main results. 

Tables 2.1 and 2.4 show the VGO-C feed quality properties and the test conditions of the Riser Simulator experiments. The three catalysts tested were the same ones used in the FFB reactor experiments. Temperature for the LZM catalyst was lower than for the other catalysts to reproduce typical conditions used for mid-distillate maximization in commercial units.

FCC catalyst testing prior to use in commercial reactors is essential for assuring acceptable performance. Purely correlative relations for ranking catalysts based on laboratory tests, however, can be erroneous because of the complex interaction of the hydrodynamics in the test equipment with the cracking kinetics. This paper shows how the catalyst activity, coke-conversion selectivity and other product selectivities can be translated from transient laboratory tests to steady state risers. Mathematical models are described which allow this translation from FFB and MAT tests. The model predictions are in good agreement with experimental data on identical catalysts run in the FFB, MAT and a laboratory riser. 

A model for the riser reactor of commercial fluid catalytic cracking units (FCCU) and pilot plants is developed This model is for real reactors and feedstocks and for commercial FCC catalysts. It is based on hydrodynamic considerations and on the kinetics of cracking and deactivation. The microkinetic model used has five lumps with eight kinetic constants for cracking and two for the catalyst deactivation. These 10 kinetic constants have to be previously determined in laboratory tests for the feedstock-catalyst considered. The model predicts quite well the product distribution at the riser exit. It allows the study of the effect of several operational parameters and of riser revampings. 

This paper describes experience with residue processing in catalytic cracking units in the industry, both on a commercial and pilot plant scale. Specific changes which have been made to the design and operating procedures of the Shell Canada Oakville Research Centre (ORC) riser pilot plant are also discussed. 

Using equilibrium catalyst from commercial FCC units, we modified the MAT reactor conditions in order to meet the simulation criteria. This work was complemented with ARGO pilot riser plant tests, exploring the influence of the main process parameters such as residence time, mixing, reactor temperature and temperture profile. 

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