Non-Linear Multivariable Control of a Fluid Catalytic Cracking Process

Constrained nonlinear multivariable control of a fluid catalytic cracking process

Dynamic matrix control (DMC) has been widely applied in many industrial processes due to the simple design for multivariable process control. However, lack of the adaptability restricts its application in the highly nonlinear and complex processes. The nonlinear model predictive controller for processes is needed, but, from a computational perspective, it has quite comprehensive demands. In this paper, modified quadratic dynamic matrix control (MQDMC), which integrates DMC with the neural network model, is proposed. The predictive model control strategy linearizes the model by applying instantaneous linearization to the nonlinear neural network model at each sampling time. MQDMC has two advantages. First, less computation of linear DMC is used. Second, the nonlinear characteristics of neural networks can be incorporated into predictive control design. In the simulation studies, the performance of MQDMC matches that of nonlinear neural network model predictive control.

The performance of a dynamic matrix control (DMC) algorithm was investigated for the control of a fluidized catalytic cracking (FCC) process operated under full and partial combustion modes. Several types of hierarchical control systems consisting of a supervisory controller and a basic regulatory controller were designed according to the control purpose and the combustion mode. Then, the designed control systems were applied for supervisory unconstrained and constrained control of the FCC process. The dynamic matrix controllers for the unconstrained control showed better performance than PI-controllers for tracking set-points and for rejecting disturbances under both the combustion modes. The supervisory constrained control using the dynamic matrix controllers also showed good performance.

The incorporation of nickel onto a commercial FCC catalyst and co-feeding H2 into the reaction system improves the catalytic performance of rapeseed oil cracking, with respect to gasoline and light olefins (propene and butenes) production. On the other hand, the incorporation of platinum, with or without co-feeding of H2, is detrimental to both the conversion and the selectivity. Thus, a judicious choice of metal is vital for performance during vegetable oil cracking.

A new method is presented for the resolution of the problem of input saturation in nonlinear multivariable process control by means of elementary nonlinear decoupling (END). Input saturation can have serious consequences particularly in multivariable control because it may lead to very undesirable system behaviour and quite often system instability. Many authors have searched for systematic techniques for designing multivariable control systems in which saturation may occur in any of the control variables (inputs, manipulated variables). No generally accepted method seems to have been presented so far which gives a solution in closed form. The method of elementary nonlinear decoupling (END) can be applied directly to the case of saturation control variables by deriving as many control strategies as there are combinations of saturating control variables. The method is demonstrated by the multivariable control of a simulated Fluidized Catalytic Cracker (FCC) with very convincing results

Numerical investigation of influence of treatment of the coke component on hydrodynamic and catalytic cracking reactions in an industrial riser

FUZZYFCC: Fuzzy logic control of a fluid catalytic cracking unit (FCCU) to improve dynamic performance

Fluid Catalytic Cracking handbook: An expert guide to the practical operation, design, and optimization of FCC units

Abstract-Because the request to the quality of cold rolling sheet strips is higher and higher, the hydraulic AGC (Automatic Gauge Control) has been a requisite means for improving the quality of cold rolling strips' finished products. But the PID control strategy, being comprehensively used in the locale, is difficult to satisfy the request of improving the control precision of cold rolling mill, because robustness is not very strong. The dynamic matrix control, brought forward by Cutler, is one of predictive control theories. It adopts the non-parameter model based the step response of the controlled object, and adopts strategies of multi-step prediction, receding-horizon optimization and feedback correction, which has the good tracking characteristic. The dynamic matrix control has succeeded to be applied in the industry field, so it is indispensable and feasible to explore its application in the hydraulic AGC system of the cold rolling mill. But the step response of the whole hydraulic AGC can't be gained easily in the practical project, so it restricts the application of the dynamic matrix control in the hydraulic AGC. In this article, using for reference the thought of the cascade control, the predictive control is combined in the cascade structure. In the thickness loop of the hydraulic AGC, it adopts PID control. And in the inner loop of the screw-down servo system, it adopts the dynamic matrix control. The cascade predictive control in this article solves the problem of gaining the step response of the whole hydraulic AGC difficultly. When adopting the dynamic matrix control, the state observer is constructed, which makes the control system have the state feedback form with the observer, strengthens robustness of the system by correcting the predictive model, and makes the system have the intelligence. It synthesizes merits of PID control, which possesses of the easy algorithm and adjusting the parameter conveniently, the characteristic of the dynamic matrix control including of good tracking characteristic and strong robustness. The result of the experiment shows that the adopted control strategy makes the dynamic quality of the system improved largely. The response time and the control precision of the screw-down servo system are improved. And the thickness precision of the strip is improved too.

DESIGN CONSIDERATIONS FOR A HYDROCRACKER PREFLASH COLUMN MULTIVARIABLE CONSTRAINT CONTROLLER

During fluid catalytic cracking (FCC) operations FCC catalyst particles become contaminated with various metals. These metals impact FCC performance and currently requires equilibrium catalyst (ECAT) mixtures consisting of a blend of FCC particles with a time spent in the reactor ranging from minutes to several months to be continuously extracted and sold as low value products or sent to landfills. Here a unique method to recycle FCC ECAT particles is presented, which separates ECAT particles by metal content by synthesizing carbon nanotubes and nanofibers on the ECAT particles surface and using a biphasic system. ECAT with low metal content can be sent back to the FCC unit for further use while ECAT with high metal content can be used for other purposes. Further, we show these treated ECAT materials of high metals content will absorb oil on the surface of water and may prove useful for oil spill clean‐up applications.

The Fluid Catalytic Cracking unit (FCC) is a key process that plays an important technical and economic role in the refining industry. Over the past years, there has been an increased interest in applying advanced process modelling and control that would lead to a significant economic benefit of FCC operation. This study presents a summary of the study on the preparation of a feedstock (atmospheric residue) from the RFCC unit (fluidized catalytic cracking process). The atmospheric residue, being the last cut drawn from the bottom of the atmospheric distillation column at a high boiling point > 350°C, may contain many impurities such as solids content, density, metal content, water content, residual carbon, etc. However, to ensure proper fluid catalytic cracking operation, it is necessary to characterize it to determine the appropriate type of preliminary treatment. Thus, the main objective of this study was to characterize the feedstock (atmospheric residue). In the environmental context, the characterization of the feedstock gave us an overall idea of its susceptibility to producing atmospheric pollutants such as SOX, COX, and NOX and allowed us to predict the severity of the cracking process in order to reduce the emission of these pollutants and limit coke formation. The characterization results, such as density at 15°C (925.52 kg/m³), residual carbon (6.842% mass), iron content (0.965 mg/kg), nickel content (24.905 mg/kg), vanadium content (0.385 mg/kg), lead content (0.09 mg/kg), copper content (0.06 mg/kg), calcium content (0.74 mg/kg), led to the conclusion that the FCC unit feedstock is ready to be sent to the FCC unit. The adverse impact on the cracking process, the environment, and the quality of the resulting products is minimal. The results also allowed us to conclude that the metal contents determined in the atmospheric residue studied have a low degree of contamination. This has earned Niger's atmospheric residue exceptional quality, making it much more competitive in international markets.

Investigation of the hydrodynamics in the regenerator of fluid catalytic cracking unit integrated by chemical looping combustion

Industrial experiments on the addition of H2S to the fluid catalytic cracking (FCC) feed (hydrotreated vacuum gas oil) were carried out in the commercial FCC unit at Lukoil Neftochim, Bulgaria. It was found that during cracking of pure hydrotreated vacuum gas oil to which was added about 550 ppm H2S that the FCC gasoline contained about 12 ppm more sulfur than the nonspiked feed. Both gasolines obtained from the pure feed and the H2S-spiked feed contained the same type of sulfur compounds: mercaptans, thiophenes, and benzothiophenes. In the case of the H2S-spiked feed, the additional FCC gasoline sulfur formed was about 1.2% of the sulfur in the H2S added to the feed. The FCC gasoline sulfur formed from the pure FCC feed, on the other hand, was about 2.5% of the sulfur in the feed. The higher percent of sulfur conversion of the pure FCC feed relative to the conversion of the H2S suggests that both reaction of H2S with olefins or diolefins (from the catalytic cracking of the hydrocarbons of the feed) and transformation of heavy sulfur compounds contained in the feed may be responsible for the entire FCC gasoline sulfur compounds formation.

The control problem of fluid catalytic cracking (FCC) units is a challenging task due to its model complexity, on linear dynamics, constrained variables and cross coupling interaction between inputs and outputs. Mathematical Control of FCC is challenging and there is a strong incentive to use multivariable control schemes. In this paper, first principle Model of FCCU is developed after analysis of dynamic behavior of this complex process which was sufficiently complex to capture the major dynamic effects that occur in an actual system. Difficulties caused by the interactions are always encountered in the design of multi-loop control systems for MIMO processes like FCCU.The investigated control approach is the multivariable PID which uses BLT tuning. In this detuning method, each controller in the system is designed based on the corresponding diagonal element and ignore the interactions from other loops. The controllers are then detuned to take into accounts the interactions until some prescribed limit (e.g. the biggest log-modulus) is attained.