No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Hydrothermal treatment of C-N-O-H wastes: Model-based reactor effluent control
Abstract
In this work, we present model-based control and estimation algorithms developed to control the effluent composition for a hydrothermal oxidation reactor. The reactor is used to oxidize the organic compounds present in the hydrolysate solutions obtained from the destruction of HMX-based high explosives by base hydrolysis. The objective of the model-based control is to minimize the total amount of aqueous nitrogen compounds in the effluent of the reactor while maintaining the desired excess oxygen concentration in the reactor to ensure the complete destruction of the organic carbon compounds. A novel aspect of the controller design for this reactor is that the total aqueous nitrogen effluent concentration is locally uncontrollable at the desired optimal operating conditions. The controller uses a plug-flow reactor model with a reduced kinetic model describing the oxidation - reduction reactions in the hydrothermal oxidation reactor. Simulation and reactor implementation results are used to verify the closed-loop control algorithm.
... These studies are based on unidimensional or bidimensional a steady state models and have had as purpose to determine the final conversion and temperature profile that can be achieved in a reactor. Only a few papers [15,16] have been reported on the response of a SCWO reactor to a transitory phenomena such as those present during the start-up, or to a sudden change in the process conditions, which is more important than predicting the steady state reactor profiles, because the possibility of reaching runaway conditions or the formation of hot spots inside the reactor must be analyzed and avoided. ...
Supercritical Water Oxidation (SCWO), is a high-efficiency, thermal oxidation process capable of treating a wide variety of hazardous wastewaters. SCWO processing systems are fully enclosed and do not produce hazardous air pollutants (HAPS) or NOx. The simulation of SCWO process is a crucial step in the optimization of the process and the energy generation, to explore the scale-up of the process, to optimize changes in operating conditions and to implement new improvement to the process for a complex wastewater. Many attempts have been carried out successfully in stationary state, however, a transitory state simulation is needed in order to achieve an optimal simulation. The software Engineering Equation Solver (EES) have been used to develop the simulation in transitory state. This software is widely used in many engineering problems and simulations involving thermodynamical processes in steady state, because of its huge thermodynamical properties and models database for many compounds. In this work, a transitory state simulation is built-up for the tubular reactor of a supercritical water oxidation plant using the SCWO of isopropanol to model the system. The main problems are both that the transitory state is not a well-known field and that the mathematical expressions involved are quite complex to solve out.
... These studies are based on unidimensional or bidimensional a steady state models and have had as purpose to determine the final conversion and temperature profile that can be achieved in a reactor. Only a few papers [13,14] have been reported on the response of a SCWO reactor to a transitory phenomena such as those present during the start-up, or to a sudden change in the process conditions, which is more important than predicting the steady state reactor profiles, because the possibility of reaching runaway conditions or the formation of hot spots inside the reactor must be analyzed and avoided. ...
The simulation of the Supercritical Water Oxidation (SCWO) process is a crucial step to optimize and to scale up this process. A simulator allows us to know easily the optimization of changes in operating conditions and the performance of new modifications previous to their implementation in the process. Many attempts have been carried out successfully to simulate the SCWO process in steady state, however, only a transitory state simulation is suitable to explore the start-up and to reduce its energetic requirements. The software used in this work have been both Engineering Equation Solver (EES) and Matlab. The combination of both programs is really powerful to solve complex engineering problems and simulations involving thermodynamical properties. The main development of the model has been carried out with Matlab, and EES has been used to determinate the properties of compounds, because EES counts on a huge thermodynamical properties and models database for many compounds. In this work, a transitory state simulation is built-up for the tubular reactor of the supercritical water oxidation pilot plant located at the University of Cádiz. In the course of the start-up, the pressure is remained constant at 250 bar and the temperature is continuously increased until the reaction of oxidation release enough heat to make the process energetically self-maintained. A preliminary model has been built in order to know those requirements of energy, the working pressure is approximately 250 bar and the flow rates are 25 l/h for liquid stream, composed by a mixture of 3% isopropanol diluted in water, and 90 g/min for air stream used as oxidant. The main problems are both, that the transitory state is not a well-known field and there are a considerable number of mathematical expressions involved, being many of them interrelated, so the whole system is quite complex to solve out.
... Hu and colleagues (2001) found that first-order kinetics described the rate of oxidation of printing and dyeing wastewater by WAO. The treatment of hydrolysate solutions (generated from the destruction of high explosives by base hydrolysis) by hydrothermal oxidation was studied by Muske et al. (2001). The treatment goal was minimization of the total dissolved nitrogen. ...
In this chapter, the physicochemical processes used in the treatment of aqueous streams such as domestic and industrial wastewaters, drinking water, contaminated groundwater, and aqueous residuals from soil treatment are reviewed. Processes that have their own chapter in the WEF review are not included in this chapter.
... For the industrial application of the supercritical water oxidation (SCWO) is necessary the development of new reactors able to stand the harsh operational conditions and to overcome the corrosion and salt deposition problems. Due to the severe operating conditions and the high experimental cost, interest in modeling of the SCWO process is increasing [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. To obtain accurate results in the simulations, precise values of densities, enthalpies and heat capacities are needed, both for water and for aqueous mixtures. ...
Corrosion and salt deposition are the main problems for the industrial development of supercritical water oxidation (SCWO). For solving these problems new reactors designs are being developed. The high costs of the research in SCWO make modeling an essential step in the development of new reactors. For getting reliable simulations of the reactors, it is necessary to possess accurate values of the thermodynamical properties of water and aqueous mixtures in the surroundings of the critical point of water, specially the heat capacities.Anderko–Pitzer (AP) EoS was especially developed for aqueous systems at high temperatures and pressures, and it is able to predict accurately volumetric properties and phase equilibrium. But for using this EoS is necessary to fit a large number of parameters, requiring extensive experimental data and making it time-consuming.In this work, parameters have been correlated in order to use the AP EoS to calculate volumetric properties and phase equilibrium of the system water–air. The properties calculated by AP EoS are compared to those calculated using the Peng–Robinson EoS with the translated volume correction, showing notable discrepancies in the heat capacity calculation.Heat capacity calculated by AP EoS is applied in a previously developed mathematical model made by the High Pressure Process Group (HPPG) of the University of Valladolid (UVa), that describes the behavior of the transpiring wall reactor (TWR) of the UVa. The model is able to reproduce the experimental results obtained with the reactor satisfactorily. Experimental temperature profile data are used to validate the predictions of the model.
Supercritical water oxidation (SCWO) has the potential to be considered a clean energy generation process, as the process effluent is a high temperature, high pressure stream with a high enthalpy content that can be converted to heat and shaft work. In this work the state of the art of SCWO has been reviewed, focusing on energy production. For the description of thermodynamic and transport properties, there are some methods recommended for pure substances, but the applicability of those methods for mixtures at supercritical state is yet not clear. Most of the work found in literature use cubic equations of state and linear mixing rules. The design of reactors has evolved in order to reduce the drawbacks of corrosion and salt deposition, in general, through the dilution of reaction products. In order to make the process profitable energetically different strategies must be used to keep the products at the highest temperature without compromising the safety, and the hydrothermal flames if correctly stabilized are a good choice. Reactors and reaction systems able to process feeds consisting of suspension with high inorganic contents without diluting the effluent reducing its temperature must be developed. On the other hand, the systems of energy recovery must be improved, especially the expanders, in order to recover the pressure work as well as the thermal energy. Modeling tools can help in both aspects. But for developing good models a good comprehension of thermal and transport properties of mixtures at supercritical state, as well as oxidation kinetics under that condition are essential data that must be further investigated in order to find energetically efficient processes.
The influence of the internal configuration of vessel reactors for the Supercritical Water Oxidation Process is evaluated by simulation and compared to experimental data. A one equation model is used to close the RANS equations and allows the reproduction of the experimental results. The model can be used for designing reactors working under hydrothermal flame looking at performance and flame stabilization. Geometrical parameters studied here are the distance between injector׳s outlet and reactor׳s ceiling and the injector inner diameter. The influence of operational parameters like flow velocity and inlet temperature is also verified.
In the intensive care unit patients benefit from being fed and from having well controlled glucose levels. Insulin and glucose infusion serves as manipulated inputs to regulate blood glucose, while glucose infusion serves as a sole nutritional input. In this paper, a model predictive control strategy, based on simultaneously manipulating glucose and insulin infusion, is developed to improve blood glucose regulation in intensive care unit patients. In the short term, glucose infusion is used for tighter glucose control, particularly for disturbance rejection, while, in the long-term (24 h period), glucose infusion is used to meet nutritional needs. The “habituating control” algorithm is proposed and tested against a model predictive control (MPC) strategy that only manipulates insulin. The simulation results indicate that the Habituating MPC strategy outperforms the single input–single output MPC by providing faster setpoint tracking and tighter glucose control for a patient population, and producing less glucose variability while rejecting disturbances in insulin infusion and insulin sensitivity.
The results of experiments examining the thermal decomposition of NO and its reactivity with methane in supercritical water at approximately 500 C and 30 MPa are presented. The rate of thermal decomposition is observed to be close to the rate predicted by extrapolating an Arrhenius expression from the literature that has been shown to be valid at 750 C and 1.0 MPa. The observed first-order rate constant at 500 C is 9.4 x 10 s¹. There is no significant effect on NO stability due to the presence of supercritical water relative to ambient pressure. Measurements exploring the conversion rate of methane in the presence of NO reveal that simple oxidation chemistry competes with polymerization. The data suggest that much of the carbon in the system is converted to (CH){sub n} oligomers that separates from the supercritical phase. A detailed kinetic mechanism is used to explore characteristics of these competing processes.
Bench-scale studies demonstrated the efficacy of hydrothermal oxidation for the treatment of wastes derived from the alkaline hydrolysis of the high explosive PBX 9404 (94% HMX, 3% nitrocellulose, and 3% chloroethyl phosphate). Specifically, chemical kinetics studies were used to deduce major global reaction pathways, and to develop a kinetic model. Although the hydrolysis liquor is a complicated waste matrix, a three-parameter kinetic model captured major reaction paths. The kinetic model used total organic carbon (TOC) as a bulk parameter for dissolved organic materials, while NOx- was used to represent the oxidized nitrogen species in solution (NO2- and NO3-). With the use of the kinetic model, an optimal treatment strategy using two oxidation stages was derived. The first stage involved balancing NOx- and O2 redox chemistry to minimize aqueous nitrogen in the effluent, while the second stage mineralized the remaining TOC.
Numerous limitations accompany the use of the plug-flow treatment of tubular-flow reactor data. In this paper we present design criteria, summarizing the findings of earlier workers, which overcome these limitations and assure the legitimacy of the plug-flow idealization. By use of a laminar-flow reactor designed to satisfy these criteria, studies were made of the vapor-phase thermolysis of tert-butyl alcohol, whose rate law is well established. A state-of-the-art nonlinear least-squares kinetics algorithm was used to analyze the tubular-flow reactor data. When the plug-flow idealization was employed, calculated values of E and In A were found to enjoy good agreement with literature values obtained by using other techniques.