Luis G. Palacín

An analysis of lignin removal in a fixed bed reactor by reaction of cereal straws with ozone

The chemical pretreatment with ozone of rye and wheat straws was carried out in a fixed bed reactor. The effect of ozone pretreatment time on lignin removal was determined. Glucose and xylose concentrations in the hydrolysates were also measured after the subsequent enzymatic hydrolysis step. Acid insoluble lignin reacts with ozone within the first 90 min reaction. Insoluble lignin reduction was about 50%. The higher hydrolysis yields were obtained after 120 min ozonation: the glucose yield ranged from 40% to 50% for rye straw and from 34% to 39% for wheat straw, whereas xylose yields were about 30%, independently of the cereal straw. The glucose yields corresponding to the untreated raw straws were considerably lower, about 10%. Longer ozonation time sharply reduced the production of monosaccharides, probably due to the formation of side products. The kinetic model, with the reaction parameters estimated, predicted reasonably well the experimental data.

Evaluation of the recovery of osmotic energy in desalination plants by using pressure retarded osmosis

ABSTRACT The current paper explores the possibility of using pressure retarded osmosis (PRO) as part of the post-treatment of existing desalination plants: a membrane-based PRO system would be used to transform osmotic energy of the retentate into hydraulic pressure; this pressure is then used to generate electricity in a turbine. For this, a source of water with lower osmotic pressure would be needed: municipal or industrial wastewater, brackish water, etc. From the point of view of implementation, except for the PRO membranes, this additional PRO post-treatment uses a small number of additional components, which are similar to those already standards in desalination industry. A model of the process is developed, and some feasibility studies will be discussed, to evaluate the potential for varying mixing rates.

Operation of Medium-size Reverse Osmosis Plants with Optimal Energy Consumption

Abstract This paper deals with the optimal operational strategy of a reverse osmosis (RO) plant for remote sites. The electricity supply to these plants comes usually from renewable energies (wind and solar), when they are not temporarily available, they are complemented by a diesel generator and batteries. The water demand of small settlements in arid regions suffers strong variations along a day. As the higher demand of water usually occurs when solar energy is more available, the operational expenses can be reduced by considering the RO plant as an active load. A good control strategy, will implement a variable operation point, taking into account the predictions of water demand, the expected variation of the available energy sources and the scheduling of cleaning operations in the RO plant, in order to optimize the energy use. In this paper a hybrid predictive control is proposed to implement this task. Simulations of a specific plant show that an adequate operation reduces the diesel energy consumption, while satisfying the variable water demand.

Integrated design using dynamic simulation of reverse osmosis plants

This paper presents a proposal for optimal design of desalination plants using dynamic simulation. In particular it is shown how using integrated design based on simulation, the plant structure can be improved and a better operation point can be achieved, with significant cost reductions. This integrated design takes into account the control structure for the final plant (predictive control) and the plant objectives: fulfil the changing water demand, minimizing the energy consumption and avoiding underflows or overflows of the storage tanks, taking into account several restrictions: operation limits, physical restrictions of the pumps and the necessity of periodic cleanings.

Initial validation of a reverse osmosis simulator

Reverse Osmosis (RO) is the most common technique to produce drinkable water in arid regions. The desalination plants are usually designed for a short number of constant operation points. A dynamic strategy of control would help to decrease the operation expense and the equipments cost. However, the lack of dynamic simulation tools for this kind of plants, avoids the optimal design, which would use a continuously changeable operation point. For this, a new dynamic simulation library of RO plants was presented elsewhere. Now, the present paper deals with the validation of that library, using experimental data from a real RO plant.

Modelling for dynamic simulation of pretreatment in Reverse Osmosis plants

The development of mathematical dynamical models of the pretreatment process in reverse osmosis plants is presented. The objective is to use the models for testing and comparison of control strategies in reverse osmosis plants. Thus, these models have been developed to implement them using off-the-shelf software (EcoSimPro), so that advanced control algorithms can be easily tested. During modeling, the parameters are selected to be simple to obtain from available plant measurements.

Scheduling of the membrane module rotation in RO desalination plants

Abstract This work deals with the optimization, in reverse osmosis desalination plants, of the scheduling of membrane cleanings and rotation of the membrane modules inside each pressure vessel. Each pressure vessel consists of several membrane modules (typically around seven) in series. The modules closer to the feed inlet are prone to be damaged by biofouling and solids, while the modules closer to the reject outlet are prone to be damaged by scaling due to increased salt concentration. Besides, the permeate flux varies for different modules along the pressure vessel. In order to increase the life of the membrane modules, it is a good practice to rotate the modules, thus spreading the difference effects in each module. The topic of this work is to suggest a way to calculate the number and time instants for the rotations, and the optimal operation scheduling. This depends on several factors, such as the time instant for cleanings, the percentage of replacements, the quality of the feed water, etc. Due to ...

Modelling of the pretreatment section for dynamic simulation of water production using reverse osmosis

Abstract The development of mathematical models for the dynamic simulation of the pretreatment section in Reverse Osmosis plants, used for drinking water production, is presented. The objective is to use these models to reduce energy consumption and exploitation costs by testing and comparing advanced control strategies. Thus, these models have been developed for implementation using off-the-shelf software (EcoSimPro), so that advanced control algorithms can be easily tested, while the parameters are selected to be simple to obtain from available plant measurements, so the models can be easily adapted to specific plants.

Optimum Operation of a Beer Filtration Process

This paper deals with the optimum operation of a beer filtration process that uses membranes for this task. Due to fouling, the operation requires cleaning, which damages the membranes, and creates a discontinuous operation. The optimal economic operation can be defined in terms of minimizing the number of chemical cleanings, as well as the use of energy, when processing a certain amount of beer in a given time. The problem is hybrid in nature, due to the discontinuities created by the cleanings. The corresponding optimization problem is formulated in the framework of predictive control but integrating the economic operation as target of the controller and different time scales. Also, instead of using binary variables for representing the discontinuities, the problem employs a sequential approach, embedding them in the dynamic simulation of the process model combined with a control parameterization that allows computing the solution in terms of the continuous variables that represent its degrees of freedom. Results of the optimal operation are presented.

Reduced Model of a Beer Microfiltration Plant

The use of membrane microfiltration in the production of beer is becoming an attractive alternative. This paper discusses the opportunities for a more efficient operation of such a plant, shows the simulations results of a detailed distributed dynamical model of the filtering medium, and presents a reduced order model which is deemed appropriate for on-line optimization.