The obtaining of a model for Cementos Cienfuegos S. A. rotary dryer
Drying of the materials that are used in the cement industry is a process of great importance into the whole preprocess of them, because is a fact that the consumption of energy is minimum when the drying and the milling process are accomplished separately.
The drying process in the cement industry can be done in rotary dryers, fast dryers, milling-drying on tandem, on cyclones, etc. In the case of the Cementos Cienfuegos S.A. factory, the drying process is accomplished into a rotary dryer.
The moisture content of the solids in the output of the rotary dryer is the main variable of the whole drying process. For that reason, the control of this variable is essential for the obtaining of a material with the required quality. In the Cementos Cienfuegos S.A. factory, doesn’t exist a measurement element for the moisture content of the solids in the output of the rotary dryer, but a conventional control is made for this variable through the control of the output gases temperature of the rotary dryer, manipulating the fuel flow that is used in the burning with a PID regulator. In the same way the input pressure to the dust filter is controlled, another variable of great importance into the drying process, manipulating the position of the process air valve. This control is accomplished with a PID regulator too.
The implementation of advanced control techniques has increased during the last years, not only for the achievement of an efficient regulation, but for the possibility to add optimization functions to the process control. For all this reasons, the introduction of advanced control techniques has been considered for the drying process of the Cementos Cienfuegos S.A. rotary dryer.
Most of the advanced control techniques are based in the use of a prediction model, for that reason obtaining a model to predict the behavior of the controlled variables when changes into manipulated variables are made is the first step to the introduction of these advanced control techniques. Therefore we have decided to work in the identification of a prediction model for the control of the rotary dryer output gases and the dust filter input pressure, manipulating the fuel fl ow and the process air valve
position respectively, and using the inflow of material to the dryer as a measurable perturbation. On this paper is exposed all the related to the obtaining of this model. The resulting model would be used for the implementation of advanced control techniques that guarantee an effi cient control of these variables and the minimization of the used fuel.
Alkali-activated slag-rich cement pastes with sodium silicate and water glass
The infl uence of sodium silicate (SS) as well as water glass (WG) on slag-rich cement pastes was investigated. The results showed that the water of consistency as well as setting times decreased with both admixtures content, but decreased with WG more than SS. The combined water contents increased till 1.5% admixture content and then tend to be nearly constant.
The flexural and compressive strengths also increased with admixture content till 1.5%, but then decreased slightly. This means that the optimum dose of SS or WG is 1.5% because its activation eff ect stopped or decreased at <1.5%. The sodium silicate mineral admixture can act as a filling or grinding aid when solid (SS) and as an activating material when liqui (WG). So, WG is more eff ective than SS. The DTA thermographs showed that the endothermic peaks of CSH increased with the incorporation of SS or WG, while those of free lime decreased. The SEM images revealed that the hydration products of cement pastes activated with WG are more developed and compact than those activated with SS.
High efficiency cement terminal in Motril Harbour (Granada, Spain)
A fluidized extraction system in halls for marine cement terminals, where the concept fi rst in fi rst out is not a priority, but where the priority is the optimal utilization of the premises area, avoiding the construction of vertical silos which in many harbours simply are not accepted by the authorities and avoiding also the use of front loader machines inside flat storage halls.
Natural radioactivity of building materials. Concrete application. Part I. External radiation: activity concentration indeX
This article discusses several issues related to the concept of natural radioactivity by deepening in the existing types of radioactivity in natural radioactive materials NORM (Naturally Occurring Radioactive Materials) used in construction, as well as their sources and infl uences. This text is the first part of another paper published by the same authors, in the present journal, which refers to the internal radiation due to radon gas naturally emitted by building materials.
We propose an approach to the need to establish some control criteria in this type of materials and we discuss the establishment of different activity indexes depending on each country. Also, we make a review of the existing regulatory framework, both international and national, on these NORM materials.
This work is part of the doctoral thesis of the first author, Beatriz Piedecausa Garcia, to whom the other authors appreciate the efforts to prepare the text now published and the authorization and the facilities provided to access to her work.
Sludge management and the Kyoto protocol. Thermal drying and cement industry combustion
Thermal sludge drying has developed greatly over the past few years, as one of the main ways of stabilising sludge and as a pre-treatment prior to final recycling. One of the main drawbacks of this technology is its high energy consumption. More over nowadays climate change and need for independence regarding energy suppliers are strong drivers for developing alternative ways of energy production for all industries. Within this context, coupling several sectors of the industry to take advantage of the overall energy balance raises much interest and has shown much development over the past few years.
This paper details a full-scale case study of complete integration of a sludge dryer within the cement factory in Spain. The overall benefits include the use of a substitute fuel in the cement kiln while the quality of the cement is guaranteed, and a reliable end-use for the sludge, energy self-sufficient and 0-odour sludge drying. The paper explains these benefits, including a special emphasis on the CO2 quota balance.
STC has developed a project for thermal sludge drying using residual gases from cement production processes, with a system that generates a 90/75 ºC closed air circuit resulting from the exhaust gas exchange in the cement production process.
Consequently, as all the energy used for the drying process comes from the cement production process, there is no need to consume primary energy, and this ultimately optimises the overall process. The sludge thermal drying process allows the overall efficiency of the production process to be improved by achieving more useful energy for the same primary energy consumption (which, moreover, implies a CO2 quota). Moreover, the combustion of sewage sludge in the production process provides an additional CO2 quota.
The following is a proposal for a combination of both processes that results in environmental and financial synergies.
ARF Co processing in Cimpor Brazil
The accumulation of used tires of the increasing fleet of vehicles demand of all society an eff ort to collect, to carry and to destine of environmentally adequate form these wastes.
The co-processing in clinker kilns is the solution more adopted for used tires destination. According to data of Brazilian Portland Cement Association, in the period of 2003 the 2008 had been destined 690,000 t, equivalent the 138 million tires of light cars, for co-processing in cement plants in Brazil.
Cimpor Brazil initiated the activity of used tires co-processing in 2002, and in 2006 initiated the whole tires co-processing in some units to adjust it reality of the market and to increase the total amount beyond increasing the heat substitution in kilns without precalciner. Example: Cajati Plant.
Bridge on the Turia river between Manises and Paterna (Valencia). First international experience on the use of recycled concrete in a cable-stayed bridge
The highway CV-371, which connects the towns of Manises and Paterna, in the metropolitan area of Valencia (Spain), crossed the Turia river with an old bridge, 145 m long, with 9 short spans.
To provide a safety circulation to both pedestrians and bikers it was necessary to widen the bridge. In addition, its morphology did not allow the pass of the foreseen maximum flow of the Turia river.
Therefore a new bridge was designed, with two spans of 55 and 90 m respectively, in the same place of the existing one. This implied its demolition. For that reason, it was proposed to recycle its concrete to be used as aggregate in the new bridge.
The main features of both the existing and the new bridge are described in the article, as well as the propreties of the concretes of the former, the specifi cations of the recycled concrete, the demolition process of the existing bridge, the processing of the concrete to obtain the recycled aggregate, the characterization of the constituents of the recycled concrete, its mix design and the the construction process of the new bridge.