Pump-as-turbine for Energy Recovery Applications: The Case Study of An Aqueduct☆

Abstract Pump-as-Turbine (PaT) technology is taking the field in different small-hydro or energy recovery applications. These machines can be installed in water distribution grids to have pressure levels adjustment and electrical energy production. A PaT working in turbine mode has a different best efficiency point due to a variation of the fluid-dynamic operating conditions. In this paper, laboratory tests are performed to investigate its performances in pump and turbine mode. Hydraulic efficiency, torque and mechanical power are evaluated in several load conditions. In conclusion, an energy evaluation is shown considering a test case of a water distribution grid

THERMOPHILIC ENZYMES FOR BIOMASS CONVERSION

There is a growing interest in the conversion of lignocellulose biomasses into useful products since the exploitation of agro-industrial waste could provide alternative substrates for low-cost fuels and chemical productions. A key factor for the fruitful utilization of the biomasses is represented by an efficient hydrolysis (saccharification step) of cellulose and hemicellulose using enymes as alternative to the chemical hydrolysis. Since in lignocelluloses the chains of carbohydrates are embedded in a lignin matrix which hinders the enzyme action, a pre-treatment of the biomasses is required for a more effective saccharification. The drastic conditions required by many pre-treatment techniques, give rise to problems when using conventional enzymes in the saccharification step, for the lack of thermostability of most cellulases and hemicellulases. In this context, thermophilic bacteria have received considerable attention as source of cellulolytic and xylanolytic enzymes since they are thermostable, active at high temperatures (thermophylic) and resistant to solvents and detergents. These unusual properties make them attractive candidates for the development of enzymatic biomass conversion processes. Here we report on thermostable cellulolytic, hemicellulolytic and glycolytic activities, isolated from thermophilic bacteria and archaebacteria, that are of potential interest for biomass conversion. Some (hyper)thermophilic microorganisms have been tested for their ability to grow on complex carbohydrates as primary carbon and energy source. Several activities, able to degrade cellulose at acidic pH and high temperature, have been identified in the thermophilic bacterium Alicyclobacillus acidocaldarius. Moreover, a xylanolytic activity from the bacterium Thermus thermophilus has been detected when grown in medium added with xylan. The hyperthermophilic archaeon Sulfolobus solfataricus, originally isolated from a solfataric field in the area of Naples, is another interesting source of enzymes for biomass conversion. From this organism, a bi-functional xylanase/cellulase with optimal temperature and pH of 90/95°C and 4.0/3.5 respectively, is the last of a series of glycoside hydrolases, involved in cellulose and hemicellulose degradation, isolated and characterised from this source in our Institute. Enzymes involved in the hydrolysis of oligomers of starch, cellulose, xylan, mannan, and xyloglucan have also been identified and characterised. Remarkably, these enzymes are all active at temperatures higher than 90°C and acidic pH. Therefore, cocktails of endo- and exo-glycoside hydrolases from this source could convert, in “one pot”, at high temperatures and acidic pH a variety of complex polysaccharides into fermentable sugars. References - Cobucci-Ponzano B, Perugino G, Trincone A, Mazzone M, Di Lauro B, Giordano A, Rossi M and Moracci M (2003) Applications in biocatalysis of glycosyl hydrolases from the hyperthermophilic Archaeon Sulfolobus solfataricus. Biocatalysis and Biotransformation 21, 215-221. - Cannio R, Di Prizito N, Rossi M, Morana A (2004) A xylan-degrading strain of Sulfolobus solfataricus: isolation and characterization of the xylanase activity. Extremophiles 8, 117-124. - Morana A, Paris O, Maurelli L, Rossi M, Cannio R. (2007) Gene cloning and expression in Escherichia coli of a bi-functional b-D-xylosidase/a-L-arabinosidase from Sulfolobus solfataricus involved in xylan degradation. Extremophiles 11, 123-132. - Morana A, Esposito A, Maurelli L, Ruggiero G, Ionata E, Rossi M and La Cara F (2008) A novel thermoacidophilic cellulase from Alicyclobacillus acidocaldarius. Protein Pept. Letters 15, (available online)

a generalized theoretical methodology to forecast flow coefficient head coefficient and efficiency of pumps as turbines pats

Abstract Among the most used hydraulic machines in the small-scale hydropower sector, Pump-as-Turbine (PaT) technology is suitable for both practical and economical aspects. These machines are already profitably applied in remote and rural zones for electricity production and in energy recovery applications in both civil and industrial plants, like Water Distribution Networks (WDNs) and chemical plants. Several studies aimed to provide theoretical formulas able to forecast flow rate and head at the Best Efficiency Point (BEP) in turbine mode obtaining, however, contrasting results and a lack of generalization. In this work, a generalized theoretical methodology for forecasting the flow rate, the head and the efficiency of PaTs at their BEP is studied. Specific correlations between the non-dimensional parameters of PaTs in pump and in turbine mode are presented and discussed. The accuracy of the presented methodology is compared to the ones available in literature showing a good generalization capability and a significant improvement in forecasting the behaviour of the PaT, starting from the available performance characteristics in pump mode

analytical prediction models for evaluating pumps as turbines pats performance

Abstract: The hydropower sector is moving to the small-scale generation due to the exploitation of the majority water reservoirs with the aim of providing electrical energy in rural zones. Pump-as-Turbines (PaTs) is one of the most interesting technology due to their use for recovering energy in different industrial applications. Several studies aimed to study the performance of the tested PaTs and to describe their performance curves. The efficiency of these machines at their Best Efficiency Point (BEP) is comparable as much as the pump mode. In this work, a general analytical method for forecasting PaTs performance in turbine mode was investigated

Residues at the Active Site of the Esterase 2 fromAlicyclobacillus acidocaldarius Involved in Substrate Specificity and Catalytic Activity at High Temperature

The recently solved three-dimensional structure of the thermophilic esterase 2 from Alicyclobacillus acidocaldarius allowed us to have a snapshot of an enzyme-sulfonate complex, which mimics the second stage of the catalytic reaction, namely the covalent acyl-enzyme intermediate. The aim of this work was to design, by structure-aided analysis and to generate by site-directed and saturation mutagenesis, EST2 variants with changed substrate specificity in the direction of preference for monoacylesters whose acyl-chain length is greater than eight carbon atoms. Positions 211 and 215 of the polypeptide chain were chosen to introduce mutations. Among five variants with single and double amino acid substitutions, three were obtained, M211S, R215L, and M211S/R215L, that changed the catalytic efficiency profile in the desired direction. Kinetic characterization of mutants and wild type showed that this change was achieved by an increase in k(cat) and a decrease in K(m) values with respect to the parental enzyme. The M211S/R215L specificity constant for p-nitrophenyl decanoate substrate was 6-fold higher than the wild type. However, variants M211T, M211S, and M211V showed strikingly increased activity as well as maximal activity with monoacylesters with four carbon atoms in the acyl chain, compared with the wild type. In the case of mutant M211T, the k(cat) for p-nitrophenyl butanoate was 2.4-fold higher. Overall, depending on the variant and on the substrate, we observed improved catalytic activity at 70 degrees C with respect to the wild type, which was a somewhat unexpected result for an enzyme with already high k(cat) values at high temperature. In addition, variants with altered specificity toward the acyl-chain length were obtained. The results were interpreted in the context of the EST2 three-dimensional structure and a proposed catalytic mechanism in which k(cat), e.g. the limiting step of the reaction, was dependent on the acyl chain length of the ester substrate

a predicting model of pats performance in off design operating conditions

Abstract The aim of this work is to propose a predicting model for evaluating Pump-as-Turbines' (PaTs) performance in off-design operating conditions. The predicting model has been derived from an elaboration of experimental test data available in literature on a set of several pumps operating in reverse mode. The performance prediction capability of the model has been compared with the results of the Computational Fluid Dynamics (CFD) analysis of a centrifugal pump running in turbine mode for several operating conditions. The comparison of the performance predicted by the model and the ones obtained with the numerical analysis has allowed to evaluate the effectiveness of the proposed model, highlighting its pros and cons and possible improvements. In general, it is possible to conclude that the proposed model is able to correctly assess the work and the efficiency of the studied PaT within errors in the range of few percentage points, especially for operating conditions not so far from the designed one

A MILP algorithm for the optimal sizing of an off-grid hybrid renewable energy system in South Tyrol

The exploitation of renewable energy sources through sustainable energy technologies are taking the field to decrease the pollutions' emissions into the Earth's environment. To offset the limitations of such resources, hybrid energy systems are becoming fundamental in grid-connected applications as well as in off-grid ones. However, the unsteady behavior of renewable sources, such as Sun and Wind, complicates the prediction of the energy production's trend. The main factors and components involved in the design of hybrid energy systems are: (i) type of generators, (ii) their optimal number, (iii) storage systems and (iv) optimal management strategies. All of them have to be considered simultaneously to develop the optimal solution aimed at either reducing the dependence from fossil fuels or granting the supply of energy. In this paper, a methodology based on the Mixed Integer Linear Programming (MILP) is presented and adopted to meet the electric demand of a mountain lodge located in a remote area in South-Tyrol (Italy). The methodology has been developed implementing an algorithm through the Matlab ©software. The algorithm is capable of evaluating the optimal size of a hybrid off-grid Solar–Wind system with battery storage in order to replace an Internal Combustion Engine (ICE) fueled by diesel. Keywords: Hybrid off-grid energy system, Mixed integer linear programming, Matlab©, Optimization algorithm, Renewable energ

effects of viscosity on the performance of hydraulic power recovery turbines hprts by the means of computational fluid dynamics cfd simulations

Abstract Centrifugal pumps are used for increasing the energy content of a liquid: this technology is used in chemical processes with liquids having specific chemical and physical characteristics. Most of the processes are closed-loop, meaning that the liquid is reused after a proper physical or chemical washing treatment is performed. Therefore, the pressure of the liquid has to be decreased by means of a lamination valve or a Hydraulic Power Recovery Turbine (HPRT) with the advantage of recovering energy. HPRTs are generally tested in both pump and turbine modes using water as working fluid. The technical report ISO/TR 17766 indicates the procedure to evaluate the performance of centrifugal pumps handling viscous liquids by supplying correction factors with respect to water, but no indications are given in turbine mode. This work provides correction factors able to evaluate also the performance of HPRTs handling viscous fluids in turbine mode by varying the proposed formulae in the technical report. Computational Fluid Dynamics (CFD) simulations of two tested HPRTs are performed using, at first, water as working fluid for validating the experimental results and, subsequently, the SELEXOL® solvent. Results show that the original correction factors are still valid for the HPRT B that has a parameter B, which is the main one to be involved in the evaluation of the correction factors, lower than 1. A better accuracy, instead, is achieved by modifying the correction factors of the HPRT A, having a value of B higher than 1

technical and economic analysis of pumps as turbines pats used in an italian water distribution network wdn for electrical energy production

Abstract The use of renewable resources is fundamental for achieving the emissions reduction targets. Small-scale hydropower is a viable solution that has only partially been exploited so far for producing electrical energy in rural/remote zones and for recovering energy where there is availability of pressure gradients and flow rates, like in Water Distribution Networks (WDNs) or in other industrial processes. In this paper, Pumps-as-Turbines (PaTs) are studied as a potential energy recovery and pressure regulation device, considering the case study of the Egna municipality WDN, a city located in the North of Italy. An innovative analytical approach is used for selecting PaTs, depending on WDN operating data, and for forecasting the machine performance under varying operating conditions. A MATLAB® Simulink model is developed for simulating two different set-ups configurations and installation of PaTs. Finally, an economic analysis is performed by evaluating the potential energy recovery and the PayBack Periods (PBPs)

Study of a Pump-as-Turbine (PaT) speed control for a Water Distribution Network (WDN) in South-Tyrol subjected to high variable water flow rates

Abstract The development of renewable energy technologies for producing clean energy has more and more become a priority worldwide. Research activities have not just to target the technological improvement of such systems, but they have also to consider their market deployment. In such a scenario, hydraulic machines, in particular Pumps-as-Turbines (PaTs), can play a key role in energy recovery applications. One of the main open issues of PaTs is the performance forecast in turbine mode, due to the lack of data from manufacturers, and their use in some applications with high flow rate and pressure variability, especially at part-load operating conditions like in energy recovery applications within Water Distribution Networks (WDNs). In this work, a MATLAB® Simulink model is developed for simulating a branch of the WDN located in Laives (South-Tyrol), where specific PaTs have been selected and used to substitute Pressure Reducing Valves (PRVs). A speed control by means of an inverter is performed due to the high variability of the flow rate inside the grid branch, allowing the machines to operate at their Best Efficiency Point (BEP). A preliminary analysis showed that it is possible to increase the energy production of about 23% with respect to a constant-speed machine, leading to a significant decrease of the PayBack Period (PBP)