Improving combined cycle power plant performance in arid regions

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.In arid regions, where cooling water supplies are limited and highly regulated, combined cycle power plants (CCPPs) are turning to air-cooled condensers instead of water-cooled condensers. However, performance of air-cooled condensers can decline as ambient temperatures increase and result in loss of steam turbine power output. At the same time, as ambient temperature rises, net output of the gas turbine also can decline due to increased power consumption by the compressor and reduced power output by the gas turbine. In this paper, it is proposed to remedy these problems by pre-cooling the inlet air to the air-cooled condenser as well as the compressor, using a low-temperature thermal energy storage (TES) system. The TES is maintained around 5ºC by an absorption refrigeration system driven by the waste heat in the stack gases. A thermodynamic analysis of a 500-MW CCPP incorporating the above concept is presented.vk201

Dual-purpose power-desalination plant augmented by thermal energy storage system

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.This paper presents a novel application of a sensible Thermal Energy Storage (TES) system for simultaneous energy conservation and water desalination in power plants. First, the TES mitigates negative effects of high ambient temperatures on the performance of air cooled condenser (ACC) that cools a 500 MW combined cycle power plant (CCPP); next, the same TES satisfies the cooling requirements in a 0.25 mgd multi-effect distillation (MED) plant. Stack gases from CCPP are used to drive an absorption refrigeration system (ARS) which maintains the chilled water temperature in a TES tank. A process model integrating CCPP, ARS, TES, and MED has been developed to optimize the volume of the TES. Preliminary analysis showed that a tank volume of 2950 m3 was adequate in meeting the cooling requirements of both ACC and MED in both hot and cold seasons. The proposed TES has the potential to save 2.5% of the power loss in a CCPP/ACC on a hot summer day. Further, our modeling results reveal that a desalination capacity of 0.25-0.43 mgd can be achieved with top brine temperatures between 100 ºC and 70 ºC of MED. The proposed integrated system, process modeling and simultaneous advantages of enhanced CCPP performance and sustainable desalination system will be discussed in the presentation.dc201

Future of 2D materials in biosensing applications

Work presented at the International Biodeterioration & Biodegradation Symposium (IBBS18), 6-9 September 2021 | Online conferenceThe atomically thin 2D materials have unique physicochemical properties useful for sensing applications in chemical, biological and corrosion science.1, 2 The high surface-to-volume ratio of these layered materials facilitates efficient response due to the ultrafast carrier mobility of surface atoms. These surface atoms form physiosorbed bonds with adsorbed analyte through electrostatic interactions that can be envisioned in terms of locally induced strain (%) and charge redistribution (n) compared to its pristine state.3 The non-covalent interaction between the analyte and 2D materials shift the Fermi energy level of the host, useful for the selectivity as it offers unique ‘figureprints’ in the optical spectrum. Here, I will present an overview of a systematic study of surface analysis techniques, in particular, using scanning probe microscopy and Raman spectroscopy to uncover physical strain and doping in different 2D materials of graphene and MoS2 for physio-adsorption of analytes. The present study strengthens the possibility of sensing the interaction between several organic and biomolecules toward different 2D materials which is essential in biological and polymeric systems

Effect of combined microwave-ultrasonic pretreatment of real mixed sludge on the enhancement of anaerobic digester performance

The anaerobic biodegradability of combined microwave-ultrasonic pretreated thickened excess activated sludge (PTEAS) mixed with raw primary sludge (PS) was investigated in this study. The pretreatment resulted in the enhancement of mesophilic anaerobic digester performance which in turn improved biogas production capacity and quality, total and volatile solid reduction, dewaterability, protein solubilisation and significant reduction of pathogens to produce class A biosolid. This study presented the results of two continuously stirred mesophilic anaerobic digesters charged with various proportions of a mixture of PTEAS and PS similar to the large-scale industrial practice. Digester 1 was charged with 75 % PTEAS and 25 % PS, while digester 2 was fed with 25 % PTEAS and 75 % PS. The methane production was 122 mL CH4/g total chemical oxygen demand for digester 2 after 20 days of anaerobic digestion. This amount further increased for both digesters with digestion time. The biogas quality in terms of methane to carbondioxide ratio (CH4/CO2) was significantly improved for digester 1 compared with digester 2 after 20 days of digestion. Volatile solid reduction of 76 and 57 % was achieved for digester 1 and digester 2 respectively after the same 20 days of digestion. The CH4/CO2 ratio reached 2.2:1 and 1.1:1 after 20 days of digestion for digester 1 and digester 2, respectively. Higher percentage of PTEAS increases the digestion kinetics, the methane production capacity and the biogas quality. Furthermore, total coliform reduction of 84 and 44 % was achieved for digester 1 and digester 2 respectively after 22 days of digestion. Hydrolysis rate and biochemical methane production were improved for both digesters based on the results of Gompertz kinetic model and the hydrolysis rate constants as determined by model fitting of the experimental data