THE THERMAL CHARACTERISTICS AND ECONOMIC ANALYSIS OF A SOLAR POND COUPLED LOW TEMPERATURE MULTI STAGE DESALINATION PLANT PART I: THERMAL CHARACTERISTICS

Salt Gradient Solar Ponds (SGSP) have the potential of providing low grade energy with the advantage of an annual thermal energy storage cycle. The development of Multi-Stage Flash (MSF) distillation plants operating below 100°C allows SGSP to be considered as the heat source for these systems.

In this paper, two schemes of matching the SGSP with the MSF distillation plant are presented. The first scheme is based on the assumption that the solar pond is to be used as the sole heat source for the distillation plant (i.e. all the plant's thermal energy requirements are provided by the solar pond). The second scheme considers a hybrid system (solar + fuel), where a 20,000 m² solar pond is linked to an otherwise stand alone, fuel driven desalination plant. Both options are simulated with the same daily product water output of 1000m³/day. The thermal simulation of the MSF desalination process was predicted by using a mathematical model based on stage by stage calculations taking into account the variations in fluid properties and flow conditions. The generated simultaneous equations of the mass and energy balances were combined and arranged in a matrix form and then translated into algorithm to predict process variables such as temperature and flash evaporation rates.     

SOLVENT EXTRACTION OF PAKISTAN COALS (III) EXTRACTION AND CHARACTERIZATION OF THE EXTRACTS BY SPECTROSCOPIC TECHNIQUES

Abstract

The Makerwal coal of Pakistan gives higher extractibi1ity with Tetrahydrofuran ( THF ) as compared to Sharigh, Sor-Range and Lakhra coals. The structural characterization of Pakistan coal extracts by FT-IR spectroscopy indicates that all the extracts contained less condensed aromatic rings in comparision to their original coal.     

An Integrated Mineralogical Approach to the Biooxidation of Sulphide-Bearing Refractory Gold Ores

Abstract

The deportment of gold in the biooxidation feed and product, from the Harbour Lights biooxidation plant in Western Australia, was determined using optical microscopy, SIMS (Secondary Ion Mass Spectrometry), TOF-LIMS (Laser Ionization Mass Spectrometry), and EPMA (Electron Probe Microanalysis).

Visible gold, which is enclosed in sulphide minerals, is liberated as the host mineral is dissolved in the bioleaching environment. ‘Invisible’ or submicroscopic gold is either concentrated on the surface of the host sulphide mineral as a submonolayer or could be released into the liquid phase, where at typical operating conditions it is unstable and will adsorb onto the surface of other ore particles with a net negative surface charge. By virtue of its position on the surface of the particles this gold is now rendered readily cyanidable. Zones of gold enrichment in pyrite and arsenopynte particles have been confirmed to be preferred sites for bacterial oxidation.     

THE THERMAL CHARACTERISTICS AND ECONOMIC ANALYSIS OF A SOLAR POND COUPLED LOW TEMPERATURE MULTI STAGE DESALINATION PLANT PART II: ECONOMIC ANALYSIS

This paper presents the thermal performance and economic feasibility of matching the SGSP with the MSF destilation plant with a daily product water output of 1000 m³/day. The analysis are based on the assumption that the solar pond is to be used as the sole heal source (thermal energy) for the distillation plant. The thermal simulation of the MSF desalination process was predicted by using a mathematical model based on stage by stage calculations taking into account the variations in fluid properties and flow conditions. The generated simultaneous equations of the mass and energy balances were combined and arranged in a matrix form and then translated into algorithm to predict process variables such as temperature and flash evaporation rates.

The paper discusses optimisation of the size of the pond and the number of stages for three different storage zone temperatures taking into account the large variation in quantity of energy supplied by the pond between summer and winter. One result is that oversizing the pond, leading to some rejection of the heat collected during the summer (which is referred to as peak clipping), will result in a higher utilisation factor of the desalination plant and a reduction in the summer/winter yield ratio. Optimum peak clipping days, leading to the minimum product water cost, for each storage zone temperature and performance ratio is presented.

The sensitivity analysis of the various factors affecting the overall water costs show that the capital costs comprise about two thirds (2/3) of the total desalinated water costs. This demonstrates and re-emphasises the inherent and basic fact that solar desalination is a capital intensive enterprise. Each 1% increase in interest rate increases solar pond thermal energy costs by about 13–15% and desalinated water costs from SP/MSF combination by about 10–13%.