Plant Design Considerations Research Articles

Brackish water desalination in the Algerian Sahara—Plant design considerations for optimal resource exploitation

A huge geothermal aquifer is located in the northern Algerian Sahara, with brackish water free from toxic inorganic compounds and organic matter. Therefore, this water is appropriate for good quality potable water production after partial desalination. This paper deals with the basic desalination plant design considerations in the context of overall optimal aquifer exploitation. The main types of criteria for such optimization are economic and environmental. Implementing the concept of “blending” reservoir water (at appropriate proportion) with desalinated water, allows cost-effective and environmentally attractive resource exploitation; the latter would be achieved by reinjecting the retentate (after desalination) free from any chemicals that may degrade the reservoir water quality by accumulation over the years. Results are summarized of a typical case study based on low pressure reverse osmosis (RO) membrane desalination. Key RO membrane performance data from a pilot unit are employed in support of this study. The results highlight the main features and the constraints in plant design and desalinated water recovery; constraints are mainly imposed by the need to avoid membrane scaling with no use of undesirable synthetic anti-scalants. The proposed cost-effective plant configuration and operating mode are in accord with the overall optimum resource exploitation. A cost analysis is also performed for a typical potable water production plant. Finally, possibilities are outlined of integrated exploitation of this geothermal reservoir, whereby energy is extracted in addition to potable water production.

Energy system feasibility study of an Otto cycle/Stirling cycle hybrid automotive engine

The aim of this study was to investigate the feasibility of utilising a Stirling cycle engine as an exhaust gas waste heat recovery device for an Otto cycle internal combustion engine (ICE) in the context of an automotive power plant. The hybrid arrangement would produce increased brake power output for a given fuel consumption rate when compared to an ICE alone. The study was dealt with from an energy system perspective with design practicalities such as power train integration, location of auxiliaries, manufacture costs and other general plant design considerations neglected. The study necessitated work in two distinct areas: experimental assessment of the performance characteristics of an existing automotive Otto cycle ICE and mathematical modelling of the Stirling cycle engine based on the output parameters of the ICE. It was subsequently found to be feasible in principle to generate approximately further 30% useful power in addition to that created by the ICE by using a Stirling cycle engine to capture waste heat expelled from the ICE exhaust gases over the complete range of engine operating speeds.

Membrane filtration and reverse osmosis purification of sewage: Secondary effluent for re-use at Eraring Power Station

This paper describes the membrane filtration and reverse osmosis (RO) process currently being adopted for purification and re-use of secondary treated effluent at Pacific Power's Eraring Power Station. Reasons for selection of this purification scheme and plant design considerations are described. Secondary treated effluent is being made available by the Hunter Water Corporation from a new sewage plant being installed on the western side of Lake Macquarie. Effluent volume will rise from an initial 2 megalitres d to about 5 ML d by 2010 with an increase in population. The purification plant size will be increased in stages to match the increase in effluent quantity. Ultimately 95% of the power station's fresh water requirements of 4 ML d will be met by use of recycled water. Membrane filtration will be used for suspended solids removal and disinfection, chlorination for residual disinfection and RO for dissolved solids reduction. The treated effluent will be used at the station as feed to the water demineralizing plant for boiler make-up, direct make-up to the auxiliary cooling water system and for general station uses such as washdown and fire service systems. A separate recycled water storage and distribution system is being installed to service these requirements. The reduction of domestic water requirements at the station will reduce Pacific Power's operating cost by around $800,000 per annum, and domestic water supplies for the Hunter Region will be conserved. Hunter Water has been able to defer for 15 y the construction of a $2.7 million ocean discharge pipeline.

The development of a falling cloud heat exchanger—Air and particle flow and heat transfer

Air and particle flow and heat transfer tests for steel and alumina particles were carried out on the Falling Cloud Heat Exchanger rig at the University of Aston in Birmingham. The rig was operated up to extremes of air flow and temperature conditions. Initial tests revealed that the formation of eddy currents in the vicinity of the air entry section reduced the effective heating length and the thermal ratings of the rig. Further tests were, therefore, conducted under constant air flow conditions. The heat-transfer coefficient for steel particles was found to be greater than that for alumina. But the higher specific heat and specific surface area resulted in alumina recovering more heat per unit mass of the particles. There was some evidence of the heat-transfer coefficient increasing directly with particle concentration in the heat column. It was more pronounced for alumina. The overall effects of this need investigation. The effects of particle material and particularly the particle change due to contaminated hot gases are discussed. Suggestions for further work together with pilot plant design considerations and progress are mentioned. Included also, are the possible applications of the Falling Cloud Heat Exchanger in industries producing dusty or corrosive effluent gases.