Salinity energy requirements

Minimal Energy Requirements. The relative effect of the cost of the energy on the cost of the freshwater produced depends on local conditions, and is up to one-half of the total. In attempting to reduce this cost, it is of interest to determine the minimal energy amount thermodynamically needed for separating the water from the saline solution. The physical background to this will be introduced in a simple example. Because of the negligible... 

Energy Requirements The thermodynamic hmit on energy is the idealenergy needed to move water from a saline solution to a pure phase. The theoretical minimum energy is given by ... 

Among the more important economic factors involved in large-scale conversion of saline water are the amount and cost of the energy necessary for operation of the conversion processes. The purpose of this paper is to establish the theoretical energy required by certain idealized conversion processes utilizing freezing. 

Thus from a cold start at atmospheric pressure and without intervention by the operator distillation is in full swing in less than 45 minutes. The space heater is now in intermittent use, merely to float the still at the chosen operating temperature. Both load and capacity increase considerably with the temperature, so that the setting of the thermostat controls the output of the still. The constant electrical load of the still is now of the order of (1200 + 200 + 600) 100 ta 1500 100 watts. Factor rj is the proportion of time, less than unity, that the heater is energized and the factor 100 allows for the selected still temperature and the nature of the feed water, brackish or strongly saline. A breakdown of the energy requirements is shown in Table V. 

Processes, which recover sodium or potassium chlorides from natural brines originating from the ocean or salt lakes probably, have the least salination impact on surrounding lands. Since many of these operations use solar evaporation, they also have a low external energy requirement. The ratio of reserves to annual production rates, even for the salt lakes, is so large that there is not likely to be any noticeable salinity decrease for many years. 

Murphy, G. W., Minimum Energy Requirements for Sea Water Conversion Processes, Office of Saline Water, Progr. Rept. 9 (1956).. ... 

Temperature range (optimum) (°C) pH range (optimum) Salinity 02 requirement Energy metabolism Growth substrates Major waste products time (min) density (cells m - ) ... 

First we will illustrate the minimum energy required to separate a small amount of mixture for the following processes evaporation of water from a saline solution recovery of water by reverse osmosis separation of an ideal binary gas mixture by membrane permeation. Then we will consider the definition of net work consumption for thermally driven processes. Next we will consider a variety of separation processes vis-k-vis their minimum energy requirement for separation. 

Using the expression for the minimum energy required to desalinate sea water (salinity, s = 35) at 25 °C, calculate the minimum energy required per m of fresh water produced if the final volume of the concentrated sea water (= V2) is 90%, 75%, 50% and 25% of the original sea-water volume Vi. 

The driving force for the reverse osmosis process is the applied pressure. The amount of energy required for osmotic separation is directly related to the salinity of the solution. Thus, more energy is required to produce the same amoimt of water from solutions containing higher salt concentrations. 

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