Energy consumption membrane plants

Large Plants The economics of microfiltration units costing about ilO " is treated under ultrafiltration. When ceramic membranes are used, the cost optimum may shift energy consumption upward to as much as 10 kWh/m. ... 

In the membrane process, the chlorine (at the anode) and the hydrogen (at the cathode) are kept apart by a selective polymer membrane that allows the sodium ions to pass into the cathodic compartment and react with the hydroxyl ions to form caustic soda. The depleted brine is dechlorinated and recycled to the input stage. As noted already, the membrane cell process is the preferred process for new plants. Diaphragm processes may be acceptable, in some circumstances, but only if nonasbestos diaphragms are used. The energy consumption in a membrane cell process is of the order of 2,200 to 2,500 kilowatt-hours per... 

The development of the membrane cell cut the energy consumption in chlor-alkali production. A good cell will produce a ton of caustic for around 2400 kWh. Membrane caustic can only be produced up to around 35%. Several cell designers have tried to develop a cell and membrane combination that would allow 50% caustic to be made, but this has proved to be commercially elusive so far. Membrane cells have probably reached the theoretical limit on energy consumption for a commercial plant. In Japan, power consumption has been cut by 30% over the last 20 years as the conversion from mercury cell progressed. 

Krupp Uhde (KU) know-how and technology is based on extensive experience in chlorine production and provides clients with short shutdown periods for the conversion of chlorine plants to membrane technology, low-energy consumption and includes special technologies for higher chlorine quality and hydrogen-free production. 

Modern data acquisition and evaluation help to optimise the plant under review within a short period of time, to eradicate faults in plant operation and to determine the best materials for the operation of the chlorine electrolysis plant being examined. In this way, inter-relationships are examined between the energy consumption and variables such as membrane types, anode and cathode coatings, temperature, pressure, and concentrations as well as plant shutdowns, brine impurities, materials of construction and manufacturers. It is conceivable that other inter-relationships will come to light that have so far not been considered. 

Innovative process designs are being developed to reduce the size of the membrane unit and the energy needed to separate, condense and inject the carbon dioxide. It seems possible to reduce the energy consumption of the membrane process to about 20-25% of the power plant output. If this work is successful and these membrane plants are built, this application will dwarf all other gas-separation membrane processes. 

As previously reported, membrane contactors present interesting advantages with respect to traditional units. Moreover, they well respond to the main targets of the process intensification, such as to develop systems of production with lower equipment-size/production-capacity ratio, lower energy consumption, lower waste production, higher efficiency. In order to better identify the potentialities of membrane contactors in this logic, they have been recently compared to traditional devices for the sparkling-water production in terms of new defined indexes [24]. In particular, the comparison has been made at parity of plant capacity and quality of final product. The metrics used for the comparison between membranes and traditional units are ... 

Energy Consumption. Electric power consumption of electrolysis is the major part of the energy consumption in a chlor-alkali process. The power consumption of the membrane process has recently been greatly reduced by various improvements. The latest performance of Asahi Chemical s membrane process realized at a commercial plant and also in an industrial scale cell is shown in relation to current density in Figure 13 (82). 

Pervaporation is a membrane process in which a liquid is maintained on the feed side of a membrane and permeate is removed as a vapor on the downstream side of the membrane. Pervaporation is used, because of its low energy consumption and low cost, to separate dissolved organics from water, purify waste water or volatile chemicals, and break azeotropes. Pervaporation plants range from processing a few grams per hour up to thousands of tons per year. For waste water treatment flow of less than 76 L min pervaporation is more cost-effective than other treatment options, such as chemical oxidation, ultraviolet destruction, air stripping followed by carbon adsorption, steam stripping, or distillation/incineration [262]. 

Modern distillation plants have unit capacities of about 25,000 t/d. The energy consumption is approximately 95 KWh/to distillate in the form of saturated steam of a pressure of about 2.2 bar and 4 to 5 KWh/to distillate in form of power for the pump drives. All distillation processes produce a distillate containing only 20 to 30 ppm salts (total dissolved solids). Reverse osmosis (RO) will be the alternative to distillation. The modules which are successfully employed are of the "spiral wound" or the "hollow fiber" configuration. Under favorable conditions, the economic service lifetime of the modules resp. the membranes is about 5 years and warranties for such a figure are given by manufacturers. 

Second, an analysis such as life cycle analysis or environmental impact assessment should be performed on water treatment systems. This analysis should include issues such as treatment plant construction, membrane manufacturing, chemicals consumption, waste production (concentrate streams, sludge, membranes), energy consumption (with the option to apply alternative energies), as well as health aspects and risk assessment. 

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