Utilities demineralized water

Utilities. The utility requirements for a process are obtained from both a material and energy balance. The unit costs for each utility may be obtained from plant expense sheets, the accounting department, or a utility superintendent. These costs often increase continually, so they should be reviewed frequently. Utilities are usually steam (high-, medium-, and low-pressure) and their associated unit costs, electricity, natural gas, cooling tower water, and treated or city water. Sometimes instrument air, demineralized water, and refrigeration are considered utilities if they come from a central source and are not tied to a given process. 

The services or utilities available in the laboratories are steam, low-pressure air, gas, hot and cold soft water, 110-volt single-phase and 220-volt three-phase power, demineralized water, and telephone All but the last two have connection outlets at 8-ft intervals along a bench. Demineralized water and telephones are provided on the basis of one outlet per laboratory, regardless of whether the laboratory is a 12- or 24-ft-wide room. All services are brought into the room from the supply headers located in the basement. Floor slots for these pipes are centered on the 12-ft module separation lines. 

Utilities are generally the first to be commissioned in order to provide facilities such as electric power, cooling water, demineralized water, instrument air, plant air and inert gas. Individual plant systems and equipment items are then checked for completeness against line diagrams, component drawings and schedules while lists are prepared of outstanding items (see Chapter 7). 

Area 500 accepts or generates, then stores, all of the utilities within the facility. These include caustic, oxygen, demineralized and deionized water, hot water, primary cooling water, recycle water, potable water, secondary cooling water, steam, propylene glycol, hydrogen, instrument air, natural gas, nitrogen, and carbon dioxide. 

Wastewater streams from the utility functions include boiler and cooling tower blowdowns and waste brine and sludge produced by demineralizing and other water treatment systems. The quantity and quality of the wastewater streams depend on the design of the systems and the water source. These streams usually contain high dissolved and suspended solids concentrations and treatment chemicals from the boiler and cooling tower. The blowdown streams also have elevated temperatures. 

In Universal-Pressure boilers, there are no drams to concentrate the boiler-water salts and impurities, and blowdown is not utilized. Purification takes place by continuously passing all or part of the condensate through demineralizers in a process called condensate polishing. 

The allowable current density—normality ratio for electric membrane operation has been approximately doubled by an improved tortuous path spacer with strap turbulence promoters and by operation at higher pressures up to 60 p.s.i. As a result, twice as much water can now be demineralized per square foot of membrane utilized and/or greater demineralization achieved per pass in electric membrane units. One practical result of this development is a new continuous-flow, two-stage single-stack demineralizer which will provide 93% demineralization at a capacity of 5000 gallons per day and 72% demineralization at a capacity of 30,000 gallons per day. These units produce from 67 to 150% more water per unit membrane area than previously used automatic batch-recirculating units and are far simpler in construction and operation. 

An important factor to be remembered is that in some cases water supplies unsatisfactory for processing to high purity water may be the only sources available. Preliminary demineralization by reverse osmosis will make this water suitable for subsequent demineralization by ion exchange. It is thus apparent that such an economically important factor as plant site location, which may be dependent on the availability of suitable water, can be made more flexible through the use of reverse osmosis. It may be possible now to utilize seawater as a source of industrial process water. 

The demineralized (DM) water make up requirement of a 300 MW(e) AHWR is about 350 m /d. An additional requirement of about 150 m /d.of fresh water for drinking and other purposes is envisaged. It is therefore proposed to set up a 500 m /d low temperature multi effect distillation (LT-MED) seawater desalination plant utilizing low pressure steam from the turbine to meet the DM water requirements. Figure XI-8 provides a schematic flow sheet of the desalination plant of AHWR. 

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