Description of industry 



Task force I was concerned with quality criteria 

 for water used by virtually all industries for steam 

 generation and cooling. The task force's study in- 

 cluded Standard Industry Classifications 20 

 through 39, with the exception of 23 and 27, plus 

 the electrical utility industry. Water used for steam 

 that comes into direct contact with a product and 

 cooling water that comes into contact with a prod- 

 uct were, by definition, considered to be process 

 waters and, therefore, were not included in the 

 report of this task force. 



Steam generation and cooling are unique water 

 uses in that they are required in almost every in- 

 dustry. Both uses are encountered under a very 

 wide variety of conditions that require a corres- 

 pondingly broad range of water quality criteria. 



For example, steam may be generated in boilers 

 that operate at pressures ranging from less than 10 

 pounds per square inch (psig) for space heating to 

 more than 3,500 psig for electric-power generation. 

 For any particular operating pressure, the required 

 boiler water quality criteria depend upon many 

 factors in addition to the water temperature in the 

 steam generator. Thus, the amount of potentially 

 scale-forming hardness that is present in the make- 

 up water to a very low pressure boiler is of far less 

 importance when the steam is used for space heat- 

 ing than when it is used for humidification of air. 

 In the first case, virtually all of the steam is re- 

 turned to the boiler as condensate, whereas in the 

 second case, none of it returns to the boiler. Even 

 when operating at the same drum pressure and 

 makeup rate, a higher hardness is acceptable in 

 the makeup water to boilers with low-heat transfer 

 ratings than to those with high ratings. 



From these few examples, it should be apparent 

 that any general criteria for boiler feed water 

 quality could not be applied directly to an indi- 

 vidual boiler plant without further consideration of 

 operating temperatures and pressures, boiler de- 

 sign, makeup rates, and steam uses. All of these 

 afi'ect the nature of the water-caused problems that 

 might be anticipated in the boiler and its 

 auxiliaries. 



Cooling water uses are similarly diverse. They 

 may be once through or recirculated. Once through 

 cooling waters are drawn from amply large sources 

 such as rivers, lakes, or extensions of the sea. They 

 are returned to those sources or to other large bod- 

 ies of water after having passed through heat ex- 

 change equipment just once. The quantities of 

 water required for once through cooling are so 

 huge that it is rarely economically feasible to alter 



their quality by treatment. The most common ex- 

 ception is chlorination for control of biological 

 organisms that interfere with waterflow or heat 

 transfer. 



In recirculating, cooling water systems, the water 

 withdrawn from the river or lake is small in com- 

 parison with the rate of circulation through the 

 heat transfer equipment. Under these conditions, 

 water treatment is economically feasible. Indeed, 

 it becomes a necessity because of the changes in 

 water composition produced by evaporation and 

 other processes encountered during recirculation. 

 As in the case of steam generation, there is such 

 a great variety of cooling equipment used, such a 

 wide range of chemical and physical changes that 

 can take place in the cooling water, and such a 

 variety of water treatment and conditioning meth- 

 ods available, that quality criteria for makeup 

 water to recirculating cooling systems can have 

 only very limited practical significance. The needs 

 of any specific system must be established on the 

 basis of the construction and operating character- 

 istics of that particular system. 



Processes utilizing water 



steam Generation 



Intake: In 1964, manufacturing plants used 

 about 960 billion gallons of water for boiler feed 

 (makeup), sanitary service, and uses other than 

 process or cooling (7). No basis is given for a 

 breakdown of this figure into its components, but 

 boiler feed (makeup) is the larger part. 



No data are available for boiler makeup require- 

 ments of thermal electric powerplants. However, 

 these are small compared with their cooling water 

 requirements. It is estimated, therefore, that the 

 boiler makeup requirements of thermal power- 

 plants approximate the "boiler-feed, sanitary serv- 

 ice, and other uses" (7) in the industrial require- 

 ments so that the total intake for steam generation 

 in the year 1964 is assumed to have been approxi- 

 mately 960 billion gallons. 



Recycle: Recycle of condensed steam back to 

 the boiler will vary from 0-percent for some indus- 

 trial uses and district steam plants to almost 100 

 percent for thermal power generation plants. 



Consumption: Boiler makeup will vary from 

 negligible losses and blowdown in the thermal 

 powerplants to substantially the total water intake 

 in district steam plants with no returned steam 

 condensate. Even for these, the condensate usually 



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