Sanyo DE Management of cooling water quality, Quality control of cooling water, Water treatment

ENVIRONMENTALLY FRIENDLY TECHNOLOGY

Management of cooling water quality

Quality control of cooling water

The cooling water of an open-type recycling cooling tower lowers tem-	gradually be degraded. As the water and air always come in contact with
perature of the cooling water using vaporized latent-heat, and is reused.	each other in the cooling tower, sulfurous acid gas, dust, sand and etc. in
At this time, the water is evaporated and dissolved salts. Hardness mate-	the atmosphere will mix into the water, further degrading the water qual-
rials sulfate ion, etc. in the water will increase. Namely, condensation	ity. In the cooling water system, problems with water are caused by these
phenomena of such materials occurs in the water, and water quality will	factors. Typical problems are corrosion, scales and slimes.

Water treatment

SUPER ABSORPTION

Table 19. Water quality standard values for cooling water and chilled water

				Cooling water system		Chilled water system		Tendency
			Recirculating type		Once through	Recirculating	Make-up water	Corrosive	Scale forming
			Recirculating	Make-up water	(One way) type	below 20° C
	pH(25° C)		6.5 to 8.2	6.0 to 8.0	6.8 to 8.0	6.8 to 8.0	6.8 to 8.0
	Electrical	(ms / m)	80 or less	30 or less	40 or less	40 or less	30 or less
	conductivity 25° C
items
	Chloride ion	(mgCI- / I)	200 or less	50 or less	50 or less	50 or less	50 or less
	Sulfate ion	(mgSO42- / I)	200 or less	50 or less	50 or less	50 or less	50 or less
Standard
	Acid consumption	(mgCaCO3 / I)	100 or less	50 or less	50 or less	50 or less	50 or less
	pH 4.8
	Total hardness	(mgCaCO3 / I)	200 or less	70 or less	70 or less	70 or less	70 or less
	Calcium hardness	(mgCaCO3 / I)	150 or less	50 or less	50 or less	50 or less	50 or less
	Ionic silica	(mgSiO2 / I)	50 or less	30 or less	30 or less	30 or less	30 or less

As with any system utilizing an open or closed loop water circuit, the use of water treatment is a necessity to insure long life and efficient operation of the entire system.

Impurities in the water such as scale, dirt, bacteria, etc. will adhere to heat transfer surfaces causing a loss of efficiency, higher operating costs, and a potential for mechanical damage.

Proper and continued water treatment by a reputable water treatment company should be continued for the life of the equipment. Water treat-

ment specialists can also help determine the necessary time intervals for tube inspections and/or tube brushing/cleaning.

Added attention must be given on retrofit jobs when the existing piping is reused. Air infiltration into the piping will cause a rapid build-up of rust and corrosion inside the piping. Scale and debris may break loose from the inside walls of the piping during retrofit operations. The use of water strainers and water treatment will be necessary to remove the larger par- ticles from the system and keep the smaller particles in suspension.

	Iron	(mgFe / I)	1.0 or less	0.3 or less	1.0 or less	1.0 or less	0.3 or less
	Copper	(mgCu / I)	0.3 or less	0.1 or less	1.0 or less	1.0 or less	0.1 or less
items	Sulfide ion	(mgS2- / I)	No detected	No detected	No detected	No detected	No detected
	Ammonium ion	(mgNH4+ / I)	1.0 or less	0.1 or less	1.0 or less	1.0 or less	0.1 or less
Reference	Residual chlorine	(mgCI / I)	0.3 or less	0.3 or less	0.3 or less	0.3 or less	0.3 or less
	Free carbon	(mgCO2 / )	4.0 or less	4.0 or less	4.0 or less	4.0 or less	4.0 or less
	dioxide
	Ryzner stability	(RSI)	60 to 7.0	***	***	***	***
	index

Figure 69. Temperature control of cooling water

Table 20. Water quality standard values for mid-range temperature water

Automatic three way control valve

MV

From chiller

Cooling

Water pump

To chiller

Cooling water thermostat for three-way control valve

Constant flow	Cooling tower
blow valve

Water supply

Blow

Chemicals adding pump

Chemicals tank

Cooling water thermostat for cooling tower fan

				Mid-range temperature (20-90°C) water system			Tendency
			Lower level (20 to 60° C)		Higher level (60 to 90° C)		Corrosive	Scale forming
			Recirculating	Make-up water	Recirculating	Make-up water
	pH(25° C)		7.0 to 8.0	7.0 to 8.0	7.0 to 8.0	7.0 to 8.0
	Electrical	(ms / m)	30 or less	30 or less	30 or less	30 or less
	conductivity 25° C
items
	Chloride ion	(mgCI- / I)	50 or less	50 or less	30 or less	30 or less
Standard	Sulfate ion	(mgSO42- / I)	50 or less	50 or less	30 or less	30 or less
	Acid consumption	(mgCaCO3 / I)	50 or less	50 or less	50 or less	50 or less
	pH 4.8
	Total hardness	(mgCaCO3 / I)	70 or less	70 or less	70 or less	70 or less
	Calcium hardness	(mgCaCO3 / I)	50 or less	50 or less	50 or less	50 or less
	Ionic silica	(mgSiO2 / I)	30 or less	30 or less	30 or less	30 or less
	Iron	(mgFe / I)	1.0 or less	1.0 or less	1.0 or less	0.3 or less
	Copper	(mgCu / I)	1.0 or less	1.0 or less	1.0 or less	0.1 or less
items	Sulfide ion	(mgS2- / I)	No detected	No detected	No detected	No detected
	Ammonium ion	(mgNH4+ / I)	0.3 or less	0.1 or less	0.1 or less	0.1 or less
Reference	dioxide	(mgCI / I)	0.25 or less	0.3 or less	0.1 or less	0.3 or less
	Residual chlorine
	Free carbon	(mgCO2 / )	4.0 or less	4.0 or less	4.0 or less	4.0 or less
	Ryzner stability	(RSI)	***	***	***	***
	index

Notes :

1)The nomenclature of items, definition of terms and units shall comply with the JIS K 0101.

2)The mark K indicates factors affecting the corrosive or scale-forming tendencies.

3)When temperature is high (above 40° C), corrosiveness generally increases.

Especially, when the iron/steel surface has no protective film and directly contacts water,

it is desirable to adequately take countermeasures against corrosion, such as the addition of a corrosion inhibitor and deaeration treatment.

4)As for the cooling water system using a closed type cooling tower, the water quality standard for

the mid-range temperature water system shall be applied to the closed circuit recirculating/sprinkling water and its make-up water, while the water quality standard for the recirculating cooling water system shall be applied to the sprinkling water and its make-up water, respectively.

5)City water, industrial water and ground water shall be used as source water, and demineralized water reclaimed water, softened water, etc. shall be excluded.

6)The 15 items listed above show typical factors of corrosion and scale problems.

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