Test And Result Description

Five test series were performed testing several velocities and surface temperatures (eg, see test 2 in Fig. 4). Typical fouling time histories are shown in Figure 5 along with the operating conditions. Notice that the PHE fouling resistances establish a stable asymptotic value after about 600-900 h of operation. The results of the other tests are shown in Figure 6 only as the values of the asymptotic

Cooling water

Figure 3. APV plate heat exchanger with three parallel countercurrent parallel passages for both the cooling water and the hot water.

Cooling water

Figure 3. APV plate heat exchanger with three parallel countercurrent parallel passages for both the cooling water and the hot water.

ft y

Table 3. Cooling-Water System Characteristics

Tower and circulation system

Circulation rate 140,000 gpm

Temperature difference across tower 23.4°F

Number of sidestream filters 2

Corrosion rate from carbon steel coupon tests <1 mil/yr

Water description Cooling-tower water Makeup water

Treatment 10 cycle concentration Unclarified San Jacinto River 1000 gpm

Blowdown from coolers and sidestream filters Clarified San Jacinto River 2400 gpm

Lissie Sand Well 475 gpm

Typical composition

Total hardness as CaC03, ppm 520 48

Calcium as CaC03, ppm 420 40

Magnesium as CaC03, ppm 120 8

Methyl Orange alkalinity as CaC03, ppm 20 34

Sulfate as S04, ppm 1600 34

Chloride as CI, ppm 800 48

Silica as Si02, ppm 150 18

Total inorganic phosphate as P04, ppm 10

Orthophosphate as P04, ppm 7

Specific conductance, micromhos, 18C 5000 300

Chromate as Cr04, ppm 25

Chromium as Cr, ppm 0.5

Soluble zinc as Zn, ppm 2.5

Total iron as Fe, ppm 0.8

Suspended solids, ppm 100 10

fouling resistances, as these are the data required for design.

The chemical analysis of the fouling deposit was made after each test and the results are summarized in Table 4. The primary elements found were phosphorus, zinc, and chrome from the water treatment and silicon from suspended solids in the water.

The photograph of the plates of the PHE shown in Figure 4 at the termination of test 2 indicates that fouling occurred only in the upper third of the plates. This is the region near the hot-water inlet and cold-water outlet, re gion of high surface temperature. Figure 5 shows a surface temperature profile for test 2 conditions of 2.8 ft/s and an inlet bulk temperature of 90°F. From the water chemistry parameters, the saturation temperature for calcium phosphate above which precipitation is expected was calculated to be 163°F (6). The shaded region on Figure 7 indicates the expected precipitation region and corresponds closely to the fouled region seen in Figure 4.

The surface temperatures during some of the tests were higher than those experienced in normal PHE operation. This is the result of the setup condition criteria that the

Figure 4. Fouled plates, test 2.

Figure 5. Typical PHE fouling curves.

Figure 5. Typical PHE fouling curves.

Table 4. Fouling Deposit Analysis, %

Series 2 Series 3 Series 4 Series 5 Series 6

Loss of ignition

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