Chapter 8 · Scale · Ten playable problems

PROBLEM 71 · SCALE — LSI +1.1, NO SCALE

A tower runs at LSI +1.1 with no visible scaling. Pick two operational reasons this can be true — two of these six are false.

PROBLEM 72 · SCALE — WHY THE EXCHANGER, NOT THE BASIN

The bulk water looks stable — LSI −0.20. Heat the tube wall and watch the boundary film cross a line the bulk never reaches.

PROBLEM 73 · SCALE — SUPERSATURATION

Define supersaturation in one sentence — then explain how water past its solubility limit can stay perfectly clear for weeks.

PROBLEM 74 · SCALE — CALCIUM PHOSPHATE

A phosphate-based inhibitor can become its own scale. Click the four steps in the order they betray you.

PROBLEM 75 · SCALE — "OUR LSI IS NEGATIVE, SO WE'RE FINE"

The makeup carries 80 mg/L silica and the tower runs 5 cycles. Cycle it up, watch the silica against its ~150 mg/L working limit, then rule on the treater's claim.

PROBLEM 76 · SCALE — CYCLES FROM CONDUCTIVITY

Makeup 850 µS/cm, tower 3,400 µS/cm. Estimate the cycles of concentration.

PROBLEM 77 · SCALE — SULFURIC ACID'S CONTRIBUTION

Makeup sulfate 50 mg/L, tower at 6 cycles. Prediction: 300. Measured: 480. Where did the extra sulfate come from?

PROBLEM 78 · SCALE — pHₛ AND LSI

pH 8.6 · 40°C · TDS 2,200 · Ca 320 · M-alk 220. The four factors are computed below — assemble pHₛ, and the LSI follows.

PROBLEM 79 · SCALE — RSI ON THE SAME WATER

Same water, second opinion: RSI = 2 pHₛ − pH. Dial it and read the interpretation band.

PROBLEM 80 · SCALE — PSI, THE BUFFERED OPINION

PSI swaps the measured pH for the equilibrium pH the alkalinity implies: pHeq = 1.465 log₁₀(220) + 4.54. Dial the index.