Normal operation and control plan for circulating water

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**Commissioning and Normal Operation Plan for the Recirculating Water System**

**I. Purpose and Significance**
The recirculating cooling water system is one of the essential conditions for the stable operation of the plant. Safely and smoothly commissioning this system ensures the proper functioning of all equipment and process pipelines within the system. This, in turn, plays a crucial role in maintaining the required process parameters for normal production.

**II. Preparatory Work**
1. Pressure testing and flushing of the recirculating water pipelines have been completed; the water remaining in the pipes is clean.
2. Individual tests on the recirculating water pumps P-601A/B/C have been concluded. All faults have been rectified, and power supply remains stable. Lighting in the pump house and water tanks is also functioning properly.
3. The fire water tank serving as the source of recirculating water contains sufficient water, and its level gauge provides accurate readings.
4. Preparations for pre-filming of the recirculating water system are complete. Sufficient quantities of biocides, algaecides, and corrosion/inhibitor agents have been prepared, with precise measurements taken.
5. All heat exchangers in the system have been properly treated during flushing; there are no leaks or abnormalities at any connections, allowing for immediate commissioning.

**III. Operating Procedures**
1. After flushing and purging of the recirculating water system, pipeline cleaning and pre-filming procedures must be carried out. Specific steps are outlined separately.
2. Following pre-filming and water replacement, the system should be transitioned to a cold-state operating mode. Return water should not enter the cooling towers but instead flow via a bypass line into the recirculating water tank.
3. During normal operation, biocides, algaecides, and corrosion/inhibitor agents must be added regularly to the water tank. The specific schedule is as follows:
**I.** Biocides and algaecides:
- Months 1, 2, 3, and 4: Add once per month.
- Months 5 and 10: Add every 20 days.
- Months 6, 7, 8, and 9: Add every 15 days.
- Months 11 and 12: Add once per month.
When adding DC-S002 biocide/algaecide, use a dosage of 150 g per ton of total water volume. Increase this amount proportionally based on any additional water input. After application, cease blowdown operations; after 50 hours of system operation, perform a full blowdown/recharge cycle.
DC-S004 biocide/algaecide consists of an active agent (B bottle) and a catalyst (A bottle). Prior to use, mix one bottle of DC-S004B into one barrel of DC-S004A, then allow it to mix for 5 minutes. Subsequently, add the mixture at a rate of 150 g per ton of total water volume, adjusting according to any additional water input. Immediately stop blowdown operations post-application; after 30 hours of operation, conduct another full blowdown/recharge cycle.
**II.** Corrosion/inhibitor agent DC-S213B should be added at a concentration of 15 mg/L relative to the total system volume. Within 1–2 days, total phosphorus content should reach 1.5–2.5 ppm, after which normal operation can commence. Thereafter, dosing should be based on daily water replenishment volumes, maintaining the same concentration level.
The control parameters for recirculating water are listed below:

| Parameter | Unit | Value |
|-----------|------|-------|
| Total Phosphorus | ppm | 1.5–2.5 |
| Chloride (Cl⁻) | mg/L | ≤85 |
| pH | – | ≤8.90 |
| Magnesium (Mg²⁺, expressed as CaCO₃) | mg/L | ≤110 |
| Conductivity | µS/cm | ≤1550 |
| Turbidity | mg/L | ≤20 |
| Total Hardness (expressed as CaCO₃) | mg/L | ≤310 |
| Concentration Ratio | times | ≤2.7 |
| Total Alkalinity (expressed as CaCO₃) | mg/L | ≤700 |
| Calcium (Ca²⁺, expressed as CaCO₃) | mg/L | ≤200 |

**III.** Should total phosphorus levels fall short of the required range during operation, additional DC-S213B must be added. The required quantity is calculated using the formula:
*Quantity to add (kg) = (Desired ppm – Actual ppm) × Total water volume / Percentage of phosphorus content × 1000.*
**IV.** If the concentration ratio exceeds permissible limits, increase blowdown rates accordingly. Calculation formula:
*Blowdown volume (m³) = (Actual concentration ratio – Permissible concentration ratio) / (Actual concentration ratio – 1) × Total water volume.*
4. Upon commissioning, heat exchangers should be activated sequentially from top to bottom—starting with those located at higher elevations. Once all heat exchangers are operational, on-site personnel must conduct thorough inspections to ensure no air pockets form.
5. Post-commissioning, monitor outlet temperatures closely and adjust return water flow rates as needed.
6. Before starting recirculating water pumps, ensure all preparations are complete. Pump C has two outlet paths: one for recirculating water and another for fire-fighting water. Verify the correct path prior to startup; never activate the wrong pathway. Pump outlet valve openings must remain within safe limits (typically no more than 1/3 of maximum opening) to prevent excessive current draw. Maintain close communication with electrical staff post-startup to monitor current levels.
7. In cases where water volume is insufficient or when both units operate simultaneously, seek approval from supervisors to activate two pumps if necessary.
8. Once the system reaches full load, close the bypass line returning water to the tank, open valves leading to both cooling towers, and activate fans.
9. Upon reaching full load, process operators must verify proper water flow into all heat exchangers.

**IV. Precautions**
1. While the system operates, on-site personnel must regularly monitor pump performance, outlet pressure, current levels, and motor temperature. Any irregularities must be addressed promptly and reported.
2. Should any operating pump develop issues, upon receiving instructions from superiors, do not shut down the pump immediately. Instead, first start the standby pump; only after confirming its stability may the original pump be deactivated. Never shut down a pump before ensuring stability of the backup unit.
3. Accurate records must be maintained for all pump startup, operation, and shutdown phases, including pressure, temperature, and current values under normal conditions.
4. Chemical dosing must adhere strictly to supervisor directives. Personnel applying chemicals must wear protective gear and position themselves upwind. Rinse face and mouth thoroughly following application.
5. Should significant water loss occur due to leaks or natural evaporation, replenish the tank with measured amounts of clean water sourced from the fire water tank. Continuous supervision is mandatory during replenishment; valves must be closed afterward, and recorded data must include exact water volume added alongside corresponding chemical dosages.
6. As a reserve water source, the fire water tank must maintain a high water level. Post-every recirculating water recharge, replenish the fire water tank accordingly. On-site personnel must meticulously document water levels and quantities added.
7. Operators working near the recirculating water tank must prioritize personal safety to avoid accidental falls. Operations require multiple personnel, with designated supervisors overseeing tasks.