Energy consumption management of circulating water in petrochemical plants

There are not many ways to reduce energy consumption. Previously, there was no side filter; one was added to reduce the amount of wastewater discharged. Another approach is to use some auxiliary chemicals to improve water quality, thereby reducing emissions. The fans should be turned on or off depending on weather conditions and the load on the equipment. If possible, 1-2 of the fans can be modified to become water turbines. For circulating water motors, it’s best to choose those that are efficient and energy-saving

Conduct a thorough inspection across the entire plant to keep the temperature difference between the inlet and outlet water of the circulating water within 4–7°C. If this difference is too low, it is necessary to reduce the amount of water used in order to balance the pressure throughout the plant. If there is a surplus amount of water, consider shutting down one of the circulating water pumps, or shutting down one large pump and running a smaller one, thereby saving electricity.

May I ask what determines that the temperature difference between the inlet and outlet water of the circulating water should be maintained at 4–7°C? Thank you

The operation of the circulating water fan is adjusted according to the temperature of the upper water layer – for example, by starting or stopping it, adjusting its speed, or adjusting the amount of water fed into the tower. The temperature difference in the circulating water is generally kept between 7-8°C; if this difference is higher, scaling is likely to occur during summer

A suitable chemical formula should be selected based on the quality of the raw water, and the dosage of these chemicals must be carefully controlled. Cleaning and pre-coating procedures should be carried out before starting up the system. During operation, it is essential to strictly monitor water quality parameters, pH value, and the concentration ratio; where possible, the concentration ratio should be increased to reduce wastewater discharge. Good water quality is a prerequisite for stable operation as well as for energy savings and reduced consumption. The temperature difference between the inlet and outlet of the circulating water is generally 10°C, with an inlet temperature of 28°C and an outlet temperature of 38°C being standard values. The operation of the cooling tower fans should be adjusted according to this temperature difference. In recent years, there have been several examples of systems that utilize the backpressure from the recycled circulating water to drive the cooling tower fans, which helps to reduce electricity consumption

The last edit to this post was made by pzhmotor on 1/9/2019 at 15:06; it is provided here for reference: The temperature difference between the inlet and outlet water in a cooling tower (efficiency) is directly related to the water flow rate and the wet-bulb temperature. For small mechanical ventilation cooling towers, the designed outlet water temperature is 8–10°C higher than the wet-bulb temperature. In places such as Chongqing and Jiujiang, the wet-bulb temperature is relatively high during summer, making it difficult to achieve the designed temperature difference between the inlet and outlet water (it is therefore necessary to select a larger capacity when designing the system, and build a larger tower). Unfortunately, when the temperature difference between water entering and exiting the system decreases during summer, users tend to open the valves wider for cooling, which results in an even lower outlet water temperature. In my opinion, in addition to water quality management and the temperature difference between inlet and outlet, keeping records of flow rate (measured or estimated through the current used by the pump) and wet bulb temperature is beneficial for optimizing operating conditions. Just from the perspective of saving power consumption, it is advantageous to adopt different fan operation regimes in summer and winter. I encountered an extreme case in Haichuanli: at a refinery in Canada, where the outdoor temperature in winter is around -40°C, the condensate freezes once it returns to the tower, so the return pipes lead directly back to the tank.

After production becomes stable, appropriate adjustments can be made, such as adjusting the water flow by modifying the outlet valve of the cooler, or using frequency conversion to control the operation of the circulation pump. As for the temperature difference, it depends on the requirements of your process; if there is room for adjustment in the temperature after cooling, then the outlet valve can be adjusted accordingly. However, usually only when the operation is stable will the operator not ask you to do this, to avoid instability in production.

Due to the differences in the performance of various devices and the manufacturing processes, there are no specific figures available. I’ve seen temperature differences of around 25 degrees. The inlet temperature of the circulating water is generally influenced by the air temperature