Vibration Monitoring Systems for Cooling Towers

Vibration monitoring is essential to the proper operation of a cooling tower

Vibration Monitoring Systems for Cooling Towers
Cooling towers are a vital part of the infrastructure of many industries. They remove heat from various sources, such as chemical plants, power plants, nuclear power plants and manufacturing facilities. Cooling towers come in multiple shapes and sizes, but they all have one common goal - to remove heat from water or other liquid. This happens by circulating water or the liquid through the cooling tower tubes and allowing the tubes to come into contact with the air or water that evaporates. The air, as it passes by the cooling coil, heats up and removes the heat from the cooling coil. In a similar manner, when the water evaporates, it takes heat with it, leaving the remaining water within the tubes cooler.

In general, cooling tower manufacturers discuss four cooling tower problems:

• Corrosion
• Biological contamination
• Fouling
• Scaling

If the above cooling tower problems are uniform and consistent, you may not see these problems in the vibration signature. However, they are rarely uniform and result in an unbalance. Corrosion can lead to blade failure. Bacterial contamination, fouling and scaling can all lead to unbalance. For example, scaling can fall off of one blade, leaving the other blades heavy, resulting in unbalance.

Cooling towers utilize airflow regardless of whether they are dry or wet. In very large cooling towers, the induced draft caused by the heat moving upward creates the necessary flow without using fans. For example, a nuclear power plant uses a water spray and airflow to cool down the circulating water. Other cooling towers have fans that are powered directly or indirectly depending on their type and construction:

● Motor
● Shaft
● Gearbox
● Drive belt
● Fan Blades

In this blog post, we will be highlighting the cooling tower problems, which can occur with the above components.

Cooling Tower Efficiency 

The efficiency of a cooling tower depends on several factors, one of which is the vibration of the tower. Vibration can cause several problems, including:

Decreased efficiency. Vibration can cause parts, or scaling or fouling, to loosen and fall off, as well as damage the structure of the cooling tower. This can lead to a decrease in the efficiency of the cooling tower and an increase in operating costs.
Increased noise. Vibration can also cause an increase in the noise level emitted by the cooling tower. This can be a nuisance to nearby businesses and residents.
Safety concerns. In some cases, vibration can cause the cooling tower to collapse. This can pose safety hazards for nearby people and property.
Increased wear and tear. Vibration can cause increased wear and tear on the cooling tower parts, like motors, gear boxes and fan blades. This can lead to a shortened lifespan for the cooling tower.

Vibration monitoring is essential to the proper operation of a cooling tower. By monitoring the vibration of the cooling tower, it is possible to have early warning of problems and take corrective action to prevent further damage. 

Cooling Tower Monitoring Considerations

Cooling tower manufacturers need to provide protection against catastrophic failure. This will prevent or minimize cooling tower problems from impacting people and the facilities at a minimal cost. After several years of service, plants usually remove the mechanical switches and install electronic switches with 4-20 mA outputs, or they install vibration transmitters with the 4-20 mA outputs going to the control system, SCADA system, PLCs, and other types of distributed control. Monitoring of cooling towers generally moves from a supplied mechanical switch to a vibration system that provides a 4-20 mA output for early warning and protection.

Value of Seismic Sensors for Cooling Towers

Seismic sensors are an essential tool for monitoring the vibration of cooling towers. Historically, the sensors were designed to measure the ground motion caused by an earthquake. However, they can also measure the vibration of a structure, such as a cooling tower. A seismic vibration sensor is well suited for this task because it can measure very low-frequency vibration, which is common in cooling towers. Seismic sensors are also very rugged and can withstand the cooling tower’s harsh environment.

Cooling Tower Vibration Transmitters

The seismic sensor can be part of an electronic vibration switch or a vibration transmitter. Installing an electronic vibration switch on a cooling tower is a simple process. The sensor is attached to the base of the cooling tower and the 4-20 mA output is connected to a data logger or other control system. In like manner, a vibration transmitter can be installed directly on the fan, gear box, or motor bearing housing to monitor for vibration changes. The 4-20 mA data is recorded over time so trends can be observed. Analyzing the seismic sensor data makes it possible to detect problems with the cooling tower, such as a decrease in efficiency or a change in vibration level.

The 4-20 mA output is used to monitor the vibration of a cooling tower. Electronic switches and vibration transmitters, typically velocity transmitters due to the ability to pick up lower frequencies, are designed to measure the vibration of a structure and transmit the 4-20 mA data to a remote location. This allows for real-time monitoring of the cooling tower.

Benefits of Using Condition-Based Monitoring
When it comes to rotating and reciprocating machinery, there is a great deal of equipment that needs to be monitored to make sure it functions properly. The benefits of using a condition monitoring system on your machines include:

Early detection of problems. Monitoring a cooling tower's vibration makes it possible to detect problems early. This allows for corrective action to be taken before the problem becomes serious.
Reduced downtime. Detecting issues early makes it possible to reduce the time the cooling tower is out of service.
Reduced operating costs. When you catch a problem in advance you have the ability to plan and you can reduce the amount of money spent on repairs.
Improved safety. By detecting a problem early, it is possible to prevent the cooling tower from catastrophically failing. This can reduce the risk of injury to nearby people and damage to property.

Stop Cooling Tower Failure with Vibration Monitoring

When monitoring cooling towers, customers usually start with a mechanical switch and then transition to an electronic switch, a miniature protection system, or a vibration transmitter. The electronic switch and the vibration transmitter both have a 4-20 mA output that can be used by a control system to provide early warning. Using an accelerometer into a two-channel signal conditioner can be effective to monitor the integrated velocity on channel 1 for rotor related issues like blade faults, unbalance, misalignment and, on channel 2, monitor for rolling element bearing defects.

The experts at Metrix Vibration can help you choose the right system for your cooling towers. We offer a variety of systems, including seismic sensors, electronic switches, velocity transmitters and velocity transmitters with switches. Contact us today to learn more.

By Gertjan van den Dolder, Regional Sales Manager Europe