How to Maintain Your Heat Exchanger

A heat exchanger is a part of equipment developed for efficient heat transfer from one medium to another. They are widely used in various technical and mechanical machines such as heating, refrigerating, air conditioning, oil refineries, petrochemical plants and natural gas processing and sewage plants. As per the application of heat exchanger and the usage they need to be maintained to ensure efficient use and savings.

Over a period of time, there are various scale deposits of magnesium, calcium and silica that form a layer on heat exchangers. The heat transfer tends to slow down as layers of deposits settle into the exchanger, resulting in overheating or failure of the mechanism. This consequently reduces the energy efficiency of the machine and also acts as a catalyst to its wear and tear. 

Fuel oil combustion deposits as well as coal or wood waste melt onto heat transfer surfaces. Once these deposits have melted, they form a glass-like insulating layer which is difficult to remove. Inefficient heat exchange is caused due to scale and sediment buildup.

Hazards of a Cracked Heat Exchanger:

Cracks in metal surfaces are caused by strain and flexing of the metal. Each time you turn on the system, the exchanger heats up and cools down. This cycle causes the metal surfaces to contract and expand, putting more pressure to the metal and eventually resulting in a crack or failure of the heat exchanger. In due course of normal operation, those small cracks ultimately turn into bigger cracks. 

Premature cracks can also occur early in the life of your furnace if installation or maintenance is improper.

Grounds of Premature Heat Exchanger Cracks:

• Inappropriate Air Flow

Dirty filters, closed off exhaust and blocking of furniture can add to improper air flow to your unit that causes the system to work harder.

• Improper ignition of Gases

Due to airflow restrictions burners may not be igniting properly and hence they may run hotter or at lower efficiency.

• Improper dislocation of Condensation

Condensation mounts up in the heat exchanger, sooner or later rusting the system.

Materials used in Heat Exchangers that may Cause Fouling:

The shelf life of any heat exchanger is about twenty years with regular maintenance of gas heating systems.  Gas Package Units are supposed to wear out faster than other units as they are exposed to the weather and vulnerable to the heating and cooling process and more often to condensation cycle.

Maintenance of plate heat exchangers (PHEs) can help in saving energy and reducing operational costs to companies by up to 30%. 

As the heat exchangers get polluted, the amount of energy needed to run the compressors multiplies and the system is no longer runs at full capacity. Fouling happens when contaminated deposits on the heat exchange surface. This decreases the efficiency of heat transfer over the period of time.

 Also the evaporation temperature decreases and condensation temperature increase providing problems for original start ups. This condition can be avoided with preventive maintenance.

Rubber gaskets used in heat exchangers are available in boundless variants and each variant differs in its quality, characteristics and lifetime. Low quality rubber may be economical while purchase but needs to be changed frequently hence adding up the cost and resulting in wear and tear of the machinery.

Heat Exchanger Maintenance

Plate heat exchangers must be dismantled and cleaned periodically. While Tubular heat exchangers can be cleaned by different methods such as sandblasting, high-pressure water jet, acid cleaning, bullet cleaning and drill rods.

Assessment of plate and tubular heat exchanger can be done by the conductivity or helium gas methods. These methods confirm the reliability of the plates or tubes to prevent any cross contamination and check the condition of the gaskets.

Also, one can leverage software and the internet to perform Online monitoring of commercial heat exchangers for the purpose of tracking the heat transfer coefficient over a period of time. It has been noticed that over a period of time the heat transfer coefficient tends to decline due to fouling.

As the owner of the heat exchanger, it is up to you to estimate the cleaning of the heat exchanger required and can be economically attractive by calculating the overall heat transfer coefficient from exchanger flow rates and temperatures at regular intervals.