Effective ways to optimise heat exchangers

Published: 13-Apr-2018

Heat exchangers are used within a wide range of process industries as a way to transfer heat between two fluid streams across a medium in an energy conservative way

A heat exchanger is designed to improve material contact in a conduit network, whereby one material exchanges heat and the other material flows within the network, either counter- or cocurrently. To improve and optimise the performance of a heat exchanger, it must operate within its designed and specified limits. It’s important to identify the operating parameters and properties of the heat exchanger that could affect its performance — such as feed material, poor maintenance, a high degree of fouling, climatic effects, etc. Let’s look at some of these parameters and how they affect heat transfer.

Operating pressure

The pressure difference between the suction and discharge of each fluid stream is the primary driving force of that stream. This pressure differential can be affected by fluid flow rates, the number of heat exchanger passes, pipe surface friction, bulk density and viscosity. If any deposits are present in the exchanger, the available surface area will reduce and the pressure differential will increase, thus resulting in an inadequate flow. If you notice a pressure difference, it’s critical to quickly identify the cause.

Operating temperature

The operating temperature of the heat exchanger will affect how heat is exchanged. The stream temperatures can vary because of changes in the operating procedures. If there is any change in the stream temperature, it will create variations in the approaches, such as log mean difference and heat duty. A low approach difference will result in a corresponding log mean temperature difference and high load, and vice versa. If the operating temperatures exceed defined parameters, then the material will condense and form deposits that coat the interior of the heat exchanger. This will produce a wall temperature that will be lower than the bulk limit temperature. You must monitor the inlet and outlet temperature to maintain the correct operating temperature.

Nature and properties of heat exchanger

It is extremely crucial to pay attention to the chemical relationship between the materials of construction and the chemical nature of the fluid stream in transit. For instance, it wouldn’t be advisable to use a heat exchanger that is designed to handle cooling water for a hydrocarbon application, as the materials of construction would probably not withstand the conditions of the application.

Changing the flow rate

Check if the flow of fluids in both the primary and secondary side of the heat exchanger has the correct velocity or not. Increasing the flow rate of the fluids will enhance the capacity of the heat exchanger and increase heat transfer. However, this does not mean that you should increase the velocity excessively … as it will add to the mass. This will make it more difficult for the energy to be removed.

Removing corrosion

If you see any hint of corrosion on the heat exchanger, remove it immediately

If you see any hint of corrosion on the heat exchanger, remove it immediately; corrosion has the capacity to make the device inefficient. If the corrosion is really bad and advanced, replace the tube plates. Ensure that your technicians remove and replace the corroded parts immediately.

A heat exchanger that is installed properly and well maintained will function efficiently for a long period of time. If you make sure that it runs smoothly and quickly troubleshoot any issues, you will get better results and save money in the long run.

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