The Pros and Cons of Direct and Indirect Heating Technology

Posted by Staff Reporter on Apr 27, 2019 05:10 PM EDT
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Almost every industrial application in the world relies on heating, cooling, or drying at some point in the cycle, and temperature-controlling technologies play a huge role in making a wide range of products ready for the market.

It should come as no surprise, then, that these technologies also play an outsized role in the overall energy efficiency of a plant, factory, or mill. Huge amounts of energy are often required just to handle heating alone, and the first thing businesses that want to reduce their carbon footprint and move toward a more efficient approach to production often need to do is find more efficient ways of heating.

Here is a breakdown of the two most common heating methods, with an analysis of their respective energy efficiency.

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Direct Heating: The Standard Approach

Direct heating has, for most of industrial history, been the standard approach in both domestic and industrial heating processes. Direct heating involves direct contact between a heating agent (usually a gas) and the materials being heated - think of a tumble dryer that uses hot air to evaporate water from clothing.

While direct heating is a fairly straightforward technology, it is one that relies on a variety of different processes that can have undesirable side effects. For example, applying directly heated air to a bulk solid introduces the possibility of contamination; if this is to be avoided, companies need to invest in air purification systems that will clean the air before it is heated.

This means that larger amounts of energy are required, and most of this energy cannot be retrieved or recycled for other purposes, making direct heating both cumbersome and wasteful.

Indirect Heating: An Energy Efficient Alternative

Indirect heating processes rely on a medium to transfer the heat to the material being heated. Not only does this remove the possibility of contamination (because the heated air, steam, or oil is not coming in direct contact with the bulk solids being heated), it also makes the energy easier to control and reuse, improving the overall efficiency of the operation.

Most engineering and design experts acknowledge that indirect processes are the heating and cooling technology of the future insofar as they reduce contamination and operate with a much greater degree of efficiency. In some cases, indirect heating and cooling can reduce emissions by as much as ninety percent.  

As recent scientific reports have made clear, the window of opportunity for avoiding the most catastrophic scenarios for climate change is closing faster than previously imagined, and this places the onus on business to find more efficient ways of conducting their operations.

Replacing direct heating, cooling, and drying equipment with indirect heat exchangers is one of the first and most straightforward steps that can be taken if western countries are to meet their goals for emissions reduction. In the process, producers will also reduce their overhead, improve working conditions, and cut down on waste, making this a solution that is not only ethical, but also economical.

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