Wanted: More Efficient Heat Exchange

Article by Gerard O'Connor CEng FIChemE

Gerard O’Connor gives insight into the work of a heat exchanger consultancy

IMAGINE if heat exchange of process fluids in an industrial setting was as simple as boiling a jug of water. We all know the process is not as simple as that, and companies can experience a raft of different issues and challenges that require new and innovative technical solutions. That’s what keeps chemical engineers in business.

While we often see companies dealing with process capacity issues, an even more common and topical issue today is around how we - chemical engineers - can help companies improve their overall energy use and deal with increasing energy costs, particularly through more efficient heat transfer technology.

In New Zealand and many other countries, we’ve drawn a line and have made a commitment to reduce our energy consumption and resources to improve our environmental footprint. The primary sector, in particular, is stepping up and looking for new ways to reduce emissions and counter climate change.

More companies are now approaching PDV Consultants and others in our sector with a goal to invest in capital to reduce energy consumption.

At the time of writing this article, we’re modelling different heat transfer options to reduce energy consumption with at least six New Zealand-based companies.

Strategically, they’re now often prioritising this type of capital investment over capacity increases because they want to do the ‘right thing’ whilst also reducing their operating costs.

What factors impact efficient heat transfer?

1. The product

For example, if you are working with thick viscous product, the liquid will have poor heat transfer properties because it is so viscous. That’s because the heat put into the product will not mix well into the bulk of the fluid.

2. Fouling on heat exchangers

If the fluid fouls as it gets hot (eg as milk burns onto a heating surface and creates a coating on it), then that creates a resistance during the heat transfer process.

3. The material that you are heating through

The material that’s transferring the heat from one point to the other is important, and can have a significant impact on heat transfer efficiency. For example, a thin copper pipe will transfer heat far more efficiently than a thick steel plate.

4. The heating medium

The heat transfer coefficient (HTC) of the heating medium can be affected by its quality. For example, steam that has air in it has a significantly lower HTC and reduces how fast the steam can condense and transfer heat. This can be an issue in evaporators which operate under a vacuum and is therefore prone to air ingress through any leaking joints. If there are any leaks, heat transfer will be poor and the plant will suffer performance issues.

Article by Gerard O'Connor CEng FIChemE

Managing Director, PDV Consultants, New Zealand

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