WATER & WASTEWATER MANAGEMENT
sludge, leading to further blockages and a consequent reduction in heat exchange effi ciency. As a result, manufacturers of SHEs also claim that their units are easy to clean. However, it is not uncommon to have to remove 40-50 bolts just to open the unit. Once opened, the construction means that the service fl uid channel contains a large number of brackets which not only give the heat exchanger its rigidity, but also make cleaning diffi cult in sludge-to-sludge situations. T ere is also the issue of the expensive bespoke gaskets which are used to seal SHEs, and which need to be replaced each time the cover is refi tted. Manufacturers of SHEs know that
users don’t want to remove 50-odd bolts before they can clean the unit, (and have to do them all up to the correct torque again). T ey also acknowledge that many materials, such as sewage sludge, require frequent cleaning. To overcome this they produce SHE models with hinged covers, which are held shut with C-clamps, so you don’t have to undo the bolts. Although this type of design improves access, it increases the amount of space required for the installation and contradicts claims of SHEs being self-cleaning.
CHOOSING THE BEST SOLUTION In many situations, a corrugated tube heat exchanger is the best solution for challenging materials such as sludge. However, in the most extreme cases with a very high fouling risk, it will be necessary to use a scraped-surface heat exchanger such as either the HRS rotating R Series or the reciprocating Unicus Series. To select the best solution it is necessary to accurately assess the physical properties of the product or sludge to be treated, as well as the service fl uid, inlet and outlet temperatures and the amount of heat regeneration required (if any). When comparing specifi cations or quotations for
diff erent solutions – for example SHEs compared to corrugated tubes – it is important to make sure that you are comparing like-for-like and that the performance specifi cations are identical. You should also assess whether any gains in effi ciency or lower capital cost will be off set by increased fouling or operational costs over the full life of the unit.
Matt Hale is with HRS Heat Exchangers
www.hrs-heatexchangers.com
The HRS DTI series in situ
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