Water treatment heat exchanger cleaning

Struvite is magnesium ammonium phosphate. It crystallises out of digested sludge liquor wherever there is turbulence, a pressure drop or a temperature change. The result is a hard crystalline scale that grows steadily and binds whatever else is present into a single mass.

Standard descaling chemistry is formulated for calcium carbonate, and struvite is a different compound with different solubility behaviour. It does dissolve under acid conditions, but the treatment has to be aimed at it specifically, and where it has grown thick, mechanical removal is usually faster than waiting for chemistry to work through it.

It is common, and it is a screening problem instead of an exchanger problem. Rag, wipes and textile that reach the sludge line will accumulate at every direction change and low-velocity section, and cleaning the exchanger on a shorter cycle treats the symptom.

Wipes have made this considerably worse across the industry, and sites that have improved inlet screening generally see exchanger cleaning intervals extend substantially. Worth reviewing the screening before committing to a cleaning frequency.

Usually, because most works have more than one heating loop or can accept the digester cooling slowly for a limited period. Digesters have considerable thermal mass and a short interruption is generally tolerable.

What is not tolerable is a long one. Letting digester temperature fall far enough disrupts the biology and recovery takes weeks, so the work is planned against how long the digester can be left, not against how long the cleaning would ideally take.

Substantial, and they normally dominate the plan. Sludge and digester plant means hydrogen sulphide, methane and oxygen deficiency, so any entry is a confined space entry with gas testing, continuous monitoring, rescue provision and a permit.

Wherever the work can be done without entry, rodding from outside, jetting through open covers, cleaning in place, it is, because avoiding the entry removes the largest risk and most of the programme with it.

Usually back to the works inlet, which is one of the few genuine advantages of doing this work on a treatment site. Jetting water carrying sludge solids is material the works is already equipped to treat.

Acid used for struvite removal is different and needs agreement. It has to be neutralised and its effect on the biological process considered before discharge, so the route is confirmed as part of the method rather than assumed.

Sometimes, and abrasion is what decides it. Grit-laden sludge erodes surfaces over years, and a unit that has been repeatedly cleaned may have lost enough wall thickness that further cleaning is not the right investment.

Worth checking thickness at the same visit while the unit is open. It is a small addition to a job where the access has already been arranged, and it converts a replace-or-clean question into a decision with evidence behind it.

Access and confined space requirements first, deposit second. A spiral unit that can be opened and rodded externally is a straightforward job; the same duty needing entry, permits and rescue cover is a different scale of operation.

Struvite pushes it up, because it is slow to remove whichever way it is tackled. Saying in the enquiry whether struvite is present, and roughly how thick, makes a real difference to how firm a price can be.

More often than most sectors, and it is condition-driven. Circulation rate and digester temperature against heating duty are the practical indicators, and both are normally already logged.

Rate varies enormously with screening performance and sludge source. Sites with good inlet screening and controlled grit removal go substantially longer between cleans, which is usually a better investment than a shorter cleaning cycle.