Pair of big Flat Plate HX clogged

Turbo Dave

Hello all. District hot water side of HXs did not shut off last summer. System side of HX stagnant and cooking @ 230 for months. Awful quality system fluid. 26 and 22 psi pressure drop across exchanger. Customer's on-site staff pumped a strong solution of Sizzle though each for 2 hours. A lot of black gunk came out of one, but the other showed little sign of action. Pressure drop down to 22 and 18psi. Flat plate spec is max 12psi @ 300gpm. I'm looking for suggestions on how to further clean the HX. Thank you.

Jamie Hall

You may need to see if you can get a sample of the crud and analyze it, and then contact Hercules Chemical (a division of Oatey) or Rhomar to see if they have any bright ideas.

hot_rod

How do you know the actual flow rate? Could it be you are pumping more than 300 gpm. As flow increases so would that pressure drop.

At some point on systems with chronic fouling problems a bolted type HX, plate and frame, may be better.

Here is the HX on the Peppermill deep well GEO, it gets serviced often due to that deep hot water well and the minerals that come along.

Big Ed_4

If plugged replace heat exchanger , are we talking plate

Turbo Dave

Jamie- •A system fluid sample was collected during the summer. I called the company who analyzed it, Watcon in IN. They didn't have a suggestion, other than add more of the system conditioner they sold months ago. The fluid should have been replaced with new 50% glycol mix years ago. As we are entering 3 months of subzero temperatures, now is not the time. Hercules' Sizzle is what they tried the other day, though I believe it needs to be run though for a much longer period than 2 hours. Sending a sample out to Hercules and Rhomar is a good suggestion. I didn't get enough information from the company they used.

Hot Rod- • Looking at the pump curve, observing the VFD and listening to the pump (rpm range is easy to hear, pumps at EOL as well), it is operating well below 300gpm. I reduced the pressure differential setting to provide heat the building without building up 90psi on the supply side and zero on the suction (Incredible, several victualic seals leaking, I hit the shutoff switch immediately when I entered mechanical room and saw the gauges!) Nice photo: you've reminded me that size is always relative.

Hot Rod and Ed- • These are brazed flat plate, rather than plate and frame. They would have been much better off with the latter. If the existing cannot be cleaned sufficiently, that is what we will bid for replacement. There was no thought to future service and/or replacement for any of the components. All against the back wall with the piping in the front, blocking everything in. With the failed isolation valves, It will be very difficult to replace either HX without shutting down the heat for a period of time that is far too long at subzero temps.

• Someday the customer's bean counters may learn the value of scheduled and preventative maintenance. At this moment in the winter, restoring sufficient flow by cleaning is the only workable solution.

hot_rod

Any Y strainers in the loop that could be plugged?

Turbo Dave

Unfortunately not. This job looks to have been done by the lowest bidder. I put gauges on the flush bibbs on either side of the HX to verify. They did improve flow with their acid flush, but not sufficiently.