Since the backflushing takes place while the heat exchanger is in operation, the cost of manpower, cleaning equipment, and standstill or production losses are minimized. Also, it extends the interval between cleaning sessions.
In plate heat exchangers, backflushing washes away debris stuck at the cooling water inlet of the unit. For shell and tube heat exchangers, the back-flush works best in combination with brushes that travel through the tubes in response to the reversed flow. They nestle in catch baskets, designed for minimal flow restrictions, at the end of each tube during normal operation.
Our recommended solution: the patented Eqobrush Swingbox Reversal Valve. A slightly higher investment (CAPEX) pays back in years of worry-free operation with minimal pressure loss and Cross-over of cold water to the warm water stream.
Pressure loss only occurs during the cleaning cycle of the system, a total of about 5 minutes per 24 hours of operation.
The 4-Way valves is difficult to fit in to piping solutions due to its shape.
The set of 3-Way valves need to be synchronized to reverse flow without the water coming to rest over a too long period of time.
4 Butterfly valves need to be synchronized to reverse flow without the water coming to rest over a too long period of time.
The forces applicable within the valves are directly proportional to the water volumes flowing through the pipes. They are expressed as a square function of the pipe diameter, based on constant water speed. These forces limit the application of the complex valves, such as the Eqobrush swing box flow reversal valve.
Also, the width of the valve body will, above certain pipe diameters, no longer be practical to consider. The practical limitation is set to a (cooling tower to heat exchanger or condenser) pipe diameter of 600 mm.
Obviously, when applying a solution that involves 2 or 4 valves, the coordination and synchronization become an issue. The process management system should provide precautions to avoid the water flow coming to a halt or the heat exchanger from being bypassed for an extended period.
The above schematic drawings make it clear that more valves require a complex pipe layout. The practical aspects of this in terms of available space as well as the cost of installation may prove burdensome, not in the least in the case of retrofitting existing installations.
Simpler solutions cause lower pressure loss. Complex pipework means more pressure loss, subsequently the energy consumption of the system pump increases. This particularly applies to the 4-way valve.
Old fashioned flow reversal valves and standard of the shelf 2-3 or 4-way valves may come with the defect of substantial cross-over: the leaking of cool water (from the cooling tower) into the return hot water stream. This basically reduces cooling tower capacity, as the less cool water reaches the process. In practice, up to 5% of the capacity may be lost via cross-over.
Simple valve solutions can be cheaper in material investment. However, this may be countered by cost of installation and the cost of the process management system.
For critical processes where lots of gains can be achieved, the “short-term gain, long-term pain” principle may apply to cheap solutions. We recommend careful consideration of the best solution in terms of return on investment (ROI) and worry-free operations over a long period of time.
Reading tip on backflushing of heat exchangers: