Determining When to Clean
The standard method for determining when to chemically clean a coal fired boiler is to take a boiler tube sample and have the deposit amount measured—a deposit weight density —and the composition of the deposit analyzed. But there are other conditions besides the Deposit Weight Density(DWD) that require that the boiler be cleaned.
Using Deposit Weight Density to Determine When to Clean
The standard DWD test should not only provide a deposit loading but also an analysis of chemical composition of the deposit on the tube. This chemical analysis of the deposit can be done quantitatively, using an inductively coupled plasma emission spectrometer, but it is more commonly determined semi-quantitatively using electron dispersion spectroscopy. Occasionally, X-ray diffraction data is also provided to indicate the chemical compounds that are present.
The Actual Cleaning Process
In forced circulation boilers, one critical piece is the flow of purge water through the boiler circulation pump motors. It is different from the coal fired boiler. This purge water protects components in the motor from the solvents, by providing a constant outward flow past the motor cavity and into the boiler. Purge water should be on all boiler circulation pumps (in service or not) as long as there is chemical in the boiler. Since the purge water is designed to provide water to the pump during normal operation, the system is set up to overcome normal boiler pressure. These high-pressure pumps can produce high purge water flow rates during the cleaning and can be difficult to control. If the purge water flow is excessive, the level in the boiler is constantly rising to the point where solvent has to be drained before it goes out of sight in the temporary sight glass. Every gallon of purge water dilutes the solvent and generates more waste that will need to be disposed of at the end of the cleaning. ZG has make tremendous efforts on all kinds of boilers.