| Because of the need to minimize solids in the boiler water, blowdown
control is of utmost importance. It is vital to maintain a properly controlled
steam genertion and water treatment. Maintaining desired levels of dissolved
solids in the boiler water is accomplished by continuous blowdown from below
the water level in the boiler drum or steam separator. Manual bottom-blowdown
from any low point in the system primarily removes suspended solids.
Optimizing Bottom-Blowdown from BoilersManual bottom-blowdown is necessary even in systems that use continuous blowdown to mimimize sludge buildup in the lower sections of the boiler. Continuous blowdown removes concentrated water and solvents from the boiler. Settled sludge must be removed by occasional manual bottom-blowdown. As the sludge volume in the boiler water increases, additional manual blowdown becomes even more important to minimize acccumulations and and possible flow restrictions. At least, weekly bottom-blowdown is recommended.
Obtaining Efficient BlowdownDespite strict adherence to a bottom-blowdown schedule, problems with excessive sludge buildup may still develop. This is usually due to improper timing of the blowdown periods. Experience has proven that frequent bottom-blowdown of short duration are more effective in removing sludge than occasional bottom-blowdown of longer duration. When the latter method is utilized, sludge removal is only effective for the first few seconds of the blow. After the initial surge, only dilute boiler water is discharged. Bottom-blowdowns of long duration initaially creat a great deal of turbulance in the mudd rum, stirring up the sludge. This sludge may be swept into the riser tubes rather than discharged, where it could restrict water circulation, or it may deposit and bake into the generating tubes surfaces. Extended bottom blows wast good dilute treated boiler water.
When frequent blowdown of short duration, about 10 seconds, are used, sludge is removed during the initial blowdown period. When the blowdown is halted, the sludge is allowed to settle with little turbulence. Succeeding blowdown remove more and more of the sludge. Thus this short bottom-blowdown is more effectiveand the overall boiler operation more efficient.
By adhering to these recommendations, sludge buildup will be minimized.