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The following equipment should be considered for a complete boiler system installation. This equipment is designed to protect the boiler from harmful water conditions.
A chemical feed system is used to provide the appropriate amount of chemicals into the boiler system to combat scaling and corrosion. A chemical feed system is typically comprised of a tank, stand, pump, and motor. The feed system is controlled in a way that will allow it to operate in unison with the boiler feed water system or dearator. This ensures that the proper amounts of chemicals are being fed on a consistent basis.
A water softener is used to remove hardness from the boiler make-up water. They are available in a wide range of sizes and configurations. By removing hardness in the water you will protect your boiler from the formation of scale that can rob the boiler of its ability to transfer heat efficiently.
Blowdown is a very important part of any water treatment program. Its purpose is to limit the concentration of impurities in the boiler water. The right amount of blowdown is critical: too much results in energy loss and excessive chemical treatment cost; too little and excessive concentrations of impurities build up. There are no hard and fast rules as to the amount of blowdown because of the variation in water quality varies from place to place. It can range from 1% (based on feedwater flow) to as much as 25%.
There are two types of boiler blowdowns - continuous and manual. A continuous blowdown utilizes a calibrated valve and a blowdown tap near the boiler water surface. As the name implies, it continuously removes dissolved solids from the top level of the boiler water at a predetermined rate. A continuous blowdown is an optional feature and is not included on all boilers. However, all steam boilers must include a means for manual blowdown as standard equipment. Manual blowdowns allow for the removal of solids that settle at the bottom of the boiler. Manual blowdown is also used to keep wate level control devices and cutoffs clean of any solids that would interfere with their operation. All steam boiler require manual blowdown whether or not they are supplied with continuous blowdowns.
Proper manual blowdown is performed as follows:
Blowdown should be done with the boiler under a light load. Open the blowdown valve nearest the boiler first. This should be a quick opening valve. Crack open the downstream valve until the line is warm. Then open the valve at a steady rate to drop the water level in the sight glass ½ inch. Then close it quickly being sure that the hand wheel is backed off slightly from full close to relieve strain on the valve packing. Close the valve nearest the boiler.
Repeat the above steps if the boiler has a second blowdown tapping. Water columns should be blown down at least once a shift to keep the bowls clean. Care should be taken to prevent low water shutdown if this will affect process load. Be sure blowdown piping is not obstructed.
Low pressure boilers typically blowdown directly from the boiler to a floor drain. However, even with low pressure boilers the presence of live steam, very hot water and blowing contaminates can be a safety issue. Also, where the boiler drain is connected to a city sewer, local code may require that the blowdown water be cooled to less than 120F before it enters the sewer. This is accomplished by mixing with cold, fresh water.
Blowdown separators take water from the boiler during blowdown and reduce it to atmospheric pressure for disposal. The separator accomplishes this by separating the subsequent flashed steam from the hot water. As the blowdown enters the vessel, it is forced into a centrifugal pattern by means of a striking plate. The steam is vented to the atmosphere through a top connection. Separators are built as per requirements Section VIII of the ASME Code and stamped by the National Board of Pressure Vessel Inspectors.
Blowdown tanks are used as an alternative system for cooling the bottom boiler blowdown. The function of a blowdown tank allows undesirable discharge from the boiler that is to be discharged directly out of the system. These tanks retain the blowdown water volume from one blow after the flash steam, which has been vented to the atmosphere and allow the water to cool down by natural convection over 6-12 hour period. The cooled water will be below 140 ° Fahrenheit when it is displaced by the next blowdown and forced out of the overflow drainpipe.
Check with the local jurisdiction having authority as to which system is required.
Dearators are used to remove non-condensable gases from boiler feed water. This is done by heating and aggressively agitating the incoming make-up water. This process reduces the oxygen content of the water and protects the boiler from oxygen pitting and corrosion.
A feedwater system is used to store and return preconditioned make-up water and hot condensate into your boiler. A feedwater system includes a tank, pumps and a stand. Some feedwater system include a steam sparge tube, which is used to pre-heat make-up water. This helps to eliminate some of the oxygen in the make-up water.