Steam boiler systems require high quality water to function safely and efficiently. Deaerators (DA’s) help to protect boilers from corrosion by removing dissolved gases from the feed water, and provide storage of clean, treated water for transfer to the boiler as needed.
Lockwood Products has over 75 years’ experience in the design, manufacturing, selling and servicing deaerators, feedwater systems, condensate return systems, vacuum and heat recovery systems, pumps and boiler room ancillary equipment.
Deaerators perform three basic functions:
- Remove dissolved gases – primarily oxygen and carbon dioxide – from the boiler feed water
- Storage of feedwater so it is ready when required by the boiler system
- Transfer of the feedwater to the boiler under the right temperature and pressure to quickly allow the boiler to recover safe water levels during evaporation
How it works:
- Water is collected from two different sources: make-up from the softener system, and condensate return from the steam system to the DA. Sometimes there is no condensate return, and boiler feedwater is made up from 100% make-up water.
- Water is sprayed as a fine mist into a column of steam. This breaks up the water and increases the surface area, while the steam heats it to the saturation temperature, allowing the dissolved gases to escape.
- The heated water is stored and ready for transfer to the boiler system, while the gases are separated and allowed to vent to atmosphere.
- For comparison, feedwater that has been heated to 180°F can hold up to 5,000 parts per billion (ppb), while deaerator water heated to 212°F -225°F achieves a dissolved oxygen content of 5 ppb, a 99.9% removal rate.
- Normally, a deaerator is sized to provide from 10 – 15 minutes of storage for a boiler system running at full capacity.
Types of Deaerators
Spray Tray Type ST: This style uses two stages of deaeration – a spray nozzle and a tray section. The returned condensate and make-up water are sprayed into a tower column of pressurized steam, which increases surface area and rapidly heats the water to saturation temperature, so gases can escape. It falls through a series of trays, which further breaks up surface tension and releases the remaining traces of the dissolved gases.
- Spray Tray deaerators are better suited to applications where the blended temperature of the condensate and make-up water exceeds 180°F and when there are significant changes in load conditions in the steam system.
- Oxygen content to 0.005 cc/Liter, or 5 ppb
Spray Scrubber Type SS: The spray scrubber type also uses two stages of deaeration – a spray nozzle and a scrubber section. The returned condensate and make-up water are sprayed into a column of pressurized steam, and then is collected into a dish and funneled into the scrubber section, which forces steam bubbles to further agitate and “scrub” the dissolved gases.
- Spray Scrubber deaerators are a solid choice for most applications, providing a high level of deaeration at a reasonable price.
- Oxygen content to 0.005 cc/Liter, or 5 ppb
Atmospheric Type AD: These deaerators operate at atmospheric pressures, so the storage vessel is not pressurized. A common style is to have a single tank divided into two compartments – a pre-heated surge compartment and a deaerating compartment. The surge compartment includes a steam sparge heater to pre-heat the water to 180°F. The water is then pumped through a heat exchanger which, because the water is under pressure, can be heated to approximately 220°F. This water is sprayed into the deaeration compartment via a spray nozzle. Because the deaeration section is at atmospheric pressure, the 220°F water will flash into steam, were the dissolved gases are separated and vented with the steam to atmosphere. The remaining water will be at saturated temperature, or 212°F.
- Atmospheric Deaerators are less expensive than pressurized deaerators (ST or SS), and provide a level of dissolved gas removal better than an atmospheric feedwater tank
- Oxygen content to 0.03 cc/Liter, or 30 ppb
Surge Tanks: If there are higher levels of returned condensate, a surge tank may be required. When returned condensate makes up 50% or more of the total boiler feedwater, surge tanks are recommended for the following reasons:
- The Lockwood type SRG surge tank blends returned condensate with make-up water, providing a good mix of softened, chemically treated water for the boiler DA. It includes an atmospheric tank on stand, with recirculation pumps, level controls and an optional steam sparge for pre-heating water.
- Condensate return pumps typically return water at 2-3 times the normal evaporation rate, which causes a “surge” of condensate during heavy process start-up loads. This surge can potentially overflow the deaerator and send high quality water to the drain. A surge tank acts as a buffer and protects against waste of good quality water.
- Low-pressure gravity returns cannot overcome the pressure inside the deaerator tank, so they must be returned to an atmospheric surge tank, which then pumps the water under controlled pressure to the deaerator’s spray valves
- If the deaerator needs to be shut down for annual inspections, the pumps from the surge tank can be piped through a deaerator by-pass line directly to the feedwater pump inlets. This allows the deaerator to be shut down temporarily for inspection or maintenance while the boilers remain in operation.
Boiler Feed Systems: If a boiler system operates on a 24/7 basis, a deaerator is recommended to maintain a continuous supply of high-quality water. However, if a boiler system is not in continuous operation, a simple boiler feed system may be considered as a lower-cost alternative.
- Lockwood’s Type G boiler feed system includes an atmospheric receiver/tank with a steam heating sparge, make-up water level control, pump suction and discharge piping, sight glass, temperature gauge, pumps, and a control panel with pump starters, selection switches, alarm horn, indicating lights and a power disconnect.
- Typically, these systems will include a single pump per boiler, plus a redundant back-up pump. The pumps are sized to provide pre-heated feed water – usually 180°F to 200°F – to the boilers at pressures just above the operating limit of the boiler, and at 1.5 to 2.0 times the evaporation rate of the boiler. This allows the water level in the boiler to be quickly controlled.
- Lockwood’s Type GV incorporates a vertical tank designed for tighter spaces, where height can be used to reduce the footprint of the system
Blowdown Separators: Boiler blowdown is a critical step in the process of protecting boiler systems. Regular blowdown helps to keep the boiler clean and prevents build up of particles and sludge in the bottom of the boiler pressure vessel. As the blowdown is under high pressure, it remains liquid until it is exposed to atmosphere, and “flashes” to steam. This flash steam is separated from the liquid blowdown water by means of a blowdown separator. Also, the water must be cooled below 140°F to prevent damage to drainage pipes.
- Lockwood’s Type BDS blowdown separator performs these functions in a single unit, which includes a pressure vessel in which the blowdown water is separated from flash steam, and the steam is vented to atmosphere. Also included is an after-cooler assembly which uses cooler water to temper the blowdown water before it goes to drain. This after-cooler assembly includes a tempering valve with a thermal sensing bulb, a strainer, and a temperature gauge
Condensate Return Systems: In a typical steam system, steam condensate is considered a valuable commodity, not to be wasted. As steam gives off it’s heat energy, it changes into the liquid phase called condensate. This condensate is pure, clean, heated water, and by returning it to the boiler room, users can save a considerable amount of money in fuel, water and chemicals by returning a much condensate as possible back into the system.
Pumps and Pump Skids: Lockwood maintains an inventory of various types of pumps – centrifugal, turbine, and multi-stage vertical pumps, and others. With a full engineering team, Lockwood can design, and manufacture pumps skid for a wide variety of applications. Pump skids typically include the pumps mounted on a stand, with the connecting suction and discharge piping and trim components, and a control panel that can be integrated into a customer’s facility or system.
Parts: Lockwood stocks a wide variety of replacement parts for their systems, and for boiler rooms in general. These include, but are not limited to the following:
- Level Controls
- Solenoid Valves
- Sight Glass Gauges
Please contact us for further information on Lockwood Products.