Last updated:
Tuesday, 07 February 2012
Feed Water Systems-Information

We specialize in economical boiler feedwater systems. With units ranging from 50 to 1,000 gallons sized with Simplex, Duplex and Triplex pump configurations for low-pressure or high-pressure steam systems.

atlantic feedwater systems offers a full range of sizes, with units ranging from 50 to 1,000 gallons. Oversized vessels are available.

Horizontal Boiler Feed Systems:

  • Size designed for firetube and commercial watertube boiler applications.

  • Standard horizontal unit sizes.

  • Packaged unit, shipped complete with the pumps and pump suction piping factory installed. Most components are factory installed.

Compact Vertical Units:

  • Size designed for Apartments and Office Buildings, and replacements.

  • Maximum size diameter of 34" fits through 36" doorways.

  • Simple/Low cost design.

  • 50, 100, 150 and 190 gallon unit sizes.

  • Many in stock for next day shipments.

Oversized Vessels Available:

  • Standard options are available to increase the tank to the next larger size.

  • Handles condensate surges.

  • Provides extra capacity.

The appropriate size of the tank is dependent upon several factors, including the amount of feedwater, pump operating pressure, and amount of condensate.   We are sure to satisfy all of your boiler feedwater needs.  We provide the following guidelines to help you (our customers) decide which type of system is best for your application. To help you select the best boiler feed system for the job, a boiler feed system is sized with five parameters in mind:

How much feedwater?

The pumps for the atlantic feedwater systems are pre-selected to make it easy for you to select a system. For example, a model 100 FS is sized to supply one 100 HP boiler if it is chosen with one or two feed pumps. If the three pump unit is chosen, it includes two pumps sized for 50 HP each, with one 50 HP pump for standby. All catalog pump selections are based on "On-Off" pump control. Consult the factory if modulating feedwater control is used.

If you would like to size the pump yourself, here is how:

  1. Convert the Boiler Horsepower

    • Convert the boiler horsepower to the amount of water the boiler needs to make the full capacity steam rating. For most firetube and commercial water tube boilers convert the horsepower to pounds (#) of steam per hour. Then divide the # per hour of steam by 500 to get the evaporation rate.

  2. Calculate the Pump Flow Rate

    • The flow rate is determined by the amount of water the boiler needs to make steam at full capacity.

    • On-Off Pump Control: If the boiler level is controlled by turning the feed pump on and off, the pump is usually sized to pump twice the rate the boiler requires at full load. This provides enough capacity for the pump to catch up with the boiler when it is turned on.

    • Modulating Feedwater Control: If a modulating valve controls the boiler water level, the feed pump is sized to provide 25% more water than the full load evaporation rate. A second adjustment is required to provide for recirculation flow required to protect the pump.

Boiler operating pressure?

atlantic feedwater systems specializes in economical boiler feedwater systems that use Simplex, Duplex, and Triplex centrifugal pumps. Simplex systems use one pump, Duplex use two pumps for one boiler feedwater system, and Triplex systems have two boilers with three pumps (one pump is standby). Centrifugal pumps make customary boiler feed pump oversizing unnecessary due to their extremely low wear characteristics.

Standard Centrifugal Pumps:

  • Higher efficiency than turbine type pumps.

  • Less maintenance.

  • Less wear and tear on the centrifugal pumps than on turbine type pumps.

  • Single stage for low-pressure steam systems.

  • Multistage for high-pressure steam systems.

 

The Boiler Feed Pumps are available in standard sizes for easy selection. The feed pumps are cataloged for specific discharge pressures. The discharge pressure listed in the literature is the operating pressure of the boiler. The pump chosen includes additional head to overcome the pipe losses between the feed pump and the boiler. All sizing assumes "On-Off" feedwater control.

If you would like to size the pump, or the discharge pressure is different than the catalog sizing, calculate the discharge pressure this way:

  1. Add for pressure drop in the piping

    • If On-Off pump control is used, add for the pipe loss between the boiler and pump, as well as for the drop across the feedwater stop and check valves. Common practice allows about 20 psig for these pressure drops.

    • If Modulating Feedwater Control is used, an additional pressure drop is required by the feedwater valve. Most feedwater valves are sized in the range to produce between 10 psig and 30 psig pressure drop at full flow. Most people use 25 or 30 psig pressure across the valve for sizing purposes. This is in addtion to the piping valve losses.

  2. Convert the discharge pressure to Total Dynamic Head in feet (TDH)

    • Pump discharge pressure is rated in feet of head. To convert from psig to feet of head, multiply the calculated pressure by 2.31 to get Total Dynamic Head in feet (TDH).

    • If the water is near the boilng point, you may wish to correct for the specific gravity of the water. At 212º F water divide the TDH by 0.96 to get the head to use to find the pump discharge pressure.

Tank storage capacity? New or replacement tank?

atlantic feedwater systems specializes in economical boiler feedwater systems. The tank storage capacity is an important parameter to consider when selecting your feedwater system.

How Big is the Tank?

The standard tank size provides about 1 gallon of storage for each boiler horsepower of boiler capacity. For example, a 100 HP boiler would have at least 100 gallon of storage capacity.

When Should You Use a Larger Tank?

  • If the system has a large amount of condensate returning, you may wish to use a tank which provides more than the typical 1 gallon per boiler horsepower of capacity. The larger tank capacity allows the vessel to receive large condensate surges with less chance of the condensate overflowing to drain. It is best to eliminate condensate over-flow. Losing condensate to the drain wastes valuable water and energy. If the feed system has a large enough tank, this will not happen.

  • If the condensate returns exceed 50% of the total unit flow, you may wish to increase the tank size to the next larger size. This will increase the capacity to 1.5 gallons or 2 gallons per boiler horsepower. We have seen some people use storage capacities of as much as 3 gallons per boiler horsepower on large campus type systems. The larger tank is a small investment to make in order eliminate condensate loss during surges. For example, the cost to increase a 100 gallon horizontal tank to 220 gallons is only $330.

Do You Need a Replacement Tank?

Over time, boiler feed systems fail during operation. The primary cause of failure is vessel corrosion due to high levels of make up in a vessel using a steam sparge tube to heat the feedwater in the vessel. If oxygen corrosion caused the vessel to fail in 3 or 4 years, you should consider replacing the vessel with a corrosion resistant vessel. The initial higher cost of a stainless steel replacement vessel will be offset by its extended life. We can provide replacement vessels for any system in the field.

When choosing a replacement vessel try to answer these two questions:

  • Why did the vessel fail?

  • How old was the vessel?

Is feedwater heat required?

atlantic feedwater systems specializes in economical boiler feedwater systems.Feedwater heat is required to protect the boiler from damage under normal operating conditions. Most boilers require feedwater to be at least 150º F.

If a system has 80% of the condensate returning at 200º F with 20% make up at 60º F, the blended feedwater temperature would normally be about 170º F. This should be adequate temperature for most firetube or commercial watertube boilers.

If, for example, the system has 50% make-up at 60º F and 50% returns at 200º F, the blended feedwater temperature would be about 130º F at normal operating conditions. This system would normally require feedwater heat to protect the boiler.

A sparge tube with a temperature switch and steam supply valve is available. This is an inexpensive way to heat the feedwater to acceptable levels.

The heater assembly has a solenoid or self-contained type control valve with a 250 lb. screwed body up through 2" (the 2-1/2" has a 125 lb. flanged body), heater tube, y-strainer, and required piping. The selection is determined by percentage make-up, type of heater valve (solenoid or modulating), and pressure level of steam (low pressure of 15 lb. versus high pressure of 100 lb.). Heater assembly options are listed as part of the select and customization process.

Is corrosion protection required? 

atlantic feedwater systems specializes in economical boiler feedwater systems. Optional corrosion resistant construction is available to extend the life of the unit.  Boiler make-up water and condensate can be very corrosive. Make-Up has oxygen. Higher level of make-up in a system introduce more oxygen. Higher levels of make-up require more steam for feedwater heat. If the water is heated in the tank by injecting steam through a sparge tube, there can be oxygen corrosion in the vessel. More steam and more oxygen result in faster corrosion in the vessel. If the condensate is acidic, which is normal, the condensate can increase the rate of corrosion further.  It is common for system with 70% or 80% make-up to wear out in 4 or 5 years due to oxygen corrosion. How can you guard against premature failure of the vessel? Use a corrosion resistant material or coating to protect against oxygen corrosion. Using a coating or stainless steel will extend the vessels life. The higher the level of make-up, the greater the need for a corrosion resistant lining. The severity of the expected corrosion may suggest on option over the other.

Corrosion Resistant Options:

Hot Dipped Galvanized Vessel Construction

Baked Epoxy lining (330 to 1,000 gallon vessels)

304 Stainless Steel