A Step-by-Step Guide to the Proper Boiler Feed Pump Selection for your System

What are Boiler Feed Pumps? As the name implies, Boiler feed pumps (also known as feed pumps) supply a boiler, a nuclear reactor or any other steam generator with feed water that is proportionate to the amount of steam generated. Majority of the boiler feed pumps in use today are centrifugal pumps. Earlier, they were made of unalloyed steels, but today boiler feed pumps are made with steel that has a chrome content of 13-14%. Today, boiler feed pumps have a rotational speed  even more than 6000 rpm, thanks to erosion and corrosion resistant materials like chrome steels that have anti-seizure properties and the advance in the technology of all pump components (including shaft seal, bearings and pump hydraulic system). Why the Boiler Feed Pump matters in an Industrial Steam Boiler? An industrial steam boiler is a highly pressurised tank. To avoid catastrophic failures, it’s essential that it always has the right amount of water. To ensure the correct water levels, the feed water pump must have a flow that is always higher than what’s required by the boiler for regular error-free operation. Additionally, other factors like the vented-receiver, temperature all have an impact on the mechanical design & seal of the boiler feed pumps. Steam boilers are used in various industries. They are available in a broad range of sizes, horsepower (100 to 1200) and design pressure (150 to 500 psig). ? Additionally, it’s common practice to use more than one boiler parallel to one another in several industries. Two Common Types of Feed-water pumping system designs are:

• Direct Feed – This is the most commonly used system. It’s easy to maintain, and you can switch out a pump without impacting the rest of the system.
• Booster Sets – In this type of system, there are no individual feed pumps. The boilers aren’t directly connected to supply Instead, there’s a booster set that provides water to a standard storage system. The water then moves from the common manifold to individual boilers with the help of a modulating feed water valve.

The Steps to determine the right boiler feed water pump for your System:

1. Determine the control method. Check the specification of the system.
2. Determine the base flow rate.

The formula to calculate base flow rate is: The maximum horsepower of the boiler * 0.069 * C You can find out the maximum horsepower of the boiler in the manufacturers manual. The value “C” depends on the mode of operation. C is 1.50 when the pump operates in an intermittent mode (on and off cycle), and C is 1.15 when the pump runs in continuous feed mode.

3. Factor in the continuous boiler blow-down flow

This step is optional. It’s usually 10% of the pump’s best-efficiency flow rate; however, it can vary depending on the water treatment procedures. The continuous blow-down flow removes all the dissolved solids( silica content) from the water.

4. Add bypass flow, if needed

Some systems use a feed valve and flow bypass recirculation line. The bypass flow ensures that the minimum amount of water passes through the pump at all times, thereby avoiding operation near to the shutoff head. This amount varies from one application to another but is generally 20 – 30% of the pump’s average flow rate.

5. Determine the total flow rate

This is the sum of the base flow, continuous blow-down flow, and bypass flow.

6. Calculate the base head for the feed pump

For the total dynamic head, make sure that you consider all the factors on both the suction side and discharge side. The formula is: Basehead in feet = 2.31 * 1.03 * maximum operating pressure of the boiler/liquid specific gravity

7. Add all the suction-piping and discharge piping head components

Make sure you factor in all friction losses on both sides of the pump.

8. Determine the total pumping head

This is the sum of the base head with the safety factor, discharge-side piping system head, and suction-side piping head.

9. Calculate head at the boiler-safety-valve setting

Apart from reaching the correct head at the required flow rate, the pump must be able to achieve a shut-off head at the required flow rate.

10. Find out the water temperature of the boiler’s feed-tank
11. Calculate the net positive suction head

The formula for this is: Absolute pressure in the feed-water tank ± elevation of the minimum water level in the reservoir that lies above the feed pump – vapour pressure of the water – friction loss at the suction line

12. Shortlist a few pumps

Make sure that all the pumps you choose meet the conditions listed above

13. Check if the shutoff head is 3% or more than the safety-valve-setting
14. Check if the net positive suction head is reached
15. Ensure if the material of the pump is compatible

Check for both temperature and pressure compatibility. Once you have followed these fifteen steps, you can find the right boiler feed pump for your application. Not sure how to make the right choice? Worry not, just get in touch with our Pump Experts at Sintech to find the right boiler feed pumps that fit your system perfectly. Sintech Pumps are one of the leading industrial water pump manufacturers, and we supply pumps to several countries all over the globe. Get in touch with us by ringing us at +91-120-4176000 or drop in a line at info@sintechpumps.com.