Horizontal multistage Boiler Feed Pump
Horizontal Multistage Boiler Feed Pump
What is a horizontal multistage boiler feed pump?
A horizontal multistage boiler feed pump is a particular class of high-pressure centrifugal that serves to feed a steam generator such as a boiler or a nuclear reactor with water for steam production. It is usually designed for horizontal installations with multiple impellers to generate the high pressure required to feed the boiler. Horizontal multistage boiler feed pump manufacturers employ a between-the-bearings design for the units, where the rotor is supported on bearings at either end, to provide more support and dynamic balancing and enhance the rotational efficiency of the impellers. The horizontal multistage boiler feed pumps are essential components of various industrial plants and production facilities, such as very large boiler systems. They are made from high-grade stainless steel or cast steel and are often lined with a suitable material to protect against corrosion. Horizontal multistage boiler feed pumps have a low net positive suction head requirement (NPSHr) and reliably deliver medium to low flow rates at high pressure.
Figure: Showing the configuration of a horizontal multistage boiler feed pump
Components of a horizontal multistage boiler feed pump
The pump casing also referred to as the housing, is the major stationary component of the horizontal multistage boiler feed pump, covering the impeller and other internal parts. The pump casing also helps to convert the pumped liquid’s kinetic energy into the pressure head and to direct the flow to the discharge connection. The Horizontal multistage boiler feed pump manufacturers make the pump casings using suitable grade stainless steel, cast steel, and ductile cast iron.
The shaft is a rotary cylindrical mechanical component centrally located in the pump and supported by bearings on either end. Its purpose is to carry the impeller and connect the rotor assembly to the motor via coupling. It is made from the high-quality forging of suitable grade stainless steel or alloy steel.
The horizontal multistage boiler feed pump manufacturers fit the units with angular contact ball bearings, which are oil-lubricated and designed to deal with the axial thrusts in both directions. The bearings hold the shaft and the rotor assembly in place, aligning them correctly with the fixed ends under the radial and axial loading.
In a high-pressure boiler feedwater Pump, the electric motor is connected to the pump body by mechanical coupling. The electric motor is the source of power for the pump.
The impeller consists of backward-curved vanes and rides on the pump shaft. Its purpose is to impart kinetic energy to the pumped liquid and move it through the pump body. The delicate clearance between the impeller and the pump casing prevents slippage and recirculation. The shrouded-type impeller can be manufactured from similar materials as the pump casing, cast iron, ductile cast iron, or stainless steel. The horizontal multistage boiler feed pump manufacturers fit the impellers to the rotor shaft so it is readily removable and can ensure freedom from thermal distortion.
suction inlet and discharge outlet
The pumped fluid enters the pump through the suction inlet and exits through the discharge outlet, which links with the delivery connections.
How does a horizontal multistage boiler feed pump work?
The horizontal multistage boiler feed pump converts mechanical energy into hydraulic energy using the centrifugal force of rotating impellers. When the pump starts running, the impeller rotates with the priming liquid inside the pump casing, creating a vacuum at the impeller’s eye, which allows the boiler feed water to flow into the pump casing. Once the boiler feed water enters the impeller eye, the centrifugal force acting on the impeller blades moves it radially outwards, away from the impeller center of rotation, at high tangential velocity. The swirling flow at the exit of the impeller then enters into the diffuser, where the extreme fluid flow speed decelerates due to the gradually expanding flow channel. The high kinetic energy of the boiler feed water also converts into a high-pressure head. Finally, the boiler feed water discharges from the pump under elevated pressure into the boiler, and the cycle continues.
Figure: Working of a horizontal multistage boiler feed pump
Types of horizontal multistage boiler feed pumps
Stainless steel horizontal multistage boiler feed pump
This pump features a complete stainless-steel construction of all components that come into contact with the liquid to protect against corrosion. The horizontally oriented pump shaft can be coupled to different prime movers, e.g., a turbine, an electric motor, or an engine. The pump is easier to install and maintain because the spacer coupling provides space for a maintenance operation, and the pump’s internal components are easily accessible. The stainless steel horizontal multistage boiler feed pump is perfect for heavy-duty applications because it can generate higher fluid pressure. It is also suitable for indoor applications where vertical space is limited.
Figure: Stainless steel horizontal multistage boiler feed pump.
Horizontal multistage single suction boiler feed pump
A horizontal multistage single suction boiler feed pump features a closed-type single suction impeller. A single suction impeller admits water from one side of the impeller and discharges it from the other. Therefore, this pump’s whole volume of boiler feed water goes through a single impeller’s eye. While it is simple in design and cost-effective, the horizontal multistage single suction boiler feed pump is prone to cavitation due to increased flow at the inlet.
Horizontal multistage double suction boiler feed pump
The Horizontal multistage double suction boiler feed pump comprises the double suction impeller, which is made of two back-to-back impellers. A double suction impeller allows the boiler feed water to simultaneously enter the center of the impeller blades from both sides. The double suction design eliminates axial thrust on the impeller, making the pump manage higher flows than the single suction pump. It is also cavitation free.
Applications of horizontal multistage boiler feed pumps
Horizontal multistage boiler feed pumps find applications in boiler systems that produce steam for various industrial uses such as power generation, building heating, sanitation processes, etc. Additionally, they are used in many other units and production facilities to transfer liquids such as water, fuels, and solvents. Common uses include:
- The horizontal multistage boiler feed pump is used to maintain the desired water in the steam boiler to prevent failure.
- High-pressure boiler feed pumps apply in the supply of fresh water from the condenser to a boiler. Condensation that forms in the boiler systems is typically recycled and fed back into the boiler with condensate return pumps.
- They are used to intermittently or continuously pump hot chemically treated feed water at high pressure.
Advantages of a horizontal multistage boiler feed pump
- Horizontal multistage boiler feed pumps have less maintenance and operation cost.
- They can tolerate high temperatures and pressure.
- They have a balanced shaft loading and adequate rotor support because of using a between-the-bearing design.
- They are highly reliable and easy to install and maintain.
- Horizontal multistage boiler feed pumps prevent thermal shock to the boiler or the deaerator by raising the temperature of the feed water.
- They have significant energy savings and operating efficiency.
- The double suction type is free of cavitation due to reduced flow at the pump inlet.
- They provide a steady and continuous output.
- The multistage configuration can work with small-size impellers because the head per stage is less.
Disadvantages of a horizontal multistage boiler feed pump
- Horizontal multistage boiler feed pumps produce high outlet pressure that may damage the matching equipment.
- They have high initial acquisition and installation costs.
- The horizontal multistage boiler feed pump manufacturers must fit the relevant equipment with pressure-reducing valves to prevent damage due to excessive pressure. This further raises the cost of necessary equipment.
Troubleshooting a horizontal multistage boiler feed pump
The pump fails to start
- There is a blown-out fuse or tripped circuit breaker. Inspect the horizontal multistage boiler feed pump for a blown-out fuse and replace it if necessary.
- The power supply to the panel is insufficient. Ensure that the voltage and current supply to the pump match the amount specified in the horizontal multistage boiler feed pump manufacturer’s manual.
- The voltage is irregular due to dirt or corrosion at the pressure switch. Inspect the pressure switch and clean it of any debris or pollution.
- The fuse receptacles are dirty or corroded. Inspect and clean fuse receptacles if necessary.
The pump overheats and seizes
- There is too much thrust due to mechanical failure inside the pump. Inspect the pump assembly and correct any shortcomings.
- The viscosity of the liquid is different from the design. Ensure the pump applies to the correct fluid following the Horizontal multistage boiler feed pump manufacturer’s manual and product data sheet.
- The pump bearings are worn-out. Inspect and replace the bearings if necessary.
- The pump needs priming. Ensure that casing is filled and water comes out from the air cock.
- Rotating parts are rubbing on the stationary part. Disassemble the pump and correct the assembly.
The pump loses its prime after starting
- The suction lift is too high. Reduce the suction lift by lowering pump elevation or increasing the water level.
- The water seal pipe is clogged. Clean or change the water seal pipe.
- There is an excessive amount of air in the liquid. This may be due to air entering via the suction joints. Inspect the suction joint and seal it as necessary.
The pump capacity is insufficient
- The pump or suction pipe is not filled with water. Inspect the foot valve for leakage and correct it.
- The pump is operating in reverse. Check that the direction of the motor rotation matches the direction indicated by the Horizontal multistage boiler feed pump manufacturers on the nameplate. Be sure to reverse the motor polarities.
- Clogged impeller. Inspect the impeller and remove any material.
- The total head of the system is higher than the design head of the pump. Measure the pump head using a pressure gauge. Refer to the horizontal multistage boiler feed pump manufacturers’ manual for the pump’s design pressure head.
- There is air pocked in the suction line. Be sure to fill the suction pipe with the pumped liquid. Eliminate concentric to avoid negative suction.
The pump is noisy, or it vibrates
- The pump assembly is loose. Tighten pump components to the torque level recommended by the horizontal multistage boiler feed pump manufacturers.
- There are unbalanced components in the vertical turbine pump. Inspect and rebalance the elements.
- The impellers are severely worn-out or defective. If necessary, inspect the impellers and replace any worn-out impeller with another one from the horizontal multistage boiler feed pump manufacturers.
- Foreign matter in the impeller. Open and clean the pump to remove foreign materials.
- The pump shaft is bent. Dismantle and inspect or replace the pump.
- The horizontal multistage boiler feed pump’s foundation is not rigid. Check vibration and hollowness on the base frame.
A horizontal multistage boiler feed pump is a unique high-pressure centrifugal pump used to supply feedwater to a boiler or a nuclear reactor. It is usually manufactured in a horizontal orientation with multiple impellers to attain the high pressure necessary to feed the steam generator. Horizontal multistage boiler feed pump manufacturers create the units with a between-the-bearings design, where the rotor rides on bearings at either end. The between-bearing design provides adequate rotor support and dynamic balancing, enhancing impeller rotational efficiency. Horizontal multistage boiler feed pumps mainly find applications in boiler systems but have been used in many other industrial units and production facilities to pump liquids. Horizontal multistage boiler feed pumps have less maintenance and operation costs and can tolerate high temperatures and pressure. They can also raise the feedwater temperature to protect the boiler from thermal shocks. The high-grade stainless steel or cast steel devices are also sometimes lined with a suitable material to protect against corrosion.