Hot Water Circulation Pumps for Offshore Economiser

Today we’re going to be talking about a project we undertook recently with a client who operates in the marine sector.

They have a floating offshore platform with a boiler which incorporates an economiser with two hot water circulating pumps. These pumps were over 40 years old and reaching the end of their working life, so our client was looking for alternative solutions.

What is an economiser and how does it improve boiler efficiency?

An economiser is a heat exchanger that recovers waste heat from hot exhaust gases, like flue gas in boilers or exhaust gases in buildings. It then uses these to preheat fluids such as boiler feedwater, or fresh air. This can significantly boost the efficiency of the system, cutting fuel costs and lowering emissions.  The economiser reuses energy that would otherwise be lost, making industrial processes and HVAC systems much more economical. 
How it works:

Hot flue gases leaving the boiler pass through the economiser which is essentially a series of tubes

The economiser absorbs this heat and transfers it to the cooler which contains incoming feedwater

As the water is  already warm, less fuel is needed to bring it to boiling point thereby increasing overall efficiency

Key Benefits:

Energy savings from reduced fuel consumption

Cost savings through lower operating expenses

Environmental benefits from decreased carbon footprint and lower emissions

Improved performance thanks to better overall thermal efficiency

The problem of mechanical seal failure

There was an important factor we had to consider. Pumps operating at high temperatures in a boiler often have issues with mechanical seal failure. So, gland packing is used as the primary sealing method in many of these applications.

Also known as compression packing, gland packing is a soft and flexible material made into rings. These are inserted into the annular space or stuffing box to seal the rotating or reciprocating component of the equipment, such as a pump or valve.

Gland packing can be braided, laminated or extruded, and made from graphite, aramid or PTFE or polytetrafluoroethylene, commonly known as Teflon. This is a synthetic fluoropolymer known for its exceptional non-stick properties and high heat resistance up to 260°C

Obviously, the choice of packing for each application depends on the specific requirements for temperature, pressure and chemical resistancE

How does gland packing work?

Whatever the type of gland packing chosen, it’s specifically designed to leak. The leaking fluid then lubricates and cools the installed packing, helping it to work as intended.

It‘s normally used in applications where the fluid might create problems for a normal mechanical seal. These are fluids that are sticky or which solidify when unheated. They can cause a seal to seize when the hot water circulating economiser pump is switched off or stopped.

If the seal chamber is not sufficiently heated when the pump is restarted, this can make the seal faces stick. This leads to the seal tearing at the bellows, which causes it to leak and need replacing.

Fluids which can cause problems like this include bitumen, wax, adhesives and resin. In addition, high temperature liquids can also reduce seal life due to the constantly high operating temperatures.

The drawbacks of gland packing

Gland packing is not without its problems though. Sometimes, untrained or inexperienced operators might see the gland packing leaking and decide to tighten it to stop the leak. This can cause the shaft to prematurely wear, the pump to seize or the gland packing to set alight.

Moreover, having gland packing installed on a pump also means that fluid is always leaking out of it. This will need additional monitoring, as well as careful management of the containment and disposal of these fluids.

Obviously, this is completely unadvisable in the case of liquids which pose a risk to the environment or are hazardous to humans.

What was our specification for this client?

At North Ridge Pumps, we’re not restricted to specifying just one type of pump. We use our specialist knowledge to come up with the right solution for every client - not a basic pump model picked off the shelf.

In fact, we’re the largest pump maker in the UK with over 25 years in the business, so we’ve acquired the experience to expertly select pumps for a vast range of applications.

In short, we select the right pump for every project brief, every client and every application, always offering the best long-term option.

Which pumps did we select

We chose two hot water circulating economiser pumps from our XCP range. These are ISO 2858-designed pumps specially built for arduous duty in demanding industrial and marine environments.

XCPs are large, heavy duty, close-coupled centrifugal process pumps with high flow and high-pressure capabilities.

Dealing with high temperatures

They’re designed to pump low viscosity clean or slightly contaminated fluids which don’t contain solid or fibrous solids, such as fuels like diesel, petrol and kerosene, as well as fresh water and sea water.

Typical applications range from irrigation, water supply and treatment, pressurisation, grey water and dewatering, to fuel transfer, firefighting, marine and mining applications

A proven pump design with many benefits

In this design, the centrifugal process pump and motor have separate shafts. This means that only the pump shaft needs replacing if it breaks. Other less robust pumps available only incorporate a motor shaft. So, if the shaft breaks, the whole motor needs to be switched.  

In addition, the long-coupled design has a large space between the pump and motor. This helps to stop fluid getting in if there’s ever a seal failure. The long-coupled configuration also means that the pump head can be reached without taking out the motor, making it all very easy to maintain.

What’s more, the back pull-out design means that the motor can be removed while the economiser feed water pump is still connected to the pipework. This saves time whenever the pump is being serviced or maintained.

Above all, this unit is purposely designed for continuous use and long operational life. That’s because it’s fitted with extra bearings in the pump head which take a great deal of strain away from the motor during operation.

Certified for use in explosive environments

These two XCP horizontal long-coupled pumps are also available in ATEX versions for handling flammable fluids or being installed in a non-safe area.

These pumps will primarily be working as hot water circulating pumps delivering around 200L/min at 3 bar, and handling water at up to 170°C continuously for extended periods of time. 

To produce this level of performance, we supplied the pumps with motors specifically rewound for 460V 50Hz operation. This is quite unusual as 460V is normally a 60Hz voltage.

Dealing with high temperatures

As discussed, high temperature pumps can often have issues with mechanical seal failure. So, in this application, we chose gland packing as the primary sealing method.

In addition, we supplied each economiser feed water pump with a flushing connection to make sure that the packing stays cool even in high temperatures.  To put this in perspective, many centrifugal pumps have elastomers which can fail at temperatures as low as 65°C and in this application the pump would see temperatures as high as 170°C.

The pumps were built with a ductile iron casing and a stainless steel 316 impeller, guaranteed to provide many years of uninterrupted service.

This application used two XCP horizontal long-coupled pumps, learn more about how Centrifugal Pumps work.

What was our specification for this client?

At North Ridge Pumps, we’re not restricted to specifying just one type of pump. We use our specialist knowledge to come up with the right solution for every client - not a basic pump model picked off the shelf.

In fact, we’re the largest pump maker in the UK with over 25 years in the business, so we’ve acquired the experience to expertly select pumps for a vast range of applications.

In short, we select the right pump for every project brief, every client and every application, always offering the best long-term option.

If you have a project which needs a high volume transfer pump in a proven, easy-to-maintain, low maintenance unit, speak to North Ridge Pumps today.

For more information on Hot Water Circulation Pumps for Offshore Economiser talk to North Ridge Pumps Ltd