Hot Water Circulation Pumps for Offshore Economiser

We recently completed a project for a marine-sector client operating a floating offshore platform with a boiler system that includes an economiser served by two hot-water circulating pumps. These pumps were over 40 years old and nearing the end of their working life, so the client asked us to identify a modern replacement solution to improve reliability and performance.

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

An economiser is a heat exchanger that recovers waste heat from flue or exhaust gases to preheat boiler feedwater or fresh air, improving system efficiency while reducing fuel use, costs, and emissions. Hot gases pass through a tube bank to transfer heat to incoming water, reusing energy that would otherwise be lost and enhancing overall thermal performance. Because high-temperature boiler pumps are prone to mechanical seal failure, gland packing is commonly used; this consists of heat-resistant soft rings made from materials such as graphite, aramid, or PTFE, selected according to operating temperature, pressure, and chemical resistance.

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.

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.

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.

The long-coupled design prevents fluid ingress and allows easy pump-head access for maintenance.

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.

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, centrifugal pumps could be operating at temperatures as high as 65°C which can cause many elastomers to fail if not correctly specified.

Certified for use in explosive environments

The pumps operate as hot-water circulation units delivering approximately 200 L/min at 3 bar and handling water at up to 170 °C continuously. To achieve this, the motors were specially rewound for 460 V, 50 Hz operation, which is unusual as 460 V is typically used at 60 Hz.

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

If you have a project which needs our help. Please contact North Ridge Pumps.