Case study

AES Itabo I Power Plant Dominican Republic

Replacement of primary plate heaters with Howden custom designed rotary air preheaters.

The Itabo I Power Plant coal-fired boiler was originally fitted with two plate heat exchangers.

For a period, oil was substituted as the fuel increasing the risk of a heater fire. Fouling and resulting poor thermal performance were also problems affecting the recuperative plate heaters.

By replacing the units with rotary air heaters, we greatly improved thermal performance, increased availability, reduced environmental impact and brought significant savings in operating costs.

The challenge

The plate heaters in the Itabo I Power Plant were installed in 2001.

Initially, the unit was designed for coal-fired operation. However, changes in circumstances meant that, for a period, oil was substituted as the fuel. The changes this brought about in the composition of the flue gas led to increased fouling and a serious risk of fire. The heater had previously caught fire twice, and had to be replaced each time.

The loss of availability, fouling and poor thermal performance combined to raise operation costs to an unacceptable level.

Our solution

After thoroughly investigating the operating conditions at the Itabo I plant and the persistent problems the operators were encountering, we concluded that the most efficient, safe and cost effective remedy would be to entirely replace the plate heaters with Howden package rotary air preheaters. Using specially developed software, we can precisely model the conditions under which the air preheater will be working. This allows us to customise the design to match the situation, and very accurately predict the unit’s actual performance and behaviour.

For the Itabo I units we recommended our HS elements, using a combination of the HS8 profile which offers excellent thermal performance and the HS9 which brings good cleanability. In this way we ensured the air preheaters had the right balance of characteristics to overcome the problems that the plate heater had encountered.

Semi-retractable sootblowers were fitted to both the hot and cold sides for effective, efficient cleaning.

We also fitted a fire detection and fire fighting system to warn of and combat any future outbreak of fires.

To minimise leakage over the whole lifetime of the units, we equipped them with fixed sector plates and triple sealing.

Figure 1: An image from our innovative 3D air preheater design software.

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A central drive unit was fitted which has a number of advantages over peripheral drives. It offers greater economy, easier installation and replacement, and more straightforward maintenance. It also removes the need for a rack arrangement round the rim of the rotor. This allows the axial seals to run the full length of the rotor, and so helps to minimise leakage. Each air preheater drive also had a second, backup, electric motor.

Rotary air preheaters differ substantially from plate heaters in size and configuration, so it was necessary to redesign and manufacture new ductwork for the units (Figure 2).

To minimise installation costs, the heaters were pre-assembled in the factory. During on-site installation, the new units were positioned alongside the old ones so that the redundant plate heaters could be dismantled and removed while the new rotary units and ducting were being installed. This reduced the overall downtime.

At the request of the Itabo plant operators, the units were pre-assembled at our factory and securely shrink-wrapped before transit, to prevent damage (Figures 3 and 4).

Howden package air preheatersHowden pre-engineered package air preheaters have been subject to continual product development and enhancement over many decades, driven in recent years by the need to reduce fuel consumption and minimise environmental impact. Today they offer remarkable levels of thermal performance, long term reliability, ease of maintenance and cleanability, with very low leakage levels.

Where we are asked to provide a replacement for an existing rotary heater we can almost always match the infrastructure of the old machine, using the same foundations, ductwork, power supplies and other ancillary arrangements. This greatly reduces the cost of the project and the time taken for installation and commissioning. The improved thermal performance and reliability will normally bring sufficient savings in fuel costs and reduced stoppages to recoup the initial investment within a remarkably short time.

The outcomeThe new air preheaters (Figure 5) have significantly improved the performance of the power station. The HS profile elements are more resistant to fouling and the fire risk has been minimised, so the availability is far higher. The increased thermal performance and reduced leakage has brought valuable savings in fuel consumption, with benefits to both running costs and the environment.

For information about other Howden Air & Gas handling products/services for the global power industry, please visit our website: www.howden.com

AES Itabo I Power Plant, Dominican Republic

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Figure 2: The new ductwork design.

Figure 3: The new unit being prepared for transit.

Figure 4: The shrink-wrapped unit leaving the factory.

Figure 5: The new air preheater installed on site.