Method for Online Cleaning of Air Preheaters

Abstract

A method of cleaning air preheaters of the type having a rotor which passes through a stream of flue gas and a stream of intake combustion air is disclosed. A soot blower is operated in step-wise fashion to blow a soot blowing medium through passageways in the rotor. The passageways are arranged in concentric rings and move at a tangential velocity which depends on the speed of the rotor and the location of the passageway relative to the center of the rotor. In the present method the speed of the rotor is adjusted in accordance with the position of the soot blower so that every passageway moves over the soot blower at the same or substantially the same tangential velocity.

Description

FIELD OF THE INVENTION[0001]The present invention is directed toward a method for cleaning rotating regenerative air heaters used in coal-fired electricity generating plants.BACKGROUND[0002]Techniques for preheating of air have been known and used for many years in connection with boilers to improve combustion and boiler efficiency. One such preheating technique employs a Ljungstrom air preheater. This air preheater has two side-by-side ducts with flue gas flowing through one duct while an inflow of combustion air is passed through the other duct, the two gas flows being in opposite directions. A rotor is positioned to rotate through both ducts about an axis between the two ducts, transferring heat from the flue gas to the combustion air. Air preheaters, are normally operated at sufficiently high temperatures to inhibit condensation inside the heat exchanger of pollutants such as sulfuric acid vapor present in the flue gas. For example, in typical published temperature guide lines f...

AI Technical Summary

Benefits of technology

[0016]The present invention is directed toward a method of cleaning those sticky deposits, including ammonium bisulfate, sulfuric acid and other materials, from a rotary air preheater without shutting down the steam generating system. Further, this method can be used to mitigate the accumulation of deposits to the point of pluggage by changing the operating strategy of conventional soot blowers. This method is particularly effective when used with the type of rotary air preheater shown in FIG. 1. This type of preheater has a heat exchange rotor containing adjacent passageways through which air and flue gas are directed and which is rotated about an axis. A soot blower is capable of being positioned adjacent any selected depth from the outer circumference of the rotor such that a soot blowing medium can be blown from the soot blower into passageways at the selected depth as the rotor is rotated.

Problems solved by technology

As these deposits build up, the flow paths for the air and flue gas become blocked and the heat transfer capacity is reduced.

This causes a more rapid deterioration of the heat exchange elements in the rotor usually toward the center and outside periphery of the rotor.

On an industrial scale, these requirements can only be achieved to a limited extent with acceptable capital outlay.

Consequently, it is inevitable that ammonia slippage may occur distributed unevenly across the cross-section of the reactor.

Because ammonium bisulfate is so sticky, it captures ash particles and rapidly plugs the gas passages of the device.

These deposits may also cause corrosion.

Nevertheless, it is impossible to rule out the possibility of a higher level of ammonia slippage than the mean occurring at some locations over the reactor cross section.

Therefore, in some cases a relatively high—even excessively high—ammonia concentration may occur, so that the air preheater is damaged in this area by the above-mentioned processes.

Soot blowers as mentioned above are seldom effective in removing ammonium bisulfate deposits.

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