Tube leak condenser

NOTE When a boiler first starts up from cold, there is always some initial condensation arising from combustion (which generally falls to the rear of the boiler and may form a pool of water). This quickly evaporates and should not be confused with tube leaks that leave evaporated solids behind. 

In services using water-cooled condensers, a tube leak can lead to water being refluxed into the coliunn. In one case (358), this caused a pressure surge and severe tray damage. The effect of a condenser tube leak should be examined if a pressure surge may result, water removal facilities should be provided at the reflux drum. 

Tube leaks may occur in the reboiler, condenser, preheater, precooler, or any other heat exchanger linked with the column. Several experiences where leakage caused poor performance have been reported (71, 238, 239). The effect of a leaking heat exchanger tube depends on the magnitude, the direction, and the location of the leak. 

Effects of heat exchanger tube leaks into the column include off-spec products and/or undesirable chemical reactions. In some cases, this reaction may lead to rapid corrosion or plugging. It is important to realize that material leaking at the condenser or at an intermediate exchanger may travel to the column base and decompose there. In one vacuum column, water leaking at the condenser reached the reboiler and caused a pressure surge and tray damage (358). 

Effects of heat exchanger tube leaks out of the column include inability to maintain column pressiure, erratic performance of reboiler or condenser, and erratic performance in other units because of contamination of the heat transfer medium. One classic experience (239) of an extremely sick column performance caused by a leaking reboiler was described in Sec. 1.2. 

In the case of a tube leak, no water should enter the SO3 side. The tubes in the falling film condenser are open to the sky and, in the case of a leak, the pressure gets released to the top opening. 

In cases where water should not come into contact with the vapours being eon-densed, the shell side may be operated at negative pressure, that is, under siphoa In case of a tube leak, the condensing vapour will get mixed with water and get earned away from the condenser due to the siphon. An on-line pH meter can indicate the leak if the vapour is acidic. Some other detector, for example, conductivity meters, can also be used. For example, Condenser for Liquid SO ... 

Fission product noble gases entering the water-steam circuit in the event of a tube leak are completely volatilized and transported with the steam to the main condenser where they are extracted and released via the off-gas stack. This release is monitored by a continuously operating detector device located in the condenser off-gas line. Non-volatile fission and activation products which are transported over the leak to the water-steam circuit remain completely in the water phase of the steam generator by the action of the blowdown purification system their activity concentration is kept at a level which is controlled by the injection rate on the one hand and by the purification rate on the other. Because of the very low vapor pressures of these elements and their chemical compounds (dissolved ions or insoluble oxides/hydroxides), their transport to the steam under the prevailing conditions (270 °C, 7 MPa) is only possible by droplet entrainment. This means that partitioning between liquid and steam phases is proportional to the steam moisture content, which is usually well below 0.1%. 

Measure amount ol lost capacity Coked catalyst High-pressure boiler leaks Condenser tube leaks Plugged seal legs Improperly installed catalyst support screens... 

Damage to catalyst and reduced conversion can be a consequence of many other factors besides lost activity carbon deposits, leaking condenser tubes, damaged support screens, sulfuric acid formation, operation at the sulfur dew point. These problems are, however, invariably associated with increasing pressure drop. 

Tube leaks may also occur in the low-pressure steam condensers. The leaking condenser is identified through a pressure drop survey. Measure the pressure drop across each condenser. The first condenser in the train exhibiting a disproportionately high pressure drop is the leaker. If the leaking tubes are found in the bottom of the condenser, formation of sulfuric acid may be the cause (see following section on start-up tips). 

The condensate polishing system chemically cleans up the condensate by passing it through ion exchange resins to remove corrosion products and ionic impurities. It is required during start-up, imtil the desired water quality is attained, but during power operation would be used only when abnormal secondary conditions exist, such as a continuous condenser tube leak. 

In direct cycle plants, an additional source of secondary system contamination that needs to be considered is leakage from equipment for concentrating radioactive waste that involves steam heating. One such source of contamination is through tube leaks that allow contaminated waste to enter the condensed heating steam. Contaminated condensed water from such steam may then be introduced into the secondary system. 

This is a problem in process plant steam heaters. There are always some residual carbonates in boiler feed water. When the water is turned into steam, some of these carbonates decompose into CO Thus, all steam is contaminated with CO. The CO being far more volatile than water gets trapped and accumulates in the high points of steam heaters. With time, the CO condenses in the water to form carbonic acid. This causes corrosion and tube leaks. To avoid CO accumulation, the exchanger high points can be vented. 

About 15 years before the explosion, corrosion of the condenser tubes had caused a series of exchanger tube leaks. The cause of failure was thought by Shell to be due to acidic components (HCN, CO2, HjS) in the vapor phase. To combat the tube failures, two changes were made ... 

The cause of the tube leaks is cold flue gas. But the cause of the cold flue gas is tube leaks. The real cause of the tube leaks is sulfuric acid corrosion. The sulfuric acid condensation is the result of the low temperatures of the flue gas. To avoid this problem, the flue gas must not be cooled too much by the cold air. 

Note System must be free of air leaks steam must be dry and condenser tubes clean. 

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