Selección de boquillas

The material used to make up the drum and internals is primarily high strength carbon steel.

The nozzles in the drum heads are provided for attachment of water level gauges and indicators, vent valves, and safety valves.

Prior to an outage, take steam samples individually from the sampling nozzles installed in the steam outlet tubes along the drum. These samples will detect the presence of localized carryover

ALSTOM Power Revision: 0 7-7

Copyright 2005 04/02/05

Project: NUBARIA POWER STATION I & II

CHEMICAL FEED

FEED LINE INLET

CONTINUOUS BLOWDOWN LINE

Figure 7-1: HRSG Steam Drum, Typical WARNING:

Before entering the drum, ensure that the drum has been purged and that the environment is safe.

WARNING:

If the unit has been laid up with nitrogen, make sure that the steam drum is vented completely before any inspection is performed.

Place an air mover in the end of the drum not being inspected; this will provide adequate ventilation. A second person should remain outside the drum as a safety precaution.

As previously stated, the steam drum serves several functions:

• Provides a point for separating the steam and water

• Houses the equipment used for purifying the steam after separation

• Houses the header used to distribute the incoming feedwater. Examine the steam/water separating equipment. Inspect the separators, both the primary and secondary stages.

Look for corrosion, deposits, erosion, missing parts, etc. Examine the condition of the corrugated plate dryers and the return piping.

Drum Inspection Reminders:

• Check the condition of the seal around the manway door.

• Check the area around the inside of the manway door.

• Check the interior of the drum for corrosion and deposits.

• Check the condition and mounting of the blowdown pipe and the feedwater distribution header.

• Check the downcomer nozzles, screens, and vortex eliminators.

• Check all drum internals for wear and fit.

• Pay particular attention to the areas behind the primary and secondary separators.

• Thoroughly examine the drum internals for cracks. Missing fasteners or separation of the plates will allow boiler water to bypass the steam separation equipment and allow the carryover of boiler water into the superheater.

Headers

Headers are located throughout the water and steam circuits of the boiler. They collect water or steam from a group of tubes and are not physically accessible for entrance. However, they may have handhole inspection ports which allow for a visual internal inspection. During an inspection, thoroughly inspect the headers inside and out.

Header Internal Inspection

To perform an internal inspection, remove the handhole inspection ports on the header.

Examine the interior for corrosion, deposits, or any other foreign material. Check the area around the handhole for any signs of cracking. Check the handhole seal.

ALSTOM Power Revision: 0 7-9

Copyright 2005 04/02/05

Project: NUBARIA POWER STATION I & II

ALSTOM Power

D4006-Bu042

Figure 7-2: Typical Header Connections

Header External Inspection

During an external inspection, visually check the entire header for corrosion, erosion, etc.

Visually check the header nipple welds for signs of cracking. If any cracking is found, determine the depth and location, and consult the manufacturer for recommended repairs. Inspect the area around each header for signs of potential problems.

7.5 DESUPERHEATERS

To assist in controlling the final temperature of the steam going to the turbine, a superheater desuperheater is located at the superheater outlet. (Figure 7-3)

A desuperheater is also located in the reheat outlet line to provide final reheat steam temperature control during transient conditions.

A spray type desuperheater employs spraywater as a cooling medium to the superheated steam. Water is sprayed directly into the steam flow thus adjusting the steam temperature.

FROM

SPRAY WATER SOURCE (BOILER FEED PUMP)

Figure 7-3: Desuperheater Schematic

A replaceable liner is installed for protection against erosion and thermal shocking of the desuperheater heavy wall-connecting link by the cooler spraywater. Spraywater desuperheaters must utilize feedwater quality water because of the location of the desuperheater in the steam circuitry. By design, there is sufficient time for evaporation of the spray water over the control

ALSTOM Power Revision: 0 7-11

Copyright 2005 04/02/05

Project: NUBARIA POWER STATION I & II

Monitor condition of spray water control and block valves to insure valves maintain tight seals when spray is not required.

Inspection

The purpose of the desuperheater is to control steam temperature through the use of cool tempering water. Desuperheaters are installed in both the superheater and reheater circuits.

The typical in-line desuperheater, shown in Figure 7-4, consists of a shell, liner, and spray nozzle assembly. The shell acts as housing. The spray nozzle assembly introduces the tempering water. The liner protects the shell from thermal shock when the relatively cold tempering water is injected into the steam system.

Figure 7-4: Typical Desuperheater Details

Superheater and desuperheater liner inspections should be conducted every three to five years.

This inspection is accomplished with a boroscope. The boroscope is inserted through the spray water nozzle opening after removing the spray water control valve or via a hand hole plate.

Examine the liner for any gross deformations. Examine the spray nozzles for any enlargement of the nozzle holes. If extensive wastage is found, replace the spray nozzle.