Card 11. Boilers. Shutting down

Shutting-down of the plant may occur in two ways: first, a scheduled shut-down for planned maintenance, or lack of load; second, a forced shut-down due to failure of equipment or circumstances that make it impossible for the plant to continue operation.

The boiler is to be taken off the line at once in case of water loss, tube overheating and rupture, soot burning in flues, fire in the boiler-room, brickwork collapse, failure of all feeding systems.

The boiler must be immediately taken off the steam line if water gets into the steam piping.

When shutting down the boiler the following routine should be adopted:

1. Operate soot blowers, if practicable.

2. Shut off fuel to the burners and shut air registers. Check that air registers are fully closed to prevent quick cooling and spalling of refractory.

3. Stop draught air fans and shut off steam to air heater.

4. Raise the water level to three-quarters of a glass.

5. Shut boiler steam and feed stop valves. The time interval between shutting fuel and shutting stop valves must be found from experience. If stop valves are shut too early residual heat within the boiler may generate further steam and it may be necessary to crack open the superheater circulating valve to prevent the safety valves lifting.

shutting-down - остановка

lack of load - отсутствие нагрузки

tube rupture - разрыв трубы

soot burning in flues - возгорание сажи в трубах

brickwork collapse - разрушение кладки

spalling of refractory - отслаивание кирпича

to prevent valve lifting - предотвратить срыв клапана

Card 12. Turbines starting

Before starting a unit certain precautions ought to be taken to make sure that the unit is ready for operation. The unit should be absolutely clean inside and out, and all parts securely fastened.

The following procedure for starting the unit should be observed: measure clearances where indicators are installed. See that the turbine rotors and gears move freely. This may be done by turning the units by means of a motor-driven turning gear.

All valves and cocks for draining water from the main steam pipe, maneuvering valves and turbine casings should be opened.

All steam valves at the maneuvering gear and about the turbines should be closed.

The cocks to the pressure and vacuum gauges on the turbine and condenser should be open.

Determine that there is a supply of circulating water through the oil cooler by turning on the water and then turning it off.

Inspect the lubricating oil system carefully. It sometimes happens that the oil in the system becomes cold and viscous because of the weather or of the location of the oil tanks. Therefore, before starting the equipment it may be necessary to heat the oil in the tanks sufficiently to allow it to flow freely. The initial temperature of the oil should not be generally lower than 90°F.

Warm up turbine by running slowly, alternately ahead and astern. It is desirable to allow a reasonable time for warming up, say for one hour. If conditions are such as to preclude alternate running ahead and astern, it is preferable to omit the warming operation entirely. In this event it is especially important that the first opening of the throttle valve be sufficient to start the turbine turning at once, to avoid unequal heating of the rotor and consequent warping. If the unit has been shut down for a few hours only, and the turbines are still warm, it is essential that the rolling alternately ahead and astern be carried out before bringing the unit up to speed.

Start first stage of the air ejectors, bringing vacuum up to normal.

Unit is now ready to maneuver or operate.

precaution - предосторожность

to fasten - закреплять

securely - надежно

to measure clearances - замерить зазоры

turning gear - валоповоротка

to become viscous - становиться вязким

to warm the turbine up - прогреть турбину

to preclude - исключать

preferable - предпочтительный

to omit - опускать

throttle valve - дроссельный клапан

sufficient - достаточный

to avoid - избегать

unequal heating - неравномерный прогрев

consequent - последующий

warping - перекос, изгиб

rolling - прокатка, проворачивание