One Question per Day 20181213

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What issues should be considered when supplying steam to the shaft seal before starting the unit? (1) Before supplying steam to the shaft seal, the steam supply pipe should be warmed up first to drain any condensate. (2) Steam must be supplied to the shaft seal under continuous turning of the shaft. For hot start, steam should be supplied to the shaft seal first, followed by vacuum evacuation. (3) The timing of steam supply to the shaft seal must be appropriate; supplying steam to the shaft seal too early before startup can increase the temperature difference between the upper and lower cylinders or the expansion differential. (4) Attention should be paid to the matching between the temperature of the steam supplied to the shaft seal and the metal temperature. For hot start-up, using an appropriate backup steam source is beneficial for controlling the expansion difference; it is even better if the system allows the temperature of the shaft seal steam to be adjusted to be higher than the temperature of the shaft seal itself. For cold start-up, a low-temperature steam source should be used. (5) Care must be taken when switching the steam source for the high and low temperature shaft seals; a too rapid switch not only causes significant changes in the thermal expansion difference but may also lead to uneven thermal deformation at the shaft seal sites, thereby resulting in friction and vibration.