Hotwell, condensers

The installation of pumps requires special care to provide enough suction head to avoid cavitation. The net suction head can disappear if a pump generates too much heat in the condensate. It is important to maintain enough flow through the pump at all times to prevent this. Minimum flow can be provided by recycle controlled by an automatic valve or by placing an orifice assembly in a recycle line. As a rule of thumb, a flow of 1 hr is necessary for each 12kW of input if the temperature rise is to be kept to 10° C. The recycle flow must be cooled or go into a heat sink such as a condensate hotwell or boiler feed deaerator. A simple recycle into the pump suction line is inadequate. 

The main condenser, which does not serve or support any safety fiinction and has no safety design basis, is a single-shell type deaerating unit with its shell located directly beneath the low pressure turbine. The shell has tube bundles through which circulating water flows. The condensing steam is collected in the condenser hotwells (the lower shell portion) which provide suction to the condensate pumps. 

Two 50% capacity condensate pumps operate in parallel during normal operation. A third 50% capacity condensate pump is provided and maintained in standby for automatic starting if required. Each pump is electric -motor driven, vertical and installed at an elevation that allows operation at low condensate level in the main condenser hotwell. 

It removes from the feed water those dissolved gases originating from air leaking into the sub-atmospheric parts of the condensate system and from gases dissolved in the condensate in the condenser hotwell. 

Condensate is pumped out of the main condenser hotwell, which is at sub-atmospheric pressure, by the condensate pumps. The water passes through the low-pressure feedwater heaters, whieh heat it using steam bled from the low-pressure turbine eylinders the largest and last low-pressure heater is incorporated into the de-aerator tank, which also removes dissolved air from the feed water and, by virtue of its substantial volume, acts as a reservoir of feed water equivalent to several minutes supply at full delivery flow. 

The hotwells have a condensater storage capacity of three minutes of feed flow at maximum power flow rate. The hotwell level controller provides automatic make-up or extraction of condensate to maintain a normal level in the condenser hotwells. On low level, the make-up... 

An innovation is a direct-contact condenser mounted on the vapor body. A short piece of vertical pipe connects the vapor body with the condenser to minimize piping and pressure drop. This design also eliminates structural steel for support of a separate condenser. For cooling tower applications, the hotwell is elevated to permit gravity flow of water from the hotwell to the top of the cooling tower, thus eliminating the need for a pump. 

Where joints are unavoidable, they should be welded. Steam coils should drain freely from inlet to outlet. Steam traps, usually of the bucket type, should also be provided. Condensate from steam coils should be drained to waste, unless adequate provision is made to drain trace quantities before return to the hotwell. Where hot-water coils are used, the water supply should be heated through a calorifier. These recommendations will avoid any risk of oil reaching the boiler plant. 

Piping arrangements are very important [25]. Pressure drops must be very low because of the low absolute pressure on the gas side and the use of flashing gravity flow on the liquid side. Condensate piping between condensers and hotwells should have a... 

Vacuum Testing. The vacuum test should take place with water at approximately normal levels in all effects. It requires sufficient water in hotwells serving the main condenser, ejectors, and intercondensers to fill the tailpipes. To the extent possible, pumps should be isolated from the evaporator system to prevent the entry of air through their seals. 

If sufficient height is not available for a barometric leg, condensate may be collected in a small accumulator tank, the liquid level controlled, and condensate removed from the tank with a centrifugal pump. Such systems are called "low-level" hotwells and are illustrated in Figure 23-6. Each intercondenser must have its own accumulator, pump, and level control. Because this is costly, most jet systems are located high in the structure and use the barometric leg and hotwell system. 

A surface type double-circuit condenser with a reamer tank, hotwell and safety... 

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