Turbine-driven pumps operation

It is quite important not to operate a turbine-driven pump by throttling the steam flow to the turbine. Let s assume that the operators have set the turbine speed at 3500 rpm, by adjusting the steam inlet gate valve upstream of a malfunctioning governor. Suddenly, the discharge flow-control valve cuts back, and the pump s flow decreases from 2000 to 1200 GPM. The pump speed will then increase, because fewer pounds of liquid are being pumped, and less horsepower is required to spin the pump. 

T is the transient of main feed-water loss due to loss of electric power supply. M, B indicate the lack of recovery of the outside lines and the non-operation of the station diesels for at least three hours (in the Rasmussen report, the probability of non-recovery of the outside lines in one hour is assumed equal to 2x 10" and the probability, to be combined with the preceding one, of nonrecovery for the other two hours of the same lines, is assumed equal to 5 x 10 ). L indicates the malfunction of the auxiliary feed-water system and therefore also of the turbine-driven pump. 

Many years ago, working as an outside operator during a strike (i.e., I was a scab), I noted that on some of my steam turbine-driven pumps, the level of oil in the oiler glasses rose perhaps Vito 1 inch every day. I actually thought that in some mysterious way, that lubrication oil was being produced inside the bearing housing. Of course, it was just water. 

Failure of the cooling water pump is an important consideration, and the number of cooling water circulation pumps needs to be established carefully. The number of cooling water circulation pumps can be equal to the number of steam turbine-driven pumps that normally operate. 

The steam balance in the plant shown in Figure 2 enables all pumps and blowers to be turbine-driven by high pressure steam from the boiler. The low pressure exhaust system is used in the reboiler of the recovery system and the condensate returns to the boiler. Although there is generally some excess power capacity in the high pressure steam for driving other equipment, eg, compressors in the carbon dioxide Hquefaction plant, all the steam produced by the boiler is condensed in the recovery system. This provides a weU-balanced plant ia which few external utiUties are required and combustion conditions can be controlled to maintain efficient operation. 

Backup systems which depend upon the action of automatic cut-in devices (e.g., a turbine-driven standby spare for a motor-driven cooling water pump, with PLCI control) would not be considered an acceptable means of preventing a utility failure for normal pressure relief design purposes, even though their installation is fully justified by improved continuity and reliability of plant operations. 

Figure 17.4 shows a centrifugal pump, driven by a steam turbine. The correct operating speed for the pump and turbine is that speed that puts the process-control valve in a mostly open, but still controllable, position. As we slow the turbine to force open the process-control valve, the turbine s governor valve will close. Steam flow to the turbine will decline in accordance with fan laws ... 

Interrupted on April 23 for a few days by a fast shutdown that occurred as a result of faulty water flow control following the activation of a turbine-driven feedwater pump, this period of steady state operation ended, running solely on the B train turbo-generator. The A train transformer was shut down as the analysis made periodically of the cooling oil of the transformer had revealed that a preventive internal inspection was required. 

An example is that a large pump is driven by a steam turbine operating between ISOpsig and atmospheric condition. 3800 Ib/h steam is measmed online. The pump power requirement is estimated by equation (8.1) as 72 hp. On the other hand, the theoretical power supplied by the steam mrbine can be estimated from the theoretical steam table. The steam table indicates the specific steam rate of 18.22 Ib/kWh, which indicates the steam turbine can deliver 208.6 kW (38001b/h/18.221b/kWh) or 279.6 hp. Thus, the overall efficiency of the turbine and pump is only 26% (72/279.6). This efficiency is much lower than design. It was found that steam turbine blades were severely eroded over time and no inspection and maintenance work was ever done on the turbine for a long time. 

Three feed water pumps are installed which are driven by steam turbines. Two pumps are used in normal operation. Each has a flow capacity of 50% of full reactor power operation and one feed water pump trip does not cause any reactor scram. 

In contrast, there are disadvantages to automatic isolation of EFW. If both channels of the controlling isolation logic systems were to spontaneously actuate either during normal operation or in the course of a transient, the availability of EFW would be lost and the main steam isolation valves would close. Most newer plants use turbine-driven main feedwater pumps. Thus, main feedwater would also be lost, resulting in complete loss of the secondary heat sink. Capability to lock-out the isolation logic is necessary to preclude such scenarios. 

Number of feedwater pumps required for full power operation - the number of main feedwater pumps that are normally in operation at rated unit power. It is usual for some of the available feedwater pumps to be on standby in case an operating pump trips. If turbine-driven and motor-driven feedwater pumps are operated simultaneously, the value should be entered in the following form "number of operating turbine-driven feedwater pumps/ number of operating motor-driven feedwater pumps". 

H3 Procedures used in case of black-out (total loss of external and internal electrical sources), in case of primary circuit closed, energy is extracted like for HI procedure, a specific GUS (ultimate backup device) turbine generator (gas turbine) for 1300 and 1400 MW subseries or diesel for 900 MW subseries, (allows to maintain seal water injection to the primary coolant pump via the test pump, and necessary control for operators), in case of break on primary circuit makeup is realized using a specific motor-driven pump, (control in a safe state for about 10 hours). 

NUREG-1275, Vol. 10, Operating experience feedback report - Reliability of steam turbine-Driven standby pumps, October 1994. 

The decay heat and residual heat could be cooled for about 30 minutes through the natural circulation of primary coolant in the primary system, and through the operation of turbine operation auxiliary water supply pump and the main steam safety valve. Necessary power for the safety protection systems and the turbine-driven auxiliary feedwater systems is supplied from highly reliable batteries to secure the safety of reactor even during the total loss of power. 

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