TEPCO Fuel & Power is making efforts to improve thermal power station operations, including efforts directly linked to reduced fuel costs, starting with increased operation of cost-competitive coal and high-efficiency LNG-fired thermal power stations. To increase operation rates, it is important to reduce power station downtime and expand possible operation time.
Thermal power generation facilities are operated at high temperatures and high pressure. Due to the harshness of such environments, the facilities need to be inspected and maintained periodically. Any deteriorated parts also need to be regularly replaced or repaired. Such periodic inspections include those whose implementation is prescribed by law* and those that are implemented voluntarily. Periodic inspections are performed systematically in 2- to 4-year cycles. During the inspection period, power generation facilities are shut down, each unit of equipment is disassembled and inspected, consumable parts are replaced, and equipment soundness is checked. Also, depending on the results of the inspection, repairs may be made to ensure equipment and facility safety.
*According to the Electricity Business Act, steam turbine and other units must be inspected within 4 years, and boiler facilities within 2 years, after commencement of operation or completion of a periodic inspection.
A periodic inspection requires several tens of days. During that period, equipment is shut down, causing the operation rate to drop. Therefore, efforts are being made to shorten the inspection period. Increasing the high operation rate of high-efficiency LNG-fired power stations and coal-fired power stations in particular can decrease fuel consumption, use cheaper fuel, and thus reduce fuel costs. Priority is, therefore, being given to this inspection reduction effort.
By monitoring the operating condition data at thermal power stations in operation, it becomes possible to notice changes from normal operating values and detect problems early. Such "predictive management" is being implemented to prevent shutdowns caused by abnormalities and defects.
If high-temperature gas leaks from a boiler, flue, etc., the plant may have to be shut down for safety and repairs. To detect gas leakages early, high-temperature areas discovered during operator rounds of inspection and areas where past problems have occurred are given priority monitoring.
To improve the thermal efficiency of power generation facilities, part of the steam from the steam turbine is sent to the feedwater heater to raise the temperature of the feedwater that enters the boiler. To detect feedwater heater defects early, performance is evaluated and monitored from changes in inlet/outlet steam temperature, changes in feedwater temperature, and such.
To prevent thermal power stations from having to shut down due to malfunctions that occur when, for instance, electricity demand is high, efforts are being made to implement "preventive shutdowns." In this way, when signs of an equipment problem are detected through predictive management, a plant can be systematically shut down for equipment repairs during a period when electricity consumption is low.
To minimize the impact on supply capability should a shutdown occur due to a problem or defect, a variety of work process and other "early restoration" measures have been taken to restore power station operations as quickly as possible.
To achieve "early restoration" of facilities as quickly as possible when a problem occurs, a system that secures "people" and "materials" has been established ahead of time.
To ensure that facilities can be restored as quickly as possible when unexpected equipment repairs become necessary, a "facility emergency contact system" has been established to ensure that communication with suppliers and others is always available.
For highly risky repair parts, such as those that "require many days to procure" or that "have a large impact when defective," steps are available to ensure early procurement, including the methods below.
In this example, the technical skill of the operator on duty was used to avoid a shutdown of all units at the power station.
|Defect/malfunction||To reduce and clean the NOx (nitrogen oxide) contained in the boiler exhaust gas, the thermal power station is equipped with a system that removes NOx by ammonia gas. If the supply of ammonia gas were to be stopped, the total NOx emissions from the boiler exhaust gas would exceed the environmental regulations, making it necessary to shut down the power station's operation. Due to a defect in the ammonia gas storage facility at the Kawasaki Thermal Power Station, the ammonia gas supply stopped.|
|Restoration||Normally, all power generation facility units that are supplied ammonia gas by the ammonia storage facility would be shut down so that the cause of the defect could be found and repairs made. In this case, however, only 1 of the 4 power generation facility units was shut down to find the defect cause, and a new restoration method was considered. As a result, the cause of the defect was found, the ammonia gas supply (normally an automatic supply) was resumed manually, and the system was restored without shutting down all 4 units.|
In this example, early restoration was achieved by emergency action taken in preparation for the next day's high demand.
|Defect/malfunction||At this thermal power station, seawater is used to cool generated steam. If shellfish or other things get inside the cooling system's "condenser" and accumulate, the unit's output will drop, forcing a shutdown. A large amount of shellfish found in Unit 4 of Group 1 at the Chiba Thermal Power Station caused the "ball collector," a device that collects condenser cleaning balls, to fail. It became necessary to inspect, repair, and clean the unit because of its shutdown.|
|Restoration||To meet the next day's high demand, the unit was restored through emergency action taken on the day of the unit shutdown, by carrying out internal cleaning and making use of substitute equipment for repair. This helped secure the next day's supply capability.|