A combined cycle power plant and a method for operating a combined cycle power plant are presented. The combined cycle power plant includes a condensate recirculation pump to recirculate flow medium from downstream of a condensate preheater system to upstream of the condensate preheater system. An adequate flow temperature at the upstream of the condensate preheater system may be maintained to prevent acid gas dew point corrosion. The condensate recirculation pump may use a venturi effect to convert a high pressure of a condensate supplied by a condensate extraction pump to a suction pressure for the recirculation.

Heat recovery steam generator comprises a casing, low-pressure evaporator coils, preheater booster coils upstream thereof and feedwater heater coils downstream thereof, a water-to-water heat exchanger having low and high temperature paths; a first conduit from the preheater to the high-temperature path, and a second conduit from the feedwater heater to the preheater. A conduit can extend from feedwater heater to low-pressure evaporator. A conduit can extend from the water-to-water heat exchanger to the feedwater heater. High-pressure economizer coils can be upstream of the preheater, with a conduit exiting the feedwater heater to the high-pressure economizer. Additional coils can be upstream of the high-pressure economizer. The feedwater heater can comprise first and second sections, or first, second and third sections; or more sections. The connections among the various components and sections can be near their upstream and downstream faces.

A device for controlling injection of chemical into a boiler and a chemical injection method can control an injection amount such that a chemical concentration is obtained as per a target even in a boiler feed-water facility where a flow rate of feed-water varies to a large extent in a short period. The device controls an amount discharged by a chemical injection pump in proportion to a flow rate measured by a flowmeter. An average chemical concentration in a feed-water is calculated from an amount of feed-water per predetermined period obtained by the flowmeter and a reduction in the amount of chemical in a tank per predetermined period obtained by a sensor. The chemical injection pump is controlled on the basis of the calculated average chemical concentration and a preset target chemical concentration of the feed-water so that the average chemical concentration is within the target chemical concentration range.

A method for improving effectiveness of a steam generator system includes providing a steam generator system including a steam generator vessel, an air supply system and an air preheater. The air supply system is in communication with the steam generator vessel through the air preheater and the steam generator vessel is in communication with the air preheater. The air supply system provides a first amount of air to the air preheater. At least a portion of the first amount of air is provided to the steam generator vessel. A flue gas mixture is discharged from the steam generator vessel. At least a portion of the flue gas mixture flows into the air preheater. SO.sub.3 in the flue gas mixture is mitigated before the flue gas mixture enters the air preheater.

A nuclear power plant comprising a primary coolant circuit, a steam-water circuit separated from the primary coolant circuit and a steam generator connected to the primary coolant circuit and the steam-water circuit to transfer heat from the primary coolant circuit into the steam-water circuit has at least one dosing point in the steam-water circuit to inject a reducing agent into the steam-water circuit, wherein the reducing agent is an organic compound consisting of carbon, hydrogen and oxygen. Furthermore, a method for operating said nuclear power plant and the use of the method for downtime preservation of the secondary side of a steam generator of a nuclear power plant are provided.

An injection device for injecting injection fluid (chemicals) into piping through which fluid flows, the injection device comprising: an injection line through which the injection fluid flows, the injection line being connected to the piping; an injection pump disposed on the injection line; an extrusion line connected downstream of the injection pump and upstream of a target portion for air removal on the injection line; and an extrusion pump for feeding extrusion fluid to the extrusion line, wherein a discharge capacity of the extrusion pump is greater than a discharge capacity of the injection pump.

A chemical solution injection system 30 of an embodiment includes: a chemical solution reservoir 31 that stores a chemical solution containing a depositing substance to deposit to a member in contact with cooling water for absorbing heat in a plant; a pipe 32 through which the chemical solution passes; a first heat exchanger and a second heat exchanger that exchange heat between the cooling water and the chemical solution; a cooling water pipe 49 which connects the heat exchangers in series and in which the cooling water passes; and a pump 34 that conveys the chemical solution. The temperature of the chemical solution in the chemical solution reservoir 31 is lower than that of the cooling water. The pipe 32 sequentially connects the chemical solution reservoir 31, the first heat exchanger, the second heat exchanger and the plant. The cooling water guided from the inside of the plant passes through the second heat exchanger and subsequently passes through the first heat exchanger. The chemical solution passes through the first heat exchanger and subsequently passes through the second heat exchanger.

The present invention provides a corrosion-resistant structure for a high-temperature water system comprising: a structural material 1; and a corrosion-resistant film 3 formed from a substance containing at least one of La and Y deposited on a surface in a side that comes in contact with a cooling water 4, of the structural material 1 which constitutes the high-temperature water system that passes a cooling water 4 of high temperature therein. Due to above construction, there can be provided the corrosion-resistant structure and a corrosion-preventing method capable of operating a plant without conducting a water chemistry control of cooling water by injecting chemicals.

A dual-bed system for preventing a boiler heating surface from being contaminated comprises a fluidized bed, a cyclone separator, a coal ash distributor, an ash-coal mixer, a lower pyrolysis bed, a return feeder and a cleaner, wherein the cyclone separator is connected with the upper lateral side of the fluidized bed; the inlet end of the coal ash distributor; the two outlets of the coal ash distributor are respectively connected with the inlet of the return feeder and the inlet of the ash-coal mixer; the outlet of the ash-coal mixer is connected with the inlet of the lower pyrolysis bed; the return feeder close to the lower lateral side of the fluidized bed is connected with the inlet on the lower lateral side of the fluidized bed; and the outlet of the cleaner is connected with the inlet on the lower lateral side of the fluidized bed.

An injection device for injecting injection fluid (chemicals) into piping through which fluid flows, the injection device comprising: an injection line through which the injection fluid flows, the injection line being connected to the piping; an injection pump disposed on the injection line; an extrusion line connected downstream of the injection pump and upstream of a target portion for air removal on the injection line; and an extrusion pump for feeding extrusion fluid to the extrusion line, wherein a discharge capacity of the extrusion pump is greater than a discharge capacity of the injection pump.