A method for improving the efficiency of a fired heater without an air preheat system is described. The method involves the use of an additional outboard convection section which is separate from the regular convection section of the fired heater. The outboard convection section uses the boiler feed water or an alternate cold sink to reduce the temperature of the flue gas, thereby improving the efficiency.

A thermal power generation system includes: a boiler; at least one steam turbine; a generator; a condenser; at least one low-pressure feed water; a high-pressure feed water pump; at least one high-pressure feed water heater capable of heating water pumped by the high-pressure feed water pump by utilizing extracted steam; a catalyst device including at least one kind of catalyst capable of promoting reduction reaction of nitrogen oxide and oxidation reaction of metallic mercury, the nitrogen oxide and the metallic mercury both being contained in the exhaust gas; at least one mercuric oxide removing device capable of removing mercuric oxide produced by the oxidation reaction of the metallic mercury from the exhaust gas; and an exhaust gas temperature adjustment device capable of adjusting a temperature of the exhaust gas at the catalyst device, by adjusting heating of the water by the at least one high-pressure feed water heater.

A thermal power generation system includes: a boiler; at least one steam turbine; a generator; a condenser; at least one low-pressure feed water; a high-pressure feed water pump; at least one high-pressure feed water heater capable of heating water pumped by the high-pressure feed water pump by utilizing extracted steam; a catalyst device including at least one kind of catalyst capable of promoting reduction reaction of nitrogen oxide and oxidation reaction of metallic mercury, the nitrogen oxide and the metallic mercury both being contained in the exhaust gas; at least one mercuric oxide removing device capable of removing mercuric oxide produced by the oxidation reaction of the metallic mercury from the exhaust gas; and an exhaust gas temperature adjustment device capable of adjusting a temperature of the exhaust gas at the catalyst device, by adjusting heating of the water by the at least one high-pressure feed water heater.

A method for operating a waste heat steam generator, in particular one designed according to the forced flow principle, having an evaporator, through which a flow medium flows; an economizer having a number of economizer heating surfaces, and having a bypass line, which on the flow medium side is connected in parallel to a number of economizer heating surfaces. A variable that is characteristic of the heat energy supplied to the waste heat steam generator for controlling or regulating the flow rate of the bypass line is used, wherein the regulating or controlling of the flow rate of the flow medium through the bypass line takes place at the inlet of the evaporator subject to a supercooling target value. The regulating or controlling of the flow rate of the flow medium through the bypass line also takes place at the outlet of the evaporator subject to an overheating target value.

A method for operating a waste heat steam generator, in particular one designed according to the forced flow principle, having an evaporator, through which a flow medium flows; an economizer having a number of economizer heating surfaces, and having a bypass line, which on the flow medium side is connected in parallel to a number of economizer heating surfaces. A variable that is characteristic of the heat energy supplied to the waste heat steam generator for controlling or regulating the flow rate of the bypass line is used, wherein the regulating or controlling of the flow rate of the flow medium through the bypass line takes place at the inlet of the evaporator subject to a supercooling target value. The regulating or controlling of the flow rate of the flow medium through the bypass line also takes place at the outlet of the evaporator subject to an overheating target value.

An exhaust gas cooler includes: a steam drum containing first water; an economizer for heat exchange between exhaust gas and the first water supplied from the steam drum; and a feedwater pipe for supplying the first water with second water having a lower temperature than the first water. The exhaust gas cooler is configured such that the first water flowing out of the economizer is introduced into the steam drum. The second water is divided and supplied to the first water flowing out of the economizer and the first water flowing into the economizer

The method in a recovery boiler comprises estimating the first melting temperature T.sub.0 of the fly ash depositing on heat transfer surfaces, the estimating being based on potassium (K) content of the fly ash; measuring or estimating the temperature T.sub.ss of superheated steam; evaluating a temperature difference T.sub.D1 between the first melting temperature T.sub.0 and the temperature T.sub.ss of the superheated steam, the temperature difference T.sub.D1 providing an estimate of the risk of corrosion; and selecting a control action for influencing the temperature difference T.sub.D1. Alternatively or additionally, the method comprises estimating the sticky temperature T.sub.STK of the fly ash depositing on heat transfer surfaces, the estimating being based on potassium (K) and chlorine (Cl) contents of the fly ash; measuring or estimating the temperature T.sub.FG of the flue gases; evaluating a temperature difference T.sub.D2 between the sticky temperature T.sub.STK and the temperature T.sub.FG of the flue gases; the temperature difference T.sub.D2 providing an estimate of the risk of plugging; and selecting a control action for influencing the temperature difference T.sub.D2.

The method in a recovery boiler comprises estimating the first melting temperature T.sub.0 of the fly ash depositing on heat transfer surfaces, the estimating being based on potassium (K) content of the fly ash; measuring or estimating the temperature T.sub.ss of superheated steam; evaluating a temperature difference T.sub.D1 between the first melting temperature T.sub.0 and the temperature T.sub.ss of the superheated steam, the temperature difference T.sub.D1 providing an estimate of the risk of corrosion; and selecting a control action for influencing the temperature difference T.sub.D1. Alternatively or additionally, the method comprises estimating the sticky temperature T.sub.STK of the fly ash depositing on heat transfer surfaces, the estimating being based on potassium (K) and chlorine (Cl) contents of the fly ash; measuring or estimating the temperature T.sub.FG of the flue gases; evaluating a temperature difference T.sub.D2 between the sticky temperature T.sub.STK and the temperature T.sub.FG of the flue gases; the temperature difference T.sub.D2 providing an estimate of the risk of plugging; and selecting a control action for influencing the temperature difference T.sub.D2.

An exhaust gas latent-heat recovery device includes: a heat transfer tube disposed inside a duct through which exhaust gas flows, the heat transfer tube having a water supply inlet into which water to be heated for recovering latent heat of the exhaust gas is supplied and a water supply outlet through which the water to be heated is discharged; and a water supply control part configured to control supply of the water to be heated to the water supply inlet. The water supply control part is configured to control supply of the water to be heated from the water supply inlet so that an outlet temperature being a temperature of the water to be heated at the water supply outlet is at a set temperature.

An exhaust gas latent-heat recovery device includes: a heat transfer tube disposed inside a duct through which exhaust gas flows, the heat transfer tube having a water supply inlet into which water to be heated for recovering latent heat of the exhaust gas is supplied and a water supply outlet through which the water to be heated is discharged; and a water supply control part configured to control supply of the water to be heated to the water supply inlet. The water supply control part is configured to control supply of the water to be heated from the water supply inlet so that an outlet temperature being a temperature of the water to be heated at the water supply outlet is at a set temperature.