A system for deriving 100% quality steam for steam assisted gravity drainage (SAGD) injection or other applications features a once through steam generator (OTSG), a steam-water separator connected downstream of the OTSG's radiant tubes to separate steam and water from a two-phase flow received therefrom, superheater tubes installed in the convection section and connected to a steam outlet of the steam-water separator in downstream relation thereto to receive and heat dried steam therefrom to a superheated state, and a desuperheater connected downstream of the superheater tubes to receive the superheated steam therefrom and use same to vaporize blowdown water from the steam-water separator, whereby the vaporized blowdown water and the superheated steam collectively form a superheated steam output for the intended application, typically after additional separation of solid particles therefrom for optimal steam quality.

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.

A modification of a power boiler is disclosed, which comprises water walls enclosing the furnace for heating water and producing steam; a superheater system provided above the furnace for superheating steam; an additional superheater mounted in the furnace for further superheating steam from the superheater system. A modifying method of a power boiler is also disclosed, which comprises steps of mounting an additional superheater on water walls in a furnace; connecting an output of a superheater system to an inlet of the additional superheater; and connecting an outlet of the additional superheater to a turbine for producing power at an improved plant heat rate.

A system for cogenerating gas-steam based on gasification and methanation of biomass, the system including a gasification unit, a shift unit, a purification unit, a methanation unit, and a methane concentration unit. A waste heat boiler is provided in an upper part of a gasifier of the gasification unit. The methanation unit includes a first primary methanation reactor, a second primary methanation reactor, a first secondary methanation reactor, and a second secondary methanation reactor connected in series. An outlet of the second primary methanation reactor is provided with two bypasses, one of which is connected to an inlet of the first primary methanation reactor, the other of which is connected to the first secondary methanation reactor. The second secondary methanation reactor is connected to the methane concentration unit.

A system for cogenerating gas-steam based on gasification and methanation of biomass, the system including a gasification unit, a shift unit, a purification unit, a methanation unit, and a methane concentration unit. A waste heat boiler is provided in an upper part of a gasifier of the gasification unit. The methanation unit includes a first primary methanation reactor, a second primary methanation reactor, a first secondary methanation reactor, and a second secondary methanation reactor connected in series. An outlet of the second primary methanation reactor is provided with two bypasses, one of which is connected to an inlet of the first primary methanation reactor, the other of which is connected to the first secondary methanation reactor. The second secondary methanation reactor is connected to the methane concentration unit.

An evaporator includes an introducing portion that introduces a heat source gas from a heat source gas pipe, a heat source gas passage through which the heat source gas introduced from the introducing portion flows, a heating portion that is disposed in the heat source gas passage and at which a working fluid is heated by the heat source gas, an increasing portion at which a cross-sectional area of the heat source gas passage gradually increases from an upstream side towards a downstream side in the heat source gas passage, and a flow regulating plate that is disposed on an upstream side from the heating portion in the heat source gas passage and that has a plurality of holes which allow the heat source gas to pass through the plurality of holes.

An evaporator includes an introducing portion that introduces a heat source gas from a heat source gas pipe, a heat source gas passage through which the heat source gas introduced from the introducing portion flows, a heating portion that is disposed in the heat source gas passage and at which a working fluid is heated by the heat source gas, an increasing portion at which a cross-sectional area of the heat source gas passage gradually increases from an upstream side towards a downstream side in the heat source gas passage, and a flow regulating plate that is disposed on an upstream side from the heating portion in the heat source gas passage and that has a plurality of holes which allow the heat source gas to pass through the plurality of holes.

An annular superheater element for superheating steam within firetubes of firetube boilers comprising concentric inner and outer tubes and a specially designed return end cap. Saturated steam introduced into the outer tube of said superheater element is superheated while traveling towards the burner end of the tube, is directed into the inner tube by means of the return end cap, and travels away from the burner side of the element where it is exhausted for use as superheated steam. While traversing the inner tube, the superheated steam gives off heat energy through the wall of the inner tube to the steam traveling in the outer tube towards the burner end of the tube, conserving energy. The improved superheater element produces superheated steam more efficiently, with less fuel, and steam capable of doing more work, than conventional superheater elements and can be used to retrofit existing firetube type boilers.

An annular superheater element for superheating steam within firetubes of firetube boilers comprising concentric inner and outer tubes and a specially designed return end cap. Saturated steam introduced into the outer tube of said superheater element is superheated while traveling towards the burner end of the tube, is directed into the inner tube by means of the return end cap, and travels away from the burner side of the element where it is exhausted for use as superheated steam. While traversing the inner tube, the superheated steam gives off heat energy through the wall of the inner tube to the steam traveling in the outer tube towards the burner end of the tube, conserving energy. The improved superheater element produces superheated steam more efficiently, with less fuel, and steam capable of doing more work, than conventional superheater elements and can be used to retrofit existing firetube type boilers.