FI128267B

FI128267B - Menetelmä ja järjestelmä höyryä höyryturbiinille tuottavan kattilan käsittävän voimalaitoksen kuormitusalueen laajentamiseksi

Info

Publication number: FI128267B
Application number: FI20175419A
Authority: FI
Inventors: Juhani Isaksson; Matti Nieminen
Original assignee: Valmet Technologies Oy
Priority date: 2017-05-10
Filing date: 2017-05-10
Publication date: 2020-02-14
Also published as: ES2848053T3; DK3415816T3; EP3415816B1; FI20175419A; PL3415816T3; PT3415816T; EP3415816A1; HUE052435T2

Abstract

null

Description

A METHOD AND A SYSTEM FOR EXTENDING THE LOAD RANGE OF A POWER PLANT COMPRISING A BOILER SUPPLYING STEAM TO A STEAM TURBINE

FIELD OF THE DISCLOSED SOLUTION

The disclosed solution relates to the operation of a steam turbine power plant comprising a boiler for steam generation.

BACKGROUND OF THE DISCLOSED SOLUTION

Steam turbine power plants are commonly used for production of electricity. In combined heat and power (CHP) plants, thermal energy not captured by the steam turbine is additionally utilized as useful heat.

In steam turbine power generation, a boiler, burning suitable fuel, produces steam with a mass flow rate, which steam is conveyed to a steam turbine. Steam refers to water in a gaseous state. In the boiler, thermal energy released by the burnt fuel is transferred into the steam. The steam entering the steam turbine is typically pressurized at 80-180 bar and has a temperature typically in the range of 450-560 °C. Typically, when a power plant is in operation, i.e. electricity is being produced, the pressure of the steam entering the turbine is kept constant while its temperature may change. The steam turbine converts thermal energy in the steam into rotary motion on the turbine output shaft. This shaft then drivers an electric generator via a suitable driveline.

A steam turbine requires steam of sufficiently high quality for viable operation. This typically means that the steam entering the steam turbine must contain a sufficiently high amount of thermal energy to be released in the steam turbine as the steam travels through the turbine. If the incoming steam contains too little thermal energy it is not acceptable for the steam turbine, since such steam may condense prematurely and thereby risk steam turbine damage or failure. For this reason, the load range of a steam turbine power plant can not be lowered below a threshold at which the boiler bums just enough fuel so that the thermal energy

20175419 PRH 10 -01- 2020 transferred in the boiler into the steam enables satisfying the minimum quality criteria for the steam entering the steam turbine. Below this threshold, i.e. the minimum viable rated load of the power plant, the power plant may not be viably operated.

Therefore, steam turbine power plants have a limitation with respect to their downward load range flexibility, which limits their use in electricity production namely, with low loads i.e. low volume of electricity production.

Publication GB 682410 A discloses a power plant including an auxiliary superheater for use 10 with high loads only. Another power disclosed is shown in publication US 3002347 A.

SUMMARY OF THE DISCLOSED SOLUTION

The method according to the disclosed solution is defined by what is stated in claims 1 and 2. An additional method according to the disclosed solution is defined by what is stated in claim 7. The system according to the solution is defined by what is stated in claims 8 and 9.

The solution comprises a method of extending the load range for viable operating Wv of a 20 steam turbine power plant comprising a boiler with a superheater for supplying superheated steam to a steam turbine, the steam turbine having a required minimum viable temperature Tv of steam entering the steam turbine, the load range for viable operating Wv of the steam turbine power plant being extended by means of controllably using an auxiliary superheating chamber comprising an auxiliary superheater to further superheat steam.

Such controllable use of the auxiliary superheating chamber may entail that based on determining the temperature T of the steam entering the steam turbine:

(1) when the temperature T of the steam entering the steam turbine is above an alert temperature Ta, which alert temperature Ta is higher than the required minimum viable 30 temperature Tv: fuel is burned in the boiler to generate thermal energy to be transferred into steam in the superheater to generate superheated steam satisfying the required minimum viable temperature Tv of the steam entering the steam turbine; the superheated steam from the superheater is conveyed to the auxiliary superheater of the auxiliary superheating chamber; fuel is burned with a burner in the auxiliary superheating chamber to keep the superheating chamber in a hot standby temperature; and the superheated steam is conveyed from the auxiliary superheater to the steam turbine;

and (2) when the temperature T of the steam entering the steam turbine is at or below the alert temperature Ta: fuel is burned in the boiler to generate thermal energy to be transferred into steam in the superheater to generate superheated steam; the superheated steam is conveyed from the superheater to the auxiliary superheater of the auxiliary superheating chamber; the superheated steam is further superheated by burning fuel with a burner in the auxiliary superheating chamber to generate thermal energy to be transferred into the superheated steam in the auxiliary superheater such that the required minimum viable temperature Tv of steam entering the steam turbine is satisfied; and the superheated steam is conveyed from the auxiliary superheater to the steam turbine.

Alternatively, such controllable use of the auxiliary superheating chamber may entail that based on determining the temperature T of the steam entering the steam turbine:

(1) when the temperature T of the steam entering the steam turbine is above an alert temperature Ta, which alert temperature Ta is higher than the required minimum viable temperature Ty: fuel is burned in the boiler to generate thermal energy to be transferred into steam in the superheater to generate superheated steam satisfying the required minimum viable temperature Ty of the steam entering the steam turbine; the superheated steam is conveyed from the superheater to the steam turbine by bypassing the auxiliary superheater with a steam diversion pathway; fuel is burned with a burner in the auxiliary superheating chamber to keep the superheating chamber in a hot standby temperature;

20175419 PRH 10 -01- 2020

The solution thereby enables the required minimum viable temperature Tv of steam entering the steam turbine to be satisfied both within the load range for normal operating of the power plant and the load range for low load operating of the power plant.

In addition, the solution comprises a method of maintaining in hot standby mode a steam turbine power plant, which entails generating product gas in the gasifier; supplying product gas from the gasifier to a burner in the auxiliary superheating chamber to maintain the superheating chamber in a hot standby temperature, which temperature is higher than ambient temperature; and supplying product gas from the gasifier to the boiler to be burned in the 10 boiler to maintain the boiler in a hot standby temperature, which temperature is higher than ambient temperature.

The solution further comprises a system which may comprise a boiler with a superheater for supplying superheated steam to a steam turbine, the steam turbine having a required minimum 15 viable temperature Tv of steam entering the steam turbine; a controllably usable auxiliary superheating chamber comprising an auxiliary superheater and a burner, the auxiliary superheater installed in a steam forward conveyance pathway between the superheater and the steam turbine; and a control unit adapted to:

determine the temperature T of the steam entering the steam turbine;

- when the temperature T of the steam entering the steam turbine is above an alert temperature Ta, which alert temperature Ta is higher than the required minimum viable temperature Tv: control the burning of fuel in the burner such that the superheating chamber is kept in a hot standby temperature; and when the temperature T of the steam entering the steam turbine at or below the alert 25 temperature Ta: control the burning of fuel in the burner such that thermal energy is transferred into the superheated steam in the auxiliary superheater such that the required minimum viable temperature Tv of steam entering the steam turbine is satisfied.

Alternatively, the control unit may be adapted to:

determine the temperature T of the steam entering the steam turbine;

when the temperature T of the steam entering the steam turbine is above an alert temperature Ta, which alert temperature Ta is higher than the required minimum viable temperature Tv: control a valve arrangement such that superheated steam is

20175419 PRH 10 -01- 2020 conveyed from the superheater to the steam turbine, the steam thereby bypassing the auxiliary superheater via a steam diversion pathway; and control the burning of fuel in the burner such that the superheating chamber is kept in a hot standby temperature; and

- when the temperature T of the steam entering the steam turbine at or below the alert temperature Ta: control the valve arrangement such that superheated steam is conveyed from the superheater to the auxiliary superheater; and control the burning of fuel in the burner such that thermal energy is transferred into the superheated steam in the auxiliary superheater such that the required minimum viable temperature Tv of 10 steam entering the steam turbine is satisfied.

The system may thereby enable the required minimum viable temperature Tv of steam entering the steam turbine to be satisfied both within the load range for normal operating of the power plant and the load range for low load operating of the power plant.

Typically, a steam turbine has specified minimum quality requirements for incoming steam. Steam quality typically refers to (1) steam temperature, (2) steam pressure and (3) proportion of entrained liquid content in the steam. High quality steam is of high enough temperature and pressure and contains little to no entrained liquid. If steam is not of high enough quality, it will 20 condense too early along its way through the steam turbine, whereby condensate water droplets may cause problems. Such problems comprise, for example, formed water droplets hitting turbine blades, typically towards the end of the steam turbine, which creates a risk of turbine damage or failure. The disclosed solution alleviates this problem by enabling supplying, by controllably using an auxiliary superheating chamber comprising an auxiliary 25 superheater, steam of sufficiently high quality also in situations in which the thermal energy production in the boiler is insufficient alone to maintain sufficient steam quality.

Steam of sufficiently high quality requires that a sufficiently large amount of thermal energy is produced in the boiler and then transferred to the steam. Such energy transfer is typically 30 brought about so that water is pre-heated in the boiler to form steam, whereafter steam is further heated in a superheater or superheaters installed in the boiler. Superheater is a device preferably used to convert steam into superheated steam.

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Superheated steam is steam at a temperature which is higher than the boiling point of the substance such as water at a particular pressure. Steam in a superheated state contains no entrained liquid. Thus, the temperature of superheated steam may decrease by some amount before entrained liquid begins to form. Therefore, the higher the temperature of superheated 5 steam, the more it may cool, i.e. release energy, before entrained liquid begins to form.

Typically, steam of sufficiently high quality for a steam turbine refers to steam which is superheated to such a temperature that the superheated steam contains high enough energy so that it will not condensate prematurely in the steam turbine as it releases energy while 10 travelling through the steam turbine.

Typically, the pressure of the steam entering the steam turbine is kept constant in a power plant system. This pressure begins to decrease once steam enters the steam turbine, wherein the steam starts to release energy and expand.

Lower boiler load, i.e. lower heat generation in the boiler, results in less thermal energy being transferred to the steam which, in turn, results in lower quality steam. Boiler load may be controlled by adjusting the amount of fuel being fed into the boiler to be burned. As is well known in the industry, the amount of thermal energy generated in the boiler and/or 20 transferred into the steam can be inferred, for example calculated, from the volume of fuel per unit of time being fed into the boiler and the type of fuel being fed. Typically, the boiler comprises an arrangement for automatically adjusting the amount of air and/or other gases required in the fuel burning process as a function of the amount of fuel being fed. Such automatic adjustment of air and/or other gases may be effected, for example, by measuring 25 the level of oxygen present in the combustion gases and adjusting the feed of fuel and/or the air and/or other gases such that an optimal oxygen level in the combustion gases, known as the lambda value, is obtained.

When the load of a boiler is reduced, the volume of steam produced in terms of mass flow 30 rate typically decreases relatively linearly as a function of the load. When the steam mass flow is reduced, the electricity output of the plant, i.e. the load of the power plant, is correspondingly reduced.

20175419 PRH 10 -01- 2020

At and above its minimum rated load a boiler is capable of transferring sufficient amount of thermal energy to the produced steam mass flow for the steam to be of sufficient quality for the steam turbine. Below the minimum rated load of the boiler, the amount of thermal energy transferred to the produced steam mass flow is no longer sufficient for the steam to be of sufficient quality for the steam turbine, even though the reduced mass flow rate of the steam could still be appropriate for electricity generation purposes at that time.

Thus, the minimum rated load of a boiler is the minimum load with which the boiler is capable of producing steam of sufficient quality for the steam turbine. Below this minimum rated load, the steam is not of acceptable quality for the steam turbine. In practice this usually means that the steam is not sufficiently hot, since the pressure of the steam entering the turbine is typically kept constant when electricity is being produced.

With regard to a large-scale electrical grid, the increasing generation of electricity from renewable sources such as solar and wind power poses challenges. This is because such renewable energy sources are inherently variable in terms of their power output because of, for example, weather conditions and the night-day sunlight cycle. Consequently, in an electrical grid comprising such renewable or otherwise variable power production, other modes of power production in the grid such as steam turbine-based power generation should preferably be capable of flexibly adjusting their power output in order to appropriately complement the variable power sources so that the demand for electricity in the grid is met at all times. As is well known, demand for electricity is variable as well.

An advantage of the disclosed solution is that steam turbine-based power generation may be made more capable of such flexible adjusting of power production. This is because below the minimum rated viable load of the boiler, the auxiliary superheating chamber comprising an auxiliary superheater may be employed to further superheat steam thereby ensuring supplying steam of sufficient quality to the steam turbine.

Without such further superheating, the minimum rated viable load of a boiler defines the minimum rated viable load of a power plant comprising a boiler for steam production. Below this minimum rated viable load of a power plant, the power plant typically must be shut down in order to avoid risking a steam turbine damage. Thus, the minimum rated viable load of a boiler currently in practice defines the range of downward load flexibility of a power plant, from the full rated load of a power plant to its minimum rated viable load. The disclosed solution enables extending the viable load range of a steam turbine power plant downwards below the minimum rated viable load of the boiler.

Conventionally, the minimum rated viable load of a power plant is about 30-40% below its full rated load. Some power plants comprising fluidized bed boilers have a minimum rated viable load of about 60% below the full rated load.

Conventionally, a further hindrance for the load range flexibility of steam turbine power plants is that their shutdown and start-up times may be considerably long, such as up to 12 hours. Therefore, such power plants are not capable of flexibly adjusting to changing electricity demand conditions by means of shutdown-start-up cycles. Such non-productive shutdown and start-up periods are costly as well. The disclosed solution enables reducing the need for such shutdown-start-up cycles by way of enabling a steam turbine power plant to be operated with an extended load range by controllably using an auxiliary superheating chamber comprising an auxiliary superheater to further superheat steam supplied to the steam turbine.

Thus, the disclosed solution enables running a steam turbine power generation plants with a wide load range for viable operating, particularly such that the load range for viable operating of the power plant extends below the minimum rated viable load of the power plant as typically determined by the minimum rated viable load of the boiler. Such extended load range for viable operating of the power plant below its minimum rated viable load, as enabled by the disclosed solution, has the benefit of enabling the power plant to better respond to changing power demand conditions.

BRIEF DESRCIPTON OF THE FIGURES

Figure 1 schematically illustrates the steam production system of a steam turbine power plant according to an example embodiment, the system comprising an auxiliary superheating chamber for further superheating steam as needed.

Figure 2 schematically illustrates the steam production system of Figure 1, wherein the fuel supplied to the auxiliary superheating chamber and optionally supplied to the boiler is gaseous and produced in a gasifier.

Figure 3 schematically illustrates the steam production system of Figure 1, wherein steam may be selectably conveyed and not conveyed through the auxiliary superheating chamber.

Figure 4a schematically illustrates the idealized relationships of the mass flow (m) of steam and the temperature (T) of steam entering a steam turbine to the load (W) of a steam turbine power plant in a conventional steam production system.

Figures 4b-c schematically illustrate the idealized relationships of the mass flow (iti) of steam and the temperature (T) of steam entering a steam turbine to the load (W) of a steam turbine power plant in a steam production system according to the disclosed solution.

Figure 5 schematically illustrates the steam production system of a steam turbine power plant according to another example embodiment, the system comprising an auxiliary superheating chamber for further superheating steam as needed.

Figure 6a schematically illustrates the idealized relationship between the load (W) and the heat consumption of a power plant.

Figure 6b schematically illustrates the idealized relationship between the fuel consumption and the heat consumption of a power plant.

The figures are not in scale or suggestive of the physical layout or the dimensions of system components.

DETAILED DESCRIPTION OF THE INVENTION

In the text, reference is made to the figures with the following numerals and denotations:

20175419 PRH 10 -01- 2020

w	Load of a power plant at a point of time
Wf	Full rated load of a power plant
5 Wmv	Minimum rated viable load of a power plant
Wmva	Minimum viable load of a power plant
Wn	Load range for normal operating of a power plant
Wl	Load range for low load operating of a power plant
Wu	Load range for unviable operating of a power plant
10 Wv	Load range for viable operating of a power plant
T	Temperature of steam entering a turbine
T_F	Temperature of steam entering a turbine with full power plant load
Tv	Minimum viable temperature of steam entering a steam turbine
m	Mass flow rate of steam
15 riiF	Mass flow rate of steam with full boiler load
1	Auxiliary superheating chamber
2	Auxiliary superheater
3	Steam turbine
4	Gasifier
20 5	Cooler
6	Fuel source
7	Filter
8	Heat exchanger
9	Generator
25 10	Boiler
11	Superheater
13	Electricity-consuming process
14	Condenser
15	Heat exchanger
30 20	Pump
21	Fuel source
22	Heat-consuming process
23	Control unit
24	Burner

25	Heat exchanger
26	Valve arrangement
30 to 58	Line
70	Driveline
71	Duct
72	Burner

In the text and in the figures, the notion of a “line” is used to refer to any suitable conveyance passageway without any definite characterization of the physical properties of the passageway. It is to be appreciated that a person skilled in the art is capable of determining the physical properties of a passageway according to the properties and the volume of the material to be conveyed as well as other such pertinent conveyance parameters and requirements.

In the text, unless otherwise specified, the notion of a “power plant” is used to refer to a steam turbine power plant wherein a steam turbine 3 may be used to convert thermal energy of steam into mechanical work, which mechanical work may be converted into electricity by a generator 9.

Figure 1 schematically illustrates, according to an example embodiment, a system for producing steam to be used in a steam turbine 3 according to the solution. Steam enters the steam turbine 3 with a mass flow rate m, defined as the mass of steam entering the steam turbine 3 per unit of time. The steam turbine may have minimum requirements for the properties of the steam entering the steam turbine for viable operating of the steam turbine 3.

Such minimum requirements may comprise, for example, a minimum viable temperature Tv for the steam entering the steam turbine 3 such that if the temperature T of the steam entering the steam turbine is below the minimum viable temperature Tv, the steam turbine may not be operated viably. There may be additional such minimum requirements as well, such as a minimum viable pressure for the steam entering the steam turbine 3 such that if the pressure of the steam entering the steam turbine 3 is below the minimum viable pressure, the steam turbine 3 may not be operated viably.

Determining steam properties may be performed by installing a flowmeter and/or a pressure sensor and/or a temperature sensor in a steam conveyance line, and relaying the signal(s) from

20175419 PRH 10 -01- 2020 this/these instruments to an apparatus such as a dedicated steam flow computer and/or a control unit 23 for processing and/or storage. It is to be appreciated that determining steam properties is well known in the industry and appropriate equipment for this purpose commercially available. Steam properties, once determined for example through measurement, 5 may be used as control input data by the control unit 23.

Referring to Figure 1, steam properties may be determined by way of measurement at least in a line 31 at its terminus at the steam turbine 3. In addition, as will be explained below, steam properties may be determined otherwise as well, for example based on measurements in other 10 loci in the system.

Determining of the properties of steam, including its temperature, as it enters into the steam turbine 3 may be indirect. This means that steam properties are measured further upstream or downstream, for example in the steam conveyance pathway which terminates at the steam 15 turbine 3, and that the measurement results are converted into values for the properties of the steam to be determined, for example as it enters into the steam turbine 3, by using known conversion factors. Such known conversion factors may be obtained through, for example, comparative measurements at loci of interest, of they may be derived from calculations based on the physical properties of the system. The notion of determining steam properties, as it 20 used in this text, includes also indirect determining as just described.

In a power plant, the pressure of the steam may be kept constant, at least when the power plant produces electricity, in which case the minimum requirements for the properties of the steam entering the steam turbine 3 may in practical terms be captured by the minimum viable 25 temperature Tv for the steam entering the steam turbine 3.

The steam turbine 3 may be adapted to drive, via a driveline 70, an electric generator 9 which may supply electricity to an electricity-consuming process via a line 44. The electricityconsuming process may be a specific and/or localized process such as in a manufacturing 30 facility, or the electricity-consuming process may be aggregate electricity consumption in an electrical grid such as a district, a regional or a national electrical grid.

In the system, superheated steam is produced by superheating steam in a superheater 11 installed in a boiler 10. As is well known, apparatuses upstream from the superheater 11, such

20175419 PRH 10 -01- 2020 as a heat exchanger 25 or a plurality of such heat exchangers may be employed to vaporize the water circulating in the system such that the water is already steam when it enters the superheater 11. In addition, upstream from the superheater 11 may be additional apparatuses such as a heat exchanger or heat exchangers 15 for pre-heating the circulating water before 5 vaporization.

The superheater 11 may be a single superheater device. Alternatively, the superheater 11 may be an aggregate of a plurality of individual superheater devices. Superheating the steam is brought about by transferring to the steam thermal energy resulting from burning fuel in in 10 the boiler 10 with a burner (not depicted). The same applies to the heat exchanger or heat exchangers 25.

The boiler 10 may be of a known type, such as of the fluidized bed type or of the pulverized coal-fired type. Fuel may be supplied from a fuel source 21 via a line 49 to the boiler to be 15 burned. Air or other suitable gas or gas mixture required for burning the fuel may be conveyed to the boiler 10 via a line 50 or multiple such lines. Non-gaseous combustion residues such as ash resulting from burning the fuel may be expelled from the boiler 10 via a line 51. Combustion gases resulting from burning the fuel may be expelled from the boiler 10 via a duct 71.

Before combustion gases are expelled from the boiler, thermal energy may be captured from the combustion gases with means in addition to the superheater 11. According to the embodiment depicted in Figure 1, such additional means of thermal recovery may comprise a heat exchanger or heat exchangers 15. The varieties and using of heat exchangers are well 25 known in the industry, and such knowledge readily applies to the heat exchanger or heat exchangers 15.

The power plant may be run with a load W, which refers to the amount of electricity generated by the generator 9 per unit of time, as driven by the steam turbine 3. As is well 30 known in the industry, the amount of electricity generated by the generator 9 per unit of time,

i.e. the power output of the generator 9, may be measured based on the voltage and current of the electricity output. Alternatively or in addition, the load W of the power plant may be inferred from the heat consumption of the power plant, since it is well known that the load W of a power plant is highly correlated with its heat consumption. The heat consumption, in

20175419 PRH 10 -01- 2020 tum, can be inferred from the amount of fuel burned in a unit of time for the purposes of heat generation in the power plant. The precise relationships between the amount of fuel burned in a unit of time and heat consumption, and between heat consumption and load W is typically plant-specific due to, for example, plant-specific energy losses. Figures 6« and 6b 5 illustrate the idealized relationships between these measures. Such measurements are a part of normal power plant instrumentation.

The volume of fuel being burned in a power plant for the purposes of producing and heating steam and the load W of the power plant have a correlation which is characteristic for each 10 power plant and known by the operators and/or programmed into the control apparatuses of the power plant. Thus, the load W of the power plant may be controlled by adjusting the fuel being burned for the purposes of producing and heating steam.

The power plant may be run with different loads W, as illustrated in Figures 4« to 4/.

Figure 4λ represents the operation of a conventional system for producing steam to be used in a steam turbine 3. Figures 4£ to 47 represent the operation a system for producing steam to be used in a steam turbine 3 according to the disclosed solution comprising a controllably utilizable auxiliary superheating chamber comprising an auxiliary superheater.

As illustrated in Figure 4#, a power plant may have a full rated load Wf. This refers to the load W of the power plant which may be obtained with a full rated load of the boiler 10, i.e. when a maximum amount of thermal energy is being transferred in the boiler 10 into the steam fed into the steam turbine 3. At this full rated load Wf of the power plant, the temperature T of the superheated steam entering into the steam turbine 3 is at its maximum, i.e. at the temperature Tf of the steam with full power plant load.

Decreasing the load W of the power plant from the full rated load Wf means that less thermal energy is being transferred in the boiler 10 into the stem fed into the steam turbine 3.

Consequently, the temperature T of the superheated steam entering into the steam turbine 3 decreases from the temperature Tf obtainable at with the full rated power plant load Wf. Typically, the pressure of the superheated steam is kept constant, but the mass flow rate m of the superheated steam entering the steam turbine 3 typically decreases as a function of the energy being transferred in the boiler 10 into the steam, as illustrated in Figure 4«.

20175419 PRH 10 -01- 2020

Still referring to Figure 4a, when further decreasing the load W of the power plant as just described, the temperature T of the superheated steam entering into the steam turbine 3 further decreases and eventually reaches a minimum viable temperature Tv, which refers to 5 the lowest acceptable temperature for the superheated steam entering the steam turbine 3.

This load W of the power plant, at which the temperature T of the steam entering the steam turbine 3 is at the minimum viable temperature Tv is referred to as the minimum rated viable load Wmv of the power plant. Conventionally, the load range between for viable operating Wv of the power plant is, inclusively, the load range between the minimum rated viable load Wmv 10 and the full rated load Wf.

The load range for unviable operating Wu of the power plant is the load range with loads below the range for viable operating Wv15 Thus, in the range for viable operating Wv a power plant, the temperature T of the steam entering the steam turbine 3 is at or above the minimum viable temperature Ty. In the range for unviable operating Wu of a power plant, the temperature T of the steam entering the steam turbine 3 is below the minimum viable temperature Ty.

According to the solution, as illustrated in Figure 1, the system comprises an auxiliary superheating chamber 1 which comprises an auxiliary superheater 2. The auxiliary superheater 2 may be used to further superheat the steam originating from the superheater 11 of the boiler 10. The auxiliary superheater 2 may be a single superheater device. Alternatively, the auxiliary superheater 2 may be an aggregate of a plurality of individual superheater devices.

The auxiliary superheating chamber 1 may include a burner 24 which burns fuel thereby releasing thermal energy. Fuel may be burned in the burner 24 in such an amount that the released thermal energy is transferred to steam flowing through the auxiliary superheater 2 of the auxiliary superheating chamber 1 to the extent that the steam is further superheated in the 30 auxiliary superheater 2.

The auxiliary superheating chamber 1 may additionally be connected to a line 54 constituting an inlet supplying incoming air or other suitable gas or gas mixture for the fuel burning process.

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According to the solution and Figure 1, the auxiliary superheating chamber 1 comprising the auxiliary superheater 2 is installed in a steam forward conveyance pathway comprising lines 30, 31. The steam forward conveyance pathway thus runs from the superheater 11 to the steam 5 turbine 3.

A back conveyance pathway begins with a line 34 at the steam turbine 3 and terminates with a line 55 at the superheater 11. In the back conveyance pathway, water circulating in the system may at a given point be in a gaseous state, i.e. steam, and/or in a liquid state, depending on its 10 temperature and/or its pressure at that given point.

According to the embodiment depicted in Figure 1, steam may be continuously conveyed through the auxiliary superheater 2 en route from the superheater 11 to the steam turbine 3.

According to another embodiment depicted in Figure 3, steam may be selectably conveyed either through the auxiliary superheater 2 en route from the superheater 11 to the steam turbine 3 or by bypassing the auxiliary superheater 2 via a line 58 constituting a steam diversion pathway. Such selectable conveyance may be effected by a valve arrangement 26. The valve arrangement 26 may be controlled by the control unit 23. The control unit 23 may 20 effect the selected conveyance, i.e. control the valve arrangement 26, by using steam quality measurements as input data. Such input data may comprise, for example, at least the temperature T of the steam entering the steam turbine 3, for example as measured at the terminus of the line 31 at the steam turbine 3, whereby steam may be selectably conveyed via the auxiliary superheater 2 when the temperature T of the steam entering the steam turbine is 25 near, at or below the minimum viable temperature Ty.

According to the embodiment depicted in Figure 1, fuel may be burned continuously in the auxiliary superheating chamber 1 when the power plant is producing electricity or is in a hot standby mode. Hot standby means that while electricity is not being produced in the power 30 plant, the boiler 10 and the superheating chamber 1 and the steam turbine 3 are kept at an elevated temperature, i.e. above ambient temperature, in order to reduce the time required to heat the said system components to a production temperature.

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The volume of fuel being burned in the auxiliary superheating chamber 1 may vary. A low amount of fuel being burned in the auxiliary superheating chamber 1 may be such that the auxiliary superheating chamber 1 may be kept at a hot standby temperature. This hot standby temperature of the auxiliary superheating chamber 1 may be defined such that at such a 5 temperature the superheated steam travelling through the auxiliary superheater 2 is not further superheated in the auxiliary superheater 2. For example, such a hot standby temperature may be equal to or less than the temperature T of the superheated steam entering the auxiliary superheater 2. The hot standby temperature is higher than ambient temperature.

It is to be appreciated that the notion of temperature and its measurement with respect to both the boiler 10 and correspondingly the auxiliary superheating chamber 1 is well known in the industry including established methodology and equipment for this purpose.

According to the embodiment depicted in Figure 1, the boiler 10 produces steam with a mass 15 flow rh and a temperature T. The auxiliary superheater 2 may be used to further superheat this steam as needed. In other words, the auxiliary superheater 2 may be used, as needed, to increase the temperature T of the steam originating from the boiler 10 before the steam enters the steam turbine 3. Thus, the auxiliary superheater may be controllably used to superheat steam.

Such controllable use refers to controlling the amount of fuel being burned in the burner 24 in the superheating chamber 1, thereby controlling the amount of thermal energy released and transferred into the steam flowing through the auxiliary superheater 2. Furthermore, in embodiments comprising a steam diversion pathway 58, as is depicted in Figure 3, such 25 controllable use additionally refers to the selective conveyance and non-conveyance of steam through the auxiliary superheater 2, for example as effected by a valve arrangement 26.

Referring to Figure 4£, when the power plant operates in the load range Wn for normal operating, i.e. between its full rated load Wf and minimum rated viable load Wmv, inclusively, 30 the thermal energy transferred into the steam in the boiler 10 is sufficient to maintain the temperature T of the steam entering the steam turbine 3 at or above the minimum viable temperature Tv. In such a case, the auxiliary superheating chamber 1 may be kept at a standby temperature as explained above.

20175419 PRH 10 -01- 2020

Still referring to Figure 4£, when the power plant operates in the load range below its minimum viable load Wmv, the thermal energy transferred into the steam in the boiler 10 may not be sufficient alone to maintain the temperature T of the steam entering the steam turbine 3 at or above the minimum viable temperature Ty. In such a case, the auxiliary superheating 5 chamber 1 may be employed to further superheat the steam conveyed through the auxiliary superheater 2. Such further superheating may be brought about by increasing the volume of fuel being fed to the burner 24. Hence, the more the load W of the power plant is below its minimum rated viable load Wmv, i.e. the minimum viable load without further superheating of steam between the boiler 10 and the steam turbine 3, the higher the load of the auxiliary 10 superheating chamber 1 advantageously may be set.

The load of the auxiliary superheating chamber 1 and/or the boiler 10 may controlled by the control unit 23. The control unit 23 may effect such load control by using steam quality measurements as input data and/or controlling the volume of fuel fed to the burner 24 15 and/or the boiler 10. The said input data may comprise, for example, at least the temperature

T of the steam entering the steam turbine 3, for example as measured at the terminus of the line 31 at the steam turbine 3.

Still referring to Figure 4£, there may be an alert temperature Ta for the temperature T of the 20 steam entering the steam turbine 3. Advantageously, the alert temperature Ta is higher than the minimum viable temperature Tv and lower than the temperature of steam entering the steam turbine 3 with full power plant load Tf. The primary purpose of the alert temperature Ta is to serve as a control signal for the controllable use of the auxiliary superheating chamber 1 such that lowering the load of the boiler 10 does not result in the temperature T of the 25 steam entering into the steam turbine 3 dropping below the minimum viable temperature Ty until the load W of the power plant reaches the minimum viable load Wmva with the auxiliary superheating chamber 1 in use.

That the alert temperature Ta serving as a control signal means that when the temperature T 30 of the steam entering the steam turbine 3 reaches the alert temperature Ta, this may be used as a trigger for control actions. Such control actions may be effected, for example, by the control unit 23.

20175419 PRH 10 -01- 2020

According to what is depicted in Figure 4b, the alert temperature Ta may be fixed to a certain temperature, for example as being a certain number of temperature degrees above the minimum viable temperature Ty.

Alternatively, according to what is depicted in Figure 4d, the alert temperature Ta may be variable, for example as a function of the load W of the power plant, or depending on the rate with which the temperature T of the steam entering the steam turbine 3 is changing. Thus, the value or the value function of the alert temperature Ta may be specified according to the properties of the power plant system and its behavior in different situations such that the 10 auxiliary superheating chamber 1 may be appropriately employed to further superheat steam so that lowering the load of the boiler 10 does not result in the temperature T of the steam entering into the steam turbine 3 dropping below the minimum viable temperature Ty until the load W of the power plant reaches the minimum viable load Wmva with the auxiliary superheating chamber 1 in use.

Even if the alert temperature Ta is specified to be a fixed temperature, the controllable use of the auxiliary superheating chamber 1 does not necessarily have to be such that it strictly maintains the steam at a fixed temperature at or near the alert temperature Ta. In other words, the employment of the auxiliary superheating chamber 1 may be such that the temperature T 20 of the steam entering the steam turbine 3 may fluctuate above the minimum viable temperature Ty, as illustrated in Figure 4c.

Using the alert temperature Ta as a control signal as described above, and in accordance with Figures 4b to 4d, the range of load W of the power plant in which the auxiliary superheating 25 chamber 1 is used to further superheat steam is referred to as the load range for low load operating Wl of the power plant. Thus, with the auxiliary superheating chamber 1, the load range for viable operating Wy of the power plant may be extended below the minimum rated viable load Wmv (Wmv being unviable without the auxiliary superheating chamber 1 used to further superheat the steam originating from the superheater 11) such that the load range for 30 viable operating Wv comprises both the load range for normal operating Wn and the load range for low load operating Wl, as illustrated in Figures 4b to 4d.

Thus, decrease in the load of the boiler 1, as effected by decrease in the fuel feed into and to be burned in the boiler 10, may result in decrease in the mass flow m and the temperature T in

20175419 PRH 10 -01- 2020 the steam originating from the boiler 10. As a result of the decrease in the mass flow ill of the steam, the load W of the power plant decreases. And, when the decreased load of the boiler 1 no longer is sufficient to produce steam at or above the alert temperature Ta as the steam enters the steam turbine 3, the load of the superheating chamber 1 may be increased, by 5 increasing the fuel feed to the burner 24, to compensate the reduced load of the boiler 1, and thusly maintain the reduced mass flow rate m of the steam at or above the minimum viable temperature Tv when the steam enters the steam turbine 3.

In accordance with Figures 4b to 4d, as the load W of the power plant still decreases, 10 eventually the capacity of die superheating chamber 1 is no longer sufficient to transfer a sufficient amount of energy to the steam so that the minimum viable temperature Tv of the steam entering the steam turbine could be satisfied. This low load W is referred as the minimum viable load Wmva of the power plant (with the auxiliary superheating chamber 1 in operation). The range of load W of the power plant below this minimum viable load Mmva is 15 referred to as the load range for unviable operating Wu of a power plant comprising an auxiliary superheating chamber 1.

Referring to Figures 4b to 4d, the load range for viable operating Wv of the power plant may be extended downwards below the minimum rated viable load Wmv (without the auxiliary 20 superheater 2, as illustrated in Figure 4d) by installing and controllably using the auxiliary superheater 2 between the boiler 10 and the steam turbine 3.

According to the embodiment depicted in Figure 3, such controllable use of the auxiliary superheater may additionally mean selectably conveying or not conveying steam through the 25 auxiliary superheater 2 with the valve arrangement 26 as explained above.

Thus, referring to Figures 4b to 4d, according to the solution, the minimum viable temperature

Tv of the steam entering into the steam turbine 3 may be satisfied according to the solution both within the load range Wn for normal operating of a power plant as well as within the 30 load range Wl for low load operating of a power plant.

According to the embodiment illustrated in Figure 1, fuel may be supplied to the auxiliary superheating chamber 2 from a fuel source 6 via a line 42. Such fuel may be the same as supplied to the boiler 10. Alternatively, the fuel may be different from the fuel which is

20175419 PRH 10 -01- 2020 supplied to the boiler 10. In the case of the boiler 10 and the auxiliary superheating chamber 1 consuming the same fuel, the fuel sources 6, 21 may be, but need not be, combined into a common fuel source.

According to the embodiment illustrated in Figure 2, the fuel supplied to and burned in the auxiliary superheating chamber 1 may be product gas generated by gasification with a gasifier

4. In such a case, the fuel supply 6 may contain initial fuel to be gasified into final fuel burned in the auxiliary superheating chamber 1. Such initial fuels to be gasified may comprise, for example, biomass and/or waste. As illustrated in Figure 2, initial fuel may be conveyed from the fuel source 6 via a line 39 to the gasifier 4. The final fuel may be conveyed from the 10 gasifier 4 to the auxiliary superheating chamber 1 via a line or lines 40, 41, 42.

The gasifier 4 may be of a known type, such as of the fluidizing bed type. For gasification, air or other suitable gas or gas mixture may be supplied to the gasifier 4 via a line 38 or multiple such lines. Gasification residues may be expelled from the gasifier via a line 36.

In the embodiment in which the auxiliary superheating chamber 1 uses as fuel product gas 15 generated with the gasifier 4, the product gas conveyance pathway comprising the lines 40, 41, may further comprise a cooler 5 for cooling the product gas and/or a filter 7 for filtering out undesirable substances from the product gas before the product gas is supplied to the auxiliary superheating chamber 1. The varieties and using of coolers and filters are well known in the industry, and such knowledge readily applies to the cooler 5 and the filter 7.

If the cooler 5 is so used, as illustrated in Figure 2, heat energy may be conveyed from the cooler 5 to a heat exchanger 8 installed in the back conveyance pathway between lines 32 and 48, wherein the heat energy may be released into the water in the back conveyance pathway en route to be vaporized. Such heat conveyance from the cooler 5 to the heat exchanger 8 may be brought about by circulating an appropriate heat transfer medium in the lines 52 and 53 between the cooler 5 and the heat exchanger 8. Thus, the heat exchanger 8 may be used to pre-heat the water to be vaporized.

In the embodiment in which the auxiliary superheating chamber 1 uses as fuel product gas generated with the gasifier 4, product gas may be additionally conveyed via line 47 to die boiler 10 to be used as fuel. Such fuel use may be advantageously used, for example, as fuel 30 being burned during hot standby, and/or as supplementary fuel, and/or as main fuel and/or as the only fuel for the boiler 10. During hot standby, the fuel conveyed via line 47 to the

20175419 prh 10 -01- 2020 boiler may be burned with a burner 72 installed in the boiler 10. This burner 72 may be dedicated to burning fuel to maintain the boiler 10 in hot standby. Alternatively, the burner 72 may have multiple functionalities, such as burning fuel conveyed via lines 49 and/or 47 during normal operations when electricity is being produced in the power plant and/or burning fuel 5 conveyed via lines 49 and/or 47 during hot standby.

Advantageously, fuel is continuously consumed in the burner 24 of the auxiliary superheating chamber 1 and/or the boiler 10 so that the gasifier 4 may be kept in continuous operation. This has the benefit of avoiding start-up (i.e. heating) and shut-down periods for the gasifier 4. Such start-up and shut-down periods may be several hours in duration, which imposes 10 disadvantageous restrictions on the flexibility in terms of the load variability of the power plant.

The combustion gases resulting from burning fuel in the auxiliary superheating chamber 1 may be conveyed via a gas conveyance passage into the boiler 10 in which thermal energy may be recovered from the combustion gases. The combustion gases may be conveyed from the 15 auxiliary superheating chamber 1 into the boiler 10 via a line 43 as the gas conveyance passage as illustrated in Figure 1. If the auxiliary superheating chamber 1 is installed to the outer wall of the boiler 10 the combustion gases may be conveyed from the auxiliary superheating chamber 1 to the boiler 10 via an opening between the auxiliary superheating chamber 1 and the boiler 10. Thermal recovery of the said combustion gases in the boiler 10 may be effected, 20 for example, by the superheater 11 and/or the heat exchanger 15 and/or any other means of recovering thermal energy that the boiler 1 comprises.

According to another embodiment, as illustrated in Figure 5, the combustion gases resulting from burning fuel in the auxiliary superheating chamber 1 may be vented out from the auxiliary superheating chamber via a line 37 such that the said combustion gases are not 25 conveyed into the boiler 10. In such a case, the said combustion gases may be conveyed via a line 37 to elsewhere in the system (not shown), or alternatively to another system or process (not shown), or alternatively to the atmosphere (not shown). In the case that the said combustion gases are not conveyed into the boiler 10, thermal energy may be captured from these gases with a suitable heat exchanger arrangement, for example in a manner similar to 30 how the heat exchanger 15 may be used to capture thermal energy from the combustion gases expelled from the boiler 10.

20175419 PRH 10 -01- 2020

Referring back to Figure 1, after the steam conveyed to the steam turbine 3 has been utilized in the steam turbine 3, it (i.e. water either in a gaseous or in a liquid state depending on its temperature and pressure) may be conveyed back to the boiler 10 via a line or lines 34, 35, 33, 32, 48, 55 which constitute the back conveyance pathway terminating at the superheater 11.

As illustrated in Figure 1, the back conveyance pathway may additionally comprise a condenser 14 for recovering heat from the steam and transferring it to a heat-consuming process 22. The condenser 14 may comprise a single condenser device, or it may comprise a plurality of individual condenser devices. The varieties and using of condensers are well known in the industry, and such knowledge readily applies to the condenser 14. The 10 condenser 14 may be connected to a heat-consuming process 22 with lines 45, 46, in which a heat transfer medium, such as water, may circulate between the condenser 14 and the heatconsuming process 22.

In addition, or alternatively, the back conveyance pathway may comprise a pump or pumps 20 for effecting the circulation of the circulating substance between the boiler 10 and the steam 15 turbine 3.

In addition, or alternatively, the back conveyance pathway may comprise a heat exchanger 25 in the boiler 10 for pre-heating or preferably vaporizing the water before it enters the superheater 11. The heat exchanger 25 may comprise a single heat exchanger device, or it may comprise a plurality of individual heat exchanger devices. The properties and use of such heat 20 exchangers is well known in the industry and this knowledge readily applies to the heat exchanger 25. According to an example embodiment, the heat exchanger 25 may comprise a plurality of tubes (not specifically illustrated) integrated into the side walls of the boiler 10.

Additional pre-heating of water in the back conveyance pathway may be effected by a heat 25 exchanger 15 installed in the boiler 10, such as in the duct 71 for expelling the combustion gases from the boiler 10 as illustrated in Figure 1. The heat exchanger 15 installed in the boiler 10 may comprise a single heat exchanger device, or it may comprise a plurality of individual heat exchanger devices. If installed in the duct 71 as illustrated in Figure 1, the heat exchanger 15 may capture thermal energy from the combustion gases of the boiler 10 and/or the 30 auxiliary superheating chamber 2 before the combustion gases are expelled from the boiler 10 via the duct 71 of the boiler.

20175419 PRH 10 -01- 2020

Advantageously, and referring to Figures 4b to 4d, the capacity of the auxiliary superheating chamber 1, i.e. the amount of thermal energy it can generate in a unit of time, is selected such that when the power plant is run with a load W below its minimum rated viable load Wmv, the auxiliary superheating chamber 1 is capable of further superheating the steam originating from 5 the superheater 11 such that the minimum viable temperature Ty of the steam entering the steam turbine 3 is satisfied. That is, when the thermal energy transferred to steam in the superheater 11 is not sufficiently high for the steam fulfil the minimum viable temperature Ty of steam entering the turbine 3 due to the boiler 10 being run at a low load, the auxiliary superheating chamber 1 advantageously is capable of transferring to the steam the thermal 10 energy required after the steam has been superheated at the superheater 11 so that the temperature T of the steam entering the steam turbine 3 is at least the minimum viable temperature Ty such that the load range Wl for the low load operating of the power plant extends substantially below its minimum rated viable load Wmv15 In this manner, and according to the disclosed solution, the auxiliary superheating chamber 1 comprising the auxiliary superheater 2 may be used to extend the load range for viable operating of a power plant Wy such that the load range for viable operating Wv of the power plant comprises both the load range for normal operating Wn and the load range for low load operating Wl, wherein the auxiliary superheating chamber 1 may be used to further superheat 20 steam in the load range for low load operating Wl. According to the disclosed solution, the auxiliary superheating chamber 1 may be used within the load range for normal operating of the power plant Wn as well for example so as to use the auxiliary superheater 2 to further superheat the steam originating from the superheater 11 already before the minimum viable temperature Ty of the steam entering the steam turbine 3 is reached, as illustrated in Figures 25 4b to 4d.

Referring to Figures 4b to 4d, in practice there may a minimum viable load Wmva of a power plant with an auxiliary superheating chamber 1 in operation such that with a load of the power plant W below the minimum viable load Wmva the thermal energy generation capacity of the 30 auxiliary superheating chamber 1 is not sufficient to satisfy the minimum viable temperature

Tv of steam entering the turbine 3. Consequently, the load range for viable operating Wv of the power plant is, inclusively, the load range between its minimum viable load Wmva and its full rated load Wf.

The auxiliary superheating chamber 1 may additionally be utilized as a means to maintain the system in a hot standby mode. Standby means that no electricity is being produced in the power plant, in which case the boiler 10 may be run down for example by way of no or very little fuel being burned in the boiler 10, or kept in a hot standby mode by way of burning fuel 5 in the boiler in an amount sufficient to keep the boiler 10 at an elevated temperature. Hot standby for the system means that the circulating water, in gaseous and/or liquid state, is maintained in such a high temperature that the system can be started up, i.e. electricity production with the generator 9 be started, with a start-up time substantially shorter than would be the case of the system was shut down without maintaining high temperature in the 10 circulation of the circulating substance.

During hot standby, the thermal energy release to the circulating water required for maintaining the system in a hot standby temperature may be brought about by the superheating chamber 1 in which case no fuel or very little fuel may be burned in the boiler 10. Alternatively, during hot standby, the thermal energy release to the circulating water required 15 for maintaining the system in a hot standby temperature may be brought about by both the superheating chamber 1 and the boiler 10.

The disclosed solution is not limited to the examples and embodiments presented above. Furthermore, these examples and embodiments should not be considered as limiting but they 20 can be used in various combinations to provide desired results. More specifically, the disclosed solution is defined by the appended claims.

20175419 prh 10 -01- 2020

1. A method of extending the load range for viable operating (Wv) of a steam turbine power plant comprising a boiler (10) with a superheater (11) for supplying superheated steam to a steam turbine (3), the steam turbine (3) having a required minimum viable temperature (T_v) of steam entering the steam turbine (3), the load range for viable operating (Wv) of the steam turbine power plant being extended by means of controllably using an auxiliary superheating chamber (1) comprising an auxiliary superheater (2) to further superheat steam; the method comprising:

determining the temperature (T) of the steam entering the steam turbine (3); when the temperature (T) of the steam entering the steam turbine (3) is above an alert temperature Ta, which alert temperature (Ta) is higher than the required minimum viable temperature (Tv);

• burning fuel in the boiler (10) to generate thermal energy to be transferred into steam in the superheater (11) to generate superheated steam satisfying the required minimum viable temperature (Tv) of the steam entering the steam turbine (3);

• conveying the superheated steam from the superheater (11) to the auxiliary superheater (2) of the auxiliary superheating chamber (1);

• burning fuel with a burner (24) in the auxiliary superheating chamber (1) to keep the superheating chamber (1) in a hot standby temperature;

• conveying the superheated steam from the auxiliary superheater (2) to the steam turbine (3); and when the temperature (T) of the steam entering the steam turbine (3) is at or below the alert temperature (Ta), • burning fuel in the boiler (10) to generate thermal energy to be transferred into steam in the superheater (11) to generate superheated steam;

• further superheating the superheated steam by burning fuel with a burner (24) in the auxiliary superheating chamber (1) to generate thermal energy to be transferred into the superheated steam in the

20175419 PRH 10 -01- 2020 auxiliary superheater (2) such that the required minimum viable temperature (Tv) of steam entering the steam turbine (3) is satisfied;

• conveying the superheated steam from the auxiliary superheater (2) to the steam turbine (3).

2. A method of extending the load range for viable operating (Wv) of a steam turbine power plant comprising a boiler (10) with a superheater for supplying superheated steam to a steam turbine (3), the steam turbine (3) having a required minimum viable temperature (T_v) of steam entering the steam turbine (3), the load range for viable operating (Wv) of the steam turbine power plant being extended by means of controllably using an auxiliary superheating chamber (1) comprising an auxiliary superheater (2) to further superheat steam; the method comprising:

determining the temperature (T) of the steam entering the steam turbine (3); when the temperature (T) of the steam entering the steam turbine (3) is above an alert temperature (Ta), which alert temperature (Ta) is higher than the required minimum viable temperature (Tv);

• conveying the superheated steam from the superheater (11) to the steam turbine (3) by bypassing the auxiliary superheater with a steam diversion pathway (58);

when the temperature (T) of the steam entering the steam turbine (3) at or below the alert temperature (Ta), • burning fuel in the boiler (10) to generate thermal energy to be transferred into steam in the superheater (11) to generate superheated steam;

• further superheating the superheated steam by burning fuel with a burner (24) in the auxiliary superheating chamber (1) to generate thermal energy to be transferred into the superheated steam in the auxiliary superheater (2) such that the required minimum viable temperature (Tv) of steam entering the steam turbine (3) is satisfied;

3. The method according to claim 1 or 2, the method further comprising conveying combustion gases from the auxiliary superheating chamber (1) to the boiler (10) for thermal energy to be recovered from the said combustion gases.

4. The method according to claim 1 or 2, the method further comprising conveying combustion gases via a line (37) from the auxiliary superheating chamber (1) elsewhere than into the boiler (10), for example in the atmosphere.

5. The method according to any of the preceding claims, the method further comprising generating product gas by gasification with a gasifier (4) and supplying the product gas to the burner (24) to be used as the fuel being burned.

6. The method according to claim 5, the method further comprising conveying at least some of the product gas generated in the gasifier (4) to the boiler (10) to be used as fuel being burned in the boiler (10) with a burner (72) during hot standby, and/or as supplementary fuel, and/or as main fuel and/or only fuel for the boiler (10).

7. A method of maintaining in hot standby mode a steam turbine power plant comprising a boiler (10) with a superheater (11) and an auxiliary superheating chamber (1) with an auxiliary superheater (2) adapted to supply superheated steam to a steam turbine (3), and a gasifier (4) adapted to generate product gas;

the method comprising generating product gas in the gasifier (4), supplying product gas from the gasifier (4) to a burner (24) in the auxiliary superheating chamber (1) to maintain the superheating chamber (1) in a hot standby temperature, which temperature is higher than ambient temperature;

supplying product gas from the gasifier (4) to a burner (72) in the boiler (10) to maintain the boiler (10) in a hot standby temperature, which temperature is higher than ambient temperature.

8. A system comprising a boiler (10) with a superheater (11) for supplying superheated steam to a steam turbine (3), the steam turbine (3) having a required minimum viable temperature (Tv) of steam entering the steam turbine (3);

a controllably usable auxiliary superheating chamber (1) comprising an auxiliary superheater (2) and a burner (24), the auxiliary superheater (2) installed in a steam forward conveyance pathway (30, 31) between the superheater (11) and the steam turbine (3);

a control unit (23) adapted to:

• determine the temperature (T) of the steam entering the steam turbine (3);

• when the temperature (T) of the steam entering the steam turbine (3) is above an alert temperature (Ta), which alert temperature (Ta) is higher than the required minimum viable temperature (Tv), control the burning of fuel in the burner (24) such that the superheating chamber (1) is kept in a hot standby temperature;

• when the temperature (T) of the steam entering the steam turbine (3) at or below the alert temperature (Ta), control the burning of fuel in the burner (24) such that thermal energy is transferred into the superheated steam in the auxiliary superheater (2) such that the required minimum viable temperature (T_v) of steam entering the steam turbine (3) is satisfied.

9. A system comprising:

a boiler (10) with a superheater (11) for supplying superheated steam to a steam turbine (3), the steam turbine (3) having a required minimum viable temperature (Tv) of steam entering the steam turbine (3);

a control unit (23) adapted to:

• determine the temperature (T) of the steam entering the steam turbine (3);

• when the temperature (T) of the steam entering the steam turbine (3) is above an alert temperature (Ta), which alert temperature (Ta) is higher than the required minimum viable temperature (Tv), control a valve arrangement (26) such that superheated steam is conveyed from the superheater (11) to the steam turbine (3), the steam thereby bypassing the auxiliary superheater (2) via a steam diversion pathway (58);

control the burning of fuel in the burner (24) such that the superheating chamber (1) is kept in a hot standby temperature;

• when the temperature (T) of the steam entering the steam turbine (3) at or below the alert temperature (Ta), control the valve arrangement (26) such that superheated steam is conveyed from the superheater (11) to the auxiliary superheater (2);

control the burning of fuel in the burner (26) such that thermal energy is transferred into the superheated steam in the auxiliary superheater (2) such that the required minimum viable temperature (T_v) of steam entering the steam turbine (3) is satisfied.

10. The system according to claim 8 or 9, the system further comprising gas conveyance passage (43) adapted to convey combustion gases from the auxiliary superheating chamber (1) to the boiler (10).

11. The system according to claim 8 or 9, the system further comprising a line (37) adapted to convey combustion gases from the auxiliary superheating chamber (1) to elsewhere than the boiler (10), for example in the atmosphere.

12. The system according to any of the claims 8 to 11, the system further comprising:

a gasifier (4) adapted to generate product gas; and lines (40, 41, 42) adapted to convey the product gas from the gasifier to the burner (24).

13. The system according to claim 12, the system further comprising a line (47) adapted to convey product gas from the gasifier (4) to the boiler (10).

Claims

PATENTTIVAATIMUKSET

1. Menetelmä höyryturbiinivoimalan käytettävissä olevan kuormitusalueen (W_v) laajentamiseksi, joka höyryturbiinivoimala käsittää kattilan (10), jossa on tulistin (11) tulistetun

5 höyryn syöttämiseksi höyryturbiiniin (3), jolla höyryturbiinilla (3) on vaadittava höyryturbiiniin (3) menevän käyttökelpoisen höyryn minimilämpötila (Tv), jolloin höyryturbiinivoimalan käytettävissä olevaa kuormitusaluetta (W_v) laajennetaan käyttämällä kontrolloidusti lisätulistuskammiota (1), joka käsittää lisätulistimen (2) höyryn lisätulistamiseksi, jossa menetelmässä:

10 - määritetään höyryturbiiniin (3) menevän höyryn lämpötila (T);

kun höyryturbiiniin (3) menevän höyryn lämpötila (T) on varoituslämpötilan (Ta) yläpuolella, joka varoituslämpötila (Ta) on korkeampi kuin vaadittava käyttökelpoisen höyryn minimilämpötila (Tv);

• poltetaan kattilassa (10) polttoainetta tulistimessa (11) höyryyn siirrettä-

15 vän lämpöenergian tuottamiseksi tulistetun höyryn aikaansaamiseksi, joka täyttää höyryturbiiniin (3) menevän käyttökelpoisen höyryn minimilämpötilan (Tv) vaatimuksen;

• johdetaan tulistettu höyry tulistimesta (11) lisätulistuskammion (1) lisätulistimeen (2);

20 · poltetaan lisätulistuskammiossa (1) olevalla polttimella (24) polttoainetta lisätulistuskammion (1) pitämiseksi kuumassa valmiuslämpötilassa;

• johdetaan tulistettu höyry lisätulistimesta (2) höyryturbiiniin (3); ja kun höyryturbiiniin (3) menevän höyryn lämpötila (T) on varoituslämpötilassa (Ta) tai sen alapuolella,

25 · poltetaan kattilassa (10) polttoainetta tulistimessa (11) höyryyn siirrettävän lämpöenergian tuottamiseksi tulistetun höyryn aikaansaamiseksi;

• johdetaan tulistettu höyry tulistimesta (11) lisätulistuskammion (1) lisätulistimeen (2);

• lisätulistetaan tulistettu höyry polttamalla lisätulistuskammiossa (1) ole-

30 valla polttimella (24) polttoainetta lämpöenergian tuottamiseksi siirrettäväksi lisätulistimessa (2) tulistettuun höyryyn siten, että höyryturbiiniin (3) menevän käyttökelpoisen höyryn minimilämpötilan (Tv) vaatimus täyttyy;

• johdetaan tulistettu höyry lisätulistimesta (2) höyryturbiiniin (3).
2. Menetelmä höyryturbiinivoimalan käytettävissä olevan kuormitusalueen (W_v) laajentamiseksi, joka höyryturbiinivoimala käsittää kattilan (10), jossa on tulistin tulistetun höyryn syöttämiseksi höyryturbiiniin (3), jolla höyryturbiinilla (3) on vaadittava höyryturbiiniin (3) menevän käyttökelpoisen höyryn minimilämpötila (Tv), jolloin höyryturbiinivoimalan käytettävissä olevaa kuormitusaluetta (Wv) laajennetaan käyttämällä kontrolloidusti lisätulistuskammiota (1), joka käsittää lisätulistimen (2) höyryn lisätulistamiseksi; jossa menetelmässä:

määritetään höyryturbiiniin (3) menevän höyryn lämpötila (T);

kun höyryturbiiniin (3) menevän höyryn lämpötila (T) on varoituslämpötilan (Ta) yläpuolella, joka varoituslämpötila (Ta) on korkeampi kuin vaadittava käyttökelpoisen höyryn minimilämpötila (Tv);

• poltetaan kattilassa (10) polttoainetta tulistimessa (11) höyryyn siirrettävän lämpöenergian tuottamiseksi tulistetun höyryn aikaansaamiseksi, joka täyttää höyryturbiiniin (3) menevän käyttökelpoisen höyryn minimilämpötilan (Tv) vaatimuksen;

• johdetaan tulistettu höyry tulistimesta (11) höyryturbiiniin (3) ohittamalla lisätulistin höyrypoikkeutuskanavan (58) avulla;

• poltetaan lisätulistuskammiossa (1) olevalla polttimolla (24) polttoainetta lisätulistuskammion (1) pitämiseksi kuumassa valmiuslämpötilassa;

kun höyryturbiiniin (3) menevän höyryn lämpötila (T) on varoituslämpötilassa (Ta) tai sen alapuolella, • poltetaan kattilassa (10) polttoainetta tulistimessa (11) höyryyn siirrettävän lämpöenergian tuottamiseksi tulistetun höyryn aikaansaamiseksi;

• johdetaan tulistettu höyry tulistimesta (11) lisätulistuskammion (1) lisätulistimeen (2);

• lisätulistetaan tulistettu höyry polttamalla lisätulistuskammiossa (1) olevalla polttimolla (24) polttoainetta lämpöenergian tuottamiseksi siirrettäväksi lisätulistimessa (2) tulistettuun höyryyn siten, että höyryturbiiniin (3) menevän höyryn minimilämpötilan (Tv) vaatimus täyttyy;

• johdetaan tulistettu höyry lisätulistimesta (2) höyryturbiiniin (3).

20175419 prh 04-10- 2018
3. Patenttivaatimuksen 1 tai 2 mukainen menetelmä, jossa lisäksi johdetaan palamiskaasuja lisätulistuskammiosta (1) kattilaan (10) lämpöenergian talteenottamiseksi mainituista palamiskaasuista.
5 4. Patenttivaatimuksen 1 tai 2 mukainen menetelmä, jossa lisäksi johdetaan palamiskaasuja linjan (37) kautta lisätulistuskammiosta (1) muualle kuin kattilaan (10), esimerkiksi ilmakehään.

5. Jonkin edellisen patenttivaatimuksen mukainen menetelmä, jossa lisäksi tuotetaan tuo-

10 tekaasua kaasuttamalla kaasuttimella (4) ja syötetään tuotekaasua polttimeen (24) käytettäväksi poltettavana polttoaineena.
6. Patenttivaatimuksen 5 mukainen menetelmä, jossa lisäksi johdetaan ainakin osa kaasuttimessa (4) tuotetusta tuotekaasusta kattilaan (10) käytettäväksi kattilassa (10) polttimolla

15 (72) poltettavana polttoaineena kuuman valmiustilan aikana ja/tai lisäpolttoaineena ja/tai pääpolttoaineena ja/tai ainoana polttoaineena kattilassa (10).
7. Menetelmä höyryturbiinivoimalan pitämiseksi kuumassa valmiustilassa, joka voimala käsittää

20 - kattilan (10), jossa on tulistin (11), sekä lisätulistuskammion (1), jossa on lisätulistin (2), joka on sovitettu syöttämään tulistettua höyryä höyryturbiiniin (3), ja kaasuttimen (4), joka on sovitettu aikaansaamaan tuotekaasua;

jossa menetelmässä tuotetaan kaasuttimessa (4) tuotekaasua,

25 - syötetään tuotekaasua kaasuttimesta (4) lisätulistuskammiossa (1) olevaan polttimeen (24) tulistuskammion (1) pitämiseksi kuumassa valmiuslämpötilassa, joka on korkeampi kuin ympäristön lämpötila;

syötetään tuotekaasua kaasuttimesta (4) kattilassa (10) olevaan polttimeen (72) kattilan (10) pitämiseksi kuumassa valmiuslämpötilassa, joka on korkeampi kuin 30 ympäristön lämpötila.
8. Järjestelmä, joka käsittää kattilan (10), jossa on tulistin (11) tulistetun höyryn syöttämiseksi höyryturbiiniin (3), jolla höyryturbiinilla (3) on vaadittava höyryturbiiniin (3) menevän käyttökelpoisen höyryn minimilämpötila (Tv);

kontrolloidusti käytettävän lisätulistuskammion (1), joka käsittää lisätulistimen (2) ja polttimen (24), joka lisätulistin (2) on asennettu höyryn eteenpäinsiirtokanavaan (30, 31) tulistimen (11) ja höyryturbiinin (3) väliin;

ohjausyksikön (23), joka on sovitettu:

• määrittämään höyryturbiiniin (3) menevän höyryn lämpötilan (T);

• kun höyryturbiiniin (3) menevän höyryn lämpötila (T) on varoituslämpötilan (Ta) yläpuolella, joka varoituslämpötila (Ta) on korkeampi kuin käyttökelpoisen höyryn vaadittava minimilämpötila (Tv);

ohjaamaan polttoaineen polttamista polttimessa (24) siten, että tulistuskammio (1) pidetään kuumassa valmiuslämpötilassa;

• kun höyryturbiiniin (3) menevän höyryn lämpötila (T) on varoituslämpötilassa (Ta) tai sen alapuolella, ohjaamaan polttoaineen polttamista polttimessa (24) siten, että lämpöenergiaa siirtyy lisätulistimessa (2) olevaan tulistettuun höyryyn siten, että höyryturbiiniin (3) menevän käyttökelpoisen höyryn minimilämpötilan (Tv) vaatimus täyttyy.
9. Järjestelmä, joka käsittää:

kattilan (10), jossa on tulistin (11) tulistetun höyryn syöttämiseksi höyryturbiiniin (3) , jolla höyryturbiinilla (3) on vaadittava höyryturbiiniin (3) menevän käyttökelpoisen höyryn minimilämpötila (Tv);

kontrolloidusti käytettävän lisätulistuskammion (1), joka käsittää lisätulistimen (2) ja polttimen (24), joka lisätulistin (2) on asennettu höyryn eteenpäinsiirtokanavaan (30, 31) tulistimen (11) ja höyryturbiinin (3) väliin;

ohjausyksikön (23), joka on sovitettu:

• määrittämään höyryturbiiniin (3) menevän höyryn lämpötila (T);

• kun höyryturbiiniin (3) menevän höyryn lämpötila (T) on varoituslämpötilan (Ta) yläpuolella, joka varoituslämpötila (Ta) on korkeampi kuin vaadittava minimilämpötila (Tv);

säätämään venttiilijärjestelyä (26) siten, että tulistettua höyryä johdetaan tulistimesta (11) höyryturbiiniin (3), joka höyry täi

20175419 PRH 04-10- 2018 löin ohittaa lisätulistimen (2) höyrypoikkeutuskanavan (58) kautta;

ohjaamaan polttoaineen polttamista polttimessa (24) siten, että tulistuskammio (1) pidetään kuumassa valmiuslämpötilassa;

5 · kun höyryturbiiniin (3) menevän höyryn lämpötila (T) on varoituslämpötilassa (Ta) tai sen alapuolella, säätämään venttiilijärjestelyä (26) siten, että tulistettua höyryä johdetaan tulistimesta (11) lisätulistimeen (2);

ohjaamaan polttoaineen polttamista polttimessa (26) siten, että
10 lämpöenergiaa siirtyy tulistettuun höyryyn lisätulistimessa (2) siten, että höyryturbiiniin (3) menevän höyryn minimilämpötilan (Tv) vaatimus täyttyy.

10. Patenttivaatimuksen 8 tai 9 mukainen järjestelmä, joka käsittää lisäksi kaasunsiirtokana-

15 van (43), joka on sovitettu johtamaan palamiskaasuja lisätulistuskammiosta (1) kattilaan (10).
11. Patenttivaatimuksen 8 tai 9 mukainen järjestelmä, joka käsittää lisäksi linjan (37), joka on sovitettu johtamaan palamiskaasuja lisätulistuskammiosta (1) muualle kuin kattilaan

20 (10), esimerkiksi ilmakehään.
12. Jonkin patenttivaatimuksen 8-11 mukainen järjestelmä, joka käsittää lisäksi:

kaasuttimen (4), joka on sovitettu tuottamaan tuotekaasua; ja linjoja (40, 41, 42), jotka on sovitettu johtamaan tuotekaasua kaasuttimesta polt25 timeen (24).
13. Patenttivaatimuksen 12 mukainen järjestelmä, joka käsittää lisäksi linjan (47), joka on sovitettu johtamaan tuotekaasua kaasuttimesta (4) kattilaan (10).