Method of obtaining information on combustion quality of liquid in a chemical recovery boiler and method of controlling a chemical recovery boiler

Abstract

A method for obtaining information about a quality of combustion of a liquid in a chemical recovery boiler. The method comprises inputting a value of a first input parameter to a computational model configured to determine a value of the quality of combustion of the liquid in the chemical recovery boiler based on the value of the first input parameter, and first running the computational model to obtain a first modeling result. The method comprises measuring a value indicative of a carryover from the chemical recovery boiler to obtain a measurement result, comparing the first modeling result to [a] the measurement result or [b] a result derived from the measurement result to obtain a primary comparison result, and adjusting the value of the first input parameter based on the primary comparison result to obtain an adjusted value of the first input parameter. The method comprises inputting the adjusted value of the first input parameter to the computational model, and second running the computational model to obtain the information about the quality of combustion of the liquid in the chemical recovery boiler.

Description

TECHNICAL FIELD

[0001] The present invention relates to a chemical recovery boiler. The present invention relates to a method for obtaining information about the combustion quality of a liquid in a chemical recovery boiler. The present invention relates to a method for obtaining information about the combustion conditions inside a chemical recovery boiler. The present invention relates to a method for controlling a chemical recovery boiler. The present invention relates to a computational model for modeling the combustion quality of a liquid in a chemical recovery boiler. The present invention relates to a computational model for modeling the combustion conditions in a chemical recovery boiler. A chemical recovery boiler is used in the production of pulp to recover cooking chemicals by combusting black liquor or brown liquor. BACKGROUND

[0002] In the pulp and paper industry, a chemical recovery boiler is used in the production of pulp to recover cooking chemicals by combusting black liquor or brown liquor. Black liquor is an intermediate product in the kraft pulp process, i.e. the sulphate process, while brown liquor is an intermediate product in the sulphite process. In the recovery process, concentrated black liquor (in the sulphate process) or brown liquor (in the sulphite process) is fed in the form of droplets into the furnace of the recovery boiler by means of a lances. In addition, combustion air is fed to the chemical recovery boiler to enable combustion of the liquid (black liquor or brown liquor). When the liquid is combusted, heat is formed and hot flue gas is produced. In the chemical recovery boiler, heat is first recovered from the flue gas by means of a superheater, and also recovered from the flue gas thus cooled by means of an economizer, both of which are heat exchangers. The chemical recovery boiler has two main tasks. First, cooking chemicals are recovered from the bottom of the chemical recovery boiler in the form of a melt. While the cooking chemicals are the residue of the black liquor, the combustion of the liquid also reduces the cooking chemicals (e.g. in the sulphate process, sodium sulphate Na2SO4 is reduced to sodium sulphide Na2S), which requires optimal temperature and oxygen content for the reduction to be sufficiently efficient. Second, heat is recovered and typically used in a steam turbine operating a generator to produce electricity. Efficient heat recovery is thus required. In addition, the maintenance intervals of the recovery boiler should be as long as possible. The maintenance intervals are affected, for example, by the accumulation of deposits on the superheater. The deposits can be formed, for example, by the liquid or by the residue of the liquid. The reduction and accumulation of the deposits are affected by the combustion conditions inside the chemical recovery boiler. The reduction and accumulation of the deposits also describe the combustion quality of the liquid in the chemical recovery boiler. The chemical recovery boiler can be controlled based on information about the combustion quality of the liquid that can be obtained from the combustion process conditions inside the chemical recovery boiler.

[0003] In the recovery process, concentrated black liquor (in a sulphate process) or brown liquor (in a sulphite process) is fed to the furnace of the recovery boiler in the form of droplets. Depending on the size of the droplets, some of the droplets fall on the char bed, forming part of the char bed, to be reduced therein, while some of the droplets can flow upwards with the flue gas. The droplets flowing upwards cause a carryover problem, which is a phenomenon where droplets can flow onto the heat transfer surfaces of the chemical recovery boiler. This increases the deposit thickness on the superheater. Excessive deposits on the superheater tubes hinder the heat transfer to steam / water and can also cause malfunction and / or corrosion of the chemical recovery boiler. If enough information about the quality of the combustion of the liquid in the chemical recovery boiler is available, the carryover can be controlled. For example, the flow rate of the gas, the oxygen content, the temperature and the droplet size affect the amount of carryover. Carryover is a difficult phenomenon to control, because the carryover usually changes dynamically during the operation of the chemical recovery boiler, and the process conditions inside the furnace affect the carryover. In addition, the process conditions themselves change due to the carryover.

[0004] Information about the combustion conditions inside the chemical recovery boiler can be obtained from the chemical recovery boiler by means of measurements or by means of computational modelling.

[0005] Computational modelling is a feasible tool for obtaining information about the quality of the combustion of the liquid in the chemical recovery boiler. For example, the computational model can be a model for calculating the combustion process conditions, such as the gas temperature and velocity distribution. In principle, a computational model is used such that the values of the input parameters are input to the model, the model is run, and as a result of this, information about the combustion conditions inside the chemical recovery boiler can be determined, i.e. calculated.

[0006] Currently, the computational models related to chemical recovery boilers have the disadvantage of lacking all relevant information, even though most of the relevant information is available. In particular, the particle size of the liquid droplets in the chemical recovery boiler is needed to, for example, calculate the entrainment. Currently, however, the value of the particle size distribution is assumed, and if the value does not correspond to reality, the result is inaccurate. Another such parameter is the thickness of the deposits on the superheater of the chemical recovery boiler. Factors affecting the thickness of the deposits include the amount of fly ash produced in the furnace, the amount of entrainment, and the effectiveness of the soot removal. Deposits affect the flow of flue gases inside the chemical recovery boiler, for example, by hindering or preventing the flue gas flow. High flow resistance caused by the deposits increases the pressure difference in the boiler, which typically smoothes the variance in the flue gas flow distribution. In addition, the deposits affect the heat exchange from the flue gases flowing outside the superheater tubes to the steam / water flowing inside the superheater tubes. Currently, neither the size of the entrained particles nor the thickness of the deposits can be measured directly on all heat exchange surfaces. Therefore, the skilled person cannot measure the correct particle size distribution and / or the thickness of the deposits distribution and input it into the computational model. In addition, the value of each of these parameters changes during the operation of the chemical recovery boiler. Therefore, even if the correct value of another moment in time can be available, the correct value of the exact moment in time is still unknown. This makes it difficult to obtain accurate information about the quality of the combustion by calculations. SUMMARY

[0007] It has now been found how more accurate information about the quality of the combustion of the liquid in the chemical recovery boiler can be obtained. First, the value of such a parameter, i.e. the value of a first parameter, whose value is only assumed, is input to a computational model, which is subsequently run to obtain a first modelling result. If necessary, the value of such a parameter, i.e. the value of a second parameter, whose value is known, is also input to the computational model before running the computational model. Next, the first modelling result is compared to a measured value or a value derived from one or more measured values. Thereafter, the value of the first parameter is adjusted on the basis of the result of the comparison. For what is measured, the method comprises measuring a value indicative of the entrainment from the chemical recovery boiler to obtain a measurement result. Finally, the adjusted value of the first parameter is input to the model, which is subsequently run again, to obtain more accurate information about the quality of the combustion of the liquid in the chemical recovery boiler. The method is disclosed in more specific terms in claim 1.

[0008] For the computational model, the computational model can comprise a primary part for calculating the combustion process conditions (e.g. gas temperature and velocity distribution) and a secondary part for calculating the quality of the combustion of the liquid from the combustion process conditions.

[0009] The phenomenon of entrainment can relate to at least one of the following: the presence of entrained particles, a change in the amount of entrained particles, and the amount of entrained particles.

[0010] Generally, the control of a chemical recovery boiler as a continuous process lasts for a long period of time, for example from one maintenance to another. In addition, as described in detail in the background art, accurate information on the quality of combustion is difficult to obtain and is accurate at most only for a short period of time. Therefore, in the prior art, computational models have not been used in the control of a chemical recovery boiler. It has now been found that the information obtainable by the above-described method is sufficiently accurate for the purposes of controlling a chemical recovery boiler. The information on the quality of combustion of the liquid in the chemical recovery boiler can be used for controlling the chemical recovery boiler, as described in detail in claim 18.

[0011] For example, two simulations can be run with different parameters to determine whether a certain control procedure should be taken, as described in detail in claim 19. In a similar manner, several simulations can be run to simulate the effect of different control procedures, and from the results it can be decided which of these control procedures should be taken, as described in detail in claim 20. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 Main side view of a chemical recovery boiler with a thermometer for measuring the temperature profile;

[0013] Figure 2 Main side view of a chemical recovery boiler with a camera for measuring the size of the semi-coke bed;

[0014] Figure 3 Main side view of a chemical recovery boiler with a thermometer for measuring the temperature profile and a camera for measuring the size of the semi-coke bed;

[0015] Figure 4a Main side view of a chemical recovery boiler with a thermometer for measuring the temperature profile, a camera for measuring the size of the semi-coke bed, and a screen;

[0016] Figure 4b Main side view of a chemical recovery boiler with a thermometer for measuring the temperature profile, a camera for measuring the size of the semi-coke bed, and a screen;

[0017] Figure 5a The hearth area of a chemical recovery boiler covered by a computational model is shown;

[0018] Figure 5b The area of a chemical recovery boiler covered by a part of a computational model and connecting two parts of the computational model is shown;

[0019] Figure 6A method for obtaining information about the quality of the combustion of a liquid in a chemical recovery boiler is shown, wherein the results of a modelling are compared with the results of a measurement;

[0020] Figure 7 A method for obtaining information about the quality of the combustion of a liquid in a chemical recovery boiler is shown, wherein the results of a modelling are compared with results derived from a measurement;

[0021] Figure 8 An iterative method for obtaining information about the quality of the combustion of a liquid in a chemical recovery boiler is shown, wherein the results of a modelling are compared with the results of a measurement;

[0022] Figure 9 A method for controlling a chemical recovery boiler is shown, wherein, if a control program (according to a computational modelling) improves the quality of the combustion of a liquid in a chemical recovery boiler, the control program is applied; and

[0023] Figure 10 A method for controlling a chemical recovery boiler is shown, wherein, among several control programs, if a control program (according to a computational modelling) most improves the quality of the combustion of a liquid in a chemical recovery boiler, the control program is applied.

[0024] In the attached figures, the arrow G indicates the direction of gravity and is directed downwards. DETAILED DESCRIPTION

[0025] In this specification, the term parameter refers to one or several physical quantities. In the case where a parameter relates to several physical quantities, each of these quantities is referred to as a component of the parameter. A parameter can be, for example, a height. A parameter can be a pair composed of a mass and a height. In the latter case, the components of the parameter will be the mass and the height. The term parameter value refers to the value of such a parameter. For example, if the parameter is a height, the value of the parameter value can be, for example, 170 cm. For example, if the parameter is a pair composed of a mass and a height, the parameter value can be the pair (70 kg; 170 cm). The components of a parameter value refer to the values of the components of the parameter. For example, if the parameter is a pair composed of a mass and a height, the parameter value can be the pair (70 kg; 170 cm); the first component of the value will thus be 70 kg, which will be the value of the first component of the pair (mass; height). A parameter can comprise several physical quantities, in which case the parameter value can be a vector having the same number of elements. This definition applies in particular to the first parameter and the second parameter and to their values, which will be defined later.

[0026] The present invention is described in the context of a sulphate pulp process, where concentrated black liquor is burned in a chemical recovery boiler to recover cooking chemicals. However, the principle is also applicable to a chemical recovery boiler of a sulphite process (i.e. a soda recovery boiler). The only difference in view of the presented embodiments is that in a sulphite process brown liquor (or concentrated brown liquor) is burned instead of black liquor (or concentrated black liquor). This applies to all embodiments presented below.

[0027] Figure 1 、 2 and 3 show a chemical recovery boiler 100 configured to burn concentrated black liquor to produce heat and smelt, as discussed in the context of the background art. Heat is produced by burning concentrated black liquor, which is fed to the furnace 105 in the form of droplets 152. The droplets 152 and / or their combustion residues form a char bed 150 in the lower part of the furnace 105 of the chemical recovery boiler 100. The char bed 150 comprises smelt. The smelt is discharged from the boiler 100 through a smelt spout 160 to be further used as part of green liquor, as known in the art.

[0028] The heat thus produced is recovered by heat exchangers comprising superheaters 210 and an economizer (not shown). The economizer is arranged in the flue gas channel downstream of the superheaters; downstream in the direction of the flue gas flow. Heat can also be recovered at other heat transfer surfaces, such as boiler tube banks and / or a screen 320 (see Figure 4a and Figure 4b ). Here, the superheaters are generally denoted by reference numeral 210, while a first superheater is denoted by reference numeral 212. The screen 320 (if present) can then be a superheater. Other possible uses of the screen 320 include use as a reheater, an economizer or a boiler tube, such as a riser. Steam is fed to the superheaters from a drum 220 (shown only in Figure 1 ). Typically, the drum 220 is configured to separate saturated steam from saturated water, which steam is thereafter superheated in the superheaters 210.

[0029] The chemical recovery boiler 100 comprises a bullnose 190 narrowing the furnace 105. At least a part of the first superheater 212 is arranged at a higher vertical level than the bullnose 190. The purpose of the bullnose 190 is to protect at least one of the superheaters 210 (e.g. the first superheater 212 or the second superheater 214) from radiative heat transfer of the superheated and / or to protect from direct exposure to the carryover. The purpose of the bullnose 190 is to direct the flue gas flow through the superheaters 210, in particular also through the first superheater 212. For these reasons, at least a part of the first superheater 212 is arranged at a higher vertical level than the bullnose 190.

[0030] To facilitate the combustion of black liquor, the chemical recovery boiler 100 includes a channel 140 for supplying concentrated black liquor into the boiler 100. The concentrated black liquor is supplied to the furnace 105 via injection guns 148, typically multiple injection guns 148, 148'. The injection guns 148, 148' form droplets 152 of concentrated black liquor within the furnace 105. The droplets 152 may fall onto the semi-coke bed 150 due to gravity and / or flow upwards as carry-on particles 153 along with air.

[0031] To provide oxygen for the combustion of black liquor, combustion air is supplied to the furnace. Combustion air is supplied at a first vertical level 110, and more typically at several vertical levels, such as the first level 110, the second level 120, and the third level 130 (see...). Figure 3 ). Reference Figure 3 Combustion air passes through several air inlets I n m Supply, these air inlets I n m It can be located on different walls of the furnace, such as on all walls of furnace 105. Figure 3 In this context, the symbol "i" typically refers to the combustion air inlet; the subscript (1, 2, or 3) indicates the vertical level of the air inlet, and the superscript (1, 2, or 3) indicates a specific air inlet at the vertical level indicated by the subscript. Air can usually be supplied from two, three, four, or five different vertical levels. Typically, at each vertical level, there are at least two, three, or four different locations for supplying air, for example, at at least one location on at least two walls at each vertical level. Therefore, the total air supply is divided both among the different vertical levels and among the different air inlets within those vertical levels. This is achieved through different air inlets i at different levels n and locations m. n m The airflow rate affects the combustion quality of the liquid. Even with several layers and several different air inlets at each layer, only... Figure 3 As shown in the context, the aforementioned air supply and inlet are also generally applicable to all chemical recovery boilers, and therefore applicable to all embodiments.

[0032] Depending on the size of the droplets 152 and the airflow rate within the furnace 105, some of the droplets fall onto the semi-coke bed 150, thus forming part of the semi-coke bed 150, and some of the droplets 152 may flow with the flue gas toward the superheater 210. The particles flowing with the flue gas are generally referred to as carry-over particles 153, and this phenomenon is called carry-over. Therefore, carry-over can refer to one or more of the following: the presence of carry-over particles 153, changes in the amount of carry-over particles 153, and the quantity of carry-over particles 153.

[0033] Carryover particles 153 can stick to the surface of the superheater 210 and in this way prevent heat transfer and / or clog the flue gas passages between the heat transfer tubes of the superheater 210. Furthermore, when intermingled with fly ash, the carryover lowers the melting point of the fly ash. In this way, some of the fly ash can become liquid or sticky due to the intermingling with the carryover. The resulting compound is highly corrosive. Thus, the carryover also increases the risk of corrosion. In this way, preferably, the amount of carryover is minimized to a low level that is practically possible.

[0034] Carryover is affected by the size of the droplets 152. Small droplets 152 tend to flow upwards with the flue gas, while large droplets tend to fall onto the char bed 150 due to gravity. Thus, the droplets 152 should not be too small to avoid carryover. Furthermore, the flow and temperature of the gas can affect the carryover.

[0035] In the pulp and paper industry, the recovery of sodium sulfide from black liquor in a chemical recovery boiler is important to pulp manufacturers because the chemicals are used to break down the lignin of the fibers in pulping to produce pulp. In a kraft pulp process mill, the concentrated black liquor contains sodium sulfate (Na2S04) due to the kraft process, and the chemical recovery boiler 100 converts a portion of the sodium sulfate to sodium sulfide (Na2S) according to the following reaction

[0036] 2C + Na2S04→ 2C02+ Na2S.

[0037] The portion of sodium sulfate that is reduced to sodium sulfide can be referred to as the reduction efficiency. With respect to sulfite processes, the chemical reactions for recovering the chemicals can be different. Furthermore, sulfite processes can use calcium, ammonium, magnesium, or sodium as the base, and the recovery reactions depend on the base material.

[0038] The reaction is not always perfect, whereby some of the sodium sulfate can remain unreacted in the char bed 150. In particular, the temperature of the char bed 150 affects the reduction, as does the oxygen content within the furnace. For example, supplying too much black liquor relative to the combustion air supply can have the effect of lowering the char bed 150 temperature. This effectively reduces the reduction efficiency of the chemical recovery boiler 100. Thus, the temperature of the char bed 150 should be within a design range to ensure good reduction efficiency. Generally, a high temperature of the char bed 150 indicates a high reduction efficiency. Generally, reduction begins at about 800°C, whereby the temperature of the char bed 150 is at least 800°C, preferably in the range of 850°C to 1100°C. Higher temperatures can be problematic in view of the thermal resistance of the materials. For example, a char bed 150 that is too hot can cause high thermal stresses on the structure and / or the materials can not be designed to withstand such high temperatures.

[0039] Thus, for a chemical recovery boiler, there is a need to produce a large amount of energy with good efficiency and high reduction efficiency. In order to control the combustion process, information about the combustion quality of the liquid (black or brown liquid) in the chemical recovery boiler is needed. However, the combustion quality is not always directly measurable.

[0040] In the present invention, computational modelling is used to obtain information about the combustion quality of the liquid (black or brown liquid) in the chemical recovery boiler 100.

[0041] Generally, a computational model, whether based on computational fluid dynamics (CFD) or on machine learning, receives parameter values describing the process and is configured to produce information about the combustion quality of the liquid by using these parameter values for calculations. Only the part of the chemical recovery boiler that carries the most impact needs to be modelled. However, more information can be obtained if also other parts are modelled. Thus, and with reference to Figure 5a , it is enough to model only the hearth area of the chemical recovery boiler to obtain information about the combustion quality. However, with reference to Figure 5b and Figures 1 to 3 if the model covers both the hearth area of the chemical recovery boiler and the superheater area of the chemical recovery boiler, even more precise information can be obtained.

[0042] As mentioned above, the exact value of at least one parameter can be unknown, but can be assumed. In the following, the value(s) of at least one parameter whose value is only assumed is referred to as first input parameter. Thus, the value of the first input parameter can be, for example, a vector having one numerical component or more than one numerical component.

[0043] As mentioned above, the exact value of at least one other parameter can be known exactly. In the following, the at least one parameter whose value(s) is known is referred to as second input parameter. Thus, the value of the second input parameter can be, for example, a vector having one numerical component or more than one numerical component. As to the division of several parameters into “first parameters” and “second parameters”, here the first parameters only include such quantities whose value is assumed and accordingly not known exactly. The quantities whose value is known exactly and used in the computational model form the second parameters.

[0044] Examples of the first input parameter include one or both of [A] the model particle size of the black liquor or brown liquor within the chemical recovery boiler and [B] the model deposit thickness on the superheaters of the chemical recovery boiler. For alternative [B], preferably, the first parameter includes the deposit thickness on all superheaters of the chemical recovery boiler. Therefore, examples of values ​​for the first input parameter include one, two, or all of one or more values ​​of [A] the model particle size of the black liquor or brown liquor within the chemical recovery boiler, [B] the model deposit thickness on the superheaters of the chemical recovery boiler, and [C] the model deposit thickness on each superheater of the chemical recovery boiler. (Refer to...) Figure 5b and Figures 1 to 3 The model deposit thickness on the superheater can be used in the context of a model that also covers the superheater region of the boiler. However, referring to... Figure 5a , 5b and Figures 1 to 3 The model particle size can be used in the context of a model covering at least the furnace region of the boiler. For alternative [A], the term "particle size," particle size can refer to one or more statistical measures of the particle size distribution, including the mean, median, several percentage values, several differences of percentage values, variance, and / or standard deviation. As described in detail above, these values ​​[A], [B], and [C] are neither precisely known nor measurable. However, assumptions can be made in any case. Furthermore, these parameters are not constant over time, which makes their use even more problematic. It is insufficient to optimize the values ​​of these parameters only once; instead, the value varies depending on the circumstances and changes over time as the process in the chemical recovery boiler progresses. Therefore, even if the values ​​of other parameters (e.g., the second input parameter) do not change over time, the correct value of this parameter will change due to the combustion process within the chemical recovery boiler.

[0045] Examples of second input parameters for the furnace area of ​​a chemical recovery boiler include one or more of the following:

[0046] -Through the first air inlet i n1 m1 The first combustion air flow rate entering the chemical recovery boiler and through the second air inlet i n2 m2 The second combustion air flow rate entering the chemical recovery boiler (n1≠n2 and / or m1≠m2),

[0047] -First air inlet i n1 m1 Effective cross-sectional area and second air inlet i n2 m2 Effective cross-sectional area,

[0048] - the temperature of the combustion air at the first vertical level (110, 120, 130) and the temperature of the combustion air at the second vertical level (120, 130, 110),

[0049] - the first flow rate of black or brown liquor into the chemical recovery boiler by the first lances 148,

[0050] - the second flow rate of black or brown liquor into the chemical recovery boiler by the second lances 148’,

[0051] - the pressure in the drum 220 of the chemical recovery boiler,

[0052] - the dry matter content of the black or brown liquor fed into the chemical recovery boiler,

[0053] - the chemical content of the dry matter of the black or brown liquor fed into the chemical recovery boiler,

[0054] - the heat value of the black or brown liquor fed into the chemical recovery boiler 100,

[0055] - the temperature of the black or brown liquor fed into the chemical recovery boiler 100,

[0056] - the pressure of the black or brown liquor fed into the chemical recovery boiler 100,

[0057] - the first angle of the first lances 148 feeding black or brown liquor into the chemical recovery boiler,

[0058] - the second angle of the second lances 148’ feeding black or brown liquor into the chemical recovery boiler,

[0059] - the volumetric or mass flow rate of concentrated non-condensable gases (CNCG) into the furnace of the chemical recovery boiler,

[0060] - the volumetric or mass flow rate of another auxiliary fuel into the furnace of the chemical recovery boiler, and

[0061] - the oxygen content of the flue gas.

[0062] The flow of combustion air through the air inlet in combination with the effective cross-sectional area of the air inlet defines a velocity of the air flow. This influences the velocity distribution of the gases within the furnace. The pressure in the drum is positively correlated to the temperature of the walls of the furnace of the boiler. In addition to the liquid, auxiliary fuel(s) can also be combusted in the furnace. Most commonly, at least concentrated non-condensable gases (CNCG) are combusted. Other possible auxiliary fuels include soap, biological sludge, methanol, stripper offgas (SOG), and turpentine. Typically, the dry matter content of the black or brown liquor fed into the chemical recovery boiler and / or its chemical content does not need to be measured continuously, but can be measured e.g. monthly or e.g. twice a year.

[0063] For the temperature of the liquid fed into the boiler, as Figures 1 to 3 indicated, a heat exchanger 146 can be used to heat or cool the liquid fed into the boiler. This effect will be discussed below.

[0064] Examples of second input parameters regarding the superheater area of the chemical recovery boiler include one or more than one of the following:

[0065] - a first temperature of the steam fed into the first superheater 212,

[0066] - a first pressure of the steam fed into the first superheater 212,

[0067] - a first mass flow of the steam fed into the first superheater 212,

[0068] - a second temperature of the steam fed into the second superheater 214,

[0069] - a second pressure of the steam fed into the second superheater 214,

[0070] - a second mass flow of the steam fed into the second superheater 214,

[0071] - a third temperature of the steam exiting the second superheater 214, which can be equal to the first temperature of the steam fed into the first superheater 212,

[0072] - a third pressure of the steam exiting the second superheater 214, which can be equal to the first pressure of the steam fed into the first superheater 212,

[0073] - a third mass flow of the steam exiting the second superheater 214, which can be equal to the first mass flow of the steam fed into the first superheater 212,

[0074] - a fourth temperature of the steam exiting the first superheater 212,

[0075] -The fourth pressure of the steam discharged from the first superheater 212,

[0076] -The fourth mass flow rate of steam discharged from the first superheater 212,

[0077] - The outlet temperature and pressure of the superheated steam discharged from the final superheater, which is the last superheater in the boiler along the steam flow direction, typically located before the steam turbine that utilizes the steam.

[0078] - For each superheater (210, 212, 214, 320), the temperature, pressure, and flow rate of the steam entering the superheater, and the temperature, pressure, and flow rate of the steam leaving the superheater.

[0079] -Weight of the first superheater 212

[0080] -The weight of the second superheater 214, and

[0081] - The velocity distribution of the gas in the superheater region.

[0082] For steam flow, steam flows from one superheater to another, for example, from the second superheater 214 to the first superheater 212 (see...). Figure 1 Steam can flow from the first superheater 212 to the second superheater 214 (not shown). The final superheater (see above) can be the first superheater 212, the second superheater 214, or a sieve 320. In the case where the sieve 320 is used as a superheater, in this embodiment, the sieve 320 receives steam from the drum 220 without passing through another superheater (not shown). Water can be injected into the steam cycle between the different superheaters 212, 214, 320 to control the outlet temperature and / or outlet pressure. Thus, the mass flow rate, temperature, and / or pressure of the steam can be varied between the superheaters. The weight of the superheater can be measured, for example, using a strain gauge. The weight indicates the total amount of deposits accumulated on the superheater. The gas velocity can be measured, for example, by an ultrasonic detector, by a laser, or by using a Pitot tube (i.e., a Pitot tube probe).

[0083] The value of the second parameter includes the same number of numerical components as the parameter itself. The value of the second parameter includes the values ​​of the aforementioned quantities.

[0084] The values of the second input parameters can be measured, for example, in contrast to the first input parameters. All second input parameters can be such parameters whose values can be measured. Thus, embodiments comprise measuring the values of the second input parameters and inputting the measured values of the second input parameters to the computational model. Further, the values of the second parameters can correspond to such process parameters of the actual chemical recovery boiler that are adjustable. Thus, the values of the second input parameters can also be set by an operator for both the model and the actual chemical recovery boiler. It is also possible to measure the values of some components of the second input parameters and to set the values of other components of the second input parameters for both the model and the actual chemical recovery boiler. Thus, embodiments comprise measuring the values of the components of the second input parameters and inputting the values of the second input parameters to the model. Further, this or another embodiment comprises determining the values of the components of the second input parameters, inputting the values of the second input parameters to the model and controlling the actual chemical recovery boiler accordingly, i.e. in a way that the values of the process parameters correspond to the values of the second input parameters. Other methods for controlling a chemical recovery boiler will be described in detail below.

[0085] With reference to Figure 6 , the method comprises inputting values of the first input parameters to a computational model configured to determine values of the combustion quality of the liquid in the chemical recovery boiler on the basis of the values of the first input parameters. Here, the term "inputting" comprises all means for feeding the values of the first parameters to the model. After inputting the values to the model, the method comprises running the computational model for the first time to obtain a first modelling result. The first modelling result is related to the combustion quality of the liquid in the chemical recovery boiler, however, the first modelling result can be inaccurate due to inaccurate values of the first input parameters.

[0086] As mentioned above, the computational model can use values of second parameters whose values are accurately known in addition to the values of the first parameters whose values are not accurately known. Thus, and with reference to Figure 6 , an embodiment of the method comprises inputting values of the first input parameters and values of the second input parameters to a computational model configured to determine values of the combustion quality of the liquid in the chemical recovery boiler on the basis of the values of the first input parameters and the second input parameters. Here, the term "inputting" comprises all means for feeding the values of the first and second parameters to the model. After inputting the values to the model, the method comprises running the computational model for the first time to obtain a first modelling result.

[0087] In embodiments, the computational model is based on fluid dynamics. In embodiments, the computational model is a simplified model, such as a data-driven neural network model. For example, such a simplified model can be taught using data available from fluid dynamics calculations. In preferred embodiments, the computational model is based on fluid dynamics and comprises a part for calculating values of the combustion quality of the liquid from results of fluid dynamics calculations. The model can cover the entire chemical recovery boiler Figures 1 to 3 ), only the furnace area and the superheater area Figure 5b ), or only the furnace area Figure 5a ).

[0088] The term combustion quality of the liquid in the chemical recovery boiler can refer to one or several aspects of the combustion process inside the chemical recovery boiler, including:

[0089] - the growth rate of the size of the semi-coke bed 150,

[0090] - the presence of entrained particles at the location of the first superheater 212,

[0091] - the amount of entrained particles at the location of the first superheater 212,

[0092] - the uniformity of the flue gas flow and / or temperature through the superheater 210,

[0093] - the content of carbon monoxide (CO) of the flue gas leaving the furnace area of the boiler,

[0094] - the content of nitrogen oxides (NOx) of the flue gas leaving the furnace area of the boiler,

[0095] - the temperature profile of the flue gas leaving the furnace area of the boiler,

[0096] - the velocity profile of the flue gas leaving the furnace area of the boiler,

[0097] - the heat flux profile to the walls of the furnace of the chemical recovery boiler,

[0098] - the accumulation of liquid droplets of the black (or brown) liquid to the furnace walls of the chemical recovery boiler,

[0099] - the location and size of ash sticking areas inside the chemical recovery boiler, and

[0100] - the reduction efficiency inside the semi-coke bed 150.

[0101] Regarding the reduction efficiency, the efficiency can be calculated based on the temperature profile and oxygen content profile in the vicinity of the semi-coke bed. As described in detail above, the computational model can comprise a primary part for calculating the combustion process conditions (e.g. gas temperature and velocity profiles) and a secondary part for calculating the combustion quality of the liquid from the combustion process conditions.

[0102] In particular, the term "combustion quality of the liquid in the chemical recovery boiler" can refer to the same quantity measured or derived from the measurement. However, the quality can be calculated from intermediate results of the model.

[0103] With reference to Figure 6 , the method comprises measuring, from the chemical recovery boiler, a value indicative of entrainment, to obtain a measurement result (i.e. Figure 6 the measured result in the chemical recovery boiler).

[0104] The value indicative of entrainment can be indicative of, for example:

[0105] - presence of the particles 153 in the cross section A of the furnace at the locations li, I3,

[0106] - variation of the amount of the particles 153 in the cross section A of the furnace at the locations li, I3, and / or

[0107] - amount of the particles 153 in the cross section A of the furnace at the locations li, I3.

[0108] Along the flow direction of the flue gas in the chemical recovery boiler 100, the locations li, I3are located downstream of the injection lances 140, 148' configured to feed the black or brown liquor into the chemical recovery boiler 100. Preferably, the locations li, I3are also located upstream of the superheaters 210, 212, 214, 320. More preferably, the locations li, I3are also located upstream of the first superheater 212, which has been defined above.

[0109] In embodiments, the value indicative of entrainment is measured directly with an entrainment detector. Examples of the entrainment detector include an entrainment camera (or a combination of several entrainment cameras) and an entrainment probe. The entrainment probe can be used in combination with image detection. From these images, the presence and / or the amount of the entrainment particles 153 can be detected.

[0110] In embodiments, the value indicative of entrainment is measured indirectly. For example, the descending bed of semi-coke 150 can be indicative of the entrainment, as when the bed of semi-coke descends, it does not receive as many droplets 152 as expected. In addition, the temperature profile within the cross section of the furnace can be indicative of the entrainment. Too high temperature and / or too large variation of the temperature profile can be indicative of the entrainment.

[0111] Therefore, in embodiments, the values indicative of entrainment are measured by measuring one or both of [A] a size of the semi-coke bed 150 and [B] a temperature or temperature profile at positions li, 13 along a flow direction of the flue gas in the chemical recovery boiler downstream of a liquid lancing lance 148 of the chemical recovery boiler configured to feed a liquid to be combusted into the chemical recovery boiler and upstream of a superheater of the chemical recovery boiler, from the chemical recovery boiler, to obtain measurement results. Here, the term "size" refers to a height or a volume of the semi-coke bed 150. Preferably, the volume of the semi-coke bed 150 is measured.

[0112] It has been found that at least these measurement values, both separately and in combination with each other, can provide important information about the combustion process inside the chemical recovery boiler. Furthermore, these values are measurable. With respect to the size of the semi-coke bed 150, one or more cameras 410, 420, 430 can be used to measure the size of the semi-coke bed 150, as shown in Figure 2 and 3 For example, the term "size" can relate to a local height, or an average height, which can be measured with only one camera. Preferably, "size" refers to a volume, which can be determined by using at least two cameras imaging the semi-coke bed from two different angles. With respect to the temperature or temperature profile at positions li or 13, the temperature profile can be measured with a thermometer 310 as shown in Figure 1 and Figure 3 The thermometer can be based on acoustic pyrometry. Other possibilities will be described in detail below. The term temperature profile refers to a plurality of temperature values on a two-dimensional surface within the chemical recovery boiler. The temperature profile can be measured, for example, on a cross-sectional plane A of the chemical recovery boiler. A surface normal of the plane A can be substantially parallel to an average flow direction of the flue gas within the boiler at the location of the plane A.

[0113] When using one camera 410 or a plurality of cameras 410, 420, 430 to measure the size of the semi-coke bed 150, preferably, the camera(s), optionally in connection with a processing unit, is / are configured to also measure a temperature of the semi-coke bed 150. Thus, the camera(s) 410, 420, 430 can be used as a pyrometer. This has the effect of obtaining information about the temperature of the semi-coke bed 150. As described in detail above, a good reduction requires an appropriate temperature of the semi-coke bed 150.

[0114] With reference to Figure 6 and Figure 7 the method comprises comparing the first modeling results with [A] the measurement results or [B] results derived from the measurement results, to obtain a primary comparison result. In Figure 6In embodiments of the first modelling result is compared directly to the measurement result (i.e. "measured result"). In Figure 7 In embodiments of the first modelling result is compared to a result derived from the measurement result (i.e. "derived result"). The result derived from the measurement result can also be derived from another measurement. For example, the growth rate of the char bed 150 can be derived from two measured dimensions.

[0115] The different possible interpretations of the term "combustion quality of the liquid in the chemical recovery boiler" have been described in detail above. Note that, as mentioned above, the first modelling result does not have to be the combustion quality of the liquid in the chemical recovery boiler. However, the first modelling result [i] can be compared to the measurement result or a result derived therefrom, and [ii] can be used to determine the combustion quality.

[0116] Thus, the first modelling result can comprise at least one of:

[0117] - the growth rate of the dimensions of the char bed 150,

[0118] - the presence of entrained particles at the hearth area,

[0119] - the amount of entrained particles at the hearth area, and

[0120] - the temperature profile at the hearth area.

[0121] With reference to Figure 6 and Figure 7 the method comprises adjusting the value of the first input parameter based on the primary comparison result to obtain an adjusted value of the first input parameter; inputting the adjusted value of the first input parameter to the computational model; and thereafter, running the computational model for the second time to obtain information about the combustion quality of the liquid in the chemical recovery boiler. In embodiments, the value of the second parameter is not adjusted based on the primary comparison result if the value of the second parameter is used. However, it can be adjusted for other reasons, e.g. if the value changes for some other reason, e.g. due to actual control of the air flow into the boiler or when determining how a planned control program will affect the quality of the combustion.

[0122] The information about the combustion quality of the liquid in the chemical recovery boiler obtained from this is more accurate than the information derivable from the first modelling result, since the value of the first parameter was adjusted before the second time. Furthermore, even if the value of the second parameter is used, it is not necessary to input the value of the second parameter to the model again, since the model can remember the value of the second parameter. In an alternative, the value of the second parameter can also be adjusted before the second time, if any component of the value of the second parameter changes (see e.g. above).

[0123] For the first modeling result to be related to the quality of the combustion of the liquid in the chemical recovery boiler, it is noted that the first modeling result (or the second modeling result) is adjusted when the calculation model is calculated for the second time. The adjusted first modeling result typically describes the combustion process more accurately than the first modeling result. However, the adjusted first modeling result is not necessarily the quality of the combustion of the liquid in the chemical recovery boiler as such. Instead, further calculations can be needed to calculate the quality of the combustion of the liquid in the chemical recovery boiler from the adjusted first modeling result. However, it is already possible to consider using the adjusted first modeling result as such to describe the quality of the combustion of the liquid in the chemical recovery boiler.

[0124] Typically, the measurement result is a value of a parameter that is based on the measurement result. In the method, the first input parameter whose value is adjusted is neither the parameter that is measured nor the parameter that is based on the result derived from the measurement. In addition, in order to be able to make a meaningful comparison, the first modeling result also describes the measurement result or the result derived from the measurement.

[0125] With reference to Figure 1 , 2 , 3, 4a and 4b, in an embodiment, the calculation model is a model that describes the area of the furnace 105, the area of the superheater 210, and the area between the furnace 105 and the superheater. With reference to Figure 5b , in an embodiment, the calculation model is a model that describes the area of the furnace 105 and the area of the superheater 210, but not the area between the furnace 105 and the superheater. With reference to Figure 5a , in an embodiment, the calculation model is a model that describes only the area of the furnace 105. In Figure 1 embodiments 1 to 4 and Figure 5b , the calculation model takes into account at least the furnace area of the chemical recovery boiler and the superheater area of the chemical recovery boiler. In Figure 1 embodiments 1 to 4 and Figure 5b , the calculation model comprises a first part that describes the furnace area inside the chemical recovery boiler and a second part that describes the superheater area inside the chemical recovery boiler. In addition, the output of the first part is used as an input to the second part.

[0126] With reference to Figure 1 , 2 , 3, 4a and 4b, if a single model based on CFD is used to describe the area of the furnace 105, the area of the superheater 210, and the area between the furnace 105 and the superheater 210, the first part of the model describes the furnace area inside the chemical recovery boiler and the second part of the model describes the superheater area inside the chemical recovery boiler. In addition, following the principles of CFD, the output of the first part is naturally used as an input to the second part in the calculation.

[0127] With reference toFigure 5b If the model comprises two part CFD models, where the first part is used to describe only the region of the furnace 105 and the second part is used to describe only the region of the superheater 210, whereby CFD is not used to model the part between these regions, the output of the first part can be used as input to the second part. With Figure 1 , 2 This approach typically saves computational time compared to the full model of 3, 4a and 4b.

[0128] Preferably, the computational model is configured to model the combustion conditions inside the chemical recovery boiler and to calculate the value of the combustion quality of the liquid in the chemical recovery boiler by using the combustion conditions inside the chemical recovery boiler as modelled in this way. This computational model can be based on computational fluid dynamics (CFD), wherein CFD is used to model the combustion conditions inside the chemical recovery boiler. The combustion quality of the liquid in the chemical recovery boiler can be one of the combustion conditions or a value derived from the combustion conditions. The combustion conditions inside the chemical recovery boiler within the furnace region include one or more of:

[0129] - the presence of entrained particles,

[0130] - the amount of entrained particles,

[0131] - the temperature near the semi-coke bed,

[0132] - the oxygen (O2) content near the semi-coke bed,

[0133] - the size of the semi-coke bed,

[0134] - the temperature profile of the gases,

[0135] - the variance of the temperature profile of the gases,

[0136] - the symmetry of the temperature profile of the gases,

[0137] - the flow velocity profile of the gases,

[0138] - the variance of the flow velocity profile of the gases,

[0139] - the heat flux through the walls of the furnace of the chemical recovery boiler,

[0140] - the accumulation of black (or brown) liquor droplets on the walls of the furnace of the chemical recovery boiler,

[0141] - the content of carbon monoxide (CO),

[0142] - the oxygen (O2) content,

[0143] and

[0144] - the content of nitrogen oxides (NOx).

[0145] The combustion conditions inside the chemical recovery boiler at the superheater region include one or more of the following:

[0146] - the presence of entrained particles,

[0147] - the amount of entrained particles,

[0148] - the temperature profile of the gas,

[0149] - the variance of the temperature profile of the gas,

[0150] - the symmetry of the temperature profile of the gas,

[0151] - the temperature profile of the surface of the superheater,

[0152] - the flow velocity profile of the gas,

[0153] - the variance of the flow velocity profile of the gas,

[0154] - the turbulence of the flow velocity of the gas,

[0155] - the location and size of ash sticking regions,

[0156] - the content of carbon monoxide (CO),

[0157] - the oxygen (O2) content, and

[0158] - the content of nitrogen oxides (NOx).

[0159] In the above, the term "temperature profile of the surface of the superheater" refers to the temperature of the deposits on the superheater, if present.

[0160] For example, once the amount of liquid, the air flow at different vertical levels, the size (distribution) of the liquid droplets and the content of the liquid droplets are known, the growth rate of the semi-coke bed can be calculated, which can be a first modelling result to be compared with the results derived from the measurements. The growth rate of the semi-coke bed can be calculated, for example, by calculating the size of the semi-coke bed at two modelled instances of time and calculating the difference.

[0161] With reference to Figure 7 In embodiments, the first modelling result is compared with results derived from the measurements and another measurement. Figure 7A specific example of an embodiment of the application is an example in which the first modeling result comprises a growth rate of the char bed 150. Furthermore, as mentioned above, the particle size or size distribution of the black or brown liquor within the chemical recovery boiler is not precisely known. Therefore, in this embodiment, the first input parameter comprises a model particle size or size distribution of the black or brown liquor within the chemical recovery boiler. Correspondingly, the value of the first input parameter comprises a value of the model particle size of the black or brown liquor within the chemical recovery boiler, or a value of more than one statistical measure of the particle size distribution. Examples of such statistical measures have been described in detail above. Note that the char bed is within the furnace area of the boiler. Therefore, in this embodiment, the computational model covers the furnace area of the boiler (see Figure 5a ), and can also cover other areas (see Figure 5b and Figures 1 to 4b ).

[0162] Since the first modeling result comprises the growth rate of the char bed 150, the result derived from the measurement result is also the growth rate of the char bed 150. Therefore, this embodiment comprises:

[0163] - measuring a first size of the char bed 150 inside the chemical recovery boiler 100 at a first time instance,

[0164] - measuring a second size of the char bed 150 at a second time instance, and

[0165] - determining a real growth rate of the char bed 150 using the first size and the second size.

[0166] The difference between the second time instance and the first time instance can also be used when determining the real growth rate.

[0167] Furthermore, a value of the first parameter comprising at least the model particle size or size distribution of the black or brown liquor is input to the computational model to obtain the first modeling result describing the growth rate of the char bed, which in this embodiment is the combustion quality of the liquid in the chemical recovery boiler. In this way, this embodiment comprises using the first modeling result to determine a model growth rate of the char bed. A value of a second parameter comprising values of precisely known parameters (e.g. air flow, content of the liquid, and liquid feed) can be input to the model before the model run.

[0168] This embodiment comprises comparing the real growth rate of the char bed with the model growth rate of the char bed to obtain a first comparison result, and adjusting the value of the model particle size (i.e. the value of the first parameter) based on the first comparison result to obtain an adjusted value of the first parameter.

[0169] As described in detail above, the adjusted value of the first parameter is then input into the computational model and the model is re-run to obtain more precise information about the quality of combustion of the liquid in the chemical recovery boiler.

[0170] For the value of the first parameter, which in this embodiment is the value of the model particle size, in the case where the real growth rate is greater than the model growth rate, this means that the value of the model particle size is too small, since small particles flow with the flue gas in the model, while in reality larger particles fall on the semi-coke bed. The adjustment is made accordingly. Thus, the embodiment comprises determining that the real growth rate is greater than the model growth rate, and the step of adjusting the value of the first input parameter comprises increasing the value of the model particle size. Furthermore, the opposite is also true, so that the embodiment comprises determining that the real growth rate is less than the model growth rate, and the step of adjusting the value of the first input parameter comprises decreasing the value of the model particle size. As already described above, the value of the first input parameter is adjusted on the basis of the primary comparison result to obtain an adjusted value of the first input parameter.

[0171] With reference to Figure 2 and Figure 3 , the size of the semi-coke bed can be measured using the camera 410 or a plurality of cameras 410, 420, 430. Preferably, the growth rate of the semi-coke bed 150 is measured by determining a first value indicative of the volume of the semi-coke bed at a first time instance and a second value indicative of the volume of the semi-coke bed at a second time instance and by determining the growth rate from these values. When the value is indicative of the volume of the semi-coke bed, at least two cameras are used to measure the value. The volume of the semi-coke bed can be determined, for example, from the images of the cameras.

[0172] Another specific example, which is not mutually exclusive with the previous examples but can be combined therewith, relates to Figure 6 , 4a and 4b. As described above, entrainment is another parameter related to the quality of combustion. Furthermore, it has been noted that the temperature or temperature profile in the chemical recovery boiler at locations (li, 13), which are arranged along the flue gas flow direction inside the chemical recovery boiler downstream of the injection lances 148, 148' configured to feed black or brown liquor into the chemical recovery boiler and upstream of the superheater 210, is related to entrainment. For example, a large variation in the temperature profile is indicative of the presence of entrained particles at the above-mentioned locations. As another example, a high temperature is indicative of the presence of entrained particles at the above-mentioned locations. Note that the locations (li, 13) can be in the furnace area of the boiler (see Figure 5a ) or in the superheater area of the boiler (see Figure 5b , upper part). Thus, in this embodiment, the computational model covers the furnace area of the boiler and can also cover other areas.

[0173] Thus, in embodiments, the value of the first input parameter comprises a value of a model particle size of the black or brown liquor within the chemical recovery boiler; or a value of more than one statistical measure of a particle size distribution. Further, the embodiments comprise measuring a real temperature distribution at a location l3. Figure 3 , 4a and 4b depict some possible locations l3. The location l3 is arranged along the flow direction of the flue gas inside the chemical recovery boiler downstream of a lancing gun 148, 148’ configured to feed the black or brown liquor into the chemical recovery boiler and upstream of a superheater (e.g. Figure 4a 212 in Figure 4b 212 and 320) in the chemical recovery boiler. The real temperature distribution is measured with a thermometer 310 configured to measure the temperature distribution from the location l3.

[0174] The embodiments comprise determining a model temperature distribution at the location l3 using the first modeling result; comparing the real temperature distribution at the location l3 with the model temperature distribution at the location l3 to obtain a second comparison result, and adjusting the value of the model particle size based on the second comparison result.

[0175] Even though the location l2 and another thermometer 315 are shown in Figure 4a and Figure 4b above, these are not required in embodiments, wherein the real temperature distribution at the location l3 is used as an indication of the carrying.

[0176] The real temperature distribution at the location l3 can be measured by one or more of acoustic pyrometry, optical pyrometry, suction pyrometers, laser spectroscopy, and thermometers. Preferably, the real temperature distribution at the location l3 is measured by acoustic pyrometry. It has been found that acoustic pyrometry can provide accurate results even in the highly fluctuating environment inside the chemical recovery boiler. Further, the components of the acoustic pyrometer, i.e. the sound source and the sound detector, are less sensitive to deposit build-up than, for example, optical components. When acoustic pyrometry is used, the time of flight of the acoustic signal is related to the temperature inside the boiler. Further, by using at least two sound sources and at least four sound detectors, a two-dimensional distribution of the temperature is measurable.

[0177] Another specific example, which is not mutually exclusive with the previous examples and can be combined with one or both of them, is depicted in Figure 6 , 1Related to 3. As mentioned above, the temperature profile of the surface of the superheater is another parameter related to the quality of the combustion. However, the deposit thickness has a huge impact on this. The deposit thickness determines the efficiency of the superheater, i.e. how rapidly the temperature of the flue gas drops. Typically, a thick deposit layer increases the temperature on the superheater. In addition, the deposit thickness affects the pressure loss of the flue gas in the superheater area, and thus the flow distribution at the superheater area, which further affects the ash sticking zone. When the deposit accumulates, the ash sticking zone moves towards the boiler tube bank, which also affects the operation of the boiler tube bank.

[0178] In an embodiment, the value of the first input parameter comprises a value of a model deposit thickness on the superheater of the chemical recovery boiler, for these reasons. More preferably, the value of the first input parameter comprises a value of a model deposit thickness on each superheater of the chemical recovery boiler. The method comprises measuring a real temperature or a real temperature profile at a location 11 (see Fig. 1) on the superheater of the chemical recovery boiler. Figure 1 and Figure 3 The location 11 is arranged along the direction of the flue gas flow inside the chemical recovery boiler downstream of the injection lance 148 configured to feed black or brown liquor into the chemical recovery boiler and upstream of the superheater 212. Figure 4a and Figure 4b The location 13 of the superheater can also be used as the location 11, whereby the location 11 can be arranged upstream or downstream of the screen 320 if a screen is used. Note that the deposit thickness on the superheater is related to the superheater area of the boiler ( Figure 5b , the upper and / or Figures 1 to 4b ). Thus, in this embodiment, the calculation model covers the superheater area of the boiler, and preferably also the furnace area of the boiler.

[0179] The method comprises measuring a real temperature or a real temperature profile at a location 12, wherein the location 12 is arranged such that at least the superheater (212, 214) is arranged between the location 11 and the location 12 along the direction of the flue gas flow inside the chemical recovery boiler. Preferably, at least a part of at least such superheater arranged above the outer fillet 190 is arranged between the location 11 and the location 12 along the direction of the flue gas flow inside the chemical recovery boiler.

[0180] This embodiment comprises determining a real temperature difference using the real temperature or the real temperature profile at the location 11 and the real temperature or the real temperature profile at the location 12.

[0181] This embodiment comprises:

[0182] - determining a model temperature or a temperature profile at the location 11 using the first modelling result,

[0183] - determining a model temperature or a temperature profile at the location 12 using the first modelling result, and

[0184] - determining a model temperature difference using the model temperature or temperature profile at position 11 and the model temperature or temperature profile at position 12.

[0185] Further, the embodiment comprises comparing the real temperature difference with the model temperature difference to obtain a third comparison result, and adjusting the value of the model deposit thickness on the superheater based on the third comparison result.

[0186] In case the value of the model deposit thickness is higher than its actual value, heat is not well recovered in the superheater in the model, whereby the model temperature difference can be higher than the real temperature difference. Thus, an appropriate adjustment would be to decrease the value of the model deposit thickness on the superheater of the chemical recovery boiler.

[0187] Thus, the embodiment comprises determining that the real temperature difference is greater than the model temperature difference, and increasing the value of the model deposit thickness on the superheater of the chemical recovery boiler. Correspondingly, the embodiment comprises determining that the real temperature difference is less than the model temperature difference, and decreasing the value of the model deposit thickness on the superheater of the chemical recovery boiler.

[0188] The real temperature or temperature profile at position L1 can be measured by one or more of acoustic pyrometry, optical pyrometry, suction pyrometer, laser spectroscopy, and a thermometer (for temperature) or thermometers (for temperature profile). Preferably, the real temperature profile at position L1 is measured by acoustic pyrometry. Positions 11 and 13 can be the same.

[0189] The real temperature or temperature profile at position 12 can be measured by one or more of acoustic pyrometry, optical pyrometry, suction pyrometer, laser spectroscopy, and / or one or more thermometers. In an embodiment, a temperature profile comprising the temperature at position 12 is measured. In an embodiment, the temperature profile comprising the temperature at position 12 is measured using acoustic pyrometry.

[0190] In addition to the real temperature at position 12, several other temperatures at this position can be measured in order to obtain a temperature profile at position 12.

[0191] Another specific example, which is not mutually exclusive with the previous examples and can be combined with them, relates to the direct measurement of the entrainment. Preferably, the entrainment is measured from position (11, 13), such position (11, 13) being arranged along the direction of the flue gas flow inside the chemical recovery boiler downstream of the injection lances 148, 148’ configured to feed black or brown liquor into the chemical recovery boiler and upstream of the superheater 210. Note that position (11, 13) can be in the furnace area of the boiler (see Figure 5a ) or in the superheater area of the boiler (see Figure 5bThe upper part). Thus, in this embodiment, the computational model covers the furnace area of the boiler and can also cover other areas.

[0192] When the entrainment (e.g. the amount of entrained particles) is directly measured, it can be compared to the first modelling result.

[0193] In case the first modelling result indicates more entrainment is observed, it means that the value of the model particle size is too large, because in the model large particles do not flow with the flue gas, while in reality smaller particles flow upwards as entrainment. The adjustment is made accordingly.

[0194] Thus, the embodiment comprises determining that the real amount of entrainment is greater than the model amount of entrainment, and the step of adjusting the value of the first input parameter comprises decreasing the value of the model particle size. Furthermore, the opposite is also true, so that the embodiment comprises determining that the real amount of entrainment is smaller than the model amount of entrainment, and the step of adjusting the value of the first input parameter comprises increasing the value of the model particle size.

[0195] In case the amount of entrainment, in particular the amount of entrained particles, is directly measured, the result can also be compared to the first modelling result. As appropriate variations, the above described content relating to measuring the amount of entrained particles also applies.

[0196] With reference to Figure 8 The method can also be used in an iterative manner. In other words, the value of the first input parameter can be adjusted more than once, and the computational model can be run more than twice to obtain even more precise information about the quality of the combustion of the liquid in the chemical recovery boiler. For example, the value of the first input parameter can be adjusted twice and the computational model can be run three times. In this case, the iteration is stopped after a predetermined number of adjustments. As an alternative, the process can simply be iterated as long as the modelling result differs from the measurement result (or a result derived therefrom) or until the modelling result does not get better even if iterated.

[0197] Correspondingly, with reference to Figure 8 The value of the first input parameter as described above can be the result of adjusting an initial value of the first parameter.

[0198] Thus, the embodiment comprises, before inputting the value of the first input parameter to the computational model,

[0199] - inputting an initial value of the first input parameter to the computational model,

[0200] - running the computational model to obtain an initial modelling result describing the quality of the combustion of the liquid in the chemical recovery boiler,

[0201] - comparing the initial modelling results with [a] the measurement results or [b] results derived from the measurement results to obtain initial comparison results, and

[0202] - adjusting the initial value of the first input parameter based on the primary comparison results to obtain a value of the first input parameter.

[0203] However, if the criterion for ending the iteration is that the modelled results only differ slightly from the true results, then the computational model is run a second time only if the difference between the modelled results and the true results exceeds a threshold value. Accordingly, embodiments comprise determining that the primary comparison results exceed the threshold value. While this applies to running the model a second time, such a comparison can be made to determine whether the model needs to be run a third time, a fourth time, etc. with appropriate variations.

[0204] The information obtained about the quality of the combustion of the liquid in the chemical recovery boiler can be used to control the chemical recovery boiler. Thus, a method for controlling a chemical recovery boiler comprises:

[0205] - obtaining information about the quality of the combustion of the liquid in the chemical recovery boiler as described in detail above, and

[0206] - using the information about the quality of the combustion of the liquid in the chemical recovery boiler to control the chemical recovery boiler.

[0207] The step of controlling can be performed by an operator, e.g. a human operator, or automatically, e.g. by an electronic control unit. In embodiments, the step of controlling the chemical recovery boiler is performed by an electronic control unit, such as a microcontroller.

[0208] Controlling the chemical recovery boiler can comprise controlling at least one of:

[0209] - the temperature of the black or brown liquid supplied into the furnace of the chemical recovery boiler,

[0210] - the pressure of the black or brown liquid supplied into the furnace of the chemical recovery boiler,

[0211] - the angle of the injection lance 148 configured to supply liquid into the chemical recovery boiler,

[0212] - controlling the first angle of the first injection lance 148 independently of the second angle of the second injection lance 148’,

[0213] - the flow of the black or brown liquid through the injection lance 148,

[0214] - controlling the first flow of the black or brown liquid through the first injection lance 148 independently of the second flow of the black or brown liquid through the second injection lance 148’,

[0215] - the flow of combustion air into the furnace,

[0216] - the flow of combustion air through the second air inlet i n2 m2 - the flow of combustion air through the first air inlet i n1 m1 - the flow of combustion air through the first air inlet i

[0217] - the effective cross-sectional area of the second air inlet i n2 m2 - the effective cross-sectional area of the first air inlet i n1 m1 - the effective cross-sectional area of the first air inlet i

[0218] - the temperature of the combustion air through the first air inlet i n1 m1 - the temperature of the combustion air through the first air inlet i

[0219] - the temperature of the combustion air through the first air inlet i n2 m2 - the temperature of the combustion air through the first air inlet i n1 m1 - the temperature of the combustion air through the first air inlet i

[0220] The temperature of the combustion air can for example be controlled by controlling a combustion air preheater (not shown).

[0221] The temperature of the liquid can be controlled by the heat exchanger 146. Generally, by increasing the temperature (i.e. heating the liquid), the viscosity of the liquid decreases, which results in smaller droplets 152. Correspondingly, by cooling the liquid, the viscosity increases and larger droplets 152 are formed. The pressure of the liquid can be controlled by the pump 144.

[0222] In the above, the angle (or first angle) of the (first) lances 148 refers to the angle between the direction in which the lances 148 supply the black / brown liquid and the vertical direction downwards. This applies mutatis mutandis to the second angle. This influences the entrainment on the one hand and the position in which the droplets 152 are supplied on the other hand. The electronic control unit or the operator can control the angle (or the first angle and / or the second angle).

[0223] The flow of black or brown liquid through the lances 148 can for example be controlled by controlling the pump 144 configured to pump the black liquid (see Figures 1 to 3The flow of black liquor is controlled by a valve 142 configured to limit the flow rate of the black liquor. If necessary, the flow of black liquor through a specific injection gun 148 can be stopped by using valve 142 and / or pump 144. Pump 144 can be configured to control the pressure by which black liquor is supplied through injection gun 148. A pressure setpoint can be used to control pump 144 and / or valve 142 in a manner that controls the pressure of black liquor in injection gun 148. Alternatively, the orifice of injection gun 148 can be controlled in a manner similar to valve 142. By opening the orifice, more black liquor will be supplied, and by closing the orifice, less black liquor will be supplied. The operator can also change the orifice of injection gun 148 by applying a flow restrictor to injection gun 148. Such a flow restrictor can be applied, for example, manually. If necessary, at least one of pump 144, valve 142, and the orifice of injection gun 148' can be controlled such that the flow through injection gun 148' is stopped. Accordingly, the black liquor will flow through another injection gun 148. An electronic control unit or operator can control at least one of the pump 144, valve 142, and orifice of injection gun 148.

[0224] Reference Figure 3 For example, by controlling a fan (114, 124, 134) configured to supply combustion air and / or by controlling a valve (112, 113, 122, 123, 132, 133) configured to control the flow rate of combustion air, the flow through air inlet i can be controlled. n m The flow rate of combustion air is (n = 1, 2, 3; m = 1, 2, 3). If a nozzle is used to supply combustion air, the nozzle orifice can be controlled if necessary. Figure 3 In this configuration, fan 114 is used to deliver air to the first level 110; fan 124 is used to deliver air to the second level 120; and fan 134 is used to deliver air to the third level 130. Figure 3 In this configuration, valve 112 is used to control the flow of air to the first stage 110. Therefore, valve 112 can be used to control the flow through air inlet i1. m Total airflow. In Figure 3 In this configuration, valve 122 is used to control the flow of air to the second level 120. Therefore, valve 122 can be used to control the flow through air inlet i2. m Total airflow. In Figure 3 In this configuration, valve 132 is used to control the flow of air to the third level 130. Therefore, valve 132 can be used to control the flow through air inlet i3. m Total airflow.

[0225] Air inlet i n m The effective cross-sectional area can be controlled by valves 113, 123, and 133 (see...).Figure 3 This can be controlled by using baffles. The effective area and corresponding flow rate can also be controlled using baffles. In an alternative, the air inlet i... n m The effective cross-sectional area can be controlled by controlling the orifice of the nozzle supplying air.

[0226] exist Figure 3 In the middle, valve 113 is used to control the different air inlets i1 through the first vertical layer 110. 1 i1 2 i1 3 Airflow. In Figure 3 In the middle, valve 123 is used to control the different air inlets i2 through the second vertical layer 120. 1 i2 2 i2 3 Airflow. In Figure 3 In the middle, valve 133 is used to control the different air inlets i3 through the third vertical layer 130. 1 i3 2 i3 3 The airflow rate. Thus, each of valves 112, 122, and 132 can be used to control the total amount of combustion air to one of the vertical layers, as described above. Furthermore, valve 113 can be used to control the air distribution within the first vertical layer, valve 123 can be used to control the air distribution within the second vertical layer, and valve 133 can be used to control the air distribution within the third vertical layer. Typically, a baffle can be used as a valve 113, 123, or 133 responsible for the air distribution within a specific vertical layer. An electronic control unit or operator can control at least one of pumps 114, 124, and 134 and / or at least one of valves 112, 113, 122, 123, 132, and 133.

[0227] Note that all parameters disclosed above pertain to process control in the furnace region of a chemical recovery boiler. Therefore, applying this computational model that only considers the furnace region of the chemical recovery boiler may be sufficient.

[0228] To improve the quality of process control, chemical recovery boilers can be controlled predictively. Predictive control can be implemented in at least two ways. (See reference...) Figure 9 Before implementing actual process control, the expected outcome of the control program can be computationally checked. Subsequently, if the modeled control program yields favorable results (i.e., combustion quality improves according to calculations), the control program can be implemented by controlling the process based on it. However, if the modeled control program yields unfavorable results, it is unnecessary to implement it. (Refer to...) Figure 10It is also possible to simulate the results of at least two different control programs. Thereafter, it can be analyzed which of the control programs has the best influence on the quality of the combustion, and the process control can be performed in accordance with this control program. If none of the control programs seems to improve the quality, none of these control programs need to be implemented.

[0229] In an embodiment corresponding to Figure 9 The method for controlling a chemical recovery boiler comprises obtaining information about the quality of the combustion of the liquid in the chemical recovery boiler as described in detail above. For the sake of clarity, such information can be referred to as primary information about the quality of the combustion of the liquid in the chemical recovery boiler. The values of the second input parameters are also used in the calculation model. Furthermore, a control program is defined. Moreover, the method comprises adjusting the values of the second input parameters in accordance with the control program to obtain adjusted values of the second input parameters. For example, if the control program involves increasing the air flow at the air inlet i n m of the chemical recovery boiler, the values of the corresponding components of the second input parameters are increased accordingly to obtain adjusted values of the second input parameters.

[0230] The embodiment comprises inputting the adjusted values of the second input parameters to the calculation model; and for example, running the calculation model for the third time to obtain secondary information about the quality of the combustion of the liquid in the chemical recovery boiler. Finally, the information about the quality of the combustion of the liquid in the chemical recovery boiler, i.e. the primary information, is compared with the secondary information about the quality of the combustion of the liquid in the chemical recovery boiler to obtain a secondary comparison result. When the secondary comparison result indicates that the quality of the combustion indicated by the secondary information about the quality of the combustion of the liquid in the chemical recovery boiler is superior to the quality of the combustion indicated by the primary information about the quality of the combustion of the liquid in the chemical recovery boiler, the process can be controlled accordingly. Thus, the embodiment comprises controlling the chemical recovery boiler using the secondary comparison result. In other words, the method comprises determining that the quality of the combustion indicated by the secondary information about the quality of the combustion of the liquid in the chemical recovery boiler is superior to the quality of the combustion indicated by the primary information about the quality of the combustion of the liquid in the chemical recovery boiler, and controlling the chemical recovery boiler in accordance with the control program.

[0231] In an embodiment corresponding to Figure 10 The method for controlling a chemical recovery boiler comprises obtaining information about the quality of the combustion of the liquid in the chemical recovery boiler as described in detail above. For the sake of clarity, such information can be referred to as primary information about the quality of the combustion of the liquid in the chemical recovery boiler. The values of the second input parameters are also used in the calculation model.

[0232] Further, a first control program is defined. Further, the method comprises adjusting the values of the second input parameters according to the first control program to obtain first adjusted values of the second input parameters. For example, if the control program involves increasing the air flow at the air inlet i n m corresponding component of the second input parameters is increased accordingly to obtain the first adjusted values of the second input parameters. This embodiment comprises inputting the first adjusted values of the second input parameters to the computational model; and running the computational model a third time to obtain secondary information about the combustion quality of the liquid in the chemical recovery boiler.

[0233] Further, a second control program is defined, and the method comprises adjusting the values of the second input parameters according to the second control program to obtain second adjusted values of the second input parameters. For example, if the control program involves increasing the temperature of the black liquor, the values of the corresponding component of the second input parameters is increased accordingly to obtain the second adjusted values of the second input parameters. This embodiment comprises inputting the second adjusted values of the second input parameters to the computational model; and running the computational model a fourth time to obtain tertiary information about the combustion quality of the liquid in the chemical recovery boiler.

[0234] Finally, the following information can be compared:

[0235] - the information about the combustion quality of the liquid in the chemical recovery boiler (i.e. the primary information),

[0236] - the secondary information about the combustion quality of the liquid in the chemical recovery boiler, and

[0237] - the tertiary information about the combustion quality of the liquid in the chemical recovery boiler,

[0238] to obtain the best combustion quality of the liquid. The chemical recovery boiler can be controlled by applying the control program that provides the highest combustion quality; or, if each of the control programs seems to deteriorate the quality, the control is omitted.

[0239] In other words, the embodiments comprise:

[0240] - determining that the combustion quality indicated by the secondary information about the combustion quality of the liquid in the chemical recovery boiler is superior to both [i] the combustion quality indicated by the primary information about the combustion quality of the liquid in the chemical recovery boiler and [ii] the combustion quality indicated by the tertiary information about the combustion quality of the liquid in the chemical recovery boiler; and

[0241] - controlling the chemical recovery boiler according to the first control program.

[0242] The first control program is particularly suitable when it produces the best results from the simulation. Naturally, it can happen that the second control program produces the best results from the simulation. The description above regarding determination and control applies mutatis mutandis. Thus, in this case, the chemical recovery boiler is controlled according to the second control program.

[0243] Even if Figure 10 Only two control programs have been disclosed, but before actually controlling the recovery boiler in a similar manner, the results of a larger number of control programs can be calculated, and the best one of the control programs is selected.

[0244] With particular regard to the control of the chemical recovery boiler, attention is drawn to the control in a continuous process, which is required to be performed all the time the chemical recovery boiler is in operation. In addition, the chemical recovery boiler is in operation for the time of maintenance intervals, which can be, for example, one or two years. However, as described in detail above, during such a long period of time, the process conditions inside the chemical recovery boiler change, and in particular, the values of the quantities corresponding to the first input parameters of the model change. This emphasizes why it is required to adjust the values of the first input parameters as described in detail above, in particular, for the purpose of controlling the chemical recovery boiler.

[0245] In addition, as described above, the process control is continuous, and different control programs can be applied subsequently. Thus, in an embodiment, during a first time period, the chemical recovery boiler is controlled as described in detail above. In addition, the embodiment comprises obtaining second information about the combustion quality of the liquid in the chemical recovery boiler during a second time period as described in detail above; and controlling the chemical recovery boiler using the second information about the combustion quality of the liquid in the chemical recovery boiler, for example, by means of an electronic control unit. Here, the second time period is later in time than the first time period. As an example, in an embodiment, the second time period starts at least 1 minute after the end of the first time period. The second time period can start at least 15 minutes or at least 1 hour after the end of the first time period. Between these time periods, the combustion conditions inside the chemical recovery boiler change, and typically change so much that the quantities corresponding to the first parameters change. Thus, the adjusted value of the first parameters as calculated during the first time period is no longer an accurate value for the value of the first parameters during the second time period. This emphasizes the need to adjust the value of the first parameters continuously.

Claims

1. A method for obtaining information about the combustion quality of a liquid in a chemical recovery boiler, the method comprising: - inputting a value of a first input parameter to a computational model configured to determine a value of the combustion quality of a liquid in the chemical recovery boiler based on the value of the first input parameter, - running the computational model for a first time to obtain a first modeling result, - measuring a value indicative of carryover from the chemical recovery boiler to obtain a measurement result, - comparing the first modeling result to [a] the measurement result or [b] a result derived from the measurement result to obtain a primary comparison result based on the value indicative of carryover, - adjusting the value of the first input parameter based on the primary comparison result to obtain an adjusted value of the first input parameter, - inputting the adjusted value of the first input parameter to the computational model, - running the computational model for a second time with the adjusted value of the first input parameter to obtain information about the combustion quality of a liquid in the chemical recovery boiler, and controlling at least one parameter selected from the group consisting of: a temperature of black or brown liquor fed into a furnace of the chemical recovery boiler, a pressure of black or brown liquor fed into a furnace of the chemical recovery boiler, and using the information about the combustion quality of a liquid in the chemical recovery boiler.

2. The method of claim 1, wherein, The value indicative of carryover is measured by: - a direct measurement with a carryover detector, and / or - by measuring one or both of [i] a size of a bed of semi-coke and [ii] a temperature or temperature profile at a location along a flow direction of flue gas in the chemical recovery boiler downstream of a liquid injection lance of the chemical recovery boiler and upstream of a superheater of the chemical recovery boiler, wherein the liquid injection lance is configured to feed combusted liquid into the chemical recovery boiler.

3. The method according to claim 1 or 2, wherein, - the computational model is based on fluid dynamics, or - the computational model is a simplified model.

4. The method of claim 1 or 2, wherein, The value of the first input parameter comprises one or both of: - a value of a model particle size of black or brown liquor within the chemical recovery boiler, and - a value of a model deposit thickness on a superheater of the chemical recovery boiler.

5. The method according to claim 1 or 2, wherein, - the computational model comprises at least a first portion describing a furnace region of the chemical recovery boiler.

6. The method according to claim 1 or 2, wherein, - the computational model comprises a portion describing a furnace region of the chemical recovery boiler; the method comprising: - also inputting a value of a second input parameter to the computational model, wherein the value of the second input parameter comprises one or more of: - a first combustion air flow through a first air inlet into the chemical recovery boiler and a second combustion air flow through a second air inlet into the chemical recovery boiler, - an effective cross-sectional area of the first air inlet and an effective cross-sectional area of the second air inlet, - a value of a model particle size of black or brown liquor within the chemical recovery boiler, and - a value of a model deposit thickness on a superheater of the chemical recovery boiler. - the temperature of the combustion air at a first vertical level and the temperature of the combustion air at a second vertical level, - a first flow rate of black or brown liquor into the chemical recovery boiler through a first lancing gun, - a second flow rate of black or brown liquor into the chemical recovery boiler through a second lancing gun, - the pressure in the drum of the chemical recovery boiler, - the dry solids content of the black or brown liquor fed into the chemical recovery boiler, - the chemical content of the dry solids of the black or brown liquor fed into the chemical recovery boiler, - the heat value of the black or brown liquor fed into the chemical recovery boiler, - the temperature of the black or brown liquor fed into the chemical recovery boiler, - the pressure of the black or brown liquor fed into the chemical recovery boiler, - a first angle of the first lancing gun into which black or brown liquor is fed into the chemical recovery boiler, - a second angle of the second lancing gun into which black or brown liquor is fed into the chemical recovery boiler, - the flow rate of concentrated non-condensable gases into the furnace of the chemical recovery boiler, - the flow rate of another auxiliary fuel into the furnace of the chemical recovery boiler, and - the oxygen content of the flue gas.

7. The method according to claim 1 or 2, wherein, - the computational model comprises a first part describing a furnace area of the chemical recovery boiler and a second part describing a superheater area of the chemical recovery boiler; the method comprises: - also inputting values of a second input parameter into the computational model, wherein the values of the second input parameter comprise one or more than one value of: - a first combustion air flow rate into the chemical recovery boiler through a first air inlet and a second combustion air flow rate into the chemical recovery boiler through a second air inlet, - the effective cross-sectional area of the first air inlet and the effective cross-sectional area of the second air inlet, - the temperature of the combustion air at a first vertical level and the temperature of the combustion air at a second vertical level, - a first flow rate of black or brown liquor into the chemical recovery boiler through a first lancing gun, - a second flow rate of black or brown liquor into the chemical recovery boiler through a second lancing gun, - the pressure in the drum of the chemical recovery boiler, - the dry solids content of the black or brown liquor fed into the chemical recovery boiler, - the chemical content of the dry solids of the black or brown liquor fed into the chemical recovery boiler, - the heat value of the black or brown liquor fed into the chemical recovery boiler, - the temperature of the black or brown liquor fed into the chemical recovery boiler, - the pressure of the black or brown liquor fed into the chemical recovery boiler, - a first angle of the first lancing gun into which black or brown liquor is fed into the chemical recovery boiler, - a second angle of the second lancing gun into which black or brown liquor is fed into the chemical recovery boiler, - the flow rate of concentrated non-condensable gases into the furnace of the chemical recovery boiler, - the flow rate of another auxiliary fuel into the furnace of the chemical recovery boiler, - the oxygen content of the flue gas, - a first temperature of the steam fed into the first superheater, - a first pressure of the steam fed into the first superheater, - a first mass flow of the steam fed into the first superheater, - a second temperature of the steam fed into the second superheater, - a second pressure of the steam fed into the second superheater, - a second mass flow of the steam fed into the second superheater, - a third temperature of the steam discharged from the second superheater, - a third pressure of the steam discharged from the second superheater, - a third mass flow of the steam discharged from the second superheater, - a fourth temperature of the steam discharged from the first superheater, - a fourth pressure of the steam discharged from the first superheater, - a fourth mass flow of the steam discharged from the first superheater, - an outlet temperature and an outlet pressure of the superheated steam discharged from the last superheater, wherein the last superheater is the last one in the flow direction of the steam, typically before a steam turbine utilizing the steam, - for each superheater, a temperature, a pressure and a flow of the steam into the superheater and a temperature, a pressure and a flow of the steam leaving the superheater, - a weight of the first superheater, - a weight of the second superheater, and - a velocity of a velocity distribution of the gas in the superheater area.

8. The method of claim 1 or 2, wherein, The computational model comprises a first part describing a furnace area of the chemical recovery boiler and the computational model is configured to: - model a combustion condition inside the chemical recovery boiler, and - calculate a value of a combustion quality by using the combustion condition inside the chemical recovery boiler as modelled, wherein the combustion condition inside the chemical recovery boiler comprises one or more than one of: - an existence of carried particles in the furnace area, - an amount of carried particles in the furnace area, - a temperature in the vicinity of the semicoke bed, - an oxygen (O2) content in the vicinity of the semicoke bed, - a size of the semicoke bed, - a temperature distribution of the gas in the furnace area, - a variance of the temperature distribution of the gas in the furnace area, - a symmetry of the temperature distribution of the gas in the furnace area, - a flow velocity distribution of the gas in the furnace area, - a variance of the flow velocity distribution of the gas in the furnace area, - a heat flux through a wall of the furnace of the chemical recovery boiler, - a black or brown liquor droplet accumulation on the wall of the furnace of the chemical recovery boiler, - a carbon monoxide (CO) content in the furnace area, - an oxygen (O2) content in the furnace area, and - a nitrogen oxide (NOx) content in the furnace area.

9. The method of claim 1 or 2, wherein, The computational model comprises a first part describing a furnace area of the chemical recovery boiler and a second part describing a superheater area of the chemical recovery boiler and the computational model is configured to: - model a combustion condition inside the chemical recovery boiler, and - calculate a value of a combustion quality by using the combustion condition inside the chemical recovery boiler as modelled, wherein the combustion condition inside the chemical recovery boiler comprises one or more than one of: - an existence of carried particles in the furnace area and / or in the superheater area, - an amount of carried particles in the furnace area and / or in the superheater area, - a temperature in the vicinity of the semicoke bed, - an oxygen (O2) content in the vicinity of the semicoke bed, - a size of the semicoke bed, - a temperature distribution of the gas in the furnace area and / or in the superheater area, - a variance of the temperature distribution of the gas in the furnace area and / or in the superheater area, - a symmetry of the temperature distribution of the gas in the furnace area and / or in the superheater area, - a flow velocity distribution of the gas in the furnace area and / or in the superheater area, - a variance of the flow velocity distribution of the gas in the furnace area and / or in the superheater area, - a heat flux through a wall of the furnace of the chemical recovery boiler, - a black or brown liquor droplet accumulation on the wall of the furnace of the chemical recovery boiler, - a carbon monoxide (CO) content in the furnace area and / or in the superheater area, - an oxygen (O2) content in the furnace area and / or in the superheater area, and - a nitrogen oxide (NOx) content in the furnace area and / or in the superheater area. - the temperature in the vicinity of the semi-coke bed, - the oxygen (O2) content in the vicinity of the semi-coke bed, - the size of the semi-coke bed, - the temperature profile of the gas in the furnace area and / or in the superheater area, - the variance of the temperature profile of the gas in the furnace area and / or in the superheater area, - the symmetry of the temperature profile of the gas in the furnace area and / or in the superheater area, - the temperature profile of the surface of the superheater, - the flow velocity profile of the gas in the furnace area and / or in the superheater area, - the variance of the flow velocity profile of the gas in the furnace area and / or in the superheater area, - the turbulence of the flow velocity of the gas in the superheater area, - the location and size of the ash sticking area in the superheater area, - the heat flux through the wall of the furnace of the chemical recovery boiler, - the accumulation of black or brown liquor droplets on the wall of the furnace of the chemical recovery boiler, - the carbon monoxide (CO) content in the furnace area and / or in the superheater area, - the oxygen (O2) content in the furnace area and / or in the superheater area, and - the nitrogen oxides (NOx) content in the furnace area and / or in the superheater area.

10. The method of claim 1 or 2, wherein, The values of the first input parameters include values of a model particle size of black or brown liquor within the chemical recovery boiler, the method comprising: - measuring, at a first time instance, a first value indicative of a first size of a semi-coke bed inside the chemical recovery boiler, - measuring, at a second time instance, a second value indicative of a second size of the semi-coke bed, - determining a real growth rate of the semi-coke bed using the first value and the second value, - determining a model growth rate of the semi-coke bed using the first modeling result, - comparing the real growth rate of the semi-coke bed with the model growth rate of the semi-coke bed to obtain the primary comparison result, and - adjusting the model particle size based on the primary comparison result.

11. The method according to claim 10, wherein - the first value indicative of the first size of the semi-coke bed is measured using a camera configured to image the semi-coke bed.

12. The method of claim 1 or 2, wherein, The values of the first input parameters include values of a model deposit thickness on a superheater of the chemical recovery boiler, the method comprising: - measuring a first real temperature or temperature profile at a first location arranged downstream of a lancing lance and upstream of a superheater along a flow direction of flue gas inside the chemical recovery boiler, the lancing lance being configured to feed black or brown liquor into the chemical recovery boiler, - measuring a second real temperature or temperature profile at a second location, wherein the second location is arranged such that at least the superheater is arranged between the first location and the second location along the flow direction of flue gas inside the chemical recovery boiler, - determining a real temperature difference using the first real temperature or temperature profile and the second real temperature or temperature profile, - determining a first model temperature or temperature profile at the first location using the first modeling result, - determining a second model temperature or temperature profile at the second location using the first modeling result, - determining a model temperature difference using the first model temperature or temperature profile and the second model temperature or temperature profile, - comparing the real temperature difference to the model temperature difference to obtain the primary comparison result, and - adjusting the value of the model deposit thickness on the superheater based on the primary comparison result.

13. The method according to claim 12, wherein - the values of the first input parameters comprise values of a model deposit thickness on each superheater of the chemical recovery boiler, the method comprising: - adjusting at least one of the values of the model deposit thickness.

14. The method of claim 12, wherein, The second real temperature or temperature distribution is measured by: - acoustic pyrometry, - optical pyrometry, - a suction pyrometer, - laser spectroscopy, and / or - one or more thermometers.

15. The method of claim 1 or 2, wherein, The values of the first input parameters comprise values of a model particle size of black or brown liquor within the chemical recovery boiler, the method comprising: - measuring a third real temperature distribution at a third location arranged along a flow direction of flue gas within the chemical recovery boiler downstream of a lancing lance configured to feed black or brown liquor into the chemical recovery boiler and upstream of a superheater, - determining a third model temperature distribution at the third location using the first modeling result, - comparing the third real temperature distribution to the third model distribution to obtain the primary comparison result, and - adjusting the value of the model particle size based on the primary comparison result.

16. The method of claim 15, wherein, The first real temperature or temperature distribution and / or the third real temperature distribution is measured by: - acoustic pyrometry, - optical pyrometry, - a suction pyrometer, - laser spectroscopy, and / or - one or more thermometers.

17. The method according to claim 1 or 2, comprising, before inputting the values of the first input parameters to the computational model, - inputting initial values of the first input parameters to the computational model, - running the computational model to obtain initial modeling results describing a combustion quality of the liquid in the chemical recovery boiler, - comparing the initial modeling results to [a] the measurement results or [b] results derived from the measurement results to obtain an initial comparison result, and - adjusting the initial values of the first input parameters based on the primary comparison result to obtain the values of the first input parameters.

18. The method according to claim 6, comprising: - defining a first control procedure, - adjusting the values of the second input parameters according to the first control procedure to obtain first adjusted values of the second input parameters, - inputting the first adjusted values of the second input parameters to the computational model, - thereafter, running the computational model to obtain secondary information about the combustion quality of the liquid in the chemical recovery boiler, and - using the secondary information about the combustion quality of the liquid in the chemical recovery boiler to control the chemical recovery boiler.

19. The method according to claim 18, comprising: - defining a second control procedure, - adjusting the values of the second input parameters according to the second control procedure to obtain second adjusted values of the second input parameters, - inputting a second adjusted value of the second input parameter to the computational model, - thereafter, running the computational model to obtain tertiary information about the combustion quality of the liquid in the chemical recovery boiler, and - using the secondary information and the tertiary information about the combustion quality of the liquid in the chemical recovery boiler for controlling the chemical recovery boiler.

Images