FI118929B - Method, system and control unit for controlling the boiler feed water flow - Google Patents

Description

118929

Method, rigid system and control unit for controlling the boiler feed water flow

BACKGROUND OF THE INVENTION The invention relates to power plants, and in particular to steam power plants, the turbine of which is driven by hot water steam.

Feed water flow control

It is important for the operation of the power plant that the water supply to the boiler 10 is as undisturbed and secure as possible. Therefore, the water is stored in the feed water tank before the actual heating process. The purpose of the feed water tank is to ensure that the boiler cylinder has water in all situations. The volume of the cylinder of the boiler is not very large, which is why the regulation of the amount of water in the cylinder must function properly and prevent, for example, the surface of the sieve 15 from falling below the so-called dry cooking limit. The malfunctions result in power fluctuations that cause changes in cylinder pressure and hence in its surface measurement.

The feed water pump continuously supplies water to the cylinder. The control of the feed water flow is implemented in the prior art based on the boiler cylinder height: V 20. The goodness of previous adjustments has been assessed mainly by: T: how well the surface of the boiler cylinder stays in place.

: Single-point adjustment measures the height and adjustment of the cylinder's water surface ·· ♦ ♦: Performs according to the cylinder's water level. In point control, the adjustment affects:. in addition to the water level in the tank, ensure the flow of feed water. In the three-point adjustment, the temperature of the cylinder, the vapor flow from the cylinder, and the feed water flow are affected by the · ··· 25 work.

.. The boiler has traditionally used three-point control. The known * · · control systems are effective in themselves, but in practice they continuously over- or under-control the flow of feed water, since at the power plant the time constants of such 30 controls are high. On average, the prior art • «····. adjustments seem to give good adjustment results, but one-cycle oscillation can be significant. The problem with known adjustments is therefore the · · · * · * [adjustment instability, oscillation and instability.

• · 2 118929

Syringe flow control

At the power plant, the feed water is pumped from the feed water tank to the boiler cylinder. The water from the cylinder is circulated naturally to the cooling pipes of the furnace walls, where the vapor generated is separated off in the droplet separator of the cylinder. From there, the steam 5 is directed to a multi-stage superheater where the temperature control is carried out between the superheater stages by injection coolers. The boiler feed water is used as the spray water.

The purpose of spraying is to maintain the desired final steam temperature and to dampen rapid changes in temperature due to process disturbances. 10 The control can be considered as a critical control, since the boiler output is largely determined by the steam temperature and the mass flow rate. The boiler's safe operation also requires precise control of the steam temperature, since too fast temperature changes can significantly reduce the durability of the steam piping. The turbine may also be damaged if the temperature changes too quickly. In addition, care must be taken to ensure that no water droplets enter the turbine as these cause heavy wear.

The boiler must be equipped with a sufficient number of superheaters so that it can be run at partial load. In this case, increase the amount of steam with the spray water. A situation in which the last syringe contributes significantly to the vapor temperature control should be avoided. In this case, even a slight adjustment error is immediately visible at the final steam temperature of 1 · **.

»· 1: Controlling the temperature of superheated steam is challenging due to long time constant • · * and especially in biofuel boilers with irregular fuel supply. Injection control is as important for boiler plant balancing as • 25-cylinder surface control. Vibrating injection control reduces the life of superheaters and, in extreme cases, shortens the life of the steam piping and turbine. Changes in the mass flow rate in the water balance are a major distraction in boiler pressure control and thus in fuel control, and together may • ♦ · enhance the distraction factor in the power plant process.

• ♦ *: 1 30 ♦ ♦ · «• · ·« · · * 1 1 1 1 1 1 1 # # # # # # 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 3 3

Brief Description of the Invention

It is thus an object of the invention to provide a method and a system and control unit implementing the method so that the above problems can be solved. The object of the invention is achieved by a method, a system and a control unit characterized by what is stated in the independent claims. Preferred embodiments of the invention are claimed in the dependent claims.

One object of the invention is to provide a method for controlling the flow of boiler feed water.

Another object of the invention is to provide a system for regulating the boiler feed water flow.

A third object of the invention is to provide a control unit for regulating the boiler feed-water flow.

The invention aims to keep the feedwater flow as constant as possible. However, even if the cylinder surface is high, the feed water flow is not greatly reduced. If the feed water were reduced drastically, boiling in the cylinder would be intensified, whereupon the steam bubbles would displace more water and the surface would rise. The method according to the invention does not regulate the surface of the cylinder, but utilizes the surface information of the cylinder to a limited extent in the control of the feed water flow. The adjustment according to Kek, 20 is therefore based on the balance sheet calculation. Balance calculation • · ·: The incoming feedwater mass flow rate is maintained to be the same as the mass flow rate from the cylindrical steam.

• · i.i: The method eliminates the principle of three-point adjustment of the cylinder surface adjustment, where the surface height is mistakenly too significant: 25. In the system of the invention, the height of the surface plays a role in assisting the adjustment. The method according to the invention takes into account that the changes in the surface height of the cylinder also depend on the steam cup. v. amount and density of evaporator in the evaporator.

• · «

The control unit software of the invention is not system-dependent: *: **. The software can run on an existing automation system • · \ * ·· or independently as a JAVA application. The software of the invention converts injection controls and cylinder surface controls into mathematical models that. are not parameter dependent.

«· ·]. The method is self-learning and automatically stabilizes 35 processes, which can significantly reduce energy loss, improve plant availability and reduce emissions during boiler ramps.

4, 118929

The development of the balancing method started with the realization of developing a water supply system in a biofuel boiler plant. There were great difficulties there, especially during the start-up phase, when the cylinder was manually operated causing unintentional shutdowns. The use of multiple fuels also added inconvenience, since conventional adjustments are tuned to operate at certain fixed operating points, and these adjustments do not take into account changes in different situations.

In a biofuel boiler, the amount of thermal energy of the fuel varies considerably, as it boils both coal, wood and forest residues and peat at the same time. It is essential for the operation of the boiler that the boiler 10 is stable and does not have very large and abrasive fluctuations.

After shutdowns during ramp-ups, the boiler must be ventilated repeatedly and oil restarted. Disruptions in the Kat space water cycle, such as cylinder bursting, caused unintentional shutdowns, necessitating always starting from zero. In a cylindrical boiler, there are variations in the volume of water and steam that cause significant changes in the mass flow of the water balance. These are interfering factors in boiler pressure control and hence in fuel control, and together they can amplify interference in the power plant process.

The cylinder volume, the surface measurement lability, and the traditional three-to-20 pin point control that controls the cylinder surface, are not always able to adjust the situation. that occur in boiler processes that are difficult to control. Thus, the measurement of the cylinder surface is in some cases labile and when the feed water is added, the boiling • · **, * decreases and the surface measurement interprets this cylinder as a decrease in the surface even though: ·: actually water has been added.

«: 25 At start-up, when the evaporation starts, the surface of the cylinder also easily escapes, and in the rapid change of the load there is a so-called. This can lead to a safety trip and the burners are shut down, after which the non-combustible gases have to be vented from the boiler, whereupon the boiler cools down and the stored energy is vented to the sky breeze. Start-up by balancing methods saved about 60,000 liters of oil compared to the previous V ·: start-ups of the power plant in question.

«··

The invention utilizes the computational properties of modern control systems in such a way that it is possible to control the closed circulation circuit of the boiler 35 and that all different situations and phenomena can be considered and "taught" to the control system.

118929 5

Of course, the concept of balancing also involves the management of syringe adjustments. Traditionally, the injector valves of superheaters are controlled by a Temperature Controller. Nowadays the temperature is measured after superheat, whereby the adjustment process is always late and this causes fluctuations in the adjustment.

As an example, one boiler was found to have a fluctuation of the syringes affecting steam production up to 5 kg / s, which is 2.5% of the boiler output. The mathematical model was implemented by adjusting the balance so that the amount of water injected into the superheaters is always close to the correct one.

The injection control calculation model is self-learning and also mimics the non-linearity that may occur and possibly change in the control valves. In addition, it was also observed that the standard deviation of residual oxygen was halved from 0.8 to 0.4, thus showing a direct effect in reducing emissions. Balancing stabilizes the process and increases safety by reducing emergency shutdowns. Unplanned shutdowns are always a security risk as the process is momentarily completely out of control.

The power boiler is practically slow in its basic functions, but there too very rapid changes occur, especially in the cylinder. The functions of the controller must be made to work quickly, and it is important to optimally combine these parameters. The method according to the invention is not a traditional control technique, but a bundle of parameter control.

... Significantly, the same method works for all cylindrical boilers • · · ** ... · 1 regardless of fuel. The method works particularly well in biofuel boilers, where the quality of the fuel varies considerably. "The balancing software according to the invention also allows the boiler to run: 25 automatically. The method according to the invention can be carried out in all boilers where: is a modern computer-based control: ***: system, whatever the boiler type, the method is suitable for all types of boiler plants, from incineration to recovery boilers.

Boiler ramp up with heavy fuel oil before solid .1 ··. Up to 30 fuels can be burned. Balancing is a method of accelerating up and down cylindrical boilers • ·, and smoothing steam production fluctuations in fuel and power transients, as well as reducing equipment and production costs due to control fluctuations * • 1.

• ·· * · · • a · • · 6 118929

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described in connection with preferred embodiments, with reference to the accompanying drawings, in which:

Fig. 1 shows a principle diagram of a power plant water-steam balance 5 adjustment and a single injection water adjustment;

Fig. 2A illustrates the structure and operation of a syringe control for a pulley; Figure 2B shows an example of calculating the fire rate of the reins of the system of Figure 2A;

Figure 3 shows the variation of feed water and fresh steam mass flows at 10 conventional three-point control;

Figure 4 illustrates the variation of the feed water and fresh steam mass flows in the balance control according to the invention;

Figure 5 shows the variation of the cylinder surface in conventional three-point adjustment; Figure 6 shows the variation of the cylinder surface in the balancing adjustment according to the invention;

Figure 7 shows the level variation during the turbine strip;

Figure 8 shows the variation in the surface level of the cylinder during the turbine strip; Figure 9 shows the amount of oil used during the turbine strip; ... 20 Figure 10 shows the variation in boiler power and feed water mass flow rate • «m: 4> ** with conventional three-point control; Fig. 11 shows the variation of boiler power and feed water mass flow in the balance control according to the invention; Fig. 12 shows the situation with conventional control and according to the invention *: 25 with balance control where the plant power is reduced overnight; : ***: Figure 13 shows the variation in boiler power and injection rates by conventional control;

Figure 14 shows the variation of boiler power and injection rates in the balancing control according to the invention; Fig. 15 shows an example of the variations in vapor temperatures in conventional spray control and balance control according to the invention;

Figure 16 shows an example of secondary syringe injection rates, ···, variations in conventional injection control and in the inventive control; Fig. 17 shows an example of an orthostatic boiler flue gas in conventional injection control and in accordance with the balance control of the invention; 7 118929

Fig. 18 shows an example of the required maximum powers with conventional control and the balance control according to the invention;

Fig. 19 shows an example of power differences with conventional control and the balance control according to the invention; Figure 20 shows an example of boiler fuel power differences with conventional control and the balance control according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1, there is shown a schematic diagram of a power plant water-steam balance control and a single injection water control.

10 ADJUSTMENT OF THE BOILER'S WATER-STEAM BALANCE STRUCTURE OF THE BALANCE ADJUSTMENT

The surface adjustment of the cylinder 10 is based on the balance of the mass flow from and to the cylinder. Its core is formed by two controllers, which are the cylinder level regulator 11 and the feed water flow controller 12. The actual control acting on the process 15 is the output of the regulator which controls both the feed water valve 13 and the feed water pump 14 depending on the driving situation.

STRUCTURE OF THE SURFACE CONTROL

: * · *: The cylinder surface adjuster 11 measures the height of the cylinder surface for measurement.

• ·

The remote setpoint of the cylinder surface regulator 11 is determined by the pressure of the cylinder 10:. 20 as a function of the following formula: t «·

Ml I t · • · ·

! #J S j J

Γ! \ Κ = ^ Ρι + 33 ^> where • · · Sr Q A 1 * 3

··· · J J

Lsp = setpoint for cylinder surface regulator [mm] p, = cylinder pressure [bar].

: Y: 25 • ·

The level controller 11 can be in either remote or local mode. In local ·· * mode, the operator can enter the desired setpoint. Remote by selecting the setpoint - * ;.] · vo comes from a set of pairs of tables set according to the boiler characteristics. The pin controller 11 and flow controller 12 operate in incremental mode. This meant *: 30 that the new control calculated by the controller is subtracted from the previous control:: ** · and this difference is added to the read back control.

118929

O

con = Δ con + conb where con = new control Aeon = change of control 5 conb = read back control

The read back control, conb, receives a value of zero each time, ie the output of the controller is directly counted as a change in the controls.

The control of the level controller 11 is both maximum and minimum constrained. When the difference value of Viγιο rear adjuster 12 is less than a certain process value and when the cylinder surface is greater than a certain value, the control of level regulator 11 is limited to -0.03. The critical difference value, in turn, depends on the pressure of the cylinder 10 as follows: 15 e fr = -15 for a cylinder pressure p, £ 3 bar e fr = -20 for a cylinder pressure p, <3 bar.

When one or both of the control valves 13 are in the automatic position and the shut-off valve thereafter is closed, the control of the level controller 11 is limited to zero for a certain period of time, e.g. after 20 seconds. In this case, the minimum of the level regulator 11 is also limited to zero, i.e. the regulator does not adjust.

• I

If the surface of the cylinder 10 is above a limit value, for example 350 mm, the limit -. * / Is set to the output of level controller 11 to -1. Thus, the valve is driven at a speed of 1 * V / 1 rpm.

•• s * 25 In a boiler-free situation, the supply water flow rate is greater than! :: 30 kg / s and the cylinder surface is less than 350 mm, the maximum of the level regulator 11 output ··· is zero. The minimum control limit for the level controller 11 normally operates directly with the flow controller 12.

• · • · ·

*. \ Y FLOW CONTROL STRUCTURE

• ♦ • · 30 The flow regulator 12 is always on the automatic when the level regulator 11.

It is always in remote mode, so the setpoint cannot be set by the operator, but • ·· comes from the calculation. The flow regulator 12 receives a flow of feed water directly for measurement. The setpoint of the flow controller 12 is obtained by the following calculation. If the fire is in the boiler, the starting point for calculating the setpoint is • · 9 118929 10 mass flow rate, ie what comes out of and from cylinder 10. If the fire is not in the boiler, only the feed water mass flow is counted.

mloul = m, h - - mn2 +. where 5 mlout = mass flow rate from cylinder [kg / s] m, h = mass flow of fresh steam after superheaters [kg / s] mM = mass flow rate of primary syringes [kg / s] m „2 = mass flow rate of secondary syringes [kg / s] mup = mass flow rate of cylinder blow-off [kg / s].

10

From the mass flow from cylinder 10 calculated above, as well as from mass flow to cylinder 10, averages over a given period of time, for example a 15 minute period, are subtracted. A small number is added to the calculation, the value of which depends on the difference value of the cylinder surface regulator 11. If this difference is greater than or equal to -120 mm, the value to be summed is 3 kg / s, while if less than -120 mm, the value is 12 kg / s. It should be noted that the cut-off values and the values to be summed may vary depending on the process in question. The formula is as follows: 20 = «Μ * - + <. Where ·· * • ♦ · ^ kaerom is the difference between the mean mass flow from and from the cylinder corrected for additional water * · · • · · mkaiout = outgoing from the cylinder 15 mins average [kg / s]: 25 mmin = 15 min incoming to the cylinder. mean mh = additional water (3 or 12) [kg / s].

··· ♦ · • t ·· «

Next, the mass flow rate from the instantaneous cylinder is subtracted from the mean mass flow difference: • m »• t _ _ 30 ™ sp = rhlout - where • · · • * * • · * · msp = flow control setpoint [kg / s]: T: mlout = mass flow from the cylinder [kg / s] 35 = difference between the mean mass flow from the cylinder and the input mass, corrected for additional water [kg / s].

118929 10

The value obtained goes to the remote setpoint of the flow controller 12. When the control valves are in automatic, the minimum control is limited by the following formula: 5 F = L -1. Where contain con 9

Feon min = minimum control of flow controller

Lcon = Cylinder Level Controller Control.

The flow regulator 12 is forced to be controlled when both of the feedwater control valves are manually controlled or when the surface of the cylinder 10 is higher than the upper limit, for example 280 mm. With the flow control 12 forced on, the control becomes a value of -1. Thus, this also passes to the minimum control of the level controller 11. The purpose of the mass balance calculation is to keep the flows of the condensate and feed water circuits steady. This ensures consistent power to the turbine and generator and avoids unnecessary adjustments to the water-steam circuit.

INJECTOR FLOW CONTROL BUILDING STRUCTURES

** *: V 20 Figure 2A illustrates the construction and operation of a superheater control of superheaters.

• o v: Steam heating is usually performed on several series mounted superheaters 20. They are generally referred to as the primary, secondary, and tertiary superheaters, depending on the direction of the steam. Steam passes through superheaters 20 along two pipelines (left and right). To ensure the balance of the lines, run the boiler ··· *. ·· *. 25 generally symmetrically so that both lines receive approximately the same heat output. The steam temperature control ensures that after the last superheater> Vi, the lines produce the desired steam. In addition, the lines are often cross-linked so that the right end of the previous manifold goes to the left end of the next manifold * ·. ·· '. This improves the uniform superheat of the steam. The adjustment thus consists of two identical sets (left and right steam lines). The syringe control is implemented by cascade control, i.e. the control of the upper t. | Aa becomes the setpoint of the lower t.

i · S

♦ • · 118929 11

STRUCTURE OF THE DETAILED INJECTION REGULATION

Injection adjustments work the same way with each other. Only the upper level controller of the cascade has a different value set by the operator. The desired temperature is set by the operator after the superheater.

5 The master controller is limited to a suitable range depending on the maximum steam flow of the steam. For this control, a number is added which is linearly dependent on the difference between the setpoint of the master controller and the measurement. Summing is only done when the difference value exceeds a certain threshold.

In addition, the term control obtainable by starting from the spraying energy balance is summed to control the controller. The starting point for the calculation is to determine, both by measurement and by calculation, the amount of energy at which the final steam temperature reaches its setpoint. In practice, therefore, the energy content of the steam is lowered before the final superheat step by spraying water with the steam.

15 The calculation is based on the measurement of the steam mass flow rate. For the most reliable measurement, temperature and pressure compensation are used for flow measurement. The mass flow measurement of steam is limited to a certain range depending on the power output of the power plant. Multiplying the mass flow of steam by the specific heat capacity obtained from its graph gives the amount of energy per specific unit of time that changes the temperature of the steam by one degree. The following formula is shown below: ··· • · · · · ·

Qe = cmh

• · S

• M · • ·

St *;,: t! 25 Qc = energy flow per degree [kJ / s ° C] * · · T .: c = specific heat capacity of fresh steam [kJ / kg ° C] mh = mass flow of fresh steam [kg / sj.

φ *: * v There are two calculations for the energy flow per degree. Both ··· 30 are based on the energy flow that the spray water should add / reduce to the steam to achieve its desired end temperature. In addition, it is the duty of the other. * ··. * To ensure that the temperature of the steam does not exceed the structural temperature of the superheaters, which is specific to the superheater. For this calculation Qc: l * e * · *: a minimum limit can be given. This will make the syringe more efficient.

35 12 118929

The calculation is performed using the following formula:

Qi * (T2 - Tr) in Qc 5 Q2 = energy flow [kJ / s] T2 = temperature after injection [° C]

Tr = superheater structural temperature [° C]

Qc - energy flow per degree [kJ / s ° C].

10 The second calculation for the energy flow uses the sensor located before the syringe to measure the temperature of the steam. In addition, the calculation will set the target steam value at the temperature obtained by subtracting the superheat degree of steam from the active setpoint of the master controller. It is a function of the steam mass flow rate and depends on the design of the superheater. The energy flow is thus obtained from the formula: 15 Ö, = {TX-T,) QC, where

Qj = energy flow [kJ / s] Γ, = s temperature before injection [° C1 20 Tt = target steam temperature before superheater [° C] Ö = energy flow per degree [kJ / s ° CJ].

The target temperature of the vapor before the superheater is calculated by the following formula: "* · • ·:: * ·. * 25 ί" i Tt = Tspa -Tta. Where i · · «· • · V ··

Tt = target steam temperature before superheater [° C]: Y: Tspa = active setpoint of the temperature controller [° C] 30 Γ = superheat steam [° C], · · · · · · · · · · · · · · · · · · · · · in the calculation, * · to obtain the total energy flow at which the steam energy must be changed to reach its M · V: target temperature. Because the temperature of the steam is changed by the water ***! 35 syringes, the total energy flow must still be converted into water mass flow using the energy content of the water or enthalpy in the calculation. The injection water is extracted from the boiler feed water. If the feed water temperature of the plant is almost constant, a fixed value for its enthalpy can be used. If, on the other hand, the temperature of the feed water varies, it is necessary to measure the feed water temperature in order to calculate its energy content. The required spray water mass flow rate is given by 5 where m = +

K

mv - injection water mass flow rate [kg / s] 10 QI2 = energy flow [kJ / s] hv = injection water enthalpy [kJ / kgj].

The resulting spray water mass flow is summed to an additional term calculated from the controller output and its differential value, which is further summed to the remote setpoint of the flow controller acting as a down regulator. The flow regulator outlet directly controls the spray water control valve in the range 0-100%. The injection water flow controller receives a temperature-compensated injection water flow measurement as a measurement. This measurement must be proportional to the position information of both the left and right injection valves of the superheater if the viral measurement is common to both sides.

· · ·

A: TEACHING INJECTION REGULATION TUNER CONTROL

• · «« · ·· * / Spray controls are based on mathematical models that ···: water and fresh steam are known to behave. Since the process is never!.!!: Perfect, however, you need controls in addition to models to correct the models · *.,. · * 25 and parameters. For example, the superheat degree of superheaters changes not only as the mass flow of steam but also as a function of time, mainly due to fouling. Also, the information on the degree of superheat from the manufacturer: V may differ from what it really is.

• 9. ** ·. Therefore, it is necessary to teach the controller what the superheat rate of the superheater is at any given time.

/ (This is done by utilizing the output of the temperature coefficient controller. Its "30 deviation from zero means that the specified superheating rate differs from the actual actual superheating rate. Since the correction controller is» * · *. Directly summed by the down regulator setpoint the difference between the superheating rate with the steam stream in question and the 14 118929 updates the correct superheating rate to the table. The teaching should be done slowly so that the values obtained are real and not due to momentary disturbances.

Contrary to control calculus, teaching the degree of superheat starts in practice. Now knowing the control of the temperature correction controller, 5 can be calculated from this. change in temperature of the steam corresponding to the control. This change updates the superheat curve given during the adjustment setup phase. The calculation formula is as follows: ATh = (mv hv) / (mh c) where 10 ATh = change in steam temperature due to water mass flow by controller [C] mv = water mass flow rate by controller [kg / s] hv = enthalpy of injection water [kJ / kg ] 15 mh = water mass flow rate [kJ / kg] calculated by the regulator c = specific heat capacity of the fresh steam [KJ / kgC]. When setting the control, the values (x, y) for the superheaters are given, which is the mass flow rate and The specified range of steam mass flow is subdivided, ··, ·. so that each defined point is in the middle of the part. There are four parts in the example, but their number and width may vary depending on the application. The points. ***. 'May be, for example, as shown in Figure 2B. 60, 120, 180, and 230 µg / s. The division is then as follows: • · * ί · ί: 25 • · M: 30 kg / s <Steam mass flow <90 kg / s ··· 90 kg / s <Steam mass flow <150 kg / s 150 kg / s < Steam mass flow <210 kg / s 210 kg / s <Steam mass flow <250 kg / s.

so • Il, *, The result of the above formula is calculated as a 30-minute average

f «I

as well as the flow of fresh steam. The number of calculations is the same as the number of regions * ···. When there is a change in the mean of the temperature change, it will Hip it: 7: a calculation in which the average of the temperature difference of the previous formula is added to the degree of yield of the curve. The formula is as follows: 15 118929

Tta = Tw + AThka, where

Ti = new steam refresh rate [C]

Ttv = Old Steam Recirculation Rate [C] 5 AThka = 30 min average value of the steam temperature change due to controller control.

This calculation is performed only in the area to which the current mass flow of steam belongs. This is illustrated in Figure 2B. For example, if the steam mass flow rate 10 is 70 kg / s, it will fall within the range of 30-90 kg / s in the example. The temperature change resulting from the calculation is thus added to the superheat degree of 40C °, which corresponds to the average of its range. However, the new calculated refresh rate does not move as such, but is filtered as a first order filter so that the change is calm.

Figure 3 shows the variation of feed water and fresh steam mass flows at conventional three-point control. When using three-point control, a clear sine wave variation in the feed water mass flow is observed. The range is up to 55 kg / s. The signal has a certain phase shift due to process delay.

Figure 4 illustrates the variation of the feed water and fresh steam mass flows in the balance control according to the invention. With the new balance control, there is no appreciable sine wave variation in the feed water mass flow as shown in Figure 3. The variation in this example is only 12 kg / s.

Figure 5 shows the variation of the cylinder surface in conventional three-point • · · y \ control. When using three-point control, a distinct sine wave · · ß 25 variation is observed on the cylinder surface. The cylindrical surface has a variation of up to 275 mm.

Figure 6 shows the variation in the surface of the cylinder in the adjustment of the invention. With the new balance adjustment, there is no appreciable sine wave variation on the cylinder surface as shown in Fig. 5. The cylindrical surface variation in this example is only 110 mm.

· · · · · · · · · · · · · · · · · · · · Figure 30 shows the level variation during the turbine strip. The valve before the turbine closes to stop the mass flow of steam. The pressure in the cylinder * · »increases, stopping boiling and lowering the cylinder surface. * ···: Starter valve, which reduces steam pressure, boils and raises cylinder surface.

9 Figure 8 shows the variation in the surface level of the cylinder during the turbine strip.

From the figure it can be seen that the surface of the cylinder during the turbine strip varies up to about 16 118929 about 490 mm, but the surface of the cylinder remains under control throughout the trip and does not cause other trips. By conventional adjustment, the turbine strip always caused the boiler strip as well.

Figure 9 shows the amount of oil used during the turbine strip. After the turbine tri-5 pin, solid fuel cannot be used, so the boiler is heated with oil. As a result, the cylinder pressure rises, boiling stops and the cylinder surface decreases. Figures 7-9 show that the water / steam circuits of the invention are also stable when running on oil and fuel cutoff. Figure 10 shows the variation of boiler power and feed water mass flow with conventional three-point and 10 . From the figures it can be seen that the feed water mass flow range is considerably smaller than in the conventional three-point control of Figure 10. The vibration of conventional control increases, especially when using non-homogeneous fuels. The fluctuation of the fuel supply 15 is increased as it is intended to compensate for the pressure variation due to the fluctuation of the feed water.

Figure 12 illustrates the situation with a conventional control and a balancing control according to the invention where the plant power is reduced overnight. When driving at lower power, it is common for the surface of the cylinder to be more restless than when operating at high power. However, with the new balance adjustment, this cylinder swing is almost independent of the power of the plant.

The cylinder surfaces are shown here as 10 min averages. The old • · · * · * / adjustment here shows a clear sine wave oscillation which is caused by the adjustment itself. With this new adjustment, this oscillation is considerably reduced and • ♦: 25 results mainly from uneven fuel supply.

Figure 13 shows the variation in boiler power and injection rates by conventional control. Figure 14 shows the variation of boiler power and injection rates in the balancing control of the invention. In Balance Adjustment, the primary objective is: v; is to keep the energy content of the steam at the desired value. The old adjustment is based on the direct ···. 30 to adjust the steam temperature. The variation of the amount of water sprayed influences the amount of steam produced and thus the boiler pressure control.

:. ** i Figure 15 shows an example of the steam temperature variations in a conventional spray control and a balance control according to the invention. It can be clearly seen that the temperature variations of the steam are significantly less with the new 35 control than with the conventional control. Variations in the temperature of the steam • · 17 118929 stress the superheater and steam pipes and affect the efficiency of the entire power plant.

Figure 16 shows an example of variations in secondary syringe injection rates in conventional spray control and in the inventive balance control. For example, 5 kg / s spraying can correspond to about 2.5% of the boiler output, so a lower spray rate improves plant efficiency.

Fig. 17 shows an example of O2 levels for the boiler flue gases in conventional injection control and in accordance with the balancing control according to the invention. Balancing the water balance of the steam boiler has a direct relationship with the control of the amount of fuel and, in turn, has an effect on the CMas of the flue gas and the efficiency of the boiler.

Fig. 18 shows an example of the required maximum powers with conventional control and the balance control according to the invention. The power required by the balance control according to the invention is lower than conventional control.

Fig. 19 shows an example of power differences with conventional control and the balancing control according to the invention, where the feed water mass flow variation is ± 10 kg / s or ± 2 kg / s.

Figure 20 shows an example of boiler fuel power differences with conventional control and the balancing control according to the invention. With conventional control, the variation of the tur-20 bin power in the example is between 577.5 and 641.4 MW. With the new balance ... for example, the corresponding power variation is 603 to 615.9 MW. Thus, the adjustment according to the invention · · can be used to drive closer to maximum power, thereby also reducing the power loss of · · 1. It will be apparent to those skilled in the art that as the technical ankle develops, the basic idea of the invention can be implemented.

The invention and its embodiments are thus not limited to the examples described above, but may vary within the scope of the claims.

··· ♦ • * · * 1 1 1 1 1 1 1 1 1 1 I 1 «« 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 · · · · · · · · · ·

Claims (9)

18 118929 A method for controlling the boiler feed water flow, wherein: - determining the mass flow into the cylinder, - determining the mass flow from the cylinder, characterized by: - calculating the average values of the mass flow from the cylinder (10) and the flow into the cylinder for the difference between the outgoing and incoming mass flow averages corrected by additional water wteeroftiS subtracting the mass exiting the cylinder from the predetermined time average m, ^ BUt, ~ mkalin + mb> 15 - calculate the setpoint of the flow controller (12) by subtracting from the mass flow from the cylinder (10) the difference corrected for the mass flow averages with the formula: 20 msp = ml oul • - sets the calculated flow control setpoint to the new flow control setpoint. • · · A method according to claim 1, characterized in that the predetermined time period is a value between 10 and 40 min. Method according to Claims 1 to 2, characterized in that the mass flow from the cylinder (10) mlout is determined by the formula: W K * = mth - mM - mn 2 + ήιψ • · ·: 30. :, where mIout - mass flow rate [kg / s] * ·; · * mth = mass flow of fresh steam after superheaters [kg / s]: T: mnX = mass flow rate of primary syringes [kg / s] ····· 35 mn2 = mass flow rate of secondary syringes mass flow rate [kg / s] mup = mass flow rate of cylinder blow-off [kg / s]. 19 118929 A system for controlling the flow of boiler feed water, the system comprising: - a first measuring means for determining the mass flow into a cylinder - a second measuring means for determining a mass flow from a cylinder and a 5. flow controller (12) characterized in that the system further comprises a control unit averages of values for a predetermined mass flow mkhut, ^ Kalin i. add to this difference additional water mh, with the formula: 15 mkaerolus = mkohut ~ mkalin + mh - calculate the flow control (12) setpoint by reducing ä (10) 20 difference from the outgoing mass flow, corrected for additional water mass flow averages, using the formula: • · · • · p ~ ™ hu! ~~ ^ kaemim '- to send the calculated flow control setpoint to the flow control • ·: 25 to the new setpoint. A system according to claim 4, characterized in that it is * · *. that the mharv of auxiliary water is dependent on the difference value of the cylinder level regulator (11). »» System according to claim 4 or 5, characterized in that the predetermined time period is a value in the range of 10-40 min. . ···. 30 A system according to claims 4-6, characterized by **: **, wherein the mass flow rate from the cylinder is defined by the formula: mth - mn2 + mup m ··· · · · 35. where mloul = mass flow from cylinder [kg / s] 20 118929 m „, = mass flow of fresh steam after superheaters [kg / s] mn,} = mass flow of primary syringes [kg / s] 2 = mass flow of secondary syringes [kg / s] mlip cylinder blow-off mass flow rate [kg / s] A control unit for adjusting the boiler feed water flow, characterized in that the control unit comprises: - means for receiving measurement data for determining the mass flow into and out of the cylinder - control means for transmitting mean values, mkalln, - mkacrolm corrected by the second function block to calculate the additional mass water outputs from the cylinder to and from the cylinder by subtracting the outflow from the cylinder for a predetermined time m m 20 Mkaeram ~ ^ kaloul ~ ^ Katin ™ lv i ... - the third function block to calculate the flow controller setpoint · · · by subtracting the addition of the mass flow averages from the mass flow from the cylinder] · 1 1 water corrected by: • ♦ · i 1 · • I · 25 ήιψ = mhut -mkaerolm, * with control means adapted to transmit the calculated flow controller setpoint to the new flow controller setpoint. • · · Control unit according to Claim 8, characterized in that the additional water of the second function block is the cylinder level regulator (11) • · · .1 · 1. 30 depending on the difference value. • 1 • • • tl * · · • • • • • • • tl • · I · · * 21 118929