The TPP-210A once-through steam boiler is considered as an object of regulation, the existing control systems are analyzed, its advantages and disadvantages are noted, a structural diagram of the thermal load regulator of the TPP-210A boiler on gaseous fuel is proposed using the regulating microprocessor controller Remikont R-130
The calculation of settings parameters and modeling of the process of regulating the thermal load of the boiler TPP-210A on gaseous fuel, including, the approximation of experimental data and modeling of the control object for a two-loop control system, the calculation of the settings of two-loop control systems, as well as the simulation of the transient process in two-loop systems regulation. A comparative analysis of the obtained transient characteristics is performed.
Extract from the text
In terms of the level of automation, thermal power engineering occupies one of the leading places among other industries. Thermal power plants are characterized by the continuity of the processes occurring in them. Almost all operations in thermal power plants are mechanized and automated.
Automating Parameters Provides Significant Benefits
List of used literature
Bibliography
1. Grigoriev V.A., Zorin V.M. "Thermal and nuclear power plants". Directory. — M.: Energoatomizdat, 1989.
2. Pletnev G. P. Automated control systems for thermal power plants: Textbook for universities / G. P. Pletnev. - 3rd ed., revised. and additional — M.: Ed. MPEI, 2005, - 355 s
3. Pletnev T.P. Automation of technological processes and productions in thermal power industry. /MPEI. M, 2007. 320 p.
4. Small-channel multifunctional regulating microprocessor controller Remikont R-130″ Set of documentation YALBI.421 457.001TO 1−4
5. Pletnev G.P. Zaichenko Yu.P. "Design, installation and operation of automated control systems for heat and power processes" MPEI 1995 316 s.- ill.
6. Rotach V.Ya. Theory of automatic control of heat and power processes, - M .: MPEI, 2007. - 400s.
7. Kozlov O.S. and others. Software complex "Modeling in technical devices" (PK "MVTU", version 3.7).
User's Manual. - M .: MSTU im. Bauman, 2008.
The start-up technology of once-through boilers differs from, since they do not have a closed circulation system, there is no drum in which steam would be continuously separated from water and in which a certain supply of water would be kept for a certain time. In these, a single forced circulation of the medium is carried out. Therefore, during kindling (and when working under load), it is necessary to ensure continuous forced movement of the medium through the heated surfaces and at the same time remove the heated medium from the boiler, and the movement of water in the pipes must begin even before the ignition of the burners.
Under these conditions, the kindling mode is entirely determined by the reliability, proper temperature conditions of the metal of the pipes of screens, screens, superheaters and the absence of unacceptable thermal hydraulic adjustments.
Experience and calculations have shown that the cooling of heating surfaces during the start-up of a once-through boiler is reliable if the ignition water flow is at least 30% of the nominal one. At this flow rate, the minimum mass velocity of the medium in the screens is 450-500 kg/(m2*s) according to the reliability conditions. In this case, the minimum pressure of the medium in the screens must be maintained close to the nominal, i.e. for boilers of 14 MPa - at the level of 12-13 MPa, and for boilers of supercritical pressure - 24-25 MPa.
There are two basic firing modes for once-through boilers: once-through and separator.
In the once-through firing mode, the working medium moves through all heating surfaces of the boiler, just as when it is under load. In the first period of kindling, this medium is removed from the boiler through the ROU, and after the formation of steam with the required parameters, it is sent to the main steam pipeline or directly to the turbine (in block installations).
The figures below show a simplified scheme for starting the boiler from a “cold” state in a direct-flow mode:
Another figure below shows the change in feed water flow (1), steam pressure behind the boiler (2), temperature of the medium (3), fresh (4) and secondary (5) steam, as well as the temperature of the metal of the screens of the primary (7) and secondary (5) superheaters. As can be seen, at the beginning of kindling, when the steam pressure reaches 4 MPa, the temperature of the medium and metal in the screens of the intermediate superheater drops sharply from 400 to 300-250 °C, which is explained by the opening of the ROU to discharge the medium into the drainage system, and In the entire primary path 23-24 MPa, the operating conditions of the screens of the primary and secondary superheaters, the temperature of which exceeds 600 °C, also deteriorate sharply.
Excessive rises in the temperature of the screen metal can only be avoided by increasing the kindling water flow, and, consequently, by increasing the loss of condensate and heat compared to the separator start-up mode. Given this, as well as the fact that the once-through scheme for starting the boiler from the “cold” state does not have any advantages over the separator one, it is not currently used for start-up.
The mode of direct-flow start-up of the boiler from the “hot” and “not cooled down” state creates the danger of a sharp cooling of the most heated parts of the boiler and steam pipelines, as well as an unacceptable increase in the temperature of the superheater metal in the non-consumption mode when the BROU and ROU kindling are closed in the first period. All this makes it difficult to start from a "hot" state, which is why this mode has been replaced by a separator start circuit.
The only area of application for the once-through start-up mode was the kindling of a double-effect boiler from the “cold” state and the start-up of the once-through boiler from the hot reserve after a downtime of up to 1 hour.
When starting a double-shell boiler, both shells are fired up in turn: asymmetrical boilers (for example, TPP-110) are fired starting from the shell, in which there is no secondary superheater. Cases of symmetrical boilers are melted in an arbitrary sequence. The first body of both types of double-shell boilers is fired according to the separator mode. The kindling of the second body is started at a small electrical load of the block and is carried out according to any mode.
The kindling of the boiler after a short (up to 1 hour) stop can be carried out in a direct-flow mode, since the steam parameters still retain their operating values, and individual elements and components of the boiler unit have not had time to cool significantly. The direct-flow mode in this case should be preferred, because it does not require special training, which would be required when switching to a separator circuit, which allows you to save time and speed up the start-up of the boiler. Kindling in this case is carried out in a direct-flow mode with the discharge of the entire working medium through the ROU or BRDS through the main steam valve (MSD) until the temperature of the primary and secondary steam exceeds the temperature of the turbine steam inlet by about 50 °C. If the steam temperature during the shutdown of the block has decreased by less than 50 °C, the steam temperature behind the boiler is immediately increased to the nominal value, after which the steam supply from the ROU to the turbine is switched.
With such a start-up of the boiler from the hot reserve, it should be taken into account that during the short-term shutdown of the boiler, the temperature of the medium at the inlet and outlet in many pipes of the screens equalizes and natural circulation of the medium occurs inside individual panels and between panels. This circulation may be so stable that it persists for some time after the feed pumps are restarted. As a result, it takes some time before the working environment begins to move steadily in the right direction. Until the unstable movement of the medium stops, it is not recommended to start kindling the boiler unit in order to avoid damage to the heated pipes.
Compared to the once-through separator mode of boiler start-up, it is characterized by high stability, relatively low temperatures of the working medium and metal in the entire boiler path, and allows the turbine to be started at sliding steam parameters. The screens of the intermediate superheater of the boiler begin to cool at an early stage of start-up, and their metal does not overheat to unacceptable values. Separator start-up mode is carried out using a special kindling device, the so-called kindling unit, consisting of a built-in valve (2), a built-in separator (7), a kindling expander (9) and throttle valves 5, 6, 8. The built-in separator is designed to separate moisture from steam and is a pipe with a large cross section (425 × 50 mm), in which a screw dehumidifier is installed and which is switched on for the period of firing up the boiler between the steam generating (1) and superheating (3) surfaces of the boiler through throttle devices 5 and 6. The built-in valve 2 serves for disconnecting the screens and the convective superheater from the steam generating heating surfaces and is placed between the outlet devices of the last section of the screen surfaces and the inlet collectors of the screen superheaters. During the firing up of the boiler, the main steam valve (4) remains open in a block plant and closed in a cross-linked CHP plant.
The kindling expander is an intermediate stage between the built-in separator and the devices for receiving the medium discharged from the separator. Since the pressure in the expander is maintained lower than in the separator (usually about 2 MPa), the working medium is discharged into it through the throttle valve 8 and, after repeated throttling, partially evaporates. The steam from the kindling expander is sent to the plant's own needs collector, from where it can enter the deaerators and other consumers, and the water is discharged into the outlet channel of the circulating water, or into the reserve condensate tank, or (in block installations) directly into the condenser.
The idea of a separator start-up of a once-through boiler unit is to divide the start-up process into three phases, so that in each of these successively conducted phases the reliability of all heating surfaces is fully ensured, and in the last phase it is possible to start the power equipment of the unit on sliding steam parameters while maintaining in the steam-generating surfaces constant nominal pressure.
In the first phase of the start-up, forced circulation of the working medium is organized in a closed circuit: feed pump - boiler - ignition unit - receivers for the waste medium (in a block installation turbine condenser) - feed pump. This eliminates the possibility of dangerous thermal-hydraulic adjustments in the steam-generating surfaces, and the loss of condensate and heat is minimized. In this start-up phase, the working medium has no outlet to the superheating surfaces, since they are cut off from the steam-generating surfaces by the built-in damper and throttle valve 17, which are closed during this start-up period, and are in the so-called cost-free mode. Despite the fact that the pipes of these surfaces are not cooled from the inside with steam in a non-flow mode, the temperature of their metal remains within acceptable limits, since the starting fuel consumption during this period remains at a constant, relatively low level, not exceeding 20% of the nominal flow rate.
The safety of the non-flow mode for superheaters during the boiler start-up period was confirmed by special tests of the TPP-110 and TPP-210 boilers. As can be seen, at fuel (natural gas) consumptions up to 20% of the nominal temperature, the walls of the most heated end tubes of the screens do not exceed the allowable temperature of 600 °C in the stationary state. Taking into account that the fuel consumption in the initial period of the boiler start-up is significantly lower than 20% (for example, when the boiler is operating on fuel oil, its consumption is not higher than 14-15% of the nominal value), the non-consumption mode for superheaters can be considered quite acceptable in this kindling period.
In connection with the experiments carried out, it is noted that in none of the starts of the tested boilers did the temperature of the pipe walls exceed 550 °C throughout the entire duration of the non-flow regime. This temperature is below the maximum permissible for low-alloy steel 12Kh1MF, usually used for the manufacture of tubes of stage I screens, and even more so for austenitic steel 1Kh18N12T, used for stage II screens in convective superheaters.
Switching off the superheaters in the first phase of start-up simplifies the maneuvering and control of the boiler unit, allowing, after connecting the superheating surfaces, to smoothly increase the steam parameters and its quantity, while maintaining the stability of the feed water supply. The beginning of the second phase of the start-up is considered to be the moment when steam begins to be released in the built-in separator, which is directed to the superheating surfaces, gradually opening the throttle valve and gradually increasing the temperature and pressure of the steam. In this start-up phase, the boiler operates at two pressures: nominal - up to the built-in valve, which continues to remain closed, and "sliding" - behind the throttle valve in the overheating surfaces. This mode is possible due to the fact that the superheating surfaces are separated from the steam generating surfaces by the steam space of the separator, just like in drum boilers. In the third phase of the start-up, the boiler unit is transferred to the direct-flow mode. This transfer should begin after the steam parameters reach 80-85% of the nominal values. Gradually opening the built-in valve, bring the parameters to the nominal value and turn off the kindling unit.
At the end of the kindling of the boiler unit at a non-block TPP, it is connected to the main steam pipeline, and the connection rules remain the same as for drum boilers. The main one is the approximate equality of pressures behind the boiler and in the main steam pipeline at the time of connection.
In block installations, the start-up of the boiler is combined with the start-up of the turbine and the transfer of the boiler to the once-through mode is usually carried out after the electric load of the block reaches 60-70% of the nominal value.
The figures below show the starting characteristics of a once-through boiler of a non-block TPP in a separator mode: 1 - steam pressure behind the boiler; 2 - feed water consumption; 3 - maximum temperature of the medium at the outlet of the NRC; 4 - feed water temperature; 5 - temperature of intermediate overheating; 6 - fresh steam temperature; 8, 7 - maximum temperature of the metal of the screens II and the intermediate superheater; 9 - flue gas temperature in the rotary chamber.
Features of kindling during a "hot" start are as follows. Before ignition of the burners, the temperature of the metal of the built-in separators is reduced from 490 to 350-320 ° C by venting steam from the separators, and the rate of decrease in this case should not exceed 4 ° C / min. At the same time, the pressure in the ~~ boiler is reduced from the nominal (25 MPa) to 10-15 MPa. 30-40 minutes after the cooldown of the separators according to the same schedule as from the "uncooled" state, i.e. after establishing the minimum ignition flow rate of the feed water, the pressure in front of the closed built-in valve rises to 24-25 MPa, oil burners are switched on with a starting flow rate oil and at the same time the relief valves of 8 built-in separators open. Following this, throttle valves 5 gradually open. Further operations are the same as when starting from a "cold" state. By reducing the pressure in the boiler before kindling, condensation of steam in the screens is excluded, which are therefore cooled less than when starting in direct-flow mode.
The power unit with the TPP-210A boiler was emergency shut down by protective devices due to malfunctions in the operation of the feed pump. When the valve on the fuel oil line was automatically closed, the supply of liquid fuel was not completely turned off and in one boiler body a small amount of fuel oil continued to burn in the furnace, which contributed not only to an increase in thermal distortions and an increase in circulation in the LFC panels, but also to the appearance of individual fixed pipes in the upper bends. bubbles of slightly superheated steam, which occupied the entire section of the pipes and prevented the movement of the working medium in them. Although supercritical pressure steam has the same density as water at the time of its formation, an increase in its temperature by only a few degrees leads to a decrease in its density by tens of percent. With an increase in the speed of water, the bubbles of steam should have been carried away by its flow, however, large bubbles could temporarily linger, due to which the temperature of the metal of the corresponding pipes should have sharply increased.
After a five-minute break, the boiler was switched to a direct-flow mode, and contrary to the rules, feed water was supplied not previously, but simultaneously with a sharp increase in the supply of fuel oil to the furnace. Soon, in the unheated outlet section of one of the NRCH pipes, a temperature increase up to 570 °C was recorded. The interval between automatic recordings of this temperature was 4 minutes, but before this temperature was recorded again, an emergency rupture of the pipe occurred, in which there was a section in the zone of the burner embrasure that was not protected by incendiary belts. The boiler was again emergency shut down.
Another example relates to the deterioration of the separation, which occurred when the relief valves were not fully opened, which removed the separated moisture from the built-in separator. When the once-through boiler was fired up, these valves were closed in order to reduce the temperature of the live steam in the event of a malfunction of the injection desuperheaters. This method of regulation is associated with abrupt and significant changes in steam temperature and leads to the appearance of fatigue cracks in the superheater headers close to the built-in separator along the steam path.
Closing of valves 8 and opening 5 must be done slowly in order to avoid the release of water into the nearby collectors of the superheater due to a violation of the stable movement of the working medium in the separator. In addition, it is necessary to open the drains before and after the throttle valve 5 in advance in order to prevent the condensate accumulated in the pipelines from escaping from the ignition unit.
The slow opening of the throttle valves 5 leads to an increase in the heating time of the main steam pipelines and the duration of the boiler kindling. Of course, significant fluctuations in the steam temperature are unacceptable, however, if the boiler is fired up only a few times a year, there is no reason to additionally delay the start-up operations to prevent a slight decrease in the steam temperature. But if the boiler is fired up and stopped frequently, then even small drops of water into the screens can have dangerous consequences. Therefore, when kindling once-through boilers, it is necessary to strictly observe the start-up schedule, which regulates the slow and gradual opening of valves 5.
Fil S. A., Golyshev L. V., engineers, Mysak I. S., Doctor of Engineering. Sci., Dovgoteles G. A., Kotelnikov I. I., Sidenko A. P., engineers of JSC LvovORGRES - National University "Lviv Polytechnic" - Trypilska TPP
Combustion of low-reactivity hard coals (Vdaf< 10%) в камерных топках котельных установок сопровождается повышенным механическим недожогом, который характеризуется двумя показателями: содержанием горючих в уносе Гун и потерей тепла от механического недожога q4.
Goon is usually determined by the laboratory method on single ash samples taken from the gas ducts of the last convective surface of the boiler using regular blow-off installations. The main disadvantage of the laboratory method is the too long time delay in obtaining the Gong result (more than 4 - 6 hours), which includes the time of slow accumulation of the ash sample in the blow-away installation and the duration of the laboratory analysis. Thus, in a single ash sample, all possible changes in gong are summarized for a long time, which makes it difficult to quickly and efficiently adjust and optimize the combustion regime.
According to the data in the variable and non-stationary modes of the boiler, the ash collection coefficient (degree of purification) of the cyclone of the carry-out setting changes in the range of 70 - 95%, which leads to additional errors in determining the gong.
The disadvantages of fly ash installations are overcome by the introduction of continuous gong measurement systems, such as analyzers of carbon content in fly ash.
In 2000, eight sets (two for each vessel) of stationary continuously operating RCA-2000 analyzers manufactured by Mark and Wedell ( Denmark).
The principle of operation of the RCA-2000 analyzer is based on the photoabsorption method of analysis in the infrared region of the spectrum.
Measurement range 0 - 20% of absolute Gong values, relative measurement error in the range of 2 - 7% - no more than ± 5%.
Ash sampling for the measuring system of the analyzer is carried out from the gas ducts in front of the electrostatic precipitators.
The continuous recording of gongs was carried out on a self-recording device of the control room with a frequency of a complete measurement cycle in 3 minutes.
When burning ash of varying composition and quality, the actual absolute Gong values, as a rule, exceeded 20%. Therefore, at present, analyzers are used as indicators of changes in the relative values of the content of combustibles in the entrainment of Gv ° within the scale of the recorder 0 - 100%.
For a rough estimate of the actual Gong level, a calibration characteristic of the analyzer has been compiled, which is the relationship between the absolute Gong values determined by the laboratory method and the relative values of the analyzer G°Gong. In the range of gong change from 20 to 45%, the characteristic in analytical form is expressed by the equation
During experimental studies and normal operation of the boiler, analyzers can be used to perform the following work:
optimization of the combustion mode;
assessing the change in gong during planned technological switching of systems and units of the boiler plant;
determination of the dynamics and level of decrease in efficiency in non-stationary and post-start modes of the boiler, as well as in the case of alternate combustion of ASh and natural gas.
During the period of thermal testing of the boiler, analyzers were used to optimize the combustion regime and assess the effect of planned equipment switching on the stability of the combustion process of pulverized coal.
The experiments were carried out at stationary loads of the boiler in the range of 0.8-1.0 nominal and combustion of AS with the following characteristics: lower specific calorific value Qi = 23.06 - 24.05 MJ/kg (5508 - 5745 kcal/kg), ash content per working weight Ad = 17.2 - 21.8%, humidity on the working weight W = 8.4 - 11.1%; the share of natural gas for the illumination of the pulverized coal flame was 5-10% of the total heat release.
The results and analysis of experiments on optimizing the combustion mode using analyzers are given in. When setting up the boiler, the following were optimized:
output velocities of the secondary air by varying the opening of the peripheral gates in the burners;
output speeds of the primary air by changing the load of the hot blast fan;
proportion of flame illumination with natural gas by selecting (according to the conditions for ensuring combustion stability) the minimum possible number of operating gas burners.
The main characteristics of the combustion mode optimization process are given in Table. one.
Given in table. 1, the data indicate the important role of analyzers in the optimization process, which consists in continuous measurement and registration of current information about the change in H°h, which makes it possible to timely and
clearly fix the optimum mode, the completion of the stabilization process and the start of the boiler in the optimal mode.
When optimizing the combustion mode, the main attention was paid to finding the lowest possible level of relative values of H°un. In this case, the absolute values of gong were determined by the calibration characteristic of the analyzer.
Thus, the effectiveness of the use of analyzers to optimize the combustion mode of the boiler can be roughly estimated by reducing the content of combustibles in the entrainment by an average of 4% and heat loss from mechanical underburning by 2%.
In stationary modes of the boiler, regular technological switching, for example, in dust systems or burners, disrupts the process of stable combustion of pulverized coal.
Table 1
Characteristics of the combustion mode optimization process
The TPP-210A boiler is equipped with three dust systems with ball drum mills of the ShBM 370/850 (Sh-50A) type and a common dust bin.
From the dust system, the spent drying agent is discharged into the combustion chamber (pre-furnace) using a mill fan of the MB 100/1200 type through special discharge nozzles located above the main dust and gas burners.
The pre-furnace of each boiler body receives a full discharge from the corresponding outer dust system and half of the discharge from the middle dust system.
The spent drying agent is a low-temperature humidified and dusty air, the main parameters of which are within the following limits:
the share of waste air is 20 - 30% of the total air consumption of the body (boiler); temperature 120 - 130°C; the share of fine coal dust, which was not captured by the cyclone of the dust system, 10 - 15% of the mill productivity;
humidity corresponds to the amount of moisture released during the drying process of the milled working fuel.
The spent drying agent is discharged into the zone of maximum flame temperatures and, therefore, significantly affects the completeness of coal dust burnout.
During the operation of the boiler, the middle dust system is most often stopped and restarted, with the help of which the required level of dust is maintained in the industrial bunker.
The dynamics of changes in the main indicators of the combustion regime of the boiler body - the content of combustibles in the entrainment and the mass concentration of nitrogen oxides in the flue gases (NO) - during a planned shutdown of the middle dust system is shown in fig. one.
In the above and all subsequent figures, the following conditions are accepted when constructing graphical dependencies:
the content of combustibles in the entrainment corresponds to the values of the scales of two vertical axes of coordinates: the averaged measurements of Gong and the data of recalculation according to the calibration characteristic Gong;
the mass concentration of NO with excess air in the exhaust gases (without reduction to NO2) was taken from continuously recorded measurements of the stationary gas analyzer Mars-5 MP "Ekomak" (Kyiv);
dynamics of H°un and NO changes is fixed on
throughout the entire period of the technological operation and the stabilization mode; the beginning of the technological operation is taken near the zero time reference.
The completeness of combustion of pulverized coal fuel was estimated by the quality of the combustion mode (KTR), which was analyzed by two indicators Gong and NO, which, as a rule, changed in mirror-opposite directions. 
Rice. 1. Changes in the indicators of the combustion mode when the middle dust system is stopped
The influence of the planned shutdown of the medium dust system on the KTP indicators (Fig. 1) was analyzed depending on the sequence of the following technological operations:
operation 1 - shutting down the raw coal feeder (CFC) and stopping the supply of coal to the mill reduced the loading of the SBM drum, reduced the fineness of the coal dust and increased the temperature of the exhaust air, which caused a short-term improvement in CTE: a decrease in Hn° and an increase in NO; the process of further emasculation of the mill contributed to the removal of dust from the waste air and the increase in excess air in the pre-furnace, which negatively affected the CTE;
operation 2 - stopping the SHM and reducing the ventilation of the dust system first slightly improved the CTE, and then, with a delay with turning off the mill fan (MF), the CTE worsened;
operation 3 - stopping the MW and stopping the discharge of the spent drying agent into the combustion chamber significantly improved the CTE.
Thus, all other things being equal, stopping the dust system improved the fuel combustion process, reducing mechanical underburning and increasing the mass concentration of NO.
A typical violation of the stability of the dust system is overloading the mill drum with fuel or “smearing” the grinding balls with wet clay material.
The influence of the long-term emasculation of the drum of the end mill on the CTE of the boiler body is shown in fig. 2.
Shutdown of the PSU (operation 1) for reasons similar to those considered during the shutdown of the pulverizing system, at the first stage of mill emasculation improved the CTE for a short time. In the subsequent emasculation of the mill up to the inclusion of the PSU (operation 2), there was a tendency for the deterioration of the CTE and the growth of G°un.
Rice. Fig. 2. Changes in the indicators of the combustion regime during the emasculation of the drum of the last mill 
Rice. 3. Changes in the indicators of the combustion mode when starting the last dust system and turning off the gas burners
To a lesser extent, the automatic operation of the PSU periodically destabilizes the furnace mode, which regulates the necessary loading of the mill with coal by turning off and then turning on the PSU drive.
The influence of the starting mode of the extreme dust system on the KTP is shown in fig. 3.
The following influence of the starting operations of the dust system on the combustion mode was noted:
operation 1 - starting the MW and ventilation (warming up) of the dust system path with the discharge of relatively cold air into the pre-furnace increased the excess air in the combustion zone and reduced the temperature of the torch, which led to a deterioration in the CTE;
operation 2 - launching the SHBM and continuing the ventilation of the tract had a negative impact on the CTE;
operation 3 - starting the PSU and loading the mill with fuel with an increase to the nominal consumption of the drying agent significantly worsened the CTE.
It can be concluded that the inclusion of the dust system in operation negatively affects the CTE, increasing the mechanical underburning and reducing the mass concentration of NO.
The pre-furnace of the TPP-210A boiler body is equipped with six snail-vane dust and gas burners with a thermal power of 70 MW, installed in one tier on the front and rear walls, and two gas-oil burners above the hearth to ensure stable liquid ash removal throughout the range of boiler operating loads.
During the combustion of ASh coal dust, natural gas was supplied at a constant flow rate (about 5% of the total heat release) to the over-hearth burners and a variable flow rate through the main dust-gas burners to stabilize the combustion process of pulverized coal. The gas supply to each main burner was carried out at the lowest possible flow rate, corresponding to 1.0 - 1.5% of the total heat release. Therefore, the change in the share of natural gas for torch lighting was carried out by turning on or off a certain number of main gas burners.
The effect of turning off gas burners (reducing the share of natural gas) on the CTE of the boiler body is shown in fig. 3.
Sequential shutdown of first one gas burner (operation 4), and then three gas burners (operation 5) had a positive effect on the CTE and led to a significant reduction in mechanical underburning.
The effect of turning on gas burners (increasing the share of natural gas) on the CTE is shown in fig. 4. Sequential switching on of one gas burner (operation 1), two burners (operation 2) and one burner (operation 3) negatively affected the CTE and significantly increased mechanical underburning. 
Rice. 4. Change in indicators of the combustion mode when gas burners are turned on
table 2
Changes in the content of combustibles in carryover during technological switching of equipment
Equipment | Mode | ||
decrease | increase |
||
Extreme/Middle Dust System | |||
emasculation | Emergency | ||
raw feeder | |||
Main gas burner | Shutdown | ||
Inclusion | |||
An approximate assessment of the impact of proven technological switching of boiler equipment on the change in CTE (Kun) is summarized in Table. 2.
The analysis of the given data shows that the greatest decrease in the efficiency of the boiler plant in stationary modes occurs as a result of the start-up operations of the dust system and with an overestimated consumption of natural gas for flame illumination.
It should be noted that the need to perform start-up operations of the dust system is determined solely by technological reasons, and an overestimated consumption of natural gas for flame illumination, as a rule, is set by the operating personnel in order to prevent possible violations of the combustion process stability in the event of a sudden deterioration in the quality of the AS.
The use of RCA-2000 analyzers allows for continuous changes, timely
evaluate any changes in fuel quality and constantly maintain the value of the flame illumination at the appropriate optimal level with the minimum necessary consumption of natural gas, which helps to reduce the consumption of scarce gaseous fuel and increase the efficiency of the boiler.
conclusions
- The system of continuous measurement of the content of combustibles in carry-over allows you to quickly and efficiently evaluate the flow of combustion processes during the combustion of AS in the TPP-210A boiler, which is recommended for use in commissioning and research work, as well as for systematic monitoring of the efficiency of boiler equipment.
- The efficiency of using the RCA-2000 analyzers for optimizing the combustion mode is tentatively estimated by reducing the indicators of mechanical underburning - the content of combustibles in the entrainment by an average of 4% and, accordingly, heat loss from mechanical underburning by 2%.
- In stationary modes of the boiler, regular technological switching of equipment affects the quality of the combustion process. The start-up operations of the dust system and the overestimated consumption of natural gas for lighting the pulverized coal torch significantly reduce the efficiency of the boiler plant.
Bibliography
- Madoyan A. A., Baltyan V. N., Grechany A. N. Efficient combustion of low-grade coals in power boilers. Moscow: Energoatomizdat, 1991.
- Use of the RCA-2000 combustible content analyzer in the carry-over and the Mars-5 gas analyzer to optimize the combustion mode of the pulverized coal boiler TPP-210A of Tripolskaya TPP / Golyshev L. V., Kotelnikov N. I., Sidenko A. P. et al. - Tr. Kyiv Polytechnic Institute. Energy: economics, technology, ecology, 2001, no. 1.
- Zusin S. I. Change in heat loss with mechanical underburning depending on the operating mode of the boiler unit. - Thermal power engineering, 1958, No. 10.
In the middle of the twentieth century, the development of thermal power plants followed the path of increasing the unit capacity and efficiency of power equipment. At the same time, in the 1950s, the USSR began to build thermal power plants with power units of 100, 150, and 200 MW, and in the 60s, power plants with a capacity of 300, 500, and 800 MW were put into operation at power plants. One power unit with a capacity of 1200 MW was also put into operation. Boilers for supercritical steam parameters are installed in these units.
The transition of boilers to supercritical steam parameters was dictated by economic feasibility, which was determined by the optimal balance of fuel economy due to an increase in thermal efficiency. cycle and increase in the cost of equipment and operation. The refusal to use drum boilers in powerful units for subcritical steam parameters was determined by a significant increase in the cost of the boiler as a result of an increase in the mass of the drum, which for a boiler of a 500 MW unit reached 200 tons. base load does not exceed 400 MW. In this regard, when creating blocks of high power, it was decided to switch to once-through supercritical pressure boilers.
The first once-through boilers for 300 MW power units, models TPP-110 and PK-39, and boilers for 800 MW power units, models TPP-200, TPP-200-1, were manufactured in the early 1960s. They were made in two parts. Steam boilers TPP-110 and PK-39 were manufactured with an asymmetrical arrangement of heating surfaces in each body (monoblock).
In the TPP-110 boiler, the main part of the primary superheater is located in one building, the rest is in the second building
part of this superheater and the entire heating surface of the intermediate superheater. With such an arrangement of superheaters, the steam temperature in each of them is controlled by changing the “feed water-fuel” ratio. Additionally, the intermediate steam temperature is controlled in the gas-vapor heat exchanger.
The redistribution of the heat load between the vessels, which occurs when the steam temperature is controlled, is undesirable, since when anthracite cullet and other types of low-reaction fuel are burned, the temperature of hot air decreases, which leads to an increase in heat losses from fuel underburning.
In the double-cassette steam boiler model PK-39, manufactured according to the T-shaped scheme, the primary and intermediate superheaters are located in four convective shafts of the casings asymmetrically to the vertical axis of the boiler. When the amount of combustion products changes in the right and left convective shafts of each housing, the heat absorption by the primary and intermediate superheaters is redistributed, which leads to a change in the steam temperature. In a double-casing steam boiler with symmetrical casings of models TPP-200, TPP-200-1, the convection shafts of each casing are divided into three parts by vertical partitions. In the middle part of the convective shaft, packages of a water economizer are placed, in the two extreme ones - packages of a high-pressure convective superheater and an intermediate one.
Operating experience of TPP-110 boilers confirmed the possibility of controlling the temperature of the primary and intermediate steam by changing the "feed water-fuel" ratio in each of the buildings. At the same time, during the operation of these boilers, an increased number of their emergency stops was observed. The operation of the boilers became much more complicated. A similar picture was observed during the pilot operation of the PK-39 boiler.
Subsequently, instead of these boilers, double-casing units were produced, but with a symmetrical arrangement of heating surfaces in the casings - double blocks (TPP-210, TPP-210A, TGMP-114, PK-41, PK-49, P-50).
The use of double-shell boilers with a symmetrical arrangement of heating surfaces increases the reliability of the power unit. In case of an emergency stop of one of the buildings, the power unit can operate with a reduced load on the other building. However, single body operation is less economical. The disadvantages of double-shell boilers also include the complexity of the piping scheme, a large number of fittings, and increased cost.
The operating experience of power units with supercritical pressure boilers has shown that the utilization factor of units with one vessel is not lower than with two. In addition, due to the reduction in the number of steam-water fittings and automatic control devices, maintenance of power units with single-shell boilers is simplified. These circumstances led to the transition to the production of single-shell supercritical pressure boilers.
The steam boiler TPP-312A with a steam capacity of 1000 t/h (Fig. 2.13) is designed to operate on coal in a unit with a 300 MW turbine. It produces superheated steam with a pressure of 25 MPa and a temperature of 545°C and has an efficiency. 92%. Boiler - single-casing, with reheating, U-shaped layout with an open prismatic combustion chamber. The screens are divided into four parts according to the height of the combustion chamber: the lower radiation part, the middle one, consisting of two parts, and the upper radiation part. The lower part of the combustion chamber is shielded with studded carborundum-coated pipes. Slag removal - liquid. At the outlet of the combustion chamber there is a screen superheater, in the convective shaft there are convective superheaters of high and low pressure. The temperature of the high pressure steam is controlled by injection of feed water, and the low pressure steam is controlled by a steam-steam heat exchanger. Air heating is carried out in regenerative air heaters.
The following single-shell supercritical pressure boilers have been developed and are in operation: pulverized coal TPP-312, P-57, P-67, gas-oil TGMP-314, TGMP324, TGMP-344, TGMP-204, TGMP-1204. In 2007, TKZ Krasny Kotelshchik manufactured TPP-660 boilers with a steam capacity of 2225 t/h and a steam pressure at the outlet of 25 MPa for the power units of the Bar TPP (India). The service life of the boilers is 50 years.
At the last power unit of the Hemweg thermal power plant in the Netherlands (see section 4), a steam two-pass boiler according to Benson technology (Fig. 2.14) with a steam capacity at full load of 1980 t / h, designed by Mitsui Babcock Energy and designed to work on hard coal, is installed (as the main type of fuel) and gas in a block with a 680 MW turbine.
This supercritical pressure radiant once-through boiler generates steam at a pressure of 26 MPa and a temperature of 540/568°C.
It operates in a modified sliding pressure mode, in which the turbine inlet pressure is regulated to a level that changes with the load of the power unit.
The boiler is equipped with three superheaters with injection desuperheaters and two reheater units (although this is a single reheat cycle). The economizer is a horizontal coil of pipes with a ribbed surface. The primary superheater is arranged in the form of one horizontal and one vertical block. The secondary screen superheater is a suspended single-circuit block, and the last stage of the superheater is also made in the form of a single-circuit suspended block. The hot steam temperature at the boiler outlet is 540°C. The reheater system of the boiler has two stages - primary and final. The primary stage includes two horizontal blocks, the final reheating stage is represented by a vertical block in the form of a folded circuit located in the boiler flue. At the outlet of the boiler, the temperature of the superheated steam is 568°C.
The boiler soot blower system consists of 107 blowers driven by a programmable logic controller. The removal of the ash residue is carried out by a scraper conveyor passing under the firebox and hydraulic transport to the ash residue filter tank.
The flue gas outlet temperature is about 350°C. Then they are cooled down to 130°С in rotating regenerative air heaters.
The boiler is designed to minimize NO x emissions through the use of low NO x burners and forced draft. Achieving good environmental performance is facilitated by flue gas desulfurization, which removes SO 2 from the exhaust gases.
The modern gas-oil steam boiler TGMP-805SZ (Fig. 2.15) with a steam capacity of 2650 t/h is designed to generate superheated steam with an operating pressure of 25.5 MPa and a temperature of 545 °C for a steam turbine with a capacity of 800 MW. The once-through, gas-oil, single-casing boiler is suspended on the core beams supported on the columns of the boiler room building, and can be installed in areas with a seismic activity of 8 points. It has an open combustion chamber of a prismatic shape. It is formed by all-welded tubular panels, in the lower part of which there is an all-welded horizontal hearth screen, and in the upper part - a horizontal flue, closed from above with an all-welded tubular ceiling screen. The screens of the combustion chamber are divided by height into lower and upper radiation parts.
36 oil-gas burners are located on the front and rear walls of the boiler combustion chamber. In the horizontal flue, five vertical convective heating surfaces are placed sequentially along the gas flow - a steam-generating heating surface included in the steam-water path of the boiler up to the built-in valve, three parts of the high-pressure superheater, and the outlet stage of the low-pressure superheater.
The secondary steam temperature is controlled by recirculating gases. In the downcomer, shielded by all-welded tubular panels, the inlet stage of the low-pressure superheater and the water economizer are placed in series along the gas flow.
One of the most significant achievements of the thermal power industry at the end of the 20th century in the world was the introduction of supercritical boilers, which are currently capable of operating at an outlet steam pressure of 30 MPa and a temperature of 600/650°C. This has been made possible by developments in the technology of materials that can withstand conditions of high temperatures and pressures. Boilers (often referred to as “steam generators”) with a capacity of more than 4,000 t/h are already operating in the “big power industry”. Such boilers provide steam for power units of 1000-1300 MW at power plants in the USA, Russia, Japan and some European countries.
Currently, the development of new models of steam boilers for power units of TPPs continues. At the same time, boilers are designed for both super-supercritical, supercritical, and subcritical steam parameters. For example, at 2 power units of Neiveli TPP (India) with a capacity of 210 MW each, Ep-690-15.4-540 LT steam boilers are installed, designed to operate on low-calorie Indian lignites. These are drum boilers with natural circulation, subcritical pressure with reheating, single-shell, with solid slag removal, tower type. The steam capacity of such a boiler is 690 t/h, the steam parameters are the pressure of 15.4 MPa at the outlet of the boiler and 3.5 MPa at the outlet of the reheater, the steam temperature is 540°C.
The combustion chamber of the boiler is open and equipped with 12 twin direct-flow multi-channel burners installed on all walls of the furnace in two tiers. To clean the heating surfaces, water and steam blowers are installed.
It should be noted that the power industry of the CIS countries is based on the use of two types of steam boilers - once-through and natural circulation boilers. In foreign practice, along with once-through boilers, boilers with forced circulation are widely used.
In addition to the main ones - steam boilers of high and supercritical pressure - other types of boilers are currently used at TPPs: peak hot water boilers, boilers for burning coal in a fluidized bed, boilers with a circulating fluidized bed and waste heat boilers. Some of them will become the prototype of boilers for the future development of thermal power engineering.
