Fil S. A., Golyshev L. V., engineers, Mysak I. S., Doctor of Engineering. Sciences, Dovgoteles G. A., Kotelnikov I. I., Sidenko A. P., engineers of OJSC LvovORGRES - National University“Lviv Polytechnic” - Trypilska Thermal Power Plant

Combustion of low-reactive hard coals(Volatile yield 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.
Typically, gun is determined by a laboratory method using single ash samples taken from the flue ducts of the last convective surface of the boiler using standard entrainment units. 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 fly unit and the duration of the laboratory analysis. Thus, in a single ash sample, all possible changes in the guns are summed up over a long period of time, which makes it difficult to quickly and efficiently adjust and optimize the combustion regime.
According to the data, in variable and non-stationary boiler modes, the ash collection coefficient (degree of purification) of the cyclone, the carry-away setpoint, varies in the range of 70 - 95%, which leads to additional errors in determining Gong.
The disadvantages of fly ash plants are eliminated by introducing continuous Gong measurement systems, for example, carbon analyzers in fly ash.
In 2000, eight sets (two for each building) of stationary continuously operating RCA-2000 analyzers from Mark and Wedell ( Denmark).
The operating principle 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 2 - 7% - no more than ± 5%.
Ash sampling for measuring system analyzer is produced from gas ducts in front of electric precipitators.
Continuous recording of Gongs was carried out on a control room recorder at regular intervals full cycle measurements after 3 min.
When burning ash of variable composition and quality, the actual absolute values ​​of Gong, 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 Gv° within the scale of a recorder 0 - 100%.
For an approximate assessment of the actual Gong level, a calibration characteristic of the analyzer has been compiled, which represents the relationship between the absolute values ​​of Gong determined by the laboratory method and the relative values ​​of the Gong analyzer. In the range of Gong changes from 20 to 45%, the characteristic in analytical form is expressed by the equation

At experimental studies and normal boiler operation analyzers can be used to perform next works:
combustion mode optimization;
assessment of changes in Gong during planned technological switchings of systems and units of a boiler plant;
determining the dynamics and level of reduction in efficiency in non-stationary and post-start-up modes of the boiler, as well as during alternate combustion of ash and natural gas.
During thermal testing of the boiler, analyzers were used to optimize the combustion mode and assess the impact of planned equipment switching on the stability of the combustion process of pulverized coal fuel.
The experiments were carried out at stationary boiler loads in the range of 0.8-1.0 nominal and combustion of ash with characteristics: lowest specific heat combustion Qi = 23.06 - 24.05 MJ/kg (5508 - 5745 kcal/kg), ash content per working mass Ad = 17.2 - 21.8%, humidity per working mass W = 8.4 - 11.1 %; the share of natural gas for illuminating the pulverized coal flare was 5-10% of the total heat release.
The results and analysis of experiments to optimize the combustion regime using analyzers are given in. When setting up the boiler, the following were optimized:
secondary air output velocities by varying the opening of peripheral dampers in the burners;
primary air output speeds by changing the hot blast fan load;
the share of flare 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. 1.
Given in table. 1 data indicate the important role of analyzers in the optimization process, which consists in continuous measurement and recording of current information about changes in G °, which makes it possible to timely and
clearly record the optimum mode, completion of the stabilization process and the start of boiler operation in optimal mode.
When optimizing the combustion regime, the main attention was paid to finding the minimum possible level of relative values ​​of G°un. In this case, the absolute values ​​of Gong were determined from the calibration characteristic of the analyzer.
Thus, the effectiveness of using analyzers to optimize the combustion mode of a boiler can be roughly assessed by reducing the content of combustibles in the entrainment by an average of 4% and heat loss from mechanical underburning by 2%.
In stationary boiler modes, carrying out standard technological switchings, for example, in dust systems or burner devices, disrupts the process of stable combustion of pulverized coal fuel.

Table 1
Characteristics of the combustion mode optimization process

The TPP-210A boiler is equipped with three dust systems with ball drum mills type ShBM 370/850 (Sh-50A) and a common dust bin.
From the dust system, the spent drying agent is discharged using a mill fan type MV 100/1200 into the combustion chamber (pre-furnace) 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 extreme dust system and half of the discharge from the middle dust system.
The spent drying agent is low-temperature humidified and dusty air, the main parameters of which are within the following limits:
the share of exhaust air is 20 - 30% of the total air consumption of the housing (boiler); temperature 120 - 130°C; the share of fine coal dust that was not caught 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 grinded working fuel.
The spent drying agent is discharged into the zone of maximum flame temperatures and therefore significantly affects the completeness of burnout of coal dust.
When operating 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 dust bin.
The dynamics of changes in the main indicators of the combustion mode 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 average dust system is shown in Fig. 1.
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 coordinates: averaged GUN measurements and recalculation data based on the Gong calibration characteristic;
the mass concentration of NO with excess air in the flue gases (without reduction to NO2) was taken from continuously recorded measurements of the stationary gas analyzer Mars-5 MP “Ekomak” (Kiev);
the dynamics of changes in G°un and NO is fixed at
throughout the entire period of the technological operation and stabilization mode; the start of the technological operation is assumed to be near the zero time report.
The completeness of combustion of pulverized coal fuel was assessed by the quality of the combustion regime (CFC), which was analyzed by two indicators Gun and NO, which, as a rule, changed in mirror-opposite directions.

Rice. 1. Changes in combustion mode indicators when stopping the middle dust system

The effect of a planned shutdown of a medium dust system on the CTE indicators (Fig. 1) was analyzed depending on the sequence of the following technological operations:
operation 1 - stopping the raw coal feeder (CCF) and stopping the supply of coal to the mill reduced the loading of the CBM drum, reduced the grinding fineness of coal dust and increased the temperature of the waste air, which caused a short-term improvement in the CTE: a decrease in Gun° and an increase in NO; the process of further emasculation of the mill contributed to the removal of dust from the waste air and an increase in excess air in the pre-furnace, which negatively affected the CTE;
operation 2 - stopping the mill fan and reducing the ventilation of the dust system first slightly improved the CTE, and then, with a delay in turning off the mill fan (MF), the CTE deteriorated;
operation 3 - stopping the MV 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 a long-term drying out of the end mill drum on the CTE of the boiler body is shown in Fig. 2.
Stopping the PSU (operation 1) for reasons similar to those considered when stopping the dust system, at the first stage of mill emasculation, short-term improved the CTE. In the subsequent emasculation of the mill until the inclusion of the PSU (operation 2), a tendency was observed for the deterioration of the CTE and an increase in G°un.

Rice. 2. Changes in combustion conditions when the end mill drum is emptied

Rice. 3. Changes in combustion mode indicators when starting the extreme dust system and turning off the gas burners

To a lesser extent, the combustion mode is periodically destabilized by the automatic operation of the PSU, which regulates the necessary loading of the mill with coal by turning off and then turning on the PSU drive.
The influence of the start-up mode of the extreme dust system on the CTE is shown in Fig. 3.
The following influence of starting operations of the dust system on the combustion mode was noted:
operation 1 - starting the MV 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 flame temperature, which led to a deterioration in the CTE;
operation 2 - starting the BBM and continuing ventilation of the tract had a negative effect on the CTE;
operation 3 - starting up the PSU and loading the mill with fuel with an increase in the drying agent consumption to the nominal consumption significantly worsened the CTE.
It can be concluded that the inclusion of a dust system in operation negatively affects the CTE, increasing mechanical underburning and reducing the mass concentration of NO.
The pre-firebox of the TPP-210A boiler body is equipped with six scroll-blade dust and gas burners with a thermal power of 70 MW, installed in one tier on the front and rear walls, and two above-floor gas-oil burners to ensure stable liquid slag removal throughout the entire range of boiler operating loads.
When burning coal dust AS, natural gas was supplied at a constant flow rate (about 5% of the total heat release) to the above-floor burners and variable flow through the main dust and gas burners to stabilize the combustion process of pulverized coal fuel. Gas was supplied to each main burner at the minimum possible flow rate, corresponding to 1.0 - 1.5% of the total heat release. Therefore, changing the share of natural gas for flare illumination 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.
Consecutive 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. Serial connection 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. Changes in combustion mode indicators when turning on gas burners
table 2
Changes in the content of combustibles in entrainment during process switching of equipment

Equipment	Mode work
		decrease	increase
Extreme/middle dust system
Emasculation ShBM	Emergency
Raw feeder
Main gas burner	Shutdown
	Inclusion

An approximate assessment of the influence of proven technological switching of boiler equipment on the change in CTE (Kun) is summarized in Table. 2.
Analysis of the data presented shows that the greatest decrease in the efficiency of a boiler installation in stationary modes occurs as a result of starting operations of the dust system and with an excessive consumption of natural gas for flare illumination.
It should be noted that the need to perform start-up operations of the dust system is determined solely by technological reasons, and the excessive consumption of natural gas for flare illumination is, as a rule, established by operating personnel in order to prevent possible violations stability of the combustion process in the event of a sudden deterioration in the quality of AS.
The use of RCA-2000 analyzers allows for continuous changes in a timely manner
evaluate any changes in fuel quality and constantly maintain the flame illumination value at the appropriate level optimal level with the minimum required consumption of natural gas, which helps reduce the consumption of scarce gaseous fuel and increase the efficiency of the boiler.

conclusions

1. The system for continuous measurement of the combustible content in the entrainment allows for quick and high-quality assessment of the progress of combustion processes when burning ash in the TPP-210A boiler, which is recommended for use during commissioning and research work, as well as for systematic monitoring of the efficiency of boiler equipment.
2. The effectiveness of using RCA-2000 analyzers for optimizing combustion conditions is approximately 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%.
3. In stationary boiler modes, standard technological switching of equipment affects the quality of the combustion process. Start-up operations of the dust system and excessive consumption of natural gas to illuminate the pulverized coal torch significantly reduce the efficiency of the boiler installation.

Bibliography

1. Madoyan A. A., Baltyan V. N., Grechany A. N. Efficient combustion of low-grade coals in energy boilers. M.: Energoatomizdat, 1991.
2. Using the RCA-2000 combustible content analyzer and the Mars-5 gas analyzer to optimize the combustion mode of the TPP-210A pulverized coal boiler at Tripolskaya TPP/ Golyshev L.V., Kotelnikov N.I., Sidenko A.P. et al. - Tr. Kyiv Polytechnic Institute. Energy: economics, technology, ecology, 2001, No. 1.
3. 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.

Doctor of Technical Sciences G.I. Levchenko, Ph.D. Yu.S. Novikov, Ph.D. P.N. Fedotov, chemical sciences L.M. Khristich, Ph.D. A.M. Kopeliovich, Ph.D. Yu.I. Shapovalov, JSC TKZ "Krasny Kotelshchik"

Magazine "Heat Supply News", No. 12, (28), December, 2002, pp. 25 - 28, www.ntsn.ru

(based on a report at the seminar “New Combustion Technologies solid fuel: their current state and future use”, VTI, Moscow)

IN last decades The domestic energy industry was largely focused on gas and oil fuel. Given the presence of huge deposits of solid fuel in the country, this state of affairs can hardly be justified for a long period.

In this regard, it should be recognized as natural that the “gas pause” is ending and there has been a reorientation towards a decisive expansion of the scale of use of hard coal, brown coal and peat.

A number of factors contribute to this, including:

A socially justified prospect for reviving the coal mining industry;

Decrease in the pace of development of gas fields and volumes of natural gas production;

Growth of its export needs.

A complex of financial and transport problems in the domestic and foreign markets for energy raw materials complicates the adoption of a long-term and sustainable strategy for fuel policy.

Under these conditions, TKZ OJSC has not weakened its attention to solid fuel issues over the years and continued to modernize its pulverized coal boilers, attracting the most authoritative forces of science (NPO TsKTI, VTI, ORGRES, etc.).

The developments covered all types of boilers produced by the plant over the past 20-30 years. The main goal of such modernization developments is to increase the environmental and economic performance of boiler plants, bringing them as close as possible to world standards. This made it possible to have a sufficient amount of technical developments prepared for implementation.

In these works, the following main areas can be distinguished, covering a wide range of fuel processing and combustion technologies:

1. Various modifications of staged combustion of solid fuel;

2. Creation of highly economical and environmentally friendly installations.

In these areas, the entire variety of Russian fuels is covered: hard and brown coals of the Kuznetsk, Kansk-Achinsk and Far Eastern basins, anthracite and its waste, peat, coal-water fuel.

Staged combustion of solid fuels

Currently, harmful emissions in flue gases of power plants are regulated by two state standards GOST 28269-89 – for boilers and GOST 50831-95 – for boiler installations.

The most stringent requirements apply to emissions from boiler plants burning pulverized coal fuel. To meet these standards when burning Kuznetsk coal with solid slag removal, either a gas purification installation or the implementation of all known means of NO X suppression is required.

Moreover, the possibility of reducing NO X emissions to these values ​​by technical measures for coals of the Kuznetsk basin has not yet been tested and requires confirmation on boilers with implemented measures.

Such a boiler, TKZ, together with Sibtekhenergo, was developed on the basis of the TPE-214 boiler and supplied to the Novosibirsk CHPP-5. On this boiler for coal grades “G” and “D” it is used multi-stage scheme combustion: horizontal and vertical gradation in the burner zone, as well as the creation of a reduction zone above the burners using natural gas as a reducing agent. The aerodynamics in the furnace, tested on the model, are organized in such a way as to avoid slagging of the screens in all operating modes of the boiler. The commissioning of the TPE-214 boiler at Novosibirsk CHPP-5 will allow us to gain experience in maximizing the possible reduction of NO X emissions during chamber combustion of coal with a high nitrogen content in the fuel.

For the combustion of low-reaction coals from Kuzbass (mixtures of “T” and “SS”), a modernized TP-87M boiler was developed and supplied to the Kemerovo State District Power Plant with the organization of three-stage coal combustion under conditions of liquid slag removal. The boiler uses high concentration dust transport PPPV, burners with reduced NO X output and special dust and gas burners are used to create a reduction zone above the main burners with minimal use of natural gas (3 - 5%). To burn lean Kuznetsk coal, TKZ, together with VTI, is reconstructing the TP-80 and TP-87 boilers, as well as the TPP-210A boilers at Mosenergo CHPP-22, which also use PPVK and three-stage combustion using natural gas as a reducing agent.

For coal in the Far Eastern region, a low-cost reconstruction project of the TPE-215 boiler was completed using two-stage combustion.

For the coals of the Kansk-Achinsk basin, the plant, together with CKTI and SibVTI, developed and supplied to the Krasnoyarsk CHPP-2 a boiler with a steam capacity of 670 t/h (TPE-216), which uses a three-stage combustion scheme using coal dust as a reducing agent, as well as special measures to protect the screens from slagging: supplying a fuel-lean mixture through the burner nozzles (GPHV) from the side of the furnace screens, air blast along the screens in the reduction zone and ensuring the gas temperature in the active combustion zone does not exceed 1250 °C due to the additional supply of 10% recirculation gases from secondary air.

The technological measures included in the project (organization of low-temperature combustion and increased content of calcium oxide in the ash) make it possible not only to ensure NO X emissions at the level of 220-300 mg/m 3, but also S0 2 emissions of no more than 400 mg/m 3.

For high-moisture peat, projects have been developed for the modernization of boilers TP-208 and TP-170-1 with the organization of two-stage combustion in them.

Staged combustion of fuel in its various modifications is universal remedy significant reduction in NO X emissions, but for some types of fuel with a high nitrogen content, the use of this method, even in combination with other intra-furnace measures, may not be sufficient to achieve the standard requirements for hard coal and furnaces with solid slag removal of 350 mg/m3. In this case, it is advisable to use the NO X suppression method with a sequential combination of three-stage combustion and selective non-catalytic reduction (SNCR) of NO X.

Creation of highly economical and environmentally friendly installations

Based many years of experience work on the creation and development of steam boilers at power plants for almost all types of fuel used in the energy sector, the plant has developed designs for new generation power plants that will make it possible to achieve a breakthrough in fundamental new level technical indicators of manufactured equipment.

Modernization of the TPP-210 boiler with the installation of a “shoulder” furnace

for combustion of low-reaction coal

Known difficulties in burning AS and increasing environmental requirements raise the question of further improving the combustion process of AS, in particular with the use of so-called “shoulder” furnaces with solid slag removal in which low-reaction, high-ash fuel is burned without illumination in the load range used in practice , ensuring long-term working company of the boiler.

Advantages of a “shoulder” furnace with solid slag removal compared to the technology used for burning ash in a furnace with liquid slag removal:

Allows the use of burner devices with low air mixture velocities, which increases the residence time of particles in the burner area, thereby creating favorable conditions to warm up particles and ignite them;

Long-term residence of particles in the zone is achieved high temperatures(at least 2 times higher than in a traditional firebox), which ensures satisfactory fuel burning;

Allows the most convenient introduction of air necessary for combustion as the torch develops;

Significantly less difficulties with slag removal;

Less losses due to mechanical burn;

Lower nitrogen oxide emissions.

For a “shoulder” firebox, a slot burner is used with a gap between the primary and secondary air jets, the main advantage of which compared to a vortex burner:

No premature mixing of primary air with secondary air, which has a beneficial effect on ignition; .

Supply of primary air in the amount necessary only for burning out volatiles;

A rational combination with a firebox that allows you to create a high rate of circulation of flue gases to the root of the torch (in the ignition zone).

A gas-tight “shoulder” firebox and TVP are installed on the modernized boiler in addition to the existing convective shaft, in the cut of which an economizer is installed.

Combustion of degraded anthracite pellets in a fluidized bed

Combustion is carried out using the technology of the Altai Polytechnic Institute, the main idea of ​​which is the preliminary granulation of a mixture of ground, original fuel, ash and limestone in order to bring the composition of the fluidized bed closer to a monodisperse mixture. OJSC TKZ "Krasny Kotelshchik" together with the author of the technology carried out a project to modernize one of the existing boilers TP-230 at Nesvetai State District Power Plant for pilot-industrial combustion of granular ash of poor quality in a fluidized bed.

Currently, at Nesvetai State District Power Plant it is planned to install a pilot industrial boiler D-220 t/h with a circulating fluidized bed, the general developer and supplier of which is Belenergomash OJSC. TKZ is a co-executor.

Power plant for complex processing, combustion in molten slag and use of low-reactive coal waste

The technology for starting direct-flow boilers differs from that because 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 remain for a certain time. These carry out a one-time forced circulation environment. Therefore, when kindling (and when operating 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 burners are ignited.

Under these conditions, the kindling mode is entirely determined by reliability, proper temperature conditions metal pipes of screens, screens, superheaters and the absence of unacceptable thermal-hydraulic inspections.

Experience and calculations have shown that cooling of heating surfaces when starting a direct-flow 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, according to reliability conditions, is ensured: 450-500 kg/(m2*s). The minimum pressure of the medium in the screens must be maintained close to the nominal one, i.e. for 14 MPa boilers - at the level of 12-13 MPa, and for supercritical pressure boilers - 24-25 MPa.

There are two main modes of firing once-through boilers: direct-flow and separator.

In direct-flow firing mode, the working medium moves through all heating surfaces of the boiler, just as when it is operating under load. During 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 plants).

The figures below show a simplified diagram of starting a boiler from a “cold” state in direct-flow mode:

Another figure below shows changes in feed water flow (1), steam pressure behind the boiler (2), medium temperature (3), fresh (4) and secondary (5) steam, as well as the metal temperature of the primary (7) and secondary screens (5) superheaters. As can be seen, at the beginning of the kindling, when the steam pressure reaches 4 MPa, the temperature of the medium and metal in the screens of the intermediate superheater sharply decreases from 400 to 300-250 ° C, which is explained by the opening of the ROU to discharge the medium into drainage system, and at the end of the kindling, when the pressure in the entire primary path is 23-24 MPa, the operating conditions of the screens of the primary and secondary superheaters, whose temperature exceeds 600 °C, also sharply deteriorate.

It is possible to avoid excessive increases in the temperature of the metal screens only by increasing the ignition water flow, and, consequently, increasing the losses of condensate and heat compared to the separator start-up mode. Considering this, as well as the fact that the direct-flow scheme for starting the boiler from a “cold” state does not have any advantages over the separator one, it is not currently used for starting.

Mode direct-flow start boiler from a “hot” and “uncooled” state creates the danger of a sharp cooling of the hottest components of the boiler and steam pipelines, as well as an unacceptable increase in the temperature of the superheater metal in non-flow mode with the BROU and ROU closed in the first firing period. All this makes it difficult to start from a “hot” state, which is why this mode was replaced by a separator starting circuit.

The only area of ​​application of the direct-flow start-up mode is the firing of a double-vessel boiler from a “cold” state and the start-up of a direct-flow boiler from a hot reserve after an idle period of up to 1 hour.

When starting a double-vessel boiler, both casings are heated alternately: asymmetrical boilers (for example, TPP-110) are heated starting from the casing, which does not have a secondary superheater. The bodies of symmetrical boilers are heated in a random sequence. The first body of both types of double-shell boilers is heated according to the separator mode. The kindling of the second body begins with a small electrical load of the block and is carried out according to any mode.

The boiler can be fired up after a short (up to 1 hour) stop using direct-flow mode, since the steam parameters still retain their operating values, and the individual elements and components of the boiler unit have not had time to cool significantly. In this case, the direct-flow mode should be preferred because it does not require special preparation, which would be required when switching to a separator circuit, which allows you to gain time and speed up the start-up of the boiler. In this case, kindling is carried out in a direct-flow mode with the discharge of the entire working medium through the ROU or BROU through the main steam valve (MSV) until the temperature of the primary and secondary steam exceeds the temperature of the turbine steam inlet by approximately 50 °C. If the steam temperature during the shutdown of the unit has dropped by less than 50 °C, the steam temperature behind the boiler is immediately increased to the nominal value, after which the steam supply is switched from the ROU to the turbine.

When starting a boiler in this way from a hot reserve, it should be taken into account that during a short-term stop of the boiler, the temperature of the medium at the inlet and outlet in many screen pipes equalizes and occurs natural circulation environment within individual panels and between panels. This circulation may be so persistent that it persists for some time after the feed pumps are resumed. As a result, it takes some time before the work environment begins to move steadily in the desired direction. Until the unstable movement of the medium stops, it is not recommended to start lighting the boiler unit in order to avoid damage to the heated pipes.

Compared to the direct-flow separator mode of boiler start-up, it is characterized by high stability, relatively low temperatures of the working medium and metal throughout the boiler path and allows the turbine to be started on sliding steam parameters. The screens of the boiler's intermediate superheater begin to cool at an early stage of start-up, and their metal does not overheat to unacceptable values. The 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 moisture separator is installed and which is turned on during the period of boiler firing between the steam generating (1) and steam superheating (3) surfaces of the boiler through throttling devices 5 and 6. Built-in valve 2 serves to disconnect the screens and the convective superheater from the steam-generating heating surfaces and is located between the output devices of the last section of the screen surfaces and the input collectors of the screen superheaters. During boiler firing, the main steam valve (4) remains open in the block unit and closed in the cross-linked TPP.

The ignition expander is an intermediate stage between the built-in separator and 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. Steam from the ignition expander is directed to the station's auxiliary manifold, from where it can be supplied to deaerators and other consumers, and water is discharged into the circulation water outlet channel, or into the reserve condensate tank, or (in block installations) directly into the condenser.

The idea of ​​a separator start-up of a direct-flow boiler unit is to divide the start-up process into three phases, so that in each of these sequentially conducted phases the reliability of all heating surfaces is fully ensured, and in the last phase it becomes possible to start up the power equipment of the unit on sliding steam parameters while maintaining steam-generating surfaces constant nominal pressure.

In the first phase of start-up, forced circulation of the working medium is organized in a closed circuit: feed pump - boiler - pilot unit - receiving devices for the discharge medium (in a block installation, turbine condenser) - feed pump. This eliminates the possibility of dangerous thermal-hydraulic drilling in steam-generating surfaces, and condensate and heat losses are minimized. During this start-up phase, the working medium has no access to the steam superheating surfaces, since they are cut off from the steam-generating surfaces by a built-in valve and throttle valve 17, closed during this start-up period, and are in the so-called flow-free mode. Despite the fact that the pipes of these surfaces in the non-flow mode are not cooled from the inside with steam, 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 consumption.

The safety of the non-flow mode for steam superheaters during the boiler startup period was confirmed by special tests of the TPP-110 and TPP-210 boilers. As you can see, at fuel consumption (natural gas) up to 20% of the nominal temperature, the walls of the most heated windshield pipes do not exceed the screens in a stationary state permissible temperature 600 °C. Considering that fuel consumption in the initial period of boiler start-up is significantly lower than 20% (for example, when a boiler operates on fuel oil, its consumption is not higher than 14-15% of the nominal), we can consider the consumption-free mode for steam superheaters quite acceptable during this firing period.

In connection with the experiments carried out, it is noted that in none of the startups of the tested boilers did the temperature of the pipe walls throughout the non-flow mode exceed 550 °C. This temperature is lower than the maximum permissible for low-alloy steel 12Х1МФ, usually used for the manufacture of stage I screen pipes, and even more so for austenitic steel 1Х18Н12Т, used for stage II screens in convective steam superheaters.

Turning off the superheaters in the first phase of start-up simplifies 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 start-up phase 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 startup 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 superheating surfaces. This mode is possible due to the fact that the steam 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 start-up, the boiler unit is switched to 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.

Upon completion of the heating of the boiler unit at a non-unit thermal power plant, 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 pressure behind the boiler and in the main steam pipeline at the time of connection.

In block installations, the boiler start-up is combined with the turbine start-up and the boiler is switched to direct-flow mode usually after the unit’s electrical load reaches 60-70% of the nominal value.

The figures below show the starting characteristics of a once-through boiler of a non-unit thermal power plant in separator mode: 1 - steam pressure behind the boiler; 2 - feed water consumption; 3 - Maximum temperature environment at the exit from the NRF; 4 - feedwater temperature; 5 - intermediate superheat temperature; 6 - fresh steam temperature; 8, 7 - maximum metal temperature of screens II and intermediate superheater; 9 - temperature of flue gases in the rotating chamber.

Features of kindling during a “hot” start are as follows. Before igniting the burners, the metal temperature of the built-in separators is reduced from 490 to 350-320 °C by releasing steam from the separators, and the rate of decrease should not be higher than 4 °C/min. At the same time, the pressure in the boiler decreases from nominal (25 MPa) to 10-15 MPa. 30-40 minutes after the separators are cooled down according to the same schedule as from the “uncooled” state, i.e. after establishing the minimum ignition flow rate of feed water, the pressure in front of the closed built-in valve increases to 24-25 MPa, the fuel oil burners are turned on with a starting flow rate fuel oil and at the same time the relief valves of 8 built-in separators open. Following this, the 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 firing, condensation of steam in the screens is eliminated, which therefore cool less than when starting in direct-flow mode.

The power unit with the TPP-210A boiler was emergency stopped protective devices due to malfunction of the feed pump. When the valve on the fuel oil line is automatically closed, the supply 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 increased circulation in the NRF panels, but also to the appearance in the upper bends of individual pipes of stationary bubbles of slightly superheated steam, which occupied the entire section of the pipes and prevented movement of the working environment in them. Although supercritical steam has the same density as water at the time of its formation, increasing its temperature by just a few degrees leads to a decrease in its density by tens of percent. As the speed of the water increased, bubbles of steam should have been carried away by its flow, but large bubbles could be temporarily delayed, due to which the temperature of the metal of the corresponding pipes should have increased sharply.

After a five-minute break, the boiler was switched to direct-flow mode, and contrary to the rules, feed water was not supplied first, 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 NRF pipes, a temperature increase 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 occurred in the pipe, which had a section in the burner embrasure area that was not protected by incendiary belts. The boiler was again emergency shutdown.

Another example concerns the deterioration of separation, which occurred when the relief valves that remove separated moisture from the built-in separator are not fully opened. When firing a direct-flow boiler, these valves were closed in order to reduce the temperature of fresh steam in the event of a malfunction of the injection desuperheaters. This control method is associated with sudden 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 flow.

Closing valves 8 and opening 5 must be done slowly to avoid the release of water into nearby superheater collectors due to disruption of the stable movement of the working medium in the separator. In addition, the drains before and after the throttle valve 5 should be opened in advance to prevent the release of condensate accumulated in the pipelines from the ignition unit.

Slow opening of the throttle valves 5 leads to an increase in the heating time of the main steam lines and the duration of the boiler firing. Of course, significant fluctuations in steam temperature are unacceptable, however, if the boiler is fired only a few times a year, there is no reason to further delay startup operations to prevent a slight decrease in steam temperature. But if the boiler is heated and stopped frequently, then even small splashes of water into the screens can have dangerous consequences. Therefore, when lighting once-through boilers, it is necessary to strictly adhere to the start-up schedule, which regulates the slow and gradual opening of valves 5.

A change in at from 1.12 to 1.26 leads to a decrease from 2.5 to 1.5% for the second fuel group. Therefore, to increase the reliability of the combustion chamber, the excess air at the outlet of the furnace should be maintained above 1.2.

In the table indicated In the 1-3 range of changes in the thermal stress of the combustion volume and grinding fineness /? 90 (Fig. 6-9, c, d), their influence on the value was not detected. It was also not possible to identify the influence of the ratio of the velocities of the secondary air and the dust-air mixture in the studied range of their changes on the efficiency of the furnace operation. However, with a decrease in air flow through the outer channel (at reduced loads) and a corresponding increase through the inner channel (at constant flow through the burner) the slag yield is improved. The slag jets become thinner and their number increases.

With uniform distribution of dust and air. on burners and at at > >1.15 there is no chemical underburning at the exit from the furnace.

The gross efficiency of the steam generator when burning coal (1/g "14%) and at rated load reaches 90.6%.

The work obtained similar results confirming that the TPP-210A steam generator operates economically and reliably also when burning ash (1/g = 3.5%; 0rts = 22.2 MJ/kg; L^ = 23.5%; =

With excess air in the furnace at = 1.26h-1.28, grinding fineness /?9o = ----6-^8%, in the load range D< = 0,7-^ 1,0£)н величина потери тепла с механическим недожогом достигает 3%. Максимальный к. п. д. брутто парогенератора при номинальной нагрузке составляет 89,5%.

The work provides data stating that when burning anthracite in the combustion chamber of the TPP-210A steam generator, the value of mechanical underburning<74 в условиях эксплуатации примерно в 1,5 ниже, чем при работе котлов ТПП-110 и ТПП-210 с двухъярусным расположе­нием вихревых горелок мощностью 35 МВт.

The studies carried out, as well as long-term pilot industrial operation of the TPP-210A steam generator, showed that in the range of load changes from 0.65 to the nominal load, the combustion chamber operates economically and stably, without dust separation and without disruption of the liquid slag removal regime.

The duration of the campaign (before major repairs) of the steam generator with dust and gas burners without their repair was 14,545 hours. At the same time, the condition of the burners was satisfactory; burning of brick embrasures, warping of gas pipes and nozzles is insignificant.

During inspections of the combustion chamber during shutdowns, no accumulation of slag on the hearth or slagging of the walls of the afterburning chamber was observed. The entire studded belt was covered with a smooth, shiny film of slag. The drift of convective heating surfaces was also not observed.

Disabling any one burner or two medium burners does not reduce the stability of ignition, does not affect the mode of liquid slag removal and does not lead to a violation of the temperature regime of the NRF and VRF.

LUNTER AS AN ENERGY RESOURCE. Let us immediately make a reservation that the use of native (bedding-free) manure to meet energy needs is much more expensive in comparison with bedding manure in terms of both capital and operational...

COMPREHENSIVE METHOD FOR DISPOSAL OF CHICKEN LUNTER WITH PRODUCTION OF ORGANO-MINERAL FERTILIZERS AND COMBUSTIBLE GAS, HEAT AND ELECTRIC ENERGY Manure is a strong pollutant of soil, water and air basins. At the same time, the litter...

The direct-flow steam boiler TPP-210A is considered as an object of regulation, the existing control systems are analyzed, its advantages and disadvantages are noted, a block diagram of the heat load regulator of the boiler TPP-210A on gaseous fuel is proposed using a regulating microprocessor controller Remikont R-130

Calculation of settings parameters and modeling of the process of regulating the thermal load of the TPP-210A boiler on gaseous fuel was carried out, including approximation of experimental data and modeling of the control object for a dual-circuit control system, calculation of setting parameters of dual-circuit control systems, as well as modeling of the transient process in dual-circuit systems regulation. A comparative analysis of the obtained transient characteristics was performed.

Excerpt from the text

In terms of automation level, thermal power engineering occupies one of the leading positions among other industries. Thermal power plants are characterized by the continuity of the processes occurring in them. Almost all operations at thermal power plants are mechanized and automated.

Automation of 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.: Publishing house. MPEI, 2005, - 355 p.

3. Pletnev T.P. Automation of technological processes and production in thermal power engineering. /MPEI. M, 2007. 320 p.

4. Small-channel multifunctional regulating microprocessor controller Remikont R-130″ Documentation set 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 pp. - ill.

6. Rotach V.Ya. Theory of automatic control of heat and power processes, - M.: MPEI, 2007. - 400 p.

7. Kozlov O.S. etc. Software package “Modeling in technical devices” (PC “MVTU”, version 3.7).

User's Manual. - M.: MSTU im. Bauman, 2008.