Schematic diagram of the tap 210 boiler. Start-up of once-through boiler units
Changing am 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, it is necessary to maintain an excess of air at the outlet of the furnace more than 1.2.
In the table. 1-3 in the range of changes in the thermal stress of the furnace volume and fineness of grinding /? 90 (Fig. 6-9, c, d), their influence on the value was not found. It was also not possible to reveal the influence of the ratio of the velocities of the secondary air and the dust-air mixture in the studied range of their change 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 in air through the inner channel (at a constant flow through the burner), the slag output improves. The jets of slag become thinner and their number increases.
With uniform distribution of dust and air. there is no chemical underburning at the furnace outlet at the burners and at at > 1.15.
The gross efficiency of the steam generator when burning coal (1/g "14%) and at rated load reaches 90.6%.
Similar results were obtained in the work, confirming that the TPP-210A steam generator operates economically and reliably also when burning AS (1/g = 3.5%; 0pc = 22.2 MJ/kg;
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 paper presents data stating that when anthracite is burned 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 conducted studies, as well as long-term pilot operation of the TPP-210A steam generator, showed that in the range of load changes from 0.65 to the nominal value, the combustion chamber operates economically and stably, without dust separation and without violations of the liquid slag removal regime.
The duration of the campaign (before the overhaul) of the steam generator with dust-gas burners without their repair was 14545 hours. At the same time, the condition of the burners was satisfactory; burning of the brick embrasures, warping of gas pipes and nozzles is insignificant.
When inspecting the combustion chamber during shutdowns, no accumulation of slag on the hearth and slagging of the walls of the afterburning chamber were observed. The entire studded belt was covered with a smooth, shiny film of slag. The drift of convective heating surfaces was also not observed.
Turning off any one burner or two medium burners does not reduce the stability of ignition, does not affect the mode of liquid ash removal and does not lead to a violation of the temperature regime of the LRC and TRC.
Litter AS ENERGY RESOURCE. Let's make a reservation right away that the use of native (without litter) manure to meet energy needs is much more expensive in comparison with bedding manure in terms of both capital and operational ...
COMPLEX METHOD OF UTILIZATION OF CHICKEN MANURE WITH OBTAINING ORGANOMINERAL FERTILIZERS AND COMBUSTIBLE GAS, THERMAL AND ELECTRIC ENERGY Manure is a strong pollutant of soil, water and air basins. At the same time, litter…
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 blocks.
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 the 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. With a change in the amount of combustion products in the right and left convective shaft 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 ratio of "feed water-fuel" 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. 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 by 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 gas duct, 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 duct, 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 thermal power engineering 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 (they are often called “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, steam boilers Ep-690-15.4-540 LT are installed, designed to operate on low-calorie Indian lignites. These are drum boilers with natural circulation, subcritical pressure with reheating, single-casing, 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.
Brief description of the boiler unit "Direct-flow boiler type TPP-210"
Brief description of the boiler unit Once-through boiler type TPP-210 (p / p 950-235 GOST 3619-59 model TKZ TPP-210) with a steam capacity of 950 tons per hour for supercritical steam parameters was designed and manufactured by the Taganrog plant "Krasny Kotelshchik". The boiler unit is designed to operate in a unit with a K-300-240 condensing turbine with a capacity of 300 MW, manufactured by KhTGZ. The boiler is designed for burning anthracite sludge with liquid ash removal and natural gas from the Shebelinsky deposit. The boiler unit is made of two-case with a U-shaped layout of each case and regenerative air heaters removed from under the boiler, located outside the boiler house building. Boiler shells of the same design with a capacity of 475 t/h of steam each. The hulls can work independently of each other. General data on the boiler: Productivity 475 t/h Superheated steam temperature: primary 565 °C Secondary 565 °C Secondary steam consumption 400 t/h Primary steam pressure behind the boiler 255 kg/cm² Secondary steam pressure at the boiler inlet 39.5 kg/ cm² Secondary steam pressure at the boiler outlet 37 kg/cm² Secondary steam temperature at the inlet 307 °C Feed water temperature 260 °C Hot air temperature 364 °C Total weight of the boiler metal 3438 t Boiler width along the column axes 12 m Boiler depth along the column axes 19 m Height of the boiler 47 m Water volume of the boiler unit in the cold state 243 m³ Dimensions of the furnace in plan (along the axes of the pipes): primary and secondary steam at the outlet is reduced to 545 °C) The boiler is served by two axial smoke exhausters, two blowers with two-speed motors and two hot blast fans. Scheme of dust preparation with a bunker and transportation of dust to the burners by hot air. The boiler is equipped with three drum ball mills ShBM-50 with a capacity of 50 tons of dust per hour. Heating surfaces: Furnace screens 1317 m² Including: NRCh 737 m² THR 747 m² Reversing chamber screens and ceiling 1674 m² Superheater SVD: including: Steam heat exchanger 800 m² Intermediate convective package 1994 m² Air heater 78730 m² Outlet convection package 1205 m² Convective economizer 1994 m²
In each boiler body there are two streams (in the description of the boiler and in the instructions, the stream is called a thread). Since the hull design is similar, the scheme and design of one hull will be described in the future. Feed water with a temperature of 260 °C passes through the power unit and enters the inlet chambers of the Sh325*50 water economizer, which are also the extreme support beams of the package. After passing through the coils of the water economizer, water with a temperature of 302 ° C enters the outlet chambers Ш235*50, which are the middle support beams of this surface. After the water economizer, water is directed by bypass pipes Ш159*16 to the middle support beams of this surface through pipes Ш133*15 to the lower part (НРЧ). NRC screens consist of separate panels, and the hearth heating surfaces make up one-piece multi-pass tapes with the front and rear. Water supply to the panels is carried out through the lower chamber, and drainage from the upper one. This arrangement of the inlet and outlet chambers improves the hydraulic performance of the panel. The flow diagram of the medium through the NRC screens is as follows: First, the medium enters the rear screen panels and the rear panels of the side screen, then it is directed to the front screen and the front panels of the side screens by bypass pipes Ш 135*15. Washers Ш30 mm are installed on bypass pipes to improve hydrodynamics. After LFC, the medium with a temperature of 393 °C is sent by pipes Ш133*15 to the vertical collector Ш273*45, and from there it enters the side and front screens of the upper radiation part (RTC) via bypass pipes Ш133*15. The relative position of the inlet and outlet chambers of the TRC panels is similar to that of the RRC panels. Having passed the multi-pass panels of the front and side screens of the TCG, the steam is directed by bypass pipes Ш133*15 to the vertical mixing manifold Ш325*45, and from there it enters the N-shaped panels of the rear screen of the TRC through pipes Ш159*16.
Having passed the multi-pass panels of the front and side screens of the TRC, the steam is directed by bypass pipes Ш133*15 to the vertical mixing manifold Ш325*45, and after heating up to 440 °C in the radiant surfaces of the furnace, steam is directed to the panels of shielding side and rear walls of the rotary cameras. Having passed the screens of the reversing chamber, the steam enters through tubes into 1 injection desuperheater Ш279*36. In 1 injection desuperheater, flows are transferred across the width of the flue. After the desuperheater, steam is supplied to the ceiling superheater by pipes Ш159*16. In the ceiling superheater, steam moves from the rear wall of the flue to the front of the boiler and enters the outlet chambers of the ceiling Ш273*45 with a temperature of 463 °C. On the steam pipelines Ш273*39, which are a continuation of the outlet chambers of the ceiling superheater, valves (VZ) DU-225 built into the tract are installed. After the ceiling superheater, flows are transferred across the width of the gas duct, and the steam is directed through pipes Ш159*18 to the inlet screens of the first stage of the screen superheater, located in the middle part of the gas duct. Having passed the inlet screens, steam with a temperature of 502 °C enters the second injection desuperheater Ш325*50, after which it is directed to the outlet screens of the first stage, located along the edges of the flue. The steam receiving chamber of the inlet screens and the steam line of the second desuperheater carry out the transfer of flows along the width of the flue. Before the second injection, there is a steam pipeline Ш194*30 for removing part of the HPS steam to the gas-steam heat exchanger, and after the injection, there is a steam pipeline for returning this steam. The second injection desuperheater has a retaining washer. Behind the outlet screens of the first stage, there is a third injection desuperheater Ш325*50, the steam pipeline of which transfers flows along the width of the gas duct. The steam is then directed to the middle parts of the flue and, having passed them, is transferred by the steam pipeline Ш325*60 with a temperature of 514 °C along the width of the gas flue to the outlet screens of the second stage, located along the edges of the gas flue. After the outlet screens of the second stage, steam with a temperature of 523 °C enters the fourth injection desuperheater Ш325*60. Both inlet and outlet screens of both stages of the screen superheater have a co-current scheme of mutual movement of the steam and gases. After the desuperheater, steam with a temperature of 537 °C through the steam pipeline Ш237 * 50 enters the convective package, which is made according to the co-current scheme, passes through it with a temperature of 545 °C and is fed to the turbine. Starting from the inlet chambers of the water economizer, all bypass pipes and chambers of the SVD tract are made of 12Kh1MF steel. After the HPC of the turbine, steam with a pressure of 39.5 atm. The temperature of 307 °C is sent to the intermediate superheater in two streams. One “cold” line of low-pressure steam approaches the body; they split in two before the reheater. In the reheater of each housing there are two low-pressure steam flows with independent temperature control along the threads. Boiler design The walls of the combustion chamber are completely shielded by pipes of radiant heating surfaces. The combustion chamber of each body is divided by pinches formed by the protrusions of the front and rear screens into the combustion chamber (pre-furnace) and the afterburner. Screens in the pre-furnace area up to el. 15.00 fully studded and covered with chromite mass. Insulation of the combustion chamber and pinch in the furnace reduces the heat transfer of radiation from the core of the torch, which increases the temperature level in the pre-furnace and, consequently, improves the conditions for ignition and combustion of the fuel, and also contributes to a better formation of liquid slag. The combustion process of AS occurs mainly in the pre-furnace, however, combustion continues in the afterburner, where mechanical underburning decreases from 7.5-10% to 2.5%. In the same place, the temperature of the gases decreases to 1210 °C, which ensures the operation of the heating surfaces, the SVD superheater without slagging. The thermal stress of the entire furnace volume is Vт=142*103 kcal m 3 /hour, and the pre-furnace Vтп=491*103 kcal mі/hour.
The furnace of each of the two buildings is equipped with 12 dust-gas turbulent burners arranged in two tiers (three burners in each tier of the front and rear walls of the furnace). The gas supply to the burners is peripheral, the performance of the burner on dust is 0.5 t/h. Each turbulent burner has a built-in mechanical atomization oil nozzle with cooling and an organized air supply. To remove liquid slag, the pre-furnace has two cooled tapholes; the pre-furnace is made with a slope of 80 to the tapholes and is closed with fireclay bricks. Each furnace is equipped with two (according to the number of notches) mechanized slag removal units. Liquid slag is granulated in water baths and removed into slag-washing channels. The drying agent is discharged through rectangular burners, which are located on the side walls of the pre-furnace in two tiers: there are 4 burners in the lower tier, and 2 in the upper tier. There are manholes in the furnace for repair work. The firebox is shielded in the lower part up to 23.00 m by pipes of the lower radiation part (LRC), and in the upper part - by pipes of the upper radiation part (RTC) from the ceiling. The pipes of the rear and front screens of the NRCH have bends, which form the furnace pinch. The rear screen of the TRC in the upper part has a protrusion, which improves the aerodynamics of the gas flow at the outlet of the furnace and partially protects the screen surfaces from direct radiation from the furnace. The front and rear screens of the NRCH are structurally identical, each screen consists of six identical tapes, with pipes connected in parallel Sh42 * 6 material 12X1MF. The tape pipes are first screened under and the lower part of the pre-furnace, and then they pass to the vertical panel of the NRCH, where they make five lifting and lowering passages and exit into the upper chamber. The NRCH pipes are wired for the loopholes of burners, manholes, peepers. The side screens of the NRC consist of four panels, which are made as follows.
Leaving the lower chamber, the tape, consisting of 17 parallel-connected coils Ш42*5, material 12Х1МФ, first shields the lower part of the side wall, then moves to the vertical part, where it also makes five lifting and lowering moves, and then exits into the upper chamber. The front and rear screens of the NFC have two tiers of fixed mounts at the level of 22.00 and 14.5 m. Compensation from temperature expansion occurs due to the bending of the pipes at the pinch. The side screens are suspended by fixed mounts at 21.9 m and can be freely lowered. To prevent the exit of individual pipes into the furnace, the screens have five belts of movable fasteners. The front and rear screens of the TCG also consist of multi-pass panels with lifting and lowering steam movements. Steam is supplied to the lower chamber of the panels, removed from the upper ones. The middle panels of the front screen and all panels of the side screens consist of eight, and the extreme panels of the front screen of nine pipes connected in parallel, forming a tape. N - shaped panel of the rear screen of the TCG consists of twenty pipes connected in parallel. All heating surfaces of the VRC are made of pipes Ш42*5, material 12Х1МФ. The front and side screens of the TCG are fixedly suspended at the level of 39.975 m and expand freely downwards. The rear TCG screen has two fixed mounts at 8.2 and 32.6. Compensation for thermal expansion of the pipes occurs due to the bending of the pipes in the upper part of the rear screen of the TCG. The front and side screens have seven rows of movable mounts, the rear - three. All NRC and TRC screens have a pitch between pipes of 45 mm. The ceiling of the furnace and the top of the horizontal flue are shielded by pipes of the ceiling superheater. In total, there are 304 pipes connected in parallel (154 per thread) Ш32*4, material 12Х1МФ. Along the length of the pipes of the ceiling superheater there are 8 rows of fasteners, which are attached to the frame with rods.
Screen superheaters At the outlet of the furnace there is a screen superheater, which consists of two rows of screens. In a row of 16 screens with a pitch of 630 mm, suspended vertically. In the course of the steam, the screens of each stage are divided into inlet and outlet, which are located closer to the side walls of the gas duct. Structurally, the inlet and outlet screens of the first stage are identical (except for the location of fittings and bypass pipes on the chambers). The screen of the first stage of the boiler 20 consists of 42 coils Ш32*6, the pipe material is mainly 12Х1МФ, but for 11 extreme coils the outlet section is made by pipes Ш32*6, material 1Х18Н12Т. On the boiler, 19 screens of the first stage consist of 37 coils, material 1X18H12T. To give rigidity to the structure, the screen is connected by its 5 coils, which have fastening strips made of X20H14S2 steel. Screens of the second stage consist of 45 coils Ш32*6. The material of the entrance screens is 12Kh1MF, and the rest of the coils are made of steel 1Kh18N12T. The screen is connected by its six coils. The inlet and outlet chambers, except for the chambers of the second stage outlet screens, are joined into single manifolds separated by a partition. The chambers on rods are suspended from the frame beams. The walls of the turning chamber are shielded by four blocks. The blocks are made in the form of two-loop tapes. In each block there are 38 parallel-connected coils Ш32*6 material 12Х1МФ, which are located horizontally. Blocks have stiffening belts. The suspension of the blocks is carried out by means of three rows (per block) of fasteners. The following heating surfaces are located in the downcomer gas duct: a convective SVD stack, an LP superheater with a gas-steam heat exchanger, and a water economizer. For all convective surfaces, a staggered arrangement of coils is adopted. All surfaces are made of coils parallel to the front of the boiler.
Convective superheater SVD
The package of the SVD convective superheater of each line consists of 129 coils Ш32*6, material 1Х18Н12Т, which are based on racks made of Х23Н13 material, and those on support beams cooled by feed water. There are three rows of spacer strips made of 1X18H12T steel to withstand steps and make the structure more rigid; the package has a height of 557 mm. Low-pressure superheater The LP superheater is located behind the convective package of the SVD. The packages of each flow are located in the corresponding halves of the downcomer, the transfer of flows across the width of the flue is not carried out. The LP superheater consists of an output package, an intermediate package and a control stage. The output part of the LP superheater consists of 108 suspended coils Sh42*3.5, the material of combined steel: Kh2MFSR and 12Kh1MF. The coils are assembled in packages with racks, X17H2 material, which are suspended from the support manifolds of the high-pressure package. Package height 880 mm. The intermediate package also consists of 108 double coils Ш42*3.5 double coils Ш42*3.5 material 12Х1МФ. Package height 1560 mm. The coils are based on racks, material Kh17N2, and those on the inlet chambers of the intermediate package Sh325 * 50, material 12Kh1MF. Thus, the inlet chambers of the industrial package are also support beams for this heating surface. The chambers, in addition to insulation, have additional air cooling required during start-up modes and when the turbine is turned off. Behind the industrial package along the gas flow, on both bodies of the TPP-210 boilers, instead of the GPP TO, a control stage is installed, which is the first stage of the reheater along the steam flow, is made of pearlite steel and, according to the conditions of reliable operation of the pipes with significant devaporization, is located in the zone where the temperature of the gases is at inlet must not exceed 600°C. Its work is completely based on changing the heat absorption of the secondary steam by changing its distribution through the bypass steam pipelines. According to calculations, at the rated load of the unit, 20% of the total steam flow passes through the control stage. When the load of the unit is reduced to 70%, the steam consumption is 88%. The increase in the efficiency of the power unit is achieved by expanding the range of loads at which the design temperature of the secondary superheat is ensured with optimal excess air. The control surface is installed in the dimensions of the dismantled GPP TO, the input manifolds are lowered 300 mm lower. The control surface consists of left and right parts with a total heating surface of 2020 m² per body. Both parts are assembled from packages of twin coils and have 4 loops along the gas flow with a countercurrent steam flow pattern. The coils are made of pipes Sh32*4, steel 12Kh1MF and are arranged in a checkerboard pattern with steps of 110 and 30 mm. The coils are assembled into packages using stamped racks made of steel 12X13. 5 racks are installed along the length of each package. Two of them are installed on water-cooled collectors located in the gas duct, which are lowered 290 mm during the repair. The steam from the HPC enters the inlet chambers of the control surface Sh425*20 steel 20. Having passed the coils, the steam enters the outlet chambers with a diameter of 426*20 steel 12Kh1MF, where it mixes with the steam coming from the bypass steam pipeline. The old RKT valves were cut out along the lines "B" and "C" from the old RKT, the internal parts were taken out and the RKT bodies were scalded and used as tees. On the bypass line between the inlet and outlet manifolds, new RKT gate valves are installed. When the valve is opened to 100%, steam in the amount of 80% goes past the control surface and the p / p decreases. When the valve is closed, the steam passes through the control surface and the reheat temperature rises. KDU and control keys of the new RKT remained the same. The water economizer coils on both hulls have been replaced (100%). Retaining washers were dismantled on the manifolds of the second injection and the outlets to the GPP TO were turned off. The convective economizer is the last heating surface in the gas flow, located in the downcomer. It consists of pipes Ш32*6, material st20. The outlet and inlet chambers of the economizer are also supporting beams - the weight of this heating surface is transferred to them through the racks. The frame of the boiler is made in the form of identical frames of both buildings, interconnected by inter-hull connections and transitional scaffolds. The weight of the heating surface, lining and insulation is transferred with the help of horizontal beams and trusses to three rows of vertical columns, one row along the front of the boiler, the other between the furnace and the downcomers and the third one at the back of the boiler. To stiffen the frame, there are a number of inclined beams. Furnace lining, boiler gas ducts are made in the form of separate shields. The furnace and flues are sheathed with sheets 3 mm thick, which ensures a high density of the furnace and flues.
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 BROW and DHW 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, the boiler start-up 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 the 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 sequentially 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 block on sliding steam parameters while maintaining in steam-generating surfaces constant nominal pressure.
In the first phase of the start-up, forced circulation of the working medium is organized along 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, which is usually used for the manufacture of tubes for 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 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 steam temperature and pressure. 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, an increase in temperature up to 570 °C was recorded in the unheated outlet section of one of the NRCH pipes. 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.
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 block 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.
