Great attention is paid to the safe operation of steam boilers.
As a result of the replacement of obsolete structures (vertical-cylindrical, heat-turbine, etc.), the accident rate of steam boilers has recently decreased sharply. However, accidents have not yet been completely eliminated, especially due to loss of water. In some cases, the loss of water led to explosions of steam boilers with the destruction of the boiler room and human casualties.
In recent years, due to the equipping of steam boilers with a nominal steam output of 0.7 t/h or more with automatically operating sound alarms for the upper and lower limit positions of water levels, water loss accidents on such boilers have sharply decreased. Water leaks occurred only on boilers that did not have alarms or, due to poor maintenance, were faulty and inactive at the time of the accident.
In some cases, the consequences of the accident were aggravated by the incorrect actions of the maintenance personnel who recharged the boiler after detecting a water leak in violation of the requirements of the “Standard Instructions for Boiler House Personnel” approved by the USSR State Mining and Technical Supervision on July 12, 1979.
Analysis of accidents of steam boilers that do not have automatic power regulators installed shows that accidents due to water loss occur mainly as a result of weakening of personnel’s attention, mainly in the evening and at night. Thus, in the period from 0 to 8 a.m. the number of accidents reaches 50%, from 8 to 16 a.m. - up to 20%, and from 4 to 24 p.m. - up to 30%.
As a result of violations of personnel's production discipline, about 80% of accidents occur due to loss of water.
Loss of water in a steam boiler can occur not only due to the fault of personnel who did not refuel the boiler in a timely manner, but also due to technical malfunctions of water indicating devices, purge and feed fittings, feed devices, insufficient productivity and pressure of feed devices, rupture of the screen, boiler or economizer pipe. Let's give a few examples.
At the thermal power plant, due to a deep loss of water, an accident occurred in the TGME-454 boiler with a capacity of 500 t/h (pressure in the drum "16.2 MPa). In this case, four screen pipes ruptured, fistulas appeared in two pipes, the entire screen system was deformed with amplitude up to 250 mm (gas-tight firebox).
Material damage from the accident amounted to about 200 thousand rubles. The investigation established that the cause of the accident was: operation of the boiler with the automatic safety system turned off (cutting off the fuel supply to the boiler when the water level drops below the permissible level), incorrect actions of the boiler operator in an emergency situation.
At the thermal power plant, due to a deep loss of water, an accident occurred in the TP-35 steam boiler with a capacity of 45 t/h (pressure in the drum 3.9 MPa). In this case, two screen pipes ruptured, 40% of the screen pipes were deformed. Material damage from the accident amounted to 10 thousand rubles.
Causes of the accident: operation of the boiler with gas supply to the burners through the bypass line, excluding automatic shutdown of fuel when water is lost. The boiler operator intervened in the operation of the automatic regulation by influencing the control key of the supply control valve, and manually closed the valve on the boiler water supply unit when the water level was at an emergency low. The boiler began manual feeding, thereby violating the requirements of the job description and instructions for the prevention and elimination of accidents. Due to changes in the operating mode of the boiler, the shift manager of the thermal power plant did not ensure that his subordinate personnel complied with the requirements of production instructions, and did not take measures to emergency stop the boiler. There was an unsatisfactory state of production discipline among maintenance personnel and engineering personnel, expressed in failure to comply with the requirements of current safety rules and instructions.
In the third case, in the boiler room, due to a deep loss of water, an accident occurred with the steam boiler DKVR-2.5/13. As a result of the accident, the boiler screen and boiler pipes were damaged.
Causes of the accident: the driver left the boiler running without supervision; the boiler was operating with faulty safety automatics; maintenance personnel violated production instructions.
In the boiler room, due to a deep loss of water, an accident occurred with the steam boiler DKVR-10/13. As a result of the accident, the boiler screen and boiler pipes were damaged and the rolling connections were damaged. Damaged pipes have also been completely replaced.
Causes of the accident: incorrect actions of the driver who purged the boiler without proper control over the water level in the upper drum of the boiler; faulty state of automatic safety and alarm systems for water loss from the boiler; acceptance of a shift by a senior driver without checking the status and automatic safety; admission to servicing steam boilers of personnel who have not passed the test of knowledge of current safety rules and production instructions.
To prevent water loss in steam boilers, it is necessary:
Do not allow persons to service boilers who have not completed training in the scope of the relevant program and do not have a certificate from a qualified commission for the right to service the boiler;
Do not allow the operation of boilers with faulty water indicator, purge and feed fittings, as well as automatic safety systems that ensure normal operation of the boiler from the monitoring and control panel;
Check the serviceability of all feed pumps by briefly putting them into operation (for boilers with an operating pressure of up to 2.4 MPa within the time limits established by the production instructions, check water indicators by blowing out for boilers with an operating pressure of up to 2.4 MPa at least once per shift, for boilers with operating pressure from 2.4 to 3.9 MPa - at least once a day, and over 3.9 MPa - within the time limits established by the instructions);
Prohibit leaving the boiler during operation without constant supervision by personnel and prohibit the operator from performing any other duties not provided for in the instructions.
UDC 614.8.084
Destructions and industrial injuries
during explosions of steam boilers.
Causes of steam boiler explosions and their prevention
GOUVPO "Moscow State University of Service"
Moscow
A comparative analysis of hot water boilers used in technological processes of a number of service enterprises was carried out. In particular, for autonomous provision of dry cleaning plants and laundries.
During an explosion, a physical or chemical change occurs in a substance, accompanied by the instantaneous release of a large amount of energy.
When a steam boiler explodes, the pressure in it drops sharply and the water instantly evaporates. The volume occupied by this steam will be 700 times the volume of water.
In all cases of steam boiler accidents, the consequences are:
§ collapse of building structures;
§ destruction outside buildings;
Parts of the boiler scatter over a distance of up to 300-400 m, causing destruction beyond the territory of the enterprise.
If steam boilers are operated incorrectly, the causes of explosions are: insufficient amount of water, a large layer of scale on the walls, exceeding the design pressure.
If there is not enough water in the boiler (water is lost), the walls overheat, since the heat of hot gases, designed to heat and evaporate the water, is not removed.
As a result, the mechanical strength of the metal of the boiler walls decreases, and bulges are formed. With a further increase in pressure in the boiler, cracks appear at the bulges and the boiler explodes.
The desire to replenish lost water in the boiler by immediately supplying it only accelerates the explosion of the boiler, since water, falling on the overheated walls, instantly evaporates and a pressure exceeding the design pressure arises in the boiler.
The deposition of scale on the internal walls of the boiler from water and due to untimely cleaning also leads to overheating of the boiler walls and a decrease in its strength.
In addition, explosions are possible due to defects in metal, welding and rivet seams; changes in the structure of the metal walls during operation (temperature changes, chemical effects of water and steam); violation of metal strength due to incorrect boiler manufacturing technology.
In order to avoid accidents of steam boilers, their installation, inspection and operation must be carried out in accordance with the rules of Rostechnadzor “Rules for the design and safe operation of pressure vessels”, PB - 10 - 115 - 06. These rules apply to stationary and mobile steam boilers and steam heaters water economizers with operating pressure above 0.7 MPa, as well as for water heating boilers with water heating temperatures above 115°C.
The nominal thickness of the drum wall is taken to be at least 6 mm, with the exception of boilers with a steam capacity of no more than 0.7 t/h at an operating pressure of no more than 5 MPa, for which the nominal wall thickness is taken to be at least 4 mm.
Rice. 1. Diagram of installation of control and measuring instruments on a steam boiler:
VUV – highest water level; NUV – lowest water level; 1 – direct action water indicating devices; 2 – thermometer; 3 – thermocouple; 4 – pressure gauge; 5 – safety valve.
It should be borne in mind that as the temperature of the boiler wall increases, the rated permissible stress is reduced.
For the manufacture of steam boilers, carbon or alloy steel (sheets, pipes) is used.
Devices that indicate the water level in the boiler, steam pressure and temperature of water and steam are installed on the steam boiler. Constant control of the water level is carried out by at least two direct-acting water indicating devices (see Fig. 1).
The water indicator device has a protective device to avoid damage from glass breakage.
Boilers are also equipped with a device that automatically gives a sound or light alarm about maximum water levels.
Automatic level gauges are structurally divided into float, electromagnetic and ionization.
A safety plug made of a low-melting lead-tin alloy is installed in the boiler wall from the furnace ceiling side. If there is a lack of water in the boiler, the upper part of the boiler (palatal) stops cooling, and then the plug, heated by the flue gases, melts. Steam will begin to escape into the resulting hole and extinguish the fire in the firebox. The resulting noise will also be a signal that water has been lost in the boiler.
To ensure uninterrupted supply of water to the boiler, two pumps are installed, one of which is a backup. The drive of these pumps must be separate in terms of the energy used (for example, one with an electric drive and the other with a steam drive).
Thermometers or thermocouples for measuring water temperature are installed on the supply pipeline and for steam - at its outlet from the boiler. The pressure gauge monitors the actual steam pressure in the boiler, superheater or economizer. The maximum operating pressure allowed by this boiler is indicated on the pressure gauge scale with a red line.
The operation of pressure gauges is carried out in accordance with established rules and a schedule for their periodic inspection, during which they are sealed. In the absence of a seal, malfunctions in the mechanism, or non-compliance with inspection deadlines, pressure gauges are not allowed to be used.
If the operating pressure in the boiler is exceeded, the safety valve comes into action. On boilers with a capacity of over 100 kg/h, two safety valves are installed, communicating with the steam space of the boiler. One of them is a control one, notifying with a signal about the maximum pressure in the boiler, and the other automatically releases excess steam.
Table 1
Pressure in hot water boilers
|
Nominal excess pressure, MPa |
Pressure at the beginning of opening of safety valves |
|
|
Control valve |
Working valve |
|
|
From 60 to 140 |
Рр +0.2 MPa |
Рр +0.3 MPa |
Note, Рр – working pressure.
Safety valves are designed to protect boilers from exceeding the design pressure by more than 10%. By design, safety valves are divided into spring, lever and pulse. Safety valves on steam boilers are regulated to a pressure not exceeding the values given in table. 1. When fully opened, the safety valve must allow steam to pass through for a pressure of 0.7 to 120 MPa.
Steam boilers with chamber combustion of fuel are equipped with an automatic device that stops the supply of fuel to the burners when the water level drops below the permissible limit (ALL) (see Fig. 1). Boilers operating on gaseous fuel have an automatic device that stops the supply of gas to the burners when the air pressure drops below the permissible level.
Before putting into operation, the installed steam boiler is presented to Rostechnadzor for registration. In this case, technical documentation for the boiler, boiler room, a certificate of quality of installation of the boiler and laboratory analysis of the water used to feed it are presented.
Technical inspection of a steam boiler, carried out by Rostechnadzor, is aimed at establishing the safety of its operation. It is carried out before the boiler is put into operation, periodically during operation and ahead of schedule (for example, after repairs or commissioning after conservation).
Inspection of boilers is carried out through internal inspection and hydraulic testing. During the inspection, the condition of the boiler walls, seams, pipes, auxiliary mechanisms and instrumentation is checked.
The steam boiler, superheater, economizer and fittings are subjected to hydraulic testing. The steam boiler is tested under operating and test pressure (see Table 2).
table 2
Steam boiler pressure.
Hydraulic testing is carried out with water at a temperature of at least 5°C and held under test pressure for at least 5 minutes.
If during this test no leaks, ruptures or deformations of boiler parts are detected, it is considered that the boiler has passed the hydraulic test.
The results of the technical examination are recorded in the boiler passport.
The safe operation of steam boilers is ensured by measures to protect the boiler walls from scale: the water is treated before entering the boiler. The method of water treatment (softening) is established after its laboratory analysis. Softening the feed water with a soda-lime solution, followed by cleaning and filtration, allows scale to be separated before the water enters the boiler. Antiscale is introduced into the boiler together with water. In this case, a film is formed on the walls of the boiler, which prevents scale deposits. The latter is deposited at the bottom and is removed when blowing and washing the boiler. Magnetic treatment of boiler feed water is also practiced by passing it through alternating magnetic fields. As a result of this treatment, a layer of scale, as usual, is not deposited on the walls of the boiler, but only loose, easily washed off powder is formed. In addition, this water acquires the property of dissolving previously formed scale on the walls of the boiler.
To avoid burns when removing ash and slag from the boiler room, workers must work in respirators, goggles, canvas suits, leather boots, and gloves. Hot ash and slag are filled with water in bunkers.
When working in gas ducts and boilers, only electric lighting is allowed at a voltage not exceeding 12 V.
For the necessary evacuation of maintenance personnel in the event of a fire, at least two exits to the outside are arranged in the boiler rooms. To timely extinguish a fire, the boiler room is equipped with fire extinguishing equipment.
The boiler room is connected to the main steam consumers by telephone or other signaling means.
The illumination of control and measuring instruments must be at least 50 lux. Emergency lighting is provided with an independent power supply.
Food processing plants consume a lot of thermal energy in the form of heat from heated water, air and steam. For example, bakery products are baked at a temperature of 250-160 °C for 10-6O minutes. In pasta factories, products are dried in conveyor dryers with an air flow rate of up to 7000 m3/h, heated in steam heaters to a temperature of 85°C. The heat consumption for preparing beer wort for one brew in a mash tun with a capacity of 1650 kg is 35,400 MJ.
When producing about 22,000 dal per day of soft drinks, up to 15,000 kg of steam is consumed in the syrup-making, blending departments, kvass and washing-packing shops. When heating raw materials in confectionery factories in boilers with a volume of 100–300 dm3, 10–150 kg/h of steam is consumed. For technological needs when preparing 1 dal of beer, 7.84 kg of steam is required, and to heat water on three AMM-12 type washing machines with a capacity of 12,000 bottles/hour each, when working in 2 shifts of 7 hours, about 18,000 kg of steam is consumed.
In this regard, food enterprises widely use steam and hot water boilers, the operation and maintenance of which are classified as high-risk work. Explosions of steam boilers pose the greatest danger. The operating pressure of boilers used in bakery enterprises is 0.07 MPa, confectionery - 0.3-1.1, sugar - 4, soft drinks - 0.05-0.3 MPa,
The main causes of boiler explosions are: violation of technical operation rules, their operating modes, as well as job descriptions, safety requirements due to non-compliance with labor and production discipline by maintenance personnel; defects and malfunctions of boiler design components.
Violations of these instructions and rules lead to the following main technical reasons for boiler explosions: a sharp decrease in the water level, excess operating pressure, unsatisfactory water conditions of the boiler, scale formation, and the presence of explosive flue gases.
The largest number of accidents during the operation of steam boilers occurs due to a sharp decrease in the water level in the boiler. Due to a decrease in the water level below the line of contact of the boiler surface with hot gases in its combustion part, the boiler walls heat up above the critical temperature. In this case, the mechanical properties of the metal change, its strength decreases, and under steam pressure the walls are blown out, which can result in an explosion.
When water is released, it is strictly forbidden to supply cold water to the boiler, since in this case its explosion is inevitable due to the loss of plasticity properties by the metal of the boiler walls with a sharp change in their temperature, an increase in the fragility of the metal and the formation of cracks in it; rapid vaporization and a sharp increase in pressure in the boiler when water comes into contact with its overheated walls. If a water leak is detected, the boiler must be stopped immediately, i.e., the fuel supply to the burners is stopped. The boiler is put into operation after it has cooled, checked its condition and filled with water to the set level.
To prevent the possibility of water falling below the permissible level, boilers must be equipped with devices for automatic control of the upper and lower limit water levels, automatic shutdown of fuel supply to the burners, two direct-acting water indicators, two pumps independent of each other with a productivity of at least 110% and boiler productivity. All boilers with a steam pressure above 0.07 MPa and a productivity of more than 0.7 t/h must be equipped with automatic float-type sound alarms for the lower limit water level. Boilers with chamber combustion of fuel with a steam output of 0.7 t/h and above must be equipped with devices for automatically stopping the fuel supply to the burners when the water level drops below the permissible level, and with a productivity of 2 t/h or more - with automatic power regulators.
Rice. 27. Diagram of installation of a water indicating device on the boiler: 1 - water level in the boiler; 2 - steam; 3,5,6 - steam, water outlet valve; 4 - water measuring glass.
Two direct-acting water indicating devices, i.e., connected directly to the boiler and operating on the principle of communicating vessels, are installed on each boiler so that the water level in it can be seen from the boiler operator’s workplace. The water indicating devices installed on the boilers are checked every shift by blowing (Fig. 27).
The main reasons for exceeding the permissible pressure in the boiler are violation of the specified operating mode and malfunction of safety equipment. To prevent exceeding the permissible pressure, boilers are equipped with pressure gauges and safety valves.
Pressure gauges are installed on each steam boiler to measure pressure - in the boiler, on the outlet manifold of the superheater, on the supply line and on the economizer that is switched off by water, and on a hot water boiler - at the cold water inlet and heated water outlet. Pressure gauges must have an accuracy class of at least 2.5 (the permissible error should not exceed 2.5% of the reading range); working area in the middle third of the scale; red line on the division of the highest permissible pressure. The oks are connected to the boiler elements using a connecting siphon tube with a diameter of at least 10 mm with a 3-way tap. The latter is equipped with a flange for connecting a control pressure gauge in order to check the readings of the working pressure gauge, and also provides purging of the tube.
Pressure gauges are checked at least once every 12 months by the State Standards Authority and a stamp (seal) is placed on them. At least once every 6 months, the pressure gauge readings are checked by the company’s employees using a control test, as well as every shift using 3-way valves, which is recorded in the pressure gauge and shift logs.
Rice. 28. Safety valves:
a - spring (1 - body; 2 - seat; 3. 4 - devices for forced opening of the valve; 5 - pressure regulator; 6 - spring; 7 - cap; 8 - rod; 9 - valve plate; b - lever-load ( 1 - valve seat; 2 - lever; 3 - safety casing; 4 - device for forced opening of the valve; 5 - weight; 6 - lock; 7 - rod; 8 - body; 9 - valve plate)
The main means of preventing boiler explosions when the pressure rises above the permissible level are safety valves, which, when activated, must maintain a pressure in the boiler that exceeds the operating pressure by no more than 10%. On boilers with a capacity of less than 100 kg/h, one is installed, and at a higher capacity, at least two safety valves are installed, one of which is a control valve. According to the principle of operation, valves are spring-loaded and lever-load (Fig. 28). In the first, when the valve is closed, its plate is pressed against the seat by a spring, and in the second, by a lever with a load using a rod pivotally connected to it. When the permissible pressure is exceeded, the valve rises and releases excess steam into the atmosphere through an outlet pipe.
Safety operating and control valves must open on steam boilers operating under pressure up to 1.3 MPa - when it is exceeded by 0.03 and 0.02 MPa, respectively, and operating at higher pressure - at 1.05 and 1.03 MPa, respectively worker. The operating valves must open on the switchable water economizer - on the water inlet side at a pressure of no more than 1.25 MPa, and at the outlet - 1.1 MPa, the operating pressure on the boiler, on hot water boilers - at a pressure of no more than 1.08 MPa worker.
The capacity (kg/h) of safety valves for steam boilers is determined by the following formulas:
at a steam pressure in them of 0.07–12 MPa saturated
Gnp = 0.5a/7(10р1 + 1),
overheated
Where a is the steam flow coefficient, taken equal to 0.9 of the value set by the valve manufacturer (as a first approximation, a=0.6 can be taken); F is the valve flow area in the flow part, mm3; р1 — maximum excess pressure in front of the valve, MPa; VaB, Van - specific volume of steam, respectively, saturated and superheated in front of the valve, at a pressure of 12 MPa of superheated and saturated steam
Where V is the specific volume of steam (saturated and superheated) in front of the valve, m3/kg.
An unsatisfactory water regime, i.e., a violation of the quality, and above all the hardness, of the water feeding the boiler, causes the deposition of sludge and scale on the internal walls of its surface. For boilers with natural circulation with a steam output of 0.7 t/h and above and a working pressure of ≤3.9 MPa, the salt content in the feed water should not exceed; for gas-tube and fire-tube boilers operating on solid fuel - 500 mEq/kg, on gaseous and liquid fuel - 30; for water tube boilers with operating pressure up to 1.3 MPa - 20, and from 1.3 to 3.9 MPa - 15 mEq/kg.
If the water used to feed the boiler does not meet these requirements, boilers with a capacity of 13:0.7 t/h of steam must use different methods of pre-boiler treatment, of which the most effective are chemical cleaning using soda-lime, sodium or phosphate precipitation, and also the catinization method. Therefore, all boilers of the specified capacity are equipped with installations for boiler water treatment, and the boiler room must have a water treatment log in which the results of water tests, boiler purging modes and maintenance operations for water treatment equipment are recorded.
One of the reasons for boiler overheating is the appearance on its inner surface of a layer of scale formed from salts contained in the feed water. To prevent overheating of the boiler, they are periodically cleaned so that the thickness of the scale layer on the hottest areas of the boiler surface does not exceed 0.5 mm.
The reasons for the accumulation of explosive gases in the boiler furnace are violations of the operating modes of draft devices or fuel supply. To prevent the accumulation of explosive gases, draft control equipment is installed, which automatically stops the supply of fuel to the burners when the vacuum in the boiler furnace or behind it decreases.
Common causes of boiler explosions due to defects and malfunctions of the main components are defects in structural elements, a decrease in their mechanical strength during operation, and malfunction of safety equipment and measuring instruments.
The metal from which individual boiler elements are made has special requirements. The Gospromatnadzor authorities issue certificates for the materials used for this, as well as for the repair of boilers.
During operation, the mechanical strength of boilers decreases due to corrosion of its walls and structural elements. To prevent a boiler from exploding due to internal (hidden) defects in the materials from which it is made, a safety factor is adopted when designing and calculating its strength. The reduction in boiler strength due to corrosion is taken into account when establishing the permissible pressure in it. This pressure (in MPa) is determined by the formula
S—boiler wall thickness, cm; c—increase in wall thickness due to erosion; σ permissible stress of the wall material; φ is the strength coefficient of the weld; D is the internal diameter of the boiler, m.
The operation of faulty safety equipment, protective devices and measuring instruments is prevented by their systematic monitoring and testing, the terms of which are indicated above.
In order to timely identify possible defects in boilers and other objects operating under pressure, they are subject to technical inspection and testing before commissioning, periodically during operation and unscheduled.
A technical inspection carried out by a technical inspector of Gospromatnadzor in the presence of the head of the boiler house or the person responsible for the good condition and safe operation of facilities working under pressure provides for an internal inspection to identify the condition of internal and external surfaces and the influence of the environment on the walls - at least 1 time in 4 years ; hydraulic test with preliminary internal inspection - at least once every 8 years.
Hydraulic testing of objects operating at pressure ≤ MPa, as well as at temperatures up to 200°C, is carried out with a test pressure not exceeding 1.5 times the working pressure, but not less than 0.2 MPa, and objects operating under pressure ≤0.5 MPa, - at a test pressure of 1.25 MPa of the worker, but not less than 0.3 MPa exceeding it.
Boilers and other equipment operating under pressure that are not subject to registration with the Gospromatnadzor authorities are inspected by the person responsible for their operation. They are carried out; internal inspection and hydraulic testing of newly installed or moved boilers, as well as after their repair using welding, riveting, replacement of pipes and other elements; hydraulic testing of boilers in operation at least every 6 years, and those not available for internal inspection - after 3 years; internal inspection and hydraulic testing of boilers with working pressure after each cleaning and repair, but at least once a year, except for the above repairs that require test pressure testing.
The results of technical tests of boilers registered with the Gospromatatompadzor authorities are recorded in the boiler passport by the inspector, and for unregistered ones - by the person responsible for safe operation.
Boilers must be installed in special rooms not adjacent to production and other buildings. As an exception, their placement in adjacent buildings is allowed, provided they are separated by a fire wall with a fire resistance limit of at least 4 hours. The boiler room is built from fireproof materials, must have two exits, and be equipped with ventilation and emergency lighting.
To prevent accidents in steam boilers due to excess pressure, the Boiler Rules provide for the installation of safety valves.
: The purpose of safety valves is to prevent pressure increases in steam boilers and pipelines above established limits.
Exceeding the operating pressure in the boiler can lead to rupture of the boiler screen and economizer pipes and drum walls.
The reasons for increased pressure in the boiler are a sudden decrease or cessation of steam flow (switching off consumers) and excessive boost of the furnace,
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Table 2.3. Malfunctions of water indicating devices, their causes and solutions
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Continuation of the table. 2.3
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Especially when working with heavy oil or gaseous fuels.
Therefore, to prevent the pressure in the boiler from rising above the permissible limit, the operation of boilers with faulty or unregulated valves is strictly prohibited.
Measures to prevent an increase in pressure in a steam boiler are: regular checks of serviceability of safety valves and pressure gauges, alarm systems from steam consumers to obtain information about upcoming steam consumption, trained personnel and good knowledge and compliance with production instructions and emergency circulars. -
To check the serviceability of the safety valves of the boiler, superheater and economizer, they are purged by forcefully opening them manually:
At operating pressure in the boiler up to 2.4 MPa inclusive, each valve must be used at least once a day;
At an operating pressure from 2.4 to 3.9 MPa inclusive, one valve at a time for each boiler, superheater and economizer at least once a day, as well as at each boiler start-up, and at a pressure above 3.9 MPa, within a period of time established by the instructions.
In the practice of operating boilers, accidents still occur when the pressure in the boiler exceeds the permissible limit. The main cause of these accidents is the operation of boilers with faulty or unregulated safety valves and faulty pressure gauges. In some cases, accidents occur due to the fact that boilers are put into operation with safety valves turned off using plugs or jammed, or they allow arbitrary changes in valve adjustment, placing additional load on the valve levers in the event of a malfunction or absence of automation and safety equipment.
In the boiler room, an accident occurred with the E-1/9-1T steam boiler due to excess pressure, as a result of which the boiler room was partially destroyed. The E-1/9-IT boiler was manufactured by the Taganrog House-Building Plant to operate on solid fuel. In agreement with the manufacturer, the boiler was converted to liquid fuel, an AR-90 burner device was installed and automatic devices were installed to shut off the fuel supply to the boiler in two cases - when the water level drops below the permissible level and the pressure rises above the set one. Before putting the boiler into operation, the ND-1600/10 feed pump with a flow rate of 1.6 m3/h and a discharge pressure of 0.98 MPa, which turned out to be faulty, was replaced with a centrifugal vortex pump with a flow rate of 14.4 m3/h and a discharge pressure 0.82 MPa. The high power of the engine of this pump did not allow it to be included in the electrical circuit for automatically regulating the water supply to the boiler, so it was carried out manually. The automatic protection against low water level was disabled, and the automatic protection against overpressure did not work due to a sensor malfunction. The operator, having detected a loss of water, turned on the feed pump. The hatch cover of the upper drum was immediately torn out and the lower left manifold was destroyed at the place where the grate beam was welded to it. The accident occurred due to a sharp increase in pressure in the boiler due to a deep release of water and its subsequent replenishment. Calculations showed that the pressure in the boiler in this case could increase to 2.94 MPa.
The thickness of the hatch cover in a number of places was less than 8 mm, and the cover was deformed.
In connection with this accident, the USSR Gosgortekhnadzor suggested that owners operating steam boilers: do not allow the operation of boilers in the absence or malfunction of automatic safety equipment and instrumentation; ensure maintenance, adjustment and repair of security automation equipment by qualified specialists.
In accordance with the letter of the USSR State Mining and Technical Supervision No. 06-1-40/98 dated May 14, 1987 “On ensuring reliable operation of steam boilers E-1.0-9”, owners of boilers of this type are required to reduce the pressure allowed for operation for boilers that have a lid thickness 8 mm hatch with fastening the hatch cover with studs up to 0.6 MPa, since the plants of the Ministry of Energy of Mash produced E-1.0-9 boiler drums with a steam capacity of 1 t/h with hatch covers 8 mm thick and the thickness of the hatch cover was increased to 10 mm.
An accident occurred in the boiler room with the E-1/9T boiler due to excess pressure.
As a result of the bottom of the lower drum being torn off, the boiler was thrown from the installation site towards another boiler and, upon impact, tore off the casing, destroyed the lining, deformed 9 pipes of the side screen. Safety valves were torn out of their seats upon impact. When tested on a pressure bench 1 .1 MPa valves did not work. When disassembling the valves, it was established that its moving parts of the valve were stuck.
The investigation established that the bottom of the boiler 0 600X8 mm was made in a handicraft manner from steel that did not have a certificate.
After welding the bottom, boiler room workers carried out a hydraulic test with a pressure of 0.6 MPa, and the bottom became deformed. After a few days of boiler operation, cracks appeared in the weld, which were welded.
Due to changes in the design of the lower drum hatch cover (without the approval of the manufacturer) and unsatisfactory repairs, an accident with serious consequences became possible.
Safety valve malfunctions
To prevent accidents of steam and hot water boilers due to excess pressure in them, the State Rules
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Table 2.4. Malfunctions of safety valves, their causes and solutions
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The USSR Gortechnadzor provides for the installation of at least two safety valves for each boiler with a steam capacity of more than 100 kg/h.
On steam boilers with pressures above 3.9 MPa, only pulse safety valves are installed.
Due to improper operation of safety valves or their defects, accidents occurred in boiler rooms of industrial enterprises and power plants. Thus, at one power plant, during a sharp load shed due to a malfunction of the safety valves, the steam pressure in the boiler increased from 11.0 to 16.0 MPa. This disrupted the circulation and the screen pipe ruptured.
At another power plant, under the same operating conditions, the pressure increased from 11.0 to 14.0 MPa, as a result of which two screen pipes ruptured.
The investigation found that some safety valves did not work because the impulse lines were blocked by the valves, and the remaining valves did not provide the necessary steam release due to the use of uncalibrated springs in the impulse safety valves and, as a result, some of them broke.
The destruction of springs was observed in pulse valves after each opening. This occurred as a result of large dynamic forces from the jet of escaping steam at the moment of opening of the valve, which has a seat cross-sectional diameter of 70 mm.
The main malfunctions in the operation of lever-load and spring safety valves are given in table. 2.4.
Safety valves must protect boilers and superheaters from exceeding their pressure by more than 10% of the design pressure. An excess of pressure when the safety valves are fully opened by more than 10% of the calculated value can only be allowed if this possible increase in pressure is taken into account when calculating the strength of the boiler and superheater.
7.1. General provisions.
7.1.1. When eliminating emergency situations, personnel must act in such a way as to:
First, eliminate the threat to human life;
Secondly, ensure the safety of the equipment;
Thirdly, ensure compliance with the schedule of thermal and electrical loads;
7.1.2. If an emergency situation occurs in the CTO, the shift manager must immediately notify the NSS and the head of the SSE or his deputies about it.
7.1.3. The person responsible for preventing and eliminating accidents is the shift supervisor, and in his absence, the senior driver.
The general manager for emergency response is the NSS.
7.1.4. Persons who are not part of the shift during an emergency do not have the right, regardless of their official position, to distract personnel from work with conversations and questions. Those who violate this rule are required to be removed from the CTO by the shift manager.
7.1.5. Handover and acceptance of shifts during emergencies is prohibited until normal operation of the equipment is restored. Acceptance - handing over of the shift in these cases is carried out by order of the head of the SSE or his deputy.
The personnel who came on duty are involved in eliminating the accident under the leadership of the head of the working shift.
7.1.6. KTO personnel on duty during an accident must be guided by the following sequence of actions when eliminating it:
Based on instrument readings and external signs, get an idea of what happened:
In accordance with emergency instructions, immediately take measures to eliminate the danger to people and equipment to restore normal operation of the equipment;
Determine the nature and location of the damage, as well as the volume of the area affected by the accident through inspection;
You should notify your immediate supervisor about each stage of the emergency response, if possible immediately, without waiting for his questions.
7.1.7. When dealing with an accident, you should act calmly, quickly and accurately.
7.1.8. If an order is received during an accident, the duty officer must repeat it. Immediately report the execution of the order to the person who issued the order.
7.1.9. The duty personnel of KTO-1 are obliged to carry out all operational orders of the shift supervisor immediately and unconditionally.
7.1.10. In the event of incorrect actions by the shift supervisor, the head of the SSE or his deputy is obliged to intervene in the course of liquidation of the accident, up to taking over leadership and responsibility for the further progress of liquidation of the accident, with mandatory notification of the NSS.
7.1.11. At every convenient moment during the emergency response period, personnel are obliged to carefully record all the circumstances of the occurrence, course and liquidation of the emergency situation with an accurate indication of the time of the operations performed.
7.1.12. Responsibilities of personnel during emergency response.
Boiler operator
Directly eliminates an accident on the boiler in accordance with the instructions of this instruction and reports the incident to the shift supervisor, and also warns the drivers of neighboring units.
Senior driver
Manages the load distribution on the remaining boilers, ensures the normal specified operating mode of the boilers.
Monitors the correctness of personnel actions and assists the unit driver in eliminating the accident.
Performs the necessary switching operations in the boiler department as directed by the shift supervisor.
CTO shift supervisor
Directly manages the emergency response and controls the actions of personnel.
Reports the incident to HCC and service management and maintains constant contact with them.
Ensures normal start-up of backup equipment to restore normal operation.
7.2. Emergency cases of boiler shutdown and personnel actions.
The boiler must be immediately switched off by protection or personnel in the following cases:
If all water level indicators in the drum fail;
When the water level in the drum increases (+200 mm) or decreases (-100 mm);
If the water level in the drum quickly decreases, despite increased power supply to the boiler;
If all feed pumps fail;
When the pressure in the steam-water path increases above the protection settings;
If 50% of the safety valves stop operating;
Rupture of steam-water path pipes or detection of cracks, bulges, gaps in welds in the main elements (drum, manifold, steam, water indicator and drain pipes with a diameter of more than 50 mm), in steam pipelines, supply pipelines and steam-water fittings;
The extinguishing of the torch in the firebox;
Reducing gas pressure to 0.88 kgf/cm 2 behind the control valve;
In the event of an explosion in the furnace, explosion or ignition of deposits in gas ducts or a convective shaft, red-hot heating of the load-bearing beams of the frame during the collapse of the lining, as well as other damage that threatens personnel or equipment;
A fire that threatens personnel or equipment, as well as the remote control circuits of the shutdown valves included in the boiler protection circuit;
Loss of voltage on remote and automatic control devices and on all control and measuring instruments;
Gas pipeline rupture within the boiler;
Combustion of deposits in a convective shaft.
The steam generator must be stopped if:
Detection of fistulas in heating surface pipes, steam and water transfer pipes, boilers, steam pipelines, manifolds, supply pipelines, as well as steam in fittings, flange and rolling connections;
Inadmissible excess of the temperature of the metal of the heating surfaces, if it is not possible to reduce the temperature by changing the boiler operating mode;
Failure of all remote water level indicators in the boiler drum;
A sharp deterioration in the quality of feed water against the stopped standards;
Malfunctions of individual protections or remote and automatic control devices, as well as instrumentation.
The boiler shutdown time in these cases is determined by the chief engineer of the station.
In emergency situations, the boiler is stopped by protections, and in case of failure of protections, by acting on the emergency stop key.
In the event of an emergency shutdown of the boiler, it is necessary to monitor the correctness of the boiler shutdown using the protections, and in case of failure of the protections and interlocks, perform the following operations:
Extinguish the firebox by closing the shut-off valves on the gas pipeline and turning off the dust, close the shut-off valves on the gas supply to the boiler, followed by closing the valves at the burners;
Turn off dust feeders;
Open the purge plugs on the gas pipeline;
Check that there is no combustion in the firebox;
Close the first gas treatment plants and open the valves for purge of the superheater;
Close the valves on the feed water supply to the boiler (if the drum is leaking or overfilling);
Close the valve on the supply of its own condensate to the injection unit;
Stop blower fans and smoke exhausters 10 minutes after the torch goes out.
7.3. Loss of water from the boiler drum.
7.3.1. Reasons for water loss:
Loss of water from the boiler drum can occur:
In case of malfunction of water indicating devices;
When the pressure in the supply line decreases;
Due to a malfunction of the control valve on the supply line or auto-controllers;
In case of severe leaks of drainage fittings;
If the screen pipes, water economizer or drain pipes are damaged;
If the driver has insufficient control over the water supply to the boiler.
7.3.2. Personnel actions.
If it is found that the water level in the boiler decreases at normal pressure in the supply line, it is necessary:
7.3.2.1. Increase the boiler power supply, open the control valve to the bypass of the boiler power supply unit if necessary. Switch the boiler power supply to remote control.
7.3.2.2. Check the readings of the lowered level indicators against the water level indicators. Close all boiler blowdowns, including continuous.
7.3.2.3. Establish particularly careful monitoring of the water level in the boiler drum and the pressure in the feed line. If the pressure in the feed line is insufficient, request that an additional feed pump be started immediately.
7.3.2.4. Check the readings of the steam and water meters of the boiler. If the water meter shows significantly more steam meters, then this fact indicates the formation of leaks in the water path of the boiler.
7.3.2.5. Check:
The density of the boiler purge fittings (the tightness of the fittings is checked by touch);
By listening, check for damage to the screen pipes, superheater, water economizer and drain pipes.
7.3.2.6. If, despite the measures taken to increase the water supply to the boiler, the level in the boiler drum has reached a low emergency limit of 100 mm and the protection has not worked, turn off the boiler using the emergency stop key,
Extinguish the fire by closing the shut-off valves on the boiler gas pipeline, followed by closing the valves at the burners or turning off the dust feeders,
Close the main steam valves;
By closing the control feed valves and gate valves, stop supplying the boiler with water.
The question of the time for subsequent heating of the boiler is decided by the chief engineer of the station; replenishment and firing of the boiler should be carried out after a thorough inspection of the evaporative heating surfaces.
7.4. Refilling the boiler with water.
7.4.1. Signs of overdrinking:
Increasing the water level in the boiler drum according to lowered level indicators and water-indicating columns above the highest permissible limit of 150 mm;
Reducing the temperature of superheated steam;
Increase in salt content of superheated steam.
Overfeeding of the boiler can occur due to:
Malfunctions of reduced water level indicators in the drum and water indicator columns of the boiler;
Malfunction of the control valve on the supply line or automatic regulators;
Insufficient control over the boiler power supply by the unit operator.
7.4.2. Personnel actions.
7.4.2.1. When the water level in the boiler drum rises above +50 mm. necessary:
Check the correct operation of the reduced level indicators by checking their readings with water measuring columns;
Switch the boiler power supply from automatic control to remote control and reduce the water supply to the boiler using the PPK control valve.
7.4.2.2. If, despite the measures taken to reduce power, the level in the drum has reached +100, open an emergency discharge of water from the drum, if the level does not decrease and has reached the highest emergency limit of +200 mm. and the protection did not work, turn off the boiler using the emergency stop key:
Close emergency reset when normal level is reached;
Find out the reason for the overheating and, with the permission of the NSS, begin lighting the boiler.
7.4.2.3. When the water level in the drum rises and it is thrown into the superheater and the temperature of the superheated steam sharply drops with the observation of water hammer, it is necessary to turn off the boiler using the emergency stop key.
Open the emergency drain from the drum.
Open the superheater drains and purge.
Cover the guide vanes of the smoke exhauster and blower fan, then stop after 10 minutes.
Carefully monitor the level decrease and, when the pilot level is reached, close the emergency release valves.
Find out the reason for over-watering the boiler.
The question of the time for subsequent heating of the boiler is decided by the chief engineer of the station after a thorough inspection of the steam superheating surfaces of the boiler.
7.5. Screen pipe rupture.
7.5.1. Causes of damage to screen pipes:
The water loss from the boiler drum is below - 100mm. and failure to take timely measures to eliminate the accident;
Formation of steam bags in screen pipes when circulation is disrupted;
The presence of scale inside the pipes (the most common cause of vents, fistulas and pipe ruptures) due to the boiler being supplied with unsatisfactory water quality, improper chemical treatment regime and unsatisfactory control over the quality of boiler and feed water;
Pipe blockage during installation or repair by foreign objects;
Large leaks of drainage fittings;!
Wear of pipes by a stream of steam flowing from previously damaged pipes and timely undetected “crawls”;
Inconsistency of pipe material or defective pipe manufacturing at the factory, installation or during repairs.
7.5.2. Signs of rupture of screen pipes are:
A sharp noise of escaping steam in the furnace and flue ducts of the boiler;
A sharp increase in water consumption to the boiler and a decrease in steam consumption;
A rapid decrease in the water level in the drum and a drop in steam pressure;
Knocking out steam and gases from hatches in the boiler lining;
A sharp decrease in vacuum in the furnace up to the point of going off scale to “plus”.
7.5.3. Actions of personnel in case of rupture of screen pipes:
After stopping the smoke exhausters, if necessary, maintain a vacuum at the top of the firebox of 3 - 5 mm using the guide vanes of the smoke exhausters.
7.6. Drain pipe rupture.
7.6.1. Causes of damage to water indicator pipes:
Insufficient compensation for thermal expansion when the lower chambers or drain pipes themselves are pinched;
Poor quality welding of joints;
Pipe metal corrosion;
Violation of bending production technology (change in metal structure, thinning of the wall, violation of strength and ductility);
Metal fatigue.
7.6.2. Signs of a broken drain pipe:
Loud noise in KTO-1 and filling of the KTO-1 room with steam;
A rapid decrease in the water level in the drum and a drop in steam pressure in the boiler;
Discrepancy in the readings of the steam meter and water meter (a sharp increase in water consumption and a decrease in steam consumption).
7.6.3. Actions of personnel in case of rupture of a drain pipe:
Immediately turn off the boiler using the emergency stop key;
Monitor the level in the drum;
Remove all personnel from the danger zone and fence off the danger zone.
7.7. Main steam line ruptured.
7.7.1. A rupture of the main steam line can be caused by the following reasons:
Hydraulic shocks in the steam pipeline;
Insufficient compensation for thermal movements or pinching of the pipeline;
Unsatisfactory metal quality (including the use of steel grades that do not correspond to the design);
Creep of steam pipeline metal;
7.7.2. Signs of a rupture:
Loud noise of escaping steam and filling of KTO-1 rooms with steam;
A sharp decrease in pressure behind the boiler;
A sharp rise ("swelling" of the water level in the boiler drum;
If the rupture occurs before the flow washer, there will be a large difference in the readings of the water and steam flow meters.
7.7.3. Action of personnel in the event of a steam line rupture:
Immediately turn off the boiler using the emergency stop key;
Close the valves in front of the turbine;
Monitor the level in the drum
Intensively ventilate the KTO-1 room, creating draft by opening windows and doors;
7.8. Damage to the supply pipe.
7.8.1. Possible malfunctions and accidents with supply pipelines can be caused by:
Vibration of the pipeline, hydraulic shocks;
Unsatisfactory fastening of pipelines;
By knocking out gaskets and seals on the supply pipeline fittings;
Failure of control valves, shut-off valves, check valves;
Poor quality welding of joints.
In case of water hammer and vibration of the pipeline, the boiler operator is obliged to find out the cause of the water hammer and vibration.
7.8.2. Signs of a supply pipeline failure may include:
Pressure drop in the supply line;
Loud noise and steam emission;
Discrepancy between steam and water meter readings;
Reduced level in the boiler drum.
If gaskets, seals of fittings are knocked out and there is a strong leak, it is necessary, in agreement with the NSS, to transfer the boiler power to the reserve line and disconnect the section of the pipeline with faulty fittings.
If it is not possible to transfer the boiler power to the reserve supply pipeline or the shutdown of the damaged section is due to the fact that the boiler remains without water supply (the level cannot be maintained when the load on the boiler is reduced), the boiler stops emergency.
7.8.3. If the supply line ruptures, you should immediately:
Turn off the boiler using the emergency stop key;
Remove all personnel from the danger zone and fence off the danger zone.
7.9. Failure of all water indicating devices.
If all water indicating devices fail to operate, you must immediately turn off the boiler using the emergency stop key.
After at least two water indicators have been restored to operation and if their readings coincide, the boiler is heated with the permission of the NSS.
7.10. Pressure drop in the feed line and failure of all feed pumps.
7.10.1. A pressure drop in the supply line can occur:
Due to stoppage or malfunction of feed pumps;
Failure of operation of feed pumps due to a decrease in pressure in the deaerator;
Due to a rupture of the supply pipeline;
Due to erroneous actions of personnel when switching in pipeline diagrams;
Discovery of PEN recycling.
7.10.2. If the pressure in the supply line drops, you must:
In accordance with the circumstances, take all measures to restore pressure in the supply pipeline;
If there is a decrease in pressure in the supply pipeline, then it is necessary to unload the boiler and turbine, reduce the pressure in the boiler drum to a value that ensures the normal water level in the boiler.
If all feed pumps fail, i.e. when the water pressure in the feed pipeline has dropped to the pressure in the boiler and the restoration of pressure is delayed, the unit operator is obliged, if the protection at a level of -100 mm does not work, to immediately turn off the boiler and take urgent measures through the NSS to start the feed pumps.
7.11. Failure of 50% of safety valves.
7.11.1. The boiler is equipped with 4 pulse safety valves configured for a pressure of 116 atm with pulses from the drum and for a pressure of 105 atm with pulses from the superheated steam outlet chamber.
7.11.2. The safety valve control keys must be in the "automatic" position.
7.11.3. When the pressure in the boiler reaches the above values, the safety valves should operate automatically.
With the central control unit it is possible to remotely open and close safety valves.
7.11.4. Safety valves may not be triggered remotely or automatically for the following reasons:
There is no voltage in the electrical circuit. supply of pulse safety valves;
The winding of the solenoids (induction coils) of the lever valves is damp;
Mechanical damage (distortion of lever and main valve rods, sticking of lever valve plates, jammed main valve piston, strong return spring tension, etc.);
Damage to contact pressure gauges;
Load displacement on lever valves;
Freezing impulse lines.
7.11.5. A rise in pressure in the boiler drum and in the steam line above the normal values of 110 ati and 100 ati can be caused by the following reasons:
By shedding the load on the turbine and when personnel did not take timely measures to reduce the fuel supply and open the superheater purge;
As a result of abnormal combustion, when fuel was allowed to be thrown into the area of the screens, convective superheater and onto the underside of the combustion chamber.
7.11.6. Personnel must remember that exceeding the pressure on the boiler above normal before the safety valve activation settings can occur due to untimely measures to reduce pressure (opening the superheater purge, reducing the fuel supply, etc.).
7.11.7. If 50% of the safety valves fail, when the valves do not operate remotely and manually, and the pressure in the boiler drum and steam collection chamber has risen to the value set for the operation of the working safety valves, and continues to increase, the unit operator is obliged to immediately extinguish the boiler using the emergency stop key.
After reducing the pressure on the boiler to 100 ati, close the superheater purge.
7.11.8. The boiler unit may only be fired up after the causes of failure of the safety valves have been identified and eliminated.
Note: When lighting, it is necessary to test and adjust the safety valves before setting them to operate.
7.12. Damage to superheater pipes.
7.12.1. Causes of damage to superheater pipes can be:
Defects in the metal of superheater pipes;
Accumulation of condensate in the lower chambers of the wall-mounted superheater;
Structural defects of the superheater, uneven distribution of steam over the coils, low steam velocities, the presence of gas corridors between the coils, etc.;
Unsatisfactory management of the combustion regime, causing an increase in the temperature of the gases in front of the superheater, tightening of the torch and combustion in the area of the superheater, temperature imbalances across the width of the furnace;
The proximity of the torch to the wall-mounted superheater during heating of the boiler;
Internal contamination of coils due to poor quality of steam and boiler water;
Pinched coils and insufficient compensation for thermal expansion;
7.12.2. Signs of ruptured superheater pipes:
Temperature imbalance in the gas duct;
The difference in the readings of the steam meter and water meter;
Noise in the superheater area;
Unstable combustion, increased pulsation in the firebox;
Clogging of flue gases and steam through hatches and leaks in the lining.
7.12.3. Actions of personnel in case of damage to superheater pipes.
If there are fistulas on the superheater pipes, the escaping steam may damage the adjacent coils, so it is necessary:
Immediately contact the NSS and the service administration and agree with them on the issue of turning off the boiler. The shutdown time is set by the chief engineer of the station;
Upon receipt of permission to stop the boiler, proceed to its normal shutdown;
The smoke exhausters stop after removing steam from the boiler flues;
Carefully control the temperature of the superheater coils, not allowing them to increase above normal.
7.13. Damage to the main elements of the boiler.
7.13.1. The formation of bulges and cracks with threatening vapors in the drum body, collectors or boiler chambers can be caused by the following reasons:
Violation of the boiler firing regime, when the temperature difference between the top and bottom of the drum along the generators repeatedly exceeded 40°C;
Poor quality welding of joints;
Creep and softening of metal as a result of frequent alternating loads;
Hydraulic shock;
Insufficient compensation for thermal expansion when pinched on supports;
Unsatisfactory metal quality (including the use of steel grades that do not correspond to the design);
Operational violations associated with overfeeding, loss and excess pressure in the boiler above normal.
7.13.2. If bulges and cracks with threatening consequences appear in the main elements of the boiler (drum, steam collection chambers, steam pipeline, drain pipes), when further operation of the boiler creates a danger for personnel maintenance and a threat to the integrity of the boiler unit, the unit operator is obliged to:
Report the incident to the shift supervisor;
With the permission of the NSS, carry out a normal shutdown of the boiler;
Monitor the temperature of the metal of the drum and the gas-air path, and carry out normal cooling of the boiler.
7.13.3. Personnel must fence off areas of damage and post warning signs - “Passage closed”, “Danger zone”, preventing personnel from entering the danger zone.
7.14. Destruction of the lining and heating of the boiler frame to red hot.
7.14.1. Reasons for the destruction of the lining and furnace vaults:
Unsatisfactory combustion conditions in the firebox, concentration of high temperatures near unprotected screens of lining areas, work with pressure in the firebox;
Explosions and pops in the firebox and flues, pulsation of the torch;
Unsatisfactory repair of the lining, laying and hanging of boards with upholstered edges and corners, excessive or insufficient dimensions of expansion joints, insufficient drying of the lining after repair or excessively rapid firing of the boiler after repair, etc.;
Unsatisfactory quality of lining. Personnel servicing the boiler unit are obliged to monitor the condition of the lining of the furnace and boiler flues, inspecting them through peepholes, manholes, and checking by touch the external temperature of the lining and frame when inspecting the boiler unit.
7.14.2. Signs of damage to the firebox lining:
Clearances due to destruction of the inner and outer sides of the lining;
Heating of the boiler furnace lining or frame (occurs when the inner part of the furnace lining wears out and collapses)
7.14.3. Measures to prevent the development of an accident and eliminate an accident with lining:
In case of damage to the lining, threatening a collapse or when the boiler frame is heated to red, the boiler must be stopped immediately;
In case of minor damage to the lining, when the resulting gaps are insignificant, the boiler is allowed to operate with measures taken to protect the boiler frame from heating. At the same time, the load on the boiler must be reduced and the vacuum in the furnace increased. Carefully monitor the condition of the lining and frame;
A way to facilitate the work of the lining is to reduce the temperature in the firebox by increasing the excess air.
7.14.4. Actions of personnel in case of destruction of the lining and heating of the boiler frame to red hot:
Report to the shift supervisor KTO-1 about the immediate shutdown of the boiler;
With the permission of the NSS, a normal shutdown of the boiler is carried out;
Monitor the condition of the lining, frame, temperature of the drum metal and carry out normal cooling of the boiler.
7.15. Soot ignition in the tail section of the gas ducts.
7.15.1. Incomplete combustion of fuel with soot formation, in addition to large losses due to mechanical underburning, threatens the deposition of flammable products of incomplete combustion in the boiler flues.
If the heating surfaces and flues are not cleaned satisfactorily, these deposits can accumulate in significant quantities and, under appropriate conditions, ignite and permanently damage the boiler unit or its individual elements.
7.15.2. To prevent soot from burning in the boiler flues, you must:
Do not allow the furnace to operate with chemical or mechanical underburning due to insufficient excess air or improper distribution of air among the burners;
Do not allow the torch to be drawn into the upper part of the firebox;
Conduct the combustion process in such a way as to ensure complete combustion of fuel with the minimum permissible excess of air;
Promptly and thoroughly clean heating surfaces and boiler flues.
7.15.3. The ignition of soot accumulated in the boiler flues can be detected by an increase in the temperature of the flue gases and hot air, and a decrease in the vacuum in the furnace.
If unburnt fuel ignites in the boiler flues, you must immediately:
Stop smoke exhausters and blower fans and tightly close their guide vanes;
Carefully monitor the gas temperature in the area of the air heaters and water economizer.
7.15.4. After the combustion stops and the boiler lining has cooled sufficiently, inspect the gas ducts and make sure that there are no burning sources in them.
In the absence of burning sources and damage caused by combustion, proceed to cleaning the tail surfaces and, if the boiler has not received serious damage, prepare it for lighting and light it as directed by the NSS.
7.16. Fire in the boiler room, threatening equipment and personnel.
7.16.1. In the event of a fire in KTO-1, immediately call the fire brigade and simultaneously report the fire to the NSS and the service administration.
7.16.2. Before the fire brigade arrives, shift personnel must:
Proceed to extinguish the fire under the direction of the shift supervisor using all means available to the watch personnel. KTO-1 personnel must know the location of the taps with fire extinguisher hoses and sand;
If the source of fire threatens to damage live cables, the shift supervisor is obliged to immediately notify the NSS about this and demand voltage relief;
If the source of combustion threatens to damage the equipment or the remote control circuits of the shutdown valves included in the boiler protection system, the shift supervisor is obliged to stop this unit;
In the event of a gas ignition on the boiler or boiler equipment, the damaged area must be immediately switched off; if it is impossible to switch off, the boiler must be stopped immediately. Fire extinguishing should be carried out in accordance with the operational fire extinguishing plan in KTO-1.
7.16.3. When the fire department arrives, the shift manager is required to establish contact with the head of the fire department and monitor that the fire brigade members do not violate instructions and do not take measures that could cause a breakdown of operating equipment (water getting on electric motors, cables, electrical assemblies, etc. ).
7.17. Stopping smoke exhausters or fans.
7.17.1. When stopping both smoke exhausters or both fans when the boiler shutdown protection fails, the driver is obliged to turn off the boiler and cool it down normally.
7.17.2. Find out the reason for the shutdown of the relevant equipment and, after eliminating the malfunctions, with the permission of the NSS, begin lighting the boiler according to the lighting schedule.
7.17.3. When one DV or DS is turned off, unload the boiler to the maximum possible load on one DV or DS.
7.18. An increase in the temperature of superheated steam above - 510°C.
7.18.1. An increase in the temperature of superheated steam above normal can be:
At high vacuum in the furnace, when the torch is drawn into the area of the superheater;
When the feedwater temperature decreases;
With a large excess of air in the firebox;
When there is a lack of air in the furnace, when the torch is drawn into the area of the superheater, where the fuel burns out;
When deposits ignite on evaporative heating surfaces;
When the turbine sheds load.
7.18.2. Actions of personnel when the steam temperature rises above normal.
To reduce high superheat of steam it is necessary:
Increase injection into desuperheaters;
Reduce the vacuum in the furnace to normal if it is too high;
Bring excess air in the furnace to the standards established by the regime map and ensure complete combustion of the fuel;
Reduce the furnace boost;
Ensure that the feed water temperature is increased. When shedding the load, in addition to the specified measures to reduce overheating, open the superheater purge.
7.19. Reducing the temperature of superheated steam below 490°C.
7.19.1. The reasons for a sharp decrease in the temperature of superheated steam, in addition to boiler overfeeding, can be:
A sharp increase in the boiler load, entailing increased steam formation, resulting in a fluctuation in the water level in the boiler with its discharge into the superheater;
Foaming and rushing of water in the drum (foaming of water in the boiler can be due to high salt content or phosphates as a result of improper water management);
A sharp increase in the water level in the drum, which can occur from a sharp decrease in steam pressure in the boiler;
Increased water level in the boiler (above +50 mm) during load increase;
Insufficient air in the firebox.
7.19.2. Actions of personnel in the event of a sharp drop in the temperature of superheated steam.
If the temperature of superheated steam drops sharply, it is necessary to:
Close the injection into the desuperheater;
Strengthen control over the steam temperature in front of the turbine;
If necessary, open drains in front of the ILI;
Reduce the boiler load;
Reduce the water level in the drum to - 30 mm below the average level.
If a decrease in the superheat temperature occurred during a period of sharp increase in boiler load, reduce the load and prevent recurrence of surges.
If the water level fluctuates (even after reducing the boiler load) and increased salt content, which indicates a violation of the boiler water regime, you should:
Fully open the continuous boiler blowdown;
Report the incident to the shift manager of the chemical service, call a laboratory assistant (to establish the boiler water regime) and demand that its quality be improved.
When water foams in the drum, due to a sudden drop in pressure, the circulation of water in the boiler may simultaneously be disrupted.
To prevent rupture of pipes and a sharp drop in temperature and steam pressure, one should avoid forcing the boiler and increasing steam consumption when the load increases above 10-15 t/min, and take measures to gradually increase the pressure in the boiler.
7.20. Damage to the water economizer pipes of the convective superheater.
7.20.1. Damage to the transmission water economizer pipes can occur for the following reasons:
Cracks in welded joints;
Due to metal corrosion;
Due to metal burnout due to violation of the boiler combustion mode;
Due to natural rejection of poorly manufactured pipes and welded joints.
7.20.2. Signs of ruptured transmission water economizer pipes:
Differences in the readings of the steam meter and water meter (increased water consumption);
Noise in the area of the water economizer and superheater;
7.20.3. If the water economizer and gearbox pipes are damaged, you must:
Switch the boiler power supply to manual, turn off the automation;
Increase the water supply to the boiler and control the level in the drum, report the incident to the NSS.
7.20.4. If a fistula is detected in the pipes of the water economizer and gearbox, the boiler shutdown time is set by the chief engineer of the station.
In the event of a rupture of the pipe of the water economizer or gearbox and it is impossible to maintain the water level in the drum, the driver is obliged to inform the shift supervisor or the pumping station about this and emergency stop the boiler with power cut.
7.21. Explosion of gases in the furnace and gas ducts of the boiler.
7.21.1. An explosion of gases in the furnace and flue ducts of the boiler can occur from a large amount of accumulated mixture of gas and air in the furnace and throughout the duct during instant ignition from an incendiary torch brought into the furnace or from high temperature in the furnace.
7.21.2. It must be remembered that an explosion in the furnace and gas pipelines of the boiler is accompanied by destruction of the lining, gas ducts, smoke exhausters and other elements of the boiler.
7.21.3. The causes of a gas explosion in the furnace and gas ducts of the boiler can be:
Torch breakage in the furnace and incorrect actions of personnel during re-ignition;
Failure to comply with the boiler firing regime, unsatisfactory control over the torch;
7.21.4. If there is a pop in the firebox, without extinguishing it, when there are no significant disturbances, you should establish a normal vacuum in the firebox and air pressure in front of the burners and gradually restore combustion in the firebox.
7.21.5. Personnel (senior driver, line operator), on the instructions of the shift supervisor, are required to inspect the boiler in order to identify the causes of the explosion (pop) and the presence of damage, close the hatches and peepholes.
7.21.6. In the event of a gas explosion in the furnace and gas ducts of the boiler with destruction of the lining, deformation of pipes, etc., the boiler operator is obliged to emergency stop the boiler unit.
7.22. Torch breakage.
7.22.1. Flame failure can occur for the following reasons:
When the pressure in the gas pipeline decreases;
Fuel hanging in the storage tank;
Relieve voltage from dust feeder drives;
Reduced air pressure in front of the burners.
7.22.2. If a torch breaks, you must:
Immediately stop the supply of fuel to the firebox by closing the shut-off and gas valves and closing the valves at the burners in the supply to the boiler;
Turn off dust feeders;
Close the main steam valves, carefully monitor the water level in the drum, the temperature of the steam, metal and gas path;
Open the superheater purge;
Ventilate the furnace, burners and boiler flues for 10 minutes, take an analysis of the air in the furnace for the absence of methane;
Find out and eliminate the cause of the extinguishing and only then begin to light the boiler.
7.23. Reduced pressure in the gas pipeline.
7.23.1. A drop in pressure in a gas pipeline can occur for the following reasons:
Erroneous actions of personnel when switching gas pipeline diagrams;
Mechanical damage to valves, valves, etc.;
Gas pipeline rupture.
7.23.2. Personnel actions:
Report the incident to the NSS;
Reduce the boiler load, begin preparing a backup fuel circuit and (if there is dust in the bunker) transfer some of the burners to burning dust;
Transfer the boiler power supply from automatic to remote;
In the event of a sharp decrease in the temperature of the superheated steam and if the switching on of the reserve fuel is delayed, turn off the boiler using the emergency stop key;
Unload smoke exhausters and fans and then stop them;
Find out the reason for the drop in pressure and gas, and if necessary, switch to the reserve hydraulic fracturing line.
7.24. Partial and complete load shedding.
Load shedding is a sudden, rapid reduction and complete cessation of steam consumption by a turbine.
7.24.1. Signs of load shedding:
A sharp increase in steam pressure in the boiler drum and steam lines;
Reduced steam output;
Rapid increase in water level in the drum.
7.24.2. If the turbine load shedding is partial, then it is necessary to reduce the load on the boiler by lowering the gas pressure in front of the burners.
7.24.3. When the turbine is completely unloaded, it is necessary to:
Open the superheater purge to the atmosphere and reduce the gas flow to the boiler with a gas control valve;
Shut off the water to the desuperheaters;
Monitor the power supply to the boiler, maintaining a normal level in the drum;
When the level in the drum rises above +50 mm, open the emergency release, reduce the level to normal;
7.24.4. When completely shedding the load and turning off electrical auxiliary needs, you must:
Immediately manually close the gas control valve and valves on the gas lines to the burners;
Cover the guide vanes of smoke exhausters and fans;
Acknowledge the control keys of all shutdown motors;
If the steam pressure in the drum has crossed the red line and the control valves have not been blown up, blow them up remotely from the control room, one on each side;
Close the control valves on the power supply unit;
Close the control valves on the desuperheaters.
7.24.5. In all cases it is necessary:
Act quickly, accurately, observing operating and safety rules;
Report the incident to the service administration;
Carefully monitor the water level in the drum and the temperature of the top and bottom of the drum metal coils and steam lines, not allowing deviations above normal;
Keep in touch with the NSS and the shift supervisor of KTO-1, following all their instructions to eliminate the emergency situation.
7.25. When the voltage on the control devices disappears.
7.25.1. The readings of all recording instruments remain in the same position.
7.25.2. Personnel actions:
Immediately report to the NSS and NS of Instrumentation and Automation and demand restoration of voltage;
Maintain the boiler load constant;
Send the operator-inspector to monitor the level in the drum at the water indicator columns and the pressure in the drum and inform the boiler operator by phone.
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