Control and measuring devices (KIP)- devices for measuring pressure, temperature, flow rate of various media, liquid levels and gas composition, as well as safety devices installed in the boiler room.
Measuring device— a technical means of measurement that provides the generation of a measurement information signal in a form convenient for the observer.
Distinguish between indicating and self-recording indicator devices. Instruments are characterized by range, sensitivity and measurement error.
Instruments for measuring pressure. Pressure is measured by manometers, thrust meters (low pressure and vacuum), barometers and aneroids (atmospheric pressure). Measurements are made using the phenomenon of deformation of elastic elements, changes in the levels of the liquid, which is affected by pressure, etc.
Deformation-type pressure gauges and thrust gauges contain an elastic element (bent hollow springs or flat membranes or membrane boxes) moving under the action of medium pressure transmitted from the measuring probe into the internal cavity of the element through a fitting. The movement of the elastic element is transmitted through a system of rods, levers and gears to the pointer, which fixes the measured value on the scale. Manometers are connected to water pipelines by means of a straight fitting, and to steam pipelines by means of a curved siphon tube (condenser). A three-way valve is installed between the siphon tube and the pressure gauge, which allows the pressure gauge to communicate with the atmosphere (the arrow will show zero) and blow the siphon tube.
Liquid manometers are made in the form of transparent (glass) tubes partially filled with liquid (tinted alcohol) and connected to pressure sources (vessel-atmosphere). Tubes can be mounted vertically (U-gauge) or obliquely (micromanometer). The magnitude of pressure is judged by the movement of liquid levels in the tubes.
Instruments for measuring temperature. Temperature measurement is carried out using liquid, thermoelectric thermometers, optical pyrometers, resistance thermometers, etc.
In liquid thermometers, under the influence of heat flow, the heated (cooled) liquid expands (compresses) inside a sealed glass tube. Most often, mercury from -35 to +600 0 С and alcohol from -80 to +60 0 С are used as a filling liquid. Thermoelectric thermometers (thermocouples) are made in the form of electrodes (wires) welded together at one end from dissimilar materials placed in a metal case and isolated from it. When heated (cooled) at the junction of thermoelectrodes (in the junction), an electromotive force (EMF) arises and a potential difference appears at the free ends - a voltage that is measured by a secondary device. Depending on the level of measured temperatures, thermocouples are used: platinum-rhodium - platinum (PP) - from -20 to +1300 0 C, chromel-alumel (XA) - from -50 to +1000 0 C, chromel-copel (XK) - from - 50 to +600 0 С and copper - constantan (MK) - from -200 to +200 0 С.
The principle of operation of optical pyrometers is based on comparing the luminosity of the measured object (for example, a torch of burning fuel) with the luminosity of a filament heated from a current source. They are used to measure high temperatures (up to 6000 0 C).
The resistance thermometer works on the principle of measuring the electrical resistance of a sensitive element (a thin wire wound on a frame or a semiconductor rod) under the action of a heat flux. As wire resistance thermometers, platinum (from -200 to +75 0 С) and copper (from -50 to +180 0 С) are used; in semiconductor thermometers (thermistors), copper-manganese (from -70 to +120 0 C) and cobalt-manganese (from -70 to +180 0 C) sensing elements are used.
Instruments for measuring flow. The measurement of the flow rate of liquid or gas in the boiler room is carried out either by throttling or summing devices.
A throttle flow meter with a variable pressure drop consists of a diaphragm, which is a thin disk (washer) with a cylindrical hole, the center of which coincides with the center of the pipeline section, a pressure drop measuring device and connecting pipes.
The summing device determines the flow rate of the medium by the rotational speed of the impeller or rotor installed in the housing.
Instruments for measuring the level of liquid. Water-indicating devices (glasses) are designed for continuous monitoring of the position of the water level in the upper drum of the boiler unit.
For this purpose, at least two direct-acting water-indicating instruments with flat, smooth or corrugated glasses are installed on the latter. When the height of the boiler unit is more than 6 m, lowered remote water level indicators are also installed.
Safety devices - at devices that automatically stop the supply of fuel to the burners when the water level drops below the permissible level. In addition, steam and water-heating boiler units operating on gaseous fuels, when air is supplied to the burners from draft fans, are equipped with devices that automatically stop the gas supply to the burners when the air pressure drops below the permissible value.
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Modern heat power industry cannot be imagined without high-precision measuring instruments. The technological process at power facilities must be constantly monitored using sensors or transducers that not only passively collect information, but also allow automatic adjustment and protective shutdown in case of violation of the normal mode.
Types of instrumentation and automation in the boiler room
From the common name and the above, we can conclude that the following complexes are necessary for the trouble-free operation of gas equipment:
- measuring;
- adjusting;
- protective.
The operation of water heating and power plants without protection devices is prohibited, since in non-standard situations and breakdowns, the threat to human life and the integrity of mechanisms increases many times over. Before kindling, the staff on duty organizes a check of the operation of the protections to stop the boiler. The introduction of this clause in the PTE helped to seriously reduce the negative consequences of accidents.
Features of the work of instrumentation and automation of boiler equipment
For network and gas pipelines, both remote digital complexes and mechanical devices in place are provided. This allows maintenance personnel to monitor the state of the environment during a boiler bypass or during a power failure. The action of protections most often extends to the fuel supply, to prevent an explosion in case of violations of the combustion regime in boilers.
Maintenance of instrumentation in boiler rooms
For the correct operation of control devices at thermal power facilities, a special workshop or division is formed. This service performs the following functions:
- daily monitoring of the correctness of the readings,
- checking protection devices;
- repair and replacement of broken devices;
- periodic verification of measuring devices.
Maintaining the mode of the boiler unit is impossible without constant control by the operator of the boiler room. Several rounds per shift help to keep such measuring equipment in good working order.
Instrumentation and control devices for boiler rooms
The main measuring devices in gas boilers are:
- Pressure gauges. Necessary for pressure control in pipelines, without them operation is often impossible. According to them, the combustion process in hot water and power boilers is regulated by measuring the pressures of natural gas and air.
- Thermocouples. The coolant must be released into the city with a certain temperature. To control it, and hence the operating mode of the boiler room, several thermal converters are installed.
- Flowmeters. The economic characteristics of the production of heat and electricity are related to the costs of the working environment and fuel. To measure them, digital recording devices are used.
Mechanic of instrumentation and control of gas boilers
In modern production, all parameters obtained from measuring instruments are accumulated at the point. Computer systems on it allow you to access this information, up to a certain period. This order is useful for analysis.
Duties of the locksmith on duty include the following general items:
- ensuring the serviceability of control and protection devices;
- periodic check of measuring instruments;
- maintenance of instrumentation in the boiler room;
- accumulation and provision of holistic information on the parameters of the production process.
Operational personnel in shifts ensures the normal operation of measuring complexes at energy facilities and heating networks. He also controls the information collection system to prevent its failures.
To ensure safe and uninterrupted operation, boilers are equipped with appropriate fittings and instrumentation (KIP). Fittings include: safety, feed and check valves, valves and gate valves, as well as water-indicating and purge devices. Control and measuring devices are designed to monitor and control the process of the boiler. These include: pressure gauges, traction meters, thermometers, flow meters, gas analyzers and others. Depending on the type of boiler (steam or hot water), various fittings and instrumentation are installed on it.
Safety valve It is designed to prevent pressure increase in the boiler above the allowable one. Safety valves are spring (Fig. 5.51) and lever (Fig. 5.52) types.
When the pressure in the boiler or pipeline rises above the permissible value, the valve plate rises, freeing the seat, part of the coolant escapes into the atmosphere through the outlet, and the pressure drops to normal. The valve stem together with the plate under the action of a load (lever) or a spring (spring) is lowered to its original position, the outlet is blocked.
Rice. 5.50.
a- slip-in type valve; b - asbestos valve; in - flap type valve; 1 - roofing steel; 2 - asbestos cardboard; 3 - metal grid; 4 - a mixture of chamotte clay with asbestos; 5 - metal box; 6 - roller; 7 - door; 8 - removable frame; 9 - wire; 10 - socket
Rice. 5.51.
1 - frame; 2 - plate; 3 - spring; 4 - lever of manual undermining; 5 - stock; b - guide bushing; 7 - locking screw; ? - pressure bushing; 9 - damper bushing; 10 - lid; 11 - cap; 12 - locking bolt
Rice. 5.52.
a- single-lever; b- double lever
By moving a weight along a lever (lever valve) or by changing the amount of spring compression (spring) using a threaded pressure sleeve, the valve opening pressure can be reduced or increased.
Hot water boilers without drums with a water temperature of up to 115 ° C with a capacity of more than 405 kW, as well as boilers with drums, regardless of their performance, must be equipped with two safety valves, hot water boilers without drums with a capacity of 405 kW or less - with one valve. For steam boilers with a steam capacity of more than 100 kg / h, one valve (control) must be sealed.
If there are several hot water boilers without drums in the boiler room, instead of safety valves on the boilers, it is allowed to install two safety valves with a diameter of at least 50 mm on the pipeline to which the boilers are connected. The diameter of each safety valve is taken according to the calculation for one of the boilers with the highest productivity and is calculated using the formulas:
when installing boilers with natural circulation
- (5.11)
- (5.12)
106 pi'
when installing boilers with forced circulation
10 6 pI’
where (1 - valve passage diameter, cm;
O - maximum boiler performance, W; P - number of valves;
H - valve lift, see
When installing safety valves on a common hot water pipeline, a bypass with a check valve is provided at the shut-off valve of each boiler.
For safe operation, steam boilers with pressures up to 0.07 MPa are equipped with safety ejection devices (hydraulic seals) or self-adjusting valves KSh-07. Conventional lever or spring valves are not installed on such boilers. The safety discharge device (Fig. 5.53) is activated when the steam pressure in the boiler exceeds the working pressure by more than 10 kPa. The device works as follows. Through the supply I pipes 2, 3 and 6 are filled with water up to the plug cock 7. During the operation of the boiler, steam displaces water from the pipe 2 and its level goes down, and in the pipes 3 and 6 rises, and their water column balances the vapor pressure. When the steam pressure rises above the allowable water from the pipe 2 expelled until excess steam escapes into the tank 4 spew the atmosphere through the pipe 5. When the pressure in the boiler drops, the water from the tank through the pipe 3 will refill the pipes of the discharge device. Ejection device height H is selected in accordance with the working pressure of the steam in the boiler: at a pressure of 50, 60, 70 kPa, it is respectively taken 6, 7, m. filling height And = 0,56#.
The safety self-lapping valve KSh-07-810 (Fig. 5.54) consists of a body / closed with a cap 2. Inside the valve there is an impeller weight 3, and in the pipe with which it is attached to the steam line, a seat is pressed 4, a fungus 5 is placed on the impeller load, which closes the steam outlet from the boiler. The fungus is pressed against the saddle due to the mass of the weight-impeller, which has three arcuate blades. With an increase in the steam pressure set in the boiler, the fungus with the load rises, the steam pressure spreads over the entire area of the load and the bottom of the valve, ensuring their rise, then the steam leaves through the hole in the cap. The presence of the blades creates a torque, and the impeller load begins to rotate. After the release of excess steam, the fungus, due to rotation, sits in a new position and at the same time rubs in. To check the operability of the valve, it has a lever 7 and a handle 8. There is a signal whistle for sound indication of valve actuation. 6.
Rice. 5.53.
Pipes from safety valves are usually led outside the boiler room, and they have devices for draining water. The cross-sectional area of the pipe is at least twice the cross-sectional area of the safety valve.
A check valve and a shut-off device are installed on the supply pipeline to the steam boiler (Fig. 5.55).
To control the parameters that are necessary to monitor during the operation of the boiler house, they provide for the installation of indicating devices: to control parameters, a change in which can lead to an emergency condition of the equipment, signaling indicating devices, and for control
Rice. 5.54
the role of parameters, the account of which is necessary for the analysis of the operation of equipment or economic calculations - recording or summing devices.
For boilers with a steam pressure over 0.17 MPa and a capacity of less than 4 t / h, indicating instruments are installed to measure:
- a) temperature and pressure of feed water in the common line in front of the boilers;
- b) steam pressure and water level in the drum;
- c) air pressure under the grate or in front of the burner;
- d) rarefaction in the furnace;
- e) pressure of liquid and gaseous fuel in front of the burners.
Rice. 5.55. Shut-off valve (1) and check valve (2)
For boilers with a steam pressure over 0.17 MPa and a capacity of 4 to 30 t / h, indicating instruments are installed to measure:
- a) steam temperature downstream of the superheater to the main steam valve;
- c) flue gas temperatures;
- e) steam pressure in the drum (for boilers with a capacity of more than 10 t / h, this device must be recording);
- f) superheated steam pressure up to the main steam valve;
- l) rarefaction in the furnace;
- m) steam flow in the common steam pipeline from boilers (self-recording device);
- o) oxygen content in flue gases (portable gas analyzer);
- n) water level in the boiler drum.
If the distance from the site from which the water level is monitored to the axis of the drum is more than 6 m, or if the visibility of the water-indicating devices is poor, two lowered level indicators are installed on the drum, with one of the indicators being registering.
For boilers with a steam pressure over 0.17 MPa and a capacity of more than 30 t / h, indicating instruments are installed to measure:
- a) steam temperature after the superheater to the main steam valve (indicating and registering);
- b) temperature of the feed water after the economizer;
- c) flue gas temperatures (indicating and recording):
- d) air temperature before and after the air heater;
- e) steam pressure in the drum;
- f) superheated steam pressure up to the main steam valve (indicating and registering);
- g) steam pressure at oil nozzles;
- h) pressure of feed water at the inlet to the economizer after the regulating body;
- i) air pressure after the draft fan;
- j) pressure of liquid and gaseous fuel in front of the burners behind the regulating body;
- l) rarefaction in the furnace;
- l) rarefaction in front of the smoke exhauster;
- m) steam flow from the boiler (indicating and registering);
- o) the consumption of liquid and gaseous fuels for the boiler (summing and registering);
- o) feed water flow to the boiler (indicating and registering);
- p) oxygen content in flue gases (automatic indicating and recording gas analyzer);
- c) the water level in the boiler drum.
If the distance from the site from which the water level is monitored to the axis of the drum is more than 6 m or if the visibility of water-indicating devices is poor, two lowered level indicators are installed on the boiler drum, one of which is registering.
For boilers with a steam pressure of 0.17 MPa and below and hot water boilers with a water temperature of 115 ° C and below, the following indicating instruments are installed for measuring:
- a) water temperature in the common pipeline in front of hot water boilers and at the outlet of each boiler (up to shutoff valves);
- b) steam pressure in the steam boiler drum;
- c) air pressure after the blower fan:
- d) air pressure after the regulating body;
- e) rarefaction in the furnace;
- f) rarefaction after the boiler;
- g) gas pressure in front of the burners.
For hot water boilers with a water temperature of more than 115 ° C, indicating instruments are installed to measure:
- a) water temperature at the inlet to the boiler after the shutoff valves;
- b) water temperature at the outlet of the boiler to the shut-off valves;
- c) air temperature before and after the air heater;
- d) flue gas temperatures (indicating and recording);
- e) water pressure at the inlet to the boiler after the shut-off valves and at the outlet of the boiler before the shut-off valves;
- f) air pressure after the draft fan;
- g) pressure of liquid and gaseous fuel before the burners after the regulating body;
- h) rarefaction in the furnace;
- i) rarefaction in front of the smoke exhauster;
- j) water flow through the boiler (indicating and registering);
- k) consumption of liquid and gaseous fuels for boilers with a capacity of 30 MW or more (summing and registering);
- l) oxygen content in exhaust gases (for boilers with a capacity of up to 20 MW - a portable gas analyzer, for boilers with a higher capacity - automatic indicating and recording gas analyzers);
- m) temperature of liquid fuel at the inlet to the boiler room;
- o) pressure in the supply and return pipelines of heating networks (before and after the mud collectors);
- n) water pressure in the supply lines;
- p) pressure of liquid and gaseous fuels in the lines in front of the boilers.
In addition, recording devices are installed in the boiler room to measure:
- a) temperature of superheated steam in the common steam pipeline to consumers;
- b) water temperature in the supply pipelines of heat supply and hot water supply systems and in each return pipeline;
- c) return condensate temperature;
- d) steam pressure in the common steam pipeline to the consumer (at the request of the consumer);
- e) water pressure in each return pipeline of the heat supply system;
- f) pressure and temperature of gas in the common gas pipeline of the boiler room;
- g) water flow in each falling pipeline of heat supply and hot water supply systems (summing);
- h) steam flow to the consumer (summing);
- i) the flow rate of water supplied to feed the heating network, with its quantity of 2 t / h or more (summing up);
- j) consumption of circulating hot water supply (summing);
- k) the flow rate of the returned condensate (total);
- l) gas flow in the common gas pipeline of the boiler house (summing);
- m) liquid fuel consumption in the forward and reverse lines (summing).
Control and monitoring of the water level in the steam boiler is carried out with the help of water-indicating devices - water-indicating glasses (Fig. 5.56). water-indicating glass is a glass tube, the ends of which are inserted into the heads of the taps connected to the water and steam space of the drum. If the distance from the site from which the water level is monitored to the axis of the drum is more than 6 m or if visibility of water indicating devices is poor, in addition to those installed on the drum, reduced level indicators(Fig. 5.57). These indicators work on the principle of balancing two columns of water in communicating tubes with a specially colored liquid with a density greater than that of water.
To measure the pressure of water and steam on the boilers set pressure gauges. The pressure gauge is connected to the boiler using a curved tube in the form of a siphon loop. In the siphon, due to the condensation of steam, a water seal is formed, which protects the mechanism of the device from the thermal effects of steam.
The pressure gauge is supplied with a three-way valve with a flange for connecting a control device. On the pressure gauge scale, the red line marks the maximum allowable pressure in this boiler, above which operation is prohibited.
Rice. 5.56.
To measure the water temperature set thermometers various types and designs.
To measure the rarefaction in the furnace and the draft behind the boiler, thrust gauges are installed. They, as a rule, are liquid (Fig. 5.58). The draft-pressure meter scale is located along the inclined tube and can be moved with the help of a screw to set the pointer to the zero position against the initial liquid level. The device can be filled with colored water or alcohol. On the boiler, the draft-pressure meter is installed horizontally using a level.
Used to measure costs flow meters various kinds.
Rice. 5.57.
/ - expansion vessel; 2 - connecting tubes; 3, 6 - upper and lower water-indicating columns; 4 - condensation vessel; 5 - drainage tube
Rice. 5.58. Liquid draft gauge TNZh
1 - scale; 2 - inclined glass tube; 3 - glass vessel; 4, 5 - fittings for connecting the device; 6 - level; 7 - screw for moving the scale
The development of a boiler house automation project is carried out on the basis of a task drawn up during the implementation of the heat engineering part of the project. The general tasks of monitoring and managing the operation of any power plant are to ensure:
Generation at each moment of the required amount of heat at certain pressure and temperature parameters;
Profitability of fuel combustion, rational use of electricity for the plant's own needs and minimization of heat losses;
Reliability and safety, i.e. establishing and maintaining normal operating conditions for each unit, excluding the possibility of malfunctions and accidents of both the unit itself and auxiliary equipment.
Based on the tasks and instructions listed above, all control devices can be divided into five groups intended for measurement:
1. Consumption of water, fuel, air and flue gases.
2. Water pressure, air gas, vacuum measurement in the elements and gas ducts of the boiler and auxiliary equipment.
3. Water, air and flue gas temperatures
4. Water level in tanks, deaerators and other containers.
5. Qualitative composition of gases and water.
Secondary devices can be indicating, registering and summing. To reduce the number of secondary devices on the heat shield, some of the values \u200b\u200bare collected on one device using switches; for critical values on the secondary device, they mark with a red line the maximum permissible values they are measured continuously.
In addition to the devices displayed in the control panel, local installation of instrumentation is often used: thermometers for measuring water temperatures; manometers for measuring pressure; various draft meters and gas analyzers.
The regulation of the combustion process in the KV-TS-20 boiler is carried out by three regulators: a heat load regulator, an air regulator and a vacuum regulator.
The heat load controller receives a command pulse from the main corrective controller, as well as water flow pulses. The heat load regulator acts on the body that regulates the supply of fuel to the furnace.
The common air regulator maintains the fuel-to-air ratio by receiving fuel flow rate pulses from the sensor and pressure drop across the air heater.
A constant vacuum in the furnace is maintained by means of a regulator in the boiler furnace and a smoke exhauster acting on the guide vane. There is a dynamic connection between the air regulator and the vacuum regulator, the task of which is to supply an additional impulse in transient modes, which makes it possible to maintain the correct draft mode during the operation of the air and vacuum regulator.
The dynamic coupling device has a direction of action, i.e. only the vacuum regulator can be a slave regulator.
Power regulators are installed to monitor the consumption of network and feed water.
Mercury expansion thermometer:
Industrial mercury thermometers are made with an embedded scale and, according to the shape of the lower part with a tank, there are straight type A and angled type B, bent at an angle of 90º in the direction opposite to the scale. When measuring temperature, the lower part of the thermometers is completely lowered into the measured medium, i.e. their immersion depth is constant.
Expansion thermometers are indicating instruments located at the place of measurement. Their principle of operation is based on the thermal expansion of liquid in a glass tank depending on the measured temperature.
Thermoelectric thermometer:
To measure high temperatures with remote transmission of readings, thermoelectric thermometers are used, the operation of which is based on the principle of the thermoelectric effect. Chromel - kopel thermoelectric thermometers develop a thermo - emf, significantly exceeding the thermo - emf of other standard thermoelectric thermometers. The range of application of chromel - kopel thermoelectric thermometers is from - 50º to + 600º C. The diameter of the electrodes is from 0.7 to 3.2 mm.
Tubular - spring manometer:
The most widely used for measuring the excess pressure of liquid, gas and steam are manometers, which have a simple and reliable design, clarity of indications and small size. The essential advantages of these devices are also a large measurement range, the possibility of automatic recording and remote transmission of readings.
The principle of operation of a deformation manometer is based on the use of deformation of an elastic sensitive element that occurs under the influence of the measured pressure.
A very common type of deformation devices used to determine excess pressure are tubular - spring pressure gauges, which play an extremely important role in technical measurements. These devices are made with a single-turn tubular spring, which is a metal elastic tube of oval section bent around the circumference.
One end of the helical spring is connected to the gear, and the other end is fixed to the rack supporting the transmission mechanism.
Under the action of the measured pressure, the tubular spring partially unwinds and pulls the leash behind it, setting in motion the gear-sector mechanism and the pressure gauge needle moving along the scale. The manometer has a uniform circular scale with a central angle of 270 - 300º.
Automatic potentiometer:
The main feature of the potentiometer is that it develops thermo-e. d.s. is balanced (compensated) by a voltage equal to it in magnitude, but opposite in sign, from a current source located in the device, which is then measured with great accuracy.
Automatic compact potentiometer type KSP2 is an indicating and self-recording device with a linear scale length and a chart tape width of 160 mm. The main error of the instrument readings is ±0.5 and the recording error is ±0.1%.
The variation of readings does not exceed half of the basic error. The chart tape speed can be 20, 40, 60, 120, 240 or 600, 1200, 2400 mm/h.
The potentiometer is powered by 220 V AC, 50 Hz. The power consumed by the device is 30 V A. Changing the supply voltage by ±10% of the nominal does not affect the readings of the device. Permissible ambient air temperature is 5 - 50ºС and relative humidity 30 - 80%. The dimensions of the potentiometer are 240 x 320 x 450 mm. and weight 17 kg.
Deformation electric pressure gauges are recommended to be installed near the pressure tap, fixed vertically with the nipple down. For pressure gauges, the ambient air may have a temperature of 5 - 60ºC and a relative humidity of 30 - 95%. They must be removed from powerful sources of alternating magnetic fields (electric motors, transformers, etc.)
The pressure gauge contains a tubular spring 1, fixed in the holder 2 with the help of a sleeve 3. To the free end of the spring, a magnetic plunger 5 is suspended on the lever 4, located in the magnetic modulation converter 6 sitting on the holder. Amplifying device 7 is fixed next to the latter on a folding bracket.
The device is enclosed in a steel case 8 with a protective casing 9 adapted for flush mounting. The connection of the pressure gauge with the measured pressure is carried out using the holder fitting, and the connecting wires are connected through the terminal box 10. The pressure gauge is equipped with a zero corrector 11. The dimensions of the device are 212 x 240 x 190 mm. and weight 4.5 kg.
MPE type pressure gauges can be used with one or more secondary DC devices: automatic electronic indicating and self-recording milliammeters of types KSU4, KSU3,
KSU2, KSU1, KPU1 and KVU1, calibrated in units of pressure, magnetoelectric indicating and self-recording milliammeters of types H340 and H349, central control machines, etc. Automatic electronic DC milliammeters differ from the corresponding automatic potentiometers only by a calibrated load resistor connected in parallel to the input, the voltage drop across which from the flowing current of the pressure gauge is the measured value.
Magnetoelectric milliammeters of types H340 and H349 have a scale and chart width of 100 mm. instrument accuracy class 1.5. The chart tape is set in motion at a speed of 20 - 5400 mm / h from a synchronous micromotor, powered by an alternating current main of 127 or 220 V, frequency of 50 Hz.
Dimensions of the device 160 x 160 x 245 mm. and weight 5 kg.
Direct Acting Regulator:
An example of a direct acting regulator is a control valve.
The valve consists of a cast-iron body 1 closed from the bottom with a flange cover 2, which closes the hole for draining the medium filling the valve and for cleaning the valve. 3 stainless steel seats are screwed into the valve body. The plunger 4 sits on the saddle. The working surfaces of the plunger are lapped to the seats 3. The plunger is connected to the stem 6, which can raise and lower the plunger. The rod runs in a stuffing box. The stuffing box seals cover 7, which is attached to the valve body. To lubricate the rubbing surfaces of the rod, oil is supplied to the stuffing box from the oiler 5. The valve is controlled by a membrane-lever device, consisting of a yoke 8, a membrane head 13, a lever 1 and weights 16.17. In the membrane head, between the upper and lower cups, a rubber membrane 15 is clamped, resting on a plate 14, planted on the rod 9 of the yoke. A rod 6 is fixed in the rod 9. The rod of the yoke has a prism 12, on which the lever 11 rests, rotating on the prismatic support 10, fixed in the yoke 8.
In the upper bowl of the membrane head there is a hole in which the impulse tube is fixed, supplying a pressure pulse to the membrane. Under the action of increased pressure, the membrane bends and drags the plate 14 and the rod of the yoke 9 down. The force developed by the membrane is balanced by the weights 16 and 17 suspended on the lever. Weights 17 are used for rough adjustment of the set pressure. With the help of load 16 moving along the lever, a more precise adjustment of the valve is made.
The pressure on the diaphragm head is transmitted directly by the regulated medium.
Actuating mechanism:
Regulators are used to regulate the flow of liquid, gas or steam in the process. The movement of regulatory bodies is carried out by executive mechanisms.
Regulators and actuators can be in the form of two separate units interconnected by means of lever rods or cables, or in the form of a complete device, where the regulator is rigidly connected to the actuator and forms a monoblock.
The actuator, receiving a command from the regulator or from a command apparatus controlled by a person, converts this command into a mechanical movement of the regulatory body.
The mechanism is electric, single-turn, designed to move the regulatory bodies in relay control and remote control systems. The mechanism perceives an electrical command, which is a three-phase mains voltage of 220 or 380 V. The command can be given using a magnetic contact starter.
The actuator consists of an electric motor part
I - servo drives and control columns, II servo drive unit. The servo drive consists of a three-phase asynchronous reversible motor 3 with a squirrel-cage rotor. From the motor shaft, the torque is transmitted to gearbox 4, which consists of two stages of a worm gear. Lever 2 is mounted on the input shaft of the gearbox, which is articulated with the regulating body with the help of a rod.
By turning the handwheel 1, with manual control, it is possible to turn the output shaft of the gearbox without the help of an electric motor. When manually operating the flywheel, the mechanical transmission from the electric motor to the flywheel is disconnected.
The regulatory body is designed to change the flow rate of the regulated medium, energy or any other quantities in accordance with the requirements of the technology.
In poppet valves, the closing and throttling surface is flat. A plug-type valve with smooth working surfaces has a linear characteristic, i.e. the valve capacity is directly proportional to the plunger stroke.
The regulation is carried out by changing the flow area by translational movement of the spindle during the rotation of the flywheel using a lever articulated through a rod with an electric actuator.
Valves cannot serve as shut-off devices.
Control starter:
Starters PMTR - 69 are made on the basis of magnetic reversing contacts, each of which has three normally open power contacts included in the power supply circuit of the electric motor. In addition, the starting device has a braking device made on the basis of an electric capacitor and connected through break contacts to one of the stator windings of the electric motor. When any group of power contacts is closed, auxiliary contacts open and the capacitor is disconnected from the electric motor, moving by inertia, interacts with the residual magnetic field of the stator and induces emf in its windings.
Auxiliary contacts, closing the circuit of the stator winding of the capacitor, create in the stator its own magnetic field of the rotor and the stator causes a braking effect that counteracts rotation, which prevents the actuator from running out. The main disadvantage of starters is low reliability (burning of contacts, short circuit).
The block has three current and one voltage inputs. Block R - 12 consists of the main components: input circuits of VkhTs, DC amplifiers UPT 1 and UPT 2, MO limiting unit, while UPT 2 allows you to receive one current signal and an additional voltage signal at the output. Block R - 12 receives power from the power supply unit, which receives an additional signal from the control unit CU.
The signal from the sensor is fed to the node of the input circuits, where the signal of the setting device I z is also supplied. Next, the mismatch signal y goes to the DC amplifier UPT 1, passing through the adder, where mismatch signals are generated from the input circuits and feedback. The OM signal limiter provides its further transformation, limiting the signal to the minimum and maximum. The UPT 2 amplifier is the final amplification unit. The feedback block MD receives a signal from the output of the UPT 2 amplifier and ensures smooth switching of circuits from manual control to automatic. The feedback block MD ensures the formation of a control signal in accordance with the P -, PI - or PID control laws.
Technological protection.
In order to avoid emergency modes of equipment control systems in case of excessive deviations of parameters and to ensure the safety of work, they are equipped with technological protection devices.
Depending on the results of the impact on the protection equipment, they are divided into: those that stop or turn off the units; transferring equipment to reduced load mode; performing local operations and switching; preventing emergencies.
Protection devices must be reliable in pre-emergency and emergency situations, i.e. there must be no failures or false alarms in the protection actions. Failures in protection actions lead to untimely shutdown of the equipment and further development of the accident, and false alarms take the equipment out of the normal technological cycle, which reduces its efficiency. To meet these requirements, highly reliable instruments and devices are used, as well as appropriate construction of protection circuits.
The protection includes sources of discrete information - sensors, contact devices, auxiliary contacts, logic elements and a relay control circuit. The activation of the protections should ensure the unambiguity of the action, while the transfer of equipment to the operating mode after its protection is carried out after checking and eliminating the causes that caused the operation.
When designing thermal protection of boilers, turbines and other thermal equipment, the so-called priority of protection action is envisaged, i.e., first of all, operations are performed for one of the protections that causes a greater degree of unloading. All protections have independent power sources and the ability to fix the causes of operation, as well as light and sound alarms.
Technological signaling.
General information about signaling.
Technological alarm, which is part of the control system, is designed to notify operating personnel about unacceptable deviations in the parameters and operation mode of the equipment.
Depending on the requirements for the alarm, it can be conditionally divided into several types: alarm, ensuring the reliability and safety of the equipment; signaling, fixing the operation of the equipment protection and the reasons for the operation; alarm signaling of unacceptable deviations of the main parameters and requiring an immediate shutdown of the equipment; signaling of power failure of various equipment and equipment.
All signals are sent to the light and sound devices of the block control panel. There are two types of sound alarms: warning (bell) and emergency (siren).
Light alarms are made in two-color versions (red or green bulbs) or with the help of luminous displays, which indicate the reason for the alarm.
Newly received signals against the background of those already controlled by the operator may go unnoticed, so the signaling circuits are built so that the new signal is highlighted by flashing.
Functional diagram of the alarm device.
The signaling circuit is powered by a DC power supply, which increases their reliability. The signal for switching on the alarm CB is fed to the block of the relay signal interruption of the BRP signal, and then in parallel to the light panel ST and the sound device of the memory. At the same time, the circuit in the PDU is designed in such a way that it provides an intermittent glow on the display and a constant sound signal.
After receiving a signal and removing the sound, the circuit must be ready to receive the next signal, regardless of whether the signaling parameter has returned to its nominal value.
Each light signal must be accompanied by a sound signal to attract the attention of service personnel.
Signaling means.
Electronic contact manometer.
To measure and signal pressure, a manometer of the EKM type with a tubular spring is used. The manometer has a case with a diameter of 160 mm. with rear flange and radial fitting. The device contains an arrow 1, which sets the signal arrows 2 and 3 (minimum and maximum), set to the specified pressure values using a key. Box 4 with clamps for connecting the alarm circuit to the device. The pressure gauge mechanism is enclosed in a housing 5. The device communicates with the medium being measured through the fitting 6.
When any of the specified marginal pressures is reached, the contact associated with the index arrow comes into contact with the contact located on the corresponding signal arrow and closes the alarm circuit. The contact device is powered by a DC or AC network, 220 V.
Instrumentation and automation (KIPiA) are designed to measure, control and regulate temperature, pressure, water level in the drum and ensure the safe operation of heat generators and heat power equipment of the boiler house.
1. Temperature measurement.
To measure the temperature of the working fluid, manometric and mercury thermometers are used. A stainless steel sleeve is welded into the pipeline, the end of which must reach the center of the pipeline, it is filled with oil and a thermometer is lowered into it.
Manometric thermometer consists of a bulb, a copper or steel tube and an oval tubular spring connected by a lever transmission with an indicating arrow.
Rice. 3.1. Manometric thermometer
1-bulb; 2-connecting capillary; 3-thrust; 4-arrow; 5-dial; 6 gauge spring; 7-ribbed-sector mechanism
The entire system is filled with an inert gas (nitrogen) at a pressure of 1...1.2 MPa. When the temperature rises, the pressure in the system increases, and the spring through the lever system sets the arrow in motion. Indicating and self-recording manometric thermometers are stronger than glass ones and allow transmission of readings over a distance of up to 60 m.
Action resistance thermometers- platinum (TSP) and copper (TCM) is based on the use of the dependence of the electrical resistance of a substance on temperature.
Rice. 3.2. Resistance thermometers platinum, copper
Action thermoelectric thermometer is based on the use of thermocouple thermopower dependence on temperature. A thermocouple as a sensitive element of a thermometer consists of two dissimilar conductors (thermoelectrodes), one end of which (working) is connected to each other, and the other (free) is connected to the measuring device. At different temperatures of the working and free ends, an EMF occurs in the circuit of a thermoelectric thermometer.
The thermocouples of types ТХА (chromel-alumel), ТХК (chromel-kopel) have the greatest distribution. Thermocouples for high temperatures are placed in a protective (steel or porcelain) tube, the lower part of which is protected by a cover and a cover. Thermocouples have high sensitivity, low inertia, the ability to install recorders at a great distance. The thermocouple is connected to the device with compensating wires.
2. Pressure measurement.
To measure pressure, barometers, manometers, vacuum gauges, draft meters, etc. are used, which measure barometric or excess pressure, as well as vacuum in mm of water. Art., mm Hg Art., m of water. Art., MPa, kgf / cm 2, kgf / m 2, etc. To control the operation of the boiler furnace (when burning gas and fuel oil), the following devices can be installed:
1) pressure gauges (liquid, membrane, spring) - show the fuel pressure on the burner after the operating valve;
Rice. 3.3. Deformation gauges:
1 - membrane; 2 - active and compensating strain gauge; 3 - console; 4-arrow
2) pressure gauges (U-shaped, diaphragm, differential) - show the air pressure on the burner after the control damper;
3) draft gauges (TNZh, membrane) - show the rarefaction in the furnace.
Traction pressure gauge liquid(ТНЖ) is used to measure small pressures or rarefaction.
Rice. 3.4. Traction pressure gauge type TNZh-N
To obtain more accurate readings, draft gauges with an inclined tube are used, one end of which is lowered into a vessel of large cross section, and alcohol (with a density of 0.85 g / cm 3) tinted with magenta is used as the working fluid. The canister is connected with the “+” fitting to the atmosphere (barometric pressure), and alcohol is poured through the fitting. The glass tube is connected with the “−” (vacuum) fitting to the rubber tube and the boiler furnace. One screw sets the "zero" of the tube scale, and the other - the horizontal level on the vertical wall. When measuring vacuum, the impulse tube is connected to the "-" fitting, and barometric pressure - to the "+" fitting.
Spring gauge designed to indicate pressure in vessels and pipelines and is installed on a straight section. The sensitive element is a brass oval-curved tube, one end of which is built into the fitting, and the free end straightens under the pressure of the working fluid (due to the difference between the internal and external areas) and through the system of thrust and the gear sector transmits the force to the arrow mounted on the gear. This mechanism is located in
case with a scale, covered with glass and sealed. The scale is selected from the condition that at operating pressure the pointer is in the middle third of the scale. The scale should have a red line showing the allowable pressure.
AT electrocontact manometers EKM on the scale has two fixed fixed contacts, and the movable contact is on the working arrow.
Rice. 3.5. Pressure gauge with electrocontact prefix ТМ-610
When the arrow touches the fixed contact, the electrical signal from them is sent to the control panel and the alarm is activated. A three-way valve must be installed in front of each pressure gauge to purge, check and turn it off, as well as a siphon tube (water seal filled with water or condensate) with a diameter of at least 10 mm to protect the internal mechanism of the pressure gauge from exposure to high temperatures. When installing the pressure gauge at a height of up to 2 m from the level of the observation site, the diameter of its body must be at least 100 mm; from 2 to 3 m - not less than 150 mm; 3 ... 5 m - not less than 250 mm; at a height of more than 5 m - a reduced pressure gauge is installed. The pressure gauge must be installed vertically or tilted forward at an angle of up to 30° so that its readings are visible from the level of the observation site, and the accuracy class of the pressure gauges must be at least 2.5 - at pressures up to 2.5 MPa and not lower than 1, 5 - from 2.5 to 14 MPa.
Pressure gauges are not allowed to be used if there is no seal (stamp) or the check period has expired, the pointer does not return to zero on the scale (when the pressure gauge is turned off), the glass is broken or there are other damages. A seal or a brand is established by the State Standard when checking once a year.
Pressure gauge check must be carried out by the operator at each shift acceptance, and by the administration - at least once every 6 months using a control pressure gauge. The pressure gauge is checked in the following sequence:
1) visually notice the position of the arrow;
2) connect the pressure gauge to the atmosphere with the handle of the three-way valve - the arrow should be at zero;
3) slowly turn the knob to its previous position - the arrow should return to its previous (before checking) position;
4) turn the valve handle clockwise and put it in a position where the siphon tube will be connected to the atmosphere - for purge; 5) turn the tap handle in the opposite direction and set it to a neutral position for several minutes, at which the pressure gauge will be disconnected from the atmosphere and from the boiler - to accumulate water in the lower part of the siphon tube;
6) slowly turn the tap handle in the same direction and put it in its original working position - the arrow should return to its original place.
To check the accuracy of the pressure gauge readings, a control (exemplary) pressure gauge is attached to the control flange with a bracket, and the valve handle is placed in a position in which both pressure gauges are connected to the pressurized space. A serviceable pressure gauge should give the same readings with the control pressure gauge, after which the results are recorded in the log of control checks.
Pressure gauges must be installed on the equipment of the boiler room:
1) in a steam boiler unit - a heat generator: on the boiler drum, and in the presence of a superheater - behind it, up to the main valve; on the feed line in front of the valve that regulates the supply of water; on the economizer - inlet and outlet of water to the shut-off body and safety valve; on the
water supply network - when using it;
2) in a water-heating boiler unit - a heat generator: at the inlet and outlet of water to the shut-off valve or gate valve; on the suction and discharge lines of circulation pumps, located at the same level in height; on the feeding lines of the heating system. On steam boilers with a steam capacity of more than 10 t/h and hot water boilers with a heat capacity of more than 6 MW, a recording pressure gauge must be installed.
3. Water-indicating devices.
During operation of the steam boiler, the water level fluctuates between the lowest and highest positions. The lowest permissible level (LRL) of water in the drums of steam boilers is set (determined) to exclude the possibility of overheating of the metal of the walls of the boiler elements and to ensure a reliable flow of water into the downpipes of the circulation circuits. The position of the highest permissible level (VDU) of water in the drums of steam boilers is determined from the conditions for preventing water from entering the steam pipeline or superheater. The volume of water contained in the drum between the upper and lower levels determines the "supply reserve", i.e. the time that allows the boiler to work without water entering it.
Each steam boiler must be equipped with at least two direct-acting water level indicators. Water-indicating devices should be installed vertically or tilted forward, at an angle of no more than 30 °, so that the water level is clearly visible from the workplace. Water level indicators are connected to the upper drum of the boiler using straight pipes up to 0.5 m long and with an inner diameter of at least 25 mm or more than 0.5 m and an inner diameter of at least 50 mm.
In steam boilers with pressures up to 4 MPa, water-indicating glass (VUS) is used - devices with flat glasses with a corrugated surface, in which the longitudinal grooves of the glass reflect light, making the water appear dark and the steam light. The glass is inserted into a frame (column) with a viewing gap width of at least 8 mm, on which the allowable upper TRL and lower TRL of water (in the form of red arrows) must be indicated, and the height of the glass must exceed the allowable measurement limits by at least 25 mm s each side. The arrow of the NDU is installed 100 mm above the firing line of the boiler.
firing line is the highest point of contact of hot flue gases with the uninsulated wall of the boiler element.
Water-indicating devices for disconnecting them from the boiler and for purging are equipped with shut-off valves (faucets or valves). Valves must be clearly marked (molded, embossed or painted) with the direction of opening or closing, and the internal diameter of the passage must be at least 8 mm. To drain water during blowdown, a double funnel with protective devices and a drain pipe for free draining are provided, and a blowdown cock is installed on the firing line of the boiler.
The boiler room operator must check the water-indicating glass by blowing at least once per shift, for which it is necessary:
1) make sure that the water level in the boiler has not dropped below the NDU;
2) notice visually the position of the water level in the glass;
3) open the purge cock - the steam and water cocks are purged;
4) close the steam valve, blow out the water valve;
5) open the steam valve - both valves are purged;
6) close the water tap, blow out the steam;
7) open the water tap - both taps are purged;
8) close the purge valve and observe the water level, which should quickly rise and fluctuate around the previous level, if the glass was not clogged.
Do not close both taps when the purge valve is open, as the glass will cool down and may burst if hot water gets on it. If, after purging, the water in the glass rises slowly or takes a different level, or does not fluctuate, then it is necessary to repeat the purging, and if repeated purging does not give results, it is necessary to clean the clogged channel.
A sharp fluctuation of water characterizes abnormal boiling due to an increased content of salts, alkalis, sludge or the selection of steam from the boiler more than it is produced, as well as the ignition of soot in the gas ducts of the boiler.
A slight fluctuation in the water level characterizes partial “boiling” or clogging of the water tap, and if the water level is higher than normal, “boiling” or clogging of the steam tap. If the steam tap is completely clogged, the steam above the water level condenses, as a result of which the water completely and quickly fills the glass to the very top. If the water tap is completely clogged, the water level in the glass will slowly rise due to steam condensation or will take a calm level, the danger of which is that, not noticing the fluctuations in the water level and seeing it in the glass, one might think that there is enough water in the boiler.
It is unacceptable to raise the water level above the TDU, as water will go into the steam pipeline, which will lead to water hammer and rupture of the steam pipeline.
When the water level drops below the NDU, it is strictly forbidden to feed the steam boiler with water, since in the absence of water, the metal of the boiler walls becomes very hot, becomes soft, and when water is supplied to the boiler drum, strong vaporization occurs, which leads to a sharp increase in pressure, thinning of the metal, formation of cracks and pipe rupture.
If the distance from the water level observation site is more than 6 m, and also in case of poor visibility (illumination) of the instruments, two lowered remote level indicators should be installed; at the same time, it is allowed to install one VUS of direct action on the boiler drums. Reduced level gauges must be connected to the drum on separate fittings and have a damping device.
4. Measurement and regulation of the water level in the drum.
Diaphragm differential pressure gauge(DM) is used for proportional regulation of the water level in drum steam boilers.
Rice. 3.6. Diaphragm indicating differential pressure gauge with vertical diaphragm
1 - "plus" camera; 2 - "minus" camera; 5 - sensitive corrugated membrane; 4- transmission rod; 5 - transmission mechanism; 6 - safety valve and, accordingly, the index arrow, counting the measured pressure on the scale of the device
The pressure gauge consists of two membrane boxes connected through a hole in the diaphragm and filled with condensate. The lower membrane box is installed in the plus chamber filled with condensate, and the upper one is installed in the minus chamber filled with water and connected to the measured object (the upper drum of the boiler). The core of the induction coil is connected to the center of the upper membrane. At an average water level in the boiler drum, there is no pressure drop and the membrane boxes are balanced.
When the water level in the boiler drum rises, the pressure in the negative chamber increases, the membrane box contracts, and the liquid flows into the lower box, causing the core to move down. In this case, an EMF is formed in the coil winding, which, through the amplifier, sends a signal to the actuator and closes the valve on the supply line, i.e. reduces the flow of water into the drum. When the water level drops, the DM works in the reverse order.
Level column UK is designed for positional control of the water level in the boiler drum.
Rice. 3.7. Level measuring column UK-4
It consists of a cylindrical column (pipe) with a diameter of about 250 mm, in which four electrodes are vertically installed, capable of controlling the highest and lowest permissible water levels (HDU and NDU), the highest and lowest working levels of water in the drum (VRU and NRU), the operation of which based on the electrical conductivity of water. The side column is connected to the steam and water volume of the boiler drum by means of pipes with taps. At the bottom of the column has a purge cock.
When the water level is reached, the ASP turns on the relay and the contactor breaks the power supply circuit of the magnetic starter, turning off the drive of the feed pump. The water supply to the boiler is stopped. The water level in the drum drops, and when it drops below the NRU, the relay is de-energized and the feed pump is turned on. When the water level of the VDU and NDU is reached, the electrical signal from the electrodes through the control unit goes to the fuel supply cut-off to the furnace.
5. Instruments for measuring flow.
To measure the flow of liquids (water, fuel oil), gases and steam, flow meters are used:
1) high-speed volumetric, measuring the volume of a liquid or gas according to the flow rate and summing up these results;
2) throttling, with variable and constant differential pressure or rotameters.
In the working chamber high-speed volumetric flowmeter(water meter, oil meter) a vane or spiral fan is installed, which rotates from the liquid entering the device and transfers the flow rate to the counting mechanism.
Volumetric rotary counter(type RG) measures the total gas flow up to 1000 m 3 / h, for which two mutually perpendicular rotors are placed in the working chamber, which are driven under the pressure of the flowing gas, each revolution of which is transmitted through gears and a reducer to a counting mechanism.
Throttle flowmeters with a variable pressure drop have narrowing devices - normal diaphragms (washers) chambered and tubeless with an opening smaller than the pipeline section.
When the flow of the medium passes through the opening of the washer, its speed increases, the pressure behind the washer decreases, and the pressure difference before and after the throttle device depends on the flow rate of the measured medium: the greater the amount of substance, the greater the difference.
The pressure difference before and after the diaphragm is measured by a differential pressure gauge, from the measurements of which it is possible to calculate the rate of fluid flow through the washer hole. A normal diaphragm is made in the form of a disk (made of stainless steel) 3 ... 6 mm thick with a central hole having a sharp edge, and should be located on the side of the liquid or gas inlet and installed between the flanges on a straight section of the pipeline. The pressure impulse to the differential pressure gauge is produced through holes from the annular chambers or through a hole on both sides of the diaphragm.
To measure the steam flow on the impulse tubes, equalization (condensation) vessels are installed to the differential pressure gauge, designed to maintain a constant level of condensate in both lines. When measuring gas flow, the differential pressure gauge should be installed above the constriction device so that the condensate formed in the impulse pipes can drain into the pipeline, and the impulse pipes along the entire length must slope towards the gas pipeline (pipeline) and be connected to the upper half of the washer. Calculation of diaphragms and installation on pipelines is carried out in accordance with the rules.
6. Gas analyzers are designed to control the completeness of fuel combustion, excess air and determine the volume fraction of carbon dioxide, oxygen, carbon monoxide, hydrogen, methane in the combustion products.
According to the principle of action, they are divided into:
1) chemical(GKhP, Orsa, VTI), based on the successive absorption of gases that are part of the analyzed sample;
2) physical operating on the principle of measuring physical parameters (density of gas and air, their thermal conductivity);
3) chromatographic based on the adsorption (absorption) of the components of the gas mixture by a certain adsorbent (activated carbon) and their subsequent desorption (release) when passing through the column with the adsorbent gas.
