A solid fuel boiler, unlike gas, electric or liquid fuel boilers, does not operate continuously, but periodically, especially if it is intended for heating country house or dachas.
Why is condensation dangerous for the boiler?
When lighting a solid fuel boiler, you have to deal with the fact that the cold coolant washes the walls of the already heated combustion chamber, cools them, which leads to condensation of water vapor, which is invariably present in the flue gases. Water particles, interacting with flue gases, form acids, which leads to destruction inner surface combustion chamber and chimney.
But the negative effect of condensate is not limited to this: soot particles that settle on the walls dissolve in drops of water. Under the influence of high temperatures, this mixture sinteres, forming a dense and durable crust on the inner surface of the combustion chamber, the presence of which sharply reduces the intensity of heat exchange between the flue gases and the coolant. The boiler efficiency drops.
Removing the crust is not easy, especially if the boiler’s combustion chamber has a complex heat exchange surface.
It is impossible to completely eliminate the process of condensation formation in a solid fuel boiler, but the duration of this process can be significantly reduced.
The basic principle of protecting the boiler from condensation
To protect a solid fuel boiler from the formation of condensation, it is necessary to eliminate the situation in which this process is possible. To do this, do not allow cold coolant to enter the boiler. The return temperature should be 20 degrees less than the supply temperature. In this case, the supply temperature must be at least 60 C.
The simplest method is to heat a small amount of coolant in the boiler to the nominal temperature, create a small heating circuit for its movement and gradually add the rest of the cold coolant to the hot water.
The idea is simple, but it can be implemented different ways. For example, some manufacturers offer to purchase a ready-made mixing unit, the cost of which can be 25 000 and more rubles. For example, the company FAR (Italy) offers similar equipment for 28500 rubles, and the company Laddomat sells mixing unit for 25500 rubles.
More economical, but no less effective method Protecting a solid fuel boiler from condensation consists of regulating the temperature of the coolant supplied to the boiler using a thermostatic valve with a thermal head.
How to build a thermostatic valve
Thermostatic valves come in two types:
- mixing– flow A entering the valve is distributed into flow B and flow AB
- distributive– flow A entering the valve is divided into 2 flows
The mixing valve is installed on the return line, and the distribution valve is installed on the supply line. The operation of the valve is controlled by a thermal head with a thermal flask.
The thermoflask is attached to the surface using a special sleeve return pipeline in close proximity to the heating boiler. Inside the flask there is a working fluid, the temperature of which is equal to the temperature of the coolant before entering the boiler. If the temperature of the coolant increases, the working fluid increases in volume, and, conversely, when the temperature of the coolant decreases, the volume of the working fluid decreases. Expanding or contracting, the working fluid presses on the rod, closing or opening the thermostatic valve.
Using a thermal head, you can set a certain temperature, above (below) which the coolant will not be heated. How to set the temperature by choosing the operating modes of the thermal head is described in detail in the instructions for it.
Another feature of the thermostatic valve is that it reduces the flow of coolant to the boiler, but never closes it or opens it completely, protecting the boiler from overheating and boiling. The valve is completely closed only when the boiler is started.
How does a thermostatic distribution valve work?
The thermostatic valve is installed on the supply in front of the bypass section (pipeline section) connecting the supply and return of the boiler in close proximity to the boiler. This creates a small coolant circulation circuit. The thermoflask, as mentioned above, is installed on the return pipeline in close proximity to the boiler.
At the moment of boiler startup, the coolant has a minimum temperature, the working fluid in the thermoflask occupies a minimum volume, there is no pressure on the thermohead rod, and the valve allows the coolant to flow only in one direction of circulation in a small circle.
As the coolant heats up, the volume of the working fluid in the thermoflask increases, the thermal head begins to put pressure on the valve stem, passing the cold coolant to the boiler, and the heated coolant into the general circulation circuit.
As a result of mixing cold water, the temperature in the return line decreases, and, therefore, the volume of the working fluid in the thermal flask decreases, which leads to a decrease in the pressure of the thermal head on the valve stem. This in turn leads to the cessation of the supply of cold water to the small circulation circuit.
The process continues until the entire coolant is heated to the required temperature. After which the valve blocks the movement of the coolant through the small circulation circuit, and the entire coolant begins to move through the large heating circle.
The thermostatic mixing valve works in the same way as a distribution valve, but it is installed not on the supply pipe, but on the return pipe. The valve is located in front of the bypass, connecting the supply and return and forming a small circle of coolant circulation. The thermostatic flask is mounted on the same on site return pipeline in close proximity to the heating boiler.
While the coolant is cold, the valve allows it to flow only in a small circle. As the coolant heats up, the thermal head begins to put pressure on the valve stem, allowing part of the heated coolant to pass into the general circulation circuit of the boiler.
As you can see, the scheme is extremely simple, but at the same time effective and reliable.
The thermostatic valve and thermal head do not require electrical energy to operate; both devices are non-volatile. No additional devices or controllers are needed either. To heat the coolant circulating in a small circle, 15 minutes are enough, while heating the entire coolant in the boiler can take several hours.
This means that using a thermostatic valve, the duration of condensation formation in a solid fuel boiler is reduced several times, and along with it, the time of the destructive effects of acids on the boiler is reduced.
It remains to add that a thermostatic valve costs approximately 6,000 rubles.
To protect a solid fuel boiler from condensation, it is necessary to properly piping it, using a thermostatic valve and creating a small coolant circulation circuit.
The widespread use of boiler equipment operating on solid fuels poses special requirements for owners of private houses. Despite technological progress, which has made it possible to bring modern solid fuel heating devices to perfection, the operation of such equipment carries a certain danger. Malfunctions and violations of the operating conditions of heating equipment can cause equipment failure during peak heating season. In the worst case, the occurrence of emergency situations with a working unit can result in serious injuries to the inhabitants of the house and damage to residential buildings.
In this aspect, one of the most important conditions safe operation will protect the solid fuel boiler from overheating. Strict adherence to safety rules for the operation of heating equipment, the presence of capable automation and control devices will provide you with the necessary protection from unforeseen situations.
Let's take a closer look at what the protection of boiler equipment against overheating is based on. What could be causing the boiling of the coolant in a heated circuit and what are the consequences of such an emergency.
Reasons that may result in overheating of a solid fuel boiler
Even at the stage of selection and purchase, it is important to consider performance characteristics heating device. Many models that are on sale today have a built-in overheating protection system. Whether it works or not is the second question. However, it is necessary to adhere to certain knowledge and skills in order to create an effective and safe autonomous heating system at home.
The reliable operation of the heating unit depends on the operating conditions. In case of obvious violations of the technological parameters of heating equipment and abuse standard rules safety, high probability of occurrence emergency situation.
For reference: Exceeding the temperature in the combustion chamber of permissible parameters can cause boiler water to boil. The result of an uncontrolled process is depressurization of the heating circuit and destruction of the heat exchanger housing. In case of hot water boilers Overheating may cause an explosion.
Warn possible Negative consequences possible even at the stage of installation of a solid fuel boiler. Correct harness heating device will be the key to your safety and reliable operation unit in the future.
If we talk in detail, then in each case the protection system of a solid fuel boiler has its own specifics and features. Each heating system has its pros and cons. Eg:
- When we're talking about O solid fuel boilers with natural circulation of coolant, it is necessary to take care of the safety and performance of heating equipment even during installation. The pipes in the system are metal. Moreover, the diameter of such pipes must exceed the diameter of the pipes used to lay the circuit with forced circulation coolant. Sensors installed on the water circuit will indicate possible overheating of the coolant. The safety valve and expansion tank play the role of a compensator, reducing overpressure in system.
A significant disadvantage of a gravity heating system is the lack of an effective mechanism for adjusting the operating modes of solid fuel boilers.
- Great technological opportunities for consumers are provided by working with forced circulation of coolant in the system. Just the presence of a second circuit significantly increases the ability to regulate the heating temperature of the boiler water. The only drawback in the operation of such a system is the running pump, which can cause difficulties during the operation of the heating system.
This is due to the fact that when the power is turned off, the pump stops performing its functions. Stopping the circulation process and inertia of solid fuel heating boilers can lead to overheating of the heating unit. If the boiler equipment is not equipped, a power outage situation is fraught with extremely unpleasant consequences.
Effective protection against overheating of a working solid fuel boiler should be based on the mechanism for removing excess heat generated by the heating device.
What are the ways to protect heating equipment from overheating?
Manufacturing companies are trying, in order to increase the consumer attractiveness of their products, to introduce technical certificate boiler equipment any guarantees of its safety. The uninitiated consumer has no idea about the means of protecting a heating boiler from boiling.
Exist on this moment the following methods for ensuring the protection of solid fuel units used for autonomous systems heating. The effectiveness of each method is explained by the operating conditions of the boiler equipment, and design features units.
In most cases, the registration certificate for heating device Manufacturers recommend using tap water for cooling. In some cases heating boilers solid fuel units are equipped with built-in additional heat exchangers. There are models of boilers with remote heat exchangers. A safety valve is used to prevent overheating. The safety valve is designed only to relieve excessive pressure in the system, while the safety valve allows access when the boiler overheats tap water.
Important! In the presence of cast iron heating devices, such a measure is fundamentally incorrect. Cast iron heat exchangers are afraid of sudden temperature changes. Injecting cold water into the circuit may result in loss of integrity of the heat exchanger housing. (heated to high temperature cast iron will simply burst upon contact with cold water).
Exceeding the temperature of the coolant above 100 0C creates excess pressure that opens the valve. Under the influence of tap water, which is supplied under pressure of 2-5 bar, hot water is forced out of the circuit by cold.
The first aspect that causes controversy regarding cooling tap water– lack of electricity to power the pump. The expansion tank does not contain enough water to cool the boiler.
The second aspect that this cooling method rejects is associated with the use of antifreeze as a coolant. If an emergency occurs, up to 150 liters of antifreeze will go into the sewer along with the incoming cold water. Is this method of protection worth it?
The presence of a UPS will allow you to maintain the operation of the circulating pump in a critical situation, with the help of which the coolant will evenly disperse through the pipeline without having time to overheat. As long as the battery capacity lasts, the uninterruptible power supply guarantees the operation of the pump. During this time, the boiler should not have time to heat up to critical parameters; the automation will work, running water through a spare, emergency circuit.
Another way to get out of a critical situation would be to install an emergency circuit in the piping of a solid fuel unit. Switching off the pump can be duplicated by the operation of a spare circuit with natural coolant circulation. The role of the emergency circuit is not to provide heating for residential premises, but only to be able to remove excess thermal energy in case of emergency.
On a note: the installation of an emergency circuit can be replaced by installing a bypass, which will, in extreme cases, remove overheated boiler water into an expansion tank or heat accumulator.
This scheme for organizing the protection of the heating unit from overheating is reliable, simple and easy to use. You will not need any special funds for its equipment and installation. The only conditions for such protection to work are:
- Availability expansion tank or storage capacity in system;
- usage check valve only petal type;
- the secondary circuit pipes must be larger in diameter than the conventional heating circuit.
Conclusion
When assessing the technological capabilities of modern solid fuel boilers, you should think not only about its operating power, but also provide in advance for the installation of protection elements for the entire system. Boiler overheating is a frequent and familiar phenomenon for residents of private houses. Using available means to ensure protection will not only avoid emergency situations, but will also prolong the operation of heating units. Everyone is free to choose the means and method of protection. It will be enough for one to install an electric generator, which, together with a UPS, will not allow the water circulation in the system to stop. Other owners of a private house, on the contrary, will need to install a bypass for safety reasons or equip a spare, emergency circuit.
According to experts, installation buffer capacity or installing a bypass are the most in effective ways protecting the heating system from overheating.
Note: in the USA and European countries, the operation of solid fuel devices without a buffer tank is prohibited.
Many manufacturers of boiler equipment require that at the entrance to the boiler there be water at least a certain temperature, since cold return water has a bad effect on the boiler:
- boiler efficiency decreases,
- condensation on the heat exchanger increases, which leads to corrosion of the boiler,
- due to the large temperature difference at the inlet and outlet of the heat exchanger, its metal expands differently - hence the stress and possible cracking of the boiler body.
The first method is ideal, but expensive. Esbe offers a ready-made module for mixing into the boiler return and controlling the loading of the heat accumulator (relevant for solid fuel boilers) - the LTC 100 device is an analogue of the popular Laddomat unit.
Phase 1. Beginning of the combustion process. The mixing device allows you to quickly increase the boiler temperature, thus starting water circulation only in the boiler circuit.
Phase 2: Start loading the storage tank. The thermostat, opening the connection from the storage tank, sets the temperature, which depends on the version of the product. High, guaranteed return temperature to the boiler, maintained through the entire combustion cycle
Phase 3: Storage tank during loading. Good management ensures efficient loading of the storage tank and correct stratification in it.
Phase 4: The storage tank is fully loaded. Even at the final stage of the combustion cycle, high quality adjustment provides good control of the return temperature to the boiler while simultaneously fully loading the storage tank
Phase 5: End of combustion process. By completely closing the top opening, the flow is directly directed into the storage tank, using the heat in the boiler
The second method is simpler, using a high quality three-way thermomixing valve.
For example valves from ESBE or VTC300. These valves vary depending on the power of the boiler used. VTC300 is used for boiler power up to 30 kW, VTC511 and VTC531 - for more powerful boilers from 30 to 150 kW
The valve is mounted on the bypass line between the boiler flow and return.
The built-in thermostat opens input "A" when the temperature at output "AB" is equal to the thermostat setting (50, 55, 60, 65, 70 or 75°C). Input "B" closes completely when the temperature at inlet "A" exceeds the nominal opening temperature by 10°C.
Such a valve releasesHerz Armaturen- three-way thermomixing valve Anti-condensation. Two types of Heiz Anti-condensate valves are available- with switchable and fixed bypass.
Diagram of application of the three-way mixing valve Heiz Anti-condensate
When the coolant temperature at the outlet of valve "AB" is less than 61°C, inlet "A" is closed, and hot water flows through inlet "B" from the boiler supply to the return. If the temperature of the coolant at the outlet "AB" exceeds 63°C, the bypass input "B" is closed and the coolant from the system return flows through inlet "A" into the boiler return. Bypass output "B" opens again when the temperature at outlet "AB" drops to 55°C
When a coolant with a temperature of less than 61°C passes through the outlet "AB", input "A" from the system return is closed, and hot coolant from bypass "B" is supplied to output "AB". When the temperature at the outlet "AB" reaches more than 63°C, inlet "A" opens and water from the return is mixed with water from bypass "B". To equalize the bypass (so that the boiler does not constantly operate with a small circulation circle), it is necessary to install a balancing valve in front of inlet “B” on the bypass.When purchasing and installing a solid fuel boiler, it is necessary to take into account the peculiarities of its operation, namely the high probability of overheating in emergency situations, which can result in a serious accident and even destruction of the water jacket of the unit (explosion). Also, considerable harm can be caused by the formation of condensation on the walls of the combustion chamber, which happens under certain operating conditions. To eliminate such troubles, the solid fuel boiler must be protected from overheating and condensation, which will be discussed in our article.
How to get rid of condensation in the boiler firebox?
In solid fuel boilers, moisture may form on the inner walls of the combustion chamber. This happens when the firewood has already flared up and the boost fan (if there is one) is working at full strength, and the water in the heating system is still cold.
The temperature difference causes condensation to form, which, mixing with combustion products, settles on the walls of the chamber. This deposit causes corrosion of the metal, as a result of which the service life of the boiler is significantly reduced.
Note. Boilers with a cast iron heat exchanger are not afraid of corrosion, but, in turn, are sensitive to sudden changes in coolant temperature.
Solving this problem is not difficult, you just need to include a three-way thermostatic valve in the piping circuit, set to a coolant temperature of 55-60 ºС, as shown in the figure below. The protection of a solid fuel boiler from condensate operates as follows: until the water in the boiler heats up to the set temperature, it circulates through a small circuit. After sufficient heating three-way valve gradually adds water from the system. Thus, there is no temperature difference or condensation in the firebox.
Implementation in the scheme mixing unit also protects cast iron heat exchanger from the coolant temperature difference, since the valve will not allow cold water to get inside the heat generator.
Ways to protect the boiler from overheating
Excessive heating and boiling of the coolant in solid fuel units can occur during operation for the following reasons:
- power outage;
- the electronics or temperature sensor has failed, then the blower fan may not turn off or the ash door may not close;
- The air damper, controlled by a mechanical thermostat with a chain drive, has not closed completely.
The most popular method of protecting the boiler from overheating during sudden and frequent power outages is the use of blocks uninterruptible power supply or electric generators. In general, a prudent owner living in an area with frequent power outages should think about this in advance and take all measures to ensure the energy independence of his heating system.
Advice. In order for the system to be energy independent, it must be calculated and made gravitational with natural coolant circulation. heating equipment you need to choose as simply as possible, where there is no electronic control unit and a blower fan for the boiler.
Since, in addition to an emergency situation with a power outage, there are other malfunctions that lead to overheating, the presence of independent sources of electricity is not a panacea; more universal solutions. Here they are:
- installation of a two-way safety valve;
- introduction into the piping circuit of a bypass for natural circulation, which removes heat to a buffer tank or heat accumulator.
Note. Some models of solid fuel units are equipped with overheating protection using a built-in or remote heat exchanger. In the event of an accident, it is passed through cold water from the water supply network. This solution can also be used by those who undertake to make a solid fuel boiler with their own hands.
Using the Safety Valve
It's not the same thing safety valve. The latter simply relieves pressure in the system, but does not cool it. Another thing is the boiler overheating protection valve, which takes hot water from the system and instead supplies cold water from the water supply. The device is non-volatile and is connected to the supply and return lines, water supply network and sewerage system.
When the coolant temperature is above 105 ºС, the valve opens and, thanks to a pressure in the water supply of 2-5 Bar, hot water is forced out of the heat generator jacket and pipelines with cold water, after which it goes into the sewer. How the solid fuel boiler protection valve is connected is shown in the diagram:
The disadvantage of this method of protection is that it is not suitable for systems filled with antifreeze liquid. In addition, the scheme is not applicable in conditions where there is no centralized water supply, because along with a power outage, the supply of water from a well or pool will also stop.
Circuit with emergency bypass
The scheme below for protecting a solid fuel boiler from overheating has practically no disadvantages:
Stops when there is a power outage circulation pump, which during operation presses the petal of the check valve, thereby preventing the movement of water through the bypass. But after stopping, the valve will open and the coolant will continue to circulate naturally. Even if at this time some kind of accident occurs with the solid fuel boiler and the heating of the water does not stop, the heat will be transferred to the buffer tank until the wood in the firebox burns out.
However, several conditions must be met here:
- the presence of a heat accumulator or buffer tank of sufficient volume;
- the boiler circuit pipes up to the tank must be steel, with increased diameters and slopes appropriate for natural circulation;
- check valve - only of the petal type, mounted in a horizontal position.
Conclusion
It is better to select the protection scheme and method in accordance with the operating conditions. In one case, an electric generator will be sufficient; in another, a bypass and buffer tank cannot be used. But the use of the latter is considered preferable in some countries Western Europe The operation of solid fuel heat generators without a buffer tank is generally prohibited.
RUSSIAN JOINT STOCK COMPANY ENERGY
AND ELECTRIFICATION "UES OF RUSSIA"
STANDARD INSTRUCTIONS
BY START
FROM DIFFERENT THERMAL CONDITIONS
AND STOPPING THE STEAM BOILER
THERMAL POWER PLANTS
CROSS LINKED
RD 34.26.514-94
ORGRES SERVICE OF EXCELLENCE
Moscow 1995
DEVELOPED BY ORGRES Firm JSC
CONTRACTOR V.V. KHOLSHCHEV
APPROVED by RAO UES of Russia on September 14, 1994.
First Vice President V.V. CURLY
The Instructions take into account comments and suggestions from research and design institutes, energy enterprises and commissioning organizations.
|
RD 34.26.514-94 |
Expiration date set
from 01/01/1995
until 01/01/2000
The standard instructions are intended for engineering and technical personnel of thermal power plants. This Instruction is being issued again. Among similar works, the “Collection of instructions for servicing boilers of power plants” (M.-L.: Gosenergoizdat, 1960), “Temporary instructions for servicing a boiler of the TGM-84 type when burning natural gas and fuel oil" (Moscow: BTI ORGRES, 1966).
When operating the boiler, you should be guided by the following requirements:
current PTE, PTB, PPB, “Rules for the design and safe operation of steam and hot water boilers”, “Rules for explosion safety when using fuel oil and natural gas in boiler installations”;
factory instructions for boiler operation;
local instructions for maintenance and operation of the boiler and auxiliary equipment;
local job descriptions;
. GENERAL PROVISIONS
The procedure for turning on automatic regulators when starting the boiler is given in the appendix.
The basic principles of organizing the boiler start and stop modes are outlined in the appendix.
The scope of temperature control is given in the appendix.
During the filling process, turn on the dosing pumps of the preservation installation to supply the hydrazine-ammonia solution (Fig. ) to one of the possible points on the boiler (drum, lower points, power supply unit). When full, turn off the metering pumps and connect the boiler to the hot (or cold) feedwater assembly; perform pressure testing.
During the pressure testing process, take a sample and determine the quality of water in the boiler, including visually. If necessary, flush the screen system through the lowest points until the boiler water becomes clear. The concentration of hydrazine in boiler water should be 2.5 - 3.0 mg/kg, pH > 9.
steam valves PP-1, PP-2 for purging the boiler into the atmosphere;
steam valves PP-3, PP-4 from the superheater cut into the atmosphere;
turn on dosing pumps at the request of the chemical shop and organize a phosphating regime in the absence of phosphates in the boiler water, maintaining the pH value of the boiler water of the clean compartment at least 9.3;
install control valve cover continuous blowing the required boiler water flow from remote cyclones, making sure that the quality indicators of feedwater and steam are stabilized at the standard level.
. STARTING THE BOILER FROM A UNCOOLED STATE
. STARTING THE BOILER FROM A HOT CONDITION
. STOP THE BOILER IN RESERVE
Turn-on moment
Lowering the water level in the boiler drum
When the pressure in the drum reaches 13.0 - 14.0 MPa and the readings of the level gauges are compared with the readings of water indicating devices direct action
Increasing the water level in the boiler drum (II limit)
Extinguishing torch in the firebox
At 30% rated load
Reducing gas pressure after the control valve
With the opening of the gas valve to any burner
Reducing fuel oil pressure after the control valve
With the opening of the fuel oil valve to any burner
Reducing oil pressure in the lubrication system of mills with direct injection when it is supplied centrally
Switching off all primary air fans
Shutting off all mill fans when transporting dust with a drying agent from these fans
Tarnishing of the pulverized coal torch in the furnace
Turning off all smoke exhausters
With the opening of the fuel shut-off valves to any kindling burner
Disabling all blower fans
Disabling all RVPs
Failure to ignite or extinguish the torch of any pilot burner
Start function
Turn-on moment
Ignition water level regulator in the drum
Maintaining a constant level
After switching to a control valve on the bypass with a diameter of 100 mm of the power supply
Drum water level regulator
After switching to the main RPK
Fuel regulator
Maintaining fuel consumption as specified
According to local regulations
Fresh steam temperature regulator behind the boiler
Maintaining nominal fresh steam temperature using injection
When the nominal fresh steam temperature is reached
Continuous purge regulator
Maintaining the specified continuous blowdown flow rate
After turning on the boiler in the main
General air regulator
Maintaining a given excess air in the furnace
Primary air flow regulator
Maintaining a given primary air flow
After switching to dust combustion
Vacuum regulator in the furnace
Maintaining vacuum in the furnace
With boiler ignition
Appendix 3
BASIC PRINCIPLES OF ORGANIZING MODES OF STARTING AND STOPING THE BOILER
Previously, as is known, it was proposed, when filling a boiler that has not cooled down, to control the temperature of the water in front of the drum, which should not differ by more than 40 ° C from the temperature of the metal at the bottom of the drum. However, this requirement can only be met if the first portion of water is directed in addition to the drum. Existing schemes for supplying water to the boiler drum usually do not provide for this possibility. Nevertheless, when developing a scheme for monitoring the temperature state of the drum, it was decided to keep the measurement of the water temperature in front of the drum; control over the saturation temperature is also maintained.
Filling the drum for hydropressing is prohibited if the metal temperature of the top of the empty drum exceeds 140 °C.
The graphs given in the tasks for firing up the boiler from various thermal states are of a specific nature: testing of starting modes was carried out on a TPE-430 TPP boiler with cross braces; The schedules also apply to other types of boilers.
Rice. 9 . Temperature distribution along the superheater path:
Depending on the technology used, boiler shutdowns are divided into the following groups:
stopping the boiler in reserve;
shutdown of the boiler for long-term standby or repair (with conservation);
boiler shutdown with cooling;
Emergency Stop.
Stopping the boiler in reserve means a shortened shutdown with maintaining the water level in the drum, mainly associated with downtime of equipment that does not require repairs on weekends. When a shutdown lasts more than 1 day, the pressure in the boiler usually decreases to atmospheric pressure. When shutting down for more than 3 days, it is recommended to place the boiler under excess pressure from a deaerator or other source for conservation purposes.
The technology for stopping the boiler is adopted as simplified as possible and provides for unloading the boiler up to 20 - 30% at nominal parameters, followed by extinguishing it and disconnecting it from the main steam pipeline.
To maintain steam pressure during shutdown, the boiler purge valves do not open to atmosphere. The requirement contained in the “Scope and technical conditions for the implementation of technological protection of thermal power equipment of power plants with cross connections and hot water boilers" (M.: SPO Soyuztekhenergo, 1987), the opening of purge valves during boiler shutdowns has been revised and when listing the actions performed by technological protection, this operation is not mentioned (Circular No. Ts- 01-91/T/ “On introducing changes to the technological protection schemes of thermal power equipment of operating thermal power plants” - M.: SPO ORGRES, 1991).
It is enough to limit yourself remote control purge valve.
When placing equipment into long-term reserve or repair, this Standard Instruction provides for its preservation with hydrazine and ammonia during boiler shutdown mode. Other preservation methods are also possible.
Shutting down with cooling of the boiler and steam lines is used when it is necessary to repair heating surfaces in the firebox, flues, or warm box. Once the boiler is turned off, the draft machines remain in operation for the entire cooldown period. Cooling of the drum with steam from an adjacent boiler (through jumpers) is carried out without maintaining the water level in the drum (in this case Standard instructions This mode is given as an example) and with level maintenance. In the latter case, steam is supplied for cooling only to the upper collectors of the drum. With the help of the RROU, the rate of reduction in steam pressure is regulated, which is discharged first into the auxiliary collector, then into the atmosphere.
The rate of decrease in steam pressure must be maintained in such a way as not to exceed the permissible rate of decrease in the temperature of the lower generatrix of the drum, which when stopped is [↓Vt] = 20 °C/10 min. The temperature difference between the upper and lower parts of the drum should not exceed [ Dt] = 80 °C.
Appendix 4
VOLUME OF TEMPERATURE CONTROL
Control for temperature conditions It is advisable to carry out the superheater control during boiler startups with standard sleeve thermoelectric thermometers installed at the outlet of individual stages, abandoning measurements using coil thermoelectric thermometers. In startup modes, first of all, it is necessary to ensure control of the steam temperature in the first stages of the superheater as the most heat-stressed heating surfaces in such modes, as well as the steam temperatures at the boiler outlet along both streams. It is recommended that these measurements be automatically recorded along with the existing registration of the drum metal temperature. The latter must be brought into compliance with the requirements of the appendix section. 1.6 “Collection of administrative documents for the operation of energy systems (Thermal Engineering Part). Part 1." M.: SPO ORGRES, 1991:
the number of temperature measurements along the drum top and bottom has been reduced to six: in the center and in the outer sections;
provision is made for measuring saturation temperatures by installing sleeve or surface thermocouples on the steam outlet and drain pipes of the drum;
measurement of feed water temperatures behind the economizer is provided (for monitoring when the drum is filling).
