Instructions for the water regime of hot water boilers. Preparation of feed and make-up water

Instructions for maintaining the water chemistry regime

Coherence, which we have talked about more than once, is when the subsequent presentation in one way or another relies on the previous presentation or at least appeals to it.

First section – General provisions. It contains only scant information. This is usually accepted in the instructions. However, it can be considered an introduction to the other sections.

Second section – Fundamental thermal diagram and basic equipment. There is a fair amount of information here that is not used in any way further in subsequent sections. Whether it is superfluous is a debatable question. Traditionally, we give thermal power plant chemists some minimal “extra” knowledge about the equipment and the thermal circuit, so that they can navigate those emergency situations that cannot be fully foreseen in the instructions.

The third section is PROCESSES OCCURING IN THE STEAM-CONDENSATE-WATER TRACT. Here, in the chain of presentation, the first, second and third sections, coherence and consistency are fully observed, because in the third section we describe the processes associated with specific equipment about which we received necessary information in the previous section. The section is quite voluminous for traditional thermal power plants. But find and select on your own necessary information on the water chemistry regime of CCGT units is not yet easy for operational chemists, which is why the volume of this section has been increased.

The following sections continue to develop the topic of water chemistry management in its various aspects and ends with the Safety Measures section. The text of this section is structured so that we're talking about mainly about what safety measures must be maintained during the operation of the equipment and during the performance of work. If we were talking about safety measures that should be taken before starting to operate the equipment, then the place of this section in terms of the sequence of presentation should have been ahead, after the General Provisions section. However, safety measures must be taken both before and after the start of operation. So there is uncertainty about the place of this section. The layout of the instructions drawn up is usually agreed upon with the Customer and, depending on his wishes and other considerations, the safety section may appear in the list of sections and on last place, and on the second.>>

Scroll accepted abbreviations And symbols

The correct organization of the water-chemical regime of the boiler pursues a number of significant goals, among which we can highlight the most safe, economical and reliable operation of the equipment, optimization of the operation of the heating boiler. Moreover, it is rational organization water chemistry is also capable of preventing deposits of all known types on the walls of the heating boiler and other components of the system. Also stable water chemistry regime The boiler protects the heating system from corrosion and helps produce the purest steam possible. In order for any heating system optimal water-chemical regime was maintained, it is necessary to understand that an integral component of its organization is chemical control, organized in accordance with current standards and requirements.

The influence of salt content of water on boiler operation

The salt content of boiler water has a decisive influence on the water hardness index. Thus, the hardness of water is directly proportional to the amount of magnesium and calcium salts found in it. Scale that forms on the inner walls of pipes, as well as leading elements of the heating system, poses a significant threat, since it has negative impact on the thermal conductivity of the metal, increasing heating time and energy costs. Water treatment and a water softener for the boiler make it possible, over time, to bring the salt content of water to the required level and maintain it within the normal range for a long time. Despite the fact that measures aimed at reducing water salinity are quite expensive, it is worth noting that the amount paid for maintaining equipment in proper condition is significantly less than what might be required to repair equipment that has failed due to lime deposits. technology.

The content of anions and cations affects such an indicator as the salt content of boiler water. In turn, salinity largely affects the level of water mineralization. Due to the evaporation of water, as well as the increased influx of salts, undesirable impurities continuously accumulate in the devices. However, in most cases these impurities are absent in evaporating water, with the exception of silicon salts. To avoid negative consequences it is these salts that can cause harm components heating system. It is worth noting the exceptional role preventive measures and accounting critical level accumulation of salts. IN in this case critical is the level of salt that provokes foaming of water, when there is a significant deterioration in its performance.

Rules for choosing a filter for water softening

Rules for water chemistry, equipment care

In order to maintain a constant water-chemical balance in the heating system, it is necessary to periodically monitor the infusion internal environment. The frequency of such monitoring depends mainly on the type of boiler and its structural features, as well as from existing sanitary standards and standards. To maximize the quality of the water used and carry out all necessary procedures, which include the deaeration of water, its preparation for feeding boilers and the heating system, it is necessary to carefully study its initial properties. No less important factors the purpose of the boiler room, the requirements for the coolant, as well as its technical characteristics.

If the pipes through which boiler water flows are forced to come into contact with a corrosive environment, it is necessary to carefully consider an anti-corrosion protection system. It is permissible to put the equipment into operation only if you are confident in its serviceability, the existing filters are fully loaded and if the water circulation in the boiler is stable and not disturbed. To gain greater confidence in the serviceability of the equipment, stainless steel steam and water samplers should also be installed in areas of the water heating system that are subject to control.

Mandatory conditions for working with heating equipment to maintain the water chemical regime are adjustment, inspection and other thermochemical tests. Procedures such as replacing damaged boilers and repairing them are also mandatory. To maintain the basic properties of water, it is also necessary to change the fuel, inspect the internal space of the heating installation, analyze sediment samples taken and the inner surface of the cutouts of pipe samples, as well as installation additional equipment. The frequency of this type of work is determined primarily by the schedule of repair work.

Use of materials is permitted only if there is an indexed link to the page with the material.

Water mode of boilers

Water used in boiler plants as a working fluid has the properties of an active and almost universal solvent. The impurities contained in it, regardless of the sources of their appearance, when certain conditions may form hard deposits on pipe walls. The most intensive formation of deposits occurs in the pipes of evaporation and superheating heating surfaces located in the intense heating zone. Moreover, even a small layer of these deposits, due to its low thermal conductivity coefficient, can unacceptably increase the temperature of the metal and, consequently, lead to the destruction of pipes.

Therefore, the use of natural waters containing large amounts of salts, silicic acid, and gases as feed water is unacceptable. To prepare feed water of the required quality, natural water is subjected to special treatment. It consists in removing mineral and organic solid impurities suspended in water, hardness salts ( Sa, Mg) replacing them with easily soluble alkali metal salts ( TO, Na); general desalting in a system of evaporation units to produce demineralized condensate; desiliconization; degassing. This treatment can significantly reduce the content of impurities in the feed water. However, during boiler operation, the amount of impurities in the water constantly increases. This occurs due to the addition of water to replenish losses. working environment, transfer of corrosion products of structural materials into water. Oxygen and carbon dioxide entering the water cause corrosion of the metal pipes of the heating surfaces. Calcium and magnesium compounds, which are poorly soluble, as well as corrosion products of iron and copper, form scale. Deposits also form easily soluble compounds such as Na 3 P.O. 4 ; Na 2 SO 4 if their concentration is higher than the solubility in the working fluid (water or steam). Some of the impurities crystallize in the water volume, forming sludge.

Reliable and economical operation of the boiler is achieved by removing part of the impurities from the boiler, as well as limiting the corrosion of structural materials by organizing a water-chemical (water) regime.

In the steam-forming heating surfaces of the drum boiler, simultaneously with the formation of steam, due to the low solubility of salts in steam, their concentration in water increases. To maintain the concentration of water impurities within limits determined by the quality of the steam produced and the formation of deposits on internal surfaces pipes, salts and suspended impurities are removed from the circulation circuit along with water by organizing continuous blowing. Blowdown water is removed from the last evaporation stage in an amount of 0.5 - 10% of the boiler steam output, depending on the used method of processing additional water and the step evaporation scheme.

In addition to continuous blowing, periodic blowing is also carried out from the lower screen collectors. This removes the sludge. The purge mode is regulated by water quality and operating parameters of the environment. Violation of the regime or complete exclusion of periodic purging can lead to sticking of sludge to the surfaces of the screen pipes of the cold funnel.

In direct-flow boilers, all the water evaporates in the screens, so there is no possibility of organizing purge. Due to the difference in their solubility in water and steam, impurities in varying quantities fall out in the form of deposits on the internal surfaces of pipes, and the rest is carried away with steam. The accumulation of these deposits is periodically removed by chemically flushing the boiler. The flushing process is labor-intensive and can only be performed when the equipment is stopped.

Reducing the corrosion rate of pipe metal in modern once-through boilers is achieved by creating a slightly alkaline or neutral aqueous environment in the working fluid. The first is used if the heater pipes are made of brass, and the second is used if the heat exchanger pipes are made of corrosion-resistant steel. A slightly alkaline environment occurs in the hydrazine-ammonia complexone or hydrazine aqueous regime. Neutral environment - when dosing gaseous oxygen or hydrogen peroxide solution into the condensate.

Drum boilers are fed with water containing easily soluble compounds.
These are mainly sodium salts. Calcium and magnesium salts have low solubility and can form scale during evaporation. To prevent its formation, a corrective method of intra-boiler water treatment is used. It consists in introducing correction additives into the boiler to help convert hardness salts into non-stick sludge. Such additives are usually sodium salts of phosphate acid (for example, trisodium phosphate Na 3 P.O. 4). The water regime based on the input of phosphates is called phosphate.

Phosphating of water with the supply of solution to the drum can be carried out according to the alkaline-salt regime or the regime of pure phosphate alkalinity. In the first case, to form a non-stick, easily moving sludge, phosphates are introduced into an alkaline medium, namely, into a drum. Here, due to repeated circulation, the alkalinity of the water is much greater than in the feed water. The formed compounds leave with the purge water.

The bulk of the sludge suspended in water is removed by continuous blowing, and a small part of it, accumulating in the lower collectors, is removed by periodic blowing. To reliably bind calcium salts, a certain excess of phosphates is maintained in water, which, however, leads to significant increase water alkalinity ( pH> 11), causing metal corrosion. Therefore, when feeding a drum boiler with low-mineralized make-up water (chemically desalted), a purely phosphate alkalinity mode is used. To maintain moderate alkalinity of water, not only Na 3 P.O. 4, but also a mixture Na 3 P.O. 4 with acid salt of phosphoric acid Na 2 HPO 4 .

The water-chemical regime of steam boilers should be considered as part of the water-chemical regime of the power unit. IN general view The task of the water chemistry regime of the unit (WCR) is to ensure the reliability and efficiency of operation of all equipment of the unit. This problem can be solved by:

Ensuring the necessary purity of feed water and superheated

Limiting the formation of deposits in the steam boiler, turbine, pipelines;

Reducing the intensity of corrosion processes in equipment and pipelines to a safe level.

The solution to these problems is determined by the type of equipment, the parameters of the water coolant, the material of the equipment, the amount and composition of impurities, etc. Taking into account this variety of operating conditions of the units, it becomes clear that for each case it is necessary to choose the optimal methods for solving water chemistry problems.

The required steam purity is determined by preventing impurities from entering the turbine flow path. A steam turbine is sensitive to impurity deposits: 3-4 kg of deposits on the blades is enough for a 300 MW turbine to reduce its power and efficiency. With increasing pressure in front of the turbine, the flow area of ​​the blade apparatus decreases and, consequently, the influence of salt drift on its operation increases. Therefore, as the pressure of superheated steam increases, the requirements for its purity increase.

Table 12.2 presents steam quality standards for drum boilers and supercritical pressure boilers (GIO "Rules technical operation power stations and networks").

Steam quality is regulated by sodium, since sodium compounds make up a significant proportion of steam impurities, and silicic acid, the solubility of which in steam increases significantly with increasing pressure, and it forms deposits that are difficult to wash off in the turbine.

In drum boilers, the standards in Table. 12.2 must comply not only with superheated, but also with saturated steam, since the precipitation of impurities on the surfaces of the superheater is possible. The concentration of impurities in saturated steam C"p is determined by moisture entrainment u, %, and solubility in steam, characterized by the distribution coefficient Kp, %,

C> = (w + Kr)^

Where the concentration of impurities in boiler water SKW for a single-stage evaporation scheme is determined by the formula

Sq = (100+r) Spv

The value of C"n can be reduced by:

Improved moisture separation from steam (and decreases);

Converting impurities into compounds with a lower distribution coefficient;

Increasing purge p, switching to a two- or three-stage evaporation scheme;

Reducing the concentration of impurities in feed water.

The concentration of impurities in the steam Cp leaving the drum can be significantly reduced compared to C"p by organizing steam washing on a special device.

Thus, in a drum boiler, the quality of steam depends not only on the quality of the feed water, but also on other factors. Therefore, the feedwater quality standards for these boilers are set less stringent (Table 12.3); in this case, it is not economically profitable to use block desalting plants.

In once-through boilers, impurities in the feed water turn into steam or form intra-pipe deposits, which negatively affects the operation of the boiler. The quality of feed water for once-through boilers must be high (Table 12.3). The additional water undergoes chemical desalting. In SKD units, 100% condensate purification is organized in the treatment unit to remove mechanical impurities (undissolved corrosion products of structural materials), colloidal dispersed and dissolved substances that enter the condensate due to suction cups in the condenser.

The second task of water chemistry - limiting the formation of deposits in the boiler - is solved in a drum boiler by reducing the SW (blowdown, stepwise evaporation), and in a once-through boiler of subcritical pressure a transition zone can be allocated for the deposition of most impurities in it. In all cases, maximum concentrations of impurities in the feed water are established and corrections are made chemical composition water to reduce the amount of deposits and increase their thermal conductivity.

It is not possible to completely avoid deposits on the boiler surfaces, therefore, to remove them, periodic chemical washings of the boiler or its individual surfaces are carried out.

In drum boilers, the limitation of feed water hardness (Ca and Mg compounds) is determined by the need to avoid their deposition on the pipe walls and the formation large quantity sludge that can adhere to the surface of the pipes. With increasing pressure in the boiler (the temperature of the boiler water increases accordingly), the solubility of most Ca and Mg compounds decreases, and the risk of deposit formation increases. Therefore, with increasing pressure, the permissible hardness of the feed water decreases. For boilers burning fuel oil with high heat fluxes in the furnace, the content of Ca and Mg should be reduced.

The rationing of silicic acid in feed water is carried out based on ensuring the purity of saturated steam, taking into account boiler purging and steam washing.

There should be no free carbonic acid (CCb) in the water after the deaerator, and the pH value of the feed water should be within 9.1+-0.1. The rationing of carbonic acid and oxygen is due to the fact that they cause corrosion of the steam-water path. To bind the oxygen present in the feed water due to suction in the vacuum part of the condensate path and not completely removed during deaeration, the turbine condensate is treated with N2H4 hydrazine. Maintaining hydrazine in the range of 20-60 µg/kg in front of the boiler ensures the suppression of oxygen corrosion.

The residual concentration of carbon dioxide after the deaerator is bound by ammonia treatment of the feed water. Ammonia NH3 binds carbonic acid and increases the pH to a slightly alkaline environment, at which corrosion of carbon steels is reduced. Excessive amounts of ammonia (over 1,000 mcg/kg) leads to ammonia corrosion of brass condenser tubes and HDPE.

Iron impurities form low-thermal conductivity deposits on heat-stressed heating surfaces, leading to burnout of pipes. With increasing pressure in the boiler, the intensity of the formation of iron oxide deposits increases (solubility decreases, heat flows increase). The amount of iron compounds in feed water depends mainly on the intensity of corrosion processes during operation and during downtime. An iron content that is higher than normal indicates violations during corrective treatment of feed water. Pre-start chemical cleaning, effective preservation of equipment during downtime, etc. have a significant impact on the concentration of iron in water.

In SKD once-through boilers, the quality of the feed water must be equal to or close to the quality of the steam.

The solubility of copper, sodium and silicic acid compounds in the water coolant of the SKD is quite high, and these compounds pass through the boiler in transit. The permissible concentrations of Cu, Na and SiCb in the feed water are determined by the reliable operation of the turbine.

Decline permissible concentrations compounds of iron and hardness salts in feed water is aimed at reducing the growth rate of low-heat-conducting deposits in radiant heating surfaces, especially in boilers burning fuel oil.

The intensity of the formation of iron oxide deposits in the boiler depends not only on the concentration of iron in the feed water, but also on the rate of corrosion processes in the boiler itself. Therefore, the water-chemical regimes of once-through boilers must ensure corrosion suppression in the entire steam-water path of the unit.

As already noted, the SKD units clean turbine condensate at the treatment plant. Especially important role Condensate cleaning plays a role during startups and other unsteady conditions, when the content of corrosion products and other contaminants in the coolant increases sharply.

The third task of water chemistry - reducing the intensity of corrosion processes - is solved by introducing reagents into the condensate and feed water that reduce the corrosion rate and create protective films with high thermal conductivity on the metal surface.

Thus, to perform their tasks, water chemical regimes power plants must ensure compliance with steam and feedwater quality standards, as well as a number of other conditions that ensure reliable and economical operation of the equipment. In particular, in table. 12.4 are given valid values a number of indicators of the unit’s operation, determined by water-chemical regimes (these indicators are assessed when burning fuel oil after 7,000 hours, and when burning gas and solid fuels - after 24,000 hours of operation).

STANDARD INSTRUCTIONS

on organizing chemical control over the management of water managementchemical regime of steam, hot water boilers and heating networks.

You should know the instructions:

I. Head of the district

!. Leading heating engineer

\. Shift engineer on duty

I. Chemical engineer

5. ToVP laboratory operator

5. Head of the heating network service.

Water-chemical regime of boilers can be consideredas a system of measures to protect structuralmaterials from corrosion, limiting entry intocoolant of harmful impurities and removing them fromcircuit, preventing the formation of scale and sludgeon heat transfer surfaces. The purpose of theseactivities is to ensure safe and securecontinuous operation of equipment for a given resourcetime by maintaining the cleanliness of metal surfaces of energy circuits and maximumeffective corrosion suppression. Increased requirements to the water chemistry regime of boilers necessitate harsh and permanent chemical contact role for the quality of the coolant.

1. WATER-CHEMICAL REGIME OF STEAM, WATERHEATING BOILERS AND HEATING NETWORKS.

1.1. Steam boilers.

Maintaining a normal water-chemical regime of steam boilers is aimed at:

- obtaining clean steam;

- absence on the heating surfaces of boilers, salt deposits
4th (scale) and sticking of the resulting sludge (the so-called secondary
sipi;

- prevention all types corrosion boiler metal and steam con-
1ensatny tract carrying corrosion products into the boiler;

The listed requirements are satisfied by taking measures in two main directions:

When preparing source water;

When regulating the quality of boiler water.

Source water preparation depending on its quality and the requirements related to the design of the boiler, it can be carried out by:

- finishing water treatment with removal of scale formers Ca, Mq (Na-cationization), free and bound carbon dioxide, oxygen (deaeration), reduction of alkalinity and salt content (liming, hydrogen-cationization);

- intra-boiler water treatment (with dosage of reagents with mandatory and reliable removal of sludge).

Boiler water quality regulation carried out by blowing boilers. Application of any water treatment method; intra-boiler, pre-boiler, pre-boiler with subsequent corrective treatment of chemically purified or feed water - requires purging of steam boilers. Under operating conditions of boilers, there are two methods for purging boilers: periodic and continuous.

1.2. Water heating boilers and heating networks.

1.2.1. Cogeneration hot water boilers are mainly designed
for heating water according to a thermal schedule for several heating seasons
zones without cleaning and additional funds protection against internal corrosion
heating surfaces. In the main mode, the water heating temperature usually fluctuates
flies within 120-130 °C, in peak mode -150 °C (according to the thermal graph
fishing net 150-70 °C).

1.2.2. During the operation of heating boilers and heating networks
serious attention is paid to organizing rational water chemistry
bench press He must provide standard indicators quality additional and network
howl of water, the maintenance of which should prevent the formation of sludge and
tion, as well as corrosion damage in equipment and throughout the network path.

1.2.3. The quality of make-up and network water must first of all ensure
ensure scale-free operation of the most water-demanding units - water heaters
ny boilers.

1.2.4. The quality of water added to any type of heating network determines
with a diagram of the water treatment installation and its correct operation, as well as standards
low operation of the deaeration unit.

1.2.5. The quality of network water largely depends on the operation of the heating system.
heating equipment and heaters operated by consumers and
heating network services.

1.2.6. Scale-free, normal trouble-free operation hot water cat
fishing to the extent that it is influenced by the water chemistry regime is determined
quality of network water, since it enters the boiler as water, returns
may from consumers (return water), and water added for
covering water intake and losses in the network (open system) or only losses (closed
system). Deterioration in the quality of supply water as a result of raw water intake and
impurities have a negative impact on the operation of hot water boilers.

1.2.7. Maintaining the water-chemical regime within the limits of standards is a task not only for workers of district boiler houses (heat and water sources), but also for workers of heating networks servicing heating mains and heating points.

1.3. Water treatment and water-chemical regime of thermal plantstions and networks.

1.3.1. The operating mode of water treatment plants (WPU) and the water chemical regime (WCR) must ensure the operation of thermal stations and heating networks without damage and reduction in efficiency caused by corrosion of the internal surfaces of water treatment, heat and power and network equipment, as well as the formation of scale and sludge in equipment and pipelines thermal stations and heating networks.

1.3.2. Organization and control of water-chemical operating conditions
equipment of thermal stations and organizations operating thermal networks,
must be carried out by the personnel of the relevant department.

1.3.3. Switching on and off any equipment that can
cause deterioration of water and steam quality, must be agreed with the respective
fighting unit. X

1.3.4. Internal inspections of equipment, sediment sampling, cutting out pipe samples, drawing up inspection reports, as well as investigating accidents and malfunctions related to water chemistry must be carried out by a person! the corresponding technological workshop of the Teploenergoremont enterprise with the participation of operation.

2. TASKS AND SCOPE OF CHEMICAL CONTROL.

One of the main tasks of chemical control in boiler houses is to assess the condition of operating thermal power equipment with regard to corrosion and formation various types sediments. The second main task of chemical control is to identify various problems and defects in the operating mode of equipment.

Economical and uninterrupted operation of boilers is ensured by maintaining a rational water chemistry regime (WCR).

With the improvement of equipment, in particular, the increase in thermal stresses of heating surfaces, the danger of corrosion and scale formation increases. In this regard, the requirements for water chemistry and its control are also growing.

Current (operational) chemical control or operational control, carried out daily, ensures the required water quality in various sections of the tract, promptly establishes the magnitude of deviations from the norm and makes it possible to make the necessary decisions.

Periodic monitoring allows for a more in-depth and comprehensive assessment of equipment operation.