For complete combustion of 1 m 3 of dry gaseous fuel, the required volume of air, m3 / m3,

In the above formulas, the content of fuel elements is expressed as a percentage by weight, and the composition of combustible gases CO, H 2 , CH 4, etc. - as a percentage by volume; CmHn - hydrocarbons that make up the gas, for example methane CH 4 (m= 1, n= 4), ethane C 2 H 6 (m= 2, n= 6), etc. These numbers make up the coefficient (m + n/4)

R0 2 + 0 2 + N 2 = 100%, (31)

with incomplete combustion

R0 2 + 0 2 + N 2 + CO = 100%;

The volume of dry triatomic gases is found by dividing the masses of CO 2 and SO 2 gases by their density under normal conditions.

Pco 2 = 1.94 and Pso 2 = 2.86 kg / m3 - the density of carbon dioxide and sulfur dioxide under normal conditions.

Toxic (harmful) are chemical compounds that adversely affect human and animal health.

The type of fuel affects the composition of harmful substances formed during its combustion. Power plants use solid, liquid and gaseous fuels. The main harmful substances contained in the flue gases of boilers are: sulfur oxides (oxides) (SO 2 and SO 3), nitrogen oxides (NO and NO 2), carbon monoxide (CO), vanadium compounds (mainly vanadium pentoxide V 2 O five). Ash also belongs to harmful substances.

solid fuel. In thermal power engineering, coals (brown, stone, anthracite coal), oil shale and peat are used. The composition of solid fuel is schematically presented.

As you can see, the organic part of the fuel consists of carbon C, hydrogen H, oxygen O, organic sulfur S opr . The composition of the combustible part of the fuel of a number of deposits also includes inorganic, pyrite sulfur FeS 2.

The non-combustible (mineral) part of the fuel consists of moisture W and ash BUT. The main part of the mineral component of the fuel passes during the combustion process into fly ash carried away by flue gases. The other part, depending on the design of the furnace and the physical characteristics of the mineral component of the fuel, can turn into slag.

The ash content of domestic coals varies widely (10-55%). Accordingly, the dust content of flue gases also changes, reaching 60-70 g/m 3 for high-ash coals.

One of the most important features of ash is that its particles have different sizes, which range from 1-2 to 60 microns or more. This feature as a parameter characterizing the ash is called fineness.

The chemical composition of solid fuel ash is quite diverse. Ash usually consists of oxides of silicon, aluminum, titanium, potassium, sodium, iron, calcium, magnesium. Calcium in the ash can be present in the form of a free oxide, as well as in the composition of silicates, sulfates, and other compounds.

More detailed analyzes of the mineral part of solid fuels show that there may be other elements in the ash in small quantities, for example, germanium, boron, arsenic, vanadium, manganese, zinc, uranium, silver, mercury, fluorine, chlorine. Trace elements of these elements are distributed unevenly in fly ash fractions of different particle sizes, and their content usually increases with decreasing particle size.

solid fuel may contain sulfur in the following forms: pyrite Fe 2 S and pyrite FeS 2 as part of the molecules of the organic part of the fuel and in the form of sulfates in the mineral part. Sulfur compounds as a result of combustion are converted into sulfur oxides, and about 99% is sulfur dioxide SO 2.

The sulfur content of coal, depending on the deposit, is 0.3-6%. The sulfur content of oil shale reaches 1.4-1.7%, peat - 0.1%.

Compounds of mercury, fluorine and chlorine are behind the boiler in a gaseous state.

Solid fuel ash may contain radioactive isotopes of potassium, uranium and barium. These emissions practically do not affect the radiation situation in the area of ​​the TPP, although their total amount may exceed the emissions of radioactive aerosols at nuclear power plants of the same capacity.

Liquid fuel. IN fuel oil, shale oil, diesel and boiler-furnace fuel are used in thermal power engineering.

There is no pyrite sulfur in liquid fuel. The composition of fuel oil ash includes vanadium pentoxide (V 2 O 5), as well as Ni 2 O 3 , A1 2 O 3 , Fe 2 O 3 , SiO 2 , MgO and other oxides. The ash content of fuel oil does not exceed 0.3%. With its complete combustion, the content of solid particles in flue gases is about 0.1 g / m 3, however, this value increases sharply during the cleaning of heating surfaces of boilers from external deposits.

Sulfur in fuel oil is found mainly in the form of organic compounds, elemental sulfur and hydrogen sulfide. Its content depends on the sulfur content of the oil from which it is derived.

Furnace fuel oils, depending on the sulfur content in them, are divided into: low-sulfur S p<0,5%, сернистые S p = 0.5+2.0% and sour S p >2.0%.

Diesel fuel in terms of sulfur content is divided into two groups: the first - up to 0.2% and the second - up to 0.5%. Low-sulphur boiler-furnace fuel contains no more than 0.5 sulfur, sulfurous fuel - up to 1.1, shale oil - no more than 1%.

gaseous fuel is the most "clean" organic fuel, since when it is completely burned, only nitrogen oxides are formed from toxic substances.

Ash. When calculating the emission of solid particles into the atmosphere, it must be taken into account that unburned fuel (underburned) enters the atmosphere together with ash.

Mechanical underburning q1 for chamber furnaces, if we assume the same content of combustibles in the slag and entrainment.

Due to the fact that all types of fuel have different calorific values, the calculations often use the reduced ash content Apr and sulfur content Spr,

Characteristics of some types of fuel are given in table. 1.1.

The proportion of solid particles un carried away from the furnace depends on the type of furnace and can be taken from the following data:

Chambers with solid slag removal., 0.95

Open with liquid slag removal 0.7-0.85

Semi-open with liquid slag removal 0.6-0.8

Two-chamber fireboxes ....................... 0.5-0.6

Fireboxes with vertical pre-furnaces 0.2-0.4

Horizontal cyclone furnaces 0.1-0.15

From Table. 1.1 it can be seen that combustible shale and brown coal, as well as Ekibastuz coal, have the highest ash content.

Sulfur oxides. The emission of sulfur oxides is determined by sulfur dioxide.

Studies have shown that the binding of sulfur dioxide by fly ash in gas ducts of power boilers depends mainly on the content of calcium oxide in the working mass of fuel.

In dry ash collectors, sulfur oxides are practically not captured.

The proportion of oxides captured in wet ash collectors, which depends on the sulfur content of the fuel and the alkalinity of the irrigating water, can be determined from the graphs presented in the manual.

nitrogen oxides. The amount of nitrogen oxides in terms of NO 2 (t/year, g/s) emitted into the atmosphere with flue gases of a boiler (casing) with a capacity of up to 30 t/h can be calculated using the empirical formula in the manual.

Flue gas analysis of boilers allows you to identify and eliminate deviations from normal operating modes, thereby increasing the efficiency of fuel combustion and reducing emissions of toxic gases into the atmosphere. In order to understand how efficiently a combustion plant works and how to detect deviations in its operation using a flue gas analyzer, it is necessary to know which gases and in what concentrations are present in the flue gases.

The flue gas components are listed below in decreasing order of their concentration in the flue gas.

Nitrogen N2.

Nitrogen is the main element of the ambient air (79%). Nitrogen is not involved in the combustion process, it is ballast. Injected into the boiler, it heats up and takes with it the energy spent on heating it into the chimney, reducing the efficiency of the boiler. Flue gas analyzers do not measure the nitrogen concentration.

Carbon dioxide CO2.

Formed during the combustion of fuel. Asphyxiating gas, at concentrations above 15% by volume, causes rapid loss of consciousness. Flue gas analyzers do not usually measure the concentration of carbon dioxide, but determine it by calculation from the concentration of residual oxygen. Some models of gas analyzers, such as the MRU Vario Plus, may have built-in optical infrared sensors for measuring carbon dioxide concentrations.

• diesel burners - 12.5…14%
• gas burners - 8…11%

Oxygen O2.

Residual oxygen, not used in the combustion process due to excess air, is emitted together with the exhaust gases. The completeness (efficiency) of fuel combustion is judged by the concentration of residual oxygen. In addition, the heat loss with flue gases and the concentration of carbon dioxide are determined from the oxygen concentration.

The oxygen concentration in portable flue gas analyzers is measured using electrochemical oxygen sensors; in stationary gas analyzers, zirconium sensors are also quite often used.

• diesel burners - 2…5%
• gas burners - 2…6%

Carbon monoxide CO.

Carbon monoxide or carbon monoxide is a poisonous gas that is the product of incomplete combustion. The gas is heavier than air and in the presence of leaks or burnouts in the chimneys of boilers can be released into the working environment, exposing personnel to the risk of poisoning. At CO concentrations up to 10,000 ppm, electrochemical cells are usually used to detect it. To measure concentrations above 10,000 ppm, optical cells are mainly used, including in portable gas analyzers.

• diesel burners - 80…150 ppm
• gas burners - 80…100 ppm

Nitrogen oxides (NOx).

At high temperatures in the boiler furnace, nitrogen forms nitric oxide NO with atmospheric oxygen. Subsequently, NO is oxidized to NO2 under the influence of oxygen. The components NO and NO2 are called nitrogen oxides NOx.

The NO concentration is measured by electrochemical sensors. NO2 in simple models of gas analyzers is determined by calculation and is taken equal to 5 ... 10% percent of the measured NO concentration. In some cases, the NO2 concentration is measured by a separate electrochemical nitrogen dioxide sensor. In any case, the resulting concentration of nitrogen oxides NOx is equal to the sum of the concentrations of NO and NO2.

• diesel burners - 50…120 ppm
• gas burners - 50…100 ppm

Sulfur dioxide (SO2).

Toxic gas produced when fuel containing sulfur is burned. When SO2 reacts with water (condensate) or steam, sulfurous acid H2SO3 is formed. Electrochemical cells are commonly used to measure SO2 concentrations.

Fireproof hydrocarbons (CH).

Non-combustible hydrocarbons CH are formed as a result of incomplete combustion of fuel. This group includes methane CH4, butane C4H10 and benzene C6H6. Thermal catalytic or optical infrared cells are used to measure the concentrations of non-combustible hydrocarbons.

To measure gas concentrations in industrial emissions and flue gases, gas analyzers Kaskad-N 512, DAG 500, Kometa-Topogaz, AKVT, etc. of domestic production, or foreign-made devices from such manufacturers as Testo, MSI Drager, MRU, Kane, etc. are used .

Denis Ryndin,
chief engineer of "Water Technology"

At present, the issues of increasing the efficiency of heating installations and reducing environmental pressure on the environment are especially acute. The most promising, in this respect, is the use of condensation technology, which is capable of solving the outlined range of problems in the most complete way. Vodnaya Tekhnika has always strived to introduce modern and efficient heating equipment to the domestic market. In light of this, her interest in condensation technology, as the most efficient, high-tech and promising, is natural and justified. Therefore, in 2006, one of the priority directions of the company's development is the promotion of condensing equipment on the Ukrainian market. To this end, a number of events are planned, one of which is a series of popularizing articles for those who first come across such a technique. In this article we will try to touch on the main issues of implementation and application of the principle of water vapor condensation in heating technology:

• How is heat different from temperature?
• Can the efficiency be greater than 100%?

How is heat different from temperature?

Temperature is the degree of heating of the body (the kinetic energy of the molecules of the body). A very relative value, this can be easily illustrated using the Celsius and Fahrenheit scales. In everyday life, the Celsius scale is used, in which the freezing point of water is taken as 0, and the boiling point of water at atmospheric pressure is taken as 100 °. Since the freezing and boiling points of water are not well defined, the Celsius scale is currently defined in terms of the Kelvin scale: Celsius is equal to Kelvin and absolute zero is taken as −273.15 °C. The Celsius scale is practically very convenient, since water is very common on our planet, and our life is based on it. Zero Celsius is a special point for meteorology, since the freezing of atmospheric water changes everything significantly. In England, and especially in the USA, the Fahrenheit scale is used. This scale is divided by 100 degrees from the temperature of the coldest winter in the city where Fahrenheit lived to the temperature of the human body. Zero Celsius is 32 Fahrenheit, and a degree Fahrenheit is 5/9 degrees Celsius.

Table 1 Temperature units

In order to more clearly imagine the difference between the concepts of temperature and heat, consider the following example: Example with heating water: Suppose we have heated some amount of water (120 liters) to a temperature of 50 ° C, and how much water can we heat up to a temperature of 40 °C using the same amount of heat (burned fuel)? For simplicity, we will assume that in both cases the initial water temperature is 15 °C.

Figure 1 Example 1

As can be seen from the illustrative example, temperature and the amount of heat are different concepts. Those. bodies at different temperatures can have the same thermal energy, and vice versa: bodies with the same temperature can have different thermal energies. To simplify the definitions, a special value was invented - Enthalpy Enthalpy is the amount of heat contained in a unit mass of a substance [kJ / kg] Under natural conditions on Earth, there are three states of aggregation of water: solid (ice), liquid (water itself), gaseous (water vapor) The transition of water from one state of aggregation to another is accompanied by a change in the thermal energy of the body at a constant temperature (the state changes, not the temperature, in other words, all the heat is spent on changing the state, and not on heating) Apparent heat is the heat at which the change in the amount of heat brought to the body causes a change in its temperature Latent heat - the heat of vaporization (condensation) is the heat that does not change the temperature of the body, but serves to change the state of aggregation of the body. Let us illustrate these concepts with a graph on which the enthalpy (the amount of heat supplied) will be plotted along the ordinate axis, and the temperature along the ordinate axis. This graph shows the process of heating a liquid (water).

Figure 2 Enthalpy - Temperature dependency graph, for water

A-B water is heated from a temperature of 0 ºС to a temperature of 100 ºС (in this case, all the heat supplied to the water goes to increase its temperature)
A-C water boils (in this case, all the heat supplied to the water goes to convert it into steam, while the temperature remains constant at 100 ºС)
C-D all the water has turned into steam (boiled away) and now the heat goes to increase the temperature of the steam.

The composition of flue gases during the combustion of gaseous fuels

The combustion process is the process of oxidation of the combustible components of the fuel with the help of atmospheric oxygen, while heat is released. Let's take a look at this process:

Figure 3 Composition of Natural Gas and Air

Let's see how the combustion reaction of gaseous fuel develops:

Figure 4 Combustion reaction of gaseous fuel

As can be seen from the equation for the oxidation reaction, as a result, we get carbon dioxide, water vapor (flue gases) and heat. The heat that is released during the combustion of the fuel is called the Lower calorific value of the fuel (PCI). If we cool the flue gases, then under certain conditions, water vapor will begin to condense (transition from a gaseous state to a liquid state).

Figure 5 Release of latent heat during condensation of water vapor

In this case, an additional amount of heat will be released (latent heat of vaporization / condensation). The sum of the Lower calorific value of the fuel and the latent heat of vaporization/condensation is called the Higher calorific value of the fuel (PCS).

Naturally, the more water vapor is in the combustion products, the greater the difference between the Higher and Lower calorific value of the fuel. In turn, the amount of water vapor depends on the composition of the fuel:

Table 2. Values ​​of higher and lower calorific value for various types of fuel

As can be seen from the table above, we can obtain the greatest additional heat by burning methane. The composition of natural gas is not constant and depends on the field. The average composition of natural gas is shown in Figure 6.

Figure 6 Composition of natural gas

Intermediate conclusions:

1. Using the latent heat of vaporization / condensation, you can get more heat than is released during fuel combustion

2. The most promising fuel, in this regard, is natural gas (the difference between the higher and lower calorific value is more than 10%)

What conditions must be created to start condensation? Dew point.

Water vapor in flue gases has slightly different properties than pure water vapor. They are mixed with other gases and their parameters correspond to the parameters of the mixture. Therefore, the temperature at which condensation begins differs from 100 ºС. The value of this temperature depends on the composition of the flue gases, which in turn is a consequence of the type and composition of the fuel, as well as the air excess factor. The flue gas temperature at which water vapor begins to condense in the products of fuel combustion is called the Dew Point.

Figure 7 Dew point

Intermediate conclusions:

1. The task of condensation technology is to cool the products of combustion below the dew point and take away the heat of condensation, using it for useful purposes.

Can the efficiency of a gas boiler be more than 100%?

Let's take the technical characteristics of some arbitrary mounted boiler:

Boiler total power =23.000 Kcal/h (26.7 KW);

Net power of the boiler=21.000 Kcal/h (24.03 KW);

In other words, the maximum thermal output of the burner is 23.000 Kcal/h (the amount of heat that is released during the combustion of the fuel), and the maximum amount of heat received by the coolant is 21.000 Kcal/h.

Where does the difference between them go? Some of the generated heat (6-8%) is lost with the outgoing flue gases, and the other (1.5-2%) is dissipated in the surrounding space through the boiler walls.

If we add these quantities, we can write the following equation:

If we divide the useful power of the boiler by the total and multiply the result by 100%, we get the boiler efficiency (COP) in%.

If we carefully read the text of the definition, we will see that the total power of the boiler is equal to the amount of heat that is released during the combustion of fuel per unit of time.

Thus, this value directly depends on the Lower calorific value of the fuel, and does not take into account the heat that can be released during the condensation of water vapor from the combustion products.

In other words, this is the efficiency of the boiler, relative to the Lower calorific value of the fuel.

If we take into account the value of the heat of condensation of water vapor (see Table 1), then we can imagine the following picture of the distribution of heat flows in a non-condensing boiler.

Figure 9 Distribution of heat flows in a non-condensing boiler

Then, as in a condensing boiler, the distribution of heat flows will look like this:

Figure 10 Distribution of heat flows in a condensing boiler

Intermediate conclusions:
1. Efficiency of 100% or more is possible if the Lower rather than the Higher calorific value is taken as the starting point.
2. We cannot fully use all the heat (sensible and latent) for technical reasons, therefore the efficiency of the boiler cannot be equal to or greater than 111% (relative to the Lower calorific value of the fuel).

Operating modes of condensing boilers

Gas condensing boilers can be installed in any heating system. The value of the heat of condensation used and the efficiency, depending on the mode of operation, depend on the correct calculation of the heating system.

In order to make effective use of the heat of condensation of the water vapor contained in the flue gases, it is necessary to cool the flue gases to a temperature below the dew point. The degree of use of the heat of condensation depends on the calculated temperatures of the coolant in the heating system and on the number of hours worked in the condensation mode. This is shown in graphs 11 and 13 where the dew point temperature is 55°C.

Heating system 40/30 °C

Figure 11 Low Temperature System Operation Schedule

Of great importance is the productive capacity of condensing boilers of such a heating system during the entire heating period. Low return temperatures are always below the dew point temperature, so that condensation occurs constantly. This occurs in low temperature panel heating systems or floor heating. A condensing boiler is ideal for such systems.

Figure 12 Room temperature conditions when using underfloor and convector heating

There are a lot of advantages of water floor heating systems over traditional ones:

• Increased comfort. The floor becomes warm and pleasant to walk on, as heat transfer occurs from a large surface with a relatively low temperature.
• Uniform heating of the entire area of ​​\u200b\u200bthe room, and therefore uniform heating. A person feels equally comfortable near the window and in the middle of the room.
• Optimal temperature distribution along the height of the room. Figure 12 illustrates the approximate distribution of temperatures along the height of the room when using traditional heating and underfloor heating. The distribution of temperatures, with floor heating, is felt by a person as the most favorable. It is also necessary to note the reduction of heat loss through the ceiling, since the temperature difference between indoor air and outdoor air is significantly reduced, and we get comfortable heat only where we need it, rather than heating the environment through the roof. This makes it possible to effectively use the underfloor heating system for buildings with high ceilings - churches, exhibition halls, gyms, etc.

• Hygiene. There is no air circulation, drafts are reduced, and therefore there is no dust circulation, which is a big plus for people's well-being, especially if they suffer from respiratory diseases.
• A significant part of the heat from the floor is transferred in the form of radiant heat transfer. Radiation, unlike convection, immediately spreads heat to surrounding surfaces.
• There is no artificial dehumidification of air near heating devices.
• Aesthetics. There are no heating devices, there is no need for their design or selection of optimal sizes.

Heating system 75/60 ​​°C

Figure 13 High temperature system operation schedule

Efficient use of the heat of condensation is also possible at design temperatures of 75/60 ​​°C for a time that is 97% of the duration of the heating period. This applies to outside temperatures from -11°C to +20°C. Old heating systems, which were designed for temperatures of 90/70 °C, operate today at almost 75/60 ​​°C. Even in systems with a heating medium of 90/70 °C and with an operating mode in which the boiler water temperature is controlled according to the outside temperature, the condensing heat utilization time is 80% of the annual heating period.

High standardized efficiency

The examples in Figures 11 and 13 clearly show that the difference between these two options, but at the same time, a high percentage of condensing heat utilization has a direct impact on the energy consumption of a gas condensing boiler. To indicate the efficiency of fuel consumption of heating boilers, the concept of a standardized efficiency factor was introduced. Figure 14 shows the dependence of energy consumption on various design temperatures of the heating system.

Figure 14 Efficiency versus return temperature

The high standardized efficiencies of gas condensing boilers are due to the following factors:

– Realization of a high CO 2 value. The higher the CO 2 content, the higher the dew point temperature of the heating gases.

– Maintenance of low return temperatures. The lower the return temperature, the more active the condensation and the lower the flue gas temperature.

Intermediate conclusions:

The efficiency of a condensing boiler is highly dependent on the operating temperature of the heating system.
In new installations, all possibilities must be used for optimal operation of the gas condensing boiler. High efficiency is achieved when the following criteria are met:
1. ?Limit the return temperature to a maximum of 50 °C
2. ?Try to maintain a temperature difference between flow and return of at least 20 K
3. Do not take measures to increase the temperature of the return line (these include, for example, the installation of a four-way mixer, by-pass lines, hydraulic arrows).

Ways to implement the principle of condensation in mounted boilers

At the moment, there are two main ways to implement the principle of water vapor condensation in flue gases: a remote economizer and a stainless steel heat exchanger with a built-in economizer

In the first case, the main heat of the combustion products is utilized in a conventional convection heat exchanger, and the condensation process itself takes place in a separate unit - a remote economizer. This design allows the use of components and assemblies used in conventional, non-condensing boilers, but does not make it possible to fully unlock the potential of condensing technology.

Figure 17 Condensing boiler with remote economizer

A heat exchanger with a built-in economizer consists of 4-7 heat exchange elements (coils). Each heat exchange element in turn consists of 4 coils of a smooth stainless steel rectangular tube with a wall thickness of approx. 0.8 mm (See Figure 18).

Figure 18 Scheme of flue gas flow between the coils of the heat exchanger

There are several heat exchange elements in front of the insulating plate. They play the role of the "first stage", since only a slight condensation occurs here. The fourth and, respectively, the fifth heat exchange element is located behind the insulating plate. In this "condensation stage" the main process of condensation takes place.

The advantages of this principle lie in the very efficient heat transfer and, on the other hand, in the elimination of boiling noise caused by high flow rates in smooth pipes.
Another advantage of this heat exchanger is its low susceptibility to liming, as a high level of turbulence is created due to the small cross-sections of the tubes.
The smooth surface of the stainless steel pipes and the vertical flow direction provide a self-cleaning effect.
The heat exchanger return connection is located at the rear, the flow connection is at the front. A condensate drain is installed on the heat exchanger.
The flue gas collector is made of plastic before connecting the "air inlet / flue gas outlet" pipeline.

Figure 19 Hydraulic diagram of a condensing boiler with built-in economizer

Figure 20 Cross-section of the heat exchanger of a condensing boiler with built-in economizer

Conventional gas combustion and full premix combustion

Most boilers with an open combustion chamber have the same principle of gas combustion. Due to the kinetic energy of the gas jet, air is sucked into it.

Figure 19 Principle of gas combustion in atmospheric burners (Venturi nozzle)

Combustible gas is supplied under pressure to the nozzle. Here, due to the narrowing of the passage, the potential energy of pressure is converted into the kinetic energy of the jet. Due to the special geometric section of the Venturi nozzle, primary air is mixed in. Directly in the nozzle, a mixture of gas and air occurs (a gas-air mixture is formed). Secondary air is added at the outlet of the nozzle. The change in burner power occurs due to a change in gas pressure, respectively, the speed of the gas jet and the amount of sucked air change.
The advantages of this design are its simplicity and noiselessness.
Limitations and disadvantages: a large excess of air, limited modulation depth, an abundance of harmful emissions.

In boilers with a closed combustion chamber, the principle of gas combustion is similar to that described above. The difference lies only in the forced ejection of combustion products and the supply of air for combustion. All the advantages and disadvantages of atmospheric burners are valid for boilers with a closed combustion chamber.

Condensing boilers use the "Total pre-mixing of gas and air" principle. The essence of this method lies in the admixture of gas to the air stream, due to the rarefaction created by the latter in the Venturi nozzle.

Gas fittings and blower
As soon as the start speed of the blower is recognized by the electronics, the gas valves in series are opened.
On the suction side of the blower, a double-walled air inlet / flue gas outlet (Venturi system) is installed. Due to the annular gap, in accordance with the Venturi principle, a suction phenomenon occurs in the chamber above the main gas control membrane in the gas valve.

Figure 20 Burner Mixing Unit with Full Premix

Ignition process
The gas passes through channel 1 under the control membranes. The main gas control valve opens due to the resulting pressure difference. The gas then enters the blower through the Venturi system and mixes with the intake air. The gas-air mixture enters the burner and is ignited.
Modulation mode
The stroke of the main gas control valve depends on the position of the control valve. By increasing the speed of the blower, the pressure downstream of the main gas control valve is reduced. Channel 2 continues the pressure change to a pressure below the control valve diaphragm. The outflow outlet continues to close, whereby the rate of gas pressure reduction through channel 2 is reduced. Thus, through channel 1, the pressure under the diaphragm of the main gas control valve increases. The main gas control valve continues to open, thus more gas flows to the blower and therefore more gas to the burner.
The burner is thus modulated continuously by changing the blower flow. The amount of gas tracks the amount of air in a pre-specified ratio. Thus, over the entire modulation range, it is possible to maintain the excess air ratio at an almost constant level.

Figure 21 Full premix burner thermo module

The content of harmful substances in flue gases and ways to reduce their concentration

Currently, environmental pollution is rampant. The amount of emissions from the heat and power sector is in second place, after road transport.

Figure 22 Percentage of emissions

Therefore, the issue of reducing harmful substances in combustion products is especially acute.

Main pollutants:

1. • Carbon monoxide CO
   • Nitrogen oxides NOx
   • Vapors of acids

It is advisable to fight the first two factors by improving the combustion process (exact gas-air ratio) and lowering the temperature in the boiler furnace.

During the combustion of gaseous fuels, the formation of the following acids is possible:

Vapors of acids are perfectly removed together with condensate. Disposing of them in a liquid state is quite simple. Usually, this is done by neutralizing an acid with an alkali.

Utilization of acid condensate

As can be seen from the combustion reaction of methane:

When burning 1 m3 of gas, 2 m3 of water vapor is formed. During normal operation of the condensing boiler, about 15-20 liters are formed per day. condensate. This condensate has a low acidity (about Ph=3.5-4.5), which does not exceed the permissible level of household waste.

Figure 23 Acidity level of gas boiler condensate

Table 3 Content of heavy metals in condensate

Therefore, it is allowed to discharge condensate into the sewer, where it will be neutralized with alkaline household waste.
It should be noted that domestic drainage systems consist of materials resistant to acidic condensate.
According to ATV worksheet A 251, these are the following materials:
_ Ceramic pipes
_ Rigid PVC pipes
_ PVC pipes
_ HDPE pipes
_ Polypropylene pipes
_ Acrylonitrile-butadiene-styrene copolymer or acrylonitrile-styrene-acrylic ester (ABS/ASA) pipes
_ Stainless steel pipes
_ Borosilicate pipes

Figure 24 Condensate disposal

According to Italian regulations, the above condensate discharge scheme can be used for boiler plants with a total power of up to 116 kW (according to the German ATV A 251 standard, not more than 200 kW). If this value is exceeded, it is necessary to install special condensate granulator neutralizers.

Figure 25 Condensate neutralization using a condensate pump

1. Boiler steam trap outlet
2. Converter inlet
3. Condensate neutralizer
4. Catalyst outlet
5. Condensate supply hose to the condensate trap
6. Condensate trap
7. Condensate outlet
8. Condensate outlet hose
9. Adapter
10. Sewerage
11. Mounting clamps

Figure 25 shows an example of a neutralization plant. The condensate entering the neutralizer is first filtered through a layer of activated carbon and then neutralized in the main volume. A condensate pump is installed when it is necessary to drain condensate above the level of the condensate siphon in the boiler. This design is used when neutralizing condensate from boilers with a total power of 35 to 300 kW (depending on the power of the installation, the length of the converter varies). If the installation power exceeds 300 kW, then several neutralizers are installed in parallel.
The neutralizer is extremely easy to maintain and requires revision and addition of granulate no more than once a year. As a rule, the acidity of the condensate is also assessed using litmus paper.

Argument in favor of condensing technology