I suggest recycling activities for consideration flue gases. Flue gases are available in abundance in any town or city. The main part of smoke producers are steam and hot water boilers and internal combustion engines. I will not consider the flue gases of engines in this idea (although they are also suitable in composition), but I will dwell on the flue gases of boiler houses in more detail.

The easiest way is to use smoke from gas boiler houses (industrial or private houses), this is the most clean look flue gas containing a minimum amount of harmful impurities. You can also use smoke from boiler houses burning coal or liquid fuel, but in this case you will have to clean the flue gases from impurities (this is not so difficult, but still additional costs).

The main components of flue gas are nitrogen, carbon dioxide and water vapor. Water vapor is of no value and can be easily removed from the flue gas by contacting the gas with a cool surface. The remaining components already have a price.

Nitrogen gas is used in fire fighting, for the transportation and storage of flammable and explosive media, as a protective gas to protect easily oxidized substances and materials from oxidation, to prevent corrosion of tanks, for purging pipelines and containers, to create inert environments in grain silos. Nitrogen protection prevents the growth of bacteria and is used to clean environments from insects and microbes. In the food industry, a nitrogen atmosphere is often used as a means of increasing the shelf life of perishable products. Nitrogen gas is widely used to produce liquid nitrogen from it.

To obtain nitrogen, it is enough to separate water vapor and carbon dioxide from the flue gas. As for the next component of smoke - carbon dioxide (CO2, carbon dioxide, carbon dioxide), the range of its applications is even greater and its price is much higher.

I suggest getting more complete information about him. Typically, carbon dioxide is stored in 40-liter cylinders painted black with the word “carbon dioxide” written in yellow. The more correct name for CO2 is “carbon dioxide”, but everyone has already become accustomed to the name “carbon dioxide”, it has been assigned to CO2 and therefore the inscription “carbon dioxide” on the cylinders is still preserved. Carbon dioxide is found in cylinders in liquid form. Carbon dioxide is odorless, non-toxic, non-flammable and non-explosive. It is a substance naturally formed in the human body. The air exhaled by a person usually contains 4.5%. Carbon dioxide is mainly used in carbonation and bottling of drinks; it is used as a protective gas during welding work using semi-automatic welding machines, is used to increase the yield (2 times) of agricultural crops in greenhouses by increasing the concentration of CO2 in the air and increasing (by 4-6 times when water is saturated with carbon dioxide) the production of microalgae during their artificial cultivation, to preserve and improve the quality of feed and products , for the production of dry ice and its use in cryoblasting installations (cleaning surfaces of contaminants) and for obtaining low temperatures during storage and transportation food products etc.

Carbon dioxide is a commodity in demand everywhere and the need for it is constantly increasing. In home and small businesses, carbon dioxide can be obtained by extracting it from flue gas in low-capacity carbon dioxide plants. It is easy for people involved in technology to make such an installation themselves. Subject to compliance technological process, the quality of the produced carbon dioxide meets all the requirements of GOST 8050-85.
Carbon dioxide can be obtained both from the flue gases of boiler houses (or heating boilers of private households) and by special combustion of fuel in the installation itself.

Now the economic side of the matter. The installation can operate on any type of fuel. When burning fuel (especially to produce carbon dioxide), the following amount of CO2 is released:
natural gas (methane) – 1.9 kg CO2 from combustion of 1 cubic meter. m of gas;
coal, different fields – 2.1-2.7 kg CO2 from burning 1 kg of fuel;
propane, butane, diesel fuel, fuel oil - 3.0 kg CO2 from burning 1 kg of fuel.

It will not be possible to completely extract all the carbon dioxide released, but up to 90% (95% extraction can be achieved) is quite possible. The standard filling of a 40-liter cylinder is 24-25 kg, so you can calculate it yourself specific consumption fuel to obtain one cylinder of carbon dioxide.

It is not that big; for example, in the case of obtaining carbon dioxide from burning natural gas, it is enough to burn 15 m3 of gas.

At the highest rate (Moscow) it is 60 rubles. for 40 liters. carbon dioxide cylinder. In the case of extracting CO2 from the flue gases of boiler houses, the cost of producing carbon dioxide is reduced, since fuel costs are reduced and the profit from the installation increases. The installation can operate around the clock, in automatic mode, with minimal human involvement in the process of producing carbon dioxide. The productivity of the installation depends on the amount of CO2 contained in the flue gas, the design of the installation and can reach 25 carbon dioxide cylinders per day or more.

The price of 1 cylinder of carbon dioxide in most regions of Russia exceeds 500 rubles (December 2008). Monthly revenue from the sale of carbon dioxide in this case reaches: 500 rubles/ball. x 25 points/day. x 30 days. = 375,000 rub. The heat released during combustion can be used simultaneously for space heating, and in this case there will be no wasteful use of fuel. It should be borne in mind that the environmental situation at the site where carbon dioxide is extracted from flue gases is only improving, as CO2 emissions into the atmosphere are decreasing.

The method of extracting carbon dioxide from flue gases obtained from combustion also works well. wood waste(waste from logging and wood processing, carpentry shops, etc.). In this case, the same carbon dioxide installation is supplemented with a wood gas generator (factory or self-made) to produce wood generator gas. Wood waste (logs, wood chips, shavings, sawdust, etc.) is poured into the gas generator hopper 1-2 times a day; otherwise, the installation operates in the same mode as in the above.
The yield of carbon dioxide from 1 ton of wood waste is 66 cylinders. Revenue from one ton of waste is (at a carbon dioxide cylinder price of 500 rubles): 500 rubles/ball. x 66 points = 33,000 rub.

With the average amount of wood waste from one wood processing shop being 0.5 tons of waste per day, revenue from the sale of carbon dioxide can reach 500 thousand rubles. per month, and in the case of importing waste from other wood processing and carpentry shops, the revenue becomes even greater.

It is possible to obtain carbon dioxide from combustion car tires, which is also only beneficial for our environment.

In the case of producing carbon dioxide in quantities greater than the local market can consume, the produced carbon dioxide can be independently used for other activities, as well as processed into other chemicals and reagents (for example, using simple technology into environmentally friendly carbon-containing fertilizers, baking powder and etc.) up to the production of motor gasoline from carbon dioxide.

V.S.Galustov, Doctor of Technical Sciences, Professor, CEO SE NPO "Polytechnika"
L.A. Rosenberg, engineer, director of the Yumiran Unitary Enterprise.

Introduction.

With flue gases of various origins, thousands and thousands of Gcal of heat are released into the atmosphere, as well as thousands of tons of gaseous and solid pollutants and water vapor. In this article we will focus on the problem of heat recovery (we will talk about cleaning gas emissions in the next message). The deepest use of the heat of fuel combustion is carried out in thermal power boilers, for which in most cases economizers are provided in their tail section. The temperature of the flue gases after them is about 130-190°C, i.e. is close to the dew point temperature of acid vapors, which is the lower limit in the presence of sulfur compounds in the fuel. When burning natural gas, this limitation is less significant.

Flue gases from various types of furnaces can have significantly more high temperature(up to 300-500°C and above). In this case, heat recovery (and gas cooling) is simply mandatory, if only to limit thermal pollution of the environment.

Heat recovery units.

Even in the first message, we limited the range of our interests to processes and devices with direct phase contact, but to complete the picture, let us recall and evaluate other options. All known heat exchangers can be divided into contact, surface, and devices with an intermediate coolant. We will dwell on the first in more detail below. Surface heat exchangers are traditional air heaters that are placed directly in the flue after the furnace (boiler) and have serious disadvantages that limit their use. Firstly, they contribute significantly aerodynamic drag into the gas path and worsen the operation of furnaces (the vacuum decreases) with a designed smoke exhauster, and replacing it with a more powerful one may not compensate for the accompanying costs by saving heat. Secondly, low heat transfer coefficients from gas to the surface of the tubes determine large values required contact surface.

Devices with an intermediate coolant are of two types: periodic with solid coolant and continuous with liquid. The first are at least two columns filled, for example, with crushed granite (packing). Flue gases pass through one of the columns, giving off heat to the nozzle, heating it to a temperature slightly lower than the temperature of the gases. Then the flue gases are switched to the second column, and the first is supplied with a heated medium (usually air supplied to the same furnace, or system air air heating) etc. The disadvantages of such a scheme are obvious (high resistance, bulkiness, temperature instability, etc.), and its application is very limited.

Devices with a liquid intermediate coolant (usually water) were called contact heat exchangers with an active nozzle (CTAN), and the authors, after minor improvements, called them heat exchangers with a saturated coolant and condensation (TANTEC). In both cases, the water heated by the flue gases then transfers the resulting heat through the wall of a surface built-in heat exchanger to clean water (for example, a heating system). Compared to air heaters, the resistance of such heat exchangers is much lower, and in terms of heat exchange in the flue gas - water system, they are completely similar to the direct-flow atomization devices that interest us. However, there are significant differences, which we will discuss below.

The developers of KTAN and TANTEC devices do not consider in their publications the features of heat transfer during direct contact of flue gases and water, so we will dwell on them in a little more detail.

The main processes in the flue gas - water system.

The result of the interaction of heated flue gases (in composition and properties this is actually moist air) and water (in the form of droplets of one size or another), which we will call a heat-accumulating medium (it can be used as the main or intermediate coolant), is determined by a whole complex of processes.

Simultaneously with heating, condensation of moisture on the surface of the droplets or evaporation may occur. In fact, there are three possible options for the mutual direction of heat and moisture flows (heat transfer and mass transfer), which depend on the ratio of phase temperatures and the ratio of partial vapor pressures in the boundary layer (near the drop) and in the core of the gas flow (Fig. 1a).

In this case, the first (upper) case, when the flows of heat and moisture are directed from the droplets to the gas, corresponds to evaporative cooling water; the second (middle) - heating the droplets while simultaneously evaporating moisture from their surface; the third (lower) option, in which heat and moisture are directed from the gas to the droplets, reflects the heating of water with condensation of vapor. (It would seem that there should be a fourth option, when cooling of droplets and heating of gas are accompanied by condensation of moisture, but in practice this does not occur.)

All the described processes can be clearly represented on the Ramzin diagram of the state of humid air (H - x diagram, Fig. 1b).

Already from what has been said, we can conclude that the third option is the most desirable, but in order to understand how to ensure it, it is necessary, in addition to what has been stated above, to recall:

- the amount of water vapor contained in 1 m3 of humid air is called absolute air humidity. Water vapor occupies the entire volume of the mixture, therefore the absolute humidity of the air is equal to the density of water vapor (in given conditions) pp

— when the air is saturated with steam, there comes a moment when condensation begins, i.e. the maximum possible vapor content in the air is achieved at a given temperature, which corresponds to the density of saturated water vapor pH;

— the ratio of absolute humidity to the maximum possible amount of steam in 1 m3 of air at a given pressure and temperature is called relative air humidity f;

- the amount of water vapor in kg per 1 kg of absolutely dry air is called air moisture content x;

— moist air as a coolant is characterized by enthalpy / (heat content), which is a function of the temperature and moisture content of the air and is equal to the sum of the enthalpies of dry air and water vapor. In the most convenient form for practical use, the formula for calculating enthalpy can be presented

I= (1000 + 1.97 . 103x) t+ 2493 . . 103x J/kg dry air, where 1000 - specific heat dry air, J/kg*deg); 1.97*103 - specific heat capacity of steam, J/(kg*deg); 2493*103 - constant coefficient, approximately equal to the enthalpy of steam at 0°C; t—air temperature, °C;

I = 0.24t + (595 + 0.47t) Xkcal/kg dry air; where 595 is a constant coefficient approximately equal to the enthalpy of steam at 0°C; 0.24—specific heat capacity of dry air, kcal/(kgtrad); 0.47 — heat capacity of steam, kcal/(kgtrad);

— when the air cools (under conditions of constant moisture content), the relative humidity will increase until it reaches 100%. The corresponding temperature is called the dew point temperature. Its value is determined solely by the moisture content of the air. On the Ramzin diagram, this is the point of intersection of the vertical line x = const with the line φ = 1.

Air cooling below the dew point is accompanied by moisture condensation, i.e. air drying.

Some confusion is caused by publications that give dew point values ​​for various solid and liquid fuels about 130-150°C. It must be borne in mind that this concerns the beginning of condensation of vapors of sulfuric and sulfurous acids (denoted by eetpK), and not water vapor (tp), which we discussed above. For the latter, the dew point temperature is much lower (40-50°C).

So, three quantities - flow rate, temperature and moisture content (or wet-bulb temperature) - fully characterize flue gases as a source of secondary energy resources.

When water comes into contact with hot gases, the liquid is initially heated and vapor condenses on the surface of cold drops (corresponds to option 3 in Fig. 1a) until the temperature corresponding to the dew point for the gas is reached, i.e. boundary of transition to the second regime (3rd option in Fig. 1a). Further, as the water heats up and the partial vapor pressure at the surface of the droplets increases, the amount of heat transferred to them due to heat transfer Q1 will decrease, and the amount of heat transferred from the droplets to the flue gases due to evaporation Q2 will increase. This will continue until equilibrium is reached (Q1 = Q2), when all the heat received by water from the flue gas will be returned to the gas in the form of heat of evaporation of the liquid. After this, further heating of the liquid is impossible, and it evaporates at a constant temperature. The temperature achieved in this case is called the wet bulb temperature tM (in practice, it is defined as the temperature indicated by a thermometer whose ball is covered with a damp cloth, from which moisture evaporates).

Thus, if water is supplied to the heat exchanger with a temperature equal to (or greater than) tM, then adiabatic (at constant heat content) cooling of the gases will be observed and there will be no heat recovery (not counting negative consequences- loss of water and humidification of gases).

The process becomes more complex if we consider that the composition of the droplets is polydisperse (due to the mechanisms of liquid disintegration during spraying). Small drops instantly reach tM and begin to evaporate, changing the gas parameters towards increasing moisture content, medium drops can be between tp and tM, and large drops can be below tp, i.e.

heat up and condense moisture. All this occurs simultaneously in the absence of clear boundaries.

It is possible to comprehensively analyze the results of direct contact of droplets of a heat-storing medium and hot flue gases only on the basis mathematical model, taking into account the entire complex of phenomena (simultaneous heat and mass transfer, changes in environmental parameters, aerodynamic conditions, polydisperse composition of the droplet flow, etc.).

A description of the model and the results of analysis based on it is given in the monograph, which we recommend that the interested reader refer to. Here we note only the main thing.

For most flue gases, the wet bulb temperature is in the range of 45-55°C, i.e. water in the zone of direct contact with flue gases, as noted above, can only be heated to the specified temperature, although with fairly deep heat recovery. Preliminary humidification of gases, as provided for by the TANTEC design, not only does not lead to an increase in the amount of utilized heat, but even to its decrease.

And finally, it should be taken into account that when recovering heat even from gases that do not contain sulfur compounds, they should not be cooled below 80°C (it makes it difficult to evacuate them to environment through the flue and chimney).

Let us explain this with a specific example. Let the flue gases after the boiler in an amount of 5000 kg/h, having a temperature of 130°C and a moisture content of 0.05 kg/kg, contact the heat recovery medium (water, tH = 15°C). From the H-x diagram we find: tM= 49.5°C; tp= 40°С; I = 64 kcal/kg. Calculations using the model showed that when gases are cooled to 80°C by a polydisperse flow of droplets with an average diameter of 480 μm, the moisture content actually remains unchanged (evaporation of small droplets is compensated by condensation on large ones), tM becomes equal to 45°C, and heat content I = 50 kcal/kg . Thus, 0.07 Gcal/h of heat is utilized, and the heat-accumulating medium in the amount of 2.5 m3/h is heated from 15 to 45°C.

If you use TANTEC and preliminarily humidify - adiabatic cooling of gases to t-100°C, and then cool to 80°C at X = const, then the final gas parameters will be: tM = 48°C; I = 61.5°C. And although the water will heat up slightly higher (up to 48°C), the amount of heat utilized is reduced by 4 times and will be 0.0175 Gcal/h.

Options for organizing heat recovery.

Solution specific task utilization of flue gas heat depends on a number of factors, including the presence of pollutants (determined by the type of fuel burned and the object heated by flue gases), the presence of a heat consumer or directly hot water etc.

At the first stage, it is necessary to determine the amount of heat that, in principle, can be extracted from the existing flue gases, and evaluate the economic feasibility of heat recovery, since the capital costs for it are not proportional to the amount of heat recovered.

If the answer to the first question is positive, then the possibility of using moderately heated water should be assessed (for example, when burning natural gas, use it to prepare make-up water for boilers or heating networks, and if the target product is contaminated with dust particles, use it to prepare raw materials, for example in production ceramic products and so on.). If the water is too polluted, you can provide a double-circuit system or combine heat recovery with flue gas purification (get higher (above 45-5СРС) temperatures or a surface stage).

There are many options for organizing the heat recovery process. From choice optimal solution the economic efficiency of the event depends.

Literature:

1. Galustov B.S. Heat and mass transfer processes and devices with direct phase contact in heat and power engineering // Energy and management. - 2003. - No. 4.

2. Galustov B.S. Direct-flow spraying devices in thermal power engineering. - M.: Energoatomizdat, 1989.

3. Sukhanov V.I. and others. Installations for heat recovery and purification of flue gases of steam and hot water boilers. - M.: AQUA-TERM, July 2001.

4. Planovsky A.N., Ramm V.M., Kagan S.Z. Processes and apparatuses of chemical technology. - M.: Goskhimizdat, 1962. - P.736-738.

Heat recovery from flue gases

Flue gases leaving working space ovens have a very high temperature and therefore carry away a significant amount of heat. In open-hearth furnaces, for example, about 80% of the total heat supplied to the working space is carried away from the working space with flue gases, in heating furnaces about 60%. From the working space of the furnaces, the flue gases carry away more heat with them, the higher their temperature and the lower the heat utilization coefficient in the furnace. In this regard, it is advisable to ensure the recovery of heat from exhaust flue gases, which can be done in principle by two methods: with the return of part of the heat taken from the flue gases back to the furnace and without returning this heat to the furnace. To implement the first method, it is necessary to transfer the heat taken from the smoke to gas and air (or only air) going into the furnace. To achieve this goal, heat exchangers of recuperative and regenerative types are widely used, the use of which makes it possible to increase the efficiency of the furnace unit, increase the combustion temperature and save fuel. With the second recovery method, the heat of exhaust flue gases is used in thermal power boiler houses and turbine units, which achieves significant fuel savings.

In some cases, both described methods of waste heat recovery are used simultaneously. This is done when the temperature of the flue gases after regenerative or recuperative heat exchangers remains sufficiently high and further heat recovery in thermal power plants is advisable. For example, in open-hearth furnaces, the temperature of the flue gases after the regenerators is 750-800 °C, so they are reused in waste heat boilers.

Let us consider in more detail the issue of recycling the heat of exhaust flue gases with the return of part of their heat to the furnace.

It should be noted, first of all, that a unit of heat taken from the smoke and introduced into the furnace by air or gas (a unit of physical heat) turns out to be much more valuable than a unit of heat obtained in the furnace as a result of combustion of fuel (a unit of chemical heat), since the heat of the heated air (gas) does not entail heat loss with flue gases. The value of a unit of sensible heat is greater, the lower the fuel utilization factor and the higher the temperature of the exhaust flue gases.

For normal operation of the furnace, it is necessary to supply the working space every hour. required amount heat. This amount of heat includes not only the heat of the fuel, but also the heat of heated air or gas, i.e.

It is clear that with = const an increase will reduce . In other words, utilization of heat from flue gases makes it possible to achieve fuel savings, which depends on the degree of heat recovery from flue gases

where is the enthalpy of heated air and flue gases escaping from the working space, kW, or kJ/period, respectively.

The degree of heat recovery can also be called efficiency. recuperator (regenerator), %

Knowing the degree of heat recovery, you can determine fuel economy using the following expression:

where I"d, Id are, respectively, the enthalpy of the flue gases at the combustion temperature and those leaving the furnace.

Reducing fuel consumption as a result of using heat from exhaust flue gases usually gives a significant economic effect and is one of the ways to reduce the cost of heating metal in industrial furnaces.

In addition to saving fuel, the use of air (gas) heating is accompanied by an increase in calorimetric combustion temperature, which may be the main purpose of recovery when heating furnaces with fuel with a low calorific value.

An increase in at leads to an increase in combustion temperature. If it is necessary to provide a certain value, then an increase in the air (gas) heating temperature leads to a decrease in the value, i.e., to a decrease in the share of gas with a high calorific value in the fuel mixture.

Since heat recovery allows for significant fuel savings, it is advisable to strive for the highest possible, economically justified degree of utilization. However, it must immediately be noted that recycling cannot be complete, i.e. always. This is explained by the fact that increasing the heating surface is rational only up to certain limits, after which it already leads to a very insignificant gain in heat savings.

Evaluation of Efficiency of Deep recuperation of Power Plant Boilers’ Combustion Productions

E.G. Shadek, Candidate of Engineering, independent expert

Keywords: combustion products, heat recuperation, boiler plant equipment, energy efficiency

One of the methods to solve the problem of fuel economy and improvement of energy efficiency of boiler plants is development of technologies for deep heat recuperation of boiler exhaust gases. We offer a process scheme of a power plant with steam-turbine units (STU) that allows for deep recuperation of heat from boiler combustion products from STU condenser using cooler-condensate with minimum costs without the use of heat pump units.

Description:

One of the ways to solve the problem of saving fuel and increasing the energy efficiency of boiler plants is to develop technologies for deep utilization of the heat of exhaust gases from boilers. We propose a technological scheme of a power plant with steam turbine units (STU), which allows, at minimal cost, without the use of heat pump units, to carry out deep utilization of heat from exhaust gases. boiler of combustion products due to the presence of a cooler - condensate from the PTU condenser.

E. G. Shadek, Ph.D. tech. sciences, independent expert

One of the ways to solve the problem of saving fuel and increasing the energy efficiency of boiler plants is to develop technologies for deep utilization of heat from flue gases from boilers. We offer a technological scheme of a power plant with steam turbine units (STU), which allows, at minimal cost, without the use of heat pump units, to carry out deep utilization of the heat of combustion products leaving the boiler due to the presence of a cooler - condensate from the STU condenser.

Deep utilization of heat from combustion products (CP) is ensured when they are cooled below the dew point temperature, equal to 50–55 0 C for CP of natural gas. In this case, the following phenomena occur:

• condensation of water vapor (up to 19–20% of the volume or 12–13% of the weight of combustion products),
• utilization of physical heat from PS (40–45% of total heat content),
• utilization of latent heat of vaporization (60–55%, respectively).

It was previously established that fuel savings during deep utilization in comparison with a boiler with a passport (maximum) efficiency of 92% is 10–13%. The ratio of the amount of recovered heat to the thermal power of the boiler is about 0.10–0.12, and the efficiency of the boiler in condensing mode is 105% based on the lower calorific value of the gas.

In addition, during deep recycling in the presence of water vapor in the PS, the emission of harmful emissions is reduced by 20–40% or more, which makes the process environmentally friendly.

Another effect of deep recycling is the improvement of the conditions and service life of the gas path, since condensation is localized in the chamber where the recovery heat exchanger is installed, regardless of the outside air temperature.

Deep recycling for heating systems

In advanced Western countries, deep recycling for heating systems is carried out using condensation-type hot water boilers equipped with a condensation economizer.

Low, as a rule, return water temperature (30–40 0 C) at typical temperature chart, for example 70/40 0 C, in the heating systems of these countries allows for deep heat recovery in a condensation economizer equipped with a unit for collecting, discharging and processing condensate (with its subsequent use to feed the boiler). This scheme ensures the condensation mode of operation of the boiler without artificial coolant, i.e., without the use of a heat pump unit.

The effectiveness and profitability of deep recycling for heating boilers does not need proof. Condensing boilers were received in the West wide application: up to 90% of all manufactured boilers are condensing. Such boilers are also used in our country, although we do not produce them.

In Russia, unlike countries with warm climates, the temperature in the return line of heating networks is usually higher than the dew point, and deep utilization is possible only in four-pipe systems (which are extremely rare) or when using heat pumps. main reason Russia's lag in the development and implementation of deep recycling – low price natural gas, high capital costs due to the inclusion of heat pumps in the scheme and long payback periods.

Deep recycling for power plant boilers

The efficiency of deep utilization for power plant boilers (Fig. 1) is significantly higher than for heating boilers, due to the stable load (KIM = 0.8–0.9) and large unit capacities (tens of megawatts).

Let us estimate the heat resource of combustion products of station boilers, taking into account their high efficiency (90–94%). This resource is determined by the amount of waste heat (Gcal/h or kW), which is uniquely dependent on the thermal power of the boiler Q K, and temperature beyond gas boilers T 1УХ, which in Russia is accepted at no lower than 110–130 0 C for two reasons:

• for increase natural traction and reducing the pressure (energy consumption) of the smoke exhauster;
• to prevent condensation of water vapor in hogs, flues and chimneys.

Extended analysis of a large array 1 of experimental data from balance and commissioning tests carried out by specialized organizations, performance maps, reporting statistics of stations, etc. and the results of calculations of heat loss values ​​​​with exhaust combustion products q 2, the amount of reclaimed heat 2 Q UT and their derivative indicators in a wide range of station boiler loads are given in Table. 13 . The goal is to determine q 2 and ratios of quantities Q K, q 2 and Q UT under typical boiler operating conditions (Table 2). In our case, it does not matter which boiler: steam or hot water, industrial or heating.

Indicators table. 1, highlighted in blue, were calculated using the algorithm (see help). Calculation of the deep recycling process (definition Q UT, etc.) were carried out according to the engineering methodology given in and described in. Heat transfer coefficient “combustion products – condensate” in condensing heat exchanger were determined using the empirical methodology of the heat exchanger manufacturer (OJSC Heating Plant, Kostroma).

The results indicate the high economic efficiency of deep utilization technology for station boilers and the profitability of the proposed project. The payback period of the systems ranges from 2 years for a minimum power boiler (Table 2, boiler No. 1) to 3–4 months. The resulting ratios β, φ, σ, as well as savings items (Table 1, lines 8–10, 13–18) allow you to immediately assess the capabilities and specific indicators of a given process, boiler.

Heat recovery in a gas heater

The usual technological scheme of a power plant involves heating the condensate in a gas heater (part of the tail surfaces of the boiler, economizer) using the flue gases leaving the boiler.

After the condenser, the condensate is sent by pumps (sometimes through a block desalting unit - hereinafter referred to as BOU) to a gas heater, after which it enters the deaerator. When the quality of the condensate is normal, the water treatment unit is bypassed. To prevent condensation of water vapor from the flue gases on the last pipes of the gas heater, the temperature of the condensate in front of it is maintained at least 60 0 C by recirculating heated condensate to the inlet.

To further reduce the temperature of the flue gases, a water-to-water heat exchanger cooled by make-up water from the heating network is often included in the condensate recirculation line. Heating of network water is carried out by condensate from a gas heater. With additional cooling of the gases by 10 0 C, about 3.5 Gcal/h of heating load can be obtained in each boiler.

To prevent condensate from boiling in the gas heater, control feed valves are installed behind it. Their main purpose is to distribute condensate flow between boilers in accordance with the thermal load of the steam turbine unit.

Deep recovery system with condensing heat exchanger

As can be seen from the flow diagram (Fig. 1), steam condensate from the condensate collector is supplied by pump 14 to the collection tank 21, and from there to the distribution manifold 22. Here, the condensate using the system automatic regulation station (see below) is divided into two streams: one is supplied to the deep utilization unit 4, to the condensation heat exchanger 7, and the second to the heater low pressure(HDPE) 18, and then into the deaerator 15. The temperature of the steam condensate from the turbine condenser (about 20–35 0 C) makes it possible to cool the combustion products in the condensation heat exchanger 7 to the required 40 0 ​​C, i.e., ensure deep utilization.

The heated steam condensate from the condensation heat exchanger 7 is fed through the HDPE 18 (or bypassing 18) into the deaerator 15. The combustion product condensate obtained in the condensation heat exchanger 7 is drained into the pan and tank 10. From there it is fed into the contaminated condensate tank 23 and pumped drain pump 24 into the condensate reserve tank 25, from which the condensate pump 26 through the flow regulator is supplied to the combustion products condensate purification section (not shown in Fig. 1), where it is processed using known technology. The purified condensate of combustion products is supplied to HDPE 18 and then to deaerator 15 (or directly to 15). From the deaerator 15, a flow of clean condensate is supplied by a feed pump 16 to the heater high pressure 17, and from it to boiler 1.

Thus, the heat of combustion products utilized in the condensation heat exchanger saves fuel consumed in the power plant process flow diagram for heating the station condensate in front of the deaerator and in the deaerator itself.

The condensation heat exchanger is installed in chamber 35 at the junction of boiler 27 with the gas duct (Fig. 2c). The thermal load of the condensation heat exchanger is regulated by bypassing, i.e., by removing part of the hot gases in addition to the condensation heat exchanger through the bypass channel 37 with a throttle valve (gate) 36.

The simplest would be the traditional scheme: a condensing economizer, more precisely the tail sections of the boiler economizer, such as a gas heater, but operating in condensation mode, i.e., cooling the combustion products below the dew point temperature. But at the same time, structural and operational difficulties arise (maintenance, etc.), requiring special solutions.

Applicable Various types heat exchangers: shell-and-tube, straight-tube, with knurled fins, plate or efficient design with a new shape of the heat exchange surface with a small bending radius (regenerator RG-10, NPC "Anod"). In this scheme, heat exchange block sections based on a bimetallic heater of the VNV123-412-50ATZ brand (OJSC Heating Plant, Kostroma) are used as a condensation heat exchanger.

The choice of section layout and water and gas connections allows you to vary and ensure the speed of water and gases within the recommended limits (1–4 m/s). The flue, chamber, gas path are made of corrosion-resistant materials, coatings, in particular stainless steels, plastics is a common practice.

* There are no heat losses due to chemical incomplete combustion.

Features of deep recycling with a condensing heat exchanger

The high efficiency of the technology makes it possible to regulate the thermal power of the system within a wide range, maintaining its profitability: the degree of bypass, the temperature of the combustion products behind the condensation heat exchanger, etc. The thermal load of the condensing heat exchanger QUT and, accordingly, the amount of condensate supplied to it from the collector 22 (Fig. 1 ), is determined as optimal (and not necessarily maximum) according to technical and economic calculations and design considerations, taking into account operating parameters, capabilities and conditions of the technological scheme of the boiler and the station as a whole.

After contact with natural gas combustion products, the condensate retains high quality and requires simple and inexpensive cleaning - decarbonization (and not always) and degassing. After treatment at the chemical water treatment site (not shown), the condensate is pumped through a flow regulator into the station’s condensate line - to the deaerator, and then into the boiler. If the condensate is not used, it is drained into the sewer.

In the condensate collection and processing unit (Fig. 1, pos. 8, 10, Fig. 2, pos. 23–26), well-known standard equipment of deep recycling systems is used (see, for example,).

The installation produces a large amount of excess water (condensate of water vapor from the combustion of hydrocarbons and blown air), so the system does not need to be recharged.

Temperature of combustion products at the outlet of the condensing heat exchanger T 2УХ is determined by the condition of condensation of water vapor in the exhaust combustion products (in the range of 40–45 0 C).

In order to prevent condensation in the gas path and especially in chimney bypassing is provided, i.e. bypassing part of the combustion products through a bypass channel in addition to the deep utilization unit so that the temperature of the gas mixture behind it is in the range of 70–90 0 C. Bypassing worsens all process indicators. The optimal mode is to work with bypass in the cold season, and in the summer, when there is no danger of condensation and icing, without it.

The temperature of the boiler flue gases (usually 110–130 0 C) allows the condensate to be heated in the condensation heat exchanger in front of the deaerator to the required 90–100 0 C. Thus, the temperature requirements of the technology are satisfied: both heating the condensate (about 90 0 C) and cooling the products combustion (up to 40 0 ​​C) until condensation.

Comparison of combustion product heat recovery technologies

When making a decision on the utilization of heat from boiler combustion products, one should compare the effectiveness of the proposed deep utilization system and the traditional scheme with a gas heater as the closest analogue and competitor.

For our example (see reference 1), we obtained the amount of heat recovered during deep utilization Q UT equal to 976 kW.

We assume the temperature of the condensate at the inlet to the gas condensate heater is 60 0 C (see above), while the temperature of the combustion products at the exit from it is at least 80 0 C. Then the heat of the combustion products utilized in the gas heater, i.e., heat savings, will be equal to 289 kW, which is 3.4 times less than in the deep recycling system. Thus, the “issue price” in our example is 687 kW, or, on an annual basis, 594,490 m 3 of gas (with KIM = 0.85) costing about 3 million rubles. The gain will increase with the boiler power.

Advantages of deep recycling technology

In conclusion, we can conclude that, in addition to energy saving, with deep utilization of combustion products from a power plant boiler, the following results are achieved:

• reducing the emission of toxic oxides CO and NOx, ensuring the environmental cleanliness of the process;
• obtaining additional, excess water and thereby eliminating the need for boiler make-up water;
• condensation of water vapor from combustion products is localized in one place - in the condensation heat exchanger. Apart from the slight splash carryover after the droplet eliminator, condensation in the subsequent gas path and the associated destruction of gas ducts from the corrosive effects of moisture, the formation of ice in the path and especially in the chimney are eliminated;
• in some cases, the use of a water-to-water heat exchanger becomes optional; there is no need for recirculation: mixing part of the hot gases with cooled ones (or heated condensate with cold ones) in order to increase the temperature of the exhaust combustion products to prevent condensation in the gas path and chimney (saving energy and money).

Literature

1. Shadek E., Marshak B., Anokhin A., Gorshkov V. Deep recovery of heat from waste gases of heat generators // Industrial and heating boilers and mini-CHPs. 2014. No. 2 (23).
2. Shadek E. Trigeneration as a technology for saving energy resources // Energy saving. 2015. No. 2.
3. Shadek E., Marshak B., Krykin I., Gorshkov V. Condensation heat exchanger-recovery – modernization of boiler plants // Industrial and heating boilers and mini-CHP. 2014. No. 3 (24).
4. Kudinov A. Energy saving in heat generating installations. M.: Mechanical Engineering, 2012.
5. Ravich M. Simplified method of thermotechnical calculations. M.: Publishing House of the USSR Academy of Sciences, 1958.
6. Berezinets P., Olkhovsky G. Advanced technologies and power plants for the production of thermal and electrical energy. Section six. 6.2 gas turbine and combined cycle gas plants. 6.2.2. Combined-cycle plants. JSC "VTI". “Modern environmental technologies in the energy sector.” Information collection ed. V. Ya. Putilova. M.: Publishing House MPEI, 2007.

1 Primary source of data: inspection of hot water boilers (11 units in three boiler houses of heating networks), collection and processing of materials.

2 Calculation methodology, in particular Q UT, given in.