4. Methods for improving the efficiency of heat distribution
Reducing fuel consumption can be ensured by its high-quality combustion and reduction of irrational heat losses. High-quality automatic control of heat generation and distribution processes provides significant savings in fuel and energy resources. Significant savings in thermal energy and improvement in equipment performance can also be achieved by modernization of the hydraulic scheme.
The hydraulic circuit significantly affects the process of generation and distribution of heat and the service life of boiler equipment. Therefore, when considering it, it is necessary to take into account the following parameters - hourly dynamics of temperature changes, costs for individual circuits and the relative coefficient of the volume of boiler water to the total volume of water in the heating system f about.
The return water temperature is also an important parameter. To prevent the formation of condensate in the boiler and flue gases, the return water temperature must always be maintained above the dew point, i.e. on average from +50 to +70 °C. An exception is condensing type boilers, in which, at low temperatures of the return water, the condensation process is intensified and, as a result, the efficiency is increased.
At the same time, if f o ≤ 10%, it is necessary to take additional measures to ensure that the desired return water temperature is maintained. Such measures are the organization of mixing, the separation of circuits by heat exchangers, the installation of mixing valves and a hydraulic separator (arrows). In addition, an important factor in reducing fuel consumption and electrical energy is the determination of the coolant flow through the boiler (group of boilers) and the determination of the optimal flow ( pic. 9).
Boiler piping modernization
To modernize the piping of boilers, simple measures and devices can be recommended that can be manufactured by the operating personnel. This is the creation of additional circuits in the heat supply system; installation of a hydraulic separator ( rice. 10a), which allows you to adjust the temperature and pressure of the coolant and the scheme of parallel flows ( rice. 10 b), which ensures uniform distribution of the coolant. The temperature of the heating medium must be constantly adjusted to changes in the outside temperature in order to maintain the desired temperature in the connected circuits. In this regard, an important reserve for saving fuel is the maximum possible number of heat supply circuits and automation of the control process.
The size of the low loss header is chosen so that at full load the pressure difference between the supply and return lines does not exceed 50 mmH2O. Art. (approximately 0.5 m/s). The hydraulic separator can be mounted vertically or horizontally, when mounting ( rice. 10a) in a vertical position has a number of additional advantages: the upper part works as an air separator, and the lower part is used to separate dirt.
When connecting boilers in cascade, it is necessary to ensure equal flow rates of the coolant through boilers of the same power. For this, the hydraulic resistance of all parallel circuits must also be the same, which is especially important for water-tube boilers. Thus, equal operating conditions for hot water boilers, uniform cooling of the boilers and uniform heat removal from each boiler in the cascade are ensured. In this regard, attention should be paid to the piping of the boilers, ensuring that the flow of direct and return water is parallel.
On the rice. 10 b a diagram of parallel flows is shown, which is used for piping boilers operating in a cascade without individual pumps of the boiler circuit and fittings that regulate the flow of coolant through the boiler. This simple and cheap measure allows eliminating the formation of condensate in the boilers, as well as frequent starts and shutdowns of the burners, which leads to a reduction in electricity and extends the life of the boiler and burner device.
The proposed scheme of "parallel flows" is also used in extended horizontal systems and when connecting solar collectors and heat pumps to one common system.
5. Technical solutions to ensure the evacuation of flue gases
The fight for fuel economy, in our economic conditions, often comes down to a change in the operating modes of boiler equipment. However, this often leads to its premature failure and additional material and financial costs associated with equipment repair. A big problem when working at low loads is created by moisture in the combustion products, which is formed during the combustion reaction, due to chemical kinetics. At the same time, at a flue gas temperature of about 50 ... 60 ° C, condensate forms on the walls of the chimney and equipment.
Moisture content as a function of dew point is given on rice. 11a, this leads to the need to maintain high temperatures in the furnace and reduce the efficiency of the boiler by increasing the temperature of the flue gases. This statement does not apply to condensing boilers, where the principle of obtaining additional heat due to phase transition during condensation of water vapor. On the rice. 11 b shows a direct dependence of the dew point ( T p) on the coefficient of excess air a for various kinds fuel. The presence of water vapor in the combustion products and their condensation on the walls adversely affect the operation of chimneys, leading to corrosion of metal surfaces and the destruction of brickwork.
The condensate has an acidic environment with pH ≈ 4, which is due to the presence of carbonic acid in it, traces of nitric acid, and, when liquid fuel is burned, sulfuric acid.
To exclude negative consequences during the operation during the design and implementation commissioning special attention should be paid to the issues of safe operation of boiler equipment, optimization of the burner operation, elimination of the possibility of flame separation in the furnace and the formation of condensate in the chimneys.
To do this, draft limiters can be additionally installed on the chimneys, similar to those of the German company Kutzner + Weber, which are equipped with a hydraulic brake and a system of weights that allow you to adjust their automatic opening during the operation of the boiler and ventilation of the pipe when it stops ( rice. 12).
The operation of the valve is based on the physical principle of jet breaking and does not require an additional drive. The main requirement when installing pressure limiters is that these devices can be located in the boiler room, or, as an exception, in neighboring rooms, provided that the pressure difference in them does not exceed 4.0 Pa. With a chimney wall thickness of 24 mm or more, the device is mounted directly on the chimney or on a remote console. Permissible maximum flue gas temperature - 400 °C, response pressure safety valve from 10 to 40 mbar, air capacity up to 500 m 3 /h, control range from 0.1 to 0.5 mbar. The use of pressure limiters increases the reliability of operation of boilers and chimneys, prolongs the service life of the equipment, and does not require additional maintenance costs. Experimental verification shows the absence of conditions for the formation of condensate in the chimneys, after installing a pressure relief valve on the chimney, while reducing the concentration of harmful emissions into the atmosphere.
6. New methods of water treatment to improve the efficiency of boiler equipment operation
The chemical composition and quality of the water in the system have a direct impact on the service life of the boiler equipment and the heating system as a whole.
Deposits due to the Ca 2+ , Mg 2+ and Fe 2+ salts contained in water are the most common problem that we face in everyday life and in industry. The solubility of salts under the influence of high temperature and high pressure leads to the formation of solid (scale) and soft (sludge) deposits. The formation of deposits leads to serious energy losses. These losses can reach 60%. The growth of deposits significantly reduces heat transfer, they can completely block part of the system, lead to clogging and accelerate corrosion. It is known that scum with a thickness of 3.0 mm reduces the efficiency of the boiler plant by 2.0 ... 3.0%. On the rice. 13 the dependences of the increase in fuel consumption on the thickness of scale are given.
The presence of oxygen, chlorine, ferrous iron and hardness salts in water increases the number of emergencies, leads to an increase in fuel consumption and reduces the service life of equipment.
Deposits of carbonate hardness are formed at low temperatures and are easily removed. Deposits formed by minerals dissolved in water, such as calcium sulfate, are deposited on heat exchange surfaces at high temperatures.
Scale deposits lead to the fact that even the "Interdepartmental standards for the service life of boiler equipment in Ukraine" provide for an increase in fuel consumption by 10% after 7 years of equipment operation. Deposits are especially dangerous for automatic control devices, heat exchangers, heat meters, thermostatic radiator valves, water meters. Water softeners must be used to ensure proper operation of the system.
In the so-called "dead zones" of the system, stationary bubbles of complex chemical composition can form, in which, in addition to oxygen and nitrogen, methane and hydrogen can be present. They cause pitting of the metal and the formation of silt deposits that adversely affect the operation of the system. In this regard, it is necessary to use automatic air vents, which are installed at the upper points of the system and areas of low coolant circulation.
When using municipal tap water for make-up, it is necessary to monitor the concentration of chlorides. It should not exceed 200 mg/l. The increased content of chlorides leads to the fact that the water becomes more corrosive and aggressive, also due to the incorrect operation of the water softening filters. In recent years, the quality of source, tap and network water has generally improved due to the use of special fittings, bellows expansion joints and the transition from gravity central heating systems to closed-type central heating systems.
Deposit problems are being addressed using both physical and chemical methods. Today, chemicals are widely used in the fight against deposits. However, the high costs and complexity of the process, as well as the growing awareness of the need to protect the environment, leaves no choice but to look for physical methods. However, the method of preparing water for them in the future does not guarantee protection against corrosion and water hardness.
Used to prevent deposits different type filters, settlers, magnets, activators and their combinations. Depending on the sludge, the elements of the system protect either only against permanent corrosive components and boiler stone, or against all harmful components together with magnetites.
The simplest device for physical water treatment - mesh filters. They are installed directly in front of the boiler and have a stainless steel mesh insert with the required number of holes - 100 ... 625 per 1 cm 2. The efficiency of such cleaning is 30% and depends on the size of sediment fractions.
Next device - hydrocyclone filter, the principle of operation of which is based on the law of inertia in a rotating motion. The efficiency of such cleaning is very high, but it is necessary to provide a high pressure of 15 ... 60 bar, depending on the volume of water in the system. For this reason, these filters are rarely used.
desilter is a vertical cylindrical collector with a baffle that slows down the flow of water. Due to this, large particles are separated. The filter function is performed by a horizontal grid with the number of holes 100 ... 400 per 1 cm 2. The efficiency of such cleaning is 30…40%.
Water purification becomes more complicated if the cauldron stone must be removed from it.
Desilters mainly retain only large fractions of carbonate-calcium compounds, which are deposited on the grid. The residue circulates and settles in the central heating system.
Various devices for magnetic and electromagnetic water treatment using a constant and an alternating magnetic field. Magnetic treatment leads to the fact that substances that cause deposits are polarized under the influence of fields and remain in suspension.
The simplest device based on this principle is magnetizer. As a rule, it is a metal cylinder with a magnetic rod inside. By means of a flange connection, it is installed directly into the pipeline. The principle of operation of the magnetizer is to change the electrophysical state of the molecules of the liquid and the salts dissolved in it under the influence of a magnetic field. As a result, the boiler stone is not formed, and carbonate salts precipitate in the form of fine-crystalline silt, which no longer settles on the heat exchange surfaces.
The advantage of this method is the constant polarization of the substance, due to which even old deposits of boiler stone are dissolved. However, this undoubtedly environmentally friendly, low-maintenance method has an important drawback.
An increase in the hydraulic resistance of the system leads to an increase in power consumption and an additional load on pump equipment, in closed circulation systems, sludge deposits settle in radiators, fittings and shaped parts of pipelines, and therefore it is necessary to install additional filters, the magnetic rod in the device actively corrodes.
The efficiency of such cleaning reaches 60% and depends on the size of sediment fractions, the chemical composition of dissolved salts and the magnetic field strength from external sources.
In the last decade, there has been an active search for new methods of physical water treatment based on modern nanotechnologies. Widely spread water activators, which use the principle of water revitalization (increasing its energy activity) and protecting equipment from scale and corrosion. An example is the devices of Austrian firms BWT and EWO, German ELGA Berkelfeld and MERUS®, American Kinetico.
All of them use various design solutions and materials, original processing methods, have long service life and do not require additional capital investments for Maintenance, electricity and consumables.
On the rice. fourteen, devices of the German company are shown MERUS® which are produced using a special production process pressings of various materials such as aluminium, iron, chromium, zinc, silicon.
This technology makes it possible to obtain a unique alloy that has the ability to “remember” the magnetic field strength during subsequent technological processing. The device consists of two half-rings, which are put on the pipeline and connected by two coupling bolts. The device effectively concentrates electromagnetic fields from the environment and acts on bicarbonate anions dissolved in water, keeping them in colloidal form, and also converts rust into magnetite - by electromagnetic impulses, producing an effect similar to the effect of acoustic signals on water (ultrasound). This causes the crystallization process directly in the water volume, and not on the walls of pipes or other heat exchange surfaces. This process is better known in chemistry as bulk crystallization.
Unlike other methods of physical water treatment, devices MERUS® do not require energy sources, maintenance costs and installation of the device.
The effect produced by the device on water lasts up to 72 hours and allows water treatment on main pipelines up to 10 km.
Thanks to a new principle of action - based on the activation of water, due to the breaking of hydrogen intermolecular bonds, devices MERUS® are effectively used even in cases where known methods of water treatment are ineffective. For example, on condensate pipelines, once-through process superheaters operating on tap water without condensate return, electrothermal furnaces, when installed on plastic pipes, etc.
The efficiency of this treatment reaches 90%, allowing you to soften water without chemical components, reduce salt consumption during sodium cationization and inhibit the growth of pathogenic bacteria such as Koch's bacillus and legionella.
At the same time, the chemical composition of the water does not change, which is often important for the pharmaceutical and food industries, water treatment in swimming pools, etc.
7. Conclusions
The technical condition of the boiler equipment of the public energy sector in Ukraine is primarily affected by the lack of sufficient funding and imperfect legal and legislative framework.
Determining the efficiency of boiler equipment should begin with an energy audit.
Increasing the efficiency and service life of boiler equipment can be achieved by installing secondary radiators, which will improve the aerodynamic and kinetic processes occurring in the furnace.
Significant savings in thermal energy and improvement in the performance of equipment can be achieved by upgrading the hydraulic circuit.
The installation of draft limiters on chimneys leads to stabilization of combustion, ventilation of chimneys, elimination of the possibility of condensate formation and their reliable operation at low loads of boiler units.
During the operation of boiler equipment, it is necessary to pay attention to high-quality water treatment and deaeration of the coolant. ■
Literature
Thermal calculation of boiler units (normative method) / Ed. N. V. Kuznetsova. - M.: "Energy", 1973. - 296 p.
Basok B.I., Demchenko V.G., Martynenko M.P. Numerical modeling of aerodynamic processes in the furnace of a hot water boiler with a secondary radiator // Industrial Heat Engineering. - No. 1. - 2006.
workers characteristics, connection instructions and hydraulic diagrams for medium and large boilers. De Dietrich, 1998.-36c.
Improving the efficiency of boiler units
Safonova E.K., Associate Professor, Bezborodov D.L., Ass., Studennikov A.V., Master student.
(Donetsk National Technical University, Donetsk, Ukraine)
A large share in the structure of costs of production of electrical and thermal energy is the cost of fuel. Currently, many enterprises have a reserve for increasing the efficiency of using fuel resources by improving the control scheme of boiler units. One possible means of achieving this is the introduction of stationary gas analyzers. The effects obtained are small in relative terms, for example, an increase in boiler efficiency by 0.7% and a corresponding decrease in fuel consumption can bring tens of tons of fuel savings per day (on the scale of one station), tens of thousands of tons of fuel savings per year.
Another major strategic problem, for which it is necessary to use gas analyzers, is environmental pollution by combustion products.
In accordance with the principle of the so-called “Emission Charges” established by the Law on Environmental Protection, an increase in environmental charge rates is a likely scenario for tightening environmental policy for businesses.
An effective method like effective use all types of fuel, as well as reducing the negative impact on environment, reducing environmental charges favors the introduction of modern technologies.
The use of stationary gas analyzers allows solving the following production tasks:
Reduce production costs by saving fuel;
Reduce mandatory payments for negative environmental impact in the context of a long-term trend towards tougher environmental requirements and a shift in the fuel balance towards the use of less “environmentally friendly” fuels.
The studies carried out on the main types of boilers KVGM, DKVR, PTVM, which are currently in operation, have shown that during the operation of the boiler technological parameters are not maintained.
Figure 1 shows graphs of oxygen content in flue gases at different loads of boiler units KVGM, DKVR, PTVM.
The oxygen content exceeds the allowable in regime maps, which indicates inefficient operation of the boiler unit. Operating the boiler at the optimum amount of excess air will minimize heat loss to the chimney and increase combustion efficiency. It is known that the efficiency of combustion is a measure of how efficiently the heat contained in the fuel is converted into heat suitable for use. The primary indicators of combustion efficiency are the flue gas temperature and the concentration of oxygen (or carbon dioxide) in the flue gases.
A - boiler PTVM - 30;
B - boiler KV-GM - 1.6;
B - boiler DKVR 4 - 13;
Figure 1 - Dependence of the oxygen content of the exhaust gases on the boiler load
With perfect mixing of the combustible mixture, for the complete combustion of a given amount of fuel, an exact or stoichiometric amount of air is required. In practice, combustion conditions are never ideal and additional or “excess” air must be supplied to complete combustion of the fuel.
The exact amount of excess air is determined by analyzing the concentrations of oxygen or carbon dioxide in the flue gases. Insufficient excess air leads to incomplete combustion of combustible substances (fuel, soot, solid particles and carbon monoxide), while too much excess air causes heat losses, due to an increase in flue gas flow, thereby reducing the overall efficiency of the boiler in the process of transferring heat from fuel to steam.
The formulas show the dependence of heat loss with outgoing gases on the amount of excess air:
;
where I ux – Enthalpy of flue gases at excess air coefficient ux;
I 0 – Enthalpy of the theoretically required amount of cold air;
q 2 - Heat loss with exhaust gases;
q 4 - heat loss from mechanical incompleteness of fuel combustion.
And the efficiency, respectively, depends on the heat loss:
pg \u003d q 1 \u003d 100-q sweat
The total heat loss in the boiler is calculated by the formula:
q sweat \u003d q 2 + q 3 + q 4 + q 5.
where q 3 - losses from chemical incompleteness of fuel combustion;q 5 - losses from external cooling of the boiler.
Figure 2 shows the relationship between flue gas parameters and boiler efficiency for the condition of complete combustion in the absence of water vapor in the combustion air.
excess air
Figure 2 - Dependence of the efficiency of the boiler unit on the temperature of the flue gases
For well designed natural gas systems, a 10% excess air level is quite achievable. A commonly used rule of thumb is that boiler efficiency increases by 1% for every 15% reduction in excess air, or for every 22°C decrease in flue gas temperature.
The introduction of stationary gas analyzers at thermal power plants that control the composition of exhaust gases, in the context of slow construction of new facilities, is an important element of a set of resource-saving measures to modernize the existing capacities of thermal power plants.
The PEM-02 oxygen meter is a measuring complex consisting of an immersed probe with a solid electrolyte sensor based on zirconium dioxide, a pumping unit, and an oxygen analyzer. The cost of such a gas analyzer is currently about 13 thousand hryvnia.
The oxygen concentration is measured by the analyzer in continuous mode using a special probe (sampler) installed in the gas duct at the sampling site. The flow rate of the gas sample taken for analysis is very small and amounts to approximately 0.5 l/h.
The oxygen sensor placed directly in the probe is an electrochemical cell with a tubular solid electrolyte made of sintered zirconium dioxide. The sensor generates a signal that is proportional to the concentration of oxygen in the sample gas. This signal is processed in the analyzer and converted to an analog output signal. The accuracy of PEO-02 is ± 0.2% vol.Gas analyzers with electrochemical cells as sensors are most often used as control and adjustment devices, although there are quite a few systems designed for long-term measurements and monitoring. The principle of operation of electrochemical cells is to divide the flow of the test gas into separate components using membranes that can pass only one component of the analyzed gas mixture to the electrolyte (Figure 3.). Depending on the type of analyzed component of the gas mixture, electrochemical cells implement the conductometric or coulometric measurement method. In addition to the analyzed component, some other components of the gas mixture can also affect the readings of the cell. This phenomenon can be eliminated using special filters or by calculation, taking into account the cross coefficients previously obtained by calibration. The negative aspects should also include the possibility of "poisoning" the cell when the concentration of the test component in the sample exceeds the allowable value, which leads to errors in determining the concentrations in subsequent measurements.
Figure 3 - Schematic diagram of an electrochemical gas analyzer
1 - sampling probe; 2 - filter; 3 - condensate trap; 4-6 - membranes; 7-9 - electrochemical cells
Link List
Thermal calculation of industrial steam generators: Proc. Manual for technical colleges / Ed. V. I. Chastukhin. - Kyiv: Vishcha school. Head publishing house, 1980. - 184 p.
Methods and means of controlling atmospheric pollution and industrial emissions// TR. TRP 1987. Issue. 492.
Standard instructions for organizing a system for controlling industrial emissions into the atmosphere in industries. L .: Publishing house of the GGO im. A.I. Voeikova, 1986.
Bryukhanov O.N., Mastryukov B.S. Aerodynamics, combustion and heat transfer during fuel combustion: a reference guide. St. Petersburg: Nedra, 1994.
Automation of technological objects and processes. Poshuk young.
Energy-saving measures for boiler and furnace rooms in private houses and buildings with a total area of not more than 2000 sq.m.
Modernization and automation of boiler houses of small and medium capacity:
- increasing the energy efficiency of boiler units with
use of low-temperature and condensing boilers; - use of new principles of fuel combustion in boiler houses
aggregates; - improving the reliability of boiler units;
- use of modern burners;
- automation of boiler units;
- automation of heat carrier distribution according to loads;
- chemical water treatment of heat carrier;
- thermal insulation of pipelines;
- installation of economizers on chimneys;
- weather-dependent circuit control;
- modern fire-gas-tube boiler units.
2. Control over the temperature of the flue gases and excess air in them.
Keeping the optimal air regimes of the furnace is the main condition for ensuring the economical operation of the boiler. Furnace losses q 3 and q 4 strongly depend on excess air in the burners (α g) and in the furnace (α t). It is necessary to burn the fuel with an excess of air that ensures complete burnout of the fuel. These excesses are established during commissioning tests. Suction cups in the furnace have a significant impact on the efficiency and temperature level of combustion. An increase in the number of suction cups reduces excess air in the burners, the efficiency of mixing fuel and combustion products with air, and increases the losses q 3 and q 4 . To avoid an increase in furnace losses, the total excess air in the furnace is increased, which is also unfavorable. Ways to improve the efficiency of the furnace process are the elimination of suction cups in the furnace, the organization of the optimal combustion mode, and testing to find these conditions.
The largest losses in the boiler are losses with flue gases. Their value can be reduced by reducing the excess air in the exhaust gases, the temperature of the exhaust gases, as well as by increasing the temperature of the air taken from the environment.
The greatest attention should be paid to the decrease in α uh. It is ensured by the operation of the combustion chamber at the minimum allowable (according to the conditions of fuel burning) excess air in the furnace and by eliminating suction in the furnace and gas ducts. Decreasing α ux also makes it possible to reduce losses for own needs along the gas-air path and entails a decrease in the temperature of the exhaust gases. Air suction into the furnace of gas-oil boilers with a capacity of 320 t/h and below should not exceed 5%, above 320 t/h - 3%, and for pulverized-coal boilers of the same capacity, respectively, 8 and 5%. Air suction in the gas path in the area from the outlet of the superheater to the outlet of the smoke exhauster should not exceed (excluding ash collectors) with tubular air heaters 10%, with regenerative 25%.
During the operation of the boiler, one of the main parameters that require constant monitoring and serviceability of devices is excess air in the furnace or behind one of the first heating surfaces. The source of increased air suction in gas ducts is the wear or corrosion of pipes in tubular air heaters (mainly cold cubes), which also causes an increase in power consumption for draft and blast and leads to load limitation.
The flue gas temperature υ ux depends both on the excess air and on the efficiency of the heating surfaces. When contaminants appear on the pipes, the heat transfer coefficient from gases to pipes decreases and υ ux increases. To remove dirt, the heating surfaces should be cleaned regularly. When upgrading the boiler in order to lower υ ux, however, it should be remembered that this can cause vapor condensation on the walls of the pipes of the cold cubes of the air heater and their corrosion.
It is possible to influence the ambient temperature, for example, by switching the air intake (from the street or from the boiler room). But at the same time, it should be remembered that when air is taken from the boiler room, its ventilation increases, drafts appear, and in winter, due to lower temperatures, defrosting of pipelines is possible, leading to emergencies. Therefore, the intake of air from the boiler room in winter is dangerous. Naturally, during this period, the losses q 2 objectively increase, since the air can also have a negative temperature. The driver must maintain the air temperature at the inlet to the air heater at a corrosion-resistant level, using heating in heaters or hot air recirculation.
An increase in heat loss to the environment can occur when the lining, insulation and the corresponding exposure of high-temperature surfaces are destroyed, with the wrong choice and installation of the lining. All malfunctions should be detected when the driver walks around the boiler, recorded in the defect log and eliminated in a timely manner.
Good mixing of fuel and oxidizer with a vortex combustion scheme allows the boiler to be operated with reduced (compared to a direct-flow flare process) excess air at the furnace outlet (α”=1.12…1.15) without increasing the combustible content in the fly ash and without increasing the CO concentration. which does not exceed 40-80 mg/nm 3 (α=1.4).
Thus, lowering the temperature and excess air in the flue gases by increasing the efficiency of the furnace makes it possible to reduce heat losses with flue gases, and, consequently, increase the efficiency of the “gross” boiler unit by 1–3% even on boilers that have operated before modernization 30 ..40 years.
- Compilation of regime maps
To ensure competent economical operation for watch personnel, regime charts are developed, which should guide them in their work.
Regime card - a document presented in the form of a table and graphs, in which, for various loads and combinations of equipment, the values of the parameters that determine the operation of the boiler are indicated, which must be observed. Regime maps are compiled on the basis of test results for the optimal, most economical and reliable modes at various loads, the quality of the incoming fuel and various combinations of operating main and auxiliary equipment. In the case of installation of the same type of equipment at the station, tests of increased complexity are carried out on one of the boilers, and for the remaining boilers, tests may not be carried out or are carried out in a reduced scope (a regime chart of tested boilers is used). Regime maps should be regularly reviewed and changed (if necessary). Clarifications and changes are made during the transition to new types of fuel, after repair and reconstruction work.
For characteristic load ranges, the following parameters are entered into the regime map as determining parameters: the pressure and temperature of the main and intermediate superheated steam, the temperature of feed water, flue gases, the number, and sometimes a specific indication of the combination of operating mills, burners, draft fans and smoke exhausters; the composition of the combustion products behind the heating surface, after which for the first time sufficient mixing of gases is ensured (convective superheater or water economizer of the second stage); indicators of the reliability of the operation of individual surfaces or elements of the boiler and indicators that facilitate the management of the boiler or respond most quickly to mode deviations and emergency situations. The following indicators are often used as the last indicators: gas temperature in the region of the least reliable heating surface (for example, in a rotary chamber, in front of a convective surface that is contaminated or slagged, etc.); resistance (pressure drop) of polluted, slagged and corroded heating surfaces (checkpoint; air heater); air consumption for mills and their amperage load - especially with fuels of variable composition; medium and metal temperature in some of the most dangerous heating surfaces in terms of overheating.
In addition, the regime map reflects the frequency of turning on the heating surface cleaning means and the special operating conditions of individual elements and equipment (for example, the degree of opening of individual control air and gas dampers, the ratio of the degree of opening of the primary and secondary air dampers of the burners; the operating conditions of the gas recirculation line and working environment, etc.).
When fuel oil is burned, the temperature of its preheating is additionally entered into the regime maps, at which reliable transport of fuel oil through fuel oil pipelines and its spraying in nozzles is ensured.
Along with determining the composition of gases, in order to determine the optimality of the combustion mode, it is necessary to regularly determine the suction of gases in the furnace and in convective gas ducts.
The current opinion about the insufficient danger of air suction in the furnace, about the possibility of using this air in the combustion process is incorrect and dangerous. The fact is that most of the air entering the furnace with suction cups penetrates through relatively small leaks in the walls of the combustion chamber and cannot penetrate deeply into the combustion chamber.
Moving near the screens, in the zone of relatively low temperatures, this air participates weakly in combustion. In the main combustion zone, there is not enough air, part of the fuel, without burning out, is taken out of the furnace, raising the temperature there and creating a reducing environment. An increase in the temperature of the fuel particles (and, consequently, ash) and the reducing environment intensify the process of slagging and fouling of pipes.
In view of the importance of maintaining the optimal air regime of the combustion process, the operating personnel of the station must constantly monitor the serviceability of the gas composition devices and monitor the density of the furnace and convective gas ducts by external inspection and determination of suction cups.
The parameters included in the regime map are used when setting up protections and automatic control systems.
- High Efficiency Regulation
One of the best ways to ensure efficient operation of a boiler plant is high efficiency regulation, which can be applied to both steam and hot water boilers. Highly efficient regulation saves an average of 4 to 5% of the heat energy used and pays for itself within a year.
How can the efficiency of the boiler be improved? It is known that at a certain ratio of air and fuel consumption, the most complete combustion occurs inside the boiler. In this case, it is necessary to achieve the conduct of the combustion process with a minimum amount of excess air, however, with the obligatory condition of ensuring complete combustion of the fuel. If excess air is supplied to the furnace in a larger quantity than required for the normal operation of the combustion process, then the excess air does not burn and only cools the furnace uselessly, which in turn can lead to losses due to chemical incomplete combustion of the fuel.
It is also necessary to control the temperature of the flue gases. At an overestimated temperature of the flue gases at the outlet of the boiler, the efficiency of the unit is significantly reduced due to the release of excess heat into the atmosphere, which could be used for its intended purpose. At the same time, when operating on liquid fuels, the flue gas temperature at the boiler outlet must not be allowed to drop below 140 °C with a sulfur content of no more than 1% and below 160 °C with a sulfur content of no more than 2-3%. These temperatures are based on the flue gas dew point. At these temperatures, the process of condensate precipitation begins in the fire tubes and the smoke collection chamber. When the sulfur contained in the fuel comes into contact with condensate, as a result of a chemical reaction, first sulfurous, and then sulfuric acid is formed. The result is intense corrosion of heating surfaces.
To achieve greater efficiency of high-precision adjustment, it is necessary to first carry out a basic cleaning of the furnace and chimneys. To reduce excess air and reduce the temperature of the flue gases, it is necessary:
– eliminate leaks in the combustion chamber;
– check the draft of the chimney, if necessary, install a damper in the chimney;
– increase or decrease the rated input power of the boiler;
– monitor the compliance of the amount of air for combustion;
– optimize the burner modulations (if the burner is equipped with this function).
For gas boilers, using a gas meter and a stopwatch, you can find out whether the required amount of fuel is supplied to the burner. If the boiler is running on oil, it is checked whether the flow measured by the flow nozzle and the pressure generated by the oil pump are suitable for effective work boiler.
Short description
The issues of saving fuel and energy resources are of great importance in all sectors of the national economy, and especially in the energy sector, the main fuel-consuming industry. At each station, in the boiler house, organizational and technical measures are being developed to improve technological processes, modernization of equipment, advanced training of personnel.
Some ways to improve the efficiency of the boiler unit and the boiler house as a whole will be considered below.
Energy audit of the boiler house
Energy saving in a boiler house, of course, begins with an energy survey (energy audit) of the boiler house, which will show a real assessment of the efficiency of using the existing equipment of the boiler house and the heating system as a whole, as well as determine the potential for energy saving measures and ways to implement them.
The content of the work
Introduction
Energy audit of the boiler house …………………………………………………...3
Control over the temperature of the flue gases and excess air in them. 9
Drawing up regime maps ……………………………………………….12
High Efficiency Regulation ……………………………………………………14
Use of secondary emitters ………………………………..18
Installation of a modernized hearth slot burner in the cold funnel of the boiler (for boilers PTVM-100 and PTVM-50 ……………………20
Integrated technologies for improving the efficiency of boiler houses in the municipal energy industry ………………………………………………….22
Bibliographic list ……………………………………………...28
Description:
The cost of energy is a significant part of the operating costs for any commercial building. Modernization of engineering systems can reduce these costs. Capital investments in the modernization of boiler equipment in many cases have a short payback period.
Economic efficiency of boiler house modernization
The cost of energy is a significant part of the operating costs for any commercial building. Modernization of engineering systems can reduce these costs. Capital investments in the modernization of boiler equipment in many cases have a short payback period.
High Efficiency Regulation
One of the best ways to ensure efficient operation of a boiler plant is high efficiency regulation, which can be applied to both steam and hot water boilers. Highly efficient regulation saves an average of 4 to 5% of the heat energy used and pays for itself within a year.
How can the efficiency of the boiler be improved? It is known that at a certain ratio of air and fuel consumption, the most complete combustion occurs inside the boiler. In this case, it is necessary to achieve the conduct of the combustion process with a minimum amount of excess air, however, with the obligatory condition of ensuring complete combustion of the fuel. If excess air is supplied to the furnace in a larger quantity than required for the normal operation of the combustion process, then the excess air does not burn and only cools the furnace uselessly, which in turn can lead to losses due to chemical incomplete combustion of the fuel.
It is also necessary to control the temperature of the flue gases. At an overestimated temperature of the flue gases at the outlet of the boiler, the efficiency of the unit is significantly reduced due to the release of excess heat into the atmosphere, which could be used for its intended purpose. At the same time, when operating on liquid fuels, the flue gas temperature at the boiler outlet must not be allowed to drop below 140 °C with a sulfur content of no more than 1% and below 160 °C with a sulfur content of no more than 2-3%. These temperatures are based on the flue gas dew point. At these temperatures, the process of condensate precipitation begins in the fire tubes and the smoke collection chamber. When the sulfur contained in the fuel comes into contact with condensate, due to a chemical reaction, first sulfurous, and then sulfuric acid is formed. The result is intense corrosion of heating surfaces.
To achieve greater efficiency of high-precision adjustment, it is necessary to first carry out a basic cleaning of the furnace and chimneys. To reduce excess air and reduce the temperature of the flue gases, it is necessary:
– eliminate leaks in the combustion chamber;
– check the draft of the chimney, if necessary, install a damper in the chimney;
– increase or decrease the rated input power of the boiler;
– monitor the compliance of the amount of air for combustion;
– optimize the burner modulations (if the burner is equipped with this function).
For gas boilers, using a gas meter and a stopwatch, you can find out whether the required amount of fuel is supplied to the burner. If the boiler is running on oil, then it is checked whether the flow measured by the flow nozzle and the pressure generated by the oil pump are suitable for the efficient operation of the boiler.
An exhaust gas analyzer is used to evaluate the combustion efficiency. Measurements are taken before and after adjustment.
Boilers with pressurized gas and oil fires are the most suitable for high efficiency regulation. Less suitable are boilers with dual fuel burners, as well as gas-fired boilers with atmospheric burners.
For dual fuel burners, single fuel operation is often a compromise to maintain performance on a different fuel. And the adjustment of gas boilers with an atmospheric burner is limited by technical regulations and physical characteristics equipment.
Pass regulation
For cast-iron boilers in heating systems, when regulating the heat supply to the heating system according to the temperature of the internal air in the control room of the building (control "by deviation"), it can be carried out by periodically shutting down the system (regulation by "passes") using a temperature sensor. This will save from 10 to 15% of the consumed thermal energy and will pay off within two years.
For steel boilers, this method of controlling the water temperature is undesirable. From the point of view of strength characteristics for a steel boiler, a large temperature difference is not dangerous, but the boiler should not be operated with a water temperature in the return pipeline (at the boiler inlet) below 55 ° C. The fact is that at such a temperature of the boiler water, the temperature of the flue gases at the points of contact with the wall of the fire tube may be lower than the dew point temperature, which will cause condensation to form on the walls of the fire tubes and lead to their premature corrosion. Therefore, more often they use water temperature control using a three-way valve with a temperature sensor, the minus of this method is a long payback period, from 5 years and more. As an alternative, gap control can be used in combination with a thermostatic return water temperature sensor. This method is less economical and will pay off within 4–5 years.
Switch-off control
In general practice, in the fall, with the onset of the heating period, the operation service starts the heating system and turns it off only in the spring. This leads to the fact that even on warm days the boiler does not turn off and continues to work.
Automatic control by switching off when the outside temperature reaches +8 °C can save from 3 to 5% of the consumed heat energy and pays off in 2-3 years.
Boiler cycle control
If the operation of the boiler is regulated by "passes" depending on the outdoor temperature, the following problem often arises: during transitional periods, when the outdoor temperature changes dramatically during the day, the boiler on / off cycle is usually short, pipes and heaters do not have time to warm up properly and this leads to underheating of the building; in winter, when cold temperature is kept constant, the boiler on/off cycle is excessively long, which leads to excessive overheating of the building. To eliminate this problem, it is recommended to install a controller that regulates the minimum and maximum time the boiler is turned on. This saves from 3 to 5% of the consumed thermal energy and pays for itself in about 3 years.
Article prepared N. A. Shonina, Senior Lecturer at Moscow Architectural Institute
Economic efficiency is the effectiveness of the use of resources. It is determined by comparing the results and costs spent on achieving these results.
To determine the efficiency of production at the level of enterprises, a system of indicators is adopted, including generalization and differentiated indicators.
Differentiated indicators include indicators used to analyze the effective use of certain types resources.
Generalizing indicators characterize the economic efficiency of the use of a set of resources.
The return on assets characterizes the level of use of the main production assets site. Fixed production assets include the book value of all types of groups of production assets. The calculation of capital productivity is made according to the formula:
Where is the average tariff for 1 GJ of heat, rub.
The average tariff for 1GJ of supplied heat is 28% higher than the cost of 1GJ of supplied heat and is determined by the formula:
Capital intensity shows the number of fixed assets invested in obtaining 1 rub. products.
Capital-labor ratio is determined by the formula, thousand rubles / person
Labor productivity is estimated by the service factor and is determined by the formula, MW / person
Where H is the number of operating personnel, people.
Average monthly wage employees is determined by the formula:
The average monthly wage of workers is determined by the formula:
Where is the number of workers (main and auxiliary). people
The profit received from the annual heat supply of the boiler house is determined by the formula:
Not all profit received by the enterprise remains at its disposal. The company needs to pay real estate tax and income tax, if there are penalties. The rest of the profit goes to the enterprise.
Where - the amount of income tax, rub.
Where - the income tax rate, according to the current legislation,%.
Profitability- relative value, expressed as a percentage and characterizing the efficiency of the use of materialized labor resources or current production costs in production.
The following profitability indicators are determined: the level of profitability of the released heat, the level of profitability equity, the level of return on investment.
The level of profitability of the released heat is determined by the formula,
The level of return on equity is determined by the formula,
All the results obtained in sections 1 and 2 are summarized in table 6.
Table 6 - Main technical and economic indicators of the boiler house
|
Name |
Rationale |
Indicators |
|
Installed capacity of the boiler house, MW |
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|
Annual heat generation, GJ/year |
||
|
Annual heat supply, GJ/year |
||
|
Number of hours of use of installed capacity, h/year |
||
|
Specific fuel consumption per 1 supplied GJ of heat:
|
|
|
|
Annual fuel consumption in the boiler room:
|
|
|
|
Specific consumption of electric power for own needs, kW/MW |
||
|
Installed power of pantographs, kW |
||
|
Specific water consumption, t/GJ |
||
|
Annual water consumption, t/year |
||
|
Depreciation deductions, thousand rubles |
||
|
Number of personnel, persons |
||
|
Payroll fund for employees, thousand rubles |
||
|
Average monthly salary, thousand rubles/month:
|
||
|
Annual operating costs, thousand rubles/year |
||
|
Cost of 1GJ of heat supplied, RUB/GJ |
||
|
return on assets |
||
|
capital intensity |
||
|
Capital-labor ratio, thousand rubles/person |
||
|
Profit, thousand rubles |
||
|
Net profit, thousand rubles |
||
|
Profitability of released heat, % |
||
|
Return on equity, % |
