Cogeneration – Cogeneration units - double efficiency, double profit.

Cogeneration power plants are doubly efficient compared to power plants that produce only electrical energy. A cogeneration power plant is the use of a primary source of energy - gas, to produce two forms of energy - thermal and electrical.

The main advantage of a cogeneration power plant over conventional plants is that the fuel energy is used here with much greater efficiency. In other words, a cogeneration (cogeneration) installation allows the use of thermal energy, which usually escapes into the atmosphere along with flue gases.

When using a cogeneration unit, the overall fuel utilization factor increases significantly. The use of a cogeneration plant significantly reduces energy costs. A cogeneration plant means energy independence for consumers, a reliable supply of energy and a significant reduction in the cost of producing thermal energy.

The world's leading manufacturers of cogeneration units based on piston engines and turbines today are: Alstom, Capstone, Calnetix - Elliott Energy Systems, Caterpillar, Cummins, Deutz AG , Generac, General Electric, GE Jenbacher, Honeywell, Kawasaki, Kohler, Loganova, MAN B&W, MAN TURBO AG (MAN TURBO), Mitsubishi Heavy Industries (Mitsubishi Heavy Industries), Rolls-Royce (Rolls-Royce), SDMO (SDMO), Siemens (Siemens), Solar Turbines (Solar Turbines), Turbomach (Turbomakh), Vibro Power, Wartsila ( Vyartsilya), Waukesha Engine Division (Wokesha / Vukesha), FG Wilson (Wilson), microturbine plants / mini turbines, microturbine power plants / microturbines Ingersoll Rand (Ingersoll Rand).

Cogeneration units - design and principle of operation

A cogeneration plant consists of a power unit such as a gas turbine, an electric generator, a heat exchanger and a control system.

IN gas turbine units the main amount of thermal energy is taken from the exhaust system. In gas piston power plants, thermal energy is taken from the oil radiator, as well as the engine cooling system. The extraction of thermal energy in gas turbine units (GTU) is technically simpler, since the exhaust gases have a higher temperature.

For 1 MW of electrical power, the consumer receives from 1 to 2 MW of thermal power in the form of steam and hot water for industrial needs, heating and water supply. Cogeneration power plants more than cover the needs of consumers for electrical and cheap thermal energy.

Excess heat can be directed to a steam turbine for maximum electricity generation or to absorption refrigeration machines (ARM) to produce cold, with subsequent implementation in air conditioning systems. This technology has own definition- trigeneration.

Cogeneration plants - organic expansion into the Russian economy

The use of cogenerator power plants in megacities makes it possible to effectively supplement the energy supply market, without reconstructing networks. At the same time, the quality of electrical and thermal energy is significantly improved. Autonomous operation of a cogenerator unit makes it possible to provide consumers with electricity with stable parameters in terms of frequency and voltage, and thermal energy with stable parameters in temperature.

Potential targets for the use of cogeneration plants in Russia are industrial production, hospitals, residential facilities, gas pumping stations, compressor stations, boiler houses, etc. As a result of the introduction of cogeneration power plants, it is possible to solve the problem of providing consumers with inexpensive heat and electricity without additional, financially costly, construction of new power lines and heating mains. The proximity of sources to consumers will significantly reduce energy transmission losses and improve its quality, and therefore increase the utilization rate of natural gas energy.

Cogeneration plant - an alternative to general purpose heating networks

A cogeneration plant is an effective alternative to heating networks, thanks to the flexible change of coolant parameters depending on consumer requirements at any time of the year. A consumer who has a cogenerator power plant in operation is not dependent on the economic state of affairs of large heat and power companies.

Income (or savings) from the sale of electricity and heat, for a short time, cover all costs of the cogeneration power plant. The return on capital investments in a cogeneration unit occurs faster than the return on funds spent on connecting to heating networks, thereby ensuring a sustainable return on investment.

The cogeneration unit fits well into the electrical circuit of both individual consumers and any number of consumers through state power grids. Compact, environmentally friendly, cogeneration power plants cover the shortage of generating capacity in large cities. The emergence of such installations makes it possible to relieve Electricity of the net, ensure stable quality of electricity and makes it possible to connect new consumers.

Advantages of cogeneration power plants

The advantages of cogeneration power plants lie primarily in the economic sphere. The significant difference between the capital costs of power supply from the grid and power supply from one's own source is that the capital costs associated with the acquisition of a cogeneration unit are reimbursed, and the capital costs of connecting to the networks are irretrievably lost when newly built substations are transferred to the balance sheet of energy companies.

Capital costs when using a cogeneration unit are compensated by fuel savings.

Typically, full recovery of capital costs occurs after operating a cogeneration power plant for three to four years.

This is possible when the cogeneration unit supplies the load in a continuous operating cycle, or if it operates in parallel with the electrical network. Latest solution is beneficial for owners of electrical and heating networks. Energy systems are interested in connecting powerful cogeneration units to their networks, since in this case they acquire additional generating capacity without capital investments in the construction of a power plant. In this case, the energy system purchases cheap electricity for its subsequent resale at a more favorable tariff. Heating network get the opportunity to purchase cheap heat for sale to nearby consumers.

Application of cogenerators

The scope of application of cogenerators is very wide.

Cogeneration stations can generate energy for the needs of all industries economic activity, including:
on industrial enterprises
in agriculture
in the service sector
in hotels
shopping and administrative centers
in residential areas
private houses
hospitals, resorts and medical institutions
swimming pools, sports centers

Cogenerators and savings energy resources

In Russia, the need to use cogenerators for heat and power supply is obvious, since the quality of central supply leaves much to be desired, and the monopolistic nature of Russian energy resources forces one to purchase electricity and heat at expensive tariffs. Thus, the introduction of cogenerators makes it possible to significantly reduce the cost of consumed energy, which provides a significant economic effect for the end consumer, as well as solve the problem of peak loads and disadvantages centralized systems and thereby provide high-quality, uninterrupted energy supply

Specifics of cogenerators

The disadvantage of cogenerators is only the limited power of up to 3 MW for one machine. The average industrial consumer in Russia has an installed capacity of 1-2 MW. If necessary, several parallel operating cogenerators can be installed. Cogenerators are easy to transport and install. They allow you to decide hot topic uneven daily consumption electricity, insoluble for large generating installations. Indeed, for a cogenerator, a linear dependence of fuel consumption occurs starting from 15-20% of the rated power. By sectioning (packaging) the total power into 4-8 blocks operating in parallel, it becomes possible to work from 1.5-4% to 100% of the rated load at the calculated specific fuel consumption. When there is no load, unused cogenerators are stopped, which significantly saves the service life of the prime movers.

Cogenerator clusters

Sectioning (packaging) of cogenerators became possible only recently, when reliable, high-precision control systems based on advances in microprocessor technology and computer technology appeared. With the help of packaging (sectioning), it has become possible to build large cogenerator units, the economic efficiency of which is no worse than a single unit operating at rated load. A particularly important application of such cogenerators is the power supply of residential areas in which there are no industrial consumers and the ratio of maximum and minimum load during the day reaches dozens of times, since Russian conditions make it impossible to sell the electricity generated at night to networks such as, for example, in Europe. An important economic factor in the spread of sectionalized cogenerator systems is that the specific cost (per 1 kW of power) of small installations is lower than the specific cost of single cogenerators of higher power. Positive feature sectionalized cogenerator systems is their higher reliability. Indeed, in case of failure, scheduled repairs or maintenance, the total power of the system is (n-1)/n% of the rated power, where n is the number of units in the system. For Russian industrial and civil consumers, cogenerators with a capacity of 0.02 to 3 MW, sectionalized by units with common computer control, are offered.

Cogenerators - environmental safety

An important factor in choosing a cogenerator is its environmental safety. Such installations have a low level of toxic emissions into the atmosphere and meet the most stringent international and Russian standards. Enterprises that have their own cogeneration unit will be able to meet their own electricity needs. At the same time, not only will the cost of the main products of the enterprise be reduced, but its energy security will also significantly increase, since losses in the supply of electricity from central energy companies will not affect the progress of the technological process.

A gas piston power plant is a production system electrical energy from the internal energy of the fuel. They operate on liquefied or main natural gas, biogas, and associated gas.

The advantages of gas piston power plants are ease of use and low cost of fuel. In areas with a main gas pipeline, a gas piston power plant acts as the most economical permanent or backup source of energy.

The operating principle of a gas piston unit is quite simple. The basis of the design is a gas piston engine - an internal combustion engine. When fuel burns, the energy released is used by an electric current generator. Motors can be used in installations designed for both constant and variable operation, as well as for the simultaneous production of electrical and thermal energy (this process is called “energy cogeneration”). In the latter case, such an installation is called a “cogeneration gas piston installation”.

Cogeneration energy

Term "cogeneration" denotes the combined generation of various types of energy. In technical terms, cogeneration is a process in which heat and electricity are generated simultaneously in a special device. Such a device is called "cogenerator" and its typical example of a cogeneration application is a gas power plant. The cogenerator includes a generator, a gas engine, a heat extraction system and a control system. Cogeneration is the optimal way to provide both heat and electricity. The cogeneration principle underlies various modern technical solutions.

The design of an internal combustion engine running on gas fuel is less susceptible to damage and wear due to the absence of particles in the gas that can damage the mechanism. This is especially true at low loads (below 20%). In addition, gas piston cogeneration plants also operate on biogas with low-smoke exhaust (Euro4), which concentrates a minimal amount of harmful substances.

A gas piston cogeneration station (cogenerator thermal unit) is capable of producing heat and electricity for a residential building or an industrial enterprise - depending on its technical characteristics. If there is a main line, the cogenerator can easily provide an uninterrupted supply of electricity. In this case, fuel consumption is significantly more economical than in the case of gasoline or diesel stations. The cost of electricity is lower than the network tariff, even at mini thermal power plants (low-power cogeneration plants, mini thermal power plants).

Cogeneration mini-CHPs

Cogeneration mini-CHPs Due to their size, they are easier to place in small areas. The cogenerator runs on natural gas, and the mini-CHP cogeneration plant is one of the systems that operate on the synthesis of two sources, cogeneration. Cogeneration thermal units fit perfectly into the electrical circuit of industrial enterprises. To meet needs such as heating small facilities, low-power cogeneration units are used. A cogeneration installation allows you to significantly save the cost of generating thermal energy.

Modular power plants They are suitable for powerful power generation, and can also heat large industrial premises; in addition, they are characterized by good environmental friendliness. Modular power plants are used in premises where active production processes take place.

Gas piston generators are also used as backup stations. They are very convenient for situations where there are frequent power outages. Gas power plants are the guarantor of your energy independence.

Cogeneration

The process of generating electricity, called cogeneration, is the production of both electricity and heat in a single installation.

Separate production of electricity and heat

cogeneration installation power station energy

Basic principle of cogeneration: the desire to maximize the use of primary fuel energy (for example, the use of thermal energy that was previously discharged into the atmosphere). The overall efficiency of the power station in cogeneration mode is 80-95%.

ELTECO GLOBAL offers CGUs of various capacities, with various options performances. Considering the low cost of gas and the possibility of connection, cogeneration is a more efficient process, the investment from which is justified in 2-3 years. The power range is represented by piston engines LOMBARDINI, FORD, MAN, GUASCOR, PERKINS and DEUTZ using natural gas, landfill gas or biogas as fuel. When choosing a CGU, it is necessary to take into account the required parameters of the electrical and thermal power of the installations, the type of gas and its consumption. If it is difficult to choose, ELTECO GLOBAL provides professional advice and provides a table for selecting the required installation. Taking all factors into account, cogeneration is a modern, efficient and environmentally friendly method of generating electricity. Parallel connection of units makes it possible to increase power, and sequential operation of units increases service life. The wide range of power plants offered by Elteco allows you to solve the power supply problem as clearly as possible, and European assembly determines quality, reliability and durability.

Cogeneration plants (cogenerators) are widely used in small-scale energy (mini-CHP, MicroCHP). And for this there are the following prerequisites:

The heat is used directly at the point of receipt, which is cheaper than the construction and operation of many kilometers of heating mains;

Electricity is used largely at the point of receipt without the overhead costs of energy suppliers, and its cost to the consumer can be somewhat less than that of grid-sourced energy.

The consumer gains energy independence from power supply failures and accidents in heat supply systems.

The use of cogeneration is most beneficial for consumers with constant consumption of electricity and heat. For consumers who have pronounced “peak loads” (for example, residential, housing and communal services), cogeneration is of little benefit due to the large difference between the installed and average daily capacity - the payback of the project is significantly delayed.

In modern cogeneration plants based on gas piston engines, the coefficient of utilization of fuel combustion heat reaches 85...90% and only 10% is lost. Fuel savings when generating energy in a cogeneration cycle can reach up to 40% compared to the separate production of the same amount of electricity (condensing power plant) and thermal energy (hot water boiler house). For example, using the heat of exhaust gases and coolant of a 500 kW gas engine for heating, it is possible to provide heat to an area of 4...4.5 thousand m2, maintaining a normal temperature in the premises.

There are two main groups of cogeneration plants:

1. Installations for the simultaneous production of electrical and thermal energy (foreign analogue: SHP - combined heat and power plant);
2. Combined cycle plants (power plants) with a recovery boiler and a steam turbine (foreign analogue: SSR - combined cycle power plant). More often, these are power plants with a gas turbine, waste heat boiler and steam turbine (CCGT - high-power combined cycle gas units). But there are projects where, instead of a gas turbine, a gas piston engine and a low-power steam turbine were used

Depending on the generated electrical power, cogeneration power plants are divided into the following groups:

· micro power plants (power from 1 to 250 kW);
· mini (power from 250 to 1000 kW) and small (power from 1 to 60 MW) - often combined for simplicity;
· medium (power from 60 to 300 MW);
· large (power more than 300 MW).

Let us emphasize that here we're talking about about the total power of the power plant, and not the unit power of the energy unit. It is generally accepted that power up to 250 kW (micro power plants) is expedient and possible to cover with gas piston or diesel units (for example, DEUTZ ADG), as well as various alternative energy installations. From 250 kW to 10-15 MW - using gas piston units. Powers up to 60 MW - using gas piston units (or gas turbines with unit powers from 20 MW), and medium and high powers - using gas and steam turbines or combined cycle gas plants.

Introduction

This publication provides general information about the processes of production, transmission and consumption of electrical and thermal energy, the mutual connection and objective laws of these processes, about various types power plants, their characteristics, conditions collaboration and complex use. A separate chapter discusses energy saving issues.

Production of electrical and thermal energy

General provisions

Energy is a set of natural, natural and artificial, man-made systems designed to obtain, transform, distribute and use energy resources of all types. Energy resources are all material objects in which energy is concentrated for possible use by humans.

Among the various types of energy used by people, electricity has a number of significant advantages. This is the relative simplicity of its production, the possibility of transmission over very long distances, the ease of conversion into mechanical, thermal, light and other energy, which makes electric power the most important sector of human life.

The processes occurring during the production, distribution, and consumption of electrical energy are inextricably interconnected. Installations for the generation, transmission, distribution and conversion of electricity are also interconnected and integrated. Such associations are called electric power systems (Fig. 1.1) and are an integral part of the energy system. In accordance with energy system called a set of power stations, boiler houses, electrical and heating networks, interconnected and connected by a common mode in the continuous process of production, conversion and distribution of electricity and heat at general management these modes.

An integral part of the electrical power system is the power supply system, which is a set of electrical installations designed to provide consumers with electrical energy.

A similar definition can be given to a heat supply system.

Thermal power plants

Obtaining energy from fuel and energy resources (FER) by burning them is currently the simplest and most in an accessible way energy production. Therefore, up to 75% of all electricity in the country is generated at thermal power plants (TPPs). In this case, both joint production of thermal and electrical energy is possible, for example, at thermal power plants (CHP), and their separate production (Fig. 1.2).

The block diagram of the thermal power plant is shown in Fig. 1.3. The work proceeds as follows. The fuel supply system 1 ensures the supply of solid, liquid or gaseous fuel to the burner 2 of the steam boiler 3. The fuel is pre-prepared accordingly, for example, coal is crushed to a powder state in the crusher 4, dried and saturated with air, which is blown by a blower fan 5 from the air intake 6 through heater 7 is also supplied to the burner. The heat generated in the boiler furnace is used to heat water in heat exchangers 8 and generate steam. Water is supplied by pump 9 after it goes through a special water treatment system 10. Steam from drum 11 at high pressure and temperature enters steam turbine 12, where steam energy is converted into mechanical energy of rotation of the turbine shaft and electric generator 13. The synchronous generator produces alternating three-phase current . The steam exhausted in the turbine is condensed in condenser 14. To speed up this process, it is used cold water natural or artificial reservoir 15 or special coolers - cooling towers. The condensate is pumped back into the steam generator (boiler). This cycle is called a condensation cycle. Power plants using this cycle (PPS) produce only electrical energy. At a thermal power plant, part of the steam from the turbine is taken at a certain pressure to the condenser and is used for the needs of heat consumers.

Rice. 1.1.

G - electricity generators; T - transformers; P - electrical loads;

W - power transmission lines (PTL); AT - autotransformers

Fig.1.2.

a - combined production; b - separate production

Fig.1.3.

Fuel and its preparation. Thermal power plants use solid, liquid or gaseous organic fuel. Its general classification is shown in table 1.1.

Table 1.1. General classification fuel

The fuel in the form in which it is burned is called “working fuel”. The composition of the working fuel (solid and liquid) includes: carbon C, hydrogen H, oxygen O, nitrogen N, ash A and moisture W. Expressing the fuel components as a percentage , referred to one kilogram of mass, an equation for the composition of the working mass of fuel is obtained.

Sulfur is called volatile and makes up part of the total amount of sulfur found in the fuel; the rest of the non-combustible part of the sulfur is part of mineral impurities.

Natural gaseous fuels contain: methane, ethane, propane, butane, hydrocarbons, nitrogen, carbon dioxide. The last two components are ballast. Artificial gaseous fuel contains methane, carbon monoxide, hydrogen, carbon dioxide, water vapor, nitrogen, and resins.

The main thermal technical characteristic of fuel is the heat of combustion, which shows how much heat in kilojoules is released when burning one kilogram of solid, liquid or one cubic meter of gaseous fuel. There are higher and lower calorific values.

The higher calorific value of a fuel is the amount of heat released by the fuel during its complete combustion, taking into account the heat released during the condensation of water vapor that is formed during combustion.

The lower calorific value differs from the highest calorific value in that it does not take into account the heat expended on the formation of water vapor that is found in the combustion products. When calculating, the lower calorific value is used, because the heat of water vapor is uselessly lost with combustion products going into the chimney.

The relationship between the higher and lower calorific values for the working mass of fuel is determined by the equation

To compare different types of fuel in terms of calorific value, the concept of “conventional fuel” (c.f.) was introduced. Conventional fuel is considered to be the fuel whose lower calorific value at working masses equal to 293 kJ/kg for solid and liquid fuels or 29300 kJ/m3 for gaseous fuels. In accordance with this, each fuel has its own thermal equivalent Et = QНР / 29300.

Converting the consumption of working natural fuel into conditional fuel is carried out according to the equation

Woosl = Et? Tue.

a brief description of individual species fuel is given in Table 1.2.

Table 1.2. Fuel characteristics

Particularly noteworthy is the lower calorific value in kJ/kg of fuel oil - 38000...39000, natural gas - 34000...36000, associated gas - 50000...60000. In addition, this fuel contains virtually no moisture or mineral impurities.

Before supplying fuel to the furnace, it is prepared. The system for preparing solid fuel is especially complex, which successively undergoes cleaning from mechanical impurities and foreign objects, crushing, drying, dust preparation, and mixing with air.

The system for preparing liquid and especially gaseous fuels is much simpler. In addition, this fuel is more environmentally friendly and has virtually no ash content.

Simplicity of transportation, ease of automation of combustion process control, and high calorific value make natural gas promising for use in the energy sector. However, supplies of this raw material are limited.

Water treatment. Water, being the coolant at thermal power plants, continuously circulates in a closed circuit. In this case, the purification of water supplied to the boiler is of particular importance. Condensation from steam turbine(Fig. 1.3) enters system 10 for purification from chemical impurities (chemical water treatment - CWO) and free gases (deaeration). In the water-steam-condensate technological cycle, losses are inevitable. Therefore, the water path is recharged from an external source 15 (pond, river) through the water intake 16. The water entering the boiler is preheated in the economizer (heat exchanger) by 17 exhaust combustion products.

Steam boiler. The boiler is a steam generator at a thermal power plant. The main structures are presented in Fig. 1.4.

The drum-type boiler has a steel drum 1, in the upper part of which steam is collected. Feed water is heated in economizer 2, located in flue gas chamber 3, and enters the drum. Manifold 4 closes the steam-water cycle of the boiler. In combustion chamber 5, combustion of fuel at a temperature of 1500...20000C ensures boiling of water. Through steel lifting pipes 6, having a diameter of 30...90 mm and covering the surface of the combustion chamber, water and steam enter the drum. Steam from the drum is supplied to the turbine through a tubular superheater 7. The superheater can be made in two or three stages and is designed for additional heating and drying of steam. The system has 8 drop pipes through which water from the bottom of the drum falls into the collector.

In a drum-type boiler, natural circulation of water and steam-water mixture is ensured due to their different densities.

Such a system makes it possible to obtain subcritical parameters of steam (critical is the point of state at which the difference in the properties of liquid and steam disappears): pressure up to 22.5 MPa, and practically no more than 20 MPa; temperature up to 374°C (without superheater). At higher pressures, the natural circulation of water and steam is disrupted. Forced circulation has not yet found application in powerful drum boilers due to its complexity. Therefore, boilers of this type are used in power units with a capacity of up to 500 MW with a steam output of up to 1600 tons per hour.

In a direct-flow boiler, special pumps carry out forced circulation of water and steam. Feedwater is supplied by pump 9 through economizer 2 to evaporator pipes 10, where it is converted into steam. Through the superheater 7 steam enters the turbine. The absence of a drum and forced circulation of water and steam make it possible to obtain supercritical steam parameters: pressure up to 30 MPa and temperature up to 590°C. This corresponds to power units with a capacity of up to 1200 MW and a steam production capacity of up to 4000 t/h.

Boilers intended only for heat supply and installed in local or district boiler houses are made on the same principles as discussed above. However, the parameters of the coolant, determined by the requirements of heat consumers, differ significantly from those discussed earlier (some specifications such boilers are given in Table 1.3).

Table 1.3. Technical data of heating system boilers

For example, boiler houses attached to buildings allow the use of boilers with steam pressure up to 0.17 MPa and water temperature up to 1150C, and the maximum power of built-in boiler houses should not exceed 3.5 MW when operating on liquid and gaseous fuels or I.7 MW when operating on liquid and gaseous fuels. work at solid fuel. Heating system boilers differ in the type of coolant (water, steam), in productivity and thermal power, in design (cast iron and steel, small-sized and tent-type, etc.).

The efficiency of a steam generation or hot water preparation system is largely determined by the coefficient of performance (COP) of the boiler unit.

IN general case The efficiency of a steam boiler and fuel consumption are determined by the expressions:

Kg/s, (1.1)

where hk is the efficiency of the steam boiler, %; q2, q3, q4, q5, q6 - heat loss, respectively, with exhaust gases, chemical underburning, mechanical underburning, for external cooling, with slag, %; B - total fuel consumption, kg/s; QPC is the heat absorbed by the working environment in the steam boiler, kJ/m; - available heat of fuel entering the furnace, kJ/kg.

Fig.1.4.

a - drum type; b - direct-flow type

1- drum; 2 - economizer; 3 - exhaust gas chamber; 4 - collector; 5 - combustion chamber; 6 - lifting pipes; 7 - steam superheater; 8 - lowering pipes; 9 - pump; 10 - evaporator pipes

If the heat of the flue gases is not used, then

and with an open system for drying fuel with exhaust gases

where Nux, Notb, are the enthalpy of exhaust gases, gases at the point of selection for drying and cold air, respectively, kJ/kg; r is the proportion of gases taken for drying; ?yx - excess air in the exhaust gases.

The enthalpy of a gas at temperature T is numerically equal to the amount of heat that is supplied to the gas in the process of heating it from zero degrees Kelvin to temperature T at constant pressure.

With an open drying system, all fuel data refers to dried fuel.

In this case, the consumption of raw fuel when the humidity changes from WP to Wdry is

where Dry is the consumption of dried fuel according to (1.1), kg/s; Wdry, WP - humidity of dried and undried fuel, %.

When humidity changes, the lower calorific value of fuel also changes from to:

KJ/kg (1.4)

The lowest calorific value corresponds to the amount of heat released by the fuel during its complete combustion, without taking into account the heat expended on the formation of water vapor that is found in the combustion products.

Total available heat of fuel entering the furnace

KJ/kg, (1.5)

where is the lower heating value of fuel, kJ/kg; - additional heat introduced into the boiler by air heated from outside, steam blast, etc., kJ/kg.

For approximate calculations.

Heat perceived by the working environment in a steam boiler

KJ/s, (1.6)

where Dp is the steam output of the boiler, kg/s; hpp, hpv - enthalpy of superheated steam and feed water, kJ/kg; ?Qpk - additionally perceived heat in the presence of a superheater in the boiler, blowing with water, etc., kJ/s.

For approximate calculations? Qpc=0.2…0.3 Dp(hpp - hpv).

where?un is the share of ash carryover with combustion products; Nshl - slag enthalpy, kJ/kg; AR - working ash content of fuel, %.

The values of q3, q4, q5, Wр, Ar are given in specialized literature, as well as in textbooks.

For solid slag removal, you can take?ух=1.2…1.25; ?un=0.95; Nshl=560 kJ/kg.

In addition, at an air temperature in front of the boiler of 300C = 223 kJ/kg, and at a flue gas temperature of 1200C Nux = 1256 kJ/kg.

Calculation example. Determine the efficiency and fuel consumption for a steam boiler under the following conditions: Dп=186 kg/s; fuel - dried Berezovsky coal with Wdry=13%; open-loop drying system, r=0.34; the gas taken for drying has Nob = 4000 kJ/kg; enthalpy of superheated steam and feed water, respectively, hpp = 3449 kJ/kg, hpv = 1086.5 kJ/kg.

Solution. Preliminarily, according to (1.4), the lower calorific value of the dried fuel is determined.

Here Wр=33% and =16200 kJ/kg are taken according to .

Taking by (1.5)

we find by (1.2)

We find: q3=1%, q4=0.2%, q5=0.26% and taking into account (1.7)

To calculate fuel consumption using (1.6) we find

Consumption of dried fuel according to (1.1)

The raw fuel consumption at Wр = 33% according to (1.3) is

Steam turbine. This is a heat engine in which the energy of steam is converted into mechanical energy of rotation of the rotor (shaft) and the working blades attached to it. A simplified diagram of the steam turbine design is shown in Fig. 1.5. Disks 2 with working blades 3 are attached to the turbine shaft 1. These blades are supplied with steam from the boiler from the nozzle 4, supplied through the steam line 5. The energy of the steam causes the turbine impeller to rotate, and the rotation of the shaft is transmitted through the coupling 6 to the shaft 7 of the synchronous generator. The exhaust steam is sent through chamber 8 to the condenser.

Steam turbines are divided by design into active and reactive. In an active turbine (Fig. 1.5c), the volume of steam V2 at the entrance to the working blades is equal to the volume of steam V3 at the exit from the blades. The expansion of the steam volume from V1 to V2 occurs only in the nozzles. There, the pressure changes from p1 to p2 and the steam velocity from c1 to c2. In this case, the steam pressure at the inlet p2 and the outlet p3 from the blades remains unchanged, and the steam speed drops from c2 to c3 due to the transmission kinetic energy pair of turbine blades:

Gp?(s2-s3)2 / 2 Gt?st2 / 2,

where Gp, Gt - mass of steam and turbine impeller; c2, c3, st - steam velocity at the inlet and outlet of the blades and the speed of movement of the impeller.

The design of the jet turbine blades is such (Fig. 1.5d) that the steam expands not only in the nozzles from V1 to V2, but also between the impeller blades from V2 to V3. In this case, the steam pressure changes from p2 to p3 and the steam velocity from c2 to c3. Since V2 p3 and in accordance with the first law of thermodynamics, the elementary work of expansion of a unit of steam

where F is the area of the blade, m2; (p2 - p3) - pressure difference at the inlet and outlet of the blades, Pa; dS - blade displacement, m.

In this case, the work used to rotate the turbine impeller. Thus, in jet turbines, in addition to the centrifugal forces that arise when the speed of steam moves, reactive forces caused by the expansion of steam act on the blades.

Modern turbines are made both active and reactive. In powerful units, the steam input parameters approach the values of 30 MPa and 6000C. In this case, the outflow of steam from the nozzle occurs at a speed exceeding the speed of sound. This leads to the need for a high rotor speed. Enormous centrifugal forces arise that act on the rotating parts of the turbine.

In practice, the rotor rotation frequency, due to the design features of both the turbine itself and the synchronous generator, is 3000 1/min. In this case, the linear speed on the circumference of a turbine wheel with a diameter of one meter is 157 m/s. Under these conditions, particles tend to come off the wheel surface with a force of 2,500 times their weight. Inertial loads are reduced by using speed and pressure steps. Not all of the steam energy is given to each stage, but only part of it. This also ensures an optimal heat drop per stage, which is 40...80 kJ/kg at a peripheral speed of 140...210 m/s. The total heat drop generated in modern turbines is 1400...1600 kJ/kg.

For design reasons, 5...12 stages are grouped in one housing, which is called a cylinder. A modern powerful turbine can have a high pressure cylinder (HPC) with an inlet steam pressure of 15...30 MPa, a medium pressure cylinder (MPC) with a pressure of 8...10 MPa and a low pressure cylinder (LPC) with a pressure of 3... 4 MPa. Turbines up to 50 MW are usually built in a single cylinder.

The steam exhausted in the turbine enters the condenser for cooling and condensation. Cooling water at a temperature of 10...15°C is supplied to the tubular heat exchanger of the condenser, which promotes intense condensation of steam. For the same purpose, the pressure in the condenser is maintained within 3...4 kPa. The cooled condensate is again supplied to the boiler (Fig. 1.5), and the cooling water, heated to 20...25 ° C, is removed from the condenser. If cooling water is taken from a reservoir and then irretrievably discharged, the system is called an open-flow system. In closed cooling systems, water heated in the condenser is pumped to cooling towers - cone-shaped towers. From the top of the cooling towers, water flows down from a height of 40...80 m, cooling to the required temperature. The water then flows back into the condenser.

Both cooling systems have their advantages and disadvantages and are used in power plants.

Fig.1.5. Steam turbine design:

a - turbine impeller; b - diagram of a three-stage active turbine; c - steam work in the active stage of the turbine; d - work of steam in the reactive stage of the turbine.

1 - turbine shaft; 2 - disks; 3 - working blades; 4 - nozzles; 5 - steam line; 6 - coupling; 7 - synchronous generator shaft; 8 - exhaust steam chamber.

Turbines, in which all the steam supplied to them, after completing the work, enters the condenser, are called condensing and are used to produce only mechanical energy with its subsequent conversion into electrical energy. This cycle is called condensation and is used at state district power plants and thermal power plants. An example of a condensing turbine is K300-240 with a power of 300 MW with initial steam parameters of 23.5 MPa and 600°C.

In heating turbines, part of the steam is taken before the condenser and is used to heat water, which is then sent to the heat supply system of residential, administrative, and industrial buildings. The cycle is called heating and is used at thermal power plants and state district power plants. For example, the T100-130/565 turbine with a power of 100 MW for initial steam parameters of 13 MPa and 5650C has several adjustable steam extractions.

Industrial heating turbines have a condenser and several adjustable steam extractions for heating and industrial needs. They are used at thermal power plants and state district power plants. For example, a P150-130/7 turbine with a power of 50 MW for initial steam parameters of 13 MPa and 5650C provides industrial steam extraction at a pressure of 0.7 MPa.

Backpressure turbines operate without a condenser, and all exhaust steam goes to district heating and industrial consumers. The cycle is called back-pressure, and turbines are used at thermal power plants and state district power plants. For example, a turbine R50-130/5 with a power of 50 MW for an initial steam pressure of 13 MPa and a final pressure (back pressure) of 0.5 MPa with several steam extractions.

The use of a heating cycle makes it possible to achieve an efficiency of up to 70% at thermal power plants, taking into account the supply of heat to consumers. In the condensation cycle, the efficiency is 25...40% depending on the initial steam parameters and the power of the units. Therefore, CPPs are located in places where fuel is produced, which reduces transportation costs, and CHP plants are closer to heat consumers.

Synchronous generators. The design and characteristics of this machine, which converts mechanical energy into electrical energy, are discussed in detail in special disciplines. Therefore, we will limit ourselves to general information.

The main structural elements of a synchronous generator (Fig. 1.6): rotor 1, rotor winding 2, stator 3, stator winding 4, housing 5, exciter 6 - direct current source.

The non-salient pole rotor of high-speed machines - turbogenerators (n = 3000 1/min) is made of sheet electrical steel in the form of a cylinder located on shaft 7. Low-speed machines - hydrogenerators (n ? 1500 1/min) have a salient-pole rotor (shown in dotted lines). In the grooves on the surface of the rotor there is an insulated copper winding connected to the exciter using sliding contacts 8 (brushes). The stator is a complete cylinder made of electrical steel, on the inner surface of which three phase windings are located in grooves - A, B, C. The windings are made of copper insulated wire, are identical to each other and have axial symmetry, occupying 120° sectors. The beginnings of the phase windings A, B, C are led out through insulators, and the ends of the windings X, Y, Z are connected to a common point N - neutral.

The generator operates as follows. The excitation current iB in the rotor winding creates a magnetic flux Ф that crosses the stator windings. The generator shaft is driven by a turbine. This ensures uniform rotation magnetic field rotor with angular frequency?=2?f, where f is the frequency of alternating current, 1/s is Hz. To obtain an alternating current frequency of 50 Hz with a number of pairs of magnetic poles p, the rotor rotation frequency n=60?f/p is required.

At p = 1, which corresponds to a salient-pole rotor, n = 3000 1/min. A rotating magnetic field crossing the stator windings induces an electromotive force (EMF) in them. In accordance with the law of electromagnetic induction, the instantaneous value of the emf

where w is the number of turns.

The EMF in the stator windings is induced synchronously with the change in the magnetic field as the rotor rotates.

Fig.1.6.

a - generator design; b - winding connection diagram;

c - EMF at the terminals of the generator windings

1 - rotor; 2 - rotor winding; 3 - stator; 4 - stator winding; 5 - body; 6 - pathogen; 7 - rotor shaft (axis); 8 - slip rings

With uniform rotation of the rotor and axial symmetry of the stator windings, the instantaneous values of the phase EMF are equal to:

where EM is the amplitude value of the EMF.

If an electrical load Z is connected to the terminals of the generator stator windings, an electrical current flows in the external circuit

where is the voltage at the terminals of the windings when current i flows through them and the stator winding resistance Zin.

In practice, it is more convenient to use not instantaneous, but effective values of electrical quantities. The necessary relationships are known from the course of physics and the theoretical foundations of electrical engineering.

The operation of the generator largely depends on the excitation and cooling mode of the machine. Various excitation systems (independent and self-excitation, electric machine and thyristor, etc.) allow you to change the value of iB and, consequently, the magnetic flux Ф and EMF in the stator windings. This makes it possible to regulate the voltage at the generator terminals within certain limits (usually ±5%).

The amount of active power supplied by the turbogenerator to the electrical network is determined by the power on the turbine shaft and is regulated by the supply of steam to the turbine.

During operation of the generator, it heats up, primarily due to the release of heat in the windings flowing around the current. Therefore, the efficiency of the cooling system is essential.

Low power generators (1...30 MW) have air cooling of internal surfaces using a flow (open) or regenerative (closed) circuit. On medium-power generators (25...100 MW), surface hydrogen cooling is used in a closed circuit, which is more efficient, but requires the use of special safety measures. Powerful generators (more than 100 MW) have forced hydrogen, water or oil cooling, in which the coolant is pumped under pressure inside the stator, rotor, and windings through special cavities (channels).

Main technical characteristics of generators: rated voltage at the generator stator winding terminals, Unom: 6.3-10.5-21 kV (higher values correspond to more powerful generators); rated active power, Rnom, MW; rated power factor; nominal efficiency of 90...99%.

These parameters are related to each other:

Own needs of power plants. Not all electrical and thermal energy produced at thermal power plants is distributed to consumers. Some remains at the station and is used to ensure its operation. The main consumers of this energy are: the fuel transportation and preparation system; water and air supply pumps; purification system for water, air, exhaust gases, etc.; heating, lighting, ventilation of domestic and industrial premises, as well as a number of other consumers.

Many elements of own needs belong to the first category in terms of reliability of power supply. Therefore, they are connected to at least two independent energy sources, for example, to sources at their station and to the power grid.

Switchgear. Electricity generated by generators is collected at a switchgear (DS) and then distributed among consumers. For this purpose, the terminals of the generator stator windings are connected to the switchgear busbars through special switching devices (switches, disconnectors, etc.) with rigid or flexible conductors (busbars). Each connection to the switchgear is made through a special cell containing the necessary set of equipment. Since the transmission, distribution and generation of electricity, as well as its consumption, occur at different voltages, there are several switchgears at the station. For the rated voltage of generators, for example, 10.5 kV, generator voltage control is performed. Usually it is located in the station building and is closed by design (closed switchgear). Closely located consumers are connected to this switchgear. To transmit electricity through power transmission lines (PTL) over long distances and communicate with other stations and the system, it is necessary to use a voltage of 35...330 kV. Such communication is carried out using separate switchgears, usually open-type (OPU), where step-up transformers are installed. To connect consumers of their own needs, use RUSN. From the RUSN buses, electricity is transmitted directly and through step-down transformers to consumers at the power plant.

Similar principles are used in the distribution of thermal energy generated at thermal power plants. Special collectors, steam pipelines, and pumps provide heat supply to industrial and municipal consumers, as well as to the system’s own needs.

Cogeneration.

A cogeneration station is the use of a primary source of energy - gas, to produce two forms of energy - thermal and electrical. The main advantage of a cogeneration power plant over conventional power plants is that energy conversion occurs with greater efficiency. In other words, a cogeneration (cogeneration) installation allows you to use the heat that is usually lost. The need for fuel is significantly reduced. The use of a cogeneration plant reduces energy supply costs by ~$100/kW. A cogeneration unit means energy independence and reduced heat costs.

Construction of cogeneration plants.

A cogeneration plant consists of a gas engine, a generator, a heat extraction system and a control system. Heat is extracted from the exhaust system, oil cooler and engine cooling system. For 100 kW of electrical power, the consumer receives ~120 kW of thermal power in the form of steam and hot water for heating and water supply. Cogeneration power plants successfully cover the need for inexpensive electrical and thermal energy

*Using steam and hot water It is possible to obtain chilled water using absorption-type plants (trigenation).

Cogeneration plants - industrial expansion.

The use of cogeneration power plants in cities makes it possible to effectively supplement the energy supply market, without reconstructing networks. At the same time, the quality of electrical and thermal energy increases significantly. Autonomous operation of the installation makes it possible to provide consumers with electricity with stable frequency and voltage parameters, and thermal energy with stable temperature parameters. Potential sites for the use of cogeneration units in Russia are industrial production, oil refineries, hospitals, residential facilities, gas pumping stations, compressor stations, boiler houses, etc. As a result of the introduction of cogenerator power plants, it is possible to solve the problem of providing consumers with heat and electricity without additional construction of powerful power transmission lines and heating mains. The proximity of sources to consumers will significantly reduce energy transmission losses and improve its quality, and therefore increase the utilization rate of natural gas energy.

A cogeneration plant is an alternative to a heating plant.

A cogeneration plant is an effective alternative to heating networks, thanks to the flexible change of coolant parameters depending on consumer requirements at any time of the year. It is not subject to dependence on the economic state of affairs in large heat and power companies. The cogeneration unit produces electricity and thermal energy in a ratio of ~1:1.2. Income (or savings) from the sale of electricity and thermal energy covers all costs of the cogeneration power plant; The return on capital investment for a cogeneration unit occurs faster than the return on funds spent on connecting to heating networks, thereby ensuring a quick and sustainable return on investment. The cogeneration unit fits well into the electrical circuit of individual consumers and into the city's electrical networks when operating in parallel with the network. Cogeneration power plants cover the lack of generating capacity in cities. The appearance of installations makes it possible to relieve electrical networks, ensure stable quality of electricity and make it possible to connect new consumers.

Prospects for cogeneration.

The significant difference between the capital costs of power supply from the grid and power supply from one's own source is that the capital costs associated with the acquisition of a cogeneration unit are reimbursed, and the capital costs of connecting to the networks are irretrievably lost when newly built substations are transferred to the balance sheet of energy companies. Capital costs when using a cogeneration unit are compensated by the low cost of energy in general. Typically, full recovery of capital and operating costs occurs after operating a cogeneration power plant for three to four years. Moreover, power supply from a cogeneration plant makes it possible to reduce annual costs for electricity and heat supply compared to energy supply from power systems by approximately $100 for each kW of rated electrical power of the cogeneration power plant, in the case when the cogeneration plant operates in the basic energy generation mode (at 100% load all year round). This is possible when the cogeneration unit supplies the load in a continuous operating cycle, or if it operates in parallel with the network. The latter solution is also beneficial for electricity and heat networks.

Application of cogenerators.

The scope of application of cogenerators is very wide.
Cogeneration stations can generate energy for the needs of all sectors of economic activity, including:

At industrial enterprises
. in agriculture
. in the service sector
. in hotels
. shopping and administrative centers
. in residential areas
. private houses
. hospitals, resorts and medical institutions
. swimming pools, sports centers

Sources of heat and electrical energy - cogenerators.

Heat sources - for heating systems, to maintain a stable temperature, for use in technological processes of industrial enterprises.
Electricity sources - for joint operation with the power grid, as an autonomous source of power supply, as a backup source of power supply in the event of a power failure in the network.

Cogenerators and saving energy resources.

Currently, there is a persistent trend in the global energy sector towards an increase in energy production and consumption. Even with significant structural changes in industry and the transition to energy-saving technologies, the demand for heat and electricity will increase in the coming decades. Therefore, the particularly widespread use of cogenerators in the world indicates a new trend towards the development of local energy as the most cost-effective and environmentally friendly sector of the fuel and energy complex.
In Russia, the need to use cogenerators for heat and power supply is obvious, since the quality of central supply leaves much to be desired, and the monopolistic nature of Russian energy resources forces one to purchase electricity and heat at expensive tariffs. Thus, the introduction of cogenerators makes it possible to significantly reduce the cost of consumed energy, which provides a significant economic effect for the end consumer, as well as solve the problem of peak loads, the disadvantages of centralized systems, and thereby provide high-quality, uninterrupted energy supply

Specifics of cogenerators.

The disadvantage of cogenerators is only the limited power of up to 3 MW for one machine. The average industrial consumer in Russia has an installed capacity of 1-2 MW. If necessary, several parallel operating cogenerators can be installed. Cogenerators are easy to transport and install. They make it possible to solve the acute issue of uneven daily electricity consumption, which is insoluble for large generating installations. Indeed, for a cogenerator, a linear dependence of fuel consumption occurs starting from 15-20% of the rated power. By sectioning (packaging) the total power into 4-8 blocks operating in parallel, it becomes possible to work from 1.5-4% to 100% of the rated load at the calculated specific fuel consumption. When there is no load, unused cogenerators are stopped, which significantly saves the service life of the prime movers.

Cogenerator clusters .

Sectioning (packaging) of cogenerators became possible only recently, when reliable, high-precision control systems based on advances in microprocessor technology and computer technology appeared. With the help of packaging (sectioning), it has become possible to build large cogenerator units, the economic efficiency of which is no worse than a single unit operating at rated load. A particularly important application of such cogenerators is the power supply of residential areas in which there are no industrial consumers and the ratio of maximum and minimum load during the day reaches dozens of times, since Russian conditions make it impossible to sell the electricity generated at night to networks such as, for example, in Europe. An important economic factor in the spread of sectionalized cogenerator systems is that the specific cost (per 1 kW of power) of small installations is lower than the specific cost of single cogenerators of higher power. A positive feature of sectionalized cogenerator systems is their higher reliability. Indeed, in case of failure, scheduled repairs or maintenance, the total power of the system is (n-1)/n% of the rated power, where n is the number of units in the system. For Russian industrial and civil consumers, cogenerators with a capacity of 0.02 to 3 MW, sectionalized by units with common computer control, are offered.

Cogenerators - environmental safety.