Fuel, cold water and air are what a thermal power plant consumes. Ash, hot water, smoke and electricity are what it produces.
Thermal power plants operate on various types of fuel.
In the middle lane Soviet Union many power plants run on the local fuel - peat. It is burned in the furnaces of steam boilers in lumpy form on moving grates or in the form of peat chips - milled peat - in mine-mill furnaces or furnaces of the Ing. Shershnev.
Milled peat is obtained by removing small shavings, crumbs from the peat mass by toothed drums - cutters. Then this crumb is dried.
Burning milled peat in pure form long time remained an unresolved problem until in our USSR engineer Shershnev designed a furnace in which milled peat is burned in suspension. Milled peat is blown into the furnace by air. Unburned large particles fall, but are again taken up by a strong air stream and, thus, remain in suspension in the combustion chamber until complete combustion.
In 1931, the first power plant in the world was launched in the USSR, burning milled peat in such furnaces. This is the Bryansk regional power plant.
Later, for the combustion of milled peat, shaft-mill furnaces were constructed. In mine mills, milled peat is dried, crushed, mixed with air and already in the form of very small dried particles enters the furnace, where it burns.
In the oil regions of the USSR there are also power plants operating on liquid fuel — fuel oil (waste oil distillation). Power plants located near metallurgical plants consume blast furnace gas and coke oven gas as fuel. With the discovery of natural gas deposits, some power plants began to use this gas in the furnaces of their boilers.
But none of these fuels are as ubiquitous as coal. Most of the thermal power plants in the USSR use various types of coal as fuel.
Modern power plants are very unpretentious in terms of the quality of coal. They can use ash and Blazhny coals, which are unsuitable for burning in the furnaces of steamers and steam locomotives, in blast furnaces and open-hearth furnaces.
Previously, in power plants, coal was burned in the furnaces of steam boilers on grates - the same as in stoves for sod peat and firewood. Practice has shown that it is much more profitable to burn coal in the form of fine powder - coal dust. To obtain it, coal is ground in mills. In the same mills, it is dried. Most modern thermal power plants run on coal dust.
A thermal power plant requires a very large amount of water. Steam boilers must be fed. But most of all water is used to cool the waste steam, to condense it.
Modern large thermal power plants are mostly built on the banks of a river, lake or specially created pond. But not always in the place where the power plant is being built, there is a sufficient amount of water. In this case, they are content with a small reservoir, where the water is artificially “cooled by means of spray pools or cooling towers.
FIG. 4-4. Distribution of losses and useful energy at a steam turbine power plant.
The numbers from 7 to 6 show the losses: 1 - losses in the boiler (went into the ambient air and for heating the boiler room); 2-losses with flue gases; ^ - losses in steam pipelines; 4 - losses in the turbine and for heating the turbine hall; 5 - losses in the generator; 6 - losses with cooling water.
In a condensing power plant, the internal and cooling water losses are 77%. At a combined heat and power plant, part of the heat contained in the selected and waste steam of the turbines is used in industrial enterprises 7 and for household needs 8. The total losses are 65%.
Warm water flows to the spray pools under pressure. A piping system distributes this water between multiple nozzles. Water comes out of them small fountains, is sprayed into fine spray, cooled by the ambient air, and, already cooled, falls into the pool.
Cooling towers are tall, hollow inside the tower. Lattices are located in their lower part along the circumference. Warm water pours down on the grates in a light rain. The air passes through this artificial rain, is heated by the heat of the water, and along with the water vapor enters the central part of the cooling tower. This giant tube creates thrust. Warm air rises up and is thrown out. There are always huge clouds of steam above the cooling towers.
Combined heat and power plants - abbreviated as CHP - are power plants that, in addition to electricity, also give heat to consumers in the form of steam for the technological needs of factories and plants and in the form of hot water, going to heating homes and household needs of the population.
Combined heat and power plants are much more economical than simple or, as they are called, condensing power plants. In the latter, more than half of the heat generated by fuel combustion is carried away with the cooling water. At combined heat and power plants, these losses are much less, since a part of the steam spent in the turbines goes directly to consumers and for heating water for heating and hot water supply of the surrounding area.
So, the most common in our USSR is a thermal power plant operating on coal, burned in the furnaces of steam boilers in a pulverized state. We will visit such a power plant.
Toplavopodana
In order to generate 1 kWh of electricity at a modern power plant, only a few hundred grams of coal are spent, but even an "average" power plant consumes several thousand tons of coal per day.
Here the gates of the power plant were thrown open and, clanking with buffers, another composition of heavy Figs slowly enters. 4-5. technological process of a thermal power plant (fuel supply and boiler room). Lump coal fed in self-unloading cars to the bunkers of the unloading shed 1 through the conveyor system 2 enters the bunkers 3 of the crushing tower and through the magnetic separator 4 and the grate screen 5 - into the crusher 6, where it is crushed to pieces of 10-13 ΛίΛί in size. After the crusher, fine coal is fed through conveyor 2 to conveyors of bunker gallery 7 and through them into raw coal bunkers of boilers 8.
From the bunkers of raw coal by means of a belt feeder 9, combined with a belt weigher, coal enters the ball mill 10, where it is ground and dried with flue gases supplied to the mill through a gas pipeline 11. The mixture of coal dust and gases is sucked out of the mill by a mill fan (exhauster) 12, passes through the mill separator 13, where large dust particles are separated and returned through the dust line 14 back to the mill. Fine dust with gases enters the cyclone 15, where the dust is separated from the gases and poured into the dust bin 16. From the dust cyclone 15, gases are sucked out through the gas pipeline 17 and through the burner 19
Blown into the boiler furnace 20.
In the same flow of gases by means of dust feeders 18, the amount of dust required for a given boiler load is added. The blowing fan 21 takes heated air from the upper part of the boiler room, drives it through the air heater 22, where the air is brought to a temperature of 300 - ^ 50 °, and delivers it in the amount required for complete combustion of the dust through the air ducts 23 to the burners 19. Fire torches leaving the burners have a temperature of about 1,500 ° The incandescent flue gases formed during the combustion of dust give off part of their heat by radiation to the shield tubes 24, are sucked out of the furnace by a smoke exhauster 29 and are thrown into the chimney 31 by it through the hog 30.
On the way from the firebox, gases wash 25 boiling pipes, a superheater 26, a water heater - a water economizer 27 and an air heater 22. The gas temperature drops below 200 °. In the electrostatic precipitators 28, the exhaust gases are cleaned of ash, which is poured together with the slag from the furnace into the hydraulic ash removal channels 12, from which it is carried away by a powerful stream of water.
Water enters the boiler from the machine room through the feed water pipeline 33, passes through the water economizer 27, where it is heated to approximately the boiling point for a given pressure, is fed into the boiler drum 34 and from there fills the entire pipe system. The resulting steam is discharged from the upper part of the boiler balaban through steam pipes 35 to the superheater 26. The superheated steam through the main steam valve 37 through the superheated steam line 36 goes to the turbine hall to the turbines.
four-axle self-unloading nacelles. Everyone is capable! hold up to 60 tons of coal.
The train is fed to the wagon scales, where each gondola is weighed. Weighing of fuel is necessary to maintain accurate accounting of technical and economic performance indicators of the power plant and cash settlements with the railway and supply mines.
After weighing, some of the cars go to the coal warehouse, where they are unloaded to create coal reserves. A warehouse is needed in case of possible disruptions to transport.
The coal storage facilities of the power plant are equipped with powerful loading and unloading mechanisms - gantry cranes, cable cranes, steam or electric self-propelled grab cranes. Downtime of wagons under loading and unloading is minimized.
Depending on the fuel supply conditions, the warehouse stores enough coal to keep the plant running at full load for several days or even weeks.
Another part of the cars, which remained at the car scales, is taken by the station steam locomotive I 1 is fed to a long building - the unloading shed. The large double doors of the unloading shed open, the warning signals light up, the bell rings and the entire train, along with the steam locomotive, enters in for unloading.
Workers turn the locking levers, open the lower side shields of the nacelles, and a black stream of coal pours into large, iron-mesh, large-mesh pits located on either side of the track. These are unloading bins. The powerful electric lamps on the ceiling seem dim from the clouds of dust rising up. The coal was served dry, because there are so many Figs. 4-6. technological process (continuation of Fig. 4-5). thermal power plant (powerhouse and electrical part).
The superheated steam from the boilers through the steam line 1 enters the steam turbine 2, where the thermal energy of the steam is converted into mechanical energy. The turbine rotor rotates the rotor of the generator L connected to it. The steam spent in the turbine enters 4, where it liquefies - condenses, giving up its heat to the circulating water. The steam turned into water - condensate - is pumped out by the condensate pump b and sent to the accumulator tanks 7 and the deaerator b, in which oxygen is removed from the heated water. In the '4 deaerator, in addition to condensate, water is added through pipeline 12 from chemical water treatment to compensate for condensate losses, drainage from collecting drainage tanks 10 is also supplied here by pump 9. Depending on the water consumption of the boiler room, condensate either accumulates in the storage tank or is consumed from it to the deaerator. The release of water from oxygen dissolved in it occurs when passing through the deaerator head 11.
The feed pump / 5 takes water from the deaerator and drives it under pressure through the heater 14, where the water is heated by the selected steam from the turbine and goes through the pressure feed pipe 15 to the boiler room to the boilers. The bleed steam from the turbine, in addition to the heater, is also supplied to the deaerator head.
A powerful circulation pump 16 is pumped through the brass pipes 5 of the condenser cold water ( circulating water). The exhaust steam of the turbine washes these tubes, gives off its heat to the circulating water and condenses. Warm circulating water through the pipeline 17 enters the outlet 18 of the cooling tower, flows from there along the grate 19 in the form of fine rain and, meeting with the air flow going to the tower 20 of the cooling tower, is cooled and from the receiving pool 2 /, already cooled, returns to the intake circulation pump 16.
From the stator of the generator, the generated electricity by cable 22 through the generator disconnectors 23 and the oil switch 24 is diverted to the busbars of the switchgear 27. From the busbars, part of the electricity through auxiliary step-down transformers is sent to power the electric motors of its own consumption and to the lighting of the station. The bulk of the electricity through step-up transformers 26 and oil switches 27 goes along the high-voltage line 28 to the general high-voltage line.
power system network.
dust. But it also happens in a different way. In the autumn and winter time when it rains and snows heavily, the moisture content of the coal increases tremendously. The coal freezes and has to be knocked out of the gondolas with crowbars.
From the unloading bunkers, coal through a belt conveyor system; a ditch, first underground, and then climbing upward through inclined galleries, enters the crushing tower. Here hammer crushers grind it into pieces 10-13 mm in size. From here the coal goes to the raw coal bunkers of the steam boilers. This concludes the economy of the fuel supply workshop.
Steam factory
When you stand downstairs in the boiler room, in the aisle between the boilers, it seems as if you are on a narrow street between tall buildings... Only at home unusual kind, sheathed in black painted steel sheets and surrounded by light steel lattice walkways and ladders. Modern boilers reach the height of a five-story building.
On all sides, the boiler is smooth black sheathing. Only at the very top is a silver dome visible, as if an airship was embedded in the cauldron. This is the boiler drum. The dome of the steel drum is covered with a layer of thermal insulation and painted with aluminum bronze. There is a hatch in the dome so that you can get inside the drum during installation and repair.
In several places on the boiler casing there are small peep-holes. Let's open one of them. The face is immediately bathed in heat, an unbearably bright light strikes the eyes. The peepers go into the boiler furnace, where the fuel is burned. Opposite one of the open burners is a black tube with a glass lens at the end, like half a pair of binoculars. It is an optical pyrometer that measures the temperature in the firebox. A sensitive tube is placed inside the pyrometer tube. The wires from it go to the galvanometer, fixed on the control heat shield of the boiler. The galvanometer scale is graduated in degrees.
The temperature inside the boiler furnace is more than one and a half thousand degrees, and the lining of its walls is only warm. The flame in the furnace is surrounded on all sides by a series of pipes filled with water and connected to the boiler drum. These pipes - a water screen, as they are called - perceive the radiant energy of the incandescent gases of the furnace. Behind the pipes of the screen there is a masonry of refractory bricks... A layer of insulating diatomite bricks with very low thermal conductivity is laid behind a layer of refractory bricks. And behind this brick, directly under the steel cladding panels, another layer of glass wool or asbestos was laid. The pipes leaving the boiler are covered with a thick layer of thermal insulation. All these measures significantly reduce heat loss to the environment.
Inside the firebox
Nearby the boiler has been stopped for repairs. Through the opening in its wall, you can go inside the firebox to a temporary boardwalk made for the duration of the renovation. How gray everything is inside!
All four walls of the furnace are covered with water screen pipes. The pipes are covered with a layer of loose ash and slag. In some places on the side walls of the furnace, the pipes are divorced and gaping black holes are visible - burners through which coal dust is blown into the furnace:
At the bottom, the walls of the firebox narrow in the form of an overturned pyramid, passing into a narrow shaft. This is a slag bunker and a slag mine. Slag formed during the combustion of coal dust falls here. From the slag mines, slag and ash are washed off by a strong stream of water into the ash removal channels or poured into trolleys and transported to ash dumps.
When you stand at the bottom of the furnace, poor lighting initially conceals the height of the furnace space. But this height becomes noticeable if you look at one of the pipes of the water screen from the very bottom to the top.
Below, at the level of the platform, the pipes appear to be as thick as an arm and the gaps between them are clearly distinguishable. At the top, the coarse bends, forming a flat arch. And up there, these pipes seem to be straws laid in even rows. You have to throw your head back to inspect the firebox arch. Involuntarily, the mouth opens and ash is poured into it from above.
During the operation of the boiler, all its water pipes are continuously covered with a layer of carbon deposits, a layer of ash and soot. This impairs the heat transfer from the hot gases to the water in the pipes. During the repair of the boiler, all its water pipes are thoroughly cleaned.
Steam boiler designers adjust the speed of the incandescent gases passing through the tube bundles high enough to reduce the deposition of solids on them. Otherwise, growths like stalactites and stalagmites in caves would have formed.
In addition, during the operation of the boiler, it is supposed from time to time to blow its pipes with a strong jet of compressed air or steam.
The volume of the boiler furnace is more than a thousand cubic meters. It is scary to think what is going on in this huge space during the operation of the boiler, when it is all filled with raging flames and vortices of hot gases.
What is a coal-fired power plant? This is such an enterprise for the production of electricity, where coal (coal, brown) is the first in the energy conversion chain.
Let us recall the energy conversion chain at power plants operating in a cycle.
The first in the chain is fuel, in our case coal. It possesses chemical energy, which, when burned in a boiler, is converted into heat energy from steam. Thermal energy can also be called potential. Further, the potential energy of the steam at the nozzles is converted into kinetic energy. We will call kinetic energy velocity. This kinetic energy at the outlet of the turbine nozzles pushes the rotor blades and rotates the turbine shaft. This is where the mechanical energy of rotation is obtained. The shaft of our turbine is rigidly coupled to the shaft of the electric generator. Already in an electric generator, the mechanical energy of rotation is converted into electrical energy - electricity.
The coal-fired power plant has both advantages and disadvantages in comparison, for example, with a gas-fired one (we will not take into account modern CCGTs as usual).
Benefits of coal-fired power plants:
- low fuel cost;
- comparative independence from fuel supplies (there is a large coal warehouse);
- and ... that's it.
Disadvantages of coal-fired power plants:
- low maneuverability - due to additional restrictions on the output of slag from, if it is with liquid slag removal;
- high emissions compared to gas;
- lower efficiency for the supply of electricity - this adds losses in the boiler and an increase in own electrical needs due to the system of coal pulverization;
- more than at gas stations, the costs are due to the fact that abrasive wear and a greater number of auxiliary installations are added.
From this small comparison, it can be seen that coal-fired power plants lose out to gas-fired ones. Nevertheless, the world does not refuse to build them. This is primarily due to the economic point of view.
Take our country, for example. We have some places on the map where mining in large quantities ah coal. The most famous is Kuzbass (Kuznetsk coal basin), also known as the Kemerovo region. There are quite a few power plants, the largest - and, besides them, there are also several smaller ones. All of them run on coal, with the exception of a few power units, where gas can be used as a backup fuel. In the Kemerovo region there are so many coal-fired power plants due, of course, to the fact that coal is mined "close by." There is practically no transport component in the price of coal for power plants. In addition, some owners of thermal power plants are also owners of coal enterprises. It seems clear why gas stations are not being built there.
In addition, the proven reserves of coal are incomparably greater than the proven reserves of natural gas. This already applies to the country's energy security.
V developed countries stepped further. So-called synthetic gas, an artificial analogue of natural gas, is made from coal. Some have already adapted to this gas, which can work as part of a CCGT unit. And here there are already completely different efficiency factors (higher) and harmful emissions (lower), in comparison with coal stations, and even with old gas stations.
So we can conclude that coal, as a fuel for the production of electricity, humanity will always use.
Since 2000, the world's coal-fired generating capacity has doubled to 2,000 GW as a result of the explosive growth of investment projects in China and India. Another 200 GW is under construction and 450 GW is planned worldwide. In recent decades, coal-fired power plants have produced 40-41% of the world's electricity - the largest share in comparison with other types of generation. At the same time, the peak in electricity generation from coal was reached in 2014, and now the ninth wave of reducing the load of operating TPPs and their closure has begun. More about this in our Carbon Brief review.
Since 2000, the world's coal-fired generating capacity has doubled to 2,000 GW as a result of the explosive growth of investment projects in China and India. Another 200 GW is under construction and 450 GW is planned worldwide. There are 77 countries in the coal generators club, 13 more plan to join it by 2030.
In recent decades, coal-fired power plants have produced 40-41% of the world's electricity - the largest share in comparison with other types of generation.
At the same time, the peak in electricity generation from coal was reached in 2014, and now the ninth wave of reducing the load of operating TPPs and their closure has begun. Over the years, the EU and the US have closed 200 GW, another 170 GW must be shut down by 2030. As of April 9, 2018, 27 countries have joined the Coal Phase-Out Alliance, of which 13 have operating power plants.
Note that from 2010 to 2017, only 34% of the planned coal capacity was built or put into construction (873 GW), while 1,700 GW was canceled or postponed, reports CoalSwarm. For example, a tender for the construction of one new station can attract several applications, each of which will be counted in the "planned capacity".
According to the International Energy Agency (IEA), all untreated coal plants should shut down within a few decades if warming is to be limited to less than 2C above pre-industrial temperatures. To shed light on this story, Carbon Brief has mapped the past, present and future of all coal-fired power plants in the world as of February 2018. (https://www.carbonbrief.org/mapped-worlds-coal-power-plants), which shows all coal-fired TPPs over 30 MW each, operating in the period 2000-2017, as well as the location of the planned. The map includes about 10,000 closed, operating and planned coal plants with a total capacity of 4,567 GW, of which 1,996 GW is in operation today, 210 GW is under construction, 443 GW is planned, 2,387 GW are being discontinued and 1,681 GW were proposed to be built, but then canceled since 2010 in 95 countries of the world. There are also about 27 GW of small coal-fired thermal power plants in the world - up to 30 MW each.
Increase in coal capacity
Coal generation is primarily about the promise of cheap electricity to spur economic growth. Global coal-fired generation capacity grew annually between 2000 and 2017, almost doubling from 1.063 GW to 1.995 GW. Coal produces 40-41% of the world's electricity, the largest share in recent decades. Today coal energy is used by 77 countries of the world compared to 65 in 2000. Another 13 plan to join the coal energy club.
CO2 emissions from existing plants are enough to break the carbon budget by 1.5 or 2 degrees Celsius. According to the study, these restrictions would mean no new coal-fired power plants and the early closure of 20% of the coal-fired fleet. All raw coal power plants will have to close by 2040 to keep the world “well below” 2 degrees Celsius growth, according to the IEA. This would mean shutting down 100 GW of coal capacity every year for 20 years, or roughly one coal block every day until 2040.
However, newspaper headlines and energy forecasts suggest coal growth will not stop. These grim prospects for a worsening climate are tempered by signs of rapid changes in the energy sector. The conveyor belt for coal blocks under construction or planned has been halved since 2015. The pace of TPP closings is accelerating, reaching a cumulative level of 197 GW between 2010 and 2017.
Slowdown in coal growth
IEA believes that investment peak to the world coal energy has already passed and the industry has entered a phase of "dramatic slowdown". The IEA report says that China, which provides most current growth, no longer needs new TPPs.
A failure in investment means that growth in coal capacity is slowing. And if in 2011 82 GW was commissioned in the world, then in 2017 - only 34 GW.
The number of new stations under construction is declining faster every year, down 73% since 2015, according to the latest annual report from CoalSwarm, Greenpeace and Sierra Club. China is shutting down many hundreds of smaller, older and less efficient facilities, replacing them with larger and more efficient ones. All this means that global power coal generation may peak as early as 2022, said in a report on the state of the IEA industry.
Peak CO2 emissions
IEA data show that CO2 emissions from coal energy, perhaps already peaked in 2014 ., despite the fact that the coal capacity continues to grow. Coal CO2 emissions fell 3.9% between 2014-2016, coal production fell 4.3%.
As the capacity of coal continues to increase, existing coal-fired power plants run for fewer hours. On average, global coal-fired power plants were in operation for about half the time in 2016, with a utilization rate of 52.5%. A similar trend is observed in the US (52%), the EU (46%), China (49%) and India (60%).
A number of other factors also influence the relationship between coal-fired power plants and CO2 emissions. These include the type of coal and combustion technologies used by each plant. Thermal power plants burning low-quality lignite can emit up to 1200 tons of CO2 per GWh of electricity generated. High quality coal emits fewer emissions.
Combustion technology is also important, from less efficient "subcritical" installations to ultra-supercritical systems that increase the efficiency of the boiler at higher pressures. The oldest and least efficient subcritical units operate at 35% efficiency. New technologies raise this indicator up to 40%, and ultra-supercritical up to 45% (HELE).
However, according to the World Coal Association, even HELE coal blocks emit around 800tCO2 / GWh. This is about twice the emissions of a gas power plant and about 50-100 times higher than nuclear, wind and solar. The IEA sees no further prospect for coal-fired power in pre-2C scenarios as residual emissions are too high, even with carbon capture and storage.
There was a small spike in coal production and CO2 emissions in 2017, driven by increased production in China, although these remain below the 2014 peak.
Erosion of the coal economy
The low level of utilization of power plants (CCI) is "corrosive" for the economy of coal-fired TPPs. In general, they are designed to operate at least 80% of the time, as they have relatively high fixed costs. This is also the basis for the cost estimate for the construction of the new coal block, while lower utilization increases the cost per unit of electricity. The downward trend in CCI is particularly toxic for coal-fired power plant operators, competing with rapidly falling renewable energy prices, cheap gas in the US and soaring coal prices in the EU. Coal supply restrictions are driving up coal prices, further undermining any remaining benefits over alternatives.
New environmental regulations are driving up the cost of coal-fired power plants in many jurisdictions from the EU to India and Indonesia. Coal plant owners must invest in sewage treatment plant to meet higher environmental standards, or to close their dirty thermal power plants altogether. This combination of factors means that most stations in the existing coal fleet in the EU and even India are facing serious economic problems, according to the Financial thinktank Carbon Tracker. It was found that by 2030, for example, almost all coal-fired power plants in the EU will be unprofitable. Bloomberg New Energy Finance founder Michael Libreich says coal is facing two "tipping points." The first is when new renewable energy becomes cheaper than new coal-fired power plants, which has already happened in several regions. Second, when new renewable energy sources are cheaper than existing coal-fired power plants.
note that coal-fired power plants can continue to operate in unfavorable economic conditions, for example, with a surcharge for power. This practice was introduced by a number of EU countries in 2018.
In 2018, China, Vietnam and Thailand completely canceled the solar surcharge. The Philippines and Indonesia have significantly reduced it. And in India, solar generation is already cheaper than coal. That is, in conditions of real competition, coal generation in countries Southeast Asia is already losing out to RES and will develop more slowly than planned.
Key countries and regions
77 countries use coal to generate electricity, up from 65 in 2000. Since then, 13 countries have built coal facilities and just one country - Belgium - has closed them. Another 13 countries, which account for 3% of current capacity, have pledged to phase out coal by 2030 under the Coal Left of the Past Alliance, led by the UK and Canada. Meanwhile, 13 countries still hope to join the coal energy club.
Top 10 the countries of the world shown on the left side of the table below account for 86% of the total number of coal-fired power plants in operation. On the right in the Table - Top 10 countries planning to build 64% of the world's coal-fired capacity.
Country / operating MW / share in the world Country / MW under construction / share
China 935.472 47% China 210.903 32%
USA 278.823 14% India 131.359 20%
India 214.910 11% Vietnam 46.425 7%
Germany 50,400 3% Turkey 42,890 7%
Russia 48.690 2% Indonesia 34.405 5%
Japan 44.578 2% Bangladesh 21.998 3%
South Africa 41.307 2% Japan 18.575 3%
South Korea 37,973 2% Egypt 14,640 2%
Poland 29.401 1% Pakistan 12.385 2%
Indonesia 28,584 1% Philippines 12,141 2%
China has the largest operating coal-fired fleet and is home to the largest pipeline of 97 GW under construction in a 250 km radius along the Yangtze River Delta around Shanghai. This is more than already exists in any country with the exception of India and the United States. Russia has the fifth largest coal-fired fleet in the world, accounting for only 2% of the world's generating capacity.
China
Over the past 20 years, the most significant changes have taken place in China. Its coal-fired fleet grew fivefold between 2000 and 2017. and reached 935 GW, or almost half of the world's capacity.
China is also the world's largest emitter of CO2 and uses half of the world's coal, so its future path is disproportionately important to the global effort to combat climate change.
Industrial activity and the use of coal were stimulated prior to the appointment of Chairman Xi as a "leader for life." This energy policy could push CO2 emissions to the fastest pace in years.
However, some analysts say China's coal use could be cut in half by 2030. The government is introducing a national emissions trading scheme, and is closing and restricting new coal-fired power in response to air pollution and climate concerns. This means that the conveyor belt of coal-fired thermal power plants under construction or planned in 2017 decreased by 70% by 2016, CoalSwarm reports.
It also means the planned projects are unlikely to get the permits they need to build them, says Lauri Millivirta, an energy analyst at Greenpeace in East Asia. “Many of the planned projects in China and India are virtually dead. In India they are commercially illiquid, no one in their right mind is going to build them ... in China it makes no sense, because there is already too much capacity, a surplus. " According to the United States Energy Information Administration (EIA), power and coal production in China are more or less at their peak.
India
The second largest increase in capacity since 2000 occurred in India, where the coal-fired power fleet more than tripled to 215 GW. Recently, the state of the Indian coal generation has deteriorated sharply. IEA cut its forecast for demand for Indian coal due to a slowdown in the growth of demand for electricity and a reduction in the cost of renewable energy sources. Some 10 GW plants are deemed "unsustainable," others 30 GW are under "stress," according to the Indian Energy Minister in an interview with Bloomberg in May 2018. This is because "India's renewable energy revolution is pushing coal off the debt cliff." Matthew Gray, Analyst at Carbon Tracker.
India's latest national electricity plan targets the disposal of 48 GW of coal-fired power plants, in part due to new environmental standards. It also provides for the commissioning of 94 GW of new capacities, but this figure is considered unrealistic by key analysts of the world. The country has planned the commissioning of 44 GW projects, of which 17 GW have been suspended for many years. " In India, renewables can already supply energy at a lower cost than new and even most existing coal-fired power plants. "Says Lauri Millivirta, energy analyst at Greenpeace East Asia.
USA
The wave of disposal of old capacity has cut US coal generation by 61 GW in six years, and another 58 GW is planned to be closed, Coal Swarm notes. This will reduce the US coal fleet by two-fifths, from 327 GW in 2000 to 220 GW in the future or below.
One way to save the industry is through the Trump administration's announced plans to rescue unprofitable coal-fired power plants for reasons national security to maintain system reliability through capacity surcharges, Bloomberg describes them as "unprecedented intervention in the US energy markets."
On the other hand, market conditions currently favor gas-fired power plants and renewable energy sources. There are no new coal facilities in the United States. It is expected that the decommissioning of coal capacities in 2018 will amount to 18 GW. Last year, coal consumption in the U.S. power sector was the lowest since 1982.
European Union
Given the EU's plans to phase out coal, the union's coal-fired fleet should be reduced to 100 GW by 2030, or half of its total capacity in 2000. Along with Canada, EU countries lead the Alliance to phase out coal. Great Britain, France, Italy, the Netherlands, Portugal, Austria, Ireland, Denmark, Sweden and Finland have announced the phase-out of coal-fired power plants by 2030. Their capacity is 42 GW, including recently built power plants.
At the same time, the fourth and ninth largest national coal generating fleet in the world is located in member states EU, namely 50 GW in Germany and 29 GW in Poland. An EU commission to set a cut-off date for coal-based electricity supplies for Germany has begun to work, although the country's grid operator says only half of its coal fleet could be closed by 2030 without compromising energy security. Poland simply promised that it would not build new coal-fired thermal power plants beyond what is already being built.
IEA studies have shown that all EU coal-fired power plants must close by 2030 in order to meet the goals of the Paris Agreement. Rising CO2 prices are expected to lead to a shift from coal to gas this year, subject to suitable prices and gas availability.
Other key countries
Other Asian countries including South Korea, Japan, Vietnam, Indonesia, Bangladesh, Pakistan and the Philippines have collectively doubled their coal generating fleet since 2000, reaching 185 GW in 2017. In total, these countries will build 50 GW of new thermal power plants on their own, and an additional 128 GW are planned through funding and participation in the construction of China, Japan and South Korea.
In many of these countries, there are mixed signs of coal use. For example, the latest draft of Japan's National Energy Plan takes into account the significant role of coal in 2030, while the Paris Agreement means that Tokyo should phase out coal by then, Climate Analytics notes.
Vietnam is the third country in terms of the planned volume of coal generation - 46 GW, of which 11 GW is already under construction. “Nonetheless, the government is increasingly investing in changing this trajectory,” writes Alex Perera, deputy director of energy at The World Resources Institute. “Vietnam provides an interesting and important combination of conditions that will enable the transition to clean energy: renewable energy and the private sector striving to meet increasingly stringent clean energy targets. "
The Indonesian government has banned the construction of new coal plants on the most populous island of Java. The state utility company has been criticized for “massively overestimating the growth in electricity demand” in order to justify plans to commission new coal-fired power plants.
Turkey has significant plans to expand its coal fleet. However, currently only 1 GW is being built from the planned 43 GW pipeline.
Another country with big plans is Egypt, which has neither coal stations nor coal deposits of its own. Please note that none of the 15 GW planned new capacity went beyond the early stage approvals, has not received any permits and is not being built.
South Africa has large coal deposits and the seventh largest coal power fleet in the world. South Africa is building 6 GW of new thermal power plants and plans to introduce another 6 GW. However, following the election of Kirill Ramaphosa earlier this year, political sentiment in the country is changing, and long-term deals for the construction of renewable energy sources worth $ 4.7 billion were signed in April. ... The reason is that new coal stations will be more expensive than RES, experts say. Legislative discussions over the role of coal in South Africa's new energy investment plan will take place later this summer.
March 23rd, 2013
Once, when we drove into the glorious city of Cheboksary, with east direction my wife noticed two huge towers along the highway. "And what is it?" she asked. Since I absolutely didn’t want to show my wife my ignorance, I rummaged a little in my memory and gave out a victorious one: “This is a cooling tower, don’t you know?”. She was a little embarrassed: "What are they for?" "Well, something to cool there, it seems." "And what?". Then I was embarrassed, because I absolutely did not know how to get out further.
Maybe this question has remained forever unanswered in memory, but miracles do happen. A few months after this incident, I see a post in my friend feed z_alexey about the recruitment of bloggers wishing to visit the Cheboksary CHPP-2, the same one that we saw from the road. You have to drastically change all your plans, it will be unforgivable to miss such a chance!
So what is a CHP?
This is the heart of the CHP plant, and this is where the main action takes place. The gas that enters the boiler burns out, releasing a crazy amount of energy. "Pure Water" is also served here. After heating, it turns into steam, more precisely into superheated steam, which has an outlet temperature of 560 degrees and a pressure of 140 atmospheres. We will also call it "Pure Steam" because it is formed from prepared water.
In addition to steam, we also have an exhaust outlet. At maximum capacity, all five boilers consume almost 60 cubic meters of natural gas per second! To remove the combustion products, a non-childish "chimney" is needed. And this is also available.
The pipe can be seen from almost any area of the city, given the height of 250 meters. I suspect that this is the tallest building in Cheboksary.
There is a slightly smaller pipe nearby. Reserve again.
If a CHP plant is fired with coal, additional exhaust treatment is required. But in our case, this is not required, since natural gas is used as a fuel.
In the second section of the boiler and turbine shop, there are power generating units.
There are four of them installed in the engine room of Cheboksary CHPP-2, with a total capacity of 460 MW (megawatt). This is where the superheated steam from the boiler room is fed. He, under enormous pressure, is sent to the turbine blades, forcing a thirty-ton rotor to rotate at a speed of 3000 rpm.
The installation consists of two parts: the turbine itself, and a generator that generates electricity.
And here is what the turbine rotor looks like.
Gauges and gauges are everywhere.
Both turbines and boilers, in case emergency can be stopped instantly. For this, there are special valves that can shut off the supply of steam or fuel in a fraction of a second.
I wonder if there is such a thing as an industrial landscape, or an industrial portrait? There is beauty here.
There is a terrible noise in the room, and in order to hear a neighbor, you have to strain your hearing. Plus it's very hot. I would like to take off my helmet and undress to a T-shirt, but this cannot be done. For safety reasons, clothes with short sleeves are prohibited at the CHP, there are too many hot pipes.
Most of the time, the workshop is empty, people show up here once every two hours, during a round. And the equipment operation is controlled from the main control board (group control panels for boilers and turbines).
This is what the duty officer's workplace looks like.
There are hundreds of buttons around.
And dozens of sensors.
There are mechanical, there are electronic.
This is our excursion, and people are working.
In total, after the boiler and turbine shop, at the output we have electricity and steam that has partially cooled down and has lost some of its pressure. Electricity seems to be easier. The output voltage from different generators can be from 10 to 18 kV (kilovolts). With the help of block transformers, it rises to 110 kV, and then electricity can be transmitted over long distances using power lines (power lines).
It is unprofitable to let the remaining "pure steam" go to the side. Since it is formed from " Clean water", the production of which is a rather complicated and costly process, it is more expedient to cool it and return it back to the boiler. So in a closed circle. But with its help, and with the help of heat exchangers, you can heat water or produce secondary steam, which can be easily sold to third-party consumers.
In general, it is in this way that we receive heat and electricity into our homes, having the usual comfort and coziness.
Oh yes. And what are cooling towers for?
It turns out everything is very simple. To cool the remaining "Pure steam", before the new supply to the boiler, all the same heat exchangers are used. It is cooled with the help of industrial water, at CHPP-2 it is taken directly from the Volga. It does not require any special training and can also be reused. After passing through the heat exchanger, the process water is heated and goes to the cooling towers. There it flows down in a thin film or falls down in the form of drops and is cooled due to the counterflow of air created by the fans. And in ejection cooling towers, water is sprayed using special nozzles. In any case, the main cooling occurs due to the evaporation of a small part of the water. The cooled water leaves the cooling towers through a special channel, after which, with the help of a pumping station, it is sent for reuse.
In a word, cooling towers are needed to cool the water that cools the steam operating in the boiler-turbine system.
All the work of the CHPP is controlled from the Main Control Board.
There is a duty officer at all times.
All events are logged.
Don't feed me bread, let me take a picture of the buttons and sensors ...
On this, almost everything. In conclusion, there are few photos of the station.
This is an old, no longer working pipe. Most likely it will be demolished soon.
There is a lot of agitation at the enterprise.
Here they are proud of their employees.
And their achievements.
It seems that it is not in vain ...
It remains to add that, as in a joke - "I don't know who these bloggers are, but their guide is the director of the branch in Mari El and Chuvashia of TGK-5 OJSC, IES holding - SV Dobrov."
Together with the station director S.D. Stolyarov.
Without exaggeration, they are real professionals in their field.
And of course, many thanks to Irina Romanova, who represents the press service of the company, for a well-organized tour.
In 1879, when Thomas Alva Edisoninvented the incandescent lamp, the era of electrification began. The production of large quantities of electricity required cheap and readily available fuel. Coal met these requirements, and the first power plants (built at the end of the 19th century by Edison himself) operated on coal.
As more and more stations were built in the country, the dependence on coal increased. Since World War I, roughly half of the US's annual electricity production has come from coal-fired power plants. In 1986, the total installed capacity of such power plants was 289,000 MW, and they consumed 75% of the total amount (900 million tons) of coal mined in the country. Given the existing uncertainties regarding the prospects for the development of nuclear energy and the growth of oil and natural gas production, it can be assumed that by the end of the century, coal-fired thermal power plants will produce up to 70% of all electricity generated in the country.
However, despite the fact that coal has long been and will be the main source of electricity for many years (in the United States, it accounts for about 80% of the reserves of all types of natural fuels), it has never been the optimal fuel for power plants. Specific energy content per unit weight (i.e. calorific value) for coal is lower than for oil or natural gas. It is more difficult to transport and, in addition, burning coal causes a number of undesirable environmental consequences, in particular, acid rain. Since the end of the 60s, the attractiveness of coal-fired power plants has sharply declined due to the tightening of requirements for environmental pollution with gaseous and solid emissions in the form of ash and slag. The costs of solving these environmental problems, along with the increasing cost of building complex facilities such as thermal power plants, have made their development prospects less favorable from a purely economic point of view.
However, if you change technological base coal-fired thermal power plants, their former attractiveness may be revived. Some of these changes are evolutionary in nature and are aimed primarily at increasing the capacity of existing installations. At the same time, completely new processes of waste-free combustion of coal are being developed, i.e. with minimal damage to the environment. The introduction of new technological processes is aimed at ensuring that future coal-fired thermal power plants can be effectively controlled for the degree of environmental pollution by them, and have flexibility in terms of their use. different types coal and did not require a long construction time.
In order to appreciate the significance of advances in coal combustion technology, consider briefly the operation of a conventional coal-fired thermal power plant. Coal is burned in the furnace of a steam boiler, which is a huge chamber with pipes inside, in which water turns into steam. Before being fed into the furnace, the coal is crushed into dust, due to which almost the same completeness of combustion is achieved as when burning flammable gases. A large steam boiler consumes an average of 500 tons of pulverized coal per hour and generates 2.9 million kg of steam, which is enough to generate 1 million kWh of electricity. During the same time, the boiler emits about 100,000 m3 of gases into the atmosphere.
The generated steam passes through a superheater, where its temperature and pressure are increased, and then enters a high-pressure turbine. The mechanical energy of the turbine rotation is converted by an electric generator into electrical energy. In order to obtain higher energy conversion efficiency, steam from the turbine is usually returned to the boiler for reheating and then drives one or two low pressure turbines before being condensed by cooling; condensate is returned to the boiler cycle.
Thermal power plant equipment includes fuel feeding mechanisms, boilers, turbines, generators, as well as complex cooling systems, flue gas cleaning and ash removal. All of these primary and secondary systems are designed to operate reliably for 40 years or more at loads that can range from 20% of the plant's installed capacity to maximum. The capital cost of equipment for a typical 1,000 MW thermal power plant is typically in excess of $ 1 billion.
The efficiency with which the heat released by burning coal can be converted into electricity was only 5% before 1900, but by 1967 it had reached 40%. In other words, over a period of about 70 years, the specific consumption of coal per unit of generated electricity has decreased eightfold. Accordingly, the cost of 1 kW of installed capacity of thermal power plants also decreased: if in 1920 it was $ 350 (in 1967 prices), then in 1967 it dropped to $ 130. The price of electricity supplied also fell over the same period from 25 cents to 2 cents per kWh.
However, starting in the 1960s, the pace of progress began to decline. This trend, apparently, is explained by the fact that traditional thermal power plants have reached the limit of their perfection, determined by the laws of thermodynamics and the properties of materials from which boilers and turbines are made. Since the early 1970s, these technical factors have been exacerbated by new economic and organizational reasons. In particular, capital expenditures have sharply increased, the rate of growth in demand for electricity has slowed down, requirements for environmental protection from harmful emissions have become more stringent, and the timeframes for the implementation of power plant construction projects have been lengthened. As a result, the cost of generating electricity from coal, which had a long-term downward trend, has risen sharply. Indeed, 1 kW of electricity generated by new thermal power plants now costs more than in 1920 (in comparable prices).
Over the past 20 years, the cost of coal-fired power plants has been most influenced by stricter requirements for the removal of gaseous,
liquid and solid waste. Gas cleaning and ash handling systems in modern thermal power plants now account for 40% of capital costs and 35% of operating costs. From a technical and economic point of view, the most significant element of an emission control system is a flue gas de-sulphurization plant, often referred to as a wet (scrubber) dust collection system. A wet dust collector (scrubber) traps sulfur oxides, which are the main pollutants formed during coal combustion.
The idea of wet dust collection is simple, but in practice it turns out to be difficult and expensive. An alkaline substance, usually lime or limestone, is mixed with water and the solution is sprayed into the flue gas stream. Contained in flue gases sulfur oxides are absorbed by alkali particles and fall out of solution in the form of inert sulphite or calcium sulphate (gypsum). Gypsum can be easily removed or, if clean enough, can be marketed as construction material... In more complex and expensive scrubber systems, gypsum sludge can be converted to sulfuric acid or elemental sulfur - more valuable chemical products... Since 1978, the installation of scrubbers has been mandatory at all pulverized coal-fired thermal power plants under construction. As a result, the US energy industry now has more scrubber units than the rest of the world.
The cost of a scrubber system at new plants is usually $ 150-200 per 1 kW of installed capacity. The installation of scrubbers at existing plants, originally designed without wet gas cleaning, is 10-40% more expensive than at new plants. The running costs of scrubbers are quite high whether they are installed in old or new plants. Scrubbers generate a huge amount of gypsum sludge, which must be kept in sedimentation ponds or dumped, which creates a new environmental problem. For example, a 1000 MW thermal power plant operating on coal containing 3% sulfur produces so much sludge per year that they can cover an area of 1 km2 with a layer about 1 m thick.
In addition, wet gas cleaning systems consume a lot of water (at a 1000 MW plant, water consumption is about 3800 l / min), and their equipment and pipelines are often prone to clogging and corrosion. These factors increase operating costs and reduce overall system reliability. Finally, in scrubber systems, from 3 to 8% of the energy generated by the station is consumed for driving pumps and smoke exhausters and for heating flue gases after gas cleaning, which is necessary to prevent condensation and corrosion in chimneys.
The widespread adoption of scrubbers in the American power industry has not been simple or cheap. The first scrubber installations were significantly less reliable than the rest of the station equipment, therefore the components of the scrubber systems were designed with a large margin of safety and reliability. Some of the difficulties associated with the installation and operation of scrubbers can be attributed to the fact that industrial application of scrubber technology was prematurely started. Only now, after 25 years of experience, has the reliability of scrubber systems reached an acceptable level.
The cost of coal-fired power plants has risen, not only because of the mandatory presence of emission control systems, but also because the cost of construction itself has skyrocketed. Even taking inflation into account, the unit cost of installed capacity of coal-fired thermal power plants is now three times higher than in 1970. Over the past 15 years, the "economies of scale", that is, the benefits from the construction of large power plants, have been offset by a significant increase in the cost of construction ... This rise in price partly reflects the high cost of financing long-term capital construction projects.
The impact of the delay in project implementation can be seen in the example of Japanese energy companies. Japanese firms are usually more agile than their American counterparts in dealing with the organizational, technical and financial problems that often delay the commissioning of large construction projects. In Japan, a power plant can be built and commissioned in 30-40 months, while in the United States, a plant of the same capacity usually takes 50-60 months. With such long project implementation times, the cost of a new plant under construction (and, therefore, the cost of frozen capital) is comparable to the fixed capital of many US energy companies.
Therefore, energy companies are looking for ways to reduce the cost of building new power generation plants, in particular by using modular units of lower capacity, which can be quickly transported and installed in an existing plant to meet growing demand. Such installations can be put into operation in more short time and therefore pay off faster, even if the ROI remains constant. Installing new modules only when an increase in system capacity is required can result in net savings of up to $ 200 per kW, although economies of scale are lost with smaller units.
As an alternative to building new power generating facilities, utilities have also practiced retrofitting existing old power plants to improve their performance and extend their service life. This strategy naturally requires less capital expenditures than building new stations. This trend is justified also because the power plants built about 30 years ago are not yet morally obsolete. In some cases, they work even with higher efficiency, since they are not equipped with scrubbers. Old power plants are gaining an increasing share in the country's energy sector. In 1970, only 20 electricity generating facilities in the United States were over 30 years old. By the end of the century, 30 years will be the average age of coal-fired thermal power plants.
Utilities are also looking for ways to reduce plant operating costs. To prevent energy loss, it is necessary to ensure timely warning the deterioration of the performance of the most important areas of the object. Therefore, continuous monitoring of the state of components and systems is becoming an important part of the operational service. Such continuous monitoring of natural processes of wear, corrosion and erosion allows plant operators to take timely measures and prevent emergency failure of power plants. The significance of such measures can be correctly assessed if we consider, for example, that the forced shutdown of a 1000 MW coal-fired plant could bring the energy company losses of $ 1 million per day, mainly because the unreported energy must be compensated for by supplying electricity from more expensive sources.
The rise in the unit costs of transporting and processing coal and of ash removal has made the quality of coal (determined by moisture, sulfur and other minerals) an important factor in determining the performance and economics of thermal power plants. Although low-grade coal can cost less than high-grade coal, its consumption for the production of the same amount of electricity is much higher. The cost of transporting more low-grade coal may offset the benefit of its lower price. In addition, low-grade coal usually generates more waste than high-grade coal, and therefore requires high ash removal costs. Finally, the composition of low-grade coals is subject to large fluctuations, which makes it difficult to "tune" the station's fuel system to work with the maximum possible efficiency; in this case, the system must be adjusted so that it can operate at the worst grade expected.
In existing power plants, the quality of the coal can be improved or at least stabilized by removing some impurities, such as sulfur-containing minerals, before combustion. In treatment plants, crushed "dirty" coal is separated from impurities in many ways, taking advantage of differences in specific gravity or other physical characteristics of the coal and impurities.
Despite these efforts to improve the performance of existing coal-fired power plants, an additional 150,000 MW of power capacity will need to be operational in the United States by the end of the century if electricity demand grows at the expected rate of 2.3% per year. To maintain the competitiveness of coal in the ever-expanding energy market, energy companies will have to adopt new progressive coal combustion methods that are more efficient than traditional ones in three key aspects: less pollution of the environment, shortening the construction time of power plants and improving their performance and operational characteristics.
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| BURNING COAL IN A LIQUID LAYER reduces the need for ancillary emission treatment plants from the power plant. A fluidized bed of a mixture of coal and limestone is created in the boiler furnace by an air flow, in which solid particles are mixed and are in suspension, that is, they behave in the same way as in a boiling liquid. Turbulent mixing ensures complete combustion of coal; in this case, limestone particles react with sulfur oxides and trap about 90% of these oxides. Since the heating coils of the boiler directly touch the fluidized bed of fuel, the generation of steam is more efficient than in conventional steam boilers working on crushed coal. In addition, the temperature of the burning coal in the fluidized bed is lower, which prevents melting boiler slag and reducing the formation of nitrogen oxides. |
COAL GASIFICATION can be carried out by heating a mixture of coal and water in an oxygen atmosphere. The product of the process is a gas consisting mainly of carbon monoxide and hydrogen. Once the gas has been cooled, de-soldered and freed from sulfur, it can be used as fuel for gas turbines and then to produce steam for a steam turbine (combined cycle). The combined cycle plant emits less pollutants into the atmosphere than a conventional coal-fired thermal plant. |
Currently, more than a dozen methods of coal combustion with increased efficiency and less damage to the environment are being developed. The most promising among them are fluidized bed combustion and coal gasification. Combustion according to the first method is carried out in the furnace of a steam boiler, which is arranged in such a way that crushed coal mixed with limestone particles is maintained above the grate of the furnace in a suspended ("pseudo-liquefied") state by a powerful ascending air flow. Suspended particles behave essentially the same way as in a boiling liquid, that is, they are in turbulent motion, which ensures a high efficiency of the combustion process. The water pipes of such a boiler are in direct contact with the "fluidized bed" of burning fuel, as a result of which a large proportion of heat is transferred by thermal conductivity, which is much more efficient than radiative and convective heat transfer in a conventional steam boiler.
A boiler with a firebox, where coal is fired in a fluidized bed, has a larger area of heat transfer pipe surfaces than a conventional boiler that runs on pulverized coal, which allows to reduce the temperature in the furnace and thereby reduce the formation of nitrogen oxides. (If the temperature in a conventional boiler can be higher than 1650 ° C, then in a boiler with combustion in a fluidized bed it is in the range of 780-870 ° C.) Moreover, limestone mixed with coal binds 90 or more percent of the sulfur released from coal during combustion, since the lower working temperature promotes the reaction between sulfur and limestone with the formation of sulfite or calcium sulfate. Thus, substances harmful to the environment, formed during the combustion of coal, are neutralized at the place of formation, i.e. in the furnace.
In addition, a fluidized bed boiler is less sensitive to fluctuations in coal quality in terms of its design and operating principle. In the furnace of a conventional pulverized coal boiler, a huge amount of molten slag is formed, which often clogs the heat transfer surfaces and thereby reduces the efficiency and reliability of the boiler. In a fluidized bed boiler, coal is burned at a temperature below the melting point of the slag, and therefore the problem of clogging the heating surfaces with slag does not even arise. Such boilers can operate on lower quality coal, which in some cases can significantly reduce operating costs.
The fluidized bed combustion method is easily implemented in modular boilers with low steam output. According to some estimates, the capital investment for a thermal power plant with compact boilers operating on the principle of a fluidized bed can be 10-20% lower than the capital investment for thermal station traditional type the same power. Savings are achieved by reducing construction time. In addition, the capacity of such a station can be easily increased with an increase in the electrical load, which is important for those cases when its growth in the future is not known in advance. The planning problem is also simplified, since such compact units can be quickly assembled as soon as the need arises to increase power generation.
Fluidized bed boilers can also be incorporated into existing power plants when generating capacity needs to be rapidly increased. For example, the energy company Northern States Power converted one of the pulverized coal boilers at the station in pcs. Minnesota in a fluidized bed boiler. The alteration was carried out in order to increase the power of the power plant by 40%, reduce the requirements for the quality of fuel (the boiler can even operate on local waste), more thorough cleaning of emissions and lengthen the service life of the station up to 40 years.
Over the past 15 years, the technology used in thermal power plants equipped exclusively with fluidized bed boilers has expanded from small pilot and pilot plants to large "demonstration" plants. Such a plant with a total capacity of 160 MW is being built jointly by Tennessee Valley Authority, Duke Power and Commonwealth of Kentucky; Colorado-Ute Electric Association, Inc. commissioned a 110 MW power generating unit with fluidized bed boilers. If these two projects are successful, and that of Northern States Power, a private sector joint venture with a combined capital of about $ 400 million, the economic risk associated with the use of fluidized bed boilers in the power industry will be significantly reduced.
In another way, which, however, already existed in a simpler form back in mid XIX in., is the gasification of coal with the receipt of "clean burning" gas. Such gas is suitable for lighting and heating and was widely used in the United States until World War II, when it was replaced by natural gas.
Initially, coal gasification attracted the attention of energy companies, who hoped to use this method to obtain fuel that burns without waste and thereby eliminate scrubbing. It has now become apparent that coal gasification has an even more important advantage: the hot combustion products of the generator gas can be directly used to drive gas turbines. In turn, the waste heat of the combustion products after the gas turbine can be utilized in order to obtain steam for driving a steam turbine. This combined use of gas and steam turbines, called a combined cycle, is now one of the most effective ways production of electrical energy.
The gas obtained by gasification of coal and freed from sulfur and particulate matter is an excellent fuel for gas turbines and, like natural gas, burns with almost no waste. The high efficiency of the combined cycle compensates for the inevitable losses associated with the conversion of coal to gas. Moreover, the combined cycle station consumes significantly less water, since two-thirds of the power is developed by a gas turbine, which does not need water, unlike a steam turbine.
The viability of coal gasification combined cycle power plants has been proven by the Southern California Edison Cool Water plant. This station with a capacity of about 100 MW was put into operation in May 1984. It can operate on different types of coal. The emissions from the station are no different from those of the neighboring natural gas station in terms of purity. The content of sulfur oxides in the exhaust gases is maintained at a level significantly lower the established norm with an auxiliary sulfur recovery system that removes almost all of the sulfur in the feed fuel and produces pure sulfur for industrial purposes. The formation of nitrogen oxides is prevented by the addition of water to the gas before combustion, which lowers the combustion temperature of the gas. Moreover, the remaining unburned coal in the gasifier is remelted and converted into an inert vitreous material that, after cooling, meets the California solid waste requirements.
In addition to the higher efficiency and lower environmental pollution, combined cycle plants have another advantage: they can be built in several stages, so that the installed capacity is increased in blocks. This flexibility in construction reduces the risk of over- or under-investment associated with the uncertainty of growth in electricity demand. For example, the first stage of the installed capacity can operate on gas turbines, and not coal, but oil or natural gas should be used as fuel if the current prices for these products are low. Then, as the demand for electricity grows, a waste heat boiler is additionally commissioned and steam turbine, which will increase not only the power, but also the efficiency of the station. Subsequently, when the demand for electricity increases again, it will be possible to build a coal gasification unit at the station.
The role of coal-fired thermal power plants is a key topic when it comes on the preservation of natural resources, environmental protection and ways of economic development. These aspects of the problem at hand are not necessarily conflicting. The experience of using new technological processes of coal combustion shows that they can successfully and simultaneously solve problems of both environmental protection and reduce the cost of electricity. This principle was taken into account in a joint US-Canadian report on acid rain released last year. Guided by the proposals contained in the report, the US Congress is currently considering establishing a general national initiative to demonstrate and use "clean" coal combustion processes. The initiative, which will combine private capital with federal investment, aims to commercialize new coal combustion processes in the 1990s, including fluidized bed boilers and gas generators. However, even with the widespread use of new coal combustion processes in the near future, the growing demand for electricity cannot be satisfied without a whole range of coordinated measures to conserve electricity, regulate its consumption and increase the productivity of existing thermal power plants operating on traditional principles. Economic and ecological problems are likely to lead to entirely new technological developments, fundamentally different from those described here. In the future, coal-fired thermal power plants can turn into complex enterprises for the processing of natural resources. Such enterprises will process local fuels and other natural resources and produce electricity, heat and various products, taking into account the needs of the local economy. In addition to fluidized bed boilers and coal gasification plants, such enterprises will be equipped with electronic systems technical diagnostics and automated control systems and, in addition, it is useful to use most of the by-products of coal combustion.
Thus, the opportunities for improving the economic and environmental factors of coal-based electricity production are very wide. The timely use of these opportunities depends, however, on the government's ability to implement balanced energy and environmental policies that create the necessary incentives for the electricity industry. It is necessary to take measures to ensure that new coal combustion processes are developed and implemented rationally, in cooperation with energy companies, and not as it was with the introduction of scrubber gas cleaning. All this can be achieved if costs and risks are minimized through well thought-out design, testing and improvement of small pilot plants, followed by widespread industrialization of the developed systems.
