UNECE Project
Capacity Building for Air Quality Management
and the Application of Clean Coal Combustion Technologies in Central Asia
Report
“Energy Efficient Measures, Introducing Clean Coal
Technologies”
Executor: Evgeniy Zenyutich
International Consultant
2007
1. General items.
Coming after oil coal makes an important contribution into world balance of production of primary power resources. Coal is more frequently used for electric energy
generation: about 40% of electric energy generated in the world is produced by coal
combustion. Explored world coal reserves make 6 668 milliard tons of conventional
fuel, and 799,8 milliard tons of conventional fuel are classified as appropriate for
extraction. In difference from oil fields and gas fields geography of world coal deposits is vast, about 96% of total amount of coal deposits are located in 15 countries. But
coal is considered as ecologically inadmissible fuel, because its negative influence on
the environment may exceed all strategical and economical advantaged of its application.
At the moment there are a lot of approved technologies of reduction of emissions
of “standard” and traditional pollutants (sulphureous oxides, nitrogenous oxides,
fly ash, polycyclic aromatic carbohydrates, soot) in the atmosphere. Concerning the emissions of green houses gases there are two principally different a pproaches. The first one presupposes relative reduction of СО2 emissions per
a unit of generated heat and electric energy due to reduction of coal unit discharge
per
a unit of generated final energy, i.e. the approach is connected with increase of heat efficiency of coal power stations. The second approach towards the problem of green
house gases emissions bares more principle character and presupposes not quantitative
reduction of green house gases emissions but practical absence of the emissions in the
atmosphere. Here we speak about so called carbon sequestering when the basic
greenhouse gas (carbon dioxide) is injected into underground cavities or under ocean
water column or is transformed into firm phase in the form convenient for storage to
prevent the emission in the atmosphere.
2. Economically efficient clean coal technologies.
Existing today economically efficient technologies of coal combustion that may
be introduced in heat and electric energy generation sector in the countries of Central
Asia in order to implement the UNECE Convention on Long-Range Trans boundary Air
2
Pollution (LRTAP) and reduction of green house gases emissions differ, first of all,
by the organization of coal combustion technology.
2.1. Combustion of pulverized coal in turbulent stream. At generation of electric energy boilers are usually combined with steam cycle with undercritical steam parameters:
usually 16 atm and 538оС (or 566оС) for the main steam stream and 538оС (or 566о С)
for second superheating. Such cycle, as a rule, is implemented for boilers with unit capacity equal to 300-600 MW, for boilers with lower unit capacity of 100-200 MW steam
of lower pressure is applied.
2.2. Coal combustion in boiling bed under atmospheric pressure. In a typical firechamber of boiling bed liquid or gaseous fuel or fuel with inert material are kept in
suspension state by air supply into a low part of the chamber. The main advantage of
boiling bed is connected with possibility of direct purification of products of combustion in the chamber that provides high ecological standards. First of all it concerns sulfur oxides. Additives of lime, limestone, dolomite are introduced into boiling bed and
bind sulfur contained in coal. The degree of sulfur binding is very high and residual
contents of sulfur oxides in smoke gases does not exceed 200-400 mg/m3.
2.3. Coal combustion in boiling bed under pressure. There are important advantages connected with pressure increase in a combustion chamber of a boiler. Concentration of oxide increases pro rata pressure increase, consequently the intensity of
fuel combustion and heat tension of the chamber increase. In more dense medium the
coefficients of heat exchange between gas and heating surfaces increase. This technology combines advantages of the technology of coal combustion in boiling bed and of a
binary cycle. Thanks to low temperatures of burning (till 850°С) emissions of NОх
are not big (less than 200 mg/м3), slagging is practically absent.
2.4. Coal combustion in circulating boiling bed. In boilers with circulating boiling
bed (BCBB) high speeds of air supply are applied that causes loosening. BCBB are characterized by higher heat intensity per unit of area (up to 100 tons of steam per hour). Besides, BCBB permits combustion of firm fuel with wider fractional composition.
2.5. Coal combustion in fire chambers with liquid slag removal.
This type of a
chamber is a perspective device providing removal of undesirable sulfur and mineral sub3
stances from coal fuel till the moment of its introduction into boilers or heaters. In spite
of the fact that the chambers of the type are supposed for reconstruction of existing old
equipment they also can be applied for creation of new facilities of coal treatment due
to their compactness and flexibility of fuel utilization.
2.6. Combustion of water– and mazut-coal suspensions. Pulverized coal may be
supplied into a chamber in a dry form and in the form of liquid suspensions at the basis of
water, black oil (mazut), methanol etc.
It’s important that water –coal suspension can
be injected directly in the chamber with increased pressure. The technology of direct
combustion of water-coal fuel (WCF) may be referred to innovation technologies in coal
power generation. Economic advantages of WCF application: the cost of one ton of conventional fuel is reduced in 2 and more times; maintenance expenses on storage, transport
and combustion of fuel are reduced on 15-30%. Besides, capital investments on transfer
of heat-electric generation station and hydroelectric power station from combustion of
natural gas and oil to WCF reduce in three times. The pay-back period of introduction
of WCF makes 2-2,5 years.
2.7. Combined steam-to-gas technologies. At the basis of the conception of all combined technologies there is an idea of combination of two cycles of electric energy generation. The first cycle is implemented at the products of gasification or coal combustion, the second cycle is traditional steam-power, and is implemented by steam generated
by residual heat of products of combustion. In combined steam-to-gas cycle with boiling
bed under pressure coal is combusted in boiling / circulating bed. Formation of NOx at
such stations is relatively small,
it’s practically the same as at the stations
equipped by the torches with low emission of NOx. More over, by introduction of limestone or dolomite into boiling bed it’s possible to achieve 90% sulfur absorption.
Combined steam-to–gas cycle with coal gasification is based on partial combustion
(oxidation) of coal in a gasifier under pressure and lack of oxidizing agent. In the result
coal transfers into fuel gas - mostly into hydrogen and monoxide of carbon that after
purification can be applied in gas-to-steam cycle as ordinary gaseous fuel.
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3. Technologies of carbon capture and coal storage (sequestering).
Totality of methods that can be applied in power generation for prevention of СO2
emissions in the atmosphere are called С02 capture and storage (CCS) or geological sequester of carbon. CCS includes separation of a greater part of CO2 produced in the
course of coal transformation into useful energy and transportation of CO2 to the places where it can be kept deep under ground in porous medium
mainly in exhausted
deposits of oil and gas or in permeable geological beds saturated by salted water. Big
experience in CO2 storage is gained by enterprises dealing with purification of natural gas (especially in Canada) and at enterprises dealing with CO2 application to increase oil production (especially in the USA). Annually about 35 million tons of CO2 is
injected in old oil deposits, thanks to it 4% of total oil production in the USA is extracted.
Preliminary investigations show that existing technologies of electric energy
generation allow to capture 85-95% of СО2 emitted at coal combustion.
CO2 can be extracted from fuel gases after separation of normal pollutants. Fuel
gases posses a big amount of nitrogen (coal is combusted in the air that contains 80%
of nitrogen), so it’s necessary to extract CO2 at low concentrations and temperatures
from big volumes of gas thus making the process power consuming and expensive.
Then separated С02 is squeezed and transported to the place of storage by tubes. In
the systems where coal is not combusted, but partially oxidized in a gas generator in the
course of reaction with water steam under high pressure and in the conditions of lack
of oxygen (obtained in special installations from the air), so called synthesis gas is received. It’s not
diluted by nitrogen and consists mainly
of CO and
hydrogen.
At power stations where capture of CO2 is presupposed, synthesis gas emitted from a
gas generator, after cooling and purification from firm particles, comes into reaction
with water steam that results in appearance of gaseous mixture consisting mainly of
CO2 and hydrogen. CO2 is separated from the mixture, dried, squeezed and transported to the place of storage. The rest mixture, rich in hydrogen, is combusted for energy
generation. Pressure appearing at CO2 capture is enough for transportation of the gas
by tubes to the places of underground storage distant by hundred kilometers. Howev-
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er, for transportation for big distances pump stations may be required to compensate
pressure losses at gas-dynamic resistance.
Upon the whole at introduction of CCS at coal electric power stations the amount
of coal combusted for generation of 1 kW hr of electric energy increases on 20-30%.
Expenses on introduction of CCS will depend on the type of electric power station, on
distance to the place of CO2 storage, on characteristics of the bed into which CO2 is
injected and on possibility to sell the bed (for example, to increase oil extraction). In
case CO2 is injected in the bed saturated by salt water and located in 100 km from
electric power station the cost of generation
of 1 kW hr increases on 1.9 cent in
comparison with the case of CO2 emission in the atmosphere (4.7 cent), i.e. on 40%.
In case of utilization of captured CO2 to increase oil extraction at oil field distant from
the power station on 100 km, pure inputs on electric energy generation will not increase at all, if the price for oil barrel is not less than $35, it is much lower that today.
Studies shows that if all coal electric power stations will be equipped by the systems of CCS the content of CO2 in the atmosphere can be kept at the level 4,5*10-4
during the nearest 50 years. By 2020 it’s necessary to equip new coal electric energy
stations with total capacity 36 GW by systems of CCS (7% of new capacities of new
coal electric energy stations, construction of which is expected all over the world in
2011 – 2020, in case of invariability of economic situation).
4. Economic Analysis of recommended energy efficient Clean Coal
Technologies.
4.1. Technologies improving technological efficiency of coal boiler units.
Now there is a number of real technical possibilities for modification of existing
coal heat and electric energy generating stations with the aim to increase considerably
their economic efficiency with simultaneous reduction of emissions of pollutants.
Considered lower variants of modernization differ by the degree of perfection and
modernization of the equipment. The first variant envisages partial reequipment of
outdated stations and installation of the devices providing reduction of harmful
emissions. Reequipment can be implemented independently or in parallel
in three
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sections of the station: of fuel and water preparation, of combustion and of purification of products of combustion. Equipment installed for coal preparation provides
coal enrichment by normal ablution and by modern methods of physical, chemical
and microbiological purification.
The second variant focus on the target of considerable improvement of technical,
economic and ecological characteristics of the station and presupposes fundamental
reconstruction of the station with replacement of a bigger part of old equipment and introduction of more perfect and efficient technologies.
For the countries of Central Asia the most appropriate clean coal combustion
technologies are those that do not require big financial investments and that presuppose partial reconstruction of the station with replacement of a part of old equipment
by more perfect. At technical reequipment of coal boiler-houses in operation in the
countries of Central Asia it’s reasonable to introduce measures aimed at increase of
efficiency of heat scheme, of power equipment and their reliability, including:
 Perfection of heat scheme of a boiler according to optimal heat scheme of a power
block;
 Gas proof execution of barriers of fire-chamber and convection shaft;
 Perfection of aerodynamics of a fire chamber to provide uniform heat perception of screenful surfaces of heating and slagless mode, including expansion of the
zone of active burning and optimal positioning of the devices of outer purification on
the walls of a chamber;
 Usage of low toxic torches with application, mainly for black coal, of dust supply
in the torches with high concentration, optimization of hydraulic scheme of steam generating and steam heating part of the tract to reduce heat hydraulic reaming and hydraulic losses;
 Application of full-bore starting separators or integrated with upper steam outlet
reducing heat changes in steam heating surfaces of heat at the starts;
 Application of ribbed water economizers;
 Application of intensified and resistant to corrosion heating surfaces for air heat7
ers;
 Rational positioning of the devices of outer clearance of convection surfaces of
heating;
 Application of economically efficient forced-draft equipment with frequency adjusting;
 Application of mill-ventilators with electric
breaking for brown coal and of
half speed move with dynamic separator for black coal;
 Equipping of power blocks by digital automatic systems of control of heat pro-
cesses for optimal exploitation
of all the elements of the block independent from
modes of work and achievement of economic efficiency of power blocks due to optimization;
 Application of Automated system of control of temperature modes that will result
in reduction of production costs due to reduction of wear of the equipment, enlargement
of the periods between repair and reduction of the quantity of the personnel.
These measures will allow to raise economy of coal power blocks on 10–12% and
their efficiency on 4,5-6,7% ( from 37-38% to 42-44 %), to provide emissions of NOX
at the level of 220—300 mg/m3 and emissions of S02 at the level of not more than
400 mg/m3.
4.2. Technologies improving ecological efficiency of coal boiler units.
Above mentioned technologies of coal combustion illustrate existing possibilities to extract coal pollutants with the aim to prevent their emissions in the atmosphere. They include:
1. Removal of mineral particles and sulfur by methods of physical and chemical purification at preparatory stages before combustion or processing.
2. Binding of pollutants (mainly sulfur oxides) directly at the stage of combustion by
adding of appropriate alkaline absorbers in a combustion chamber.
3. Removal of mineral substances and heteroatoms of fuel by means of intercycle processing: gasification, pyrolysis and liquefaction.
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4. Purification of taken aside smoke gases from mineral particles, sulfur and nitric oxides by traditional and perspective methods of gas purification.
Each of these possibilities can be implemented by different technological methods,
differing by efficiency of purification, necessary capital and maintenance expenses and
by technological maturity. All ecologically- friendly technologies of combustion envisage purification of products of combustion from firm particles (dust, fly ash, soot)
with the help of electrostatic and bag filters and wet scrubbers. In many cases at combustion of coal with high sulfur content it’s necessary to use purification of smoke
gases from sulfur oxides to meet high ecological requirements towards emissions of
sulfur oxides.
4.3. Feasibility and ecological characteristics of modernization of traditional
coal power stations.
Reconstruction with introduction of steam-to-gas cycle with gasification may raise
efficiency of coal station from 35% up to more than 40% and to improve its productivity on 50-150%. That’s why thanks to increased productivity and efficiency of renovated station the price of electric energy will increase on 0.2 cent per 1 kW hr, not more.
In addition these expenses will allow to reduce emissions of sulfur oxides on 99%
and considerably reduce emissions of nitric oxides. If the technology with increased
pressure in a fire- chamber of boiling bed is applied, then it’s possible to expect the
increase of efficiency from 35% to 38% and increase of capacity on 50%. In this case
capital investments are lower (800-1000 USD per 1 kW) but taking into account
that productivity increases in smaller degree than in steam-to-gas cycle with gasification the price of electric energy raises a bit more, approximately on 0.4-06
cent per 1 kW hr. Reconstruction with application of combustion in boiling bed
under atmospheric pressure does not lead to noticeable increase of efficiency of the
station but results in 10-15% increase of the capacity. Capital investments are not
higher than 700-900 USD per 1 kW but owing to relatively small increase of the
capacity the rise in price of electric energy makes 06.-08 cent per 1 kW hr (see table1).
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Table 1.
Reduction of
Effiemissions Output
Technology
ciency
of
capacity
SOx/NOx,
%
>30;
Coal enrichSlight
Does not The same
ment
increase
influence
90-95;
Scrubber sulfur reducModerate
Does not
purification
tion
reduction
influence
Perspective pureduc>90;
Slight rerification of
tion
high
duction
smoke gases
Multi-stage
reduc50-60;
Slight recombustion
tion
moderate duction
with limestone
Fire-chamber
of preliminary
Slight
50-90;
Slight recombustion
reducmoderate duction
with slag retion
moval
Rise in
Addition- price of
al exelectric
Life term
penses
energy,
$ per kW
$ per
МW hour
Price of
Slight inadditional
2-3
crease
fuel
Does not
influence
180-200
9-11
Does not
influence
175-190
10-12
Does not
influence
80-110
5-8
Slight increase
50-60
1-2
Slight increase
10-20
Depends
on the
price of
gas
With gas afterburning
The
same
Does not
Does not
influence;
influence
moderate
Water-coal
suspension
Slight
reduction
10-60;
Does not
influence
Slight reduction
Does not
influence
20-50
11-23
Moderate increase
95-99;
Does not
influence
50-150%
increase
Moderate
increase
11001300
1-2
90-95;
60
50-70%
increase
Moderate
increase
800-1000
2-4
90-05;
60
10-15%
increase
Moderate
increase
700-900
6-8
Combined
steam-to-gas
cycle with gasification
Circulating
boiling bed under pressure
Atmospheric
(Circulating)
boiling bed
Does
not influence
Does
not influence
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5. Examples of the projects introducing clean coal technologies in the courtiers
of Central Asia.
In the frames of UNECE project Capacity Building for Air Quality Management
and the Application of Clean Coal Combustion Technologies in Central Asia business –
plans for the projects aimed at increase of energy efficiency of existing coal power stations and reduction of emissions of pollutants were developed.
5.1. Project “Modernization of electro-filters
at New-Angrenskaya HEGS.”
(Republic Uzbekistan) presupposes reduction of emissions at New-Angrenskaya HEGS
(In case efficiency of filters will reach the passport level of 98% reduction of emissions
of ashes will make 52 452 tons). The cost of the project makes 559 140 USD, expected economy is 132 749 USD.
5.2. Project "Increase of efficiency of combustion of high-ash brown coal of Angrenskaya coal-field at Angrenskaya HEGS. (Republic Uzbekistan) presupposes installation of vortical coal torches with the aim to increase efficiency of combustion of
high-ashes coal and reduction of nitric oxides production on 40-50%. Cost of the project is 615 000 USD, expected economy is 604 276 USD.
5.3. Project “Increase of the potential in the sphere of air quality management
and the application of clean coal combustion technologies in Central Asia" (Republic
Tajikistan) envisages technologies of combustion of composite water-coal fuel that
will allow to reduce considerably expenses and to reduce the level of emissions of
pollutants in the atmosphere. Cost of the project makes 634,3 thousand USD, expected economy is 132,7 thousand USD per year.
5.4. Project “Modernization of HEGS, Bishkek with introduction of the boiler
with productivity 420 tons of steam per hour” (Republic Kyrgyzstan) presupposes replacement and introduction of the system of control and regulation of temperature mode
(reduction on 10-15% of emissions of pollutants). Project cost makes 67,5 million
USD, expected economy is 14,2 million USD.
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6. Conclusions and recommendations.
For the countries of Central Asia it’s most appropriate to introduce technological
activities not connected with serious financial expenses, those that do not require considerable reconstruction of existing stations, including cheap activities directed at increase of efficiency of heat scheme, of power equipment and their reliability.
It’ rea-
sonable to include in the list of such cheap activities the following measures:
1. Gas proof execution of barriers of fire-chamber and convection shaft.
2. Usage of low toxic torches with application, mainly for black coal, of dust supply
in the torches with high concentration, optimization of hydraulic scheme of steam generating and steam heating part of the tract to reduce heat hydraulic reaming and hydraulic losses.
3. Application of full-bore starting separators or integrated with upper steam outlet
reducing heat changes in steam heating surfaces of heat at the starts.
4. Application of ribbed water economizers.
5. Application of intensified and resistant to corrosion heating surfaces for air heaters.
6. Application of economically efficient forced-draft equipment with frequency adjusting.
7. Application of mill-ventilators with electric breaking for brown coal and of half
speed move with dynamic separator for black coal.
8. Equipping of power blocks by digital automatic systems of control of heat processes for optimal exploitation
of all the elements of the block independent from
modes of work and achievement of economic efficiency of power blocks due to optimization.
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