The system for improvement of watt

Wilhelm Jan TIC* – Department of Environmental Engineering, Faculty of Mechanical Engineering,
Opole University of Technology, Opole, Poland
Please cite as: CHEMIK 2014, 68, 10, 850–855
Introduction
Heat and electricity produced in Poland come predominantly
from power units and installations using solid fuels, mainly black
coal. Strenuous efforts are taken in order to increase the production
efficiency of these plants, as it is related both to fuel saving and reduction
of quantity of pollutants emitted per unit of produced energy.
One of the methods to increase watt-hour efficiency of boilers is
to use modifiers (catalysts) added to the fuel. They improve efficiency
of combustion process, i.a. due to afterburning of heavy hydrocarbon
fractions, which are produced in fuel combustion process and thus
reducing losses arising from incomplete combustion. At the same time
this has an effect on the level of atmospheric emissions [1].
Catalysts for combustion of solid fuels
The use of coal as an energy carrier causes formation of inter
alia, smog, acid rain and particulate rainfall. Additional low content
of oxygen in the air fosters formation of soot, tar products and
carbon monoxide.
Reduction of emission of harmful substances is one of the priorities
of atmospheric protection against pollution with toxic chemical
compounds. Practically, this means the application of such solutions that
would allow for continuous conversion of pollutants to carbon dioxide
and water. The most effective in terms of almost complete removal
of the discussed compounds is a process of catalytic afterburning of
harmful components of flue gas.
Many types of catalysts allowing for the reduction of burden of coal
combustion has been developed. They exhibit oxidising properties,
which allow oxidation of tar products and soot in the place of their
origin; these products exhibit carcinogenicity, mutagenicity and toxicity
[2 – 4]. Apart from CO, polycyclic aromatic hydrocarbons (PAH) and
soot should be mentioned here.
The important benefit of reducing soot pollution is a minimization
of risk of its ignition in the chimney flues, which eliminates cause of
fires and damages of structural elements of plants. Moreover, the
accumulation of soot on the walls of installation causes the decrease
of flue draught and this hinders the removal of flue gas from the
combustion chamber and causes the increase of concentration of toxic
CO in flue gas [5].
The most commonly used catalysts for solid fuel combustion are
copper compounds and sodium chloride. Introducing NaCl into the
system has positive effect on the process of black coal combustion.
The optimum dose has been established to be about 7–8 g NaCl/m2 of
furnace area. The addition of catalyst improves heating performance
of installation and at the same time reduces atmospheric emissions of
CO and NOx. Moreover, it is possible to reduce air excess coefficient
for air fed to the combustion chamber and to reduce heat loss in
flue gas by approx. 12% [6]. Sodium chloride under conditions of
the combustion chamber converts partially into hydrogen chloride
and sodium oxide. The hydrogen chloride, while reacting with oxide,
which are solid residue of combustion process, causes formation of
Corresponding author:
Wilhelm Jan TIC – Ph.D., D.Sc., Eng., Assoc. Prof., e-mail: [email protected]
nr 10/2014 • tom 68
metal chlorides, which are more easily removed from the heating
system than sintered oxides. Addition of alkaline metal may show
disadvantageous effect in the pressure part of the boiler, thus its
concentration should be low.
While the use of ammonium chloride may protect the installation
from low- and high-temperature corrosion, it is a source of chloride in
a synthesis of toxic group of pollutants, including dioxins.
Fossil fuels have certain content of inorganic compounds, including
chlorides of metals: copper, manganese, chromium and iron. These
compounds catalyse many chemical reactions – including dioxin
synthesis. Inhibitors added to the combustion zone may exhibit activity
reducing concentration of already produced pollutants. There is also
possibility of inhibiting dioxin formation at the stage of their synthesis
using inhibitors [5].
Table 1 presents two groups of substances, which ultimately
cause reduction of dioxin concentration in flue gas.
Table 1
Chemical compounds affecting dioxin level in flue gas [5]
Dioxin synthesis inhibitors
Dioxin reducing compounds
– calcium oxide
– ammonia
– pyridine
– ammonium sulphate, sodium sulphate
– quinoline
– sodium thiosulphate
– urea
– ammonium sodium hydrogen phosphate (V)
– ethylene glycol
– sulphur
– amines
– dolomite
– EDTA
An example of an effective inhibitor is sulphur and its compounds.
They inhibit dioxin synthesis by converting CuCl2 (the most effective
catalyst and at the same time source of chlorine for dioxin synthesis)
in significantly less catalytically active CuSO4. Introducing appropriate
additive to the fuel combustion process at the industrial scale allows
for the reduction of formed dioxins, even by 90%. Dioxin inhibitor at
the same time – due to the activity in DeNOx process – may cause the
reduction of emitted nitrogen oxides. Chemical substances exhibiting
such mode of action include urea and ammonia [7].
The other effective method of soot removal is the addition of
a mixture of oxidants to the furnace. The thermal decomposition of
inorganic salts, such as nitrates (V) or manganates (VII) produces highly
reactive oxygen, which oxidises soot at relatively low temperatures.
The advantage of this method of assisting combustion process is the
production of high volume of gases as a result of decomposition of rather
small quantity of added oxidants. These gases penetrate thoroughly the
contaminated surface, even in places where mechanical cleaning would
be very troublesome.
The catalysts containing oxidisers despite aforementioned
advantages are less effective than compositions containing large
amounts of transition metal salts. These metals assist in soot oxidation
processes by atmospheric oxygen from air fed into the combustion
chamber. The important role is played by organic and inorganic
copper salts (CuSO4, CuCl2, CuO•CuCl2, copper naphtenate).
• 853
XV Conference Environmental
The system for improvement of watt-hour and
environmental efficiency of solid fuel combustion
XV Conference Environmental
The high efficiency of catalyst activity, including reduction of flue
gas temperature by approx. 100°C, was obtained not only due
to the correct choice of components, but also due to break-up of
preparation grain below 100 μm.
The active substances in the process of catalytic oxidation of
carbon deposits are chemical compounds produced as a result of
thermal decomposition of the additive components. During the
decomposition of these substance, CuO is formed, which serves as
a catalyst in the process of soot oxidation and reduces, even by half,
its oxidation temperature [8]. There are many known components
of catalysts for complete combustion of fuels. However, copper
compounds are believed to be the most effective.
Studies of the catalyst based on the mixture of Cu and Mn oxides
deposited on the porous alumina exhibit positive effect on the
reduction of the emission of CO and particulates. The modification
of this catalysts with zirconium and titanium oxides of high oxidation
potential indicates the possibility of reduction of the emission of
aforementioned pollutants in the combustion chamber [9].
Power industry uses catalysts enhancing combustion process of
coal fuel. An example is REDUXCO catalyst by DAGAS, which consists
of organic compounds containing iron atoms.
DESONOX technology for desulphurization and denitrification is
worth mentioning in the discussion on coal combustion process. In this
case, metallic catalyst is supported by synthetic zeolite. The idea of
this process is based on the continuous elimination of SO3 by binding it
with furnace waste, e.g. ash and slag. DESONOX-type catalyst reduces
level of NOx in the reaction environment – thus determining decrease
of its quantity in waste gas by catalysing reaction of high-temperature
indirect oxidation of CO by nitrogen oxides [10].
Original research on the system for improvement of watt-hour
and environmental efficiency of solid fuel combustion
Original research on the system for improvement solid fuel
combustion involved questions of selection of effective catalysts,
optimization of their synthesis process and evaluation of their catalytic
activity in the combustion process. The important element of the
system are automation solutions allowing for the precise dosage of
modifiers to the stream fed to the fuel combustion chamber and
a method of measuring energy effects in terms of billing potential
counterparties.
The developed system for dosing catalyst to the solid fuel allows for
precise feeding of assumed quantity of catalyst to fuel stream fed to the
boiler grate. The applied automation system allows to match quantity
of the catalyst both to the varying fuel stream, as well as to the assumed
catalyst concentration (Fig. 1).
In order to obtain high accuracy of catalyst dosing, catalyst were
used in the form of aqueous solution, which can be easily sprayed on
fuel stream fed to the boiler by transporting devices. The concentration
of active ingredients of catalyst was selected in such a manner that the
consumption of aqueous solution was 2 dm3 per 1 Mg of coal fuel.
Fig. 1. Diagram of catalyst dosing system for solid fuel.
(1 – solid fuel storage; 2 – conveyor; 2a – conveyor element for fuel
stream metering; 3 – catalyst tank; 4 – controller; 5 – spraying nozzle;
6 – wireless control system)
854 •
Based on the measurement of watt-hour and environmental effect
resulting from the use of catalysts, existing measuring infrastructure
and temporary measuring instruments is used during the test period. It
is possible to remotely control of catalyst dosing system and long-term
collection of measurement data.
The advantages of using catalysts in the process of solid fuel
combustion are related to maintaining high boiler efficiency and
extending its lifetime and reduction of repair costs. The reduction
of hydrocarbon content in waste gas and unburned coal in the
ash allows more effective combustion of fuel and no deposition of
unburned parts in form of carbon deposits in combustion chamber
and hence the increase of boiler efficiency. Moreover, at the same
time atmospheric emission of harmful gases is decreased and flue gas
corrosivity is reduced.
An economic effect of application of catalysts involve higher heat
output per fuel weight unit, increase of boiler efficiency, reduction of
repair costs and decrease of environmental fee. It is estimated that this
effect will reach approx. 2.5% of fuel costs.
Table 2 presents exemplary results of combustion tests for coal fuel
(ECO-PEA) using mono- and polycatalyst. The concentration of metal
and NH3 in fuel, at the level of 300 ppm, was selected as the optimum
based on the results of laboratory tests.
Table 2
Effect of catalysts on reduction of gas emissions and boiler efficiency
in the coal fuel combustion process (concentration of metal and ammonia cations – 300ppm)
NH3
Na+
Cu2+
Mg2+
E5
CO
-4.8
-2.9
-9.7
-3.1
-6.2
NOX
-6.5
-0.5
-1.4
0.0
-11.7
SO2
-1.6
2.2
-7.0
-3.4
-7.6
Boiler efficiency, %
1.0
0.8
0.5
-1.1
2.9
The effect of catalyst addition of the fuel combustion efficiency
is determined in relation to the test trial without catalyst, where
pollution emission and boiler efficiency were adopted as 100%.
Mono-metallic catalyst containing Cu2+ has the greatest effect on
the reduction of pollutant gas emissions, but it gives only small
increase of boiler efficiency. In case of using E5 catalyst, the synergy
of its components was observed and increase of the efficiency in
comparison with tests for mono-catalysts. The catalyst was an
aqueous solution of salt mixture containing: 20% NH3, 30% Na+,
40% Cu2+ and 10% Mg2+.
The important issue, at the stage of system implementation in
industrial conditions, is an innovative method of billing the customers.
It is assumed that modifiers will be delivered to the customers at the
expense of manufacturers and the payment for the use of the system
will be equal to 20–30% of calculated effect on fuel combustion. Such
a billing method minimizes risk taken by electricity producers and
increases the credibility of the company implementing the system for
the improvement of the efficiency of fuel combustion.
Summary
The increasing demand on fuels, as well as increasing environmental
requirements imposed by the European Union, force implementation
of improvements in the combustion process. One of the method is use
of catalysts and additives improving combustion process.
Based on the literature review, it may be concluded that addition
of catalysts and additives to the burned solid fuel reduces atmospheric
emissions of CO, SO2, NOx, PAH and dusts. Catalysts and additives
affect also the combustion efficiency and prolong boiler lifetime, and
hence reduce repair costs. They also reduce the risk of high- and lowtemperature corrosion in the studied system.
nr 10/2014 • tom 68
The research was carried out under the project Operational Programme
Innovative Economy 2007–2013 with reference number
POIG.01.04.00–16–159/12.
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8. Katalizator do spalania sadzy, patent application No. 365431, RP.
9. Doggalla P., Kusabab H., Einagab H., Bensaidc S., Rayalua S.,
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*Wilhelm Jan TIC – Ph.D., D.Sc., Eng., Assoc. Prof. of the Opole University of Technology has graduated from the Faculty of Chemistry at Silesian
University of Technology (1986). He obtained the title of doctor from the
Faculty of Chemistry at Poznan University of Technology (2000). He obtained his D.Sc. from the Faculty of Chemistry at Lodz University of Technology (2012). Currently he works at the Department of Environmental
Engineering at Opole University of Technology. His scientific activities include issues of chemical technology and catalysis, as well as environmental
protection and engineering.
e-mail: [email protected]
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XV Conference Environmental
The efficiency of catalyst use strongly depends on such factors as:
boiler operation parameters, structural features of the installation,
dosing method and fuel properties.