Note: Descriptions are shown in the official language in which they were submitted.
2 Q ~ 7
Method of Making and Low-pollution
Combusting of Solid Fossil Fuels
Background of the Invention
The present invention relates to a method of
preparing and low-pollution combusting of solid
fossil fuels.
Description of the Prior Art
Solid fuels are generally comminuted and
dried before combustion. If solid fuels are not
used at suitable pulverization fineness for dust-
firing, solid fuels are comminuted, dried and
pressed at high pressure to form briquettes or
pellets. The pressing of solid fuels leads to
considerable advantages in the handling of the solid
fuels during transport and storage.
The emission behavior of the impurities
contained in the solid fuel, e.g., sulfur, chlorine,
fluorine and heavy metals, is only insignificantly
affected ~y the pressing operation and high
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pollution emissions of, for example, S02, HCl and HF
occuring during combustion of the pressed solid
fuels.
It is known, for example from DE 3,440,593
S Al, to add basic additives to solid fuels to which
waste materials are added, in order to effect a
binding of the acid-forming pollutants. In this
case, it is also known that the fuel bed temperature
must not be unduly high, so that the binding of the
pollutant is not reversed during a subsequent
combustion process. It is therefore known to set
the fuel bed temperature at less than 1300C and
usually the fuel bed temperature is preferably set
between 800 and 1000C.
DE 3,717,191 Cl discloses a process which,
for low-pollution combustion of trash, provides for
an addition of a basic additive to trash which has
been adjusted to a predetermined moisture content of
15 to 35 percent by weight. The trash remains for
at least 10 minutes in a reaction space and is then
burned at a fuel bed temperature of less than 850C.
This process, however, is not intended for the
combustion of pulverized solid fuels, particularly
those in pressed form.
Summarv of the Invention
The present invention is directed to a novel
method of pressing and combusting solid fossil fuels
without the generation of high levels of pollutants
and represents a vast improvement and a completely
novel approach for satisfying and meeting the needs,
requirements and criteria for effective and useful
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combustion of fossil fuel without the problems and
disadvantages of prior art methods, particularly the
generation of high levels of pollutants, in a safe
and cost effective manner.
Accordingly, the present invention is
directed particularly to a method of combusting
solid fossil fuels accordingly, that does not
produce a high level of pollution, i.e., low-
pollution combustion of solid fossil fuels.
Accordingly, an object of the present
invention is to provide a method of combusting solid
fossil fuels without generating a high level of
polluting by-products.
Another object of the present invention is to
provide a method for low-pollution combustion of
solid fossil fuels in an efficient and cost-
effective manner.
Additional objects and advantages of the
present invention will be set forth, in the
description which follows, and, in part, will be
obvious from the description or may be learned by
practice of the invention. The objects and
advantages of the invention may be learned by and
attained by means of the instrumentalities and
combination of steps particularly pointed out in the
appended claims.
To achieve the foregoing objects and in
accordance with the purpose of the present
invention, as embodied and broadly described herein,
a preferred method of preparing combustible low-
pollution solid fossil fuel comprises communiting
the solid fossil fuel, forming a mixture by adding
an amount of basic additive to the communitied solid
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fossil fuel in a stoichiometric ratio greater than
1.0 relative to the solid fossil fuel for binding
pollutant compounds, bringing the moisture content
of the mixture to greater than 15%, holding the
mixture at a temperature range between approximately
40C - 100C for a period of time between
approximately 10 to 180 minutes in a substantially
closed reaction space and combusting the mixture at
a fuel bed temperature less than or equal to about
830C.
In another preferred embodiment of the
present invention, there is disclosed a method of
low-pollution combusting solid fossil fuels
comprising comminuting the solid fossil fuel,
forming a mixture by adding an amount of basic
additive to the comminuted solid fossil fuel in a
stoichiometric ratio greater than 1.0 relative to
the solid fossil fuel for binding pollutant
compounds, bringing the moisture content of the
mixture to greater than 15~, holding the mixture to
a temperature range between approximately 40 to
100C for a period of time between approximately 10
to 180 minutes in a substantially closed reaction
vessel, discharging the mixture from the reaction
vessel and drying the mixture and combusting the
mixture at a fuel bed temperature of less than or
equal to about 830C.
According to the present invention, a
treatment very similar to that proposed for the
combustion of trash leads to suitable pressing of
solid fuels, which - as distinct from the earlier
process technology - i8 adjusted to a relatively
high moisture content preferably greater than 20~,
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for mixing with the ba~ic additive and ad~usted to
an elevated temperature in a closed reaction space,
the reaction space preferably being heated
indirectly and preferably to a temperature of about
60C.
Detailed Descri~tion of the Preferred Embodiments
A preferred embodiment of the present
invention will now be described.
Solid fossil fuel is comminuted to an average
gain size of less than 3 mm and loaded in a reaction
chamber. At least one basic additive in particular
form is added to the comminuted solid fossil fuel.
Basic additives includes alkaline earth compounds
such as CaO3 and MgC03 as well as other compounds
that will bind pollutant compounds. The amount of
basic additives that is added to the solid fossil
fuel particles is in a stoichiometric ratio of
greater than 1.0 relation to the solid fossil fuel
to ensure complete binding of pollutant compounds.
The solid fossil fuel particles and basic
additives are mixed in the reaction chamber to form
a mixture. The moisture content of the mixture is
then made to be greater than about 15%, preferably
greater than about 20%. The mixture is heated in
the reaction chamber to a temperature between
approximately 40 - 100C, and held for a period of
time between about 10 to 180 minutes. The resulting
mixture is then dried and may be used in a
particular form or pressed to form briquettes or
pellets.
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The resulting mixture may be combusted at a
fuel bed temperature of about 830C or less with
low-pollution emission.
By subsequent pressing of the solid fuels,
briquettes or pellets can be produced in which, as
a result of the said pressing measures, the
pollutants, especially acid formers, are bound to
form salts having a high dissociation temperature,
so that, during a combustion at a fuel bed
temperature less than or equal to 830C, the bound
salts remain in the combustion residue and do not
dissociate to form the pollutants.
As a result of the invention, it is therefore
possible for the first time to make even pressed
solid fuels available which can be burned at a very
low pollutant level, for example with an S02 content
of less than 2%.
For carrying out the process, the moisture
content of the mixture in the reaction vessel is
preferably adjusted to greater than 20%. A suitable
basic additive is an alkaline earth mixture,
preferably CaC03 and/or MgC03, which is added to the
solid fuels in a stoichiometric ratio of greater
than 1Ø
As a result of the pressing, unusual for
solid fuels, by setting a predetermined moisture
content for the addition of the basic additive, the
retention of the solid fuél in a reaction vessel for
a period of preferably more than 20 minutes and
subse~uent drying of the solid fuel, low-polluting
combustion can be achieved even with bituminous coal
or lignite of high sulfur content.
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It will be apparent to those skilled in the
art that various modifications and variations can be
made in the method of the present invention without
departing from the scope or spirit of the invention.
Other embodiments of the invention will be apparent
to those skilled in the art from consideration of
the specification and practice of the invention
disclosed herein. It is intended that the
specification and examples be considered as
exemplary only, with true scope and spirit of the
invention being indicated by the following claims.
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