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1. WO1984000903 - PROCEDE D"ELIMINATION DE SUBSTANCES POLLUANTES DE L"AIR QUI SONT LE RESULTAT DE LA COMBUSTION DE CARBURANTS CONTENANT DU SOUFRE

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

"PROCESS TO ELIMINATE AIR POLLUTANTS WHICH RESULT FROM THE COMBUSTION OF FUELS CONTAINING SULPHUR".
TECHNICAL FIELD
The present invention refers to a process aimed at the elimination of air pollution caused by the burning of
Sulphur containing fuels in all kinds of industry and equipment of all sizes. The process requires less investment than other alternative processes and produces a commercial end-product.
BACKGROUND ART
One of today's main concerns has been to eliminate air polluting agents resulting from the burning of Sulphur containing fuels, without generating inadequate by-products. Many of the processes presently used require large
investments in equipments and installations, normally without return or uiith high added operational costs.
DISCLOSURE OF INVENTION
Aiming at solving or minimizing these problems, this process has been developped. Basicaly simple, easily retrofitted into the polluting equipments, with low investment costs, this process produces a high value end-product.
Specifically, the aim of this invention is to transform all Sulphur Dioxide (SC2) and Sulphur Trioxide (SO3) existing in the combustion gases, to Ammonium Sulphate. This is obtained through the reaction of SO3 and SO2 with Ammonia, preferably in gaseous state, which is injected directly into the combustion gases. The collected stable end-product is
Ammonium Sulphate [(NH4)2 SO4] which is separated from the flue gases.
These and other objectives of this invention are obtained by this process which comprises the following steps: undertake at least one injection of Ammonia (NH3) in the combustion gases at temperatures between 250ºC and 600ºC, in quantity sufficient to react with all the SO3 which is present and with part of the existing SO2; cool the gases to a
temperature lower than about 65ºC; separate the submicron and micron size particles from the combustion gases; collect the (NH4)2 SO4 from the separating equipment, and send the desulphurized combustion gases to the flue.
Considering the possibility of providing more then one injection point of Ammonia (NH3), this process has foreseer the division of the injection into: a first injection of gaseous NH3, (Ammonia) into the 250ºC to 600ºC combustion gases and in a quantity sufficient to react with all the present SO3, and a second injection of gaseous NH3 at a region where the combustion gases are at a 65ºC to 250ºC temperature range and in a quantity sufficient to react with at least a part of the existing SO2.
In this case, the first injection is directed mainly the neutralization of the SO3.
In case of injection of all the Ammonia (NH3) in the 250ºC to 600ºC combustion gases temperature range, the NH3, will react with all present SO3, and the rest of NH3 will intermix with the combustion gases stream, up to the point where the temperature permits the occurence of an irreversible reaction between the 5O2 and NH3.
As already established technically, the SO3 is a gas formed curing the combustion of Sulphur containing fuels, by the reaction αf gaseous SO2 with molecular Oxygen (O2), by the reaction of SO2 in the flame with atomic Gxygen and by catalytic oxidation of SO2 in the heat transfer Surfaces under high temperatures. The corresponding reactions are the following:


Without the presence of catalysers, the burning of Sulphur containing fuels results in up to 5% SO3 in the total of SOx compounds. In spite of the fact that gaseous Ammonia reacts with SO3 in the temperature range of 250°C to about 600ºC, it has been verified that the ideal temperature range is

300°C tα 4Q0ºC In this range, the reation of SO3 with NH3 is instantaneous resulting in (NH4)2 SO4 (Ammonia Sulphate) and eliminating the possibility of corrosion in the surfaces which would have been contacted by the SO3. This corrosion occurs due to the formation of liquid Sulphuric Acid (H2SO4) when SO3 and water of combustion (H2O) combine at
temperatures bellow the Sulphuric Acid dew point. The
quantity of injected NH3 is sufficient to insure the
formation of (NH4)2 SO4 (Ammonium Sulphate).
Smaller quantities of NH3 would result in the formation of Hydrogen Ammonium Sulphate (NH4 H SO4), which is a corrosive compound. The corresponding reactions are the following:



The minimum calculated quantity of NH3 to avoid formation of NH4 H SO4 in 3% Sulphur bearing fuel oils, for example, is O,08% of the oil weight. For higher levels of Sulphur, the percentage will correspondingly higher (up to 9%) . The reaction product (NH4)2 SO4 is stable and is carried
together with the combustion gases' stream. As previously mentionπed, this process is directed towards a complete and reliable elimination of the SO2 resulting from the
combustion of liquid, solid or gaseous fuels.
To neutralize the SO2, the gaseous NH3 is injected in one or more locations of the equipment, where the combustion gases are at a range of 65°C to 600°C. If the gaseous NH3 is totaly injected in a 200ºC to 600ºC reigion, the excess portion which does not participate in the reaction with SO3, is carried in the combustion gases' stream, forming an intimate mixture which will react when the right temperature range is reached.
At 120°C the quantities of SO2 which react with NH3
increases, and as the temperature of the gases decreases to about 108°C, an equilibrium situation is reached with 35% to 40% of the existing SO2 having reacted with NH3 according to the following reversible reations:


It has been experimentaly verified that this equilibrium situation is maintained until temperatures in the range of 65ºC are attained.
Between 65°C and 48°C it has been exoerimentaly proven that this reaction is stable with the simultaneous oxidation of Ammonium Sulphite to Ammonium Sulphate according to the following reactions:


This oxidation is processed by existing combustion air in excess or by an extra air antrainmert into the gases, just before the senaration system. The ( NH4) 2 SO4 (Ammonium
Sulphate) is astable, solid, submicron, to a low value micra sized, product.
The above mentionned facts Lead to verified results, if the combustion gases are released at higher temperatures then 65°C, part of the SO2 (even if aireacy reacted) might be released to the atmosohere, due to the reversic Le nature of the reations at that higher range.
The separation of the stable end-product (NH4)2 SO4 (Ammonium Sulphate) from the combustion gases' stream, can oe
accomplished by dry methods such as Electrostatic
Precipitators or other kinds of filters, or more economically by wet processessuch as water absorbers.

The absorption of (NH4)2 SO4 (Ammonium Sulphate) in water is possible due to the highly soluble nature of this product.
DESCRIPTION OF THE DRAWINGS
The process will now be briefly outlined so as to show an example of a feasible and tested lay-out of the
Desulphurizatioπ of Combustion Gases with Ammonia.
Figure nº 1 represents a flaw diagram of the main components of an installation comprising the equipment where the Sulphur bearing fuel is burned, two distinct Ammonia injection points, the (NH4)2 SO4 wet absorption system, an entrained water separator, the dessulphurized flue gases released to atmosphere and the concentrated Ammonium Sulphate solution collection system.
Figure nº 2 illustrates one of the several assemblies of the Ammonia injection elements, in adequate locations of the combustion gases' stream.
Figure nº 3 shows a typical configuration of the NH3
injection tubes.
BEST MODE OF CARRYING OUT THE INVENTION
As shown in Figure 1, this process is applied in industrial installations such as bailers, furnaces, ovens, dryers, etc (1), burning Sulphur bearing fuels. Heat recovery equipment (2) may or not be present. In the present process, NH3 coming from a storage tank (3) is distributed in gaseous or liquid form. If as a liquid, NH3 is vaporised or not and injected initialy in a region where the gases are preferably between 250ºC and 600°C and before the heat recovery
equipment. The quantity of the first injection is, as previously explained, adequate to insure complete reaction with the SO3, therefore eliminating corrosion problems in the heat recovery or other metallic or nan metallic
components of the existing installation. This permits the use of cheaper construction materials or results in longer life of the existing ones.
The combustion gases which leave the heat recovery equipment (2) in the example shown, are conducted by means of a duct (5) and ventilator (4) to a point where a second injection of gaseous NH3 is undertaken at lower temperature levels. Even if the gaseous NH3 is injected at only one location, the quantity will always be such as to react initialy with the existing SO3 and further on at lower temperatures with the SO2.
The combustion gases, after the last NH3 injection, are sent along the duct (5) and into an apropriately dimensioned duct (6). This duct (6) has a battery of atomizing nozzles (6a) in adequate number and sizing.
These nozzles spray a recirculating solution αf Ammonium Sulphate into the combustion gases. This solution is
recirculated under pressure by a pump and piping (7).
A water make-up system (7a) is hooked up into this r
recirculating system. This pre-washing phase insures initial absorption of the existing (NH4)2 SO4 particles and a severe temperature drop of the combustion gases. Depending on the inlet temperature of the gases to this pre-washer/absorber, the completion of the SO2 reaction to (NH4)2 SO4, may also happen in this region.
In the second stage of the (NH4)2 SO4 (Ammonium Sulphate) absorption in water, the combustion gases pass through a high pressure injector (8a) (or additional nozzles) spraying (NH4)2 SO4 solution into the gaseous stream, which is assembled on top of a solution collection tank (8). At this phase the simultaneous retention of the soluble Ammonium Sulphate particles and of the insoluble particles such as carbon, inorganic materials, etc, is achieved.
The concentrated solution of Ammonium Sulphate may be continuously or periodicaly taken away from the collection tank (8) into a storage tank (9).
This volume is substituted by make-up water.
One of the advantages of this wet separation process is that the insoluble and undesirable particles can be easily separated from the dissolved Ammonium Sulphate solution by conventional filters or gravity settling.
The system has also foreseen, for the cases where water entrained as mist should not be lost, the installation of a low pressure drop demister (10) which recovers part of the water which is returned to the solution tank (8) by piping

(11).
The combustion gases leave the solution tank (8) totaly desulphurized or, if desired, within the SO2 emission levels specified by the local Environmental Control Agency. The emission level is easily adjusted by the variation of the

Ammonia flow to be injected, with the use of proportioning or manual valves and flowmeters.
The complete system can also receive a pH controller of the tank (8) solution to insure continuous neutralization of the

SO2.
Direct or indirect measurement systems of the Ammonium
Sulphate concentration in the solution contained in the tank (8) can also be added.
The duct (5) which receives the combustion gases, can also remain connected to the existing chimney (12) through a normaly closed gate valve which functions as a by-pass to the separation system.
As shown in figures 2 and 3, the Ammonia gas injection is made in the gas ducts through perfureted tubes (20), the number and disposition of the tubes being determined by the calculated Ammonia gas flow, and by the objective of
obtaining complete intermixing with the combustion gases. The tubes are preferentialy built out of mild steel and completely cross the combustion gas ducts, each tube being divided in three equal parts, with different number and sizes of holes (21), as better detailed in figure 3. The first part has two series of holes (21) with a diameter d and a spacing of x. The second part has two lines of d1.
diameter holes, where d1 is larger than d and spaced in an interval x1, smaller than x. Likewise the third part has d2 diameter holes (d2 larger than d1) spaced at x2 intervals smaller than x1.
The usual installation requires two parallel tubes (fig.2). In this case, the NH3 gas will enter one tube from the right end of the duct while the other tube enters from the left. The NH3 gas always enters the tube going through the d diameter, x spaced holes (21).
A plug (30) blocks the end αf each tube. The two series of holes of each tube (fig. 3) are located so that a hole of one series is always in between two holes of the other series.