GB1567098A – Process for thermally deomposing salts which mainly comprise iron sulphate
– Google Patents
GB1567098A – Process for thermally deomposing salts which mainly comprise iron sulphate
– Google Patents
Process for thermally deomposing salts which mainly comprise iron sulphate
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Publication number
GB1567098A
GB1567098A
GB9469/78A
GB946978A
GB1567098A
GB 1567098 A
GB1567098 A
GB 1567098A
GB 9469/78 A
GB9469/78 A
GB 9469/78A
GB 946978 A
GB946978 A
GB 946978A
GB 1567098 A
GB1567098 A
GB 1567098A
Authority
GB
United Kingdom
Prior art keywords
gas
fluidizing
oxygen
salts
fluidized bed
Prior art date
1977-03-12
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB9469/78A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
GEA Group AG
Original Assignee
Metallgesellschaft AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
1977-03-12
Filing date
1978-03-09
Publication date
1980-05-08
1978-03-09
Application filed by Metallgesellschaft AG
filed
Critical
Metallgesellschaft AG
1980-05-08
Publication of GB1567098A
publication
Critical
patent/GB1567098A/en
Status
Expired
legal-status
Critical
Current
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Classifications
C—CHEMISTRY; METALLURGY
C01—INORGANIC CHEMISTRY
C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
C01G49/00—Compounds of iron
C01G49/02—Oxides; Hydroxides
Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
Y10S423/00—Chemistry of inorganic compounds
Y10S423/01—Waste acid containing iron
Y10S423/02—Sulfuric acid
Description
PATENT SPECIFICATION
( 11) 1 567 098 0 \ LI( 21) Application No 9469/78 ( 22) Filed 9 Mar 1978 ( 19), ( 31) Convention Application No 2710978 ( 32) Filed 12 Mar 1977 in ‘ / ( 33) Fed Rep of Germany (DE) ( 44) Complete Specification Published 8 May 1980 ( 51) INT CL 3 C Oi G 49/02 ( 52) Index at Acceptance C 1 A 3 C 2 420 421 N 13 N 48 N 4 P 11 PB 5 ( 72) Inventors: GEORG DARADIMOS MARTIN HIRSCH LOTHAR REH JORG THOMAS ( 54) PROCESS FOR THERMALLY DECOMPOSING SALTS WHICH MAINLY COMPRISE IRON SULPHATE ( 71) We, METALLGESELLSCHAFT AKTIENGESELLSCHAFT, a body corporate organized under the laws of the German Federal Republic, of Reuterweg 14, 6 Frankfurt am Main, German Federal Republic, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly
described in and by the following statement:-
This invention relates to a process for thermally decomposing salts which mainly comprise iron sulphate, in a fluidized bed, wherein a major part of the resulting metal oxide is discharged together with the gas from the top part of the shaft and is separated from the gas in a recycling cyclone and is recycled at least in part to the fluidized bed, the exhaust gas from the fluidized bed reactor is contacted with feed salt containing mainly iron sulphate, the fluidized state is maintained by oxygen-containing fluidizing gas, which has been preheated, and by oxygen-containing secondary gas, which has been preheated and fed above the inlet for the fluidizing gas, and fuel is fed into the zone between the inlets for the fluidizing gas and secondary gas.
Numerous chemical processes involve the formation of metal sulphates which must not be dumped for ecological reasons or which contain valuable substances, which can be economically recovered.
The recovery process that is most important by far is a thermal decomposition process which results in the formation mainly of metal oxides and sulphur dioxide The resulting sulphur dioxide is condensed or is used in conventional processes for producing sulphuric acid, while resulting metal oxides may be processed further by other methods.
More recently, a fluidized bed reactor has proved to be a particularly important unit in which to carry out such decomposition processes, an advantage of such a reactor being that a metal oxide which is virtually free from sulphur can be obtained in a single operation Those fluidized bed reactors which are considered as orthodox because they operate with a relatively low velocity for the fluidizing gas have the disadvantage that the throughput rate per unit of cross-sectional area is not as high as is desired Certain difficulties are also involved in the complete combustion of fuels particularly liquid or gaseous fuels.
The disadvantages of an orthodox fluidized bed are avoided by another fluidized bed process in which a so-called expanding fluidized bed can be used to decompose metal sulphates In this process, turbulent gases comprising the fluidizing gas and a secondary gas are controlled to flow at such a high gas velocity that a major part of the solids is entrained by the gas leaving the upper part of a shaft in which the bed is contained, is usually separated from the gas and is then recycled to the fluidized bed reactor However, this process is not satisfactory, particularly for the decomposition of salts which mainly comprise iron sulphate and especially when such salts contain also adherent sulphuric acid, because the exhaust gas temperature cannot be adjusted in a technologically advantageous manner since a multistage suspension-type exchange system is involved.
According to the present invention there is provided a process for thermally decomposing salts which mainly comprise iron sulphate and contain at least one mole of water of crystallization wherein the salts are contacted in a single suspension-type exchanger with hot exhaust gas and then fed into a fluidized bed comprising a shaft portion from the top part of which a major part of the resulting metal oxide is discharged together with the gas, is separated from the gas in a cyclone and is recycled, at least in part, to the fluidized bed, the exhaust gas from the fluidized bed constituting said hot exhaust gas and being contacted with the salts in said 2 1,567,098 2 exchanger, and wherein said bed is maintained in a fluidized condition by introducing into the shaft portion oxygen-containing fluidizing gas which has been preheated, oxygen-containing secondary gas which is fed above an inlet for the fluidizing gas and at least one stream of which has been preheated, and fuel into the region between the inlet for the fluidizing gas and one or more inlets for the secondary gas, the fluidized condition being such that the bed has a mean 5 density of 20 to 300 kg /m 3 in the zone between the inlets for fluidizing gas and the secondary gas, and a mean density of 1 to 20 kg /m 3 in the zone above the secondary gas inlet(s), the fluidizing gas and secondary gas being preheated by indirect heat exchange in a fuel-heated heat exchanger, and the quantity of oxygen introduced via said fluidizing and secondary gases being controlled in dependence upon the quantity of fuel and the operating conditions being 10 such that the gas leaving the suspension type exchanger has free oxygen content of 1 to 6 %by volume and a temperature of 300 to 450 WC.
The above-mentioned requirements to be met by the exhaust gas are essential for the process because they ensure that iron is oxidized to trivalent iron and any free sulphuric acid which adheres to the salt is chemically combined as a result of the increase of the valency of 15 the iron This serves to avoid an otherwide inevitable elimination of sulphuric acid or sulphur trioxide by distillation The exhaust gas temperature is also significant for the subsequent dust collection, particularly in an electrostatic precipitator, and for avoiding of corrosion.
It is particularly desirable to feed fuel at a constant rate into the zone between the inlets for the fluidizing gas and the secondary gas and to adjust the exhaust gas to the desired 20 temperature by controlling the temperature to which the fluidizing gas and the secondary gas are indirectly heated.
The oxygen contents of the fluidizing gas and secondary gas are preferably controlled so that a mean oxygen concentration of at least 25 % by volume results The mass flows of the two gases must obviously be taken into account in calculating the mean oxygen concentra 25 tion The reaction of the gas streams with fuel has not yet been considered For instance, air may be used as fluidizing gas and as secondary gas and air enriched in oxygen or pure oxygen may be fed through a gas lance directly into the zone between the inlets for the fluidizing gas and secondary gas Alternatively air may be enriched with oxygen before the air is fed to the fuel-fired heat exchanger 30 In a modification of the present process, the oxygen containing gases supplied to the fluidized bed reactor contain at least 30 % by volume oxygen, on an average, and the preheating of the fluidizing gas and secondary gas is omitted The use of gases which are so highly enriched with oxygen would otherwise involve difficulties in the control of the desired exhaust gas temperature Under these conditions, the exhaust gas temperature can easily be 35 controlled merely by the division of the gas into fluidizing and secondary gases and by the control of the fuel feed rate.
The control of the rate of fluidizing and secondary gases and the selection of the level at which the secondary gas is fed into the fluidized bed reactor are effected in conventional manner, e g, in the manner described in Opened German Specification No 17 67 628 40
In dependence upon the newly fed material, the operating conditions in the fluidized bed reactor are selected so that a suspension having a mean density of 20 to 300 kg /m 3 is obtained in the zone between the inlets for the fluidizing gas and secondary gas and a suspension having a mean density of 1 to 20 kg /m 3 is obtained in the zone above the secondary gas inlet 45 When the Froude and Archimedes numbers are used to define these conditions of operation in the fluidized bed reactor, the following ranges are obtained:
3Pg 01 < Y
