JPS5998719A - Method and device for cleaning flue gas - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention purifies the sulfur dioxide outgoing gas by flue gas desulfurization using alkaline calcium compounds as absorbents, whereby a dry waste product containing mainly calcium sulfite is obtained. It relates to methods and devices for

When burning sulfur-containing fuels such as petroleum or coal, the combustion gases contain large amounts of sulfur oxide, primarily 802, which would seriously harm the environment if released into nature.

One method of rendering the oxides harmless is to treat the flue gas by wet-dry flue gas desulfurization in a cleaning facility that includes SO, a reaction vessel, and a precipitator. This prior art is described, for example, in Czechoslovakia Patent No. 96.138.

However, the dust separated in this prior art contains large amounts of sulphites, which have hitherto been stored in storage with all their disadvantages, ie the risk of contaminating ground water in case of leakage. Ta.

The present invention seeks to provide a method and apparatus for processing sulfites into useful products. Problems arising in the storage of waste are thereby eliminated, and at the same time commercially valuable products can be obtained from worthless waste.

The present invention therefore provides a method for cleaning flue gases of sulfur dioxide by flue gas desulfurization using alkaline calcium compounds as absorbents, in which a dry waste containing sulfites is obtained and said sulfites are The method is characterized in that the salt is oxidized by heating in a rotary kiln to form a sulfate in the form of anhydrite.

The invention further relates to an apparatus for carrying out the above-mentioned method, comprising a rotary kiln receiving the waste and passing combustion gases with excess air through the kiln in the same direction as the waste to heat the sulphites. and means for oxidizing to anhydrite.

According to an advantageous development of the invention, chlorine is removed from at least a portion of the waste containing sulphites in a chloride scrubber before the oxidation.

The ratio of the chloride-washed portion of the sulfite-containing waste to the portion of the waste that bypasses the chloride cleaning equipment is acceptable to the chloride content of the waste and the anhydrite obtained by oxidation. Determined by the chloride content.

In another advantageous embodiment of the invention, the chloride-washed portion of the waste is mixed with the portion of the waste that has bypassed the chloride washing device to form a cake, and this cake is pretreated before oxidation. dry. A portion of the dried sulfite-containing waste may be returned to the mixer to impart the desired moisture content to the cake.

Washing and drying processes are only necessary if the chloride content of the waste is too high for the intended reuse. The anhydrite obtained according to the present invention can be used as a substitute for gypsum in cement production, but
Other uses are also possible.

The present invention will be explained in further detail based on the accompanying drawings.

FIG. 1 shows a conventional wet-dry flue gas desulfurization installation, which includes an 802 reaction vessel 2 and a precipitator 4.

In the reaction vessel 2, the cough flue gas is sprayed with a streaked lime suspension or a mist of an aqueous solution containing a substance that reacts with and binds to sulfur dioxide. Simultaneously with this reaction, the water introduced evaporates.

In this way, a substantially dry dusty product is obtained which is passed together with the gas to a precipitator 4 in which solid product dust, unreacted substances and other solids are collected. Substances are separated.

The precipitator 4 usually consists essentially of an electric filter or a textile filter. The purified flue gas is then passed through flue 6.
It passes through and is discharged.

The waste separated by the precipitator 4 and the So1 reaction vessel 2 has a typical chemical composition as follows.

Ca5Os3'1Hz0 50 ~6o'! 6C
aSO4xH20B ~ 15% Ca(OH)z 15 ~ 20% CaCO5
8-1391: CaC7 snow o,s ~5% A part of the material obtained in the precipitator 4 is sent together with the material recovered from the SO2 reaction section 2 to a tank 7, where it is mixed with water. Some of this mixture is brought to metering tank 8 and mixed with the Ca(OH)*M suspension as an absorbent, after which the mixture in tank 8 is used in reaction mixture 2, as shown in FIG. It is then returned to the container for further treatment.

The mixture in tank 7 is brought to a chloride cleaning device which essentially consists of a cleaning tank 1 equipped with a filter 10.
Consists of 2. (For clarity, filter 10 and tank 1
2 are shown separately. ) The wash water is sent by 5 into the tank 12, a part of which is sent back to the metering tank 7 in order to reduce the required amount of wash water used. The Ctt-containing P liquid passes through an auxiliary filter 14 that separates dry matter, resulting in a clear F liquid that can be discharged to the sewer.

From chloride cleaning equipment, Ca5Oa, Ca5Oi
, Ca(OH)2, CaC0n containing 4
A cake having a content of 5 to 80% is obtained, which is mixed in the mixer 16 with the waste from the precipitator 4 which has bypassed the chloride scrubber. This portion of the waste contains between 1 and 5 inches of moisture and has substantially the same composition as the dry matter of the cake.

The mixer 16 has a feed screw 18 and an injector 20 located at the outlet of the mixer and is arranged at the inlet of the drying path. The injector 20 injects the material into a line 22 into which drying air is blown, so that the material is carried by said air to a drying cyclone 24 . This waste, dried in cyclone 24, can be returned to the mixer and incorporated into the cake, thereby imparting the desired dry matter content to the cake. The dry matter content of the waste injected from the mixer 16 is thus as high as 85-90%.

The exhaust gas from the drying cyclone 24 is sent to the dust collector 2 by 9.
6 and in this dust collector 26.

The dried waste is separated and the cleaned flue gas is sent to the flue 6 by line 28. The precipitator 26 may be constituted by an electrical filter or a textile filter of the same type as the precipitator 4. A portion of the waste gas of the drying cyclone 24 is conveyed by conduit 30Vc to a mixing chamber 32 in which diluted air entering from 11 as well as conduit 3
4 with the flue gas coming from the rotary kiln 36 and the resulting mixture is blown into the line 22. The dry waste separated by the dust collector 26 is
The waste sulfite is sent into a rotary kiln for oxidation to sulfate. The chemical reaction that occurs here is expressed by the following formula. ;I Cash3X 3AH20(8) 10% 02(gl-
*CasO4(sl+34H20(gl+Δ■),
(S) indicates a solid phase, and (g) indicates a gas phase.

This oxidation process yields anhydrite Ca5Oa as a useful end product. At this time, chlorine acts as a catalyst (Environme, March 1981)
ntal 5science & Technology
"G, Va in Volume 15, No. 3, Page 327
n) (“Kinetics of t.
he Reaction of Calcium 5ul
Fite and Calcium Carbonat
with 5ulphur Dioxide and
Oxygen in the presence of
The reaction is exothermic and the enthalpy of reaction is ΔH0 ~ -242 kJ/9. A second reaction occurs within the kiln.

Ca5Oa・HHzO(8), KOz(g)→Ca5
O4(81+3AH20(gl(I)CaSO4・
x)hO(s) −+ Ca5O4(s)+xHzo(
gl (TI)Ca(OH)*(s)→C
a0(, slIII20(gl (
III) The heats of reaction for the above reactions at three different temperatures are given in the following table.

Table 1 In the case of a reaction at 600°C, the following results are obtained.

Table ■ In Table ■, M represents the molecular weight, ΔHr and Q represent the heat of reaction from kJ/m to kJ/load, and Qp represents the heat capacity.

It has been found to be advantageous to operate the rotary kiln 36 in single-blade countercurrent operation, in which the waste 38 from the precipitator 26 and the combustion gases with a certain excess air 40 flow through the kiln. They pass in the same direction (see Figure 3). That is, the kiln is operated in countercurrent (Gegenstro
mbetrieb), in other words, waste 38
and gas 40 pass through the kiln in opposite directions (see FIG. 2), the gas flow is severely weakened and thus loses its movement within the kiln with the solid waste η. Don't do anything to hinder it. Furthermore, as already mentioned, the reaction in question is exothermic, and as mentioned above, the kiln cannot be cooled quickly because it can only be operated with a weak gas flow. It becomes expensive. For example, if sulfite-containing waste at 50°C and combustion gas at 500°C with 15% 02 are supplied, the exhaust gas will be approximately 10%
When a large amount of O3 is contained and the reaction is terminated at 600° C., a temperature profile as shown in FIG. 2 is obtained in countercurrent operation.

Therefore, the temperature of the kiln reaches approximately 1000° C., which is high enough to generate SO2 according to the following equation.

Ca5Os・%&0(s) −+ Ca0(sl+SO
2 (gl 10 M H2O (g) and due to the high temperature,
Expensive materials must be used in the manufacture of kilns. These difficulties are eliminated by operating the kiln in single-blade countercurrent operation. The ratio of smoke to air to solid waste can then be as high as, for example, 5:1.

At this time, the oxygen content reaches well over 18 to 20 layers, and the strong gas flow provides effective cooling. In other respects the same as in the case of countercurrent operation described above, a much more favorable temperature zorophyre is obtained in the Q-rameter as shown in FIG. 3 than in the case of countercurrent operation. In particular, before the waste from the dust collector 26 is fed to the rotary kiln,
It is heated by the kiln's exhaust gas. A combustion chamber 42 is arranged at the charging end of the rotary kiln 36, into which primary air and a fuel such as petroleum natural gas or pulverized coal are supplied for combustion.
(See Figures 1 and 3) 6 The operating conditions of the kiln that were found to be favorable are shown below. : Own pressure = 5-20% by weight Temperature = 500-700℃ The lower limit of temperature is due to insufficient oxidation rate, the upper limit is 802
This is due to the high cost of construction and, as already mentioned above, the high cost of construction.

Chloride stand @: o,
(see figure), this sulfate is sent by 19 to a cooling device 44. The cooling device essentially consists of a rotating drum into which air is blown at 17. The air heated in the cooling device 44 is sent to the combustion chamber 42 of the rotary kiln 36 via the cooling device 15 . Similarly, gas from the outlet of the rotary kiln 36 is returned via conduit 13 to the combustion chamber 42 of the rotary kiln 36. The anhydrite obtained from the cooling device 44 has the form of a somewhat granular, gray powder, the temperature of which is between 20 and 100°C, and which, as already mentioned, is particularly useful as a substitute for gypsum in the cement industry. However, other uses are also possible.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram of a flue gas desulfurization apparatus according to a specific example of the present invention, Fig. 2 is an explanatory diagram showing a temperature profile that can obtain the principle function of a rotary kill y in countercurrent operation, and Fig. 3 The figure is an explanatory diagram along with a temperature profile that provides the basic functions of a rotary kiln operating in one direction. 2...SO2 reaction, 4,26...Collector, 6.
... Flue, 7, 8... Placement tank, 10.14...
Filter, 12... Washing tank, 16... Mixer,
18... Feed screw, 20... Injector, 24...
... Drying cyclone, 32... Mixing chamber, 36... Rotary kiln, 38... Waste, 40... Excess air, 42... Combustion chamber, 44... Cooling installation.

Claims (1)

[Claims] (++ Process for cleaning flue gases of sulfur dioxide by flue gas desulfurization using alkaline calcium compounds as absorbents, the method comprising: obtaining a dry waste containing sulfites; , a method characterized in that said sulfite is heated and oxidized in a rotary kiln to form sulfate in the form of anhydrite. (2) Powdered waste containing combustion gas and sulfite with excess air in a rotary kiln. (3) The method according to claim 1, characterized in that the material is passed in the same direction. (3) The method according to claim 1, characterized in that calcium oxide, calcium hydroxide or calcium carbonate is used as an absorbent. A method according to scope 1 or 2. (4) Using chlorine as a catalyst for the oxidation process with a content of 0.
The method according to any one of claims 1 to 3, characterized in that the amount is added to 1 to 2%. (5) The method according to claim 2 or 3, characterized in that the oxidation is carried out at a temperature of 500 to 700°C. (6) A method according to any one of claims 1 to 5, characterized in that the sulfite-containing powder to be oxidized remains in the kiln for 3A to 2 hours. (The method according to any one of claims 1 to 6, characterized in that at least a portion of the waste containing sulfite is passed through a chloride washing device before oxidation. ) A patent characterized in that, when being fed to the drying stage, the portion of the waste containing sulfites that has passed through the chloride washing device is mixed with the portion of this waste that has bypassed the device to form a cake. A method according to claim 7. (9) Adjusting the amount of sulfite-containing waste passed through the chloride scrubber according to the chloride content of the flue gas and the desired chloride content in the resulting anhydrite. A method according to claim 8, characterized in that the OI sulphite-containing waste is dried between the chloride wash and the oxidation, or The method according to paragraph 9. 0υ A portion of the waste dried in the drying stage is returned to the inlet of the drying stage and mixed with the latter waste in order to adjust the moisture content of the waste that has not passed through the drying stage. The method according to any one of claims 8 to 10, characterized in that: (12) The method according to any one of claims 1 to 11 can be used to prepare an alkaline calcified metal. an apparatus for cleaning flue gas of sulfur dioxide by flue gas desulfurization using as an absorbent, in the process obtaining a dry waste containing mainly sulphites, the rotary kiln receiving the waste; An apparatus characterized by a means for passing combustion gas with excess air in the same direction as the waste through a rotary kiln to heat and oxidize the sulfite to anhydrite. The apparatus according to claim 12, characterized in that a cooling device for cooling the rotary kiln is provided. 13th
The equipment described in section. (Claims 12 to 14) characterized by means for returning the 151 gas from the outlet to the inlet of the rotary kill/
Apparatus according to any of paragraphs. (161) The device according to any one of claims 12 to 15, characterized by a chloride cleaning device connected upstream of the rotary kiln and cleaning at least a portion of the waste containing sulfites. Claim 12, characterized in that there is a metering unit for a C a (OH) filtrate added to the return fraction of the waste containing sulfites, which is connected to a chloride cleaning device. equipment. A mixer is connected next to the chloride cleaning equipment.
Claim 16 or 17, characterized in that in this mixer the washed waste is mixed to form a cake with the sulphite-containing material which has bypassed the chloride washing device. The device described. 01. Apparatus according to any one of claims 16 to 18, characterized by drying means for drying the waste from the mixer before being fed to the rotary kiln.