JPS5870820A - Desulfurization of 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 provides a method for absorbing sulfur oxides present in the flue gas by spraying an aqueous suspension or solution of a basic absorbent for sulfur oxides into the heated flue gas. The present invention relates to an improved desulfurization process for flue gases in which the spray droplets are simultaneously dried, thereby preparing a powdered by-product in which a substantial portion of the sulfur oxides of the flue gases have been absorbed. The method produces by-products that have wider industrial applicability than those of conventional methods, but are also not harmful to the fR environment.

Methods of the above type are described in well-known specifications in the art and in the documents mentioned therein.

The absorbent that has found the widest application in these desulfurization processes is slaked lime, i.e. calcium hydroxide, perhaps containing some magnesium hydroxide, but also preliminarily containing carbonate (IJ) and other basic substances. It is being

These processes produce a by-product that is a powdered material, the composition and structure of which depends on several characteristics, such as the amount and composition of the fly-acqueue in the flue gas to be desulphurized and the composition of the selected absorbent, and the operational characteristics, e.g. depending on the temperature within the absorption band. The use of partial circulation of by-products for use in the preparation of absorbent liquids to be sprayed has a significant influence on the structure of the by-products purged from the process.

Tributes removed from the flue gas will be present in the powdered by-products as sulfites and sulfates. Usually, the amount of sulfite is slightly higher than the amount of sulfate. However, this relatively high sulfite content, present as either sodium sulfite, magnesium sulfite or calcium sulfite, is useful for by-product disposal or industrial use. There are some restrictions regarding

Sodium acetate, which is very soluble in water, presents a potential risk of subsoiling water when disposed of, and calcium acetate is bath-compatible with water, but its disposal may be inadvertently carried out anywhere. In order to utilize the by-products obtained in the cement industry, containing ash, ash, and fly ash and using lime as an astringent, the calcium sulfite content in the tube must be high enough. Has species restrictions.

It has now been found that a substantial reduction in the 91C salt content in the by-product is obtained in the desulfurization process of the present invention.

The new process makes it possible to obtain by-products that are either commercially available products or easily disposed of that can be used in the cement industry without undue expense in terms of equipment and operation.

By heating the sulfite containing waste absorbent according to the process of the invention, an exothermic reaction occurs whereby the sulfite is essentially completely converted to sulfate.

Several measures are contemplated for applying the heating of the present invention. In order to ensure the presence of sufficient oxygen for the oxidation of sulfite to sulfate, it is suitable to heat the waste sorbent while it is suspended in an oxygen-containing gas. Therefore, heating is preferably carried out in a fluidized bed apparatus! A treatment, where a heated oxygen-containing gas serves as a fluidizing gas, or a waste absorbent is suspended in and entrained in a stream of heated oxygen-containing gas, and a collector device, e.g. a cyclone (where the oxidized waste absorbent is collected).

Attention is first paid to Figure 1 of the drawing. In Figure 1, l
indicates a duct carrying a flow of heated flue gas to be desulphurized originating from a boiler or the like (not shown).

The temperature of the flue gas in the duct) is typically between JjO~to
o'C or higher.

In the heat exchanger, the flue gas is used to preheat combustion air for the boiler. Thereby, the temperature of the flue gas is, for example, approximately /! The temperature is lowered to θ℃.

From the heat exchanger, the flue gas is conducted through duct 3 to the blow drying-absorption unit.

The digester (5inker) j is supplied with quicklime through duct 6 and water through conduit 7.

By digesting the Ca(OH)2Ji4 suspension,
and feed the suspension into a mixing chamber (44r).

The mixing tank t is a recirculating arm absorbent through a conduit (described later).
and further receives water through conduit 10.

An aqueous suspension of Cm(OH)2 and recycled waste absorbent is fed from a mixing tank t to a drying-absorption unit, in which the aqueous suspension is atomized into the flue gas to be treated. do.

Thereby, the sulfur oxides in the flue gas, mainly SO2
A substantial portion of the adsorbent is absorbed by the atomized droplets, which are simultaneously imbedded with a calcium bibrite-containing powder (referred to herein as waste absorbent). A portion of the solite-containing powder thus prepared is collected at the bottom of the spray drying unit and is withdrawn from the unit via conduit 1/1.

The remaining part of the sulphite-containing powder is entrained by the sulfite gas and transferred in the latter to the dust separator/2, for example a bag filter. Collect the dust diffuser and l/
It is partially recirculated through the conduit line with the waste absorbent recovered through the mixing tank t, while the remaining part or portion thereof is subjected to the special oxidative heating of the present invention.

Said portion of the waste absorbent to be oxidized is introduced through conduit /3 into the fluidized bed apparatus lt, where said portion forms a fluidized bed in the heated gas. In the illustrated embodiment, the heated gas consists of a partial stream of heated flue gas from a duct), the flue gas being an oxidizing gas introduced through conduit 17, such as air or oxygen in a more pure state. The temperature of the flue gas inside is 330-400℃
If the desired temperature in the range of . The embodiment is illustrated by the duct shown in dotted lines.

From the fluidized bed device 16 the waste absorbent, in which a substantial part of the sulphite has been converted to sulphate, is recovered through the conduit/l and the fluidizing gas leaving the fluidized bed device is transferred to the duct 3. Since the gas is passed through the dust separator saw before being discharged into the chimney, no separate dust collector is required to remove entrained particles of oxidized waste absorbent therefrom.

To improve the process in terms of oxidation efficiency.

Digest the promoter! Alternatively, the oxidizing gas that can be added to the suspension in the mixing tank r and/or introduced through the /7 can consist of gases with high oxidizing potential, such as ozone and chlorine.

Obviously, many variations may be possible to the embodiment described with respect to FIG. Thus, a heating system such as that shown in FIG. 2 can be used in place of the fluidized bed apparatus shown in FIG.

In the WIJ diagram, π is the supply line of the sulfite waste absorbent, which leads the waste absorbent to the mixer 21 and the waste absorbent is ducted by the mixer 1). ). The waste absorbent is thereby preheated to, for example, JOO°C.

"Duct" is a particle collector device such as an electrostatic precipitator,
From the collector device connected to a baghouse or cyclone, the collected absorbent is transferred at a temperature of about 200°C to the lower end of a heating tower J, where it is transferred to a heating tower J at a temperature of about 300°C. suspended in a stream of hot air introduced into the bottom of the tube.

In order to increase the temperature, the heating tower is equipped with a device for directly heating the contents of the heating tower, for example a fuel burner as designated by 2J.

In the heating tower, the waste absorbent is oxidized, thereby converting a substantial portion of the sulfite to sulfate.

The temperature in the heating column reaches values of up to 400° C., in part due to the heat liberated by the exothermic oxidation.

From the top of the heating tower, the gas entrained with particulate absorbent is transferred to cyclone U, where a substantial portion of the absorbent is collected;
On the other hand, the remaining part is entrained in the gas led to the mixer 1 and then collected in the cyclone 0.The absorbent collected in the cyclone is transferred to the second cyclone U.
In the supply duct core, the heating absorbent is suspended in the fresh air flow shown in Utah, whereby a heat exchange takes place and heats the air to a temperature of e.g. 4 Aoo°C. .

From the cyclone d, the air heated in this way together with fine particles of absorbent is conducted to the bottom of the heating tower 2μ, while the main part of the treated absorbent is passed from the cyclone through a conduit 30 to be used, for example, in the cement industry or for other purposes. Calcium sulfate plaster suitable for use in
・) Collected as fly assembly.

The invention is further explained below by way of example.

Example 1 Flue gases resulting from the combustion of three different qualities of coal were desulfurized by the spray drying-absorption method described in connection with Figure 1, but omitting the oxidative heating of the waste absorbent recovered through the IS. did. Various parameters of the desulfurization process are described in U.S. Pat. It was within the range described in the specification of No. 73. The waste absorbent recovered from the process had the following sulfite and flyassy contents:

West Germany - "71% by weight 33% by weight" Samples of these three types of waste absorbent from rural areas were subjected to thermogravimetric analysis (TGA).
The results are shown in FIG.

In this figure, the weight of each sample of three qualities of waste absorbent is plotted against temperature.
The weight of the sample was recorded continuously while increasing by 0°C. Excess air was present during heating. Vertical axis scale o -to
o corresponds to the sample weight sl in the case of tests A and B and to 1ot4 of the sample weight in the case of test C.

For each graph in FIG. 3, the temperature corresponding to the point at which the tangent deflection occurs is shown. Said temperature can be considered the lowest temperature at which rapid oxidation occurs. These minimum temperatures for rapid oxidation appear to vary considerably depending on the nature of the waste absorbent, and the temperatures for the three samples in question are as follows:

A: 340°C, and 0:370°C. Example In this example, a pilot test was carried out on two samples of waste absorbent, i.e., l corresponding to the material used in Test A of Example 1.
A sample was run on a sample corresponding to the material used in Test C of Example 1, but the sample had a slightly lower sulfite content.

The samples were processed on a viroft scale by preheating in a cyclone as shown in Figure 1 at the operating conditions shown in the table below and then oxidized in a fludge and calciner. The table also shows the degree of oxidation obtained.

Absorbent throughput (K#/hour) 1
0 Oxidation temperature ('C) syo''Csro℃ Gas retention time (sec) o, t
Preheating temperature of o, r powder ('C) iro℃
Initial sulfite content at 220°C (l)
lr, J 21,0 Sulfite content after oxidation C%
) /, co j, co oxidation degree o
, ya o, ri table shows that for both types of waste absorbent, substantial conversion of sulfite to sulfate occurs by the process of the invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic illustration of a specific example showing all the steps of the method of the present invention in which a fluidized bed apparatus is used for oxidative heating, and FIG. 3 shows the results of the thermogravimetric analysis described in Example IK...Spray Drying-Absorption Unit, j
···Digestive organ,! ...Mixing tank, /Co...Dust separator, /6...Fluidized bed device, Co3...Collector device, J...Heating tower, T...Cyclone, 3...No. Two cyclones. Applicant's agent Kiyoshi Inomata F/(3,2 o Q & 31 Yumi 3 Continued page 1 of R8 to R Claim of priority @ September 8, 1981 [phase] Denmark (
DK) ■3978/81 0 Inventor Breston Leonard Beltman 212 Old Country Road, Severna Park, Maryland, United States of America

Claims (1)

[Scope of the Claims] At the same time as an aqueous suspension or solution of a basic absorbent for 4 sulfur oxides is sprayed into the heated flue gas, the sulfur oxides present in the flue gas are absorbed. A flue gas comprising drying the spray droplets, thereby preparing a dry product containing sulphites and sulphates, and recovering this dry product as a powder which also contains flyacques initially present in the flue gas. A process for desulfurizing flue gas, characterized in that at least a portion of the recovered powder is heated in the presence of an oxygen-containing gas to convert a substantial portion of the sulfite to sulfate. 10 The recovered powder contains oxygen j~100% by volume and! 10. The method according to claim 1, wherein the turbidity is carried out in a gas having a -600°C apparatus. J. Claims 1 or 1, wherein said heating of the powder is carried out in the flow of non-desulphurized flue gas upstream of the point where a suspension or solution of absorbent is sprayed into said flue gas. The method described in section. Only a portion of the recovered powder is heated in an oxygen-containing gas and then removed from the process for disposal or industrial use, while the remaining powder is recycled for the preparation of an aqueous suspension or solution to be sprayed. A method according to claim 1. j, said recovered powder contains sulfite and sulfate in a ratio (tont weight) between lO/l and ///, said ratio being reduced by heating to a value between /// and /// 00; 2. A method as claimed in claim 1, wherein 2. The method according to claim 1, wherein said heating is carried out in a fluidized bed. 7. The method according to claim 1, wherein the basic absorbent is an alkaline earth metal hydroxide. , t. The method of claim 1, wherein the basic absorbent is sodium carbonate. Prepare a suspension or aqueous solution. (b) spraying said suspension or solution into a stream of heated flue gas; (C) a dry powder consisting of the material obtained by drying and absorption in step (b) and the flyaxe present in the flue gas; (d) removing a partial stream of the heated flue gas in the direction upstream of the place where the suspension or solution is to be sprayed, said partial stream having a temperature of 330 to 100°C);
, (・) Part of the powder collected in step (C) is transferred to step (
IM in the partial stream of heated flue gas removed in d)! The average contact time of the powder is 0.1 to 0 minutes.
f) collecting from the partial gas stream at least a substantial part of the powder suspended therein as a by-product with an increased sulfate content and a -1'-° reduced sulfite content; (g) Said partial gas stream, which is free of entrained powder not collected in step (f), is added to the suspended liquid. (h) placing the remainder of the powder collected in step (c) in solution or suspension in step (a); A process for obtaining by-products with an increased sulfate content and a reduced sulfite content by desulfurization of flue gas, characterized by recycling for the preparation of a liquid. . 3. A method according to any one of claims 1 to 2, wherein a solid promoter is added to the suspension or solution of the absorbent. 71. The method of claim 70, wherein the promoter is selected from calcium chloride and iron compounds. /-2. The method according to any one of claims 1 to ta11, wherein the oxidizing gas is added to the heating gas for heating the powder. /3. A method according to claim 1.2, wherein the oxidizing gas is selected from ozone and chlorine.