GB1594855A

GB1594855A - Purification of gases

Info

Publication number: GB1594855A
Application number: GB4387177A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1975-05-06
Filing date: 1977-10-21
Publication date: 1981-08-05
Anticipated expiration: 1998-08-05

Description

(54) IMPROVEMENTS RELATING TO THE PURIFICATION OF GASES (71) I, HEINZ HOLTER, a German Citizen of Beisenstr. 39-41, 4390 Gladbeck, German Federal Republic, do hereby declare the invention for which I pray that a patent may be granted to me and the method by which this is to be performed to be particularly described in and by the following statement: This invention is concerned with the purification of gases and is an improvement in or modication of the invention the subject of my co-pending application No. 42954/78 (Serial No. 1551357).

A number of industrial and other gases have noxious components which may be regarded as contaminants. Such gases are purified or separated from one or more noxious components by contact with solid sorption agents.

The solid sorption agents are single chemical compounds or admixtures of plural ingredients; they are generally employed in a finely-divided state to present the gas with a larger available contact surface. After sorption is effected, the noxious components removed from the gas are separated from the sorption agents, which can then be reused.

In the specification of U.K. Patent No. 1,551,357, there is disclosed a method of gas purification wherein a solid absorption agent is brought into contact with the gas to be purified, to react with pollutants contained in the gas, wherein the absorption medium comprises compounds of alkali and/or alkaline earth metals, together with bog-iron ore and/or ferric oxide.

It is one of the various objects of this invention to provide a sorption agent for the removal of contaminants from contaminated gas, which in certain circumstances at least has improved performance characteristics.

According to this invention there is provided a sorption agent for the removal of contaminants from contaminated gas which is brought into contact with the sorption agent, wherein the sorption agent comprises a sorption medium comprising dust produced during iron or steel production carried on the particles of a particulate carrier material, the dust comprising ferric oxide, together with an alkali metal oxide and/or an alkaline earth metal oxide.

Harmful substances such as H2S, SO2, HCN, NOX, HF, HCI, phenol, formaldehyde maybe removed from gases by bringing the sorption agent into contact with a stream of the gas, intimately mixing the sorption agent with the gas, and thus with contaminates therein, and then subsequently separating the sorption agent from the gas.

Thus, by this invention, a use has been found for an otherwise substantially worthless byproduct of iron or steel production. No prior use for such dust, which previously had to be dumped, is known. The present invention thus provides a sorption agent (and the use of such agent) with improved sorption properties and which is available in large quantities at low cost.

Although effective contact may be achieved by merely passing a contaminated gas stream through a bed of the subject sorption agent, better results are obtained with a fluidized bed and even greater contaminant removal is effected when the sorption agent is intimately admixed with the contaminated gas stream. Such intimate admixture maybe achieved, e.g.

by conducting the sorption agent into the gas stream as the latter is passed through tube-shaped sections with venturi-like inserts. Such inserts cause turbulence in the gas stream and thus produce intensive and intimate contact between the sorption agent, the gas and any contaminants in the gas. After a comparatively short contact period, the sorption agent is removed from the gas stream. Advantageously apparatus of the kind described in detail in the specification of my U.K. Patent No. 1,551,356 may be used.

In view of the alkaline properties of the sorption medium it is extremely useful for removing noxious contaminants from gases. The following table shows quantitative analyses for three different dust samples taken from the steel industries dust-removal systems at various times and locations. Sample 1 is from a basic oxygen steel making plant; Sample 2 an open-hearth steel plant; Sample 3 a pig-iron mixer in which desulfurization is effected. Similarly useful dust obtained e.g. from dust removal equipment in an electric steel plant.

Composition % by weight 1 2 3 Annealing or Ignition loss 6.07 2.38 3.02 SiO2 1.97 1.04 0.93 Fe2O3 48.88 42.50 33.42 Al203 ' 0.00 0.50 0.20 CaO 28.75 23.20 24.34 MgO 3.70 6.25 4.02 Na2O 3.80 2.80 2.45 K2O 0.71 1.43 1.02 Pb -- 1.04 1.62 V -- 0.50 0.80 Ni -- 0.08 0.12 P2O5 -- 1.28 2.14 SO3 1.54 4.58 16.33 Zn 0.00 3.25 1.68 Higher alkalinity is imparted to the sorption medium by the addition to the dust of calcium hydroxide and/or fine white lime therewith.

Fine white lime is about 95 percent by weight of CaO; it is prepared by calcining limestone and grinding the calcined product so that 99 percent by weight thereof has a grain size of less than 3 mm. As a number of contemplated contaminants, such as H95. SO,, HCN, nitrogen oxides (NOx), HF and HCI are acidic, such higher alkalinity is advantageous in their removal from the gas stream. The sorption capability of the medium is further improved by adding bog iron ore and/or heavy metal salt, such as a salt of lead, silver, gold, mercury, bismuth or copper, e.g. cuprous chloride.

The sorption agent may be used in pelletized form, and may be used either dry or moist.

When employed in moist form, metal components form metal hydroxides, which have highly-active, properties for quantitatively binding noxious substances, such as H2S, HCN, NOX and SO,.

Any aluminum in the sorption medium is ordinarily in complex form, such as in the form of an aluminate, due to its amphoteric properties under alkaline conditions, but this does not preclude it from binding noxious contaminants.

The sorption medium may, but need not necessarily, contain components which react chemically with one or more contaminating components of the gas under conditions of contact.

The sorption medium maybe carried on the surface of. or dispersed throughout the carrier particles. Suitable carriers include sawdust. wood flour and expanded clay. e.g.

expanded vermiculite; those having particularly large surface areas are preferred.

Favorable properties are obtained when expanded ("popped" or exploded) perlite is the carrier on which the sorption medium is applied. For this purpose, the sorption medium or the dust is, e.g., stirred with water to form a sprayable suspension which is applied to or sprayed upon the perlite in a mixer.

Using expanded perlite as carrier provides a number of advantages. particularly during dry sorption. The low specific weight of the combined carrier and sorption medium makes it possible to have a large quantity of sorption medium on or throughout the carrier material particles without significantly negatively influencing the flight or flow pattern of carrier particles in the contaminated air or other gas stream being cleaned. The bizarre shape and the large surface area of perlite grains guarantee good adhesion of the sprayed-on sorption medium or dust suspension and provide favorable prerequisites for reprocessing consumed or exhausted sorption medium.

Perlite is chemically neutral; it does not burn; it is humidity and moisture resistant; and it is free of organic impurities. Moreover. the porous structure of expanded perlite permits a high degree, e.g. up to 70%, of water intake; this accounts for the improved sorption properties obtained when moistened perlite is used as carrier material. For expanded perlite or other carrier, water and caustic soda are illustrative of suitable moistening agents which can be used. Using caustic soda has the advantage of increasing the alkalinity of the sorption agent.

The high sintering temperature (about 1,000"C) and the high thermal softening temperature (from about 1,220 to about 1,320"C) of expanded perlite are advantageous carrier properties because they make it possible to use the sorption medium (applied on such a carrier) for purifying very hot gases. for example, from coal pressure gassification or from garbage burning, even when such are at temperatures of up to 750 C or more.

The high temperature resistance of expanded perlite is also advantageous for processing exhausted sorption medium thereon. Exhausted sorption medium on expanded perlite carrier is, e.g., roasted to obtain SO2-containing roasting gases, which are readily processed into sulfuric acid in a Claus system or through wet catalysis. The perlite remains preserved.

It is cooled off and reactivated by, e.g., a water spray.

Perlite carrier is preserved even when exhausted material (comprising perlite and sorption medium carried on the perlite) is treated with organic solvent, e.g. when recovering sulfur from the exhausted material. The sorption medium however, may (in such a process) be chemically converted, in which case the perlite (which remains intact) is again covered with fresh sorption medium.

Exhausted sorption medium. i.e. that which is combined with contaminant components, is readily disposed of even when on a carrier material such as perlite, because such requires only a small area in an appropriate dump. Expanded perlite is e.g., compressed to one tenth of its original volume, which also encompasses all absorbed noxious substances therewith.

The sorption agent according to the invention has sufficient alkalinity to absorb noxious and other contaminant components from gases under stable conditions and in a controlled manner. The presence of alkaline material also facilitates re-processing or further processing, for example by roasting and moistening, of sorption agents, as a result of which fast reconversion of iron components into iron-lII-hydroxide is assured.

The sorption agent according to the invention may be used in either dry or moist form for the most varied methods and mechanisms in which harmful substances are removed from gases by means of adsorption.

This invention also provides a method of gas purification in which a sorption agent, comprising a solid sorption medium carried on the particles of a particulate carrier material is introduced into a stream of gas to be purified, to react with pollutants contained in the gas, the sorption medium comprising dust produced during iron or steel production and which comprises ferric oxide together with an alkali metal oxide and/or an alkaline earth metal oxide.

The following examples are merely illustrative examples of the invention and are not limitative of the remainder of the disclosure in any way. In the examples all references to "dust" are to dust of Sample 1 (in the preceding table) from a basic oxygen steel-making plant.

The contaminated gas in Example 1 is typically a gas obtained by pyrolysis of garbage and comprising, besides the contaminants mentioned in the example, nitrogen. carbon dioxide and hydrocarbons.

The gas mentioned in Example 2 is typically a coke oven gas comprising. besides the contaminants mentioned in the example, carbon oxide, hydrogen. carbon dioxide, methane, other hydrocarbons and nitrogen.

The gas in Example 3 is typically a flue gas from coal fired electric power plants. Except the constituants mentioned in Example 3 this gas comprises oxygen. carbon dioxide and nitrogen, small quantities of carbon oxide and dust. The gas mentioned in Example 3 may also be gas deriving from burning of garbage and in this case the gas may comprise in addition larger quantities of dust and hydrochloric acid, the latter in quantities of up to or more than 1.000 mg/nm'.

The contaminated gas stream, however, is not so limited, as the principal gas is virtually any non-acid gas, e.g. rare or inert gas. air, nitrogen or oxygen.

Example 1 Pass 5,2000 nm3 per hour of contaminated gas (containing 1,500 mg/nm3 of H2S and 2,500 mg/nm3 of HC1) at 1600C through a fluidized bed (72 kg per hour) of sorption agent (42) weight percent of dust; 58 weight percent of perlite having a grain size of from 3 to 6 mm) td obtain a purified gas in which the H2S content and the HCI content are below an analytically-determinable level.

Example 2 Pass 5,200 nm3 per hour of contaminated gas (containing 1,500 mg/nm3 of H2S, 150 mg/nm3 of HCN, 40 mg/nm3 of phenol and 20 mg/nm3 of H2F2) at 30"C through a fluidized bed (72 kg per hour) of sorption agent (42 weight percent of dust; 42 weight percent of water; 16 weight percent of perlite having a grain size of from 3 to 6mm) to obtain a purified gas in which the H2S content, the HCN content, the phenol content and the HF content are.

below an analytically-determinable level.

Example 3 Pass 5,200 nm3 per hour of contaminated gas (containing 2,000 mg/nm3 of SO2, 1,000 mg/nm3 of HCI and 500 mg/nm3 of nitrogen oxides - NOx) at 1400C through a fluidized bed (72 kg per hour) of sorption agent (42 weight percent of dust; 15 weight percent of fine white lime; 20 weight percent of water; 23 weight percent of perlite having a grain size of from 3 to 6 mm) to obtain a purified gas in which the SO content is 50 mg/nm3, the HCI content is below an analytically-determinable level, and the NOX content is 150 mg/nm3.

WHAT I CLAIM IS: 1. A sorption agent for the removal of contaminants from contaminated gas which is brought into contact with the sorption agent, wherein the sorption agent comprises a sorption medium comprising dust produced during iron or steel production carried on the particles of a particulate carrier material, the dust comprising ferric oxide together with an alkali metal oxide and/or an alkaline earth metal oxide.

2. A sorption agent according to Claim I wherein the carrier material is sawdust.

3. A sorption agent according to Claim 1 wherein the carrier material is expanded clay.

4. A sorption agent according to Claim 1 wherein the carrier material is expanded pearlite.

5. A sorption agent according to Claim 1 wherein the carrier material is moistened expanded pearlite.

6. A sorption agent according to Claim 5 wherein the pearlite is moistened with caustic soda.

7. A sorption agent according to anyone of the preceding Claims wherein the sorption medium addititionally comprises calcium hydroxide and/or fine white lime as herein defined.

8. A sorption agent according to anyone of the preceding claims wherein the sorption medium additionally comprises bog-iron ore and/or heavy metal salts.

9. A sorption agent according to anyone of the preceding claims in pelletized form.

10. A sorption agent according to anyone of the preceding claims wherein the sorption medium is carried on the surface of the carrier particles.

11. A sorption agent according to anyone of Claims 1 to 9 wherein the sorption medium is dispersed throughout the carrier material particles.

12. The method of gas purification in which a sorption agent, comprising a solid sorption medium carried on the particles of a particulate carrier material. is introduced into a stream of gas to be purified, to react with pollutants contained in the gas, the sorption medium comprising dust produced during iron or steel production and which comprises ferric oxide together with an alkali metal oxide and/or an alkaline earth metal oxide.

13. A method according to Claim 12 comprising the steps: (a) introducing the sorption agent into a stream of the contaminated gas; (b) intimately mixing the sorption agent with the gas and (c) separating the sorption agent from the gas.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Example 1 Pass 5,2000 nm3 per hour of contaminated gas (containing 1,500 mg/nm3 of H2S and 2,500 mg/nm3 of HC1) at 1600C through a fluidized bed (72 kg per hour) of sorption agent (42) weight percent of dust; 58 weight percent of perlite having a grain size of from 3 to 6 mm) td obtain a purified gas in which the H2S content and the HCI content are below an analytically-determinable level. Example 2 Pass 5,200 nm3 per hour of contaminated gas (containing 1,500 mg/nm3 of H2S, 150 mg/nm3 of HCN, 40 mg/nm3 of phenol and 20 mg/nm3 of H2F2) at 30"C through a fluidized bed (72 kg per hour) of sorption agent (42 weight percent of dust; 42 weight percent of water; 16 weight percent of perlite having a grain size of from 3 to 6mm) to obtain a purified gas in which the H2S content, the HCN content, the phenol content and the HF content are. below an analytically-determinable level. Example 3 Pass 5,200 nm3 per hour of contaminated gas (containing 2,000 mg/nm3 of SO2, 1,000 mg/nm3 of HCI and 500 mg/nm3 of nitrogen oxides - NOx) at 1400C through a fluidized bed (72 kg per hour) of sorption agent (42 weight percent of dust; 15 weight percent of fine white lime; 20 weight percent of water; 23 weight percent of perlite having a grain size of from 3 to 6 mm) to obtain a purified gas in which the SO content is 50 mg/nm3, the HCI content is below an analytically-determinable level, and the NOX content is 150 mg/nm3. WHAT I CLAIM IS:

1. A sorption agent for the removal of contaminants from contaminated gas which is brought into contact with the sorption agent, wherein the sorption agent comprises a sorption medium comprising dust produced during iron or steel production carried on the particles of a particulate carrier material, the dust comprising ferric oxide together with an alkali metal oxide and/or an alkaline earth metal oxide.

14. A sorption agent according to Claim 1, substantially as hereinbefore described with

reference to any one of the Examples.