IE44558B1

IE44558B1 - Scale-inhibiting compositions

Info

Publication number: IE44558B1
Application number: IE2858/76A
Authority: IE
Original assignee: Calgon Corp
Priority date: 1976-01-07
Filing date: 1976-12-31
Publication date: 1982-01-13
Also published as: NO144619B; BR7608838A; DK153367B; LU76525A1; DE2700347A1; NO764352L; FR2337694B1; NL7614213A; GB1532391A; DE2700347C2; FI763638A; IE44558L; SE7614102L; NO144619C; CH624368A5; SE435456B; NL185221B; JPS52110288A; IT1121700B; DK566776A

Abstract

The agent contains a scaling inhibitor and a water-soluble polymer with a high molecular weight. The weight ratio of scaling inhibitor to polymer is 1:10 to 10:1. In order to inhibit scaling and deposit formation in gas scrubbers, a concentration of the agent of at least 0.01 parts by weight/million parts by weight is maintained in the aqueous gas scrubbing medium. The inexpensive agent makes possible effective prevention of sedimentation or deposit formation in gas scrubbers in an economical manner within a wide pH range. The necessity for mechanical cleaning of the scrubbing plant is greatly reduced.

Description

This invention is concerned with the control of 'deposit build-up in gas scrubbers.

During recent years, the number of wet scrubber . · . systems installed to remove gaseous and particulate < :·-material from waste stack gases has increased tremendously. Additional such systems are on the drawing ' board now. These wet scrubbers are being used-to clear effluent from boiler stacks, incinerator stacks, lime kilns, foundries, blast furnaces, basic oxygen furnaces (BOF), open hearth units, coke plants, paper mill recovery boilers, pet food manufacturing facilities, -electric furnaces (steel and aluminum), smelters, asphalt . plants and many others.

One of the most important features of a scrubber . system is the contact chamber, the device used to effect . ' transfer of gaseous and/or particulate matter from the gas to the water phase. Most wet scrubber systems involve a venturi, a packed bed, an orifice plate, a spray chamber or a turbulent bed. Some systems even use two contact chambers in series, for example, a venturi followed by a spray chamber.

Venturi or orifice plate scrubbers are generally more efficient for particulate removal while packed beds, turbulent beds and spray chambers are usually more - efficient for removing gaseous components such as S02 and HF. 4558 The present invention is concerned specifically with those scrubber systems where scaling and deposition problems due to insoluble calcium carbonate, calcium fluoride, iron oxide (Fe^O^), silica, manganese oxide, iron ore fines and slag fines are encountered. The problem which the present invention aims at minimizing is that which is found in gas scrubber systems of blast furnace operations where iron ore is being converted or processed to iron having a high carbon content.

In order to assure a complete understanding of the problem to which the present invention is addressed, a brief description of a blast furnace operation is hereafter provided.

In the production of iron, iron ore is fed together with additional ingredients such as dolomite through the top of a blast furnace fired by coke. An air stream is blown upward from the bottom of the furnace through the subsequent molten materials. The carbon of the coke reduces the iron ore (E®2°31 to Aon metal. The molten iron is tapped from the bottom of the furnace while the slag is tapped from the middle of the furnace. The by-product of the carbon reduction is of course a combination of carbon dioxide and carbon monoxide which reacts with the calcium present to form the troublesome scaleformer, calcium carbonate and other solids such as clay, slag and fines.

As can be appreciated, the air stream blown upward contributes significantly to the impurity content of the flue gas, thus putting an extreme burden on the scrubbing system. The particulate load in the scrubbing medium ranges from about 1,000 to 2,000 parts per million because of the particulate load of the flue gas. 44558 _ 4 _ The scrubbers that are used in blast furnace gas elean-up are often of the Venturi design and treat the off-gases from the furnace. These gases contain significant quantities of iron oxide, whose fine particle size allows it to be carried off in the gas stream. Also present may be coke fines to a lesser extent and to some extent, particulate slag materials, such as silicates and unused dolomites. The iron oxide has been subjected to . high temperatures within the furnace and may therefore be in a sintered form of low surface activity. However, its fine particle size presents deposition problems in scrubbers and delivery lines.

Another example of an operative system is a basic oxygen furnace (BOF) in which the BOF receives molten metal from the blast furnace plus scrap, various alloys to meet specifications, and lime and fluorspar as a flux. Oxygen is introduced through a lance to remove impurities The oxygen blow can release 4.4 tons of dust per 220 ton heat. This dust must be removed from the waste gas.

The dust consists of iron oxide, lime and fluoride.

This particulate and soluble gases are removed from the waste gas in a wet scrubber. In the scrubber water the iron oxide, calcium fluoride and calcium carbonate combine to cause massive deposit build-up on the scrubber system intervals which result in inefficient scrubber operation and high maintenance costs.

Prior methods, such as the method set forth in U.S. Patent No. 3,880,620, involve scale inhibitors, i.e. inorganic and organic phosphates; and low-molecular30 weight polymeric dispersants. This approach has not been completely successful in preventing deposition and has resulted in increased treatment costs and frequent shutdowns for mechanical cleaning. 4 5 5 8 The present invention provides a composition useful for controlling deposit build-up in gas scrubbers comprising a scale inhibitor and a water-soluble homopolymer or copolymer of 2-acrylamidomethyl propanesulphonic acid or a water-soluble salt thereof, having a molecular weight of at least 100,000, in which the ratio of scale inhibitor to polymer is in the range 1:10 to 10:1 by weight. Also in accordance with the present invention at least 0.01 ppm of such a composition is maintained in the aqueous scrubbing medium of a gas scrubber to control build-up of deposits. Usually not more than 100 ppm and preferably from 0.1 to 10 ppm of active ingredients, will be maintained in the aqueous scrubbing medium. The ratio of scale inhibitor to high molecular weight polymer is preferably from 1:5 to 5:1 by weight.

Suitable threshold scale inhibitors include phosphonates of the general formula : R in which Alk is an alkylene carbon group containing 2 to 6 carbon atoms, each R, which may be the same as or different from the others, is a hydrogen atom or a group of formula -CH2COOM or II — CH2 —Ρ—OM OM where M is a hydrogen atom or a cation forming a watersoluble salt, and n is 0 or an integer from 1 to 14, 5 S provided that where n = 0 at least one of the radicals represented by R is II —CH- - P— OK 2 I OM and where n is greater than zero at least half of the 5 radicals represented by R are II — CH2—P-OM OM In a preferred embodiment, the phosphonate has the general formula : R \ N / R where R is (οη2οη2)χ-ν —-R -ch2- P-OM OM M is H, NH^, alkali metal or combinations thereof; n is 0 or an integer from 1 to 6; and x is an integer from 1 to 6; or the general formula ; R‘ 0 II I II HO-P-C-P-OH OH X OH 4 5 5 8 where x is -OH or -NH2 and R' is an alkyl group of from 1 to 5 carbon atoms. The most suitable compounds are amino tris (methylene phosphonate) and hydroxyethylidene-1,1diphosphonic acid (HEDP) and water-soluble salts thereof.

Also useful as threshold scale inhibitors are phosphates such as polyphosphates, as for example sodium polyphosphates and phosphate esters of the formula : ROPO M wherein M may be -H, or a monovalent metal ion and R is an alkylene group having from 1 to 18 carbon atoms. Suitable polyphosphates are disclosed in U.S. Patents Nos. 2,337,856, 2,906,599 and 3,213,017.

The polymers used preferably have a molecular weight of at least 1,000,000. Examples of suitable polymers include the polymers of 2-acrylamido methyl propane sulfonic acid set forth in U.S. Patent No. 3,709,816.

The invention is further illustrated by the following examples.

EXAMPLE 1 ppm of a composition comprising a copolymer of 2-acrylamido methyl propane sulfonic acid and acrylamide of molecular weight at least 100,000 and a scale inhibitor [amino tris (methylene phosphonate)] in a weight ratio of 1:2.5 was maintained in the water supply to a basic oxygen furnace recycle scrubber system for 13 weeks at which time the system was visually inspected and no visible deposition was observed in the pumps, valves or sprays.

This is in contrast to heavy fouling of pumps, sprays and valves, which resulted in loss of gas washing and cooling 4 5 5 § efficiencies, thereby causing temporary loss of production, that occurred in a two-week period with no treatment. Previously, this system was heavily contaminated with calcium carbonate and contained significant amounts of ferric oxide.

EXAMPLE 2 6.6 ppm of a composition comprising a copolymer of 2-acrylamide methyl propane sulfonic acid and acrylamide of molecular weight at least 100,000 and a scale inhibitor [amino tris (methylene phosphonate)] in a weight ratio of 1:2.5 was maintained in the water supply to a basic oxygen furnace quencher and venturi scrubber system that had a severe build-up of calcium fluoride, iron oxide and calcium carbonate. After 1,600 heats, the system was inspected and.the gas ducts, scupper gratings and nozzles were observed to be clean.

EXAMPLE 3 ppm of a composition comprising a copolymer of . 2-acrylamido methyl propane sulfonic acid and acrylamide of at least 100,000 and a scale inhibitor [amino tris (methylene phosphonate)] in a weight ratio of 1:2.5 was maintained in the water supply to a blast furnace scrubber system having heavy iron deposits, which had previously resulted in an increase in the top pressure in the furnace resulting in furnace production loss and shutdown for descaling within one week when a low molecular weight (approximately 1000) polyacrylate and amino tris (methylene phosphonate) were used. After six weeks of treatment with the polymer/scale inhibitor composition no pressure increase or build-up was observed and the system is operating normally. 4 5 5 8 EXAMPLE 4 In order to simulate conditions in a gas scrubber system, a sample of water was prepared which had a pH of 12.0, a suspended solids (hydrated ferric oxide) concen5 tration of 2000 mg/1, a sodium hydroxide concentration of 200 mg/1, a sodium bicarbonate concentration of 260 mg/1, a calcium concentration of 450 mg/1 and a fluoride concen tration of 40 mg/1. The water was maintained at a temperature of 140 ί 4°F. and circulated through the test system at a linear velocity of between 3 and 4 ft./sec. The test system contained an unheated test section (12 inches long), a heated section (12 inches long), a spray section and a drain section. The inhibitor was added to this sample of water which was then circulated through the system for five hours at which time the system was shut down and the test sections weighed and the percent inhibition calculated in accordance with the following formula j % inhibition = 1 wt. of deposit (inhibited) Wt. of deposit (control) The results of these tests are set forth in Table I, in which the word Calgon is a registered trade mark. 5 8 Test # TABLE I % Inhibition Product and Ratio Cone entration (ppm) Weight Gained in Grams (unheated, heated, drain) Control 8.21 8.325 - 10.425 - 1 Calgon/ 5.0 3.29 59.9 ΙΟ Polymer 1 .2 .91 65.0 1:1 1.31 87.4 2 AMP/ 5.0 0.88 89.3 Polymer 1 0.59 92.9 1:1 1.16 88.9 15 3 HEDP/ 5.0 1.67 79.7 Polymer 1 1.56 81.3 1:1 0.97 90.7 4 Calgon/ 5.0 0.50 93.9 Polymer 2 0.68 91.8 20 1:1 1.20 88.5 5 AMP/ 5.0 0.69 91.6 Polymer 2 0.60 92.8 1:1 1.23 88.2 6 HEDP/ 5.0 0.80 90.3 25 Polymer 2 0.55 93.4 1:1 1.41 86.5 •I .1 5 ί, Η ! 1 Product Designations Calgon sodium hexametaphosphate AMP amino tris (methylene phosphonic acid) HEDP 5 l-hydroxyethylidene-l,l-diphosphonic acid Polymer 1 49:51 copolymer of acrylamide and 2-acrylamido-2-methyl propane-1sulfonic acid having a molecular weight of approximately 1,000,000 10 Polymer 2 homopolymer of 2-acrylamido-2-methyl propane-1-sulfonic acid having a molecular weight of approximately 500,000

Claims

1. CLAIMS;1. A composition useful for controlling deposit build-up in gas scrubbers comprising a scale inhibitor and a water-soluble homopolymer or copolymer of 2-acrylamido5 methyl propanesulphonic acid or a water-soluble salt thereof, having a molecular weight of at least 100,000, in which the ratio of scale inhibitor to polymer is in the range 1:10 to 10:1 by weight.

2. A composition as claimed in Claim 1 in which the 10 polymer is a copolymer of acrylamide and 2-acrylamido methyl propane sulfonic acid or a water-soluble salt thereof.

3. A composition as claimed in Claim 1 or 2 in which the scale inhibitor is a phosphate.

4. A composition as claimed in Claim 1 or 2 in which 15 the scale inhibitor is a phosphonate of the formula : —(Alk-N) — R I n in which Alk is an alkylene carbon group containing 2 to 6 carbon atoms, each R, which may be the same or different from the others, is a hydrogen atom or a group of formula 20 -CHjCOOM or II —CH —P-OM I OM where M is a hydrogen atom or a cation forming a watersoluble salt, and n is 0 or an integer from 1 to 14, provided that where n = 0 at least one of the radicals 25 represented by R is 4 I 5 5 8 II (’ll, 1' OM - ! OM and where n is greater than zero at least half of the radicals represented by R are II — CH 2 —P-OM OM

5. A composition as claimed in Claim 4 in which the phosphonate has the general formula : (CH 2 CH 2 )x - N· where R is — CH 2 — P — OM OM 10 M is H, NH^, alkali metal or combinations thereof; n is 0 or an integer from 1 to 6; and x is an integer from 1 to 6.

6. A composition as claimed in Claim 5 in which the phosphonate is amino tris (methylene phosphonate). 15

7. A composition as claimed in Claim 5 in which the scale inhibitor is hydroxyethylidene-1,1-diphosphonic acid or a water-soluble salt thereof. i45S@ - 14

8. A composition as claimed in Claim 1 or 2 in which the scale inhibitor is a phoiipltouat e of I he ronmiln i 0 If 0 II II II HO-P-C-P-OH I I I OH X OH where X is -OH or -NH^ an< ^ R ' an & lkyl group of from 1 5 to 5 carbon atoms, or a water-soluble salt thereof.

9. A composition as claimed in Claim 3 in which the phosphate is sodhim hexametaphosphate.

10. A composition useful for controlling deposit build-up in gas scrubbers comprising amino tris {methylene 10 phosphonate) and a copolymer of acrylamide and 2-acrylamido methyl propane sulfonic acid or its water-soluble salts having a molecular weight of at least 100,000 in which the weight ratio of phosphonate to polymer is in the range 1:5 to 5:1. 15

11. A method of controlling deposit build-up in gas scrubbers that comprises maintaining at least 0.01 ppm of a composition as claimed in Claim 1 in the aqueous scrubbing medium.

12. A method as claimed in Claim 11 in which the 20 composition is as claimed in any one of Claims 2 to 8.

13. A method as claimed in Claim 11 in which the composition is as claimed in Claim 9.

14. A method as claimed in Claim 11 in which the composition is as claimed in Claim 10,

15. A method as claimed in Claim 11 substantially as hereinbefore described in any one of Examples 1 to 3. ‘ 4 4 ft ί* Η In. A composition an claimed iii Claim I, substantia 1 ly as hereinbefore described in any one of Examples 1 to 3.

16.

17. Λ composition as claimed in Claim 1, substantially as hereinbefore described in Example 4.