CA1145119A - Use of steel plant waste dusts for scavenging hydrogen sulfide - Google Patents

Abstract

Iron rich dusts created during steelmaking, as in the basic oxygen and open hearth processes, are useful for scavenging hydrogen sulfide. For example, basic oxygen furnace dusts, which are in more abundant supply, are found to consist of fine, nearly spherical particles of iron oxide whose crystalline composition comprises Fe3O4 (major portion) and Fe2O3 (minor por-tion) as seen by X-ray diffraction. Their great surface area makes them highly reactive to hydrogen sulfide gas. Their reaction yields unexpected products, namely, free sulfur and iron hydroxides. According to the present invention such iron rich dusts are used in water based drilling muds to scavenge hydrogen sulfide encountered in well drilling.

Description

5~19 USE OF STEEL PLANT WASTE DUSTS FOR SCAVENGING HYDROGEN SULFIDE
Iron rich dusts derived from Yarious steelmaking processes have been generally thought to be the common iron oxide Fe203. These dusts are ~astes, with limited use for such minor purposes as a hardener for cement. There have been attempts at reclamation for recycling to steel furnaces. U.S. Patent No.
3,895,088, issued July 15, 1975, to ~ichigan Technological University identi-fies and describes these dusts.
It is well known that hydrogen sulfide gas may he extracted from hydrocarbon gas by reacting with iron compounds; for example, sour fuel gas is pumped through trays of wood chips impregnated with Fe203. Likewise, hydro-carbon gas may be bu~bled through an aqueous solution Qf iron hydroxides, with the following reaction:
2Fe(OH)3 + 3H2S Fe2S3 ~ ~2Q
The reaction product Fe?S3 is unstablei regeneration i5 to he expected.
In U.S. Patent No. 4,0Q8,775, I disclosed a quite different type of iron oxide particle characterized by exceptional porosity and created by the partial oxidation of iron to Fe3Q4. In this patent, I also disclosed that such porous particles are adYantageously used as an additiYe to ~ater based muds in the drilling of wells.
The present invention relates to scavenging hydrogen sulfide gas, as may be encountered in well drilling. ~ new use is found for the iron oxide dusts formed in steelmaking.
The present invention pro~ides a new use for the fine particulate iron rich dusts of steelmaking. ~asic oxygen and open hearth dust particles are exceptionally small sized; though lacking the porosity of the larger parti-cles described in said patent, they possess-tremendous total surface area for reaction. When suspended in an aqueous fluid, the tiny particies react so rapidly with hydrogen sulfide gas as to he an effectiYe scavenger. Surprisingly they yield unexpected and non-polluting products oF reaction, hoth free sulfur and iron hydroxides.
One principal use is here described. In this use,`the fluid in which they are suspended is a water hased well drilling mudi hydrogen sulfide, gas 9~

3L3L~5~1 9 escaping from the formation wall as a well i.s drilled, is entrained in the mud and reacted by the suspended particles.
The present particles Yary somewhat in color, hut ordinarily present a brownish appearance characteristi.c of the common iron oxi.de Fe2Q3. This compound, on reaction with hydrogen s.ulfide, would yield FeS, which is. unstable.
Instead, free sulfur and iron hydroxides are found to he the reaction products.
These permit safe disposal, without danger to the enYironment.
In the methods of the pres.ent i.nYention, advantage is taken of the unique physical properties of the iron-rich dusts from steelmaking and the fact that the products of their reacti:on with~hydrogen sulfide are unexpectedly stable.
As to the physical and chemical properties of th.es.e dus:ts, relatively litt1e appears to haYe been puhli.s.hed. The hest source known to applicant is U.S. Patent No. 3,89.5,088, i.ssued to Nich.igan Technological ~niYersity. Thispatent describes these dusts as w.aste products:; dealers in wastes haYe con-sidered them to be impure iron oxi.de Fe2Q3.
The patent to Michigan Technological ~niversity, f~rni~hes chemical analyses of these dusts, showing the quantity of iron present as an element, rather than in compounds. Iron generally accounts for somewhat more than 60%
by we;ght of the dusts from the Yarious steelmaking proces.ses, excluding water present from the process of collection. From a chemical standpoint, the dusts which appear to he the most similar are those from the has~c oxygen process and the open hearth process. The hasic oxygen furnace du~t is referred to as BOF.
. The physical properties of the BOF dust and open hearth. dust are quite similar.. The Michigan Technologi.cal .University patent ~tates, and elec-tronmicroscopy confirms, that BOF particles are usually spheri.cal in shape, with about 80% heing smaller than Q.5 ~icr~ns. ~pen hearth dust ZS chemically and physically quite similar, ~ut cantains less s.lag and oYerburned lime. Thissimilarity res.ults from s~imilar condi.ti:ons. in the;r formation.. The particles are formed upon rapid solidifi.cation ~f iron droplets or Yapor upon contact with the:coYer surfaces of the f.urnace:~l.ues:. Such..Papi:d solidification and the'presence of the'i.mpuriti.es des..cribQd:ahoYe inhi:~it cry~tallite formation ~2-~ 1 ~ 5 1~L~

leaving substantial amorphous iron oxide. Substantially all particles shouldpass through a 325 mesh screen, U.S. Standard, and the majority through a 500 mesh screen. BOF dusts typically contain some slag, over-burned lime and graphite and, depending upon the type of scrap used as part of a charge to the process, may include some zinc, lead and other metallic elements.
According to the Michigan Technological University patent, chemical analyses of these dusts are as follows:
BOF Qpen Dust Hearth Dust Fe 61.47 65.42 CuO 5.15 0.52 MgO 1.30 0.13 SiO,, 2.04 0.42 Al2~3 0.09 0.05 Zn l.06 0.35 Pb 0.17 0.70 S O.lO 0.05 P 0.12 0.34 Na 0.18 0.02 K 0.37 0.34 C 0.23 0.22 Test;Data Surface Area:
Tests of surface area, carried on by the Sor-Bet (a trademark~ and Absorptomat (a trademark) methods, reveal that the basic oxygen furnace dusts have a surface area of about 7.l square meters per gram. Samples will vary;
dust with an effective surface area of 4.0 square meters per gram or greater is deemed to be suitable for practicing the present methods.
Reaction Efficiency:
Tests were made by adding pure hydrogen sulfide to the reactbr ves-sel while allowing all excess to flow through a drager detector to determine - the "breakthrough" point. Flow was then diverted to a trap in order to measure the amount not being reacted. The maximum flow rate without a "breakthrough"
was determined. The sulfides in the reactor and the trap were determined using .

~L~ 53L1 9 the API Gas Train Method. The amount of hydrogen sulfide added was determined by weighing the lecture bomb containing the hydrogen sulfide hefore and after additions. Twenty-eight grams of ~OF dust were used in 500 ml. of water. It was obserYed that l4.7 grams per hour of hydrogen sulfide were removed. The reaction efficiency was then calculated by dividing the ~um of the sulfides in the reactor plus the trap by the weight percent of hydrogen sulfide added. The calculated efficiency of removal ~as ~6~ of the hydrogen ~ulfide added during the test.
Fe , Fe Titration:
Further understanding of the ~OF material was gained by contrasting X-ray diffraction analysis with an ion titration assay. X-ray diffraction analysis shows that although a small amount of crystalline Fe2Q3 is present, the major portion of crystalline iron oxide is Fe304. The titration data sum-marized hereinafter indicates that a substantial amount of the total Fe++~ iron is non-crystalline. This Fe+ + iron appears to ~e present in an amount inter-mediate to that for pure standards of Fe3Q4 and Fe2Q3, and in an amorphous state covalently honded with oxygen. Such Fe+~+ iron not incorporated into any crystalline lattice, may enter more quickly into reaction with H2S.
Ion titrations utilizing the method of Kolthoff, I.M. and E.B. Sandell, Quantitative Inorganic Analysis, 3d ed. (1~52), ~ere carried out on BOF dust.
The results, comparing the Fe++ and Fe+++ content of`BOF dust to an Fe304 standard (Bisberg, Sweden) are as follow~:
`Fe a Pure Fe O BOF
~ ``S ~ ~ rd Tota+ iron 72.3 70.Q 61.8 % Fe + 27.6 2.8 3.6 % Fe++~ 47.7 67.2 58.2 Products of reaction:
The reaction products Qf the foregoing test ~ere analyzed and found to be free sulfur and iron hydroxide~. This contrast~ ~ith the expected product of reaction with Fe203? which wQ~ld he principall~ Fe~. ~hile no explanation is offered for the ~nexpected result, it is noted tbat in reacting iron oxides with hydrogen sulfide,`a number`of competin~ rèactions occur _4_ ~L3l~53L~L9 simultaneously; possihly metallic imp~rities found in the waste du~t may act catalytically to favor what otherwise might be a mere minor reaction.
Use in well drilling:
The procedures to be used may be as disclosed in my U.S. Patent No.
4,008,775. A quantity of the fine iron rich dust particles, ;n particular the BOF or open hearth process particles, are added to drilling mud. The quantity is chosen to be sufficient to oyercome emanations of hydrogen ~ulfide from the formation wall of the well heing drilled, and may Yary in the range of 2 to 20 pounds per harrel of mud. The fine powdery particles do not clump on heing mixed into the water based mud but are s.uspended fairly evenly through it. On pumping the mud during drilling, as the mud rises from th~ drill bit up the formation wall the hydrogen sulfide will first he entrained in the mud and while entrained, reacted by the dust particles, to form ferro~s hydroxide FeO(OH) and free sulfur. These may ~e safely removed and disposed of. The reaction with the hydrogen sulfide escaping from the formation wall may be ex-pected to he complete, that is, the iron rich dusts will react with the hydrogensulfide preferentially to its reaction with other iron present. Thus, it avoids corrosion and hydrogen embrittlement of the drill pipes, while it protects against contamination of the mud.
Summary The present invention thus provides new use for the waste dust parti-cles derived from the fumes of steelmaking. They present a tremendously large surface area to react hydrogen sulfide so quickly as in effect to scavenge it.
The products of reaction are une~pected, they do not regenerate. The spherical shape of the particles, (yerified ~y electronmicroscopy as to BOF dusts~ permitsthe fine powder particles to he used in water based drilling-mud, they do not appear to adversely affect the rheological properties of the mud.
The open hearth dusts are so close i:n their phy~ical and chemical properties to the BOF dusts that similar results are to be ~chieYed. Likewise, 3Q other steelmaking dusts whose particles are of s-imilar size and comprising roughly 6Q~ iron will have simi-lar effecti~e properties.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The process of scavenging hydrogen sulfide from drilling mud compris-ing the following steps: a. adding to water based drilling mud steelmaking waste dust particles selected from the group consisting of open hearth dust and basic oxygen furnace dust, said particles having an iron oxide content of sub-stantially 85% and being of somewhat spherical shape, the greater portion of which being smaller than 0.5 microns, said particles having a surface area of at least 4 square meters per gram as determined by the Absorptomat* Method, in aquantity sufficient to react such hydrogen sulfide as may be encountered, b.
circulating the drilling mud down the interior of the drill pipe, through the drill bit and up the annular space between the drill pipe and the formation wall to the surface, c. entraining in the circulating drilling mud such hydrogensulfide as may be encountered, and d. reacting the entrained hydrogen sulfide with the said waste dust particles under the pressure there present to form free sulfur and iron hydroxides.

*Trade Mark