Patent Application
20090253085
The invention pertains to methods and compositions for inhibiting corrosion of metal surfaces in contact with a furnace.
The use of copper and other metals to enhance furnace operation is well known. For example, in accordance with the teachings of U.S. Pat. No. 6,077,325 (Morgan et al.), metallic compounds including Zr, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Al, Sn, and Pb may be added to pulverized coal that is burned as fuel in a blast furnace or the like. Pulverized coal is often used as a substitute for a portion of the coke in the preparation of iron involving the reduction of iron oxide with carbon in the blast furnace. This substitution purportedly results in less pollution since coke is being replaced in part, and since coal is less expensive than coke, economies in the process can be realized.
In typical blast furnace processes, iron bearing materials including iron ore, sinter, scrap, or other iron source along with a fuel, generally coke, and a flux, limestone, or dolomite are charged into the blast furnace from the top. The blast furnace burns part of the fuel to produce heat for melting the iron ore and the balance of the fuel is utilized for reducing the iron and its combination with carbon. The charge in a typical furnace, per ton of pig iron produced, is about 1.7 tons of ore or other iron bearing materials, 0.5-0.65 tons of coke or other fuel, and about 0.25 tons of limestone and/or dolomite. Additionally, from 1.8-2.0 tons of air are blown into the furnace during the process.
In practice, iron bearing raw materials (sinter, iron ore, pellets, etc.), fuel (coke), and flux (limestone, dolomite, etc.) are charged to the top of the furnace. Heated air (blast) is blown into a blast furnace through openings, known as tuyeres, at the bottom of the furnace. Tuyere stocks are fitted with injection lances through which supplemental fuels (gas, oil, and pulverized coal) are injected. The blast air burns the fuel and facilitates the smelting chemistry that produces iron. Combustion gases from the blast furnace are scrubbed to remove particulate and other noxious gases before being burned in stoves which are used to preheat blast air or in other applications, e.g., coke ovens, boilers, etc.
As referred to above, when pulverized coal is substituted for a portion of the coke, metals such as those disclosed in the '325 patent may be used as combustion catalysts or aids. These are of benefit since they provide the ability to use lower rank coals in the furnace and allow for greater coke replacement by the pulverized coal. Additionally, they help to minimize “coal cloud” and reduce LOI. Lowered slag content, reduced particulate emissions, and higher quality iron are also potential benefits that may be attributed to the use of these catalysts or aids.
Copper-based catalysts or combustion aids have become especially popular. However, attendant problems of corrosion have appeared as a result. The problem arises from the corrosion that the product generates on mild steel surfaces that are present in the furnace system in which the combustion catalyst/aid is applied. (As used herein, “furnace” and “furnace systems” refer to ovens, boilers, blast furnaces, or any enclosure in which a fuel is combusted).
As a consequence of this corrosion of metallic parts and components of a furnace system, the furnace equipment itself can fail, leading to process down time and costly replacement.
We have developed a technology that inhibits corrosion in furnace systems and allows use of metallic based combustion catalysts/aids, especially those employing Cu as the active component. In one aspect of the invention, the corrosion inhibiting treatment of the invention is blended with a copper combustion catalyst/aid to form a protective film on the mild steel surface in contact with the furnace combustion products.
The corrosion inhibiting treatment comprises a blend of a primary aminoalcohol (i.e., having primary amino function) and boric acid or water soluble salt or the acid. A tertiary aminoalcohol (i.e., having a tertiary amine function) may also be present in the blend. The blend is preferably sprayed onto the pulverized coal in aqueous solution form prior to injection of the coal into the furnace. Alternatively, the treatment may be applied in spray form anywhere in the furnace system including the so-called “fireside” or “cold” ends of the furnace. (See U.S. Pat. Nos. 4,458,006 and 4,224,180 herein incorporated by reference).
Metal surfaces, such as mild steel surfaces, of a furnace system are effectively treated in accordance with the invention by a corrosion inhibiting treatment comprising a blend of a primary aminoalcohol and boric acid or water soluble salt form thereof. Additionally, the corrosion inhibiting treatment may comprise a tertiary aminoalcohol. Preferably, the primary aminoalcohol is 2-aminoethanol and the tertiary aminoalcohol is triethanolamine. The invention has proven to be successful, especially in furnace systems in which pulverized coal is burned as fuel in the presence of a copper catalyst/combustion aid.
The corrosion inhibiting treatment is most preferably provided in the form of an aqueous solution. By the phrase “aqueous solution” as used herein, we mean to encompass not only true chemical solutions, but also dispersions, mixtures, and suspensions. The solution may be sprayed directly over the pulverized coal in an amount of about 100 ml to 1 L of aqueous solution per ton of coal. More preferably, the dosage rate is from about 300 ml -1 L of aqueous solution per ton pulverized coal.
Preferably, the corrosion inhibiting treatment comprises both the 2-aminoethanol and triethanolamine component. In addition, conventional corrosion inhibitors, such as water-soluble gluconic acid salts, preferably sodium gluconate, may be incorporated into the corrosion inhibiting treatment. When the pulverized coal is to be burned in the presence of copper as a catalyst/combustion aid, a copper ion source may also be incorporated into the aqueous solution that is to be sprayed over the coal.
The invention is also directed to corrosion inhibiting treatment compositions that are adapted for application or spraying onto the fuel in the form of an aqueous solution. In these compositions, the 2-aminoethanol, triethanolamine, and boric acid or salt thereof components may be present in the aqueous solution in the amount of about 1-10 wt %. Sodium gluconate may also be present in the aqueous solution in an amount of about 1-15 wt %. In those instances in which a copper ion source is also present in the aqueous solution, the copper ion source may be present in such an amount as to provide Cu++ in an amount of 1-20 wt %.
The synergistic blend of 2-aminoethanol, triethanolamine, and borate is not water soluble in the presence of copper. However, when this blend is mixed with the known mild steel corrosion inhibitor, sodium gluconate, the gluconate/“blend” mixture has a high solubility in water even in the presence of copper.
Exemplary compositions in accordance with the invention include:
More preferably, the compositions include
Based upon preliminary results, it is preferred to provide the copper ion source, sodium gluconate, 2-aminoethanol, triethanolamine, and boric acid or water soluble salt in a single aqueous solution for spray application over the pulverized coal. Exemplary copper ion sources are copper sulfate pentahydrate and copper II-D-gluconate.
The product which is presently preferred for commercial use comprises about 3% actives of a blend of 2-aminoethanol, triethanolamine, and boric acid, along with 4% active sodium gluconate, and 19% actives of copper sulfate pentahydrate along with sufficient water to equal 100% of the total weight of the formulation.
The invention will be further described in conjunction with the following examples which should be viewed as being illustrative of the invention and should not be construed to limit the invention.
All corrosion tests were carried out using a bottle test method with mild steel coupons. The coupons were cleaned with tri-sodium phosphate and pumice before and after exposure to the produce solution. Isopropyl alcohol was used to rinse the coupons after cleaning. Each low carbon steel coupon was immersed in a 1% (by weight) copper solution prepared form the indicated stock solution for 24 hours. (Only exceptions are the last two entries in the data table below which involved immersion of the mild steel coupons into the undiluted stock solution.) Total test solution weight was 100 grams. Each test was conducted at 30° C. in a water bath shaking at 40 rpm. Corrosion rates were determined by the amount of weight loss that occurred in 24 hours. All formulations tested were run in duplicate, so the corrosion rates shown represent the average of the two. The level of copper (as Cu2+ in EP9587 (4.84%) was maintained for each new stock formulation prepared. The percentage of surfactant and water and the source of copper ion were the variables manipulated. All blends were prepared based on the weight % of each component. In addition, an 11-day test using undiluted stock solutions was carried out with the better of the two corrosion blends.
Copper Based Combustion Enhancer (CBCE)=19% copper sulfate pentahydrate (which is 4.84% Cu2+, the level found in every stock solution tested below)/1.6% alkylpolyglucoside surfactant (Triton BG-10).
Corrosion Inhibitor Blend (CIB)=2-aminoethanol, triethanolamine, and boric acid (Maxhib AB-400)—available from Chemax, Rutgers Organics Corporation, Greenville, S.C. 29606.
Data Table 1 below shows the above listed as CBCE and CIB with the appropriate concentrations used.
The procedures reported in Example 1 were again performed in conjunction with comparative treatments and treatments in accordance with the invention. Results are shown in Table 2.
The present application is a continuation of U.S. patent application Ser. No. 11/581,935 filed Oct. 17, 2006, which is a divisional patent application of U.S. patent application Ser. No. 10/368,823 filed Feb. 19, 2003.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10368823 | Feb 2003 | US |
| Child | 11581935 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11581935 | Oct 2006 | US |
| Child | 12484654 | US |
