Using Binders to Briquette Carbonaceous Materials and Steel

June 2015 www.powderbulk.com As appeared in PBE Copyright CSC Publishing

Using binders to briquette carbonaceous Brian materials and steel wastes Young

ffectively briquetting premium price, there’s more carbonaceous materials flexibility regarding the binder type (including coal, char, and and concentration. Nickel fines are charcoalE made from coal, sawdust, often briquetted using a small amount and various types of biomass and of expensive organic liquid binder and agricultural wastes) and steel wastes sold on the London metal exchange, typically requires a binder such as for example, and in barbecue starch, cement, molasses, lime, or briquettes — which are typically only some combination of these to hold the affordable in the US and other briquette together and improve its developed and oil-rich countries — durability. Binders have been used to the starch binder can cost 10 times as briquette coal and charcoal for more much as the charcoal or char. than 100 years. Using cement to bind wastes from steel-making operations Background on binders is a more recent application. In this column, I’ll discuss the different Starch came into prominence as a types of binders used to briquette binder for coal and charcoal in the 19th carbonaceous materials and steel century with the large-scale wastes and what you should consider development of briquetting. In when selecting a binder for your England in 1858, John Piddington briquetting application. received a patent for using 36 pounds of starch along with 8 percent water per ton of coal.1 In 1897, in Pennsylvania, The key to a suitable binder is its cost- Ellsworth Zwoyer patented a process effectiveness. Starch, cement, for briquetting coal fines with a starch molasses, and lime are widely used binder and set up plants in New York because they’re inexpensive and and Massachusetts. Henry Ford and E. readily available. Other binders, such G. Kingsford had greater success in the as alkali cellulose or phenol aldehyde 1920s using wood waste from Ford’s resins, may offer improved automobile plant to make charcoal performance or additional benefits, pillow briquettes based on a process but they often cost more and may be patented by University of Oregon less readily available because of chemist Orin Stafford. The operation location or supply constraints. later became the Kingsford Company, and starch is still used today as a binder A company will typically use the most for barbecue briquettes. cost-effective binder in the smallest concentration that will produce Common starches used as binders briquettes with acceptable durability include maize (corn starch), potato, and weathering characteristics. and wheat, but less-common starches Durability is especially important for derived from rice and tapioca are also steel-waste briquettes, which need to used. Typically, a starch needs to be hold together under high-temperature gelatinized by thorough cooking in and reducing conditions. When the water at 55°C to 85°C (131°F to briquetted product can command a 185°F), depending on the starch. This Copyright CSC Publishing disrupts the intermolecular bonds, surface tension to pull the material’s creating hydrogen-bonding sites for particles together. It can also be a dry attaching additional water molecules solid that’s mixed thoroughly with the and making the starch soluble in cold material to be briquetted before a water. After cooking, the starch is solvent, such as water or alcohol, is dried in a spray dryer, drum dryer, or added. In this case, the solid acts as extruder. You can buy pregelatinized both lubricant and glue, forming a starch, but it’s substantially more solid bridge between particles when expensive than raw starch. the solvent dries. Examples of inactive film binders are water, alcohol, oils, various starches (maize, tapioca, Cement was used as a binder thousands potato), wheat flour, molasses, casein, of years ago by the Egyptians, Greeks, glucose, dextrin, alginates, and gum and Romans, but its use expanded arabic. greatly during the industrial revolution. A key factor was Isaac Johnson’s development in 1845 of modern Chemical film. A chemical film Portland cement by firing a mixture of binder coats a material’s particles with chalk and clay at 1,400°C to 1,550°C a thin film and causes a brief chemical (2,552°F to 2,822°F). Cement was later reaction that bonds the particles used as a binder for briquetting coal, together. The resulting briquette is char, and charcoal and subsequently for often waterproof when a chemical briquetting iron and steel wastes. film binder is used. Examples include sodium silicate and dilute acid and Molasses has long been used on its sodium silicate and lime. own or with lime — particularly slaked lime (calcium hydroxide Inactive matrix. An inactive matrix [Ca(OH)2]) — to briquette coal and binder embeds the material to be similar materials as well as steel briquetted in a matrix (or framework) wastes. Derived from sugarcane or of binder. Some inactive matrix beets, molasses’ composition can vary binders, such as coal tar pitch, need to widely depending on where the plant be heated to reduce their viscosity was grown, how it was processed, and during briquetting but will then set seasonal factors. Molasses is highly hard when allowed to cool. Examples viscous but becomes more fluid when of inactive matrix binders are heated, allowing it to be more easily petroleum asphalt, carnauba wax, mixed with slaked lime prior to paraffin, wood tar, colloidal alumina, briquetting coal or char fines. and metal stearate. Typically, a binder’s ratio of molasses to lime is between 2-to-1 and 4-to-1. Chemical matrix. A chemical matrix binder uses a chemical reaction Binder types between two binder components to Binders have been classified in many bind the material’s particles together. ways, including by binding Examples are quick lime (calcium mechanism (molecular forces, oxide [CaO]) and water, molasses and electrostatic forces, magnetic forces, slaked lime, Portland cement and or free chemical bonds),2 physical state water, and plaster of Paris. (liquid, semisolid, or solid),3 function (matrix or film), chemical type 4 Chemical reaction. A chemical (organic, inorganic, or compound), 5 reaction binder uses a chemical and behavior. In 1983, Carl A. Holley reaction to form a strong bond between outlined the following comprehensive the binder and the particles to be five-group classification system and briquetted. Examples include electric listed several examples of materials in 6 furnace dust mixed with a water and each group. quick-lime binder and fly ash (which contains lime) from a power plant Inactive film.An inactive film binder mixed with water. A reagent such as is typically a liquid solution that uses dilute sulfuric or phosphoric acid is Copyright CSC Publishing sometimes added to improve the cured To determine the best binder type and 5. Karl R. Komarek, “Selecting Binders and Lubricants for Agglomeration Processes,” briquette’s strength. amount for your application, you Chemical Engineering, December 4, 1967. should test various options using your 6. Carl A. Holley, “Binder and Binder Systems material, asking the following for Agglomeration,” Elements II — 8 Selecting a binder questions. Briquetting and Agglomeration, Volume 2, The Institute for Briquetting and Your material’s characteristics, Agglomeration, 1983. including average particle size, • Is the briquette strong, durable, and 7. Brian C. Young and G. W. Kalb, “A Survey particle size distribution, moisture weather resistant? of Briquetting Parameters and Binders,” Proceedings of the Production and content, and binding characteristics, •Is the binder environmentally influence which binder will work best Utilization of Ecological Fuels from East benign and compatible with your Central European Coals Workshop, 1994. for your application. material? 8. Brian C. Young, “Adding Value with Agglomerated Waste Materials,” Proceedings • Is the binder easily and plentifully of the Biennial Conference of the Institute for A material with a wide particle size available? Briquetting and Agglomeration, Volume 26, distribution, for example, will tend to • Is the binder effective at a reasonably 1999. bind more easily than a material with low concentration? a narrow particle size distribution because smaller particles fill the gaps •Is the binder cost-effective in between larger particles. For some relation to the briquettes’ expected selling price? Brian Young is a board member and applications, precompacting your past president of the Institute for Bri- material will release trapped air and quetting and Agglomeration and for- reduce the gaps between particles. Your material’s characteristics and mer managing director of Envirosafe the binder type will also affect the International Pty. Ltd. (brian.young Water can be integral to the binding briquettes’ curing time and method. [email protected]). He’s been active process, either directly, as part of the For example, coal briquettes with in briquetting and agglomeration for binder formula, or indirectly, as a flow calcium aluminate binder — a type of more than 25 years, authored or coau- aid to help distribute the binder evenly hydraulic cement formed by sintering thored more than 160 papers, and throughout the material to be quick lime and alumina — cure holds a PhD in physical chemistry briquetted. 7 In either case, your rapidly, while coal briquettes with from the University of Cambridge, material’s moisture level, both before molasses and lime binder cure more Cambridge, England. and after binder is added, will affect the slowly. PBE resulting briquette’s “green” (uncured) strength. The ideal moisture level For further reading depends on the agglomeration process and the binder. For bituminous and Find more information on agglom - subbituminous coal, for example, the eration and binders in articles listed mixture’s moisture content before under “Agglomeration” in Powder briquetting in a double-roll press can and Bulk Engineering’s article index range from 8 to 12 percent. (in the December 2014 issue and at www.powderbulk.com).

Optimal binder concentration depends on the binder type, the material’s characteristics, and the characteristics References of any added components, such as 1. J. Mills, Binders for Coal Briquets: biomass. Using pregelatinized starch Investigations Made at the Fuel-Testing to bind bituminous coal fines, for Plant, St. Louis, MO, Forgotten Books, example, I’ve been able to use as little 2013. as 2 percent binder by weight. In 2. Wolfgang Pietsch, Size Enlargement by Agglomeration, John Wiley & Sons, 1991. another study with coal chars, the 3. P. L. Waters, “Binders for Briquettes: A starch amount ranged from 2 to 7 Critical Survey,” CSIRO Division of Mineral percent, with strong briquettes Chemistry, Technical Communication 51, produced at 4 percent. I’ve achieved 1969. See also: “Briquet binders: A acceptably strong and waterproof coal reappraisal,” Proceedings of the Biennial Conference of the Institute for Briquetting and char briquettes using binder and Agglomeration, Volume 12, 1971. mixtures from 6 percent molasses and 4. Henry C. Messman, “Binders for Briquetting 3 percent slaked lime up to 10 percent and Agglomeration,” Proceedings of the molasses and 5 percent slaked lime. Biennial Conference of the Institute for Briquetting and Agglomeration, Volume 15, 1977.