Patent Application
20200263103
The present disclosure relates to a process for producing wood pellet, and, in particular, to a process for using a minor amount of dried spent coffee grounds as a lubricant in the pelleting process.
A process is disclosed for producing pellets in pelleting machinery. The process includes recovering spent coffee grounds having a moisture content of about 50% directly from a coffee production facility. The coffee grounds are then subject to a drying process to remove moisture from the coffee grounds to form dried coffee grounds having a moisture content of 10% or less. A mixture of about 1-5% dried coffee grounds and 95-99% wood material is then formed. The blend of wood material and the dried coffee grounds have a moisture content of from about 8% to 14%. The mixture is then compressed in a pellet mill to form wood pellets including about 1-5% coffee grounds. The coffee grounds in the wood material acts as a lubricant for the pelleting machinery and eliminate the need for other lubricants in the process.
In general, wood pellets are a renewable energy carrier which is produced from sawdust or other ground woody materials. International standards define product requirements i.e. moisture, energy density, abrasion resistance, particle size and shape for wood pellets (ISO 17225-2) which allowed wood pellets to turn into a commodity.
There are different pellets from different sources and qualities available today, such as wood pellets, animal feed pellets, torrefied pellets etc. Wood pellets of dedicated qualities are dominating and are delivered and consumed in two different markets: (1) In the electricity generation sector, they are co-fired in coal-based power plants and mono-fired in converted coal power plants to reduce greenhouse gas emission of electricity generation. (2) In the residential heating sector, they are widely used as a convenient solid biofuel application in automatic stoves and boilers. Therefor pellets with a dedicated quality are dominant, which are produced closer to the consumer and characterized by trade within the country or between neighboring countries. Delivery is realized in small scale units in the retail market and in large scale or bulk units in the power generation market.
Additional applications for the use of wood pellets are the use as fuel for mid-sized heat supply systems, such as district heating and CHP plants. Generally, pellets may be used for commercial/residential use or for industrial use. The majority of non-industrial, mostly heat market pellets traded are A1 quality, which are rated for residential heat supply.
As is known in the art, pelleting takes a finely divided, sometimes dusty, unpalatable, and generally difficult-to-handle feed material and, by use of heat, moisture, and pressure, forms the material into larger particles (pellets). These larger particles are easier to handle, more palatable and usually result in improved results when compared to the unpelleted feed or fuel Pellets may be formed with diameters from 10/64″ to 48/64″ and will be somewhat longer than their diameter. In some embodiments, pellets may be cylindrical, triangular, square or oval.
Typically, a pelleting system is composed of several different machines designed to most efficiently accomplish the pelleting task. A typical system arrangement with equipment names is shown in
In a typical pelleting operation, the mixture flows by gravity into the pellet mill die chamber where rollers press the softened mash through the holes in a circular die. Stationary knives located outside the circular rotating die, cut off the shaped dense pellet at the proper length. Most modern pellet mills used a ring type die that turns about two fixed rollers, with the die and rollers mounted in a vertical plane. A few mills are built with the dies and rollers in a horizontal plane with the rollers turning within the stationary die. In the pelleting unit, the conditioned mash is forced through holes in the die by roller pressure. Die thickness is a factor in the production of high quality pellets and must be accurately balanced with the formulation and conditioning. Starting with 24/64 inch pellets and above, some variation in the amount and depth of taper incorporated into the entry of the holes in the die may be necessary. Numerous other special entries are used in instances where satisfactory pellets cannot be produced with standard entry and taper.
Pellet mills generally incorporate some type of speed reduction device, since die speeds are less than the conventional motor speeds. In some cases, variation in die speed is desirable to produce optimum results with respect to individual groups of feeds. Speed reduction devices in use today include direct coupled gear trains, V-belts, cog belts, as well as combinations of belts and gear trains. Currently, mills are being built with speed change mechanisms. Usually these speed change mechanisms are in the form of gear shifts or two-speed motors. Such mills provide two die speeds to secure optimum results when a wide range of feeds is produced.
Most pellet mills are installed with an electric motor as the prime mover; however, internal combustion engines are sometimes used. When internal combustion engines are used, the horsepower rating should be at least twice that of the electric motor normally used. The pellet mill and motor are usually mounted on a common base to maintain alignment of the pellet mill and motor and to provide a rapid, simple and efficient method of installing the equipment. Although it is not a standard part of the pellet mill, an ammeter should be included as part of the electrical system. This will allow the operator to adjust the feed rate to secure the maximum capacity of the mill without overloading the motor. In the production of wood pellets, the mixture is fed through a pellet mill using either a flat die or a ring die compression system.
During the pelleting process, friction can occur due to the difference in temperature of the feed entering the pellet mill die and the pellets being discharged from the die. The difference reflects the mechanical energy required to produce a pellet. There are several inherent factors that can affect friction including moisture in the mixture, conditioning, particle size of the mixture ingredients, physical properties of the mixture ingredients, including mineral content, solubility, and fiber content. Additionally, friction can result according to the die size in terms of mesh diameter and thickness. Further, pelleting of woody material creates friction in the die itself, which in turn can create significant heat during the pelleting process and which becomes a limiting factor in the rate at which pellets can be produced. In certain cases, organic and/or petroleum-based materials (lubricants) are added in small quantities to the woody feedstock in order to facilitate the pelleting process, thereby reduce the friction-based heat, and increasing the overall rate of pellet production.
The addition of dried spent coffee grounds (SCG) has been found to be a suitable lubricant for reducing friction in the pelletizing process. SCG contain a significant amount of natural organic oils which contain both high BTU content as well as significant lubricating properties. When SCG are premixed with woody biomass prior to pelleting in amounts from 0.5% by weight to 5% by weight, significant lubrication of the pelleting process occurs. Binders may or may not be included with the woody biomass. Because of the reduced friction imparted by the SCG, lower heat production during the process may be realized. In addition, pellet production rates have been found to increase by up to 30% over conventional pelleting processes, using conventional lubricants. Dried coffee grounds are particularly useful as a lubricant in the pellet production process for both flat die and ring die production.
As shown in
One example of dried coffee grounds suitable for the process is:
In this embodiment, the amount of dried coffee grounds used in the wood may be 1%, 2.5% or 5% and the moisture content is between 5-15%, but may be as low as 3%. Since the coffee is substantially rich in oils, dried coffee grounds have been found to improve the efficiency of pelleting machinery at relatively low amounts in the mix. Thus, the machine is less likely to buckle, or knock during the pelleting process when coffee grounds are added to the wood material.
Not only does the coffee affect the final product by helping the material flow through the pellet machinery in a quicker fashion, the small amounts of coffee result in some increase in the BTU levels of the finished product because dried coffee grounds have a BTU content per unit of mass approximately 30% higher than the wood feedstock.
Changes and modifications of the preferred embodiments described above will become apparent to persons skilled in the art. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.
| Number | Date | Country | |
|---|---|---|---|
| 62806861 | Feb 2019 | US |
