Written by: Nancy Heimann
August 11, 2015
Enginuity Worldwide LLC scientists and engineers have invented a cost-effective process to transform annually renewable biomass feedstock and waste materials into an engineered, energy-dense solid fuel for use in power generation facilities. “Engineered” Biocoal™ fuel refers to biomass pellets, pucks, briquettes, granules, or powders derived by blending, up-grading and binding (or pulverizing in the case of powders) different types of clean cellulosic solid materials. The solid fuel is “engineered” to meet different physical, chemical, emission and thermal properties as specified by the user. Enginuity’s targeted biomass feedstock supply includes, but is not limited to, excess agricultural residues (corn stover or wheat straw), grasses from non- forage acreage (USDA designated CRP/WRP), purpose grown energy crops; consumer wastes including used pallets, coffee grounds, cellulosic wastes, food waste, food processing by- products and other landfill bound organic material and forest products including woody-waste, invasive and diseased wood.
The Enginuity facility is located at the Missouri Plant Science Center (MSPC) in Mexico, Missouri and has pilot production capacity of 1-5 tons per hour. Enginuity’s engineered solid biomass fuel product formulated from US Midwestern grown agricultural wastes is known as eCARB™ (Environmentally Continuous Annually Renewable Biomass) fuel. This facility is currently producing engineered biomass solid eCARB™ fuel for performance and emissions evaluations. By using engineered biomass solid fuel in co-firing, the technology may bring new life to legacy coal fired power generation facilities for US GHG compliance and sustainable energy independence.
The Enginuity technology allows for multiple streams, including blends, of diverse annually renewable biomass feedstock to be processed into a homogeneous, predictable and repeatable, engineered biomass solid fuel. Enginuity is focused on accessing best-in-world biomass resources to create a new source for Biopower generation, delivering clean, sustainable energy to power customers. From Canada to the Gulf of Mexico there exists a biomass corridor in America’s heartland that can produce and deliver domestically and internationally- marketable, carbon neutral or negative solid biomass fuel for power generation.
BIOFUEL FROM ROTARY COMPRESSION UNITS
The drying of biomass requires an energy input to facilitate the process. Conventional dryers utilize a broad spectrum of fuels available to produce heat, even burning a portion of the biomass for energy. These methods drive off unbound moisture by creating a temperature- induced differential in vapor pressure, a simple process practiced for decades.
A novel process has emerged recently not requiring combustion of external fuel to produce heat as in conventional dryers. The process requires no external heat or steam source to treat material, only energy to power a motor. A Rotary Compression Unit, utilizing both friction and compression, generates steam from not only unbound water but also bound or cellular water. Since the machine can readily manage processing both below and above the autoignition temperature it can produce dried material or Biochar readily, and may also be used to produce a form of “bio-coal”. The process converts biomass feedstock into engineered and upgraded biomass materials with a high heating value and energy density. These engineered biomass materials exhibit increased bulk density, and may also be densified to produce fuels (pellets, briquettes, or compacts) that are very dense, durable, and transportable. When engineered to fit the needs of the coal-fired power plant, these fuels have great potential as an effective alternative to coal that requires no changes in handling or combustion procedures/equipment.
Thermodynamics is the branch of Physics that deals with the relationship between all forms of energy. One aspect of the Second Law of Thermodynamics, simply stated in the work of Carnot, teaches “work equals heat”. Based on that principle, the Rotary Compression Unit’s only source of work is a prime mover such as an electric motor that continuously compresses biomass via a novel screw design. The general arrangement of the dryer is a compression screw within a barrel, belt driven by an electric motor, all in a horizontal plane. The material moves through a continually decreasing space sufficient to increase the surface friction, and results in increased bulk temperature. Removing moisture under “drying only” settings can readily lower moisture content (MC) from 30% MC by weight to 10% MC by weight with energy consumption efficiencies approaching 90% of theoretical evaporation energy. All biomass materials will readily dry in this process including both wood and non-woody.
As the biomass is processed through the Rotary Compression Unit, as detailed in Figure One, the materials passes through transitions of physiochemical states namely: feed /pre- compression, steam drying, followed by steam explosion as the material exits the dryer. The exit clearances of the screw/barrel can be adjusted to effect a variety of process conditions of increasing pressure and temperature. Under lower pressure conditions in the nozzle simple drying can be effected. As the biomass is processed under “light roast” conditions through the Rotary Compression Unit and the maximum temperature of the material is held below the autoignition temperature of the raw material. Feedstock input moisture parameters ranges in moisture content from 10% to 60% by weight and output is as low as 5% MC by weight. The Rotary Compression Unit is unique in its ability to dry many various types of fibrous biomass with ease.
Another aspect of the Rotary Compression Unit is in the conditioning and/or conversion of raw biomass into engineered biomass solid biofuel with increased energy density (BTU per pound) by 25-40% and increased fixed carbon content. In some cases the fixed carbon content is almost doubled. A “dark roast” is readily accomplished by adjusting the annular gap to settings that significantly increase the pressure on the biomass.
Under these conditions, as shown in Figure Two, the material sees temperatures above the autoignition temperature and is believed to experience auto/acid hydrolysis, then a steam pyrolysis phase, immediately before the steam explosion into a closed section. The steam explosion mechanism is responsible for increasing the surface area and porosity of the material by 100%. Under these conditions, Biochar is explosively ejected from the barrel/screw interface. At this instant, it is believed the Biochar loses heat to the escaping gases. The Biochar is transported to a reflux condenser while the volatiles are contained, then continuously reintroduced into the reflux condenser where they are absorbed by the biochar. An after cooler cools the new biofuel and it is discharged through a cyclone. Depending upon the process conditions and the raw material characteristics, the potential for any non-condensable gases may be mitigated through a thermal oxidizer prior to release.
The fuel produced using the Rotary Compression Unit combined with a follow-on densification process results in a low moisture, high energy, weather resistant fuel with high durability and bulk density. This remedies logistics problems normally experienced when handling biomass. The material conditioning, densification and potential weather resistant characteristics makes the fuel ideal for traveling, handling, and long-term storage.
The resulting product is unique in every aspect including BTU content, fixed carbon content, friability and flow ability. What nature took millions of years to produce, the Rotary Compression Dryer can perform in minutes without cobalt, cadmium, selenium, mercury, boron, chromium, or lead.