Break Coal Dependence

Energy production is one of the most important industries to modern life and coal fired power is the biggest contender. Some experts are worried that the world’s supply of coal will run out, leaving us incapable of producing enough energy to fuel our economy. One source claims only 112 years at today’s energy usage rates (World Coal Association).  If something should happen to eliminate the ability to use coal – running out altogether, being impractical or too costly to burn – civilization as we know it will not be able to survive. One solution is to increase the amount of renewables that are used for energy production before something happens to our largest energy source.

Breaking Coal Dependence as Featured in Bioenergy Insight Magazine 


Introduction

At the present time, about 11% (Independent Statistics & Analysis) of energy production is from renewables and about 40% from coal (Newton, 1.2).  In the realm of renewables, the options include solar, wind, geothermal, and biomass.  While the other renewables have their merits, recent technological advancements place biomass at the front of the pack to increase the amount of renewables used to power the world.  The process through which biomass can become a lead player is through torrefaction. Torrefaction is the method where biomass – woody or other – is heated in a low oxygen environment to a point where chemical changes start occurring. At the right temperature, the end product can resemble coal to a striking degree. It is so similar to coal that it is speculated to be able to burn alongside coal, or co-fired, in a coal power plant without needing to perform any costly modifications to the plant.  More readily available sources of torrefied wood will soon facilitate testing to prove this.   For this reason, torrefied wood is often referred to as biocoal, because it is coal that has recently been converted from biomass.  The torrefaction process breaks the bonds inherent in woody biomass that make it undesirable for co-firing with coal, such as gumming up the grinders and interior of the boilers, making the plant less efficient, and requiring more frequent shutdowns for cleaning and repairs.  Other than saving on shipping costs and being able to co-fire with coal, another important property of torrefied biomass is its hydrophobic nature. While raw biomass cannot be stored outside for any length of time because it will absorb water and start to compost, torrefied material can be stored outside in wet conditions indefinitely with little worry of decomposing or absorbing water.

Once biocoal can be produced economically, reliably, and in sufficient quantity to supplement the coal industry, progress toward increasing the percentage of renewable energy can really start to take root.  Economically and mass produced biocoal has been the goal of biomass and sustainable energy proponents for decades. Technology has finally caught up with the vision to be able to produce biocoal on a large enough scale that commercial plants can finally plan for its use on the horizon.  Konza Renewable Fuels, based in Topeka, KS, has recently sold a torrefaction plant that will be capable of taking woody biomass with energy content; also called Gross Heating Value, GHV, or heat value; of 20 GJ/MT, gigajoules per metric tonne, or 8,660 Btu/lb, British thermal units per pound, at bone dry conditions, 0% mcwb, also referred to as moisture content wet basis, to biocoal with energy content of approximately 22 GJ/MT or 9500 btu/lb at 0%mcwb using state-of-the-art torrefaction technology. This unit will be able to produce 12MT/hour or 26,500 lb/hour of torrefied product.  It is a continuous process reactor designed to operate 8400+ hours/year and capable of producing 100,000MT each year. There is speculation that the demand for biocoal in Europe will be 50 million tonnes per year or more by 2020 (Hein, 4).  Konza Renewable Fuels is also developing models that will produce 1MT/hr, 5MT/hr, and 24MT/hour.  500 of the 12MT/hr units would be required to satiate the biocoal demand in Europe alone.

750-BCD-06
Konza Renewable Fuels’ pilot plant. The first test samples were ran in 2010.


Challenges

Some challenges with biocoal that have yet to be overcome are the following: 1) biocoal is an unknown and experimental fuel, 2) has never been produced in large enough quantity for sufficient testing, 3) the process does not remove ash, 4) the process for densification has not been solidified, and 5) the burning of biocoal releases the same amount of greenhouse gases as does coal. To remedy some of these challenges, this new torrefaction unit will allow larger amounts of biocoal to be tested than ever before.  The more biocoal produced and tested, the closer we can come to knowing how the fuel is going to act and if it is a viable substitution for coal in power production. The best densification process, whether pelletizing or other, can be determined once larger quantities become available for testing.  Also, testing for the optimal moisture range for co-firing and densification can be pursued.


Biocoal sources

Any number of crops or byproducts can be torrefied and turned into biocoal.  A biomass end product that has previously been viewed as waste can be torrefied. The beetle-kill trees in the Western United States that are not being used for really neat home interiors and furniture can be torrefied.  The United States, in particular, has seen a decreased demand for forest products.  With more people and companies recycling, paper mills and other plants that use raw forest products have cut back leaving unharvested woody biomass for the taking. These forests have already been ear-marked for harvest.  Farmers can also raise biomass specific crops for torrefaction, such as switch grass, prairie grass, bamboo, eucalyptus, etc.  Some types of biomass will grow where no food crops will grow, so previously unusable land can now produce.

750-BCD-05
KRF’s pilot plant with inlet hopper full of biomass waiting to be tested.


Procedure

How does one torrefy biomass?  Simple.  Apply heat in a low oxygen environment.  The problem is the heat required to spur the desired reactions.  For the biomass to heat to the prerequisite 250°C – 280°C, 482°F – 536°F, the system as a whole must be much warmer than that to allow heat transfer. Metals can warp, expand, and become brittle at higher temperatures.  Add in a corrosive environment from the torrefaction gases and you have a recipe for failing equipment.  If these issues are not taken into account by the designers when selecting metals, the system could prematurely and/or catastrophically fail.

But, the higher temperatures and torrefaction gasses provide some great benefits as well. The torrefaction gases can be burned as fuel to minimize the use of purchased fuel, such as natural gas or biomass.  In fact, Josh Thompson, co-owner of Konza Renewable Fuels and co-creator of Konza Renewable Fuels’ Torrefaction Technology, says that depending on the type of biomass used and its starting moisture content, the torrefaction gas could supply 80 – 85% of the energy necessary, making the torrefaction process very efficient. Thompson also says “As a general rule the torrefaction process drives off about 10% of the energy in a pound of biomass and about 30% of the mass. This means that it takes about 1.43 pounds of bone dry biomass at 8600-Btu/lb to produce 1-lb of torrefied biomass at 11,000-Btu/lb.”  According to Konza Renewable Fuels’ latest Ultimate Analysis of their torrefied biomass, the starting raw biomass at 0%mcwb had a Gross Heating Value of 8333 Btu/lb, 19.42 GJ/MT, and the ending torrefied material at 0%mcwb had a Gross Heating Value of 9559 Btu/lb, 22.27 GJ/MT. (Twin Ports Testing, Inc.)

750-BCD-04
KRF’s pilot plant control system.


Quality

What is so special about torrefied biomass and why use it anyway? Based on a table showing wood and combustion heat values (The Engineering ToolBox, Wood and Combustion Heat Values) and applying some conversion factors, we find that the average heat value of green wood that is about 50%mcwb from the various species listed is 10.4 GJ/MT, 4,480 Btu/lb while the heat value of dry wood that is about 20%mcwb jumps to 14.9 GJ/MT, 6,400 Btu/lb. Under perfect laboratory conditions and 0% mcwb, wood contains 20.2 GJ/MT, 8,660 Btu/lb, (Wood and Combustion Heat Values).  That is a significant increase in the heating value of wood. What else does this mean? Companies do not have to spend near as much on shipping to receive the same amount of heat energy once the wood is dried.  But wait, it gets better. As mentioned, through experiments that Konza Renewable Fuels have been able to perform at their pilot plant, the final torrefied material will contain 22 GJ/MT, 9,500 Btu/lb. That is almost double the energy content of green wood. Shipping prices are cut in half, let alone getting the other benefits that biocoal provides.

How does 22 GJ/MT, 9,500 Btu/lb measure up? Again, we turn to The Engineering ToolBox (Heating Values of Standard Grade Coal) to find a chart for the heat value of coal. The chart is given in Btu/lb and kJ/kg, but to remain consistent, I have converted kJ/kg to GJ/MT.  The first two columns of Figure 1 illustrate what was found online. I just received my electricity bill for last month – August is pretty hot in Kansas, so it was a bit high—and we used 7,675 J. The third and fourth columns show how many kilograms (kg) and pounds (lb) of each of the following coal grades that would have been burned to power my house, assuming 100% efficiency – but that is a different story altogether.

breakcoal-01
Heating Value of Standard Grades of Coal and Konza’s Torrefied Biomass with theoretical Kilograms & pounds required to power author’s house in August, 2014.

 

As you can see in Figure 1, the amount of Konza’s Torrefied Biomass required to power my house for a month falls somewhere in the middle of the various grades of coal.  It is important to note that Konza’s Torrefied Biomass outperforms Subbituminous and Lignite.  Coal reserves as of 2011 contain the following: 403,197 million tonnes Anthracite and Bituminous, 287,333 million tonnes SubBituminous, and 201,000 million tonnes of Lignite (Newton, 1.9 – 1.10).  This tells us that Konza’s Torrefied Biomass at 22 GJ/MT, 9,500 Btu/lb, has a higher energy content than half the coal in the world’s reserves.

 

Quantity

Residence time during the torrefaction process is viewed as very important by many researchers and experimenters. According to one research team, the longer a particle roasts in the torrefaction reactor, the more VOCs are removed and the more the particle resembles coal and the higher the energy content becomes (Pirraglia et al., 221). However, the technology Konza Renewable Fuels has developed allows for different sizes of biomass particles to be torrefied during the same process. The larger, heavier particles stay in the reactor longer than the smaller, lighter particles allowing for a uniform end product, regardless their variation entering the reactor.  This technology also allows faster processing times to be able to produce 100,000+ MT in one year.

 

Call to Action

With a viable renewable energy source just at the tip of our fingers, it is time to reach.  It is time to support the budding technology and industry. With your support we can have clean coal and green, renewable energy for many generations to come.

750-BCD-02
3-D rendering to design the mechanical parts of our systems.

 


Works Cited

Felfli, Felix F., Carlos A. Luengo, Jose A. Suárez, and Pedro A. Beatón. “Wood Briquette Torrefaction.” Energy for Sustainable Development 9.3 (2005): 20-23. Universidad De Oriente. Elsevier on Behalf of the International Energy Initiative, 5 Jan. 2009. Web. 8 Sept. 2014. <http://www.fac.uo.edu.cu/fim/files/2013/10/7-Wood-briquettes-torrefaction.pdf>.

“Frequently Asked Questions.” Independent Statistics & Analysis. U.S. Energy Information Administration, 13 June 2014. Web. 12 Sept. 2014. <http://www.eia.gov/tools/faqs/faq.cfm?id=527&t=4>.

“Heating Values of Standard Grade Coal.” The Engineering ToolBox. Www.engineeringtoolbox.com. Web. 8 Sept. 2014. <http://www.engineeringtoolbox.com/coal-heating-values-d_1675.html>.

Hein, Treena. “Biomass Torrefaction Technologies.” Canadian Biomass. Canadian Biomass Magazine, July-Aug. 2011. Web. 8 Sept. 2014. <http://www.canadianbiomassmagazine.ca/content/view/2728/132/>.

Lipinsky, Edward S., James R. Arcate, and Thomas B. Reed. “Enhanced Wood Fuels Via Torrefaction.” Fuel Chemistry Division Preprints 47.1 (2002): 408-10. Argonne National Laboratory. Web. <https://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/47_1_Orlando_03-02_0071.pdf>.

Mitchell, Dana, and Tom Elder. “Torrefaction? What’s That?” Biomass Innovation Centre. Web. <http://www.biomassinnovation.ca/pdf/Report_Torrefaction_WhatsThat_Jan2010.pdf>. Fueling the Future: 2010 Council on Forest Engineering Annual Meeting June 6-9, 2010; Auburn, Alabama

Newton, David E. “Coal.” World Energy Crisis: A Reference Handbook. Santa Barbara, CA: ABC-CLIO, 2013. World Energy Council. World Energy Resources, 2013. Web. 12 Sept. 2014. <www.worldenergy.org>.

Pirraglia, Adrian, Ronalds Gonzalez, Daniel Saloni, Jeff Wright, and Joseph Denig. “Fuel Properties and Suitability of Eucalyptus Benthamii and Eucalyptus Macarthurii for Torrefied Wood and Pellets.” BioResources 7.1 (2012): 217-34. BioResources.com. North Carolina State University, Feb. 2012. Web. 8 Sept. 2014.

Tollefson, Jeff, and Richard Monastersky. “A Clickable Guide to the World’s Energy Use.” Nature.com. Nature Publishing Group, 30 Nov. 2012. Web. 8 Sept. 2014. <http://www.nature.com/news/a-clickable-guide-to-the-world-s-energy-use-1.11927>.

Twin Ports Testing, Inc. 09 Nov. 2010. Raw data. 1301 N. 3rd St., Superior, WI 54880.

“Where Is Coal Found?” World Coal Association. Web. 8 Sept. 2014. <http://www.worldcoal.org/coal/where-is-coal-found/>.

“Wood and Combustion Heat Values.” The Engineering ToolBox. Www.engineeringtoolbox.com, n.d. Web. 8 Sept. 2014. <http://www.engineeringtoolbox.com/wood-combustion-heat-d_372.html>.