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By Robert Rapier on Nov 20, 2014 with 17 responses

Torrefaction via Radio Waves

Tags: torrefaction

During the past five years that I spent in Hawaii, I worked on a number of different projects. The company I worked for invested in energy projects, and our focus was on converting biomass into energy. In my role, I often evaluated companies and technologies to determine the potential technical and economic viability.

I have found over the years that the vast majority of biomass to energy projects aren’t economically viable for one reason or another. I have looked at companies that utilize many different conversion technologies, and most of the time my job consisted of searching for fatal flaws of different approaches. I was the guy who said “No.” That approach saved my employer a lot of money, because none of the companies I said “No” to are thriving today. Most went out of business.

But I didn’t like always being the guy who said “No.” I wanted to put steel in the ground and build something. So I searched for ways to say “Yes”, or at least to turn “No” into “Maybe.”

You don’t always immediately know whether the answer is yes or no, but in the case where a “yes” could make a big impact, sometimes we funded basic research. I can’t talk about most of the things we were involved with due to various nondisclosure agreements, but I was recently given approval to mention a project we funded on radio frequency (RF) heating.

The gist of the idea is that like microwaves, RF waves of the right frequency can efficiently heat objects. If the frequency is right, RF waves can be utilized to make a ceramic cup glow red. The depth of penetration is directly proportional to wavelength, and since RF wavelengths are longer than microwaves, RF can be used to heat thick materials, like a log. Or a big pile of wood.

So why would you want to heat up biomass? To torrefy it. Torrefaction is a mild biomass thermal treatment usually carried out between 200 and 300 degrees C. Torrefaction upgrades the quality of biomass as fuel for combustion and gasification applications. Torrefaction can be referred to as roasting, and in fact the history of torrefaction can be traced to roasting coffee beans for easier grindability. This is also what happens to wood when torrefied. Torrefied wood has the moisture and most of the volatile organic compounds driven off, and the wood becomes brittle in the process. This makes it easier to grind, which enables the creation of pellets that are more energy dense than wood, and that are comparable to coal.

What are the implications? First, significantly more energy can be transported in a container when that material has been torrefied and pelletized, relative to wood pellets. Further, after the biomass has been torrefied it repels water and is much less biodegradable. This enables it to be stored for longer periods of time. Finally, the challenge in burning wood for electricity is that the energy efficiency isn’t great. It takes a lot of energy to grind wood down to a powder for the most efficient burn (which is still lower for wood than for coal). Because of the differences with coal, wood may only be blended in very small quantities in a coal-fired power plant. Torrefied wood, on the other hand, grinds as easily as coal, and can therefore be blended at much higher concentrations in a coal-fired power plant.

So we saw a big opportunity, but a lot of unknowns. There hasn’t been much work done in this area. Would it work? Could we find a frequency that would put the right amount of heat into the wood? Would it be energy efficient?

We worked with a company in Great Barrington, Massuchussetts called JR Technologies. “J” is Jeb Rong, and “R” is Ray Kasevich — two of the foremost RF experts in the world. You can see their biographies here, and a presentation they gave on the technology here (Their contact information is on the first slide should you wish to contact them).

We developed an experimental plan, and following an extensive literature review of the torrefaction process, built a prototype batch reactor.

Ray and Jeb
Ray and Jeb Inspecting the RF Generator and Torrefaction Reactor

In June 2011 we conducted the first set of experiments. (I spent a lot of time in the lab with them there, and was onsite for the initial tests). What we produced looked like torrefied biomass, but one thing I learned is that there are no real standards for what qualifies biomass as torrefied. There is a regime where it’s woody and fibrous (and takes a lot of energy to grind), a regime where it’s torrefied and first becomes brittle, and a regime where it’s charcoal. You want to have it sufficiently in the realm of torrefied wood. Too little torrefaction and it isn’t brittle, and too much and you drive off too much of the initial energy content.

So we secured some samples of torrefied wood, and sent that along with our material to a lab for testing. When we got the results back, we found that the material we produced was essentially the same as the torrefied control sample we sent. We did more testing, and ultimately decided to build a larger, continuous reactor.

What happened next is that my company made a decision to no longer fund the German biomass-to-liquids company Choren. (See What Happened at Choren?) Choren’s process had some synergies with what we were doing with the torrefied biomass, so we ultimately decided to stop funding the torrefaction research as well (which my boss was funding directly out of pocket). This has left development in limbo for the past couple of years.

But I remain in close contact with Ray and Jeb, and they continue to pursue their RF work. Beyond the RF torrefaction, there are a number of applications for RF heating. One of their most interesting uses of RF is for environmental remediation (see the previously-linked presentation for more details). But the RF torrefaction work is still in the “maybe” column today, and I hope to someday further this work with them.

Link to Original Article: Torrefaction via Radio Waves

By Robert Rapier. You can find me on TwitterLinkedIn, or Facebook.

  1. By GreenEngineer on November 20, 2014 at 8:22 pm

    Very interesting – thanks for sharing!
    When you describe the volatile organic compounds being driven off, my first thought was “wood gas!”. Is that accurate – is that what it actually is?

    Obviously the technology is not at this stage yet, but is it reasonable to suppose that the wood gas might be burned locally at point of production to help drive the torrefaction process?

    • By Robert Rapier on November 22, 2014 at 12:45 pm

      Our intention was to do that; to burn the gas. What comes off is a real potpourri of stuff, so you have to take some considerations with the burner design. It would have to be widely adaptable to different compositions.

  2. By Forrest on November 21, 2014 at 7:45 am

    Interesting, I wondered how the process could be cheaper than plain pellet process. An Arkansas company is building a big plant with this process in Monticello. It’s describes as proprietary black pellet production. Arkansas has a glut of forest material and this company is planning on exporting the fuel to Europe. Europe has high demand for this renewable fuel as a practical replacement for a portion of coal within cofired power plants. Exports doubled last year (3.2 million tons) as 98% headed for Europe. The process had a break through advance per recycling or condensing process of vented btu gas portion. I do think the ethanol cellulosic plants will eventually get into this process per the by product of high energy lignin and efficient handling of cellulose. The torrefaction process can utilize a wide variety of raw material as I understand. Another possibility, a young entrepreneur has well establish business per efficient pellet production from biomass. He is very studied upon Industrial Engineering and excels as practical and invented ways to make production profitable. Sorry, can’t remember the company name, but he plans on greatly improving the biofuel material handling economics. Someone like this could include this process for the power and heat market as well.

    • By Forrest on November 24, 2014 at 7:27 am

      The break through advanced described as “advanced torrefaction” utilizes an oxidation catalyst. The process efficient, green, safe, and reliable. The 10% energy value of biomass gas off during the process treatment is vented through a catalyst which operates at lower temps as compared to old process of combustion. No NOx emissions as result. The cat hot exhaust powers the torrefaction process (low oxygen). Cooling pellet VOC emissions captured by same cat to heat and burn. The patented system has a cooling process for finished material, as well.

      The cofiring of old coal plants with this environmental material is helping utility companies extend lifespan of existing equipment. This keeps cost down, helps environment concerns, and buys the utility time to put in place well thought out solutions. Europe seems to have taken up the solution quicker than U.S..New biomass markets currently being evaluated and continue to offer promising results. King Grass in desert areas offer new feed and fuel opportunities with impressive production. Hybrids of Switch Grass and like kind grasses continue to break production records for tons per acre, easily surpassing forest growth rates. And short growth cycle poplar that looks more like extremely tall and large grass is gaining respect to power biomass markets. I’ve often wondered why the federal government couldn’t think outside their usual stiffing bureaucracy and subcontract the large zones of interstate median land mass. The miles and miles of extra wide zones could be put to use of biomass growth and eliminate the cost of constructing cable or metal guard rails. Michigan is in the throws of constructing and maintaining expensive cable system (very ugly) to reduce traffic deaths of run away vehicles striking opposing traffic lanes. This has a BIG price tag. How about a simple revenue generating system of short cycle poplar that is restricted to leave one foot high stumps upon harvest . The trees are attractive, taxpayers appreciate the savings and revenue, the energy sector and farmers enjoy some additional millions of acres, since invention of the cell phone troopers need not utilize the view. I like this solution as the fuel cofiring could empower the clean coal fluidized bed process per CO2 reduction as well. The need could push biomass farming markets at earlier stage in preparation of increasing cellulosic ethanol feedstock need.

  3. By Sam Richardson on November 21, 2014 at 9:39 am

    Worldwide Recycling Equipment in Moberly, Missouri, which just celebrated its 10th anniversary, conceives, engineers and manufactures green energy products–including for biomass torrefaction. The eingeering ace at Worldwide, Nico Scheeres, is among the most well informed I’ve encountered on the topic. He is a train-the-trainers sort of guy for biomass torrefaction.

  4. By TimC on November 23, 2014 at 11:36 am

    Interesting post, but raises several questions. You said,

    “Torrefaction can be referred to as roasting, and in fact the history of torrefaction can be traced to roasting coffee beans for easier grindability.”

    Okay, but roasting can be done in air, and some oxidation reactions are desirable in the roasted product, including coffee beans. Torrefaction must be done in low O2, as oxidation reactions are undesirable, reducing the product LHV. How did you eliminate entrained air from the biomass feed in your experimental RF batch reactor, and how would air removal be accomplished in a commercial scale continuous RF torrefaction reactor? This seems like a major disadvantage of the RF approach. Torrefaction in vertical tray column reactors using flue gas to displace air (e.g. the Andritz/ECN process) should have both lower CAPEX and OPEX than RF generators, and if you have to provide an inert sweep gas to remove air, RF will not compete at any scale. Also, scalability of RF-heated reactors will be limited by the RF penetration depth, while tray columns can be scaled to large diameters. What is the advantage of using RF heating in a torrefaction process?

    “…there are no real standards for what qualifies biomass as torrefied.”

    Maybe not, but most power plants have spec sheets for any kinds of fuel that they purchase, including biomass. We talked to our local power plant a while ago, and they are being required to reduce their carbon footprint, so are eager to find torrefied biomass pellets that they can co-fire with coal in their boilers. They were happy to provide specs for biomass fuels. JR Technologies should get spec sheets from the plants they want to sell to, and work to meet those specs, not some academic standard of torrefaction. For some customers, deep-dried biomass may meet plant specs, with no need to actually torrefy biomass.

    Overall, a good project, but not one that I would put in the “maybe” column, I would toss it in the “probably not” basket.

    • By bigterguy on December 4, 2014 at 12:59 pm

      Tim, Torrefaction produces a gas stream of CO, CO2, CH4 and some other minor components. This gas could be recycled to provide the oxygen-free environemnt. Whenever RF or microwave radiation is suggested one must remember that these are more expensive sources of heat than burning the leftover wastes from these processes. And the energy of RF or microwave radiation distributes as fast as thermal energy. So the advantages are not clear to me, although there may be particular cases where it makes sense.

      • By TimC on December 4, 2014 at 6:00 pm

        Thanks, you’re right about the off-gas recycle. When I first looked at the ECN torrefaction process (page 14 of the link below) I mis-read the flow sheet and thought they were using the flue gas to displace air. On closer reading I see that you are correct, they use the torrefaction gas, superheated using flue gas in a heat exchanger, to remove air and provide heat to biomass in the tray column reactor.

        This seems like an efficient, robust process design to me. If torrefied wood pellet manufacture is going to be a commercial success, it will probably use an approach like ECN’s. I see no advantage in using RF or other exotic heating methods.

        ECN torrefaction technology:

  5. By Russ Finley on November 23, 2014 at 12:50 pm

    …learn something new every day. Technology begets technology.

  6. By Forrest on November 25, 2014 at 9:06 am

    Vega Biofuels and Agri-Tech Producers are teaming up for a new process
    for production of Bio-Coal (torrefaction). They will utilize the feedstock from fast growing trees and energy crops that have been planted upon contaminated soil sites for the purpose of root growth clean up. Upon harvest a partner company’s leaching process to remove toxins and problematic substances from biomass. EPA has 66,000 contaminated sites nationwide, totaling approximately 35 million acres.

  7. By Peter Hall on November 30, 2014 at 5:22 pm

    The torrefaction off gas has a lot of CO2 and some CO, with tiny amounts of CH4 and H. Also a lot of water, with some acetic acid in it. Its very low energy value typically. Probably need a pilot fuel to get it to burn, once the condensables have been removed. Could maybe provide up to 40% of the heat needed to do the torrafaction, or to dry the feedstock before it goes into an RF or microwave torrefaction unit.

    Company called Carbonscape ( doing some work on developing microwave based char-coaling / torrefaction.

    I have not looked at the energy in / out for traditional / RF / Microwave charring of wood, but I if anyone has I’d love to see the numbers.

    • By Forrest on December 1, 2014 at 7:11 am

      What do you think of the my 7 day old post describing “The break through advanced described as “advanced torrefaction” utilizes an oxidation catalyst.”

      I’m picking up the industry is utilizing this process for new plant construction. It is presented as solving emission problem and process energy requirement. Also, most haven’t read about new technology from Distillation Technology Inc. that is moving to pilot stage testing of dehydration process. The process cost 75% less for ethanol distillation or about 25 cents per gallon cost saving. They expect to utilize the process for grain drying and recycling water as well. In a nutshell, the ethanol beer is first entrained with air, then sprayed in vacuum column where minute bubbles in droplets again explode beer to micro particles. This 140 degree process will produce 95% pure ethanol per micro particle physics and do so with one pass. The gas vapor stage of micro particles lose surface tension. No membrane technology needed to polish off distillation or to convert waste water to process grade water. I don’t understand how the process could be utilized for grain drying, but if similar cost savings it will become standard billing. Makes one think not much of a stretch to include torrefaction. There’s another company that utilizes a torrefaction process whereupon the energy component of emissions is condensed back into fold of black pellet product. It attains a higher BTU rating and may be vitalized by this micro bubble dehydration process? Sorry have no link, just read of the process.

  8. By Torrefied of Torrefaction on December 1, 2014 at 5:10 pm


    Here’s a second vote for a back of the envelope analysis of the energy / heat transfer and energy balances for RF torrefaction. I’d also be curious as to what your take is on the value added by torrefaction. What did you expect versus what happened. I’m hoping the above isn’t too proprietary to share.

    • By Robert Rapier on December 8, 2014 at 11:02 pm

      We are pretty sure that starting from the energy to produce the electricity, we are energy positive. As far as what we expected versus what happened — were weren’t at all sure it would work.

  9. By simondc3 on December 8, 2014 at 3:07 pm


    Nice article and something to watch. Thanks.

    I wonder if this RF application can be used for biochar production as well.

    Biochar is used as soil amendment.
    Very likely you know of it, but if you haven’t Wikipedia has a nice intro to it ( and Albert Bates wrote The Biochar Solution touching on the famous Terra Prieta of the Amazons; very fertile lands which turns out the Incas amended with biochar and would be very acidic otherwise.

    • By Robert Rapier on December 8, 2014 at 10:55 pm

      There are a lot of cheap, low-tech ways to produce biochar, so I don’t think it would cost effective at that.

  10. By simondc3 on December 8, 2014 at 3:28 pm


    What have you found are the energy offsets of RF heating vs other sources of heating? I take it RF heating is cheaper / more economical, vs other sources of heating, and is what would make this torrefaction technique a possible YES as opposed to others (?)

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