To convert residue fuels such as forest or agricultural feedstock, municipal solid wastes or tires into useful clean gas or liquid fuels, the main option today is gasification. Gasification systems – bubbling, circulating and entrained beds – produce low calorific value gases, are capital intensive, and require large plant sizes to be cost effective. They are therefore inappropriate for many residue fuels such as tires or agricultural wastes. Pyrolysis, and “rapid” pyrolysis in particular, offers a possible alternative with the following advantages:

-Lower vapor volumes which reduce emissions and capital cost.
-Elimination of the production of alkali vapors, simplifying clean-up.
-Reduced operating temperatures which minimizes the formation of poly-nuclear aromatics, in turn improving the efficacy of cracking or steam reformation prior to use in the fuel cell.
– Fast pyrolysis yields larger quantities of fuel vapor with simpler organic moieties.

[Pyrolysis involves heating in the absence of oxygen, resulting in gases, liquids and char (e.g. charcoal) in varying proportions. “Fast” heating, at lower temperature, is preferred, as it results in less char and fewer complex chemical products from subsequent reactions. Gasification, in fact, can be seen as a special case of pyrolysis, where admitting some air helps to maximize gas production over liquids and char.]

Capital and operating cost for a pyrolysis plant is directly related to heat transfer rate. Presently, most rapid pyrolysis processes use conventional entrained flow or fluidized beds which have good heat transfer rates but require small particle sizes, less than 0.08 inches, to achieve the desired residence times (less than 2 seconds) for rapid pyrolysis.

“Ablative” pyrolysis can increase heat transfer rates. The particle is abraded against the hot surface, removing reaction products and exposing fresh material for reaction.

The two ablative processes which are being developed utilize centrifugal force to achieve the required pressure on the particle to sustain ablative pyrolysis. From the operating characteristics of these processes, vortex reactor of NREL and centrifugal pipe design of Enervision Inc, it would appear that these systems cannot provide enough force on the particle to sustain ablative pyrolysis throughout the residence time of the particle. As a result large particles cannot be effectively converted.

Mechanical ablative reactors with low carrier gas requirements are under development in England and the Netherlands. From the data available, it is not obvious how easy it will be to scale these systems to commercial sizes and how effective they will be in handling a wide range of materials and particle sizes.

DynaMotive, a Canadian company which acquired rights to a fluid bed technology developed at Waterloo University, is making “BioFuel” with their BioTherm Fast Pyrolysis Technology.
http://dynamotive.com/english/units/biooil/tech.html

——- references: ———
“Principles and Practice of Biomass Fast Pyrolysis Processes for Liquids”, A.V. Bridgewater, Journal of Analytical and Applied Physics 51 (1999). (20 pages) offers a thorough review of the subject. (If you have trouble getting it, I have a low quality fax copy.)

Bridgewater has also authored a couple of books on the subject.
See: http://www.cplscientific.co.uk/press/gas-relate.html
——–

Down Stream Systems, a small company in California in the waste conversion technology business, is proposing a ” mechanical ablative pyrolysis” (MAP) unit, currently patent pending in the USA, which offers the potential for the following:

– Simplicity of design with high rates of heat transfer.
– Ability to handle a wide range of particle sizes and residue materials.
– Moderate capital cost and, therefore, the ability to site close to local sources of residue fuel.
– Minimum carrier gas requirements and low vapor volumes with associated reduction in gas clean-up costs.
– System operating temperatures, which avoid the production of alkali vapors and poly-aromatic hydrocarbons. This simplifies gas treatment for use in fuel cells.

An earlier version of the process converted 50 tons per day at a high conversion efficiency. The feedstock however, had to be finely ground. The new MAP process is designed to overcome this critical limitation. It is projected that a 50 ton per day biomass system will produce 10,000 gallons of bio-oil similar to a #2 diesel, but having somewhat less than half the energy. An appropriate site and supply of 50 ton per day of biomass for a prototype system is available.

Before installing the prototype, a series of tests will be run in a 0.5 tpd pilot scale MAP reactor. The company is seeking funding to build and install the pilot scale reactor and to perform the tests.

The pilot reactor will operate under the same conversion conditions as earlier fast acting reactors except for its unique mechanical ablation feature. The test system will be tuned until it efficiently vaporizes coarse organics. A series of tests will then be run to optimize conversion parameters, followed by steady state runs at optimal conversion settings to establish mass/energy balances, characterize the products and provide design data for the commercial demonstration. An independent consulting firm will be retained to observe the control tests and confirm process viability.

The required funding is on the order of $300,000. The company has a proposal involving equity shares in a new holding company, however they are open to other arrangements. A detailed business plan and technical proposal can be provided on request.

Contact:
Bob McChesney, Vice President
Down Stream Systems, Inc., Folsom, CA
916-989-8180 rmc@Inreach.com
323-249-5303 (at their recycling facility on Los Angeles)

http://www.downstreamsystems.com/