Thermal depolymerization (TDP) is a depolymerization
process using hydrous pyrolysis for the reduction of complex organic
materials (usually waste products of various sorts, often biomass and plastic) into
light crude
oil. It mimics the natural geological processes thought to be involved in the production
of fossil
fuels. Under pressure and heat, long chain polymers of hydrogen, oxygen, and carbon decompose
into short-chain petroleum hydrocarbons
with a maximum length of around 18 carbons.
Similar
Processes
Thermal depolymerisation is similar
to other processes which use superheated water
as a major step to produce fuels, such as direct Hydrothermal
Liquefaction. These are distinct from processes
using dry materials to depolymerize, such as pyrolysis.
The term Thermochemical Conversion (TCC) has also been used for conversion of
biomass to oils, using superheated water, although it is more usually applied
to fuel production via pyrolysis. Other commercial scale processes include the
"SlurryCarb" process operated by EnerTech, which uses similar
technology to decarboxylate wet solid biowaste, which can then be physically
dewatered and used as a solid fuel called E-Fuel. The plant was designed to Rialto to process 683 tons of waste per day. However, it failed to
perform to design standards and was closed down. The Rialto facility defaulted
on its bond payments and is in the process of being liquidated. The Hydro
Thermal Upgrading (HTU) process uses superheated water to produce oil from
domestic waste. A demonstration plant is due to start up in The Netherlands
said to be capable of processing 64 tons of biomass (dry basis)
per day into oil. Thermal depolymerisation differs in that it contains a
hydrous process followed by an anhydrous cracking / distillation process.
History
Thermal depolymerization is similar
to the geological processes that produced the fossil fuels used today, except
that the technological process occurs in a timeframe measured in hours. Until
recently, the human-designed
processes were not efficient enough to serve as a practical source of fuel—more
energy was
required than was produced.
The first industrial process to
obtain gas, diesel fuels and other petroleum products through pyrolysis of coal, tar
or biomass was designed and patented in the late 1920s by Fischer-Tropsch.
In U. S. patent 2,177,557,
issued in 1939, Bergstrom and Cederquist discuss a method for obtaining oil
from wood in which the wood is heated under pressure in water with a
significant amount of calcium hydroxide
added to the mixture. In the early 1970s Herbert R. Appell and coworkers worked
with hydrous pyrolysis methods, as exemplified by U. S. patent 3,733,255 (issued in 1973), which discusses the production of oil
from sewer sludge and
municipal refuse by heating the material in water, under pressure, and in the
presence of carbon monoxide.
An approach that exceeded break-even
was developed by Illinois microbiologist Paul Baskis in the 1980s and refined over the next 15 years (see U. S.
patent 5,269,947,
issued in 1993). The technology was finally developed for commercial use in
1996 by Changing
World Technologies (CWT). Brian S. Appel
(CEO of CWT) took the technology in 2001 and expanded and changed it into what
is now referred to as TCP (Thermal Conversion Process), and has applied for and
obtained several patents (see, for example, published patent 8,003,833, issued August 23, 2011). A Thermal Depolymerization
demonstration plant was completed in 1999 in Philadelphia
by Thermal Depolymerization, LLC, and the first full-scale commercial plant was
constructed in Carthage, Missouri, about 100 yards (91 m) from ConAgra Foods'
massive Butterball turkey plant, where it is expected to process about 200 tons of turkey waste into 500 barrels (79 m3) of oil per
day.
Theory
and process
In the method used by CWT, the water
improves the heating process and contributes hydrogen to the reactions.
In the Changing
World Technologies (CWT) process,the feedstock
material is first ground into small chunks, and mixed with water if it is
especially dry. It is then fed into a pressure vessel
reaction chamber where it is heated at constant volume
to around 250 °C.
Similar to a pressure cooker (except at much higher pressure), steam naturally raises
the pressure to 600 psi (4 MPa) (near the point of saturated water).
These conditions are held for approximately 15 minutes to fully heat the
mixture, after which the pressure is rapidly released to boil off most of the
water (see: Flash evaporation). The result is a mix of crude hydrocarbons and solid minerals. The
minerals are removed, and the hydrocarbons are sent to a second-stage reactor
where they are heated to 500 °C, further breaking down the longer hydrocarbon
chains. The hydrocarbons are then sorted by fractional distillation, in a process similar to conventional oil refining.
The CWT company claims that 15 to
20% of feedstock energy is used to provide energy for the plant. The remaining
energy is available in the converted product. Working with turkey offal as the feedstock, the process proved to have yield
efficiencies of approximately 85%; in other words, the energy contained in the
end products of the process is 85% of the energy contained in the inputs to the
process (most notably the energy content of the feedstock, but also including
electricity for pumps and natural gas or woodgas for
heating). If one considers the energy content of the feedstock to be free
(i.e., waste material from some other process), then 85 units of energy are
made available for every 15 units of energy consumed in process heat and
electricity. This means the "Energy
Returned on Energy Invested"
(EROEI) is (6.67), which is comparable to other energy harvesting processes.
Higher efficiencies may be possible with drier and more carbon-rich feedstocks,
such as waste plastic.
By comparison, the current processes
used to produce ethanol and biodiesel from agricultural
sources have EROEI in the 4.2 range, when the energy used to produce the
feedstocks is accounted for (in this case, usually sugar cane,
corn, soybeans and the
like). These EROEI values are not directly comparable, because these EROEI
calculations include the energy cost to produce the feedstock, whereas the
above EROEI calculation for thermal depolymerization process (TDP) does not.
The process breaks down almost all
materials that are fed into it. TDP even efficiently breaks down many types of
hazardous materials, such as poisons and difficult-to-destroy biological agents such as prions.
Feedstocks
and outputs with thermal depolymerization
Average
TDP Feedstock Outputs
|
||||
Feedstock
|
Oils
|
Gases
|
Solids
(mostly carbon based)
|
Water
(Steam)
|
Plastic
bottles
|
70%
|
16%
|
6%
|
8%
|
Medical
waste
|
65%
|
10%
|
5%
|
20%
|
Tires
|
44%
|
10%
|
42%
|
4%
|
Turkey
offal
|
39%
|
6%
|
5%
|
50%
|
Sewage
sludge
|
26%
|
9%
|
8%
|
57%
|
Paper
(cellulose)
|
8%
|
48%
|
24%
|
20%
|
(Note: Paper/cellulose contains at
least 1% minerals, which was probably grouped under carbon solids.)
Carthage
plant products
As reported on 04/02/2006 by Discover Magazine, a Carthage, Missouri plant was producing 500 barrels per day (79 m3/d)
of oil made from 270 tons of turkey entrails and 20 tons of hog lard. This
represents an oil yield of 22.3 percent. The Carthage plant produces API 40+, a
high value crude oil. It contains light and heavy naphthas, a kerosene, and a gas oil fraction,
with essentially no heavy fuel oils, tars, asphaltenes or waxes. It can be
further refined to produce No. 2 and No. 4 fuel oils.
TDP-40
Oil Classification by D-5443 PONA method
|
|
Output
Material
|
%
by Weight
|
Paraffins
|
22%
|
Olefins
|
14%
|
Naphthenes
|
3%
|
Aromatics
|
6%
|
C14/C14+
|
55%
|
100%
|
|
The fixed carbon solids produced by
the TDP process have multiple uses as a filter, a fuel source and a fertilizer.
It can be used as activated carbon in wastewater
treatment, as a fertilizer, or as a fuel similar to coal.
Advantages
The process can break down organic
poisons, due to breaking chemical bonds and destroying the molecular shape
needed for the poison's activity. It is likely to be highly effective at
killing pathogens, including prions It
can also safely remove heavy metals
from the samples by converting them from their ionized or organometallic forms
to their stable oxides which can be safely separated from the other products.
Along with similar processes, it is
a method of recycling the energy content of organic materials without first
removing the water. It can produce liquid fuel, which separates from the water
physically without need for drying. Other methods to recover energy often
require pre-drying (e.g. burning, pyrolysis) or produce gaseous products (e.g. anaerobic digestion).
Potential
sources of waste inputs
The United
States Environmental Protection Agency
estimates that in 2006 there were 251 million tons of municipal solid waste, or 4.6 pounds generated per day per person in the USA.Much
of this mass is considered unsuitable for oil conversion.
Limitations
The process only breaks long
molecular chains into shorter ones, so small molecules such as carbon dioxide
or methane cannot be
converted to oil through this process. However, the methane in the feedstock is
recovered and burned to heat the water that is an essential part of the
process. In addition, the gas can be burned in a combined heat and power plant, consisting of a gas turbine
which drives a generator to create electricity, and a heat exchanger to heat
the process input water from the exhaust gas. The electricity can be sold to
the power grid, for example under a feed-in tariff
scheme. This also increases the overall efficiency of the process (already said
to be over 85% of feedstock energy content).
Another option is to sell the
methane product as biogas. For example, biogas can be compressed, much like natural gas, and used to power motor
vehicles.
Many agricultural and animal wastes
could be processed, but many of these are already used as fertilizer,
animal feed, and, in some cases, as feedstocks for paper mills
or as boiler fuel. Energy crops
constitute another potentially large feedstock for thermal depolymerization.
Current
status
Reports in 2004 claimed that the
Carthage facility was selling products at 10% below the price of equivalent
oil, but its production costs were low enough that it produced a profit. At the
time it was paying for turkey waste (see also below).
The plant then consumed 270 tons of
turkey offal (the full output of the turkey processing plant) and 20 tons of
egg production waste daily. In February 2005,the Carthage plant was producing
about 400 barrels per day (64 m3/d) of crude oil.
In April 2005 the plant was reported
to be running at a loss. Further 2005 reports summarized some economic setbacks
which the Carthage plant encountered since its planning stages. It was thought
that concern over mad cow disease would prevent the use of turkey waste and
other animal products as cattle feed, and thus this waste would be free. As it
turned out, turkey waste may still be used as feed in the United States, so
that the facility must purchase that feed stock at a cost of $30 to $40 per
ton, adding $15 to $20 per barrel to the cost of the oil. Final cost, as of
January 2005, was $80/barrel ($1.90/gal).
The above cost of production also
excludes the operating cost of the thermal oxidizer and scrubber added in May
2005 in response to odor complaints (see below).
A biofuel tax credit of roughly $1
per US gallon (26 ¢/L) on production costs was not available because the oil
produced did not meet the definition of "biodiesel" according to the
relevant American tax legislation. The Energy
Policy Act of 2005 specifically added thermal
depolymerization to a $1 renewable diesel credit, which became effective at the
end of 2005, allowing a profit of $4/barrel of output oil.
Company
expansion
The company has explored expansion
in California, Pennsylvania, and Virginia, and is presently examining projects
in Europe, where animal products cannot be used as cattle feed. TDP is also
being considered as an alternative means for sewage treatment in the United
States.
Smell
complaints
The pilot plant in Carthage was
temporarily shut down due to smell complaints. It was soon restarted when it
was discovered that few of the odors were generated by the plant.Furthermore,
the plant agreed to install an enhanced thermal oxidizer and to upgrade its air scrubber
system under a court order. Since the plant is located only four blocks from
the tourist-attracting town center, this has strained relations with the mayor
and citizens of Carthage.
According to a company spokeswoman,
the plant has received complaints even on days when it is not operating. She
also contended that the odors may not have been produced by their facility,
which is located near several other agricultural processing plants.
On December 29, 2005, the plant was
ordered by the state governor to shut down once again over allegations of foul
odors as reported by MSNBC.
As of March 7, 2006, the plant has
begun limited test runs to validate it has resolved the odor issue.
As of August 24, 2006, the last
lawsuit connected with the odor issue has been dismissed and the problem is
acknowledged as fixed.In late November, however, another complaint was filed
over bad smells. This complaint was closed on January 11 of 2007 with no fines
assessed.
Status
as of February 2009
A May 2003 article in Discover
magazine stated, "Appel has lined up federal grant money to help build
demonstration plants to process chicken offal and manure in Alabama and crop
residuals and grease in Nevada. Also in the works are plants to process turkey
waste and manure in Colorado and pork and cheese waste in Italy. He says the
first generation of depolymerization centers will be up and running in 2005. By
then it should be clear whether the technology is as miraculous as its backers
claim."
However, as of August 2008, the only
operational plant listed at the company's website is the initial one in Carthage,
Missouri.
The unusual Dutch Auction
type IPO failed possibly because CWT has lost nearly $20 million with very
little revenue.
CWT, the parent company of Renewable
Energy Solutions, filed for Chapter
11 bankruptcy. No details on plans for
the Carthage plant have been released.
Similar
technologies
- Plasma Converters use powerful electric arcs to reduce and extract energy from waste.
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