Richard Darrell Ruff's Page

Good afternoon Mr. Laughlin;

The proceding is a article that I wrote back in 2001. I hope you find it interesting.

Oil-From-Bio-Solids Technology

Audience: The President of these United States of America, the U.S. Department of Energy, heads of the oil industry’s refineries, municipalities, owners of trash-to-energy facilities, automobile manufacturers and environmental atmospheric air quality concerns investigators and consultants.

Purpose: To develop a viable fuel alternative to alleviate rising fuel cost by recycling and reusing bio-solids to produce a crude oil and char fuel product for commercial oil and fuel productivity.

Oil-from-bio-solids technology, formerly know as oil-from-sludge technology, is the process of oil extraction out of human and/or animal bio-solids formerly known as municipal wastewater or sewage sludge, can undergo a low temperature conversion producing liquid oil and solid char fuel products. These products can be used to provide process energy and/or marketed as fuels.

The basic concept of low temperature conversion has been known for years. Dried bio-solids are heated from 30 to 350 degrees Celsius in an oxygen free environment for about 30 minutes, and catalyzed vapor-phase reactions convert the organic to straight-chain hydrocarbons, much like those found in crude oil. The oil yield from raw bio-solids is greater then that from digested bio, and the oil from digested bio has a lower viscosity then raw. These results are expected because the volatile materials that are destroyed in the digestion process are precursors for the oil generated in the conversion process. The oil product heating value is about 39 MJ/kg; and the char’s value is 15 MJ/kg.

Based on the potential of this process, the U.S. need to conduct preliminary batch, bench-scale experiments by designing, fabricating, and patenting a continuous flow bench-scale reactor and embarking on a technology development and demonstration program. Pilot-scale studies were carried out in Canada and Australia in the early to mid 1980's. In conjunction with these studies, the end products, primarily the oil fraction, were characterized.

Bench-Scale Studies: The bench-scale reactor has a capacity of 1 kg/h dried bio and has been used to evaluate process performance and generate design information.


The reactor is subdivided by a helical gas seal into a volatilization zone and a char and gas contact zone. Solids retention time (SRT) in the reactor is controlled by varying the bio feed rate and the inventory of solids in the reactor. Bio-solids are fed to and carried through the reactor by calibrated screw conveyors. Volatile materials are withdrawn in the first zone and brought into contact with the char in either a co-current or counter-current mode in the second stage. Product gases are condensed externally in a water-cooled condenser and separated into oil and reaction water. The non-condensing gas (NCG) is vented to a stack. Inert gas is used to purge the system of oxygen, and the operating pressure is generally less than 2000 Pa. Mixed raw and anaerobically digested bio-solids from the U.S. have been studied.

Oil yields range from 13% for anaerobically digested bio to 46% for raw mix, and are primarily a function of the operating temperature. Char had yields of 40 to 73 percent, and non-condensing gas had yields of 3 to 12 percent and are also a function of the operating temperatures. Reaction water yields range from 3 to 16 percent and did not seem to be affected by operating variables. Thermal efficiencies greater than 95% were routinely obtained with the bench-scale reactor. The oil’s chemical composition is stable over a wide range of operating conditions and generally contains less than 7% oxygen, 76% carbon, 11% hydrogen, 4% nitrogen and 0.5% sulfur.

Although the oil yield varies depending on bio type and/or decomposition, the effect of temperature is identical on all bio-solids. The oil yield increases as temperature increases until the temperature reaches 400 to 450 degrees Celsius. Above the temperature range of 450 degrees Celsius, the yield decreases and conditions favor the formation of non-condensing gas. No relationship between temperature and oil calorific value has been established; however, the viscosity of the oil decreases with increasing temperature, indicating that thermal cracking of the oil occurs above certain temperatures.

Pilot-Scale Studies: In 1985 the Canada designed, constructed and operated a 40 kg/h, 1000 kg/d pilot-scale conversion reactor to confirm the bench-scale results and the projected energy savings of the oil-from-bio-solids technology. The reactor consists of 1 m3 bio-solid storage bin, a bio feed system, a 25 cm dia. x 3.2 m long reactor, a char discharge system, a packed tower direct contact condenser, an oil and water separator, and a self-contained propane and non-condensing gas fired boiler to provide hot flue gas for reactor heating. Except for the heating method, the configuration and operation of the reactor is the same as for the bench-scale reactor. The pilot-scale reactor is mounted on a 1.7 m x 7.4 m skid and is readily transportable.

In 1986, the reactor had been modified to improve operational performance. The only function of the pilot-scale reactor that was not satisfactory was oil and water separation. When the oil’s density was close to that of the water, problems encountered in discharging the oil and water separately. The reactor used three types of bio-solids and the results have confirmed that sufficient heat capacity was available to reach conversion temperatures at low solids retention times, the throughput capacity of 40 kg/h can be reached, and the oil and char can be separated by
the removal of the gravity decanter and then replacing it with a disc centrifuge, by doing so the problem of oil and water separation was alleviated.

For specific bio-solids types, the data from the bench-scale and pilot-scale reactors compare well in terms of product yield, composition, and quality.

Following the completion of a study to determine the effect of operational parameters on the pilot-scale reactor performance, the reactor was operating in a production mode bearing 450 degrees Celsius, at 25 minutes of solids retention time, and 10 to 12 h/d for several days to generate oil.


The Australians however constructed a second generation pilot-scale reactor which is heated by burners mounted directly on the reactor shell rather then by hot flue gas from a propane fired boiler like pilot-scale reactor. There have also been improvements made in the sealing of the feed and discharge zones that allow operation at pressures up to 25 k Pa. The pilot-scale reactor has been used to develop a database on bio-solids, and the information from the database is similar to that obtained by the Canadian pilot-scale reactor.

In 1989, a pilot-scale reactor program that tested unit operations in an integrated oil-from-bio-solid reactor was conducted for the Sydney Water Board at the Malabar Sewage Treatment Plant located in Sydney, Australia. The objectives included developing detailed design data, generating environmental data, assessing end uses for the oil, and refining cost estimates for a 60 ton/day facility. The process train evaluated consisted of a belt filter press for bio-solids dewatering, a direct flue gas dryer, an oil-from-bio-solids reactor, and a fluid-bed combuster.

The study was conducted on anaerobic digested primary bio-solids generated from the water pollution control facility. Average concentrations in mg/kg of heavy metal and organic contaminants were identified showing high copper concentrations.

The bio is first dewatered on a belt filter press discharging 30 to 35 percent solids and then dried to 95% solids by a direct flue gas dryer. Analyses indicated no detectable loss of heavy metals or organochlorines during the dewatering or drying stages. The dried bio was then processed using the oil-from-bio-solids technology. Contaminants were measured, with the exception of arsenic and mercury, the heavy metals were retained in the char. Small concentrations of hexachlorobenzene 1 mg/kg and polychlorinated biphenyls 0.48 mg/kg were found in the oil, but were not detected in the char or reaction water. Based on the concentrations of the contaminants in the oil, the destruction efficiency of the oil-from-bio-solids technology was greater than 85% for hexachlorobenzene and greater than 75% for polychlorinated biphenyls.

The char was combusted in a 150 mm fluid-bed combuster at a feed rate of 1 kg/h and bed temperatures from 789 to 876 degrees Celsius. Excellent organic carbon combustion efficiency was achieved at 99.992 to 99.996 percent. Nitrogen oxides were reported relatively stable at 300 to 400 parts per million (ppm). At 786 degrees Celsius, more than 99.7% of the heavy metals, except mercury, was retained in the ash. About 8% of the mercury was found in the products of fluid-bed combustion, 5.4% in the ash, and 2.6% in the flue gas. A maximum of 24 mg/kg of polycyclic aromatic hydrocarbons was detected in the char, and off gas analysis indicated a destruction efficiency of greater than 96%.

The bed ash from the fluid-bed combustor was tested for leachate toxicity using the toxic characteristic leaching procedure (TCLP), which can and is being used in some capacity to classify bio-solids as hazardous or non-hazardous. All parameters were within the TCLP limits. Off gas analysis from the dryer and the reactor showed that air emissions could easily meet requirements for heavy metals and organochlorines.

Engineering and Cost Studies: In 1984 Canada made a study to assess the commercial viability of the oil-from-bio-solids technology. A 25 ton/day conversion reactor was designed and the economics of the operations were compared to existing bio-solids management options.

To obtain incineration cost data, in1986 four bio-solids management facilities were studied and total bio-solids treatment costs for each facility were developed. The bio-solids treatment train in each facility included digestion, thickening, dewatering, conditioning, incineration and ash disposal. Capital costs were taken from actual construction contracts and were calculated by amortizing the total capital cost over a 20 year period at 10% interest. Operating and maintenance costs were determined using the facilities records and interviews of the onsite personnel. At existing flows ranging from 36 to 67 ton/day, the total cost would be $350 to $1042/ton.

Preliminary costs for the oil-from-bio-solids technology were developed based on data from the bench and pilot-scale studies. For a 45 ton/day facility, the capital cost, which includes dewatering, conditioning, drying, conversion, condensation, oil and water separation, char combustion, and ash disposal, was estimated at $17.5 million, plus $0.5 million for performance evaluation and environmental assessment. Based on an amortization rate of 11%/year over a 20 year period and an annual operating cost of $2.2 million/year, the total unit cost is $295/ton dry solids. This cost does not consider the potential value deduction that can be allocated from oil production.

Full-Scale Demonstration Facility: For the oil-from-bio-solids technology to be accepted by any form of government or other entity, it would be a great necessity to conduct a full scale demonstration.

Summary: I would like to study the Australian’s reactor and receive a grant to build a small portable bench-scale reactor and run bench-scale tests on dewatered aerobic, anaerobic and raw bio-solids from municipal water pollution control facilities as well as rural septic tank and field waste, including rejected grease trap skimmings and various types of manures (cow, horse, pig, etc.), including also alone with findings through research is cost efficiency added to the disclosure report.



Sincerely,

Richard Darrell Ruff