Background on Our Combustion and Water Purification Technologies

Between 1975 and 1985 one of our coal industry acquisition assignments helped a Montana-Wyoming coal producer acquire three low-sulfur coal mines in Indiana.   At the same time a related electric utility coal sourcing study got us acquainted with the management of Louisville Gas and Electric Company.   This farseeing enterprise had taken the lead, in the United States, in equipping coal-fueled power plants with sulfur dioxide (SO2) scrubbers, thereby reducing their SO2 emissions by more than 90%.   They graciously explained all of the advantages and disadvantages of this important environmental improvement.   Although expensive, the investment preceeded Federal emission regulations when there was no other means of reducing SO2 emissions of coal-fueled power plants.   Could there be a more economical solution?   We asked our client to consider funding discovery research.   They declined and so in 1978 we began our long research and development effort.   By 1995 we had found the solution which led to our 2005 U.S. Patent No. 6,907,845.   The concept embodies a unique condensing boiler that was not conceivable until 1990 with the development of new corrosion-resistant metals.   The combination of the condensing boiler and O2/CO2 combustion, as detailed in our patent, made it possible to obtain both improved electric power production efficiency and complete carbon dioxide (CO2) separation and recovery at an economical cost.   Next, what to do with the CO2? 

CO2: Sequestration or Utilization?

Concerns have been raised that the known rising level of CO2 in Earth's atmosphere is causing global warming, potentially leading to climate change with unknown consequences.   W.P. Krebs prepared a paper entitled "CO2 for Ocean Disposal Research", published for the 1997 32nd Intersociety Energy Conversion Engineering Conference (IECEC '97).   The idea was to provide researchers with a substantial continuous source of CO2 for deep ocean sequestration studies.   We would make available our new O2/CO2 combustion technology for a small power plant at a research center in Hawaii and recover the CO2 for the sequestration project.   Subsequently this research effort was dropped due to potential environmental damage.   Meanwhile our attention was drawn to the possibility of using CO2 at large scale to grow certain algae at high rates in a confined space.   Another long period of research resulted in the new CO2 utilization process announced in a September 13, 2010 news release.   A patent is pending.   Applications are discussed on this website in the papers Combining Municipal Services (below) and CO2 Desalinization.  Recycling CO2 will provide large savings for electric rate payers by avoiding the high costs of either ocean or underground sequestration if legislated.



Combining Municipal Services

Copyright October 27, 2005 by Krebs & Sisler L.P.
Revised April 2009


Municipalities interested in base-load electric power generation should consider adopting a new high efficiency and low emission closed-cycle method which recovers all of the CO2 byproduct of fuel combustion.   The CO2 is available without cost to potentially improve other municipal services: converting sewage sludge to biomass and purifying wastewater.

Closed Cycle O2/CO2 Combustion for Municipal Electric Power

The key to this combination of processes with cost-reducing synergies is the use of a closed Rankine cycle O2/CO2 combustion method with the flexibility to utilize virtually all fuels except nuclear without emission problems, including coal, petroleum coke, biomass, heavy oil, and natural gas.   Limited amounts of biomass and municipal solid wastes may be accepted as secondary boiler fuel.   The technology is described in detail in U.S. Patent No. 6,907,845 issued June 21, 2005.   This combustion method raises efficiency by recovering most of the "waste heat" of combustion lost to the atmosphere in the operation of state-of-art thermoelectric power generation systems.   This waste heat is 60% to 65% of the total fuel heat input into the boiler.   The method is expected to achieve about 68% efficiency in early commercialization compared to state-of-art Rankine cycle plants at about 34%, reducing fuel costs by half.   The objective is to reach 80% efficiency after complete optimization.   Also, the opportunity to be selective in the choice of fuels will be a major factor in attaining and maintaining low operating costs.

CO2 Recovery and Use in Municipal Services

In this high efficiency electric power production method, the cost of separating and liquefying CO2 in the boiler exhaust gas is charged to electric production.   After the separation of acid gases, its purity will be 97% to 99% and can be raised to food grade in an additional economical process.   However, in municipal applications, and because large volumes can be made available from new closed-cycle power plants, continuously and at no cost to the processes, best uses should be for sewage sludge conversion to biomass and for wastewater purification.


Concerns and debate about recent increases in the amount of carbon dioxide (CO2) in Earth's atmosphere are due to several misunderstandings.   It is blamed for global warming although its content is less than four one-hundredths of one percent (0.04%) versus 23% oxygen, 76% nitrogen and 1% other gases by molecular weight in dry air.   Consider also that water vapor averages about 2% planet-wide or 50 times CO2 content in the atmosphere.   Global warming and cooling is in part known to be due to sun activity cycles estimated recently to be 70 to 75 years.   Added to this natural sun cycle is some amount of human-originated (anthropogenic) warming.   One factor is the heat generated continuously by the respiration and metabolism of more than six billion humans.


Add to this the continuous heat emissions of nuclear power plants and their increasing amounts of stored spent nuclear fuel which will radiate heat for thousands of years.   Further, add the heat generated in the combustion of all hydrocarbon and biomass fuels used in power generation, transportation and space heating.   By comparison, CO2 in the atmosphere is virtually no factor, whereas nuclear fuel use creates by far the largest point sources of anthropogenic global warming.

The availability of large amounts of CO2, at no cost to the processes, should be viewed as a major opportunity for improvement in municipal services.   CO2 is the one true "greenhouse" gas in that it is known to sharply enhance the growth of plants when added to the air in a greenhouse.   Most plants use CO2 and sunlight in the process of photosynthesis for growth, and fortunately for humans, the byproduct oxygen is wasted into the atmosphere for our respiration and for our use in fuel combustion.    Oceans and all waterways are greenhouses to the extent that they contain dissolved CO2 for photosynthesis by microalgae known to utilize CO2 for growth in photosynthesis.   More than 50% of Earth's available oxygen is estimated to come from algae growth in the waterways covering 70% of the planet.   These natural processes are believed to be economically adaptable to the municipal services of converting sewage sludge to biomass and to wastewater purification.

CO2 Use in Sewage Sludge Treatment

CO2 is being studied for its application in the treatment of sewage sludge.   It is believed that CO2 infusion into state-of-art open air digesters, replacing or supplementing air or oxygen infusion in secondary sewage treatment, can greatly accelerate the conversion of the sewage to biomass.   The process requires utilization of microalgae known to utilize CO2 in photosynthesis.    Specific microbes may be cultured to become dominant in such an environment.   The process would be enhanced by nighttime use of high intensity lighting for continuous photosynthesis, conducted at ambient temperature.   Biogrowth lighting covers a light spectrum range of about 350 to 750 nanometers.   We have so far identified 15 factors which affect growth rates in photosynthesis, each one subject to control with the objective of optimizing growth of biomass in state-of-art open air sewage digesters.   Byproduct oxygen and excess CO2 would be exhausted to the atmosphere.   To the extent that treatment shifts to CO2-using microbes, the evolution of undesirable gases and their odors is eliminated or reduced.   State-of-art open digestion systems generally evolve measurable amounts of hydrogen sulfide (H2S), methane (CH4), nitrous oxide (N2O), and ammonia (NH3), all categorized as pollutants, and these emissions should be largely eliminated in the CO2 process.

CO2 Use in Wastewater Treatment

The use of CO2 to treat wastewater as a municipal service is focused on an extended or tertiary treatment of sewage wastewater after removal of all sludge and most biomass.   State-of-art open air digesters are utilized along with the same CO2-using microbes, in sunlight photosynthesis in daytime but enhancing the process with high intensity lighting at nighttime.   In a period of treatment long enough to convert any remaining nutrients in the water to biomass, and after final filtration and chlorination, it is believed the water will be of potable quality.   An alternative tertiary treatment process is being studied which should further increase the rate of nutrient conversion to biomass.   Completion of this research awaits funding as of April 2009.

Municipal Solid Wastes as Boiler Fuel

After removal of the non-combustible material in municipal solid wastes, the remainder may be utilized as a supplementary fuel, possibly to the extent of 20% to 30%, like biomass.   This use is subject to proper boiler design and, like biomass, can reduce boiler efficiency due to low heating value and excessive moisture.   However, blended with high Btu fuels, satisfactory combustion at a desired boiler temperature should be attainable in O2/CO2 combustion by adjusting the oxygen in its proportion to CO2.

Water Economy in O2/CO2 Combustion

Because of the new apparatus and processes employed in this closed single-cycle O2/CO2 combustion method, all of the condensate from fuel combustion is recovered.   After pH adjustment and filtration, it is available for boiler feedwater or potable water use.   Therefore such a plant needs a supply of fresh water only for startup.   Further, it is expected that liquid CO2 from the combustion process will provide plant cooling.    This will eliminate the need for cooling towers or any use of condenser cooling water from rivers, lakes or oceans--both of those cooling methods being contributors to global warming.

CO2 Use in Waterway Improvement

Both fresh water and marine waterways are periodically or frequently threatened by certain species of microbes which propagate in the presence of excessive nutrients and use up most or all dissolved oxygen needed to maintain healthy fisheries.   Indicators of the problem are "red tides" along the west coast of Florida and now occasionally off the coast of New England, "brown tides" in estuaries along the southeast coast of the U.S., the approximately 6,000 square mile "dead sea" region off the Mississippi River Delta nearly six months each year, endangered or dying coral reefs and periodic incidences of fish kills.   Overfertilization is strongly implicated, due to fertilizers and human and animal wastes, especially nitrates.   Elevated water temperatures must also be a factor.   The Great Lakes are similarly threatened.


See Note 1 below regarding the Milwaukee River problems.


It is believed that by making available sufficient amounts of CO2 for infusion into such distressed waterways, by the process of photosynthesis and the culturing of microbes which utilize the CO2 for growth, these waterways will recover by gaining dissolved oxygen and again be year-round healthy fisheries.   Infusion of CO2 would preferably be conducted only during daylight hours when natural photosynthesis is functional.


Increasing ocean acidity, attributed to increasing CO2 from the atmosphere entering the oceans, is now being studied by several groups of researchers.   If this premise is found valid, it could preclude wide adoption of the above improvement concept.   However, it may be more likely that if ocean acidity is increasing, then a number of other acids must be implicated.    CO2 in water converts to carbonic acid, of weak and mild acidity.   Hydrogen sulfide (H2S) is a strong acid and is generated by microbes in hypoxic (oxygen depleted) waterways.   Other acids may be present, including acetic, carbolic, hydrochloric, humic, hydrofluoric, nitric, sulfurous, sulfuric, uric, and perhaps many more.   Much more research is needed before CO2 and carbonic acid can be held responsible for increasing ocean acidity.   At this time, our view is that the addition of CO2 in estuaries and other shallow oxygen-depleted waterways should be highly beneficial as proposed above.


See Note 2 below regarding the Cyanotech CO2 algae growth processes.

Worldwide Adequacy of CO2 to Produce O2 for Human Respiration and the Combustion of Hydrocarbon and Biomass Fuels

The need for adequate resources of CO2 in Earth's atmosphere becomes clear when we confront the fact that the reduction of CO2 in photosynthesis, which natural process releases nearly all of our available oxygen for respiration and combustion, is crucial for human life.   The physicist William Thomson (Lord Kelvin) warned 150 years ago of possible oxygen depletion due to increasing demand for fuel combustion.   He could have not imagined the added oxygen demand for respiration caused by today's world population, grown to more than six billion and still growing.   So the question to be answered is: Will enough CO2 be available for photosynthesis to yield adequate resources of oxygen?

Note 1.   Milwaukee River watershed problems (Milwaukee, Wisconsin, U.S.A.)


In 2005, the Milwaukee Metropolitan Sewerage District published an excellent report on the water pollution problems of the Milwaukee River and it's tributaries.   The backflushing of the river with Lake Michigan water began in 1888 and continues today, periodically and especially in the summertime when fecal coliform and E. coli bacterial counts reach high levels.   This flushing dilutes the river water but the effluent then flows into Lake Michigan.   Beach closings are occasionally necessary along 100 miles of the Lake Michigan shoreline due to high bacterial counts.   Milwaukee River effluent has been implicated.   We believe that the daily infusion of CO2 at several points along the river is the solution.   The culturing of specific algae which require CO2 for growth in photosynthesis releases byproduct oxygen.   This natural process eliminates the basic waterway problem of insufficient dissolved oxygen.   Excessive nutrients would be absorbed by these desirable oxygen-producing algae.   Foul odor problems should also be eliminated.


The polluted condition of the Milwaukee River is not unique.   It may be typical today of thousands of streams and river estuaries around the world, all of which could benefit from CO2 infusions on a daily basis.    Municipalities would have the free availability  of substantial  amounts of CO2 by adopting  high efficiency  O2/CO2 combustion for electric power production, which system recovers all of the CO2 byproduct of fuel combustion.

Note 2.   Cyanotech CO2 algae growth processes.

The Cyanotech Corporation, Kailua-Kona, Hawaii, has for more than 20 years employed a novel algae growth method for the production of Spirulina.   This nutritious blue-green (cyanobacteria) algae requires CO2 and sunlight in nutrient-rich saltwater for growth by the process of photosynthesis.   Algae growth is greatly enhanced by adding CO2 to the growth ponds.   The Cyanotech method shows the potential for waterway remediation by CO2 infusion and by utilizing specific fresh water or marine algae to correct water pollution problems caused by excessive nutrients.


Biomass Growth Research

We are researching the biomass production potential of municipal sewage treatment plants based on the application of enhanced photosynthesis:  CO2-consuming algae and sewage nutrients are saturated with light and CO2 for rapid biomass growth.

Recycling Carbon Dioxide (CO2)

We have studied CO2 utilization because our new high efficiency O2/CO2 combustion system recovers all of the carbon dioxide from the firing of hydrocarbon and biomass fuels.   Photosynthesis captures carbon (C) and releases oxygen (O2).   But natural photosynthesis is a slow process.   Recently we have found a method of enhanced photosynthesis to yield a manyfold acceleration of the natural rate of biogrowth by photosynthesis, outlined  as follows  but requiring  further development.   The greatest economic  and environmental  benefits  may come  from locating  new power plants, adapted for CO2 recovery, near municipal sewage treatment facilities as discussed on our website at "Combining Municipal Services".

New Tertiary Sewage Treatment

We propose large scale use of carbon dioxide for sewage treatment by adding a unique tertiary process to follow the state-of-art secondary activated sewage treatment method.   For example: A midwestern U.S. city has a population of 100,000 and it's sewage plant processes an average daily influent of 14 million gallons or 53 million liters with a nitrogen content of 15 milligrams per liter or 1,752 pounds of biologically absorbable nitrogen per 24 hours.   Daily sewage sludge production for disposal, after anaerobic digestion, is about six tons dry weight basis.   A nearby 100 megawatt electric power plant can supply 1,000 tons or 17 million standard cubic feet of CO2 (197 cubic feet per second) for infusion into this tertiary treatment facility.   CO2 is 27% carbon, therefore 270 tons of carbon are available daily for biogrowth.   Biomass is about 50% carbon, therefore total biomass production may be 540 tons per day although some CO2 may be lost, outgassed or diffused into the atmosphere.   Thus a large economic gain eventuates if the handling and disposal costs for six tons per day of sludge can be replaced by 540 tons of fuel-valued biomass production.

Sewage Nutrient Conversion To Biomass

Aerobic and anaerobic microbes utilized in secondary sewage digestion produce gases, primarily ammonia (NH3), hydrogen sulfide (H2S), methane (CH4), and CO2, most of which are outgassed or diffused into the atmosphere.   Lack of light penetration into the dark sewage prohibits the participation of evolved CO2 in photosynthesis except in daylight and then only at the digester water surface.   In our sewage treatment concept, more CO2 and deep 24 hour lighting are introduced, along with CO2-consuming algae, into secondary digestion.   Both aerobic and anaerobic microbes continue their digestive functions but then are mostly displaced by autotrophic algae growth in the high CO2 and high lighting environment of the new tertiary treatment facility.   Oxygen evolves from enhanced photosynthesis and the formation of NH3, H2S, and CH4 is suppressed.


We assume that, by this method, the limiting biogrowth nutrient is nitrogen, i.e., that phosphorous, potassium, iron, sulfur, sodium chloride, and other trace minerals needed for autotrophic algae growth are contained in the sewage influent or otherwise may be supplemented if sufficient CO2 is available to maximize biomass production.   The optimum balance of CO2 and all nutrients in this production method is yet to be found.


We hypothesize that the nutrient content in the sewage inflow is sufficient for the complete conversion of all available nutrients to biomass given enough CO2, light and growth time.   This is the key area for our continuing research.

Sewage Conversion in a Small Space

In the above example for utilizing 1,000 tons per day of CO2, we are projecting the tertiary sewage treatment space requirement at five acres to treat a normal 14 million gallon daily influent flow with a maximum capability of 24 million and a theoretical limit to 48 million gallons on this space.   This is a radical reduction from the estimated space requirement of 2,560 acres to conduct natural photosynthesis utilizing the CO2 contained in the flue gas from a coal-fueled power plant, as reported in a 1993 study, per 1,000 tons of CO2 in the flue gas.   See Note 1.

A Biogrowth Evaluation

A 1993 United States Department of Energy study evaluated the use of natural photosynthesis, supplemented with the CO2 contained in the flue gas output of a coal-fueled power plant, to grow biomass in massive shallow ponds.   (Note 1).   This flue gas contains about 12% CO2, 3% O2, 10% H2O, and 75% N2 plus trace acids.   The study recommended against further near term investment (20 years) in research to grow biomass as a means to utilize power plant CO2.   We agree.   The method is impractical due to the large land area required, to seasonal, water and light limitations, lack of nutrients, large CO2 outgassing losses and to massive water losses due to evaporation.   We estimate that by this method less than 5% of the flue gas CO2 can be converted to biomass.   By comparison, we expect that more than 90% of CO2 can be converted by means of our new tertiary sewage treatment process on a relatively small land area.   See Note 2.

Sewage Biomass Uses


The biomass recovered from this new tertiary process is expected to be a satisfactory supplementary boiler fuel when blended with coal or lignite, after partial drying.   Alternatively it should be convertible to liquid biofuels by the application of modified enzymes now being developed for commercial use.

Details about this new tertiary sewage treatment method will be published when funding has been secured for an economically scaled commercial demonstration.   See our website for "Combining Municipal Services" and "Sewage-Based Biofuels".


Note 1.   This large space requirement is based on the data presented in "A Research Needs Assessment for the Capture, Utilization, and Disposal of Carbon Dioxide from Fossil Fuel-Fired Power Plants";   Volume 1, pages 25, 34, 40, 55-56 and Volume 2, Chapter 4, pages 6-23, U.S. Department of Energy, DOE/ER-30194, July 1993.   The many negative biogrowth factors cited in this DOE report are overcome in our compact tertiary sewage treatment method which has no diurnal light limitations, or seasonal or nutrient limitations, and which should lose little CO2 to outgassing.


Note 2.   We credit the above referenced 1993 DOE report for stimulating our interest in researching the problem of producing biomass at large scale in a small space.   We also credit Cyanotec Corporation, Kailua-Kona, Hawaii, for it's biogrowth process developments since 1985 for the production of Spirulina Pacifica, a high quality food supplement.   This algae has a growth rate sharply stimulated by the addition of CO2.   Our own work evolved from the need to find beneficial uses for the large amounts of CO2 to be recovered from our new high efficiency closed Rankine cycle, all fuels, steam electric power system described in U.S. Patent No. 6,907,845.   This technology is available for licensing along with a number of efficiency and construction material improvements discovered since the June 21, 2005 patent issue date.

Copyright September 2008
Revised November 2008
Krebs & Sisler, L.P.


The Cheng Cycle with O2/CO2 Combustion

The Cheng cycle was developed to capture gas turbine waste heat by regeneration of the energy to steam, for injection into the combustor, which boosts efficiency.   Our method of O2/CO2 combustion was developed to recover and virtually completely utilize Rankine cycle waste heat, which boosts efficiency.   Combining the Cheng cycle with our method of O2/CO2 combustion can further improve the operating results of many gas turbines.

Retrofittable gas turbines should achieve:
  • Zero NOx emissions.
  • Zero water losses.
  • Recovery of all combustion byproduct CO2.
  • Efficiency gains depending on the original equipment specific design features.
  • Increased operating times, towards base-load and away from short-term peaking duty, by improving fuel efficiency.

The Cheng cycle adaptation for this combustion process requires modifications beyond the basic concept proposed by Dah Y. Cheng in three U.S. patents: No. 3,978,661 of September 7, 1976; No. 4,128,994 of December 12, 1978 and No. 4,248,039 of February 3, 1981.   Our O2/CO2 combustion concept detailed in U.S. Patent No. 6,907,845 granted June 21, 2005, also requires changes to fit with the Cheng cycle.   The necessary changes have been determined for 5 to 300 megawatt gas turbines and should be applicable to the equipment of more than 20 manufacturers worldwide (ref. Gas Turbine Handbook: Principles and Practices, by Tony Giampaolo, 3rd edition, 2006).

                                           August 22, 2009