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Organic Rankine Cycle
www.OrganicRankineCycle.com

What is the Organic Rankine Cycle?

A Rankine cycle is a closed circuit steam cycle. (see www.RankineCycle.com for more information). 

An Organic Rankine Cycle uses a heated chemical instead of steam as found in the Rankine Cycle. Chemicals used in the Organic Rankine Cycle include freon, butane, propane, ammonia, and the new environmentally-friendly" refrigerants. 


Why use a chemical refrigerant? 

A refrigerant boils at a temperature below the temperature of frozen ice. Solar heat, for example, of only 150 degrees Fahrenheit from a typical rooftop solar hot water heater, will furiously boil a refrigerant. The resulting high-pressure refrigerant vapor is then piped to an organic Rankine cycle engine. 


Why is it called "organic"? 

"Organic" is a term used in chemistry to describe a class of chemicals that includes Freon and most of the other common refrigerants. 

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Organic Rankine Cycle
www.OrganicRankineCycle.com

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History of the Brayton Cycle,  Cheng Cycle,  Carnot Cycle,  Kalina Cycle, 
Rankine Cycle  and  Waste Heat Recovery: 
the Greenest of all Renewable Energy Technologies

What is the Brayton Cycle?

Gas turbines operate on the principal of the Brayton Cycle, which is defined as a constant pressure cycle, with four basic operations which it accomplishes simultaneously and continuously for an uninterrupted flow of power.

Background Information and History of Rudolph Diesel and Sadi Carnot:

Rudolph Diesel was educated at the predecessor school to the Technical University of Munich, Germany. In 1878, he was introduced to the work of Sadi Carnot, who theorized that an engine could achieve much higher efficiency than the steam engines of the day. Carnot envisioned a cycle in which a gas is compressed, heated, allowed to expand, and then cooled. After the gas is cooled, the cycle begins anew. Mechanical energy is used to compress the gas and thermal energy to heat it. In turn, expansion of the gas yields mechanical energy, and its cooling yields thermal energy. The net result is conversion of thermal energy to mechanical energy.

Diesel sought to apply Carnot’s theory to the internal combustion engine. The efficiency of the Carnot cycle increases with the compression ratio—the ratio of gas volume at full expansion to its volume at full compression. Nicklaus Otto invented an internal combustion engine in 1876 that was the predecessor to the modern gasoline engine. Otto’s engine mixed fuel and air before their introduction to the cylinder, and a flame or spark was used to ignite the fuel-air mixture at the appropriate time. However, air gets hotter as it is compressed, and if the compression ratio is too high, the heat of compression will ignite the fuel prematurely. The low compression ratios needed to prevent premature ignition of the fuel-air mixture limited the efficiency of the Otto engine.

Rudolph Diesel wanted to build an engine with the highest possible compression ratio. He introduced fuel only when combustion was desired and allowed the fuel to ignite on its own in the hot compressed air. Diesel’s engine achieved an efficiency higher than that of the Otto engine and much higher than that of the steam engine. It also eliminated the trouble-prone electric-spark ignition system. Diesel received a patent in 1893 and demonstrated a workable engine in 1897. Today, diesel engines are classified as “compression-ignition” engines, and Otto engines are classified as “spark-ignition” engines.

What is the Carnot Cycle?

The Carnot Cycle has been described as being the most efficient thermal cycle possible, wherein there is no heat losses, and consisting of four reversible processes, two isothermal and two adiabatic. It has also been described as a cycle of expansion and compression of a reversible heat engine that does work with no loss of heat.

What is the Cheng Cycle?

The Cheng Cycle is a highly flexible and efficient method of optimizing a cogeneration plant, and more specifically a combined cycle power plant, which also provides a high amount of flexibility in the power and thermal energy output.

For a Cheng Cycle to be implemented, a gas turbine and waste heat boiler or heat recovery steam generator (HRSG) is required. The gas turbine is updated to accept "steam injection" - the steam being "superheated steam" which is capable of handling up to 20% of the exhaust flow from the gas turbine. The saturated steam as well as the superheated steam, is generated from the waste heat boiler or heat recovery steam generator.

When the Cheng Cycle is in 100% power mode, all of the steam that is produced by the "waste heat" from the gas turbine, is "recycled" through the gas turbine. In cogeneration plants, the Cheng Cycle system is set-up so that steam may be used for process application and-or recycled back to the gas turbine. A duct burner is placed between the gas turbine and the waste heat boiler or the heat recovery steam generator (HRSG) which increases the total amount of steam output generated by the plant.

The Cheng Cycle has achieved the following impressive performance metrics on a number of gas turbine generators:

• Increases the power output of the gas turbine by as much as 80%

• Improves overall efficiency by 40%

• With steam injection, can reduce NOx emissions by 90% - achieving 2 PPM

• Reduces CO emissions to less than 10 PPM
  

What is the Graz Cycle?

The Graz Cycle is, without a doubt, the most efficient type of power plant available using gas turbines.  The Graz Cycle has also been heralded as a "zero emission" power plant.

In practice, net electrical cycle efficiencies for Graz Cycle power plants have approached 65.0% which is far higher than typical of state-of-the-art combined cycle plants.

According to the DOE web site, the Graz Cycle consists of a high temperature Brayton cycle and a low temperature Rankine cycle with a Heat Recovery Steam Generator. The Graz Cycle is an oxy-fuel power cycle with the capability of retaining all the combustion generated CO2 for further use. Its cycle configuration aims at highest efficiency by reducing the heat extraction in the condenser to a minimum. A thermodynamic investigation of the Graz Cycle fired with natural gas (CH4) shows a net efficiency of 52.5%, if the efforts for oxygen supply and CO2 compression to liquefaction are considered. If synthesis gas can be used from an external synthesis gas plant at 500°C, efficiencies can rise up to 56%.  Studies indicate that further efficiency improvements and simplification of the cycle are possible.


What is the Kalina Cycle?

Invented by Alexander Kalina, a Russian engineer, the Kalina Cycle uses a water and ammonia in low temperature Waste Heat Recovery applications, such as geothermal power plants, to increase thermodynamic efficiency and power output. 

Problems associated with Kalina Cycle, and why it has never gained significant appeal include;

• GE Power attempted to operate a Kalina Cycle power plant in conjunction with a gas fired power plant but found it neither economical or competitive.

• Inability to operate efficiently at high temperature or high pressure.

• Nitriding of the alloy steel superheater tubes.

• Complicated distillation columns required to recombine the turbine exhaust into the binary mixture used in the heat exchangers
  

• cycle proposals seem to be based on zero frictional pressure drop and zero temperature differences in the main process components, and it is pretty expensive to meet such requirements.

some of the above information on the Kalina Cycle from www.eng-tips.com with our thanks

What is the Rankine Cycle?

The Rankine Cycle is a thermodynamic cycle used to generate electricity in many power stations, and is the real-world approach to the Carnot Cycle. Superheated steam is generated in a boiler, and then expanded in a steam turbine. The steam turbine drives a generator, to convert the work into electricity. The remaining steam is then condensed and recycled as feed-water to the boiler. A disadvantage of using the water-steam mixture is that superheated steam has to be used, otherwise the moisture content after expansion might be too high, which would erode the turbine blades.

What is Waste Heat Recovery?

Many processes, especially in industrial applications, produce large amounts of excess heat – i.e., heat beyond what can be efficiently used in the process.  Waste Heat Recovery methods attempt to extract some of the energy as work that otherwise would be wasted.  

Typical methods of recovering heat in industrial applications include direct heat recovery to the process itself, recuperators, regenerators, and waste heat boilers.  In many applications – especially those with low-temperature waste heat streams, such as automotive applications – the economic benefits of waste heat recovery do not justify the cost of the recovery systems.  Innovative, affordable methods that are highly efficient, applicable to low-temperature streams, and/or suitable for use with corrosive or “dirty” wastes could expand the number of viable applications of waste heat recovery, as well as improve the performance of existing applications.  Our focus is on the development of innovative Waste Heat Recovery processes and techniques that are (1) more efficient than conventional methods, yet still cost-effective; and (2) applicable to waste streams from which heat cannot be recovered easily with conventional methods.

Turning to cooling, air conditioning systems consume approximately 10% of the energy used in U.S. buildings and are key contributors to peak demand.  Consequently, improving the energy efficiency of air conditioning systems would substantially reduce overall energy consumption and enhance grid reliability.  For example, compressors require cooling to dissipate the heat produced during compression and could benefit from improved surface heat transfer – innovative designs could increase the available heat-transfer area or materials enhancement could increase the heat flux between the hot and cool sides of a heat exchanger.  Similarly, a reduction in the requirement for condenser cooling could provide significant energy savings if more-efficient, cost-effective technologies were developed.  

This is where we believe waste heat recovery integrated with our Solar Trigeneration energy systems represents a unique opportunity for commercial and industrial clients. 

Industrial Waste Heat Recovery

Waste Heat Recovery from exit gases can significantly increase the energy efficiency of industrial processes.  Energy can be recovered from flue and stack gases, vent gases, and combustion gases at a variety of temperatures at large-scale industrial plants (chemical plants, petroleum refineries, biorefineries, pulp and paper mills, etc.).

How we make and distribute electricity is changing! 

The electric power generation, transmission and distribution system (the electric "grid") is changing and evolving from the electric grid of the 19th and 20th centuries, which was inefficient, highly-polluting, very expensive and “dumb.”  

The "old" way of generating and distributing energy resembles this slide:

The carbon clock tracks total carbon dioxide emissions in metric tons since 1750.

Since 1750, humans have emitted over 5 trillion pounds of carbon dioxide into the atmosphere. Roughly half of this has ended up in the oceans where it is beginning to damage the coral reefs. The other half is still in the atmosphere and causing global warming. Each pound of CO2 takes up as much space as a 500 pound person.

The formula (which should be good for a year or two) is:
C(t) = 2.58 ×1012 + 1240×t, where t is seconds since the start of 2007.

C is tons (metric tons) of carbon dioxide emissions.
2205 x C gives pounds of carbon dioxide emissions.

That comes to over 43 billion tons/year or over 86 trillion pounds/year.

Carbon dioxide (2) = 1 carbon atom with 2 oxygen atoms.
Carbon has relative weight 12 and Oxygen 16.
So it takes only 12 pounds of carbon to make 12+16+16 = 44 pounds of CO2. 

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Greenhouse Gas Emissions Linked to 
the Loss of Polar Bears

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We support the Renewable Energy Institute by donating a portion of our profits to the Renewable Energy Institute in their efforts to reduce fossil fuel use through renewable energy and their goals to end pollution from Carbon Emissions and Greenhouse Gas Emissions. 

The Renewable Energy Institute is "Changing The Way The World Makes and Uses Energy by Providing Research & Development, Funding and Resources That Create Pollution Free Power, Carbon Free Energy & Renewable Energy Technologies."

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