Explaining the Binary Power Cycle

Geothermal energy is known to be a reliable and sustainable energy source. As the world gives more attention to the state of the environment, people lean towards using more energy sources which have little to no impact on nature. Where it is true that currently no other energy source can outperform fossil fuel due to its energy concentration, geothermal energy is a good prospect as a temporary substitute until a better form of energy supply is found.

There are two types of geothermal power sources; one is known as the steam plant and the other is the Binary cycle. Binary cycles have the conceptual objectives of: high efficiency — minimizing losses; low cost to optimize component design; and critical choice of working fluid. This particular type of cycle allows cooler geothermal supply to be used, which has a huge benefit since lower temperature resources are much more common in nature.

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The way a binary cycle works can be explained using the diagram shown above. Since the temperature of geothermal source is not high enough to produce steam, hot water is fed into a heat exchanger. From there, secondary liquid with lower boiling water than water i.e. isobutane, absorbs the heat generated. As the steam of secondary liquid moves the turbine, electricity will then be produced. This whole process repeats in a cycle since the secondary fluid will then condense back to its liquid state and being used for the same process.

From the process described above, it can be seen that binary cycle is a self-contained cycle — ‘nothing’ goes to waste. This fact leads to the potential of having low producing cost energy source from binary power cycle. That being said, due to the lower temperature, the conversion efficiency of the geothermal heat is also considerably low. Consequently, Carnot efficiency of such process is lower than most power cycles. Large amount of heat is required to operate a binary cycle, leading to a better and larger equipment. Not only that since a bigger amount of heat energy has to be let out to the environment during the cycle, a sufficient cooling system must be installed. Although the production cost is found to be lower, the investment cost for installation would be very expensive. Then, the main question to this particular technology implementation would be how to improve the quality of production and economic feasibility?

First, one of the main aspect of binary power cycle is to overcome water imperfection as a main fluid. Consequently choosing optimal working fluid is a very essential step. Characteristic of optimal working fluids would include a high critical temperature and maximum pressure, lower triple-point temperature, sufficient condenser pressure, high vaporization enthalpy, and other properties.

Second, it was studied on multiple different events that well-optimized ORCs perform better than Kalina cycles. The type of components chosen in the cycle also affect the cycle performance quite substantially, i.e plate heat exchanger was found to perform better in an ORC cycle in the geothermal binary application compared to shell-and-tube. Addition of recuperator or turbine bleeding also have the potency to improve the overall performance of a binary cycle plant. It is important to model multiple thermodynamic cycle to make sure that the chosen one is the most optimized based on the boundary conditions. While designing ranges of thermodynamic cycles, it is common that the cycle is modeled based on ideal assumptions. For binary cycle in geothermal application, plant efficiency would be the most important parameter. In order to achieve a desired plant efficiency, both cycle efficiency and plant effectiveness should be maximized.

Additionally, pinch-point-temperature between condenser and heat exchanger is a substantial aspect to pay attention to, even the smallest change of in temperature is considered a significant change. Thus, including this parameter is a very important aspect.

This particular cycle has many potentials which haven’t been explored. Enhance the advantages of your binary power cycle using our thermodynamic tool, AxCYCLE.

Ref:
https://en.wikipedia.org/wiki/Binary_cycle
http://www.technologystudent.com/energy1/geo3.htm
http://www.researchgate.net/publication/229148932_Optimized_geothermal_binary_power_cycles

New Release: AxCYCLE v. 4.0

We have just released the newest version of AxCYCLE, our software tool for thermodynamic cycle design and analysis. AxCYCLE 4.0 has some brand new features that will inevitably aid you in designing optimal Gas, Steam, Combined, Turbocharger, Supercritical CO2, Organic Rankine, and Waste Heat Recovery Cycles.

Take a look at the latest updates and additions:

Turbine Efficiency Calculation
In previous versions of AxCYCLE, efficiency was an input parameter that needed to be changed manually for each off-design condition. The Calculated Efficiency option will automatically recalculate the efficiency for off-design conditions.

blog - axcycle 4.0

New Components
Several new components were added to the AxCYCLE library for more sophisticated and customizable cycles.

Bearing: Used to simulate mechanical energy losses in bearings. The estimated mechanical losses are assigned as a power value and are accounted for in the total energy balance

Gearbox: Used to simulate the mechanical energy transfer between two shafts considering mechanical energy losses in the gearbox. These losses are measured using a gearbox efficiency value.

End Seal: Used to simulate seal leakage. The value of the leakage depends on the difference between the upstream and downstream pressure.

Steam Cycle Builder
AxCYCLE’s new wizard for the creation of basic steam cycles. It can be used for steam cycles with regenerative heating, optional moisture separators, and re-heaters. The Builder creates a cycle diagram with the correct fixed conditions and initial values, meaning the generated cycle is ready for calculation! It does all of the work for you!

Learn more about AxSTREAM and AxCYCLE on our website, or email us at info@softinway.com to find out exactly how we can help with your next turbomachinery project.

TBT Webinar – Developing Reliable, High Performance, Advanced 3D Blades

It’s Throwback Thursday which means we have another one of our favorite past webinars! This week’s is called Developing Reliable, High Performance, Advanced 3D Blades. It was the first of three in a special Steam Turbine Series

Since 1884, steam turbines have been exemplary turbomachines that have improved throughout the years with modern design advances. As steam turbines became common, the competition heated up and today efficiency continues to be a hot topic. One trending technique that makes steam turbines most efficient is advanced 3D blading. Continue reading “TBT Webinar – Developing Reliable, High Performance, Advanced 3D Blades”

Come home. Book your ticket for the Turbo & Pump Symposia

The 43rd Turbomachinery and 30th Pump Symposia are quickly approaching. The 3-day event will begin on September 22nd in Houston, Texas at the George R. Brown Convention Center. The Symposia are organized in order to promote professional development, technology transfer, peer networking and information exchange among industry professionals. The event serves as a premier training and networking opportunity for professionals in both the turbomachinery and pump industries.

2013 Symposia
Source: Texas A&M Engineering Experiment Station

In ancient Greece, a symposium was a drinking party. Hosted by Socrates and philosophers alike, they were used to celebrate and discuss matters most vital to the universe. The “symposium” was a source of pride for the ancient aristocrats. Continue reading “Come home. Book your ticket for the Turbo & Pump Symposia”

Which gas turbine is the best for my combined cycle power plant conversion?

combinedcyclesThe goal of this test case is to find the gas turbine necessary to produce 58 MW of total net power for the conversion of a steam turbine to a combined gas-steam cycle while providing the highest level of cycle thermal efficiency.

The exhaust gases from the gas turbine are used to heat up steam through three HRSGs (Heat Recovery Steam Generators) in series. The steam is then used in the studied steam turbine which is comprised of two “cylinders” in series.
Continue reading “Which gas turbine is the best for my combined cycle power plant conversion?”

Co-generation Power Plants

The Kendall Cogeneration Station in Cambridge, MA
The Kendall Cogeneration Station in Cambridge, MA

Co-generation power plants are very popular in Europe compared to the U.S. market. It will be interesting to see if this type of application will take off in North America, but I’d like to share a little background information on co-generation first.
Continue reading “Co-generation Power Plants”

Retrofitting – Why Turbine Seals Are Important

Wreckage of 330 MW Turbine-generator from LP rotor burst
Wreckage of 330 MW Turbine-generator from LP rotor burst

Whether it is caused by a “poor” design, extreme operating conditions or even too much deterioration, turbine failures can occur. In order to help prevent these it is necessary to perform regular maintenance on all parts of the machine and control the conditions at which the turbine is operating at any moment in time as well as performing repairs and retrofits to keep the pieces in good shape.

One way to improve steam turbine efficiency is through better seals. However, when designed incorrectly they can create significant damages and performance losses in the turbine. Sealing steam turbine rotors presents several challenges. Any gap between the rotor and the packing lets the steam escape, dropping the pressure and wasting energy. If the packing ring is too tight, however, the rotor will rub, which creates localized hot spots. Continue reading “Retrofitting – Why Turbine Seals Are Important”

Retrofitting – When Steam Turbines Age

Steam-Turbine
Steam-Turbine

Statistics show that as a power plant reaches its rated lifetime, the number of its forced outages begins to grow substantially, and its reliability and availability fall.

Simultaneously, in the operation process the turbine’s efficiency lowers more and more, even though it is partially restored at overhauls.

It is possible to find steam turbines that have successfully operated for 40 – 50 years or more. Lately, power equipment lifetime extension has substantially gained in its scope and acquired much more serious significance. Continue reading “Retrofitting – When Steam Turbines Age”

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