Energy Efficiency

Kalina cycle

September 4, 2012, 11:34 am
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Kashima Steel Works in Japan uses the Kalina cycle.

The Kalina cycle is a technological approach of electric power production resulting in raising the efficiency of a thermal power station and reducing thus the fuel rate and discharged by twenty percent.

Theory

As is known, the efficiency of a thermal power stations (TPS) as a whole does not exceed 41% and is limited by its thermodynamic efficiency. That is why any significant result in raising the efficiency of a cycle can be achieved not by improving or upgrading its individual units or elements (the efficiency of which are already around 95%), but by increasing its thermodynamic efficiency. This can be attained by changing the thermophysical characteristics of the working medium.

As a "perfect" working medium a composition can be used that is a solution composed of different specially selected substances. In fact, that was the way that A.I. Kalina proceeded when developing his thermodynamic cycle, in which an increase in efficiency of the thermal power station is achieved by using, as a working medium, a water solution of chemicals, such as, for instance, ammonia, monoethylamine, diethylamine, and the like. For example, when ammonia is dissolved in water the heat capacity of the solution formed is lower then that of water. Besides, when dissolving one gram-molecule of ammonia in a liter of water 8.28 kilocalories (kcal) of heat are released. Just that is enough to heat up a kilogram (kg) of 14% ammonia solution formed almost to 100 °?. Thus, the heat released on dissolving can save, when heating a kg of water from 30 °? to 100 °?, about 70 kcal of heat or 0.01 kg of equivalent fuel.

Implementation

The Kalina cycle is realized as follows: some ammonia is added to feedwater before it enters the steam generator. Owing to the heat released on dissolution of ammonia and lowered heat capacity of the resulting solution its heating to the boiling temperature requires less fuel. Then the steam and gaseous ammonia are separated, condensed separately, and then the water and ammonia are mixed again before being fed to the steam generator. In the chemical industry the process of separating water and ammonia is extensively used at the stage of distilling filter liquid in producing soda ash by the Solve method.

Kalina managed to convince experts in the field that his idea was novel and advantageous. Among the promising points in support of the proposed idea there were: a 10% rise in the efficiency of the thermodynamic cycle, 20% reduction in the fuel rate, and an anticipated gain from employing A.I. Kalina’s cycle at all the heat power station in the U.S.A estimated to amount to 26 billion dollars per year.

The U.S. Department of Energy allocated the money for constructing a pilot thermal power plant using Kalina’s cycle. In the early 90s, a 1-megawatt (MW) pilot plant was built.

The pilot thermal power plant operating by the Kalina cycle has practically proved that raising the efficiency of an TPS by 10% and reducing thus the fuel rate by 20% is quite achievable. Since the character of the fuel used does not play a principal role the Kalina cycle results in reducing the discharge of dust, carbon dioxide (CO2) and sulfur dioxide (SO2) in proportion to saving fuel, which is by 20 twenty percent.

Disadvantages

The drawbacks of the Kalina cycle are:

  • Technological complexity and the bulkiness of the unit for separating the water and the chemical additive in the vapor phase, which complicates re-engineering of the operating power stations; and
  • Potential risk of the chemical additive leaking out to pollute the environment.

Further Reading

Glossary

Citation

Prisyazhniuk, V. (2012). Kalina cycle. Retrieved from http://www.eoearth.org/view/article/153990

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