Video Degas conductivity
Application of Conductivity in Steam Analysis
The measurement of conductivity in the water cycle/steam generator is usually used as an indicator of the quality of water used in the process. Excessive conductivity values ​​often exhibit high corrosion potential, especially in the case of certain ions such as chloride and acetate ions. This can severely damage the blades in a steam turbine.
Typically, there are three main types of conductivity measurements used:
- Specific conductivity, measurement showing total dissolved solids in aqueous solution
- Conductivity of the cation, measurements taken after the water sample flows through the resin bed (known as cation exchanger)
- Degas conductivity, measurements taken after the water sample flows through the resin and has removed carbon dioxide by degassing process
Generally, the degas conductivity is measured from a condensed and cooled primary vapor sample. It may also be relevant to analyze the return of condensate, especially in cases where the condensate is returned from a separate plant that uses steam in another process.
Maps Degas conductivity
Methodology
After the ions are removed from the circulating water conditioning (eg, Ammonium NH 4 ) in the cation exchanger, the ions generated from the gas component must be removed to determine the conductivity of the degass. This is usually the gas from the atmosphere that has penetrated into the system through leaks in the water-steam circuit. Of all the gases occurring in the atmosphere, it is usually only carbon dioxide (CO 2 ) that dissolves chemically into ions in circulating water. The remaining gases (oxygen, nitrogen, etc.) dissolve physically and do not form ions, and thus do not contribute to the conductivity. The chemical reaction of carbon dioxide in water is continued according to the following reaction equation (mass action law):
A 2 2 H 2 O & lt; - & gt; 3 H 3 O pK = 6.3
B) HCO 3 - 2 H 2 O & lt; - & gt; CO 3 2 - pK = 10.3
See graph showing relative CO 2 concentration. After the cation exchanger, the pH value of the sample is generally between 5.5-6, so it means almost only CO 2 is present as a gas, and only about 6% is carbon CO2 carbonate 3 2 - . Bicarbonate ions (HCO 3 - ) are practically non-existent.
However, the ionic components of carbon dioxide are much less harmful than salt component ions, eg Cl - . To obtain selective conductivity values ​​for salt-containing ions (with maximum potential for corrosion), all remaining carbon dioxide must be removed from the sample to accurately determine the presence of corrosive ions.
Generally there are two methods to remove carbon dioxide from water samples: use of reboiler to heat the sample and remove CO 2 , and use of inert gas. In the latter method, an inert gas containing no CO 2 is passed through a water sample, in which the gas component in the sample water is removed by the gas component of the inert gas. The use of bottled inert gas can be problematic in some industrial applications. Reboilers are very efficient degassing with results over 92%, but they usually require anywhere from 20-45 minutes to achieve useful results. Manufacturers of the reboiler system include Swan Analytical, Mettler Toledo, and Sentry Systems.
A new variation of the inert gas method (known as the "Gronowski dynamic method") was recently developed in conjunction with Waltron's partner manufacturer, in which the inert gas is produced in the decarbonated column by passing air through a column filled with lime soda. Carbon dioxide removal is carried out in the exchanger column based on the principle of kontraflow. Inert gas drives carbon dioxide from water samples so that no carbonate ions can be formed. What remains in water samples is like a salt (acid-like) ion and organic component, as well as oxygen and nitrogen that do not form ions in aqueous media. Gronowski's dynamic method is very fast, reaching about 94% degassing in 45 seconds, growing up to greater end efficiency. View graph (right), extracted from actual test data.
Reasons to Measure Abundant Samples from Condensed Steam
The growth of renewable (but unstable) energy sources has placed a greater burden on modern gas-fired power plants to cycle on and off to maintain stable and reliable electricity production between Renewable Energy and Basic Loads. This plant utilizes a combination of gas (70%) and steam (30%) turbines to generate electricity. Very important for the highest efficiency is ensuring that pure vapor reaches the second stage quickly.
During power plant start-up, the resulting steam purity determines whether it can be delivered to a steam turbine or if it must be bypassed to a condenser. Traditionally the instrument "Conductivity Cation" is used to analyze the vapor quality, but in addition to measuring dangerous ionic compounds (eg chloride ions), they also include CO 2 , which as stated above are not significantly harmful to steam turbine. Furthermore, a typical cation conductivity analysis takes 3-4 hours to provide a useful indication of steam purity. In many cases, this means the factory never reaches 100% efficiency before its offline cycle. That means a combined gas-turbine cycle plant will burn fuel at 100%, but it only reaches 70% output and vents excess heat and flue gas.
In the case of traditional base load power plants, cycling is much less frequent - in some cases, only twice a year for maintenance. Compared to measuring only the conductivity of the cations, the cost savings from start-up are accelerated using a potentially very large degass of conductivity. At $ 0.50/MW-minutes ($ 30/MWH), a 750MW coal plant that starts three hours faster each cycle will generate an additional $ 133,875 of annual revenue from the same fuel.
Under the same assumption, the cost savings between different degassing methodologies are significant. If a dynamic system similar to Gronowski's is used, within almost 30 minutes of start-up time stored on top of the reboiler method, a typical crop combined cycle will generate more revenue from the same fuel consumed with each and every start system, primarily using a price typical "peak" electricity. Additional benefits are better energy efficiency and reduce heat and exhaust emissions.
References
Source of the article : Wikipedia
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