APPLICATION NOTE LD12-9
Hydrocarbons measurement for Oxygen production using PlasmaDetek & Multidetek-2
เป็นที่ทราบกันว่าออกซิเจนเป็นหนึ่งในองค์ประกอบทางเคมีพื้นฐาน ออกซิเจนเป็นก๊าซที่ไม่มีสี มีความเข้มข้นมากเป็นอันดับ 2 รองจากไนโตรเจนในสัดส่วนของอากาศ มันเป็นสิ่งจำเป็นสำหรับสัตว์ และสิ่งมีชีวิตบนโลกใบนี้ นอกจากนั้น ออกซิเจนยังถูกนำไปใช้ในหลากหลายอุตสาหกรรมเช่น พาณิชยกรรม , การแพทย์, วิทยาศาสตร์ และการประยุกต์ใช้เตาหลอมเหล็ก การผลิตเคมีสังเคราะห์ เช่น แอมโมเนีย, แอลกอฮอล์ และ พลาสติกชนิดต่างๆ
การผลิตออกซิเจนบริสุทธิทุกวันนี้ นิยมใช้วิธีการแยกตัวของอากาศ (cryogenic distillation) แล้วกรองเป็นชั้นๆ เพื่อให้ได้ออกซิเจนบริสุทธิมากที่สุด ทั้งนี้ component ที่เราต้องการวัดมากที่สุดในการผลิตออกซิเจนก็คือ ไฮโดรคาร์บอน ซึ่งถือเป็น (impurity) ที่จะบอกคุณภาพของออกซิเจน High Purity Oxygen คุณภาพดีควรมีค่า hydrocarbon ต่ำ ซึ่งบทความวันนี้จะกล่าวถึงการวัด trace hydrocarbon.
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INTRODUCTION
Oxygen is one of the basic chemical elements. In its most common form, oxygen is a colorless gas found in air. It
is one of the life-sustaining elements on Earth and is needed by all animals. Oxygen is also used in many
industrial, commercial, medical, and scientific applications. It is used in blast furnaces to make steel, and is an
important component in the production of many synthetic chemicals, including ammonia, alcohols, and various
plastics. Oxygen and acetylene are combusted together to provide the very high temperatures needed for welding
and metal cutting.
The most common commercial method for producing oxygen is the separation of air using either a cryogenic
distillation process or a vacuum swing adsorption process. Nitrogen and argon are also produced by separating
them from air. The figure 1 represents a common cryogenic distillation process for producing oxygen.
Because this process utilizes an extremely cold cryogenic section to separate the air, all impurities that might
solidify—such as water vapor, carbon dioxide, and certain heavy hydrocarbons—must first be removed to prevent them
from freezing and plugging the cryogenic piping what could result to an hazardous situation. The removal of
hydrocarbons is also very important to avoid any problem in the subsequent air distillation that could lead to explosion.
Then, the operation of cryogenic distillation air separation units must be monitored by automatic analytical
instruments. As a result, their output is consistent in quality and ensures safety of the site. Periodic sampling and
analysis of the final product ensures that the standards of purity are being met. A good analytical instrument is then
necessary to monitor the various sampling points of the air separation unit.
THE SOLUTION
With its integrated plasma technology, The LDetek’s Multidetek-2 becomes the ideal tool to measure the purity of
the oxygen. Its capability to monitor the hydrocarbons level from ppb level up to high ppm level using its plasma
detector gives the ideal alternative to the standard use of a FID detector. With the use of the plasma for monitoring
the hydrocarbons, there is no more need of using Fuel/Air mixture additionally to the carrier gas. The Multidetek-2
and its plasma only require argon carrier gas. It is then a big advantage since there is no handling and storage of
hydrogen anymore on site. Moreover, the use of argon as carrier gas is also a great benefit because the argon is low
cost and is already produced and available on any air separation plant.
The use of the Multidetek-2 for monitoring hydrocarbons level in oxygen production is also the ideal tool for a safety
point of view. It is critical to have a reliable unit able to monitor 24/7 basis the level of hc’s in oxygen on ASU. Being
very sensitive to hydrocarbons, including C2H2 which is the most critical component, the Multidetek-2 becomes the
best tool to use.
The Multidetek-2 unit can have multiple configurations to allow the measurement of different sampling points of the
air separation unit. The monitoring of quality control at the end of oxygen production process can then be easily
realized with a configuration allowing low ppb detection. This will ensure an accurate reading necessary for
producing high quality grade oxygen. Using the same unit, a higher scale configured for high ppm measurement
necessary to monitor the different sampling points of the crude material is also integrated in the unit.
An analysis example of hydrocarbons measurement in pure oxygen appears on the figure 2.
The Multidetek-2 can be interfaced with any acquisition system on ASU. Analog signal or digital signal can be provided. Ethernet connection is also available for remote control. Such analyzer is easy to operate with its user friendly interface and can operate 24/24 to ensure good oxygen production. For this application, such Multidetek-2 is using the PlasmaDetek technology with its hydrocarbons selective detector. This avoids any consumable.
MORE POSSIBILITIES
A good return on investment can be also realized by configuring the same instrument for more components:
The analysis of CO2 and any other permanent gases or sulfurs impurities can be added to the same instrument.
Even more, the Multidetek-2 also offers the possibility to have multiple background gas configurations. The analysis of argon and nitrogen purity can then be added to the same unit.
One more time, with the simple use of argon as carrier gas and its integrated plasma, the Multidetek-2 can handle multiple measurements in multiple background gases.
CONCLUSION
The pay back of such analytical tool is fast. It requires only argon as carrier gas which is available at low cost on any air separation plant. There is no more need of handling and storing hydrogen what is usually more expensive due to the need of safety sensors and procedures on site. The PlasmaDetek use in the Multidetek-2 is maintenance free and is a clean detector. It requires no cleaning procedure. The Multidetek-2 will operate for many years and gives optimal efficiency of any oxygen production plant.
The combination of Multidetek-2 platform with the PlasmaDetek technology is a reliable, efficient and accurate system that any plant is looking for.
