Modeling and Simulation of Chemical Reactors Cooled by Thermosyphons

Abstract (Swedish)

I en teoretisk studie har användbarheten av thermosyphoner för att förbättra säkerheten och effektiviseringen av kemiska reaktorer. Thermosyphoner är en simpel form av en ”heat pipe”, ett ihåligt och slutet rör som är delvis fyllt av en fluid. Om röret värms upp till fluidens kokpunkt inleds en inre fasomvandling vilket används för att förbättra rörets värmeledningsförmåga. Tre simuleringsmodeller har använts i studien, varav två kommer från tidigare studier rörande reaktorsäkerhet. Resultaten har analyserats och ger en intressant inblick på potentiella möjligheter. Thermosyphonernas utomordentliga värmeledningsförmåga ger enligt studien väldigt goda möjligheter att kontrollera reaktorstemperaturen och därmed även reaktionsprocessen. Utöver den förbättrade temperaturkontrollen lyckades även thermosyphoner förhindra skenande reaktioner i scenarion där mantelvärmeväxlaren slutat fungera.

Abstract

In a theoretical study the use of thermosyphons to improve the safety and efficiency of chem-ical reactors have been evaluated. Thermosyphons is a simple form of a “heat pipe”, a hollow and closed tube that’s partially filled with a fluid. When the pipe is heated up to the boiling temperature of the fluid within a phase change is initiated. The phase-change is used to im-prove the thermal conductivity of the pipe. Three simulation models have been used in the study and two of the models is taken from previous studies regarding the thermal safety of chemical reactors. The results have been analyzed and presents an interesting indication of positive possibilities. The outstanding heat transfer of the thermosyphons gives according to the simulation good chance of a firmer control of the reactor temperature and thereby also the reaction process. Besides the improved temperature control the thermosyphons proved capable of preventing thermal runaways during scenarios when the cooling jacket was out of order.

Popular Abstract

Thermosyphons is a wickless “heat pipe” that’s capable of performing an impressive heat transfers. In a theoretical study three batch/semi-batch reactor models have been simulated, by the use of MATLAB, to observe the effect of using thermosyphons as an additional cooling method. The effect of using thermosyphons has been evaluated and both the process safety as well as the reaction efficiency have been analyzed. The results have indicated a very positive outcome and that a relatively small number of medium sized thermosyphons can both increase the control of the reaction temperature as well as prevent a runaway reaction in a worst-case scenario.

A runaway reaction (a.k.a. as a thermal runaway) is one of the major risks within the chemistry industry. Two things are required for a thermal runaway and this is at least one exothermic reaction and a reaction rate that grows when the temperature increases. When a chemical reaction is on a runaway the temperature within the reactor is rising, leading to faster reaction and that the exothermic reaction releases more energy into the system. This can be described as a bad cycle where the temperature growth eventually can lead up to a massive explosion and fire or perhaps a leak of hazardous material. In a study that was performed by the U.S Chemical Safety and Hazard Investigation Board (CSB) 167 of serious accidents that had occurred in the United Sates from 1980-2001 was examined. About 35% of these were a runaway reaction and the most common location was the chemical reactor.

A thermosyphon is a relatively simple tool that consists of a hollow and sealed pipe that’s been partially filled with a fluid. One end of the pipe is then heated at a temperature above the saturation temperature of the fluid while the other end is cooled. This will create a passive loop within the pipe where the fluid evaporates in one end and condensates at the opposite. Due to the massive heat transfer coefficient that’s reached when the fluid is boiling the thermopsyphon can transfer a lot of heat from one end of the pipe to the other.

Systems that’s been aided by thermosyphons have proven to be a lot more safe and that a thermal runaway could be prevented even in case the cooling of the original cooling system (the cooling jacket) would cease. Besides this the temperature control of the process has also been greatly improved. The impressive heat transfer prevents the reaction temperature to go very high above the boiling temperature of the fluid within the thermosyphon. This does not only increases the safety of the reaction but also the control of potential side reactions as well. By optimizing the starting temperature, the boiling temperature and the size of the reactor the process can be safer, more selective and keep the production rate up to the desired level.

All in all the thermosyphons appears to be of good use to the chemical industry, especially to processes involving numerous side reaction and where selectivity is of more importance than conversion.

• author: Hothar, Marcus
• supervisor: Hans Karlsson
• organization: Chemical Engineering (M.Sc.Eng.)
• course: KET920 20171
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry; Technology and Engineering
• keywords: Loss Prevention, Runaway reaction, Heat pipe, Thermosyphon, Chemical engineering, Reactor efficiency
• language: English
• id: 8918007
• date added to LUP: 2017-06-22 10:42:59
• date last changed: 2017-06-22 10:42:59