Research On Application Of Heat Pipe Technology To Chemical Reactor

Heat pipe is a heat transfer element with high conduction performance. It transmits heat by means of the phase change of its internal liquid medium without being driven by external power, with the features of high heat conducting, good isothermal performance, automatic adjustment of heat flux density, reversible heat flow direction, thermal diode and thermal switch characteristics, a structure allowing flexible arrangement and high reliability. This article described research on the application of heat pipe technology to the gas-liquid-solid three-phase fixed-bed bubble-column reactors for exothermic reaction, with the purpose to eliminate the external circulation of the reaction system, improve the conversion efficiency, simplify the system and raise the reliability in production. For the 2-ethylhexenal hydrogenation reactor, after the kinetic analysis, analysis of the heat and mass for flow in the reactor, a heat pipe type gas-liquid-solid three-phase fixed-bed reactor system for small scale experiment has been designed and founded. The investigation on the axial back-mix in the reactor bed, on the heat transfer performance of the reactor and heat pipes, as well as on the reaction taking place in the reactor was the performed. The major conclusions have been obtained as followings:(1) The catalytic hydrogenation reaction for 2-ethylhexenal is a serial reaction, and the kinetic equation for its reaction has been obtained based on quasi primary reaction;(2) In the heat pipe type three-phase reactor for hydrogenation of 2-ethylhexenal, flow takes place within the bubble column area, and the heat transfer between the reactor bed layer and the heat pipe heating section consists of two modes: one is the heat conduction between solid catalyst and heat pipe walls in the bed layer, and the other is the convective heat transfer of the fluid through the bed to the heat pipe walls;(3) The reactor axial Peclet dimensionless number was calculated using the tracing method with the axial diffusion model. Through experimental research on the back-mix in the heat pipe type three-phase reactor, it has been concluded that the back-mix tends to become weak with the increase of gas flow speed; the extent of back mix gradually decreases first with the increase of flow speed of liquid phase, but the back-mix intensifies when the flow speed of liquid phase increases after a givenvalue; and the presence of heat pipe has increased the back-mix;(4) Heat transfer test was performed on a single heat pipe by heating with a resistor wire, and it was concluded that under low heat flux density, the heat pipe showed good heat transfer and isothermal performance at the heat pipe liquid filling rate of 10%;(5) Cold simulation test has proved that the flow of gas in the heat pipe type three-phase reactor has promoted the heat transfer, but after the flow speed of gas phase has reached a given value, the heat transfer coefficient between the reactor bed and heat pipe heating section is irrelevant with the flow speed of gas phase, and is controlled by the flow speed of liquid phase; with regression statistics of a number of test date sets, the correlation formula of coefficient of convective heat transfer between the reactor bed and heat pipe heating section has been obtained, and this correlation formula of heat transfer has been verified by the hot simulation test;(6) Simulation calculation was performed for the heat pipe type three-phase reactor using a two-dimensional quasi homogeneous phase model, and comparison of the results of simulation calculation and test results has shown fairly good agreement between the calculated values and testes ones;(7) Results of simulation calculation have shown that the temperature distribution within the reactor, the reaction conversion rate and selectivity can be satisfactory for the heat pipe type three-phase reactor without the external circulation;(8) Tests have shown that the temperature field in the reactor is more homogeneous, and both selectivity and conversion rate have been increased to some extent in the heat pipe type reactor as compared with an adiabatic reactor. In the meantime, as the external circulation for the reactor system has been eliminated, the equipment investment and operation cost will be reduced, and the safety performance of the system improved.In summary of the above, with the heat pipe technology, it can remove the reaction heat from the gas-liquid-solid three-phase fixed-bed bubble column reactor, homogenize the bed temperature in the reactor, and improve the conversion rate of reacted products and reaction selectivity, and in the meantime, it can eliminate the external circulation, and save the equipment investment and the operation and maintenance cost, with important significance to increasing economic benefits and improving equipment safety performance.