Yi Cheng's Website

 

 
 

Research Activities
Prof. Yi Cheng’s research interests lie in the field of multiphase reactor engineering in relation to the applications for energy, environment and materials. In the early period (before 2003), major efforts were made to understand the hydrodynamics and nonlinear dynamics in various fluidized beds, involving bubbling, turbulent, circulating fluidized beds and downer, by experimental techniques and mathematical modeling (i.e., CFD). After being a faculty member in Tsinghua University in 2003, he has extended his research activities tremendously, combining conventional chemical engineering with unconventional means of process intensification (i.e., plasmas and confined micro-channel or micro-droplets), which brings new physics, new chemistry and subsequently new processes to the reactor engineering. The state-of-the-art researches on novel reactors are closely related to the process development, with the solid support of sophisticated techniques in experimental and theoretical aspects.

Novel reactors and process development with unconventional means of process intensification

  • Conventional multiphase reactors and their re-combination

Downer and downer-riser coupling reactors for clean fuel production: A series of lab-scale researches have demonstrated the advantages of downer reactors over riser reactors for conventional FCC process, to achieve high-added value low-carbon olefins and high quality gasoline as well under high severity operations. A pilot-plant riser-downer coupling reactor has been demonstrated by SINOPEC, with the refining capacity of 150 kt/a.

Multi-stage/structured fluidized bed reactors for coal to SNG (synthetic natural gas): This is to accommodate the highly exothermic methanation reaction in a well-designed fluidized bed reactor with guaranteed conversion and selectivity, instead of using the conventional technique of fixed beds in series. A lab-scale fluidized bed reactor with 50-mm i.d. has been built (max 700°C and 50 atm), together with the capability to prepare fluidized bed catalysts.

  • Plasmas [AND] multiphase reactors

Thermal plasma reactor for direct conversion of coal to acetylene: This is a millisecond process at ultra-high temperatures for clean coal conversion to chemicals; both lab-scale (at 10 kW) and pilot-plant demonstration (at 5 MW, the largest industrial demonstration in the world) of thermal plasma reactors are developed. We have extended the feedstock (i.e., coal) to natural gas/coalbed methane/shale gas, liquid hydrocarbons, coal tar, asphaltene, and other solid wastes (especially E-waste) for new process development.

In the meantime, a 10-kW RF plasma reactor has been built to produce polysillicon or nano-crystalline Si with high efficiency and high purity. This is to provide an alternative, competitive means to produce materials for solar energy utilization. The platform technique is being extended to the preparation of different high-valued materials.

Cold plasma reactors for CO2/CH4 conversion and synthesis of chlorinated polymers (CPVC, CPE, CPP): Various cold-plasma assisted multiphase reactors have been built, such as plasma-fixed bed, -fluidized bed, -vibrated bed and -circulating fluidized bed, to intensify the gas-solid contact by utilizing the special features of cold-plasma. In addition to the lab-scale research, pilot-plant plasma reactors are being developed for clean production of CPVC/CPE particles at the scale of 1 kt/a.
We recently started the research on the gas-liquid plasma process and reactor design, which ignited new interests to develop plasma physics and chemistry in chemical engineering.

  • Micro/mini-channel [AND] multiphase reactors

Micro-channel reactors for millisecond hydrogen production and syngas methanation to SNG: Catalytic reactions are intensified in confined micro/mini-channels for the improved heat and mass transfer (e.g. well-controlled temperature) so that millisecond processes are implemented for highly exothermic/endothermic reactions. In addition, foam monolith reactors are also employed in our research programs.

The running projects include: steam reforming of methane or ethanol, methanation, syngas to olefins, catalytic oxidative dehydrogenation of ethane to ethylene, acetylene carbonylation to acrylic acid and butanedioic acid.

Micro/mini-channel reactors for well-controlled production of fine chemicals and nano-medicine: a successful case has been demonstrated, using impinging jet mixer to implement the millisecond liquid-liquid reaction system to make MDI, at the industrial scale of ~100 kt/a, based on our patented technique. Current efforts have been extended to produce nano-medicines with precise control of the particle diameter and its structure.
The running projects also include: fundamentals of droplet-based microreactors, ionic liquid involved Suzuki reaction in flow chemistry, etc.  

Non-intrusive measurement techniques

  • Laser based measurement techniques: In addition to the commercial PIV, PDPA, LDA facilities in the lab, we have developed series of laser induced fluorescence (LIF) techniques to measure the dynamic concentration/temperature field in relation to the mixing and reactive mixing processes, including PLIF, reactive-LIF (for liquid-liquid and gas-liquid systems) and micro-LIF (for microfluidics research).
     
  • X-ray based measurement techniques: Both 1D and 2D X-ray based techniques have been developed, especially on the novel algorithm and fast detection of multiphase flows.
     
  • High-performance imaging techniques: involving three high-speed cameras and an IR thermal imaging camera.
     
  • iCCD plus optical spectrum: to measure the active species in plasma gas environment

Modeling and simulation of multiphase flows with chemical reactions

  • Lattice Boltzmann method (LBM): We have developed LBM approach to simulating the multiphase, multi-component flows with species transport (i.e., mixing) and chemical reactions in micro-droplets or micro-channels. The model has been further improved to simulate the hydrodynamics of a high viscosity fluid or two fluids with large ratio of viscosity.
     
  • CFD with detailed chemistry:  By incorporating complex elementary kinetics into Navier-Stokes equation based CFD models, we have been able to predict the detailed progress of millisecond reactions in the two processes, i.e., (1) catalytic partial oxidation of methane and (2) steam reforming of methane, using Ni or Rh as the catalyst.  On this basis, we implemented the theoretical analysis on a practical micro-channel reactor design for millisecond hydrogen production.
     
  • CFD-DPM model: A comprehensive computational fluid dynamics with discrete phase model (CFD-DPM) has been established to describe the rapid coal pyrolysis process in a reactor operated at ultra-high temperatures. The particle-scale physics such as the heat conduction inside solid materials, diffusion of released volatile gases, coal devolatilization, and tar cracking reactions are incorporated. The improved chemical percolation devolatilization (CPD) model is applied to describe the devolatilization behavior of rapidly heated coal based on the physical and chemical transformations of the coal structure. This model has been successfully validated for describing the complex coal pyrolysis behavior under wide operating conditions of slow pyrolysis (100 K/s), rapid pyrolysis (103 K/s) and plasma pyrolysis (105-7 K/s) of coal particles.
     
  • CFD-DEM coupled approach: A series of work using CFD-DEM method has been published, for example, with the consideration of catalyst deactivation in time in FCC riser and downer reactors. We are currently working on the simulation of particle flows in micro-channels using this method.
     
  • Two-fluid model: This is to simulate the gas-solid flows in various fluidized beds, especially in downer reactors, using kinetic theory of granular phase to close the equations. Chemical reactions with heat transfer have been incorporated, such as lumped kinetics in FCC process and the methanation reaction for coal to SNG.
 
Yi Cheng
Tsinghua University, Beijing, P.R.China
Last updated: Dec 31, 2016
 
Chemeng Dept. Tsinghua University Fluidization Laboratory of Tsinghua University English version