(80d) Comparative Study on the Collection Performance of a Coupled Cyclone with Built-in Circulating Granular Bed Filter for Geldart A and C Particles

Fossil fuel, including coal, petroleum and natural gas, remains to be the most important energy supplying substance for the world. However, serious environmental problems have been brought by the combustion of massive fossil fuel, particularly, for the high temperature flue gas emission. The traditional separators including the cyclone separator generally fail to meet the emission requirements in the harsh operating conditions such as high temperature and high pressure (HTHP). For the development of new generation of gas purification techniques, diverse separation mechanisms are attempted to be coupled into one equipment. But until now, there are no reliable coupling separators in industrial applications meeting with the increasingly strict emission regulations and the comprehensive HTHP requirements. The HTHP gas purification technique has become a bottleneck of a number of advanced fossil fuel utilization processes, including the fluid catalytic cracking, the methanol to olefins process, the integrated gasification combined cycle and the biomass gasification etc.

A coupled cyclone separator with built-in circulating granular bed filter (C-CGBF) is idealized for integrating the benefits of centrifugation and filtration, in which arrangement the built-in granular bed is located around the core tube and in parallel with the cyclone shell, as shown in Fig. 1. In the cyclone field caused by the swirling flow, most of the large-diameter dust particles are firstly removed by the centrifugal force, which effectively reduces the filtration load of the following built-in granular bed; the small-size dust particles with a diameter less than 10 μm are then filtrated by the granular bed, so that the gas-solids separation efficiency can be further improved. Thus, the synergistic strengthening of the gas-solids separation can be achieved. In order to accomplish a continuous operation and realize the reuse of the collecting granules, a riser-spouted bed regenerator is adopted to regenerate and circulate the collecting granules.

The de-dust performance of the C-CGBF for two kinds of dust including the Geldart's Group A and C particles was comparatively investigated under a wide range of operating conditions including the inlet gas flowrate, the inlet dust concentration and the granules circulating flux in this work. The UOP 13X-APG adsorbents with an average diameter of 2.07 mm were packed in the granular bed as the collecting granules.

For both the Geldart's Group A and C dust particles, the experimental results shows that the collection efficiency can be improved by increasing the inlet dust concentration, while the pressure drop increases consequentially. High inlet gas flowrate leads to a decline of the collection efficiency and an increase of the pressure drop.

A real-time monitoring method is proposed for timely reflecting the instantaneous variation of the granule circulating flux, in which way a notable critical flux is observed. Under the moving bed operating regime, there exists a minimum critical granule circulating flux (W_sc), below which the operation regime tends to transform from the moving bed into the fixed bed. The W_sc for the Geldart's Group C particles is between 0.10~0.15 kg/s, while for the Geldart's Group A particles, the W_sc is between 0.04~0.10 kg/s. Increasing the granule circulating flux is benefit for the operation stability. However, the collection efficiency is decreased.

The contribution rations of cyclone shell to the collection efficiency of the C-CGBF system are all above 80% for both the Geldart's Group A and C dust particles. Increasing both the inlet dust concentration and the inlet gas flowrate can strengthen the centrifugal separation. Indicated by the size distribution of the captured dust particles, the cyclone shell can efficiently capture the particles with a diameter above 10 μm; while the particles captured by the built-in granular bed are generally smaller than 10 μm. Comparing the influences of different type of dust particle, the volume percentage (φ) of the particles with a diameter lower than 10 μm in the inlet dust has a significant effect on the downward moving of the collecting granules and the pressure drop of the C-CGBF. With an increase of φ, the growth rates of the pressure drop under the fixed bed and moving bed operating regimes are both increased. The collection efficiency is weakened and the critical granules circulating flux is also increased.

Based on the experimental data, comprehensive correlation equations for determining the collection efficiency and the pressure drop, with respect to the operating parameters and the properties of the dust particles, are obtained respectively. The errors between the calculated value and the measured data are all within ±10%. They are anticipated to be used in the engineering design and operation.