PTQ Q4 2024 Issue

20–40 μm peak

BOD

1–2 μm peak

Design

200

400 600 800

1600 1400 1000 1200

1800

Particle size (μm)

Figure 3 Feed PSD used for conducting the experiments

from reactor vapours. However, these models cannot be directly applied to biochar service, owing to the differences in properties between the biochar and the FCC catalyst. The main difference is the density of the solids, while the gas density is relatively similar. The particle density of the FCC catalyst is around 1,500 kg/m 3 , whereas biochar parti- cle density is around 500-600 kg/m 3 . FCC catalysts contain much finer particles than the bio - char, but biochar has a higher tendency to fracture, creat- ing higher fines and less coarse particles. The Shell TSS is designed to remove practically all fines greater than 10 µm in size while having excellent separation efficiency for particles in the 2-10 µm size range. Therefore, specialised cyclone and Shell TSS models have been developed that consider the physical properties of biochar. To confirm these models, experimental studies were car - ried out at Particulate Solid Research, Inc (PSRI) in Chicago, USA. These studies indicate higher efficiency in biochar service compared to FCC catalyst service. The primary rea- son for the higher efficiency in biochar service is the particle size distribution (PSD). Biochar has a coarser PSD, making particle separation easier since coarser particles separate more effectively than finer ones. Particle size distribution and performance characteristics In FCC units, the PSD of the Shell TSS inlet typically contains two peaks: the first at 1-2 µm and the second at 20-40 µm (see Figure 2 ). The first PSD peak results from catalyst attrition, Figure 2 PSD of the catalyst exiting the FCC unit regen - erator, which typically follows a bimodal distribution curve

representing the fines fraction, while the second peak is due to cyclone efficiency, indicating the coarse fraction. At times, these curves may overlap, appearing as a single peak, and Shell software can predict the PSD that indicates these two peaks. The PSD of the Shell TSS inlet for catalyst service is defined by fines and coarse fraction’s average particle size, standard distribution. As the inlet particles are composed of varying sizes, the Shell TSS design tool classifies the PSD into fractions and develops individual separation efficiencies. The final reported efficiency is a cumulative of the individual fractional efficiencies. The biochar is also expected to have two peaks as it undergoes attrition like the FCC catalyst, owing to higher velocities. The biochar PSD has been fitted into the bimodal curve like the FCC catalyst. The characteristics are shown in Table 1. The average particle size of biochar fines is higher than the catalyst, and their percentage is much lower than the FCC catalyst. Consequently, Shell TSS performance effi - ciency is anticipated to be higher than in catalyst service, a prediction corroborated by the PSRI experimental studies. Experimental studies at PSRI PSRI conducted laboratory studies to assess the perfor - mance of the Shell TSS in biochar service, employing 10in swirl tubes and air as the testing medium. Given that bio- char is inherently coarse, it can undergo attrition in the pip- ing downstream of the reactor, as well as in the primary cyclone and Shell TSS itself. For experimental accuracy, biochar was ground and then sieved through a #35 mesh screen, enabling the primary cyclone to separate particles in the 30-40 µm range. The feed PSD used in these exper - iments is depicted in Figure 3 . Cold flow testing of a single Shell TSS was conducted by PSRI under varying inlet gas volumetric flow rates and underflow percentages, maintaining a consistent solid load - ing. The results provided four key insights. First, the study revealed that biochar fines are irregularly shaped with high aspect ratios, influencing their separation dynamics. Second, the study demonstrates that the Shell TSS exhibited robust performance over a broad range of gas volumetric flow rates, underflow percentages, and solids loadings. Given that overall collection efficiencies remained consistent across the tested gas throughputs, it is rec- ommended to adopt lower volumetric flow rates (or inlet

Particle size distribution characteristics

Shell TSS inlet

FCC catalyst

Biochar (typical)

(typical)

Fines average particle size, µm Fines standard deviation, µm Coarse average particle size, µm Fines standard deviation, µm

1-2 0.8

0.56

20-40

0.5

0.69

Percentage of fines, %

30-60 40-70

11 90

Percentage of coarse particles, %

Table 1

PTQ Q4 2024