Method for maximizing the reaction volume in a slurry phase reactor

Abstract

Method for maximizing the reaction volume in a slurry phase reactor by determining the ratio (f) between the height of the foams (H.sub.f) and the height of the reactor (H.sub.R) through an algorithm defining the gas hold-up in three zones, a first lower zone in which a bubble regime is established, a second intermediate zone where there can be the presence of foams, a third zone situated in the upper hemispherical part in which the multiphase mixture is accelerated until it reaches outlet conditions, the average gas hold-up being given by the weighted average of each of the three gas hold-ups of the three zones, characterized in that it uses nuclear densimeters positioned inside the reactor at different heights and comprises: measuring, for each nuclear densimeter used, gas density values, relating to different gas and/or slurry velocities, which correspond through said algorithm to calculated gas hold-up values, revealing, with a calculated gas hold-up of less than 40%, the absence of foams at least up to the height at which the densimeter is positioned, whose density measured corresponds to said gas hold-up, with a calculated gas hold-up higher than 70%, the presence of foams starting at least from the height of the reactor in which the densimeter is positioned, whose density measured corresponds to said gas hold-up, finally, determining through said algorithm, the ratio f and the extension in height of the possible presence of foams, calculating the consequent height H.sub.f.

Claims

1. A method for maximizing a reaction volume in a slurry phase reactor by determining a ratio (f) between a height of foams (H.sub.f) and a height of the slurry phase reactor (H.sub.R) through an algorithm to obtain gas hold-ups in three zones of the slurry phase reactor, wherein, in a first lower zone, a bubble regime is established, in a second intermediate zone, foams are optionally present, and in a third zone situated in an upper hemispherical part, a multiphase mixture is accelerated until it reaches an outlet, and wherein an average gas hold-up is obtained by a weighted average of each of three gas hold-ups of the three zones, wherein the slurry phase reactor comprises nuclear densimeters positioned inside the slurry phase reactor at different heights and the method comprises: measuring, gas density values at different gas and/or slurry velocities for each nuclear densimeter, to calculate gas hold-up values through the algorithm, identifying an absence of foams at least up to a height at which the nuclear densimeter is positioned, whose density measured corresponds to said gas hold-up, as determined by the gas hold-up value being less than 40%, or identifying a presence of foams starting at least from the height of the slurry phase reactor in which the nuclear densimeter is positioned, whose density measured corresponds to said gas hold-up, as determined by the gas hold-up value being higher than 70%, and finally, determining through said algorithm, the ratio f and a range of a height in which the foams are possibly present to calculate the foams height H.sub.f.

2. The method according to claim 1, wherein a formula for calculating the gas hold-up of the first lower zone is the model of Krishna with two bubble groups, whose parameters are a rise velocity of the bubbles and a transition hold-up, the rise velocity V.sub.∞,om of the bubbles being $V_{\infty ,\mathrm{om}}={a\left[\frac{\sigma \left({\rho }_l-{\rho }_V\right)g}{{\rho }_l^2}\right]}^{1/4}\exp \left({\mathrm{bH}}_f{\mathrm{.Math.}}_f\right)$ wherein σ and ρ.sub.l are respectively a surface tension (expressed in N/m) and a density (expressed in kg/m.sup.3) of a liquid phase inside the slurry phase reactor, ρ.sub.V is a density (expressed in kg/m.sup.3) of a vapour phase inside the slurry phase reactor, H.sub.f and ε.sub.f are a height and a hold-up of a possible foam phase present in an upper zone, and a and b are two parameters to be determined, and the transition gas hold-up ε.sub.tr obtained by: ${\mathrm{.Math.}}_{\mathrm{tr}}={C\left[\frac{{\rho }_V^{0.96}{\sigma }^{0.12}}{{\rho }_l}\right]}^{1/2}\left(1-C_1{f}_V\right)\exp \left(-C_2{U}_L\right)$ wherein f.sub.v is a volumetric fraction of solid in the slurry phase reactor, U.sub.L is a slurry velocity, C, C.sub.1 and C.sub.2 are three parameters to be determined, and a gas hold-up in the foam phase ε.sub.f being obtained by: ${\mathrm{.Math.}}_f=\frac{1}{1+\Omega \frac{U_L}{U_G}}$ wherein Ω is a slip parameter to be determined and U.sub.G is a gas velocity.

3. The method according to claim 1, wherein the gas hold-up of the third zone situated in the upper hemispherical part is not calculated, the weighted average of the gas hold-up of said third zone being considered negligible, due to a volume of said third zone and to a slip velocity equal to zero.

4. The method according to claim 1, wherein the slurry phase reactor is a conversion reactor of heavy residues to distillates or a hydrogenation or hydrodesulfurization or hydrocracking reactor.

5. The method according to claim 1, wherein the slurry phase reactor is a slurry bubble column.

6. The method according to claim 1, wherein the slurry phase reactor comprises at least two nuclear densimeters.

7. The method according to claim 6, wherein the slurry phase reactor comprises three nuclear densimeters positioned at a height between H/4 and H/5, between H/9 and H/11 and between H/6 and H/7 of the slurry phase reactor, H being a “tangent-to-tangent” height of the slurry phase reactor.

8. The method according to claim 6, wherein the slurry phase reactor comprises two nuclear densimeters positioned at a height between H/4and H/6 and between H/10 and H/5, H being a “tangent-to-tangent” height of the slurry phase reactor.

Description

EXAMPLE 1

Comparative

(1) As a first application example of this solution, a case is described relating to a laboratory mock-up illustrated in FIG. 1.

(2) The system is composed of a column having an internal diameter of 225 mm and a height of 2.41 m, a separator and a descending line in which the liquid circulates with a natural or forced circulation (by means of a pump). The column is equipped with a perforated ring distributor with 24 holes having a diameter of 1 mm. The column operates with nitrogen as gas and with water with the addition of a surfactant (SDS) as liquid phase: under these conditions, the presence of a low-density phase was verified in the upper zone of the column. The gas velocity was varied from 1 to 6 cm/s, whereas the velocity of the liquid from 0 to 12 mm/s. The gas hold-up in both the bubble zone and in the low-density zone was determined under each condition, together with the fraction of column occupied by foams.

(3) FIG. 2 shows the gas hold-up trends in the bubble zone in relation to the gas and liquid velocities.

(4) This system shows the formation of a zone of foams in the upper part of the column for a gas velocity greater than 4 cm/s when U.sub.L=1 mm/s, for a gas velocity greater than 5 cm/s when U.sub.L=2 mm/s, and for a gas velocity of 6 cm/s when U.sub.L=4 mm/s; the presence of foams is not revealed, on the contrary for U.sub.L=12 mm/s.

(5) For this system, the rise velocity of the small bubbles is 38.1 cm/s. The value of the constant “a” is 2.56. In this case, a slowdown effect of the small bubbles due to the presence of foams was not observed.

(6) As far as the transition hold-up is concerned, the constants C, C.sub.1 and C.sub.2 are respectively equal to 5.5, 0 and 26.

(7) The parameters relating to the model of foams for this system are indicated in the following table:

(8) TABLE-US-00001 Ω 7 k 0.008 c.sub.1, Pa s 0.0004 c.sub.2 2.07

(9) With these parameters, the heights of foams predicted by the model compared with the experimental data are the following:

(10) TABLE-US-00002 Ug, cm/s Ul, mm/s H.sub.f calc, m H.sub.f exp, m 4 1 0 0.18 5 1 0.37 0.41 6 1 1.24 0.56 5 2 0 0.13 6 2 0.24 0.30 6 4 0 0.11

(11) This example shows how, from an analysis of the data obtained from pressure measurements and from visual measurements of foam heights, it was possible to calibrate the parameters of the procedure, object of the invention.

EXAMPLE 2

(12) This example relates to the calibration of the procedure from data deriving from a plant under reaction conditions, where it was consequently not possible to have visual measurements of the position of the possible foamy phase, but only density measurements through the presence of 3 nuclear densimeters, the first situated below, the second halfway and the third approximately a meter from the upper tangent line.

(13) The data used can be summarized in the following table:

(14) TABLE-US-00003 Point Ug, cm/s Ul, mm/s ε.sub.bav, % ε.sub.sup, % 1 2.70 0.66 32.1 78.1 2 2.06 0.70 32.7 60.9 3 1.66 0.54 32.0 66.6 4 2.00 0.85 25.3 27.9 5 1.97 0.80 24.2 24.6 6 2.00 0.84 25.4 32.3 7 1.96 0.88 24.1 27.1 8 2.11 0.81 23.9 28.2

(15) As can be clearly seen from the table, points 1, 2 and 3 are characterized by hold-up values read at the upper densimeter typical of a foam phase: this means that under those conditions, the foam phase extended for at least a meter below the upper tangent line.

(16) As far as the gas hold-up parameters in bubble phase are concerned, the parameters a and b are equal to 1.0 and 0.135; C, C.sub.1 and C.sub.2, on the other hand, are equal to 3.0, 6.2 and 26.4. The fact that the parameter b is different from zero means that under these conditions, an effect of the presence of foams was also revealed on the hold-up of the bubbling zone.

(17) Upon analyzing the data relating to the foam zone and coupling them with those relating to the bubbling zone, the following parameters are obtained:

(18) TABLE-US-00004 Ω 7.5 k 0.006 c.sub.1, Pa s 0.06 c.sub.2 0

(19) The following table indicates the main results of the model relating to the upper zone of the reactor:

(20) TABLE-US-00005 Point Ug, cm/s Ul, mm/s H.sub.foam, m ε.sub.f, % 1 2.70 0.66 3.6 84.5 2 2.06 0.70 0.0 79.7 3 1.66 0.54 2.5 80.3 4 2.00 0.85 — — 5 1.97 0.80 — — 6 2.00 0.84 — — 7 1.96 0.88 — — 8 2.11 0.81 — —

(21) Once the solution had been calibrated from the experimental data provided by the measurements of the densimeters, it consequently allowed not only the gas hold-up values to be determined in the bubbling zone and foam zone, but also the extension of the foam zone: this kind of information can in no way be obtained with conventional methods.